ALBERT

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): J.M. Kranabetter〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Forest floor carbon (C) sequestration has been negatively correlated with manganese (Mn) availability, possibly due to reduced efficacy of Mn-peridoxase enzymes produced by Agaricomycete fungi. I examined a soil C and Mn dataset from a podzolization gradient, along with fungal sporocarp Mn concentrations, to potentially corroborate this finding. An inverse power relationship between soil C and soil Mn content across temperate rainforests was confirmed, which provides further evidence of a Mn bottleneck in C turnover. Average Mn concentrations of saprotrophic sporocarps were greater than those of ectomycorrhizal fungi, and displayed a similar inverse correlation with increasing soil C. The absence or limited effectiveness of select saprotrophic fungi across Mn-depleted forest soils may be one mechanism behind impeded turnover of recalcitrant organic matter.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Charles R. Warren〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Phospholipids are isolated from crude lipid extracts by silica solid phase extraction (SPE), but for soils we don't know if phospholipids are the only fatty acid-based lipids present in the polar lipid fraction. Lipids extracted from three soils were fractionated with a silica SPE protocol commonly used for soils, with “neutrals” eluted by chloroform, “glycolipids” eluted by acetone, and “phospholipids” eluted by methanol. Fatty acid-based lipids were identified and quantified by liquid chromatography-mass spectrometry. Phospholipids were recovered in the methanol fraction, but this fraction also included betaine lipids. In two soils the methanol fraction was 3–6% betaine lipid while in one soil betaine lipids accounted for 48% of lipids in the methanol fraction. Clearly the fraction obtained by eluting lipids from silica with methanol is not purely phospholipid but can contain significant amounts of other polar lipids.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Aikaterini Efthymiou, Birgit Jensen, Iver Jakobsen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Biochar (BC) application to soil can potentially replace mineral P fertilizers and its effectiveness as fertilizer can be improved by plant inoculation with the phosphate-solubilizing microorganism 〈em〉Penicillium aculeatum〈/em〉 (Pa). Arbuscular mycorrhiza (AM) fungi are important in plant P nutrition and may possibly act synergistically with Pa to improve the uptake of BC-P. Responses in wheat to inoculation with Pa and the AM fungus 〈em〉Rhizophagus irregularis〈/em〉 were studied in a pot experiment at two levels of BC fertilization. Pots contained a mesh-enclosed, root free compartment with 33P-labelled soil for assessment of the AM contribution to P uptake and for studying if Pa would affect P uptake by the AM fungal hyphae. AM application suppressed wheat growth, albeit AM pathway had a major role in total P uptake at the two lowest P levels (nil or 20 mg BC-P kg〈sup〉−1〈/sup〉 soil). Moreover, AM contribution had similar magnitudes in the presence and absence of Pa. Rhizosphere and bulk soil were actively colonized by Pa, both in the presence and absence of AM. The application of Pa or BC at a low rate increased AM-colonized root lengths. Although this was not translated to increased P uptake by wheat, the results suggest that AM and Pa can be combined without showing antagonistic interactions. However, more work is needed to understand how AM and Pa can be combined to increase plant growth.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Raúl Ochoa-Hueso, Manuel Delgado-Baquerizo, Paul Tuan An King, Merryn Benham, Valentina Arca, Sally A. Power〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Litter decomposition is fundamental for nutrient and carbon (C) cycling, playing a major role in regulating the Earth's climate system. Climate change and fertilization are expected to largely shift litter decomposition rates in terrestrial ecosystems, however, studies contextualizing the relative importance of these major global change drivers versus other key decomposition drivers such as substrate quality and ecosystem type are lacking. Herein, we used two independent field experiments in an Eastern Australian grassland (Experiment 1) and a forest (Experiment 2) to evaluate the role of (i) litter quality, (ii) nutrient addition (N, P and K in full factorial combination; Experiment 1), and (iii) a combination of N addition and irrigation (Experiment 2) in litter decomposition, substrate-induced respiration and microbial abundance. Regardless of experimental treatments, forest soils decomposed litter between 2 and 5 times faster than grassland soils. This was principally controlled by the greater ability of forest microbes to respire C-based substrates and, ultimately, by soil N availability. The experimental treatments accounted for only relatively small differences in our measured variables, ranging from 10 to 15% in the case of the irrigation-by-N-addition forest experiment to almost negligible in most of the grassland nutrient addition plots. In the latter experiment, decomposition and soil activity responses were associated with either K addition or interactions between K and other nutrients, suggesting a key role for this often-neglected soil nutrient in controlling litter decomposition. Our study provides evidence that while nutrient enrichment and/or irrigation have the potential to affect litter decomposition rates in grassland and forest ecosystems, land use change that results in loss or gain of forested area is likely to exert a much greater impact than these other two drivers.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Esther Guillot, Philippe Hinsinger, Lydie Dufour, Jacques Roy, Isabelle Bertrand〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil microbial communities in Mediterranean agroecosystems experience long drought periods that are typically combined with heat and frequently interspersed with rapid rewetting events. Agroforestry systems are of growing interest and viewed as possible alternative to conventional cropping systems in the context of climate change. Our aim was to evaluate the resistance and resilience of soil microbial communities against drought with or without heat stress at different distances from the tree row in an agroforestry system as compared to a conventional cropping system. Soils were sampled at several distances from the tree row in a 21-year-old walnut agroforestry system and a contiguous conventional crop in Southern France. We simulated two cycles of drying-rewetting under controlled conditions and applied three distinct treatments: control (without stress), drought and drought combined with heat stress. We monitored microbial respiration over the incubation period. The inorganic N and microbial biomass C, N and P contents (MBC, MBN and MBP) were assessed during the drying period (resistance), just after rewetting and at the end of the experiment (resilience), while bacterial and fungal abundances were measured at the end of the resistance period. We demonstrated that an agroforestry system can induce spatial heterogeneity in soil microbial biomass and functions under control conditions. Microbial biomass and activity, soil organic matter (SOM) and mineral N levels increased on the tree row. This spatial heterogeneity pattern was preserved for soil microbial response to drought combined or not with heat. Microorganisms sampled in the middle of the interrow or in the conventional crop exhibited highest biomass resistance and lowest resilience when facing combined drought and heat stress. Soil microbial biomass resistance and resilience were similar whatever the spatial position when microorganisms had to deal with drought stress only. Our findings suggested that despite higher SOM content, microbial biomass and activity at and near the tree row, the legacy effect of the tree row did not lead to higher ecological stability under stressful climatic conditions. We also demonstrated that soil microorganisms can considerably change their stoichiometry depending on the stress treatment. Soil microorganisms showed elevated MBC:MBN, MBC:MBP and variable MBN:MBP during the resistance period. A high stoichiometric flexibility of microorganisms was observed when exposed to drought stress only, while stoichiometric changes were irreversible when exposed to combined drought and heat stress.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Yufang Lu, Xiaonan Zhang, Jiafeng Jiang, Herbert J. Kronzucker, Weishou Shen, Weiming Shi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The application of biological nitrification inhibitors (BNIs) is considered an important new strategy to mitigate nitrogen losses from agricultural soils. 1,9-decanediol was recently identified as a new BNI in rice root exudates and was shown to inhibit nitrification in bioassays using 〈em〉Nitrosomonas〈/em〉. However, the effect of this compound on nitrification and ammonia oxidizers in soils remained unknown. In this study, three typical agriculture soils were collected to investigate the impact of 1,9-decanediol on nitrification and ammonia oxidizers in a 14-day microcosm incubation. High doses of 1,9-decanediol showed strong soil nitrification inhibition in all three agricultural soils, with the highest inhibition of 58.1% achieved in the acidic red soil, 37.0% in the alkaline fluvo-aquic soil, and 35.7% in the neutral paddy soil following 14 days of incubation. Moreover, the inhibition of 1,9-decanediol was superior to the widely used synthetic nitrification inhibitor, dicyandiamide (DCD) and two other BNIs, methyl 3-(4-hydroxyphenyl) propionate (MHPP) and α-linolenic acid (LN), in all three soils. The abundance of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) was significantly inhibited by 1,9-decanediol addition across the three soils. All AOB sequences fell within the 〈em〉Nitrosospira〈/em〉 group, and the dominant AOA sequences belonged to the 〈em〉Nitrososphaera〈/em〉 cluster in all three soils. Changes in the community composition of AOB were more pronounced than AOA after the application of 1,9-decanediol. The AOB community structure shifted from 〈em〉Nitrosospira〈/em〉 cluster 2 and cluster 3a toward 〈em〉Nitrosospira〈/em〉 clusters 8a and 8b. As for AOA, no significant impact on the proportion of the dominant 〈em〉Nitrososphaera〈/em〉 cluster was observed in the fluvo-aquic soil and paddy soil while only the 〈em〉Nitrosopumilus〈/em〉 cluster decreased in the red soil. 1,9-decanediol could also significantly reduce soil N〈sub〉2〈/sub〉O emissions, especially in acidic red soil. Our results provide evidence that 1,9-decanediol is capable of suppressing nitrification in agricultural soils through impeding both AOA and AOB rather than affecting soil NH〈sub〉4〈/sub〉〈sup〉+〈/sup〉 availability. 1,9-decanediol holds promise as an effective biological nitrification inhibitor for soil ammonia-oxidizing bacteria and archaea.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Andrew R. Zimmerman, Lei Ouyang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Due to expected changes in fire frequency and the potential of using pyrolyzed biomass (biochar) amendments to increase soil C storage, there is a need for better ability to predict pyrogenic C (pyC) longevity in soil and its effects on native soil C stability. However, C mineralization from biochar/soil mixtures has been shown to vary greatly and both ‘positive’ and ‘negative’ priming (increased and decreased mineralization of native C, respectively) following biochar amendments have been observed. To better understand the interactions that influence mineralization of pyC and native soil C, bagasse (sugar cane residues) and bagasse biochar pyrolyzed at 300 and 650 °C were incubated in sand over 144 d with soil microbes and dissolved organic matter (DOM) substrates of high and low reactivity (sucrose and humic acid: HA, respectively). Mineralization of particulate and dissolved C was quantified based upon the distinct C isotopic signature of CO〈sub〉2〈/sub〉 evolved from each source. Negative priming of bagasse-C mineralization by sucrose (−9.3% cumulative C mineralized) and pyC mineralization by HA (−29 and −68% for low and high temperature biochar, respectively) pointed to the mechanism of ‘〈em〉substrate switching〈/em〉’, i.e. cases in which added DOM was of greater or similar lability to the particulate OM present. In contrast, positive priming of bagasse mineralization by HA (+77%) and pyC mineralization by sucrose (+271 and 614% for low and high temperature biochar, respectively), was attributed to the mechanisms of 〈em〉soil conditioning〈/em〉 (creation of an environment more favourable to microbial growth) and 〈em〉co-metabolism〈/em〉, respectively. Inversely, presence of all the particulates enhanced the mineralization of sucrose (by 8, 58 and 91% for bagasse and low and high temperature biochar, respectively), suggesting a 〈em〉soil conditioning〈/em〉 mechanism. In contrast, the biochars had little effect on HA mineralization, likely because of their similar inherent stability and chemistry. These results show that DOM and pyC mineralization in soil is interactive and varies with OM type. Furthermore, the priming observed could be attributed to different mechanisms in different cases, the long term effect of which would likely be greater soil C sequestration than predicted by simple degradation models.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0038071718304218-fx1.jpg" width="404" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 131〈/p〉 〈p〉Author(s): Emma L. Aronson, Michael L. Goulden, Steven D. Allison〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Climate and regional air quality models predict that Southern California will experience longer and more severe droughts, and possibly wetter, more intense storms and changing nitrogen (N) deposition. We investigated how the three major soil greenhouse gas (GHG) fluxes respond to 4–6 years of exposure to a full-factorial experiment of reduced and augmented precipitation crossed with increased N in a semi-arid grassland in Irvine, CA, USA. The mean emission fluxes across all treatments were 249.8 mg CO〈sub〉2〈/sub〉 m〈sup〉−2〈/sup〉 h〈sup〉−1〈/sup〉, -16.41 μg CH〈sub〉4〈/sub〉 m〈sup〉−2〈/sup〉 h〈sup〉−1〈/sup〉, and 2.24 μg N〈sub〉2〈/sub〉O m〈sup〉−2〈/sup〉 h〈sup〉−1〈/sup〉. Added N plots released 3.5 times more N〈sub〉2〈/sub〉O than ambient N plots, and N treatment and soil moisture interacted, such that volumetric soil moisture in added N plots correlated positively with N〈sub〉2〈/sub〉O release. Soil moisture, which was higher in the added water plots, correlated positively with respiration. CH〈sub〉4〈/sub〉 consumption increased with soil moisture in the drought treatment, an opposite trend to that observed in most other studies.〈/p〉 〈p〉Our data suggest that CH〈sub〉4〈/sub〉 consumption, N〈sub〉2〈/sub〉O production, and soil respiration will decline if Southern California grasslands experience more frequent and extreme droughts. However, when drought is followed by high rainfall, the additional moisture will likely increase CH〈sub〉4〈/sub〉 consumption and N〈sub〉2〈/sub〉O release in periodic pulses. Overall, climatic shifts in this ecosystem may lead to a decrease in overall soil GHG emissions to the atmosphere. However, increased N deposition to Southern California will likely lead to increased N〈sub〉2〈/sub〉O release and a shift in the dominant N loss pathway toward gaseous release of N. If N deposition continues to increase along with severity and duration of drought, our data predict a decrease in global warming potential (GWP) of 17.2% from this ecosystem.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Liang Chen, Wenhua Xiang, Huili Wu, Shuai Ouyang, Bo Zhou, Yelin Zeng, Yongliang Chen, Yakov Kuzyakov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Plant interactions and feedbacks with soil microorganisms play an important role in sustaining the functions and stability of terrestrial ecosystems, yet the effects of tree species diversity on soil microbial community in forest ecosystems are still not well understood. Here, we examined the effects of tree species richness (1–12 species) and the presence of certain influential tree species (sampling effect) on soil bacterial and fungal communities in Chinese subtropical forests, using high-throughput Illumina sequencing for microbial identification. We observed that beta rather than alpha diversities of tree species and soil microorganisms were strong coupled. Multivariate regression and redundancy analyses revealed that the effects of tree species identity dominated over tree species richness on the diversity and composition of bacterial and fungal communities in both organic and top mineral soil horizons. Soil pH, nutrients and topography were always identified as significant predictors in the best multivariate models. Tree species have stronger effect on fungi than bacteria in organic soil, and on ectomycorrhizal fungi than saprotrophic fungi in mineral topsoil. Concluding, tree species identity, along with abiotic soil and topographical conditions, were more important factors determining the soil microbial communities in subtropical forests than tree diversity 〈em〉per se〈/em〉.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Denis Curtin, Mike H. Beare, Weiwen Qiu, Craig S. Tregurtha〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Phosphorus (P) is central to the productivity of grass-clover pastoral farming systems. Fertiliser P promotes the growth of clover, which provides an input of fixed N to complement that supplied from the soil (primarily mineralised N). If pasture productivity is limited by P availability, organic matter returns to the soil in excreta and plant residues will decline, which in turn may reduce the supply of N by mineralisation. We examined the effect of long-term P application to grass-clover pasture on mineralisation of N (and C). Net N mineralisation was measured in a 14-week aerobic incubation (25 °C; soil maintained at field capacity) using soils (0–15 cm depth) from a long-term (1952–2016) trial set up to quantify effects of single superphosphate (0, 188, or 376 kg〈sup〉−1〈/sup〉 year〈sup〉−1〈/sup〉) on productivity of irrigated, sheep-grazed pasture (no fertiliser N was applied during the trial). Although P fertilisation had only a small effect (∼10% increase) on total soil N, net N mineralisation was substantially increased (N mineralised from fertilised soil in 14 weeks was ∼1.6 times that from the unfertilised Control). In contrast, mineralisation of C was slightly greater in the Control than in fertilised soil. Nitrogen mineralisation exhibited a Mitscherlich-type relationship with available soil P, measured using the Olsen test; near-maximum mineralisation was observed at an Olsen test value of ∼10 mg P kg〈sup〉−1〈/sup〉 soil. Annual in-field N mineralisation was estimated by modifying the laboratory-measured “basal” mineralisation values using temperature and moisture adjustment factors (soil temperature and moisture data were acquired from an adjacent, irrigated trial). The results confirmed that N mineralisation was the predominant source of available N in the unfertilised Control (∼160 kg ha〈sup〉−1〈/sup〉 yr〈sup〉−1〈/sup〉 vs ∼30 kg ha〈sup〉−1〈/sup〉 yr〈sup〉−1〈/sup〉 of fixed N) and that it was an important source of N for the additional dry matter grown in response to P application (N uptake increased by ∼200 kg ha〈sup〉−1〈/sup〉 yr〈sup〉−1〈/sup〉 in response to P fertilisation vs an increase in mineralisation of ∼100 kg ha〈sup〉−1〈/sup〉 yr〈sup〉−1〈/sup〉). The increase in net N mineralisation in fertilised soil was partly because immobilisation of N was less than in the unfertilised Control.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Eric R. Johnston, Minjae Kim, Janet K. Hatt, Jana R. Phillips, Qiuming Yao, Yang Song, Terry C. Hazen, Melanie A. Mayes, Konstantinos T. Konstantinidis〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Tropical ecosystems are an important sink for atmospheric CO〈sub〉2〈/sub〉; however, plant growth is restricted by phosphorus (P) availability. Although soil microbiota facilitate organic P turnover and inorganic P mobilization, their role in carbon-phosphorus coupled processes remains poorly understood. To advance this topic, soils collected from four sites representing highly weathered tropical soils in the El Yunque National Forest, Puerto Rico were incubated with exogenous PO〈sub〉4〈/sub〉〈sup〉3−〈/sup〉 under controlled laboratory conditions. P amendment increased CO〈sub〉2〈/sub〉 respiration by 14–23% relative to control incubations for soils sampled from all but the site with the greatest total and bioavailable soil P. Metatranscriptomics revealed an increase in the relative transcription of genes involved in cell growth and uptake of other nutrients in response to P amendment. A new methodology to normalize gene expression by population-level relative (DNA) abundance revealed that the pattern of increased transcription of cell growth and division genes with P amendment was community-wide. Soil communities responsive to P amendment possessed a greater relative abundance of α-glucosyl polysaccharide biosynthesis genes, suggestive of enhanced C storage under P-limiting conditions. Phosphorylase genes governing the degradation of α-glucosyl polysaccharides were also more abundant and increased in relative transcription with P amendment, indicating a shift from energy storage towards growth. Conversely, microbial communities in soils nonresponsive to P amendment were found to have metabolisms tuned for the phosphorolysis of labile plant-derived substrates, such as β-glucosyl polysaccharides. Collectively, our results provided quantitative estimates of increased soil respiration upon alleviation of P constraints and elucidated several underlying ecological and molecular mechanisms involved in this response.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Gangsheng Wang, Wenjuan Huang, Melanie A. Mayes, Xiaodong Liu, Deqiang Zhang, Qianmei Zhang, Tianfeng Han, Guoyi Zhou〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Knowledge of microbial mechanisms is critical to understand Earth's biogeochemical cycle under climate and environmental changes. However, large uncertainties remain in model simulations and predictions due to the lack of explicit parameterization of microbial data and few applications beyond the laboratory. In addition, most experimental and modeling studies of warming-induced changes in soil carbon (C) focus on temperature sensitivity, neglecting concomitant effects of changes in soil moisture. Soil microbes are sensitive to moisture, and their responses can dramatically impact soil biogeochemical cycles. Here we represent microbial and enzymatic functions in response to changes in moisture in the Microbial-ENzyme Decomposition (MEND) model. Through modeling with long-term field observations from subtropical forests, we demonstrate that parameterization with microbial data in addition to respiration fluxes greatly increases confidence in model simulations. We further employ the calibrated model to simulate the responses of soil organic C (SOC) under multiple environmental change scenarios. The model shows significant increases in SOC in response to decreasing soil moisture and only minor changes in SOC in response to increasing soil temperature. Increasing litter inputs also cause a significant increase in SOC in the pine forest, whereas an insignificant negative effect is simulated in the broadleaf forest. We also demonstrate the co-metabolism mechanism for the priming effects, i.e., more labile inputs to soil could stimulate microbial and enzymatic growth and activity. Our study provides strong evidence of microbial control over soil C decomposition and suggests the future trajectory of soil C may be more responsive to changes in soil moisture than temperature, particularly in tropical and subtropical environments.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 131〈/p〉 〈p〉Author(s): Abdallah Awad, Andrzej Majcherczyk, Peter Schall, Kristina Schröter, Ingo Schöning, Marion Schrumpf, Martin Ehbrecht, Steffen Boch, Tiemo Kahl, Jürgen Bauhus, Dominik Seidel, Christian Ammer, Markus Fischer, Ursula Kües, Rodica Pena〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Functionally, ectomycorrhizal (ECM) and saprotrophic (SAP) fungi belong to different guilds, and they play contrasting roles in forest ecosystem C-cycling. SAP fungi acquire C by degrading the soil organic material, which precipitates massive CO〈sub〉2〈/sub〉 release, whereas, as plant symbionts, ECM fungi receive C from plants representing a channel of recently assimilated C to the soil. In this study, we aim to measure the amounts and identify the drivers of ECM and SAP fungal biomass in temperate forest topsoil. To this end, we measured ECM and SAP fungal biomass in mineral topsoils (0–12 cm depth) of different forest types (pure European beech, pure conifers, and mixed European beech with other broadleaf trees or conifers) in a range of about 800 km across Germany; moreover, we conducted multi-model inference analyses using variables for forest and vegetation, nutritive resources from soil and roots, and soil conditions as potential drivers of fungal biomass. Total fungal biomass ranged from 2.4 ± 0.3 mg g〈sup〉−1〈/sup〉 (soil dry weight) in pure European beech to 5.2 ± 0.8 mg g〈sup〉−1〈/sup〉 in pure conifer forests. Forest type, particularly the conifer presence, had a strong effect on SAP biomass, which ranged from a mean value of 1.5 ± 0.1 mg g〈sup〉−1〈/sup〉 in broadleaf to 3.3 ± 0.6 mg g〈sup〉−1〈/sup〉 in conifer forests. The European beech forests had the lowest ECM fungal biomass (1.1 ± 0.3 mg g〈sup〉−1〈/sup〉), but in mixtures with other broadleaf species, ECM biomass had the highest value (2.3 ± 0.2 mg g〈sup〉−1〈/sup〉) among other forest types. Resources from soil and roots such as N and C concentrations or C:N ratios were the most influential variables for both SAP and ECM biomass. Furthermore, SAP biomass were driven by factors related to forest structure and vegetation, whereas ECM biomass was mainly influenced by factors related to soil conditions, such as soil temperature, moisture, and pH. Our results show that we need to consider a complex of factors differentially affecting biomass of soil fungal functional groups and highlight the potential of forest management to control forest C-storage and the consequences of changes in soil fungal biomass.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 131〈/p〉 〈p〉Author(s): Adrian Ho, Hyo Jung Lee, Max Reumer, Marion Meima-Franke, Ciska Raaijmakers, Hans Zweers, Wietse de Boer, Wim H. Van der Putten, Paul L.E. Bodelier〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Aerobic oxidation of methane at (circum-)atmospheric concentrations (〈40 ppm〈sub〉v〈/sub〉) has long been assumed to be catalyzed by the as-yet-uncultured high-affinity methanotrophs in well-aerated, non-wetland (upland) soils, the only known biological methane sink globally. Although the low-affinity canonical methanotrophs with cultured representatives have been detected along with the high-affinity ones, their role as a methane sink in upland soils remains enigmatic. Here, we show that canonical methanotrophs can contribute to (circum-)atmospheric methane uptake in agricultural soils. We performed a stable-isotope 〈sup〉13〈/sup〉C〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉CH〈sub〉4〈/sub〉 labelling incubation in the presence and absence of bio-based residues that were added to the soil to track the flow of methane. Residue amendment transiently stimulated methane uptake rate (〈50 days). Soil methane uptake was sustained throughout the incubation (130 days), concomitant to the enrichment of 〈sup〉13〈/sup〉C〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉CO〈sub〉2〈/sub〉. The 〈sup〉13〈/sup〉C-enriched phospholipid fatty acids (PLFAs) were distinct in both soils, irrespective of amendments, and were unambiguously assigned almost exclusively to canonical alphaproteobacterial methanotrophs with cultured representatives. 16S rRNA and 〈em〉pmoA〈/em〉 gene sequence analyses revealed that the as-yet-uncultured high-affinity methanotrophs were virtually absent in these soils. The stable-isotope labelling approach allowed to attribute soil methane uptake to canonical methanotrophs, whereas these were not expected to consume (circum-)atmospheric methane. Our findings thus revealed an overlooked reservoir of high-affinity methane-oxidizers represented by the canonical methanotrophs in agriculture-impacted upland soils. Given that upland agricultural soils have been thought to marginally or do not contribute to atmospheric methane consumption due to the vulnerability of the high-affinity methanotrophs, our findings suggest a thorough revisiting of the contribution of agricultural soils, and the role of agricultural management to mitigation of climate change.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): 〈/p〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Chantal Koechli, Ashley N. Campbell, Charles Pepe-Ranney, Daniel H. Buckley〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soils represent one of the largest and most active pools of C in the biosphere, and soil respiration represents a major component of global C flux. Fungi are essential to soil carbon cycling due to their propensity for decomposing organic polymers such as cellulose. We performed high throughput sequencing enabled stable isotope probing (HTS-SIP) with 〈sup〉13〈/sup〉C-cellulose to characterize the dynamics of fungi and bacteria during cellulose degradation in an agricultural soil. A total of 1900 fungal taxa were observed and 190 of these assimilated 〈sup〉13〈/sup〉C-cellulose during a 30-day incubation. A majority of 〈sup〉13〈/sup〉C-labeled fungi belonged to 〈em〉Ascomycota〈/em〉, 〈em〉Basidiomycota〈/em〉, and 〈em〉Mucoromycota〈/em〉. However, most 〈sup〉13〈/sup〉C-labeled fungi could not be annotated at the species (71%, 〈em〉n〈/em〉 = 134), or genus (49%, 〈em〉n〈/em〉 = 93) level. 〈em〉Mucoromycota〈/em〉 were 〈sup〉13〈/sup〉C-labeled early, and by day 3 the most abundant 〈sup〉13〈/sup〉C-labeled organism belonged to 〈em〉Mortierella〈/em〉. In contrast, 〈sup〉13〈/sup〉C-labeled 〈em〉Ascomycota〈/em〉 increased in diversity through day 14 and their relative abundance comprised more than 40% of fungal ITS sequences by day 30. These results show that: 〈em〉i〈/em〉) the majority of fungal taxa that assimilated 〈sup〉13〈/sup〉C from 〈sup〉13〈/sup〉C-cellulose are uncultivated and poorly characterized, 〈em〉ii〈/em〉) the beta-diversity of 〈sup〉13〈/sup〉C-labeled fungi changed significantly over time during cellulose degradation, 〈em〉iii〈/em〉) a relatively small number of the 〈sup〉13〈/sup〉C-labeled taxa dominated the community response to cellulose, and 〈em〉iv〈/em〉) fungi incorporated cellulose into DNA more rapidly and in greater numbers than did bacteria. These results show that fungi in a tilled agricultural field respond rapidly to new cellulose inputs, exhibiting complex temporal dynamics that likely drive carbon flow into diverse taxa within the soil community.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Katerina Papp, Bruce A. Hungate, Egbert Schwartz〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉RNA is considered to be a short-lived molecule, indicative of cellular metabolic activity, whereas DNA is thought to turn over more slowly because living cells do not always grow and divide. To explore differences in the rates of synthesis of these nucleic acids, we used H〈sub〉2〈/sub〉〈sup〉18〈/sup〉O quantitative stable isotope probing (qSIP) to measure the incorporation of 〈sup〉18〈/sup〉O into 16S rRNA, the 16S rDNA, 〈em〉amoA〈/em〉 mRNA and the 〈em〉amoA〈/em〉 gene of soil Thaumarchaeota.〈/p〉 〈p〉Incorporation of 〈sup〉18〈/sup〉O into the thaumarchaeal 〈em〉amoA〈/em〉 mRNA pool was faster than into the 16S rRNA pool, suggesting that Thaumarchaea were metabolically active while using rRNA molecules that were likely synthetized prior to H〈sub〉2〈/sub〉〈sup〉18〈/sup〉O addition. Assimilation rates of 〈sup〉18〈/sup〉O into 16S rDNA and 〈em〉amoA〈/em〉 genes were similar, which was expected because both genes are present in the same thaumarchaeal genome. The Thaumarchaea had significantly higher rRNA to rDNA ratios than bacteria, though the 〈sup〉18〈/sup〉O isotopic signature of thaumarchaeal rRNA was lower than that of bacterial rRNA, further suggesting preservation of old non-labeled rRNA. Through qSIP of soil with H〈sub〉2〈/sub〉〈sup〉18〈/sup〉O, we showed that 〈sup〉18〈/sup〉O incorporation into thaumarchaeal nucleic acids was generally low, indicating slower turnover rates compared to bacteria, and potentially suggesting thaumarchaeal capability for preservation and efficient reuse of biomolecules.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): J.I. Rilling, J.J. Acuña, P. Nannipieri, F. Cassan, F. Maruyama, M.A. Jorquera〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Since the 1980s, plant growth‒promoting bacteria (PGPB) have been studied as a sustainable alternative to the use of chemical fertilizers to increase crop yields, and effective PGPB have been isolated from diverse plant (〈em〉e.g.〈/em〉, endosphere and phyllosphere) and soil (〈em〉e.g.〈/em〉, rhizosphere) compartments. Despite the promising plant growth promotion results commonly observed under laboratory and greenhouse conditions, the successful application of PGPB under field conditions has been limited, partly by the lack of knowledge of the ecological/environmental factors affecting the colonization, prevalence and activity of beneficial bacteria on crops. It is generally accepted that the effectiveness of PGPB depends on their ability to colonize a niche and compete with the indigenous plant microbiome under agronomic conditions. However, most studies do not include tracking or monitoring of PGPB in the environment after their application, and the beneficial effects on plants are measured by determining biomass‒ and physiology‒related parameters without confirming bacterial colonization. To date, methods based on reporter genes, immunological reactions and nucleic acids have been applied to track or monitor PGPB in seeds, soils or 〈em〉in planta〈/em〉 after inoculation. In this review, we describe, compare and discuss the methods used for tracking and monitoring PGPB, including challenges and perspectives on some novel methods.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Jing Ding, Dong Zhu, Qing-Lin Chen, Fei Zheng, Hong-Tao Wang, Yong-Guan Zhu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil fauna plays crucial roles in litter decomposition and nutrient cycling and their associated microbiota contributes to nutrient absorption, health, metabolism and immunity. However, only a few studies have focused on the associated microbiota of soil fauna, and the effects of fertilization on the bacterial community assembly of soil fauna are poorly understood. Here we collected specimens of the collembolan 〈em〉Folsomia quadrioculata〈/em〉 and the soils they lived in from a long-term fertilization experiment (including urea, sewage sludge and chicken manure). The bacterial communities of the collembolans and soils were investigated using 16S rRNA gene amplicon sequencing. A dominant core microbiota consisting of 244 OTUs were identified in the collembolans, of which 41% were shared with the soil microbiota. Community analysis indicated that the assembly of the collembolan bacterial community was a deterministic process, and a close contact of bacterial community was observed in the collembolan microbiome. The collembolan bacterial communities differed significantly from their surrounding soil samples, and their diversity was lower than that of soil microbial community. Furthermore, soil fertilization and in particular application of inorganic fertilizer altered the bacterial community and metabolic potential of the collembolan associated microbiota. Changes in the soil microbial community moreover played an important role in the shift in bacterial community and metabolic potential of the collembolan-associated microbiota. Our results suggested that long-term fertilization significantly contributed to the assembly of the collembolan bacterial community.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0038071718304255-fx1.jpg" width="263" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Michael Philben, Jianqiu Zheng, Markus Bill, Jeffrey M. Heikoop, George Perkins, Ziming Yang, Stan D. Wullschleger, David E. Graham, Baohua Gu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Increasing nitrogen (N) availability in Arctic soils could stimulate the growth of both plants and microorganisms by relieving the constraints of nutrient limitation. It was hypothesized that organic N addition to anoxic tundra soil would increase CH〈sub〉4〈/sub〉 production by stimulating the fermentation of labile substrates, which is considered the rate-limiting step in anaerobic C mineralization. We tested this hypothesis through both field and lab-based experiments. In the field experiment, we injected a solution of 〈sup〉13〈/sup〉C- and 〈sup〉15〈/sup〉N-labeled glutamate 35 cm belowground at a site near Nome on the Seward Peninsula, Alaska, and observed the resulting changes in porewater geochemistry and dissolved greenhouse gas concentrations. The concentration of free glutamate declined rapidly within hours of injection, and the 〈sup〉15〈/sup〉N label was recovered almost exclusively as dissolved organic N within 62 h. These results indicate rapid microbial assimilation of the added N and transformation into novel organic compounds. We observed increasing concentrations of dissolved CH〈sub〉4〈/sub〉 and Fe(II), indicating rapid stimulation of methanogenesis and Fe(III) reduction. Low molecular weight organic acids such as acetate and propionate accumulated despite increasing consumption through anaerobic C mineralization. A laboratory soil column flow experiment using active layer soil collected from the same site further supported these findings. Glutamate recovery was low compared to a conservative bromide tracer, but concentrations of NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 and NH〈sub〉4〈/sub〉〈sup〉+〈/sup〉 remained low, consistent with microbial uptake of the added N. Similar to the field experiment, we observed both increasing Fe(II) and organic acid concentrations. Together, these results support our hypothesis of increased fermentation in response to organic N addition and suggest that increasing N availability could accelerate CH〈sub〉4〈/sub〉 production in tundra soils.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S003807171830419X-fx1.jpg" width="215" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Srabani Das, Brian K. Richards, Kelly L. Hanley, Leilah Krounbi, M.F. Walter, M. Todd Walter, Tammo S. Steenhuis, Johannes Lehmann〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The effect of long-term versus short-term water content on soil organic carbon (SOC) mineralizability was evaluated in a six-week incubation trial. Soils were sampled from field sites in upstate New York used for rain-fed bioenergy crop production: nitrogen (N)- fertilized reed canarygrass, switchgrass, switchgrass + N, as well as a broadleaf-grass fallow. Within each cropping system, natural moisture gradients due to topography and subsoil structure allowed us to sample across regions with high (0.5 g g〈sup〉−1〈/sup〉), mid (0.4 g g〈sup〉−1〈/sup〉) and low (0.3 g g〈sup〉−1〈/sup〉) water content. Moisture of the laboratory incubations was adjusted mimicking the three average field moisture levels in a full factorial design. Increasing laboratory moisture in the incubations increased cumulative carbon mineralization per unit soil (C mineralization) and cumulative C mineralization per unit SOC (C mineralizability) (main effect p 〈 0.0001), indicating that lower average moisture as found at this site on average limited mineralization but higher average moisture did not. C mineralizability at high field moisture was 31% (25-42%) lower than at low field moisture across all cropping systems, regardless of moisture adjustment in the incubation. The mean slow C pool size of soils from high field moisture sites (997.1 ± 0.1 mg C g〈sup〉−1〈/sup〉 C) was 0.2% greater than that of soils from low field moisture sites (p 〈 0.0001), obtained by fitting a double-exponential model. The mean residence time of the slow mineralizing C pool for soils from low field moisture sites was 5.5 ± 0.1 years, in comparison to 8.0 ± 0.1 years for soils from high field moisture sites (p 〈 0.0001). While permanganate-oxidizable carbon (POXC) per unit SOC (r = 0.1) was positively correlated to C mineralizability, wet aggregate stability (r = −0.2) was negatively correlated to C mineralizability. Above-ground biomass did not affect C mineralizability (p 〉 0.05) and root biomass marginally influenced (p = 0.05) C mineralizability after correcting for soil texture variations. Additionally, after correcting for soil texture variations and biomass inputs, C mineralizability significantly decreased with higher field moisture (p = 0.02), indicating possible stabilization mechanisms through mineral interactions of SOC under high water content. Bulk contents of pedogenic iron and aluminum determined by oxalate extraction did not clearly explain differences in mineralizability. However, exchangeable calcium and magnesium contents were significantly (p 〈 0.0001) greater in high moisture soils than soils with lower moisture. Additionally, cumulative C mineralizability at 6 weeks was negatively correlated to calcium (r = −0.7) and magnesium (r = −0.6) and mean residence time of the modeled slow pool correlated positively with calcium (r = 0.4). Therefore, cation bridging by retained or illuviated base ions was more important than redox changes of iron as a stabilization mechanism in this experiment.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Yuxi Guo, Meixiang Gao, Jie Liu, Andrey S. Zaitsev, Donghui Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Research on factors determining soil metacommunity patterns across multiple spatial scales is quite rare. In this study, we aimed to compare the mechanisms that drive species co-occurrence and consequently form the ground-dwelling macro-arthropod metacommunity structure at local (10〈sup〉4〈/sup〉 m) and regional (10〈sup〉6〈/sup〉 m) scales. For the comparison, we used three distant (approximately 200 km from each other) locations within the northeast black soil region of China. At each location, we had five sampling plots (at a distance of 500 m from each other), and at each plot, we had five sampling sites within agrolandscapes (10 m away from each other). At each site, we set three pitfall traps. Animals were collected three times: in May, July and September 2015. The analysis of the elements of metacommunity structure showed that the regional level of the metacommunity always demonstrated a Clementsian structure (a grouped distribution of species along environmental gradients), while the local scale metacommunity structure was dependent on sampling month and varied between Clementsian, random and nested distributions. Based on the results of a variance partitioning analysis, including pure environmental (environmental filtering) and pure spatial predictors (dispersal), as well as the interaction of environmental and spatial factors (shared fraction), we observed that the shared fraction at the regional scale was 30% larger than at the local scale. A species co-occurrence analysis further demonstrated that the observed C-scores were not significantly higher than simulated indices for each guild separately at the local scale. Our results suggest that biotic interactions are not the key drivers of metacommunity structure at the local scale in agriculture, while environmental filtering and dispersal appear to be key drivers of metacommunity structure at the regional scale.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Helen E. Taft, Paul A. Cross, Davey L. Jones〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Drained and cultivated fen peats represent some of the world's most productive soils, however, they are susceptible to degradation and typically exhibit high rates of greenhouse gas (GHG) emission. We hypothesised that GHG losses from these soils could be reduced by manipulating water table depth, tillage regime, crop residue application or horticultural fleece cover. Using intact soil columns from a horticultural peatland, emissions of CO〈sub〉2〈/sub〉, N〈sub〉2〈/sub〉O and CH〈sub〉4〈/sub〉 were monitored over a six-month period, using a closed-chamber method. Concurrent measurements of soil properties allowed identification of the key controls on GHG emissions. Raising the water table to the soil surface provided the strongest reduction in global warming potential (〈em〉GWP〈/em〉〈sub〉100〈/sub〉; 25 ± 6 kg CO〈sub〉2〈/sub〉-e ha〈sup〉−1〈/sup〉 d〈sup〉−1〈/sup〉), compared to a free-draining control (80 ± 1 kg CO〈sub〉2〈/sub〉-e ha〈sup〉−1〈/sup〉 d〈sup〉−1〈/sup〉), but this effect was partially negated by an emission pulse when the water table was subsequently lowered. The highest emissions occurred when the water table was maintained 15 cm below the surface (168 ± 11 kg CO〈sub〉2〈/sub〉-e ha〈sup〉−1〈/sup〉 d〈sup〉−1〈/sup〉), as this stimulated N〈sub〉2〈/sub〉O loss. Placement of horticultural fleece over the soil surface during spring had no significant effect on 〈em〉GWP〈/em〉〈sub〉100〈/sub〉, but prolonged fleece application exacerbated GHG emissions. Leaving lettuce crop residues on the surface increased soil 〈em〉GWP〈/em〉〈sub〉100〈/sub〉 (105 ± 4 kg CO〈sub〉2〈/sub〉-e ha〈sup〉−1〈/sup〉 d〈sup〉−1〈/sup〉) in comparison to when residues were incorporated into the soil (85 ± 4 kg CO〈sub〉2〈/sub〉-e ha〈sup〉−1〈/sup〉 d〈sup〉−1〈/sup〉), however, there was no evidence that this promoted positive priming of native soil organic matter (SOM). For maximum abatement potential, mitigation measures should be applied during the growing season, when GHG emissions are greatest. Our results also suggest that introduction of zero- or minimum-till practices may not reduce GHG emissions. Maintaining a high water table was the only option that reliably reduced GHG emissions, however, this option is impractical to implement within current horticultural systems. We conclude that alternative strategies or a major change in land use (e.g., conversion from horticulture/arable to wetland) should be explored as a means of preserving these soils for future generations.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Jin-Tao Li, Jun-Jian Wang, De-Hui Zeng, Shan-Yu Zhao, Wan-Ling Huang, Xue-Kai Sun, Ya-Lin Hu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Global climate change is projected to intensify soil drying-rewetting (DRW) events with extended drought, especially in arid and semiarid ecosystems. However, the extent to which the soil DRW with intensified drought can alter soil respiration (〈em〉R〈/em〉〈sub〉s〈/sub〉) in forests is still under debate, and subsequent legacy effects on 〈em〉R〈/em〉〈sub〉s〈/sub〉 are not well understood. Here, we conducted a 180-d soil incubation experiment to investigate how soil DRW with different drought intensities alter the 〈em〉R〈/em〉〈sub〉s〈/sub〉 in poplar (〈em〉Populus simonii〈/em〉) and Mongolian pine (〈em〉Pinus sylvestris〈/em〉 var. 〈em〉mongolica〈/em〉) plantations. The incubation experiment included four 30-d cycles of 1) constant moisture treatment (control), 2) DRW with 10-d drying and 20-d rewetting (DRW〈sub〉10-20〈/sub〉) or 3) DRW with 20-d drying and 10-d rewetting (DRW〈sub〉20-10〈/sub〉), and then an extended 60-d incubation under constant moisture. During the four DRW cycles, the direct C release with respiration of Mongolian pine soils (27 g C·m〈sup〉−2〈/sup〉 in DRW〈sub〉10-20〈/sub〉 and 140 g C·m〈sup〉−2〈/sup〉 in DRW〈sub〉20-10〈/sub〉, respectively) decreased to a much lower extent than that of poplar soils (228 g C·m〈sup〉−2〈/sup〉 in DRW〈sub〉10-20〈/sub〉 and 498 g C·m〈sup〉−2〈/sup〉 in DRW〈sub〉20-10〈/sub〉, respectively). 〈em〉R〈/em〉〈sub〉s〈/sub〉 did not significantly change during the extended 60-d incubation in the DRW〈sub〉10-20〈/sub〉 treatment compared to control treatment. However, the respired CO〈sub〉2〈/sub〉 were increased by 68 g C·m〈sup〉−2〈/sup〉 in the poplar soils and 19 g C·m〈sup〉−2〈/sup〉 in the Mongolian pine soils in the DRW〈sub〉20-10〈/sub〉 treatment, which approximately compensated for 14% of the decreases of total respiration during four DRW cycles. This legacy effect induced by the DRW with intensified drought was attributed to the higher amount of remaining substrates and soil microbial biomass. Our study highlights that DRW can cause both direct and legacy effects on 〈em〉R〈/em〉〈sub〉s〈/sub〉, but the effects vary with drought intensity and forest type.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 18 June 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry〈/p〉 〈p〉Author(s): Reinhard Well, Caroline Buchen, Jan-Reent Köster, Dominika Lewicka-Szczebak, Lena Rohe, Mehmet Senbayram, Di Wu〈/p〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Francesca Bortolin, Giuseppe Fusco, Lucio Bonato〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Trophic niche partitioning between potentially competing species within the same coenosis has been little explored for most of the major groups of arthropod soil predators, among which are the geophilomorph centipedes. We performed a comparative study in nature on the diet of three species of Geophilomorpha living in the same site in Southern Europe. Through PCR-based molecular gut content analysis, we estimated trophic niche width and overlap with respect to three common prey groups: lumbricids, collembolans and dipteran larvae. Results show that apparently similar geophilomorph species differ significantly in prey spectrum, with quite different niche widths. Estimates of predator diet overlap gave moderate values, non-significantly different from null expectations. Within-species diet composition does not vary significantly with sex. This work, while providing the first evidence of trophic niche partitioning among coexisting geophilomorph species, contributes to recent progresses in the understanding of intra-guild interactions between predators in the soil food webs.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Naili Zhang, Yinong Li, Tesfaye Wubet, Helge Bruelheide, Yu Liang, Witoon Purahong, François Buscot, Keping Ma〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A major gap in understanding the relationship between tree diversity and litter decomposition concerns knowledge of the saprotrophic fungal communities mediating decomposition processes. Making use of experimental tree diversity plots in subtropical China, our objective was to disentangle the effects of tree species richness on diversity, abundance, and composition of saprotrophic fungal communities in freshly fallen leaf litter. We employed a meta-genomic approach and analysed enzymatic decomposition. Our results indicate the dominance of Ascomycota, with species from this phylum colonizing leaf litter more rapidly than Basidiomycota. Furthermore, Ascomycota was the most abundant when tree richness was intermediate. Both Ascomycota and Basidiomycota differed significantly in their species composition in response to varying tree species richness. However, saprotrophic fungal species diversity did not respond to tree species richness. Instead, litter C/N ratio, litter Ca and plot altitude were the strongest determinants of fungal species diversity. Carbon-degradation enzyme activities were also significantly associated with litter C/N ratio, Ca and Fe concentration and, in addition, with tree species richness. The responses of fungal species and enzyme activity to tree species richness were uncoupled from each other, although the two variables were significantly correlated. Overall, our findings highlight a significant effect of tree species richness on litter fungal species composition, but not diversity. Our findings also provide insight into the importance of enzyme-mediated C degradation for the response to tree species richness in early-stage leaf decay in subtropical forests.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Md Masudur Rahman, Lettice C. Hicks, Kris Verheyen, Johannes Rousk, Monique Carnol〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the context of future climate change, the flush of CO〈sub〉2〈/sub〉 emissions from soils after drying-rewetting events could have a strong impact on the terrestrial carbon balance. Mixed forests may be more resistant and resilient to drought events compared to monocultures, and as such may modulate the effects of drought on soil functioning belowground. We investigated the influence of mixed planting and drought legacy on respiration and bacterial growth rates (〈sup〉3〈/sup〉H Leucine incorporation) in response to drying-rewetting. Soils were sampled from a 7-year old tree diversity experiment (FORBIO), where oak (〈em〉Quercus robur〈/em〉 L.) trees admixed with one or three other tree species were subjected to ∼50% precipitation reduction for 2 years (“drought legacy”). Respiration increased immediately after rewetting, whereas bacterial growth only started after a distinct lag phase of ca. 7 h. A legacy of drought reduced bacterial growth and respiration rates upon rewetting, however tree species admixing did not modulate the drought legacy effect. Our results suggest that prolonged decrease in precipitation may lead to a reduced CO〈sub〉2〈/sub〉 pulse upon drying-rewetting and admixing up to three tree species with oak in a young afforestation would not alleviate drought legacy effects on bacterial growth and respiration rates.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Qing Zheng, Yuntao Hu, Shasha Zhang, Lisa Noll, Theresa Böckle, Andreas Richter, Wolfgang Wanek〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The ratio of carbon (C) that is invested into microbial growth to organic C taken up is known as microbial carbon use efficiency (CUE), which is influenced by environmental factors such as soil temperature and soil moisture. How microbes will physiologically react to short-term environmental changes is not well understood, primarily due to methodological restrictions. Here we report on two independent laboratory experiments to explore short-term temperature and soil moisture effects on soil microbial physiology (i.e. respiration, growth, CUE, and microbial biomass turnover): (i) a temperature experiment with 1-day pre-incubation at 5, 15 and 25 °C at 60% water holding capacity (WHC), and (ii) a soil moisture/oxygen (O〈sub〉2〈/sub〉) experiment with 7-day pre-incubation at 20 °C at 30%, 60% WHC (both at 21% O〈sub〉2〈/sub〉) and 90% WHC at 1% O〈sub〉2〈/sub〉. Experiments were conducted with soils from arable, pasture and forest sites derived from both silicate and limestone bedrocks. We found that microbial CUE responded heterogeneously though overall positively to short-term temperature changes, and decreased significantly under high moisture level (90% WHC)/suboxic conditions due to strong decreases in microbial growth. Microbial biomass turnover time decreased dramatically with increasing temperature, and increased significantly at high moisture level (90% WHC)/suboxic conditions. Our findings reveal that the responses of microbial CUE and microbial biomass turnover to short-term temperature and moisture/O〈sub〉2〈/sub〉 changes depended mainly on microbial growth responses and less on respiration responses to the environmental cues, which were consistent across soils differing in land use and geology.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Loïc Nazaries, Senani B. Karunaratne, Manuel Delgado-Baquerizo, Colin D. Campbell, Brajesh K. Singh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉There is considerable evidence that environmental properties are important for microbial niche partitioning in general. However, little is known about the environmental factors explaining this for soil methane-oxidising bacteria (or methanotrophs), which play an essential role in ecosystem functioning and climate regulation through mitigation of net CH〈sub〉4〈/sub〉 emissions worldwide. This knowledge gap limits the inclusion of taxon-based information to improve predictions of climate change-simulation models. In this study, 697 soil samples were collected across Scotland and 62 climo-edaphic properties were analysed. Combined with a set of hybrid geostatistical modelling approaches, the aim of this study was to investigate the biogeographical distribution (〈em〉pmoA〈/em〉 gene relative abundance) of key methanotrophic operational taxonomic units named Terminal-Restriction Fragments (T-RFs) and of methanotrophic community structure. The main objectives were to: 1) identify major environmental drivers influencing the distribution and composition of methanotrophs; and 2) perform spatial modelling and mapping of soil methanotrophic community assemblage and distribution of those dominant T-RFs. Herein, it was hypothesised that the assemblage of methanotrophic community and distribution of key populations across various landscapes could be predicted using a range of climo-edaphic factors optimised for spatial, climate and terrain attributes. The findings presented here suggest that the distribution of methanotrophs is strongly linked to land use and some edaphic properties, predominantly soil moisture/rainfall, nutrients and metal ions. The hybrid geostatistical approach allowed for spatial prediction of methanotrophic T-RFs and community, and demonstrated a clear niche partitioning between dominant T-RFs. Overall, these results provide novel evidence that the distribution of methanotrophs could be explained and mapped in terms of niche partitioning and predicted at the regional scale. The findings of the present study have significance for the sustainable management of ecosystems and improvement of simulation models for better prediction of ecosystem functions under predicted global changes.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Yang Ouyang, Sarah E. Evans, Maren L. Friesen, Lisa K. Tiemann〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Quantification of functional genes involved in nitrogen (N) transformation improves our understanding of N-cycling microbial population responses to environmental disturbance. Agricultural N fertilization affects N-cycling gene abundances in soil, but the general patterns and variability of N cycling gene abundances in response to N fertilization have yet to be synthesized. We conducted a meta-analysis comprising 47 field studies in agricultural ecosystems. We included five marker genes important to N-cycling: 〈em〉nifH〈/em〉 (encoding nitrogenase; key enzyme for N fixation), 〈em〉amoA〈/em〉 (encoding ammonia monooxygenase; key enzyme for nitrification), 〈em〉nirK〈/em〉 and 〈em〉nirS〈/em〉 (encoding nitrite reductase; key enzyme for denitrification), and 〈em〉nosZ〈/em〉 (encoding nitrous oxide reductase; key enzyme for denitrification). We found that N fertilization had no effect on the abundance of 〈em〉nifH〈/em〉, but significantly increased archaeal 〈em〉amoA〈/em〉 (31%), bacterial 〈em〉amoA〈/em〉 (313%), 〈em〉nirK〈/em〉 (53%), 〈em〉nirS〈/em〉 (40%) and 〈em〉nosZ〈/em〉 (75%), respectively. N fertilizer form (inorganic versus organic) strongly affected the response of most selected N-cycling genes to N fertilization; organic fertilizers often had a much stronger effect than inorganic fertilizers. N fertilization duration, crop rotation, and soil pH were also important factors regulating the response of most N-cycling genes to N fertilization. Genes involved in nitrification and denitrification were significantly correlated with each other. Improvement in understanding of the response of N-cycling gene abundance to enhanced N input will help develop quantitative models of N availability and N fluxes and improve strategies for reducing reactive N gas emissions and N management in agricultural ecosystems.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Zhongjie Yu, Emily M. Elliott〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Recent analytical and conceptual advances related to the nitrate (NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉) 〈sup〉17〈/sup〉O anomaly (Δ〈sup〉17〈/sup〉O) have opened the door to a new method that probes soil nitrification and NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 consumption using Δ〈sup〉17〈/sup〉O of soil NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉. Because biological NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 production and consumption processes in soil obey the mass-dependent fractionation law, Δ〈sup〉17〈/sup〉O of soil NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉, an index of excess 〈sup〉17〈/sup〉O over that expected from 〈sup〉18〈/sup〉O, can be used to trace gross nitrification and NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 consumption in a way analogous to the 〈sup〉15〈/sup〉NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 tracer typically employed in studies of soil NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 cycling. Moreover, coupling Δ〈sup〉17〈/sup〉O with the dual NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 isotopes (δ〈sup〉15〈/sup〉N and δ〈sup〉18〈/sup〉O) at natural abundances offers additional valuable insights into mechanisms that underlie soil NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 dynamics. In this study, we conducted both laboratory and field experiments to assess the use of Δ〈sup〉17〈/sup〉O-NO〈sub〉3〈/sub〉〈sup〉-〈/sup〉 for tracing soil nitrification and NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 consumption. Soil samples spanning a wide range of physical and chemical properties were sampled from four sites for batch incubations and amendments with a Δ〈sup〉17〈/sup〉O-enriched NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 fertilizer. After amendments, the triple isotopes (δ〈sup〉15〈/sup〉N, δ〈sup〉18〈/sup〉O, and Δ〈sup〉17〈/sup〉O) of soil NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 were measured periodically and used in a developed Δ〈sup〉17〈/sup〉O-based numerical model to simultaneously derive gross rates and isotope effects of soil nitrification and NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 consumption. The measured Δ〈sup〉17〈/sup〉O-NO〈sub〉3〈/sub〉〈sup〉-〈/sup〉 was also used in the classical isotope dilution model to estimate gross NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 turnover rates. 〈em〉In situ〈/em〉 field soil sampling was conducted in a temperate upland meadow following snowmelt input of Δ〈sup〉17〈/sup〉O-enriched atmospheric NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 to assess the robustness of Δ〈sup〉17〈/sup〉O-NO〈sub〉3〈/sub〉〈sup〉-〈/sup〉 as a natural tracer. The results show that the temporal dynamics of Δ〈sup〉17〈/sup〉O-NO〈sub〉3〈/sub〉〈sup〉-〈/sup〉 can provide quantitative information on soil nitrification and NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 consumption. In the laboratory incubations, a wide range of gross nitrification and NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 consumption rates were estimated for the four soils using the Δ〈sup〉17〈/sup〉O-based models. The estimated rates are well within the range reported in previous 〈sup〉15〈/sup〉N tracer-based studies and not sensitive to oxygen isotopic fractionations during nitrification and NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 consumption. Coupling Δ〈sup〉17〈/sup〉O-NO〈sub〉3〈/sub〉〈sup〉-〈/sup〉 with the dual NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 isotopes using the numerical model placed strong constraints on the δ〈sup〉15〈/sup〉N and δ〈sup〉18〈/sup〉O endmembers of nitrification-produced NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 and revealed soil-specific N isotope effects for nitrification and NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 consumption, consistent with the inferred differences in soil microbial community structure among these soils. Non-zero Δ〈sup〉17〈/sup〉O-NO〈sub〉3〈/sub〉〈sup〉-〈/sup〉 values, up to 4.7‰, were measured in the meadow soil following the snowmelt event. Although soil heterogeneity in the field prevents quantitative rate estimation using Δ〈sup〉17〈/sup〉O-NO〈sub〉3〈/sub〉〈sup〉-〈/sup〉, active NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 cycling via co-occurring nitrification and denitrification was revealed by the covariations in the triple NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 isotopes. Integrating the field observations with the incubation results uncovered isotopic overprinting of nitrification on denitrification in the surface soil following the snowmelt, which has important implications for explaining the discrepancies between field- and laboratory-derived isotope systematics of denitrification. We conclude that Δ〈sup〉17〈/sup〉O-NO〈sub〉3〈/sub〉〈sup〉-〈/sup〉 is a conservative and powerful tracer of soil nitrification and NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 consumption and future applications are expected to help disentangle soil NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 cycling complexity at various scales.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Rana Shahbaz Ali, Christian Poll, Ellen Kandeler〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil microbial communities mediate soil feedbacks to climate; a thorough understanding of their response to increasing temperatures is therefore central to predict climate-induced changes in carbon (C) fluxes. However, it is unclear how microbial communities will change in structure and function in response to temperature change and to the availability of organic C which varies in complexity. Here we present results from a laboratory incubation study in which soil microbial communities were exposed to different temperatures and organic C complexity. Soil samples were collected from two land-use types differing in climatic and edaphic conditions and located in two regions in southwest Germany. Soils amended with cellobiose (CB), xylan, or coniferyl alcohol (CA, lignin precursor) were incubated at 5, 15 or 25 °C. We found that temperature predominantly controlled microbial respiration rates. Increasing temperature stimulated cumulative respiration rates but decreased total microbial biomass (total phospholipid fatty acids, PLFAs) in all substrate amendments. Temperature increase affected fungal biomass more adversely than bacterial biomass and the temperature response of fungal biomass (fungal PLFAs, ergosterol and ITS fragment) depended upon substrate quality. With the addition of CB, temperature response of fungal biomass did not differ from un-amended control soils, whereas addition of xylan and CA shifted the fungal temperature optima from 5 °C to 15 °C. These results provide first evidence that fungi which decompose complex C substrates (CA and xylan) may have different life strategies and temperature optima than fungal communities which decompose labile C substrate (CB). Gram-positive and gram-negative bacteria differed strongly in their capacity to decompose CB under different temperature regimes: gram-positive bacteria had highest PLFA abundance at 5 °C, while gram-negative bacteria were most abundant at 25 °C. Bacterial community composition, as measured by 16S rRNA gene abundance, and PLFAs showed opposite temperature and substrate decomposition trends. Using multivariate statistics, we found a general association of microbial life strategies and key members of the microbial community: oligotrophic 〈em〉Alphaproteobacteria〈/em〉 and 〈em〉Acidobacteria〈/em〉 were associated with complex substrates and copiotrophic 〈em〉Actinobacteria〈/em〉 with labile substrates. Our study provides evidence that the response of C cycling to warming will be mediated by shifts in the structure and function of soil microbial communities.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): N.T. Girkin, B.L. Turner, N. Ostle, S. Sjögersten〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Tropical peatlands are a significant carbon store and source of carbon dioxide (CO〈sub〉2〈/sub〉) and methane (CH〈sub〉4〈/sub〉) to the atmosphere. Plants can contribute to these gas emissions through the release of root exudates, including sugars and organic acids amongst other biomolecules, but the roles of concentration and composition of exudates in regulating emissions remains poorly understood. We conducted a laboratory incubation to assess how the type and concentration of root exudate analogues regulate CO〈sub〉2〈/sub〉 and CH〈sub〉4〈/sub〉 production from tropical peats under anoxic conditions. For CO〈sub〉2〈/sub〉 production, substrate concentration was the more important driver, with increased CO〈sub〉2〈/sub〉 fluxes following higher addition rates of four out of the six exudate analogues. In contrast, exudate type was the more important driver of CH〈sub〉4〈/sub〉 production, with acetate addition associated with the greatest production, and inverse correlations between exudate concentration and CH〈sub〉4〈/sub〉 emission for the remaining five treatments. Root exudate analogues also altered pH and redox potential, dependent on the type of addition (organic acid or sugar) and the concentration. Overall, these findings demonstrate the contrasting roles of composition and concentration of root exudate inputs in regulating greenhouse gas emissions from tropical peatlands. In turn this highlights how changes in plant communities will influence emissions through species specific inputs, and the possible impacts of increased root exudation driven by rising atmospheric CO〈sub〉2〈/sub〉 and warming.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0038071718303444-egi10GZSJ9PDXX.jpg" width="279" alt="Image" title="Image"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Kevin M. Geyer, Paul Dijkstra, Robert Sinsabaugh, Serita D. Frey〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Accurate estimates of microbial carbon use efficiency (CUE) are required to predict how global change will impact microbially-mediated ecosystem functions such as organic matter decomposition. Multiple approaches are currently used to quantify CUE but the extent to which estimates reflect methodological variability is unknown. This limits our ability to apply or cross-compare published CUE values. Here we evaluated the performance of five methods in a single soil under standard conditions. The microbial response to three substrate amendment rates (0.0, 0.05, and 2.0 mg glucose-C g〈sup〉−1〈/sup〉 soil) was examined using: 〈sup〉13〈/sup〉C and 〈sup〉18〈/sup〉O isotope tracing approaches which estimate CUE based on substrate uptake and growth dynamics; calorespirometry which infers growth and CUE from metabolic heat and respiration rates; metabolic flux analysis where CUE is determined as the balance between biosynthesis and respiration using position-specific 〈sup〉13〈/sup〉CO〈sub〉2〈/sub〉 production of labeled glucose; and stoichiometric modeling which derives CUE from elemental ratios of microbial biomass, substrate, and exoenzyme activity. The CUE estimates we obtained differed by method and substrate concentration, ranging under 〈em〉in situ〈/em〉 conditions from 〈0.4 for the substrate-nonspecific methods that do not use C tracers (〈sup〉18〈/sup〉O, stoichiometric modeling) to 〉0.6 for the substrate-specific methods that trace glucose use (〈sup〉13〈/sup〉C method, calorespirometry, metabolic flux analysis). We explore the different aspects of microbial metabolism that each method captures and how this affects the interpretation of CUE estimates. We recommend that users consider the strengths and weaknesses of each method when choosing the technique that will best address their research needs.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Laura M. Szymanski, Gregg R. Sanford, Katherine A. Heckman, Randall D. Jackson, Erika Marín-Spiotta〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Bioenergy cropping systems have the potential to supply plant biomass as lignocellulosic feedstock for biofuels and bioproducts that will reduce reliance on fossil energy. Identifying the effects of alternative bioenergy cropping systems on soil carbon (C) is necessary to assess the sustainability of renewable fuels. We measured the response of soil organic carbon (SOC) pools to four bioenergy cropping systems using soils collected at the establishment of the field trials and after five years in two soils of contrasting texture: a fine-textured silt loam (Mollisol) in south central Wisconsin and a coarse-textured sandy loam (Alfisol) in southwestern Michigan, USA. Crop management followed region-specific practices with no till with the intention of reducing soil C losses from cultivation. Cropping systems included an annual monoculture (continuous corn), two perennial monocultures (switchgrass and hybrid poplar), and a perennial polyculture (restored native prairie). Using a 365-d laboratory soil incubation and a three-pool model, we estimated sizes and turnover times of SOC in surface (0–10 cm) and deeper soils (25–50 cm). After five years, all soils had less bioavailable C as measured by microbial respiration. To determine potential differences in soil C turnover under annual and perennial monocultures, we measured radiocarbon abundance (〈sup〉14〈/sup〉C) of bulk soils and respired CO〈sub〉2〈/sub〉 under corn and switchgrass. Respired-CO〈sub〉2〈/sub〉 was more depleted in 〈sup〉14〈/sup〉C over time, indicating preferential respiration of relatively “old C” after five years. Decreased microbial respiration rates after five years of bioenergy cropping systems offer the potential for the eventual reduction of soil C losses after conversion to no till. However, the 〈sup〉14〈/sup〉C-CO〈sub〉2〈/sub〉 data suggest that previously-protected C pools may become depleted over time, especially with continued removal of plant inputs. Results show that conversion of conventional field-crop agriculture to bioenergy cropping systems may not provide belowground C benefits in the short term, as indicated by reductions in the size of the active pool. Reduced total soil respiration over the length of the study, as well as system-specific differences in soil respiration (monoculture annuals 〈 monoculture perennial 〈 polyculture perennials), suggest C loss may decline in perennial polyculture systems as they age. SOM pools responded differently to bioenergy crop management on soils with contrasting texture, highlighting the importance of geography in predicting belowground consequences of intensified agricultural production.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Pengshuai Shao, Chao Liang, Kennedy Rubert-Nason, Xiangzhen Li, Hongtu Xie, Xuelian Bao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil microbes link aboveground and belowground ecosystem processes by modulating nutrient retention, recycling, and availability to plants. The diversity and abundance of soil microbes are influenced by biotic and edaphic factors such as plant communities and soil chemistry. Despite this general understanding, relatively few details are known about how soil microbial community structure responds to changing plant communities and soil chemistry associated with secondary forest succession. To address these gaps, we used 16S rRNA gene sequencing to investigate how diversity, composition and abundance of soil prokaryotic communities differed among five successional stages at two soil depths in a temperate forest, and then related these differences with soil properties. Oligotrophic prokaryotic taxa were more common in earlier successional stages, and community diversity declined at later forest successional stages. Prokaryotic diversity was consistently higher in topsoil than subsoil. Prokaryotic community composition varied with respect to soil organic matter (SOM) properties. The relative abundances of specific carbon (C) functional groups (e.g., aliphatic C groups, aromatic C groups and polysaccharides) revealed by mid-IR spectroscopy were strongly related with prokaryotic community composition. Overall, this study revealed that changes in soil prokaryotic community structure (diversity, composition and taxa abundance) paralleled changes in plant communities and soil chemistry associated with forest succession, and that these changes can be inferred through changes in SOM properties.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0038071718303523-fx1.jpg" width="270" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Ruiying Chang, Na Li, Xiangyang Sun, Zhaoyong Hu, Xuesong Bai, Genxu Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Dissolved organic carbon (DOC) plays a significant role in the forest soil carbon cycle and can be regulated by nitrogen (N) addition. However, the regulatory direction, mechanism and seasonal pattern of DOC under N addition are less clear. Here, in a montane evergreen forest located at the eastern edge of the Tibetan Plateau, 2 levels of N were applied over 2 years to determine the effects of N addition on DOC release from organic (O layer) and mineral soil. Frequent sampling revealed that high levels of N addition could decrease the concentration of DOC and the flux from the O layer but not from mineral soil and that moderate N addition had no effect on DOC leaching from either the O or mineral layer. The effect of N addition on DOC leaching from the O layer was seasonally dependent, showing a significant reduction in DOC leaching during autumn/winter but no changes during summer and spring. This seasonally different response of DOC to N addition affected the seasonal pattern of DOC leaching. Soil and leachate pH were not influenced by N addition in the short term, indicating that there was not enough difference in DOC retention by mineral soil to significantly affect DOC leaching under N addition. In contrast, N addition-derived reduction in DOC leaching was likely to be due to suppressed fresh litterfall–derived DOC production during autumn/winter; this speculation was supported by lower values of O layer water-extractable organic carbon and microbial biomass carbon as well as lower saccharase and cellulose activities found with high N addition. These results suggested that the processes in control of DOC leaching and their responses to N addition were different for O and mineral soil and that short-term N addition could decrease O-layer DOC leaching, which is likely associated with decreased DOC production rather than greater DOC retention.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): David J. Burke, Sarah R. Carrino-Kyker, Adam Hoke, Steven Cassidy, Lalasia Bialic-Murphy, Susan Kalisz〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The invasive plant, garlic mustard (〈em〉Alliaria petiolata〈/em〉), has the potential to affect soil microbial communities and ecosystem processes in temperate hardwood forests primarily through the release of allelopathic chemicals into the soil. These forest soils are also often affected (directly and indirectly) by the high abundance of white-tailed deer (〈em〉Odocoileus virginianus〈/em〉), which can alter plant community composition and productivity. We examined the joint effects of deer and garlic mustard on soil microbial communities, soil nutrients and a native plant species’ vital rates in a temperate forest 8 years after initiation of a paired plot deer exclusion/access study where garlic mustard was either removed from half of each plot or remained at ambient level in the other plot half. We examined soil microbial communities using DNA-based techniques and quantified nutrient availability and physicochemical properties. Deer exclusion affected the community structure of AM fungi, particularly when garlic mustard was present, but had no effect on soil chemistry. Garlic mustard removal plots showed no changes for soil fungi, but displayed higher soil carbon content. Interestingly, we found significant changes to native plant vital rates that mirrored soil responses; the presence of garlic mustard led to higher mortality of large, mature plants and reduced native plant cover and biomass. Our data suggest herbivore-plant-soil feedbacks and synergies can interact to negatively affect the soil ecology of forests. Management activities that reduce deer or invasive plant abundance may positively affect soil microbial communities and chemistry in temperate forests.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Daniele la Cecilia, William J. Riley, Federico Maggi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Microbial decomposition of Soil Organic Matter (SOM) is largely controlled by environmental and edaphic factors such as temperature, pH, and moisture. However, microbial metabolism is controlled by catabolite repression, which leads microbes to grow on preferred nutrient and energy sources first. In particular, Catabolite Repression for Carbon (CR-C) defines the hierarchical preference of bacteria for particular C sources. This control depends on the presence of signal molecules conferring bacteria a memory for recent growth conditions on less preferred C sources. The combined effect of catabolite repression and microbial memory (called here Memory-Associated Catabolite Repression for Carbon, MACR-C) has not yet been investigated in detail. First, we use observations and a numerical model to test the hypothesis that MACR-C explains substrate preferential consumption in a simple, 2-C substrate system, whereas Michaelis-Menten-Monod kinetics of competitive substrate consumption, non-competitive inhibition, or their combination, do not. Next, we carry out numerical analyses to explore the sensitivity of (1) estimated parameters to experimental observations and (2) model structure to steady-state substrate concentration under pulse or continuous substrate application. Our results show that MACR-C substantially affected substrate consumption and microbial readiness to switch between C sources.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Wenqing Chen, Ran Xu, Jun Chen, Xianping Yuan, Lei Zhou, Tianyuan Tan, Jinrui Fan, Yingjun Zhang, Tianming Hu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil fungal communities are critical to decomposition, nutrient cycling and the maintenance of plant diversity and abundance. However, despite global increases in reactive nitrogen (N) inputs to terrestrial ecosystems, due to anthropogenic activities, an explicit evaluation of the direct (resource availability) and indirect (acidification and plant community changes) effects of N enrichment on soil fungal communities in grassland ecosystems remains largely unexplored. In this study, we used Illumina sequencing of the ITS1 barcode region to elucidate the responses of soil fungal communities using a 7-year simulated N deposition experiment that spanned a broad range of N addition rates and made a systematic evaluation of the role and relative importance of N availability, plant community and soil acidification as drivers of soil fungal diversity in a semi-arid grassland ecosystem. Our results showed that N enrichment led to significant declines in soil fungal alpha diversity and promoted strong shifts in beta diversity (community composition) in both surface and subsurface soil layers. We found that N addition-induced soil acidification overwhelmed the effects of increased N availability and plant community changes, and played a primary role in shaping the observed changes in fungal alpha and beta diversity in surface soil. Conversely, in the subsurface soil layer, both fungal alpha and beta diversity were primarily controlled by N addition-induced changes in plant community attributes (i.e., aboveground plant productivity and plant community composition). Thus, our work illustrates the consistent responses of surface and subsurface soil fungal diversity (both alpha and beta diversity) to N addition that are mediated by different mechanisms and provides an integrated insight into how N enrichment could alter soil fungal diversity in semi-arid grassland in future scenarios of elevated N deposition.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Andrew Bissett, Mark V. Brown〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Microbial alpha-diversity, a fundamental ecological concept, is often determined using multiplexed amplicon sequencing approaches. Here we show, using standardized controls and 1879 soil samples, across 21 illumina MiSEQ high throughput sequencing (HTS) runs, that sample alpha-diversity estimates are highly dependent upon the overall diversity of all samples within the sequencing run, a likely result of within sequencing run cross-talk. Cross-talk, therefore, has grave implications for alpha-diversity interpretation in mulitplexed sequencing studies.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Karen Baumann, Patrick Jung, Elena Samolov, Lukas W. Lehnert, Burkhard Büdel, Ulf Karsten, Jörg Bendix, Sebastian Achilles, Michael Schermer, Francisco Matus, Rómulo Oses, Pablo Osses, Mohsen Morshedizad, Claudia Oehlschläger, Yongfeng Hu, Wantana Klysubun, Peter Leinweber〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Biodiversity of phototrophic microorganisms in South American biological soil crusts (BSCs) and their role in the biogeochemical phosphorus (P)-cycle are unknown. Richness of BSC green algae and cyanobacteria was investigated at four climatically different Chilean sites (arid, semi-arid, Mediterranean, humid). Carbon (C), nitrogen (N), sulfur (S), and P contents, P pools and P speciation as well as spatial P species distribution within the BSCs were investigated. Morphological identification of enrichment cultures revealed 24 green algal and 18 cyanobacterial taxa in total. Irrespective of climatic conditions, each BSC comprised 12 to 15 different phototrophic species. Thereby, green algal richness increased, while cyanobacterial richness decreased with increasing humidity/decreasing mean annual temperature (North to South). Total C, N, and S contents ranged between 6.7 and 41.1 g C kg〈sup〉−1〈/sup〉, 0.6–2.8 g N kg〈sup〉−1〈/sup〉 and 0.2–0.7 g S kg〈sup〉−1〈/sup〉, respectively, and increased in the order crust-free soil 〈 crust-adhering soil 〈 BSC. The total P content in BSCs ranged from 310 to 777 mg kg〈sup〉−1〈/sup〉 with lowest concentrations at the arid site and highest concentrations at the semi-arid site. Labile P was highest in BSCs from semi-arid and Mediterranean climate implying no P-shortage for BSC organisms at these sites. In BSCs of all sites, stable and non-extractable P was identified as the major P pool (sequential P fractionation) with Ca-P species dominating at all sites except for the humid site at which Al-P was the main P species as determined by P 〈em〉K〈/em〉-edge X-ray absorption near edge structure, XANES. P 〈em〉K〈/em〉-edge μ-XANES of BSC cross sections revealed apatite hotspots, a potential P source for BSC organisms except for the arid site, where other Ca-P species dominated. Further, elemental mapping of the arid BSC cross section showed distinct accumulation of S and chloride (Cl) containing compounds within green algae and on their outer surface, respectively, raising the question of function/origin of these compounds. In conclusion, this work expands our knowledge on the richness of phototrophic organisms in South American BSCs and characterizes their possible position in the P-cycle along a strong climatic gradient. Our findings suggest that biotic and abiotic factors shape the structure of BSCs phototrophic communities as well as P pools and species at each habitat.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Sarah A. Maarastawi, Katharina Frindte, Romy Geer, Eileen Kröber, Claudia Knief〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Crop rotation between paddy rice and maize is of increasing relevance because of ecological and economic reasons. The cultivation of maize in paddy soils during the dry season reduces water consumption and methane emissions, while fulfilling the increasing demand of maize for biofuel production and poultry fattening. However, introduction of upland crops in paddy fields often leads to carbon and nitrogen loss due to desiccation crack formation. Straw application can reduce crack formation and acts as fertilizer. The temporal dynamics of straw degradation under oxic conditions in paddy soils undergoing crop rotation have been scarcely studied. We identified the straw degrading microorganisms comparatively in the bulk soil and rhizosphere of maize by DNA-stable isotope probing with 〈sup〉13〈/sup〉C-labelled rice straw and amplicon sequencing of the 16S rRNA gene and ITS1 region. Moreover, the degradation process in bulk soil was investigated over time. Straw degradation was performed by aerobic microorganisms and showed a clear temporal succession. In the initial phase, fast growing bacteria became labelled, followed by the labelling of fungi, known to degrade more complex carbon compounds. In the rhizosphere, partly different microorganisms were identified as labelled than in bulk soil, indicating that the microbial straw degradation process differs to some extent between these two compartments. The size of the labelled microbial population was smaller in the rhizosphere than in bulk soil, pointing to a preferential utilization of plant root derived carbon by microorganisms in the rhizosphere.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Yakov Kuzyakov, William R. Horwath, Maxim Dorodnikov, Evgenia Blagodatskaya〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Atmospheric change encompassing a rising carbon dioxide (CO〈sub〉2〈/sub〉) concentration is one component of Global Change that affects various ecosystem processes and functions. The effects of elevated CO〈sub〉2〈/sub〉 (eCO〈sub〉2〈/sub〉) on belowground processes are incompletely understood due to complex interactions among various ecosystem fluxes and components such as net primary productivity, carbon (C) inputs to soil, and the living and dead soil C and nutrient pools. Here we summarize the literature on the impacts of eCO〈sub〉2〈/sub〉 on 1) cycling of C and nitrogen (N), 2) microbial growth and enzyme activities, 3) turnover of soil organic matter (SOM) and induced priming effects including N mobilization/immobilization processes, and 4) associated nutrient mobilization from organic sources, 5) water budget with consequences for soil moisture, 6) formation and leaching of pedogenic carbonates, as well as 7) mobilization of nutrients and nonessential elements through accelerated weathering. We show that all effects in soil are indirect: they are mediated by plants through increased net primary production and C inputs by roots that foster intensive competition between plants and microorganisms for nutrients. Higher belowground C input from plants under eCO〈sub〉2〈/sub〉 is compensated by faster C turnover due to accelerated microbial growth, metabolism and respiration, higher enzymatic activities, and priming of soil C, N and P pools. We compare the effects of eCO〈sub〉2〈/sub〉 on pool size and associated fluxes in: soil C stocks vs. belowground C input, microbial biomass vs. CO〈sub〉2〈/sub〉 soil efflux vs. various microbial activities and functions, dissolved organic matter content vs. its production, nutrient stocks vs. fluxes etc. Based on these comparisons, we generalize that eCO〈sub〉2〈/sub〉 will have little impacts on pool size but will strongly accelerate the fluxes in biologically active and stable pools and consequently will accelerates biogeochemical cycles of C, nutrients and nonessential elements.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Carbon Fluxes under Elevated CO〈sub〉2〈/sub〉: No Changes in Pools but Acceleration in Fluxes.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0038071718303535-egi10FJ64TH83M.jpg" width="269" alt="Image" title="Image"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Dominik Brödlin, Klaus Kaiser, Arnim Kessler, Frank Hagedorn〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Phosphorus (P) is a key nutrient but still we have a limited knowledge on the controls of mobilization and fluxes of P in forest soils. Our study explored the linkages between P mobilization in organic horizons and mineral soils and the P status of soils, as affected by two consecutive drying and rewetting (D/W) cycles. We sampled litter layers (Oi), mixed Oe-Oa horizons, and A horizons in three beech forests along a P availability gradient in Germany. Carbon mineralization and release of dissolved organic matter (DOC, DOP) and dissolved inorganic P (DIP) were studied in microcosms exposed to an initial harsh drying (40 °C for 72 h) and a moderate dry spell (1 month at 20 °C). In Oi horizons, net P mineralization decreased with decreasing P status despite a similar C mineralization at all sites. This supports the general concept that the stoichiometric difference between substrate and microbial biomass primarily drives P release from decomposing organic matter. Counterintuitively, P mobilization per unit soil P increased towards P-poor sites in the mineral soil, likely due to decreasing contents of reactive secondary minerals and the consequently smaller P sorption. Drying and rewetting caused stronger mobilization of DIP and DOP (+108% on average) than of DOC (+51%). The parallel decline in specific UV absorptivity of DOM suggests that lysis of microbial cells drove the drought-induced P release. The D/W effects on P mobilization were particularly strong in P-poor soils, where greater portions of P are bound to microbial biomass, which are prone to become released upon rewetting. Since mobilized P can potentially be leached from soils, our findings indicate, that drought-induced P mobilization fosters the progressive P depletion of already P-poor soils. The possible P leaching losses from mineral soils seem rather be driven by soil mineralogy than by P status.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0038071718303493-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Lei Jiang, Liang Kou, Shenggong Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Nitrogen (N) deposition may inhibit decomposition by decreasing microbial growth and activity (microbial mechanism) and/or increasing the binding of inorganic N ions to the acid-unhydrolyzable residue (AUR) in decomposing litter (chemical mechanism). How increased phosphorus (P) deposition affects decomposition and mediates the effect of N on this process, however, remains unclear. We used a nutrient-manipulative experiment to examine the individual and interactive effects of N and P on the decomposition of two fast-cycling organs (leaves vs. absorptive roots) in 〈em〉Pinus massoniana〈/em〉 and 〈em〉Schima superba〈/em〉 forests in subtropical China. The carbon fractions and microbial enzymatic activities in decomposing leaves and roots were also determined to identify the underlying mechanisms. Adding only N negatively affected the decomposition of absorptive roots but had no or a positive effect on foliar decomposition. Adding only P increased foliar decomposition but did not affect root decomposition. Adding both N and P had little effect on decomposition, except for a positive effect on 〈em〉P. massoniana〈/em〉 leaves. The nutrient additions did not affect the amount of carbon remaining in the leaves, and adding only N increased the residual AUR content in the roots. Adding only P decreased the activity of acid phosphatase (AP) in the leaves. Foliar decomposition was correlated with microbial enzymatic activity but not AUR content. Root decomposition was correlated more strongly with AUR content than microbial enzymatic activity. The increased decomposition but decreased AP activity of the leaves with P addition suggests a stronger P limitation on the decomposition of leaves than roots in these subtropical forests. The stimulating effect of P on foliar decomposition may be due to a microbial mechanism, and a chemical mechanism may dominate the inhibitory effect of N on root decomposition. Our findings facilitate the mechanistic understanding of the effects of nutrient deposition on the decomposition of leaves and absorptive roots, and highlight the role of P deposition in mediating the effect of N on decomposition.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Andrey Guber, Alexandra Kravchenko, Bahar S. Razavi, Daniel Uteau, Stephan Peth, Evgenia Blagodatskaya, Yakov Kuzyakov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil membrane zymography enables 2D mapping of enzyme activities on the surface of soil samples. The method is based on diffusion of components of enzymatically-mediated reactions to/from membrane, and, thus, reflects the distribution of enzyme activities at the intact soil surface. Zymography has been already successfully implemented in numerous soil ecology applications. Here we identify two methodological aspects for further improvement and expansion of the method at micro and macro scales: first, accounting for the area of contact between the soil surface and the zymography membranes and, second, accounting for diffusion effects during the zymography procedure. We tested three methods, namely, laser-scanning, staining with a fluorescent product (e.g. MUF: 4-methylumbelliferone), and X-ray computed micro-tomography, for assessing the area of the soil surface in contact with the membranes. We quantified diffusion of MUF, enzymes and substrate between the substrate-saturated membrane and soil as well as diffusion processes during membrane zymography via HP2 software. Diffusion of the substrate from the membrane and of the MUF-product to the membrane was detected, while there were no clear evidence of enzyme diffusion to/in the membrane. According to the model simulations, the enzyme activities detected via 2D zymography probably represent only a small portion, about 20%, of the actual reactions within the soil volume that is in both direct contact and in hydrological contact with zymography membranes. This is a result of omnidirectional diffusion of reaction products. The membrane contact with the soil surface estimated by three methods ranged from 3.4 to 36.5% further signifying that only a fraction of enzymes activity is detectable in a course of 2D soil zymography.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Emily D. Whalen, Richard G. Smith, A. Stuart Grandy, Serita D. Frey〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Long-term atmospheric nitrogen (N) deposition has been shown to reduce leaf litter and lignin decomposition in temperate forest soils, leading to an accumulation of soil carbon (C). Reduced decomposition has been accompanied by altered structure and function of fungal communities, the primary decomposers in forest ecosystems; however, a mechanistic understanding of fungal responses to chronic N enrichment is lacking. A reduction in soil and litter manganese (Mn) concentrations under N enrichment (i.e., Mn limitation) may help explain these observations, because Mn is a cofactor and regulator of lignin-decay enzymes produced by fungi. We conducted a laboratory study to evaluate the effect of Mn availability on decomposition dynamics in chronically N-enriched soils. We measured litter mass loss, lignin relative abundance, and lignin-decay enzyme activities, and characterized the litter fungal community by ITS2 metabarcoding. We observed a significant positive correlation between Mn availability and lignin-decay enzyme activities. In addition, long-term (28 years) N enrichment increased the relative abundance of ‘weak’ decomposers (e.g., yeasts), but this response was reversed with Mn amendment, suggesting that higher Mn availability may promote fungal communities better adapted to decompose lignin. We conclude that Mn limitation may represent a mechanism to explain shifts in fungal communities, reduced litter decomposition, and increased soil C accumulation under long-term atmospheric N deposition.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Clayton J. Nevins, Cindy Nakatsu, Shalamar Armstrong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Cover crop adoption in the U.S. Corn Belt region is a rapidly emerging management practice in corn (〈em〉Zea mays〈/em〉) agroecosystems. However, little is known about the impact of the inclusion of cover crops on the soil microbiome and its relation to the decomposition of the cover crop residue during the cash crop growing season. Therefore, this study sought to determine the impact of cover crop species and residue management practices on soil microbial community composition and structure during winter cover crop decomposition over the corn growing season. Cover crop treatments included hairy vetch (〈em〉Vicia villosa〈/em〉 Roth), cereal rye (〈em〉Secale cereal〈/em〉), a hairy vetch/cereal rye mixture, and a no cover crop control. Residue management practices included no-tillage and a 15 cm reduced spring tillage following cover crop termination. Soil samples were collected at five dates during cover crop decomposition that corresponded to an accumulated number of calendar days from cover crop termination, and soil bacterial communities were characterized using the small subunit (16S) rRNA gene sequences. Statistical analyses revealed that sampling date, cover crop treatment, and residue management treatment were significant determinants of soil microbial community composition (p 〈 0.05) and the effect of cover crop treatment increased as the decomposition period progressed. As cereal rye began to decompose and soil β-glucosidase (EC 3.2.1.21) potential activity increased, the relative abundance of bacteria previously identified as cellulolytic, including 〈em〉Agromyces〈/em〉, 〈em〉Agrobacterium〈/em〉, and 〈em〉Bacillus〈/em〉, contributed to the difference among the cover crop treatments (LDA score 〉 2.0). Data generated from this study leads to a deeper understanding of bacterial responses to cover crop decomposition in corn agroecosystems.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Ryan M. Mushinski, Terry J. Gentry, Thomas W. Boutton〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Intensive organic matter removal (OMR) associated with timber harvest has the potential to impart long-term alterations to soil biota and associated properties and processes; however, there is a lack of data to say if this trend persists at depth. This study investigated how OMR influences long-term stability of soil fungi to a depth of 1 m using a replicated experimental pine forest in the Gulf Coastal Plain, USA. Treatments included unharvested control stands as well as low- and high-OMR stands. Intensive OMR led to significant differences in community structure and the abundance of functional guilds in surficial soil. Saprophytic taxa increased while ectomycorrhizal (ECM) taxa decreased with intensive-OMR, which correlated strongly with increased surface temperature and reduced soil nitrogen. Ericoid mycorrhizae (ERM) also increased in intensive-OMR stands, which may indicate that following disturbance, ERM could outcompete ECM for colonization of subsequent seedlings. Overall, no differences were observed below 30 cm, except for alpha diversity, which was a function of high inter-replicate variability. Our results illustrate a distinct long-term structural and functional response of soil fungi to intensive-OMR in the upper portions of the soil profile, which could lead to altered stand productivity and ecosystem services.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Jie Yuan, Fei Cheng, Xian Zhu, Jingxia Li, Shuoxin Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Approximately 70% of the carbon (C) stored in logs is released into the atmosphere, representing an important source of CO〈sub〉2〈/sub〉 lost from terrestrial ecosystems. Log respiration (R〈sub〉log〈/sub〉) has gained attention as a core issue in global C cycle research. In forest ecosystems that contain many logs, the R〈sub〉log〈/sub〉 flux can convert forests from C sinks into C sources; thus, R〈sub〉log〈/sub〉 should be considered in relevant research to avoid underestimating the CO〈sub〉2〈/sub〉 losses in the forest C cycle. Limited information is available regarding R〈sub〉log〈/sub〉 from natural forests, and many uncertainties remain about the magnitude of R〈sub〉log〈/sub〉. In our study, R〈sub〉log〈/sub〉 was measured 〈em〉in situ〈/em〉 by infrared gas analysis in 〈em〉Pinus armandi〈/em〉 and 〈em〉Quercus aliena〈/em〉 var. 〈em〉acuteserrata〈/em〉 forests in the Qinling Mountains, China. The objectives of this study were (1) to reveal the seasonal variation patterns of R〈sub〉log〈/sub〉; (2) to systematically analyze the relationships between R〈sub〉log〈/sub〉 and various factors, including the tree species, decay class, temperature, water content, and chemical composition; and (3) to estimate the annual R〈sub〉log〈/sub〉 flux in 〈em〉P. armandi〈/em〉 and 〈em〉Q. aliena〈/em〉 var. 〈em〉acuteserrata〈/em〉 forests in the Qinling Mountains, China. This study presents a full year time series of R〈sub〉log〈/sub〉 measurements for 30 logs (3 replicate logs × 5 decay classes × 2 tree species). The R〈sub〉log〈/sub〉 measurements were repeated 468 times for each log from May 2014 to April 2015. The log temperature (T〈sub〉log〈/sub〉), air temperature (T〈sub〉A〈/sub〉), soil temperature (T〈sub〉S〈/sub〉) at a depth of 10 cm, and log water content (W〈sub〉log〈/sub〉) were measured simultaneously with R〈sub〉log〈/sub〉. Moreover, the log density (D〈sub〉log〈/sub〉) and chemical composition (C, nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg)) were determined. Our results showed significant seasonal variation in R〈sub〉log〈/sub〉 for both species, which corresponded to variations in T〈sub〉log〈/sub〉 during the study period. The annual mean R〈sub〉log〈/sub〉 of 〈em〉Q. aliena〈/em〉 var. 〈em〉acuteserrata〈/em〉 (1.69 ± 1.60 μmol m〈sup〉−2〈/sup〉·s〈sup〉-1〈/sup〉) was higher than that of 〈em〉P. armandi〈/em〉 (1.55 ± 1.43 μmol m〈sup〉−2〈/sup〉·s〈sup〉−1〈/sup〉), but the difference was not significant (〈em〉P〈/em〉 = 0.61). The decay classes, T〈sub〉log〈/sub〉, W〈sub〉log〈/sub〉, and the N, P, Ca, and Mg concentrations were positively correlated with R〈sub〉log〈/sub〉. Moreover, the K concentration was negatively correlated with R〈sub〉log〈/sub〉, and the C concentration in logs was not correlated with R〈sub〉log〈/sub〉. The total annual R〈sub〉log〈/sub〉 flux did not differ significantly between the 〈em〉P. armandi〈/em〉 (67.25 ± 7.28 g C·m〈sup〉−2〈/sup〉·y〈sup〉−1〈/sup〉) and 〈em〉Q. aliena〈/em〉 var. 〈em〉acuteserrata〈/em〉 (74.69 ± 9.31 g C·m〈sup〉−2〈/sup〉·y〈sup〉−1〈/sup〉) forests (〈em〉P〈/em〉 = 0.26). These results provide insight into the factors responsible for seasonal changes in R〈sub〉log〈/sub〉 and can improve estimates of the annual R〈sub〉log〈/sub〉 flux in natural forests.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Shengjing Shi, Donald J. Herman, Zhili He, Jennifer Pett-Ridge, Liyou Wu, Jizhong Zhou, Mary K. Firestone〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Decomposition of soil organic carbon is central to the global carbon cycle and profoundly affected by plant roots. While root “priming” of decomposition has been extensively investigated, it is not known how plants alter the molecular ecology of soil microbial decomposers. We disentangled the effects of 〈em〉Avena fatua〈/em〉, a common annual grass, on 〈sup〉13〈/sup〉C-labeled root litter decomposition and quantified multiple genetic characteristics of soil bacterial and fungal communities. In our study, plants consistently suppressed rates of root litter decomposition. Microbes from planted soils had relatively more genes coding for low molecular weight compound degradation enzymes, while those from unplanted had more macromolecule degradation genes. Higher abundances of “water stress” genes in planted soils suggested that microbes experienced plant-induced water stress. We developed a conceptual model based on Mantel analyses of our extensive data set. This model indicates that plant root effects on the multiple soil environmental and microbial mechanisms involved in root litter decomposition act through changing the functional gene profiles of microbial decomposers living near plant roots.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Gianmarco Mugnai, Federico Rossi, Vincent John Martin Noah Linus Felde, Claudia Colesie, Burkhard Büdel, Stephan Peth, Aaron Kaplan, Roberto De Philippis〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Soil inoculation with cyanobacteria to promote the formation of biocrusts is considered a potential eco-friendly method to counteract desertification spread in drylands. Research is needed to increase the number of proficient cyanobacterial strains, selected for their capability to survive in harsh conditions and to form stable biocrusts quickly.〈/p〉 〈p〉We hereby present a microcosm study to assess the capability of 〈em〉Leptolyngbya ohadii〈/em〉, native to the Negev Desert, to form biocrusts on sand collected in the same environment, during a three-month incubation period. Inoculation was carried out in sand-filled microcosms without nutrient addition and a limited water supply (equivalent to desert dew input). Parameters related to biocrusts growth and to their physico-chemical attributes were measured, and the exopolysaccharides (EPS) synthesized by the strain during biocrust formation were quantified and characterized.〈/p〉 〈p〉After 15 days of incubation, 〈em〉L. ohadii〈/em〉 was able to form biocrusts with a thickness and a physical stability superior to other test strains of cyanobacteria, and typical of much older natural biocrusts. Biocrust characteristics were dependent on the synthesis of EPS, and on the capability to migrate in the sand, stabilizing sand aggregates at different locations within the microcosms. In contrast to other tested strains, 〈em〉L. ohadii〈/em〉 produced compositionally complex EPS during the entire incubation period despite the lack of nutrients, producing biocrusts with an amphiphilic extracellular matrix, a character effective in conferring stability to sand aggregates, chelating nutrients and maintaining hydration.〈/p〉 〈p〉Overall, this study shows that 〈em〉L. ohadii〈/em〉 is a promising inoculant that may be considered to promote the formation of biocrusts in natural desert settings.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Yakov Kuzyakov, Kyle Mason-Jones〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Viruses are ubiquitous in nature and have various ecological functions. Despite their very high abundance (up to 10〈sup〉10〈/sup〉 g〈sup〉−1〈/sup〉), viruses in soil remain disregarded with just a few, mostly descriptive studies published to date. With this review we focus on the probable functioning of viruses in soil and the consequences for microbial life and turnover, related mechanisms of biogeochemical cycling of carbon (C) and nutrients, and long-term C stabilization. We draw on the limited literature for soil, the richer knowledge from aquatic ecosystems and sediments, and evidence from pure culture studies.〈/p〉 〈p〉Evidence from soil and other ecosystems indicate that the vast majority of soil bacteria are infected by phages at any time. Consequently, we introduce and adapt five concepts for the role of phages in soil: (1) 〈em〉Viral Shunt〈/em〉, (2) ‘〈em〉Forever Young〈/em〉’, (3) 〈em〉Viral Regulatory Gate of EXOMET〈/em〉, (4) 〈em〉C sequestration by microbial necromass stabilization〈/em〉, and (5) 〈em〉Microscale divergence of C/N/P stoichiometry〈/em〉.〈/p〉 〈p〉The ‘〈em〉Viral Shunt〈/em〉’ accounts for the short-circuiting of trophic C and nutrient transfers by virus-induced mortality. Phages (even without soil animals – the 〈em〉Microbial Loop〈/em〉 concept) explain bacterial death rates and the release of easily available C and nutrients, consequently accelerating biogeochemical cycles in soil. The concept ‘〈em〉Forever Young〈/em〉’ postulates that viral infection maintains the active bacterial population at a young age, because infection and lysis lead to a short life expectancy. We controversially discuss this concept in relation to hypotheses such as (1) the dormancy of most soil microorganisms, (2) maintenance energy for microorganisms, and (3) their high C use efficiency. We unify the previously suggested but unexplained concepts of ‘〈em〉Regulatory Gate〈/em〉’ and ‘〈em〉EXOMET’〈/em〉 through the lytic release of intracellular enzymes and metabolites. Due to the elemental composition of phages, infection results in 〈em〉Stoichiometric C/N/P Imbalances〈/em〉 at the microscale, with consequences for P limitation at macroscales. The recently developed concept of ‘〈em〉C Sequestration by Necromass Stabilization〈/em〉’, i.e., that C sequestered in soil derives from microbial necromass, is discussed from the new perspective of viral lysis and “entombment” of cell fragments in nano-pores.〈/p〉 〈p〉Very few studies have investigated viruses in soil, so all research directions are open, important and fascinating. The most urgent are those elucidating virus functions, their consequences for microbial life, and ecological relevance, and to confirm (or to reject) the proposed concepts. Functioning very fast at the nano-scale, the undead drivers govern microbial life in soil and biogeochemical turnover from micro to ecosystem scales.〈/p〉 〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0038071718303432-egi10L7TWLS3NC.jpg" width="273" alt="Image" title="Image"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Kang Zhao, Weidong Kong, Fei Wang, Xi-En Long, Chunyan Guo, Linyan Yue, Huaiying Yao, Xiaobin Dong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉CO〈sub〉2〈/sub〉-fixing by soil autotrophic microbes is as important as by plants in semi-arid and arid ecosystems, such as the Tibetan Plateau grassland. CO〈sub〉2〈/sub〉-fixing microbial community characteristics, capacity and their driving environmental factors remain unclear. Here we investigated the autotrophic microbial community in grassland surface soils on the Tibetan Plateau using molecular methods targeting the large subunit gene (〈em〉cbbL〈/em〉) of ribulose-1, 5-bisphosphate carboxylase/oxygenase. The CO〈sub〉2〈/sub〉 fixation capacity was assessed by the 〈sup〉13〈/sup〉CO〈sub〉2〈/sub〉 probing method. The results showed that soil autotrophic microbial abundance substantially increased from desert, steppe to meadow. The autotrophic abundance significantly increased with enhancing mean annual precipitation (MAP), soil ammonium concentration and aboveground plant biomass (APB). Forms IAB and IC autotrophic microbial communities strongly varied with grassland types. Variation partitioning analysis revealed that the structure variations were mainly explained by MAP and aridity, which explained 4.2% and 2.6% for the IAB community, and 7.6% and 8.5% for the IC community. Desert and steppe soils exhibited significantly higher atmospheric 〈sup〉13〈/sup〉CO〈sub〉2〈/sub〉 fixation rate than meadow soils (29 versus 18 mg kg〈sup〉−1〈/sup〉soil d〈sup〉−1〈/sup〉). The 〈sup〉13〈/sup〉CO〈sub〉2〈/sub〉 fixation rate negatively correlated with APB and soil ammonium concentration, demonstrating the substantially important role of autotrophic microbes in oligotrophic soils. Form IAB autotrophs were phylogenetically affiliated with 〈em〉Cyanobacteria〈/em〉. Form IC autotrophs were affiliated with 〈em〉Rhizobiales〈/em〉 and 〈em〉Actinobacteria〈/em〉, the former gradually increased and the latter decreased from desert, steppe to meadow. Our findings offer new insight into the importance of MAP in driving soil autotrophic microbial community and highlight microbial roles in carbon cycling in dryland ecosystems.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Di Wu, Zhijun Wei, Reinhard Well, Jun Shan, Xiaoyuan Yan, Roland Bol, Mehmet Senbayram〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Straw application in combination with synthetic N fertilizer could increase crop yield and improve soil fertility, however, contradictory observations have been reported on the effects of straw addition on soil N〈sub〉2〈/sub〉O emission. Straw application can affect both denitrification rate and its product stoichiometry (N〈sub〉2〈/sub〉O/(N〈sub〉2〈/sub〉O + N〈sub〉2〈/sub〉) ratio), whereas the latter remains rather unclear since the ratio is strongly regulated by other soil parameters, e.g. nitrate and oxygen concentrations at denitrifying micro-sites. In this context, we conducted an incubation experiment with a robotized continuous flow incubation system using a He/O〈sub〉2〈/sub〉 atmosphere and measured N〈sub〉2〈/sub〉O and direct N〈sub〉2〈/sub〉 fluxes over 22 days. Soil amended with and without rice straw (2.5 g kg〈sup〉−1〈/sup〉 soil) in conjunction with nitrate fertilizer (10 mM KNO〈sub〉3〈/sub〉) and non-amended control soil were incubated under 85% water-filled pore space. To simulate a short soil anoxic period, three different O〈sub〉2〈/sub〉 partial pressures phases were set (20%, 5% and 10%). Additionally, N〈sub〉2〈/sub〉O site preference signatures of soil-emitted N〈sub〉2〈/sub〉O were analyzed to identify the processes contributing to N〈sub〉2〈/sub〉O fluxes. Addition of nitrate increased cumulative N〈sub〉2〈/sub〉O fluxes and decreased cumulative N〈sub〉2〈/sub〉 fluxes compared with non-fertilized control, while rice straw amendment increased both N〈sub〉2〈/sub〉O and N〈sub〉2〈/sub〉 emissions drastically compared with the nitrate only treatment. The N〈sub〉2〈/sub〉O SP values ranged from 0.4 to 2.7‰ among all treatments, indicating denitrification/nitrifier denitrification was the dominating source. The results suggest that straw amendment can trigger high denitrification rate, whereas the effect of straw amendment on the amount of emitted N〈sub〉2〈/sub〉O and the N〈sub〉2〈/sub〉O/(N〈sub〉2〈/sub〉O + N〈sub〉2〈/sub〉) product ratio strongly depends on soil NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 concentration. As a conclusion, the present study suggests that straw amendment in conjunction with nitrate-N can increase soil N〈sub〉2〈/sub〉O emissions under conditions favoring denitrification, even though it may decrease the overall N〈sub〉2〈/sub〉O/(N〈sub〉2〈/sub〉O + N〈sub〉2〈/sub〉) product ratio.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Marc Pinheiro, Holger Pagel, Christian Poll, Franziska Ditterich, Patricia Garnier, Thilo Streck, Ellen Kandeler, Laure Vieublé Gonod〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Complex interactions between biodegradation and mass transfer of organic compounds drive the fate of pesticides in soil ecosystems. We hypothesized that, at the small-scale, co-location of degraders and pollutants in soils may be a prerequisite for efficient biodegradation of these chemicals. In non-co-localized micro-environments, however, diffusive and advective solute transport as well as active transport of microbial degraders towards their corresponding substrate may improve the accessibility of microbial substrates. The objective of this study was to test whether water flow can accelerate microbial pesticide degradation by facilitating the encounter of spatially separated pesticides and bacterial degraders at the millimeter scale.〈/p〉 〈p〉Combining natural and sterilized soil aggregates, we built soil cores with different spatial localizations of the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) and microbial degraders: (i) homogeneous distribution of microorganisms and 2,4-D throughout the soil core, (ii) co-localized microorganisms and 2,4-D in a mm〈sup〉3〈/sup〉 soil location, and iii) separated microorganisms and 2,4-D in two mm〈sup〉3〈/sup〉 soil locations spaced 1 cm apart.〈/p〉 〈p〉Following the fate of 〈sup〉14〈/sup〉C labelled 2,4-D (mineralization, extractable and non-extractable residues) as well as the abundance of bacterial 2,4-D degraders harboring the 〈em〉tfdA〈/em〉 gene over an incubation period of 24 days, we observed decreased biodegradation of 2,4-D with increasing spatial separation between substrate and bacterial degraders. We found evidence that advection is a key process controlling the accessibility of 2,4-D and pesticide degraders. Advective solute transport induced leaching of about 50% of the initially applied 2,4-D regardless of initial spatial distribution patterns. Simultaneously, advective transport of 2,4-D and bacterial degraders triggered their re-encounter and compensated for the leaching-induced separation of initially co-localized microorganisms and 2,4-D. This resulted in effective biodegradation of 2,4-D, comparable to the homogeneous treatment. Similarly, advective transport processes brought substrate and degraders into contact if both were initially separated. Thus, advection more effectively removed bioaccessibility limitations to pesticide degradation than diffusive transport alone.〈/p〉 〈p〉These results emphasize the importance of considering spatial microbial ecology as well as biogeophysics at the mm scale to better understand the fate of pesticides at larger scales in soil.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): P.E. Brewer, F. Calderón, M. Vigil, J.C. von Fischer〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Anoxic microsites can alter the habitat of upland soils and host diverse anaerobic processes that affect greenhouse gas production, nitrogen dynamics, and biodiversity. Microsites that are methanogenic indicate deeply reducing conditions that may have especially strong impacts on soil function. However, there have not been controlled studies to determine the regulators of methanogenic microsite formation or persistence and most studies have been limited to tropical or high organic matter soils. We hypothesized that upland methanogenesis, as an indicator of anaerobic activity, is primarily affected by soil moisture and organic matter. To test this hypothesis, we examined relationships between soil properties, rates of methanogenesis, and biogeochemical responses in an incubation experiment that manipulated soil source (semi-arid and mesic ecosystems), agricultural practice (conventional, no-till, and organic), and moisture (10%–95% water-filled porespace) of intact soil cores. Methanogenesis was correlated with factors related to both increased O〈sub〉2〈/sub〉 demand (e.g., soil respiration) and decreased O〈sub〉2〈/sub〉 diffusion (e.g., water-filled porespace), and the relative importance of these different mechanisms changed over four months. While the highest rates of methanogenesis occurred above 75% water-filled porespace, we observed methanogenesis over the full range of soil moistures. These are the driest soils shown to host methanogenesis, outside of biological soil crusts. Cores from plots with organic amendments had the highest rates of methanogenesis. Comparisons of methanogenesis and N-cycling revealed new relationships in upland soils: stronger methanogenesis was associated with more soil NH〈sub〉4〈/sub〉〈sup〉+〈/sup〉 and higher N〈sub〉2〈/sub〉O emissions but less NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉, likely due to reduced conditions causing increased denitrification and/or decreased nitrification. Our findings show that upland methanogenesis can arise from either increased O〈sub〉2〈/sub〉 demand or decreased O〈sub〉2〈/sub〉 diffusion, similar to wetland ecosystems, and that the presence of anoxic microsites appears to alter N-cycling. The current paradigm is that upland anaerobicity is generally a minor or moisture-related event, but we demonstrate here that it can be persistent, occur across the full range of soil moisture, and may result in significant impacts on nutrient availability. These and other anaerobic impacts on soil function and biodiversity may occur over the entire landscape of temperate ecosystems.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 June 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry〈/p〉 〈p〉Author(s): Akinori Yamamoto, Hiroko Akiyama, Yasuhiro Nakajima, Yuko Takada Hoshino〈/p〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Christine Heuck, Alfons Weig, Marie Spohn〈/p〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Ernest D. Osburn, Katherine J. Elliottt, Jennifer D. Knoepp, Chelcy F. Miniat, J.E. Barrett〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉〈em〉Rhododendron maximum〈/em〉 is a native evergreen shrub that has expanded in Appalachian forests following declines of american chestnut (〈em〉Castanea dentata〈/em〉) and eastern hemlock (〈em〉Tsuga canadensis〈/em〉). 〈em〉R. maximum〈/em〉 is of concern to forest managers because it suppresses hardwood tree establishment by limiting light and soil nutrient availability. We are testing 〈em〉R. maximum〈/em〉 removal as a management strategy to promote recovery of Appalachian forests. We hypothesized that 〈em〉R. maximum〈/em〉 removal would increase soil nitrogen (N) availability, resulting in increased microbial C-demand (i.e. increased C-acquiring enzyme activity) and a shift towards bacterial-dominated microbial communities. 〈em〉R. maximum〈/em〉 removal treatments were applied in a 2 × 2 factorial design, with two 〈em〉R. maximum〈/em〉 canopy removal levels (removed vs not) combined with two O-horizon removal levels (burned vs unburned). Following removals, we sampled soils and found that dissolved organic carbon (DOC), N (TDN, NO〈sub〉3〈/sub〉, NH〈sub〉4〈/sub〉), and microbial biomass all increased with 〈em〉R. maximum〈/em〉 canopy + O-horizon removal. Additionally, we observed increases in C-acquisition enzymes involved in degrading cellulose (β-glucosidase) and hemicellulose (β-xylosidase) with canopy + O-horizon removal. We did not see treatment effects on bacterial dominance, though F:B ratios from all treatments increased from spring to summer. Our results show that 〈em〉R. maximum〈/em〉 removal stimulates microbial activity by increasing soil C and N availability, which may influence recovery of forests in the Appalachian region.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Yuanhu Shao, Tao Liu, Nico Eisenhauer, Weixin Zhang, Xiaoli Wang, Yanmei Xiong, Chenfei Liang, Shenglei Fu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Anthropogenic nitrogen (N) deposition is an important component of global change and threatens terrestrial biodiversity. Most previous studies of the consequences of N deposition have focused on plant community responses and found that N deposition decreases plant diversity. However, the effects of N deposition on soil biodiversity and belowground biotic interactions remain poorly understood. We explored the changes in main soil food web components (microbes, nematodes, springtails, and mites) in response to elevated N deposition (60 kg N ha〈sup〉−1〈/sup〉yr〈sup〉−1〈/sup〉, starting from 2012 to 2014), and whether these changes are altered by the presence of plants (planting of shrubs in 2008) in a two-factorial field mesocosm experiment with 16 equally-sized plots (1 × 2 m). Our results showed that elevated N deposition negatively affected soil bacteria, while fungi showed rather neutral responses. Specifically, N deposition decreased bacteria Shannon's diversity index 〈em〉H′〈/em〉, richness, observed species abundance, bacterial activity, and resulted in a non-significant decrease of the relative abundance of rare bacterial taxa. By contrast, for fungi, only a non-significant decrease of richness was observed with N deposition. Importantly, those N deposition effects mostly occurred in the absence of planted shrubs. Moreover, shrub presence and N deposition also interactively affected the diversity of soil invertebrates, i.e., N deposition had little effect on them in the absence of planted shrubs, but resulted in an increase or a non-significant increase of soil invertebrate diversity in the presence of planted shrubs. Furthermore, N deposition did not affect the biomass/density of any soil food web component and biomass/density ratios related to soil food web structure regardless of absence or presence of planted shrubs; these indices were only affected by the presence of shrubs. Overall, these dissimilar responses of the diversity of soil microorganisms and animals to elevated N deposition indicate that plants are important mediators of N deposition effects on soil biodiversity. Thus, the present results may imply that an intact plant cover may mitigate detrimental N deposition effects on soil biodiversity.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): C. Abgrall, E. Forey, L. Mignot, M. Chauvat〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Biological invasions are a major threat to biodiversity with varying degrees of impact. There is increasing evidence that allelopathy often plays an important role in explaining both invasion success and impact on native taxa (e.g. novel weapons hypothesis). The effects of these secondary metabolites on plant communities and microorganisms are well known. However, their direct and indirect effects on soil fauna are unresolved, despite the importance of the latter in ecosystem processes and, potentially, invasion mitigation. Japanese knotweed (〈em〉Fallopia japonica〈/em〉), an east-Asian species, which has proved to be invasive in Europe, containing allelopathic secondary compounds inhibiting native plants and microbial communities. The focal point of this study was the allelopathic effects of knotweed on soil mesofauna (Nematoda, Collembola and Acari). During a one-month laboratory experiment we added knotweed rhizome extract (KRE) at different concentrations to soils collected in an invasion-prone area. He experiment consisted of including or excluding secondary metabolites through the use of activated carbon filtration of KRE. This enabled us to separate effects caused by nutrient addition (i.e. trophic effects) and combined (trophic and allelopathic) effects. Relative effects of nutrient and secondary metabolites addition on abiotic and biotic soil variables were then quantified. We highlighted frequently contrasting trophic and allelopathic effects influenced in some cases by KRE concentration. Microbial assemblages, through fungal/microbial biomass ratio, did not show any congruent response to KRE secondary compounds but was more negatively impacted by nutrient addition. The use of a trophic-based path analysis led us to show that changes within the soil biota had repercussions on secondary consumers (e.g. bacterivorous nematodes and Collembola). Abundance within taxa at higher trophic levels such as predatory Acari (but not predatory nematodes) was also affected although to a lesser extent, likely in part due to the limited considered timeframe. Overall, we showed that, in controlled conditions, invasive allelopathic plants such as knotweeds can have effects on soil fauna at different trophic levels through addition of both nutrients and secondary metabolites to the soil. Considering the limited knowledge of allelopathic effects on the soil fauna and soil functions, this study provides new information on above- and belowground interactions.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): Hui Wang, Shirong Liu, Xiao Zhang, Qinggong Mao, Xiangzhen Li, Yeming You, Jingxin Wang, Mianhai Zheng, Wei Zhang, Xiankai Lu, Jiangming Mo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Increased nitrogen (N) deposition endangers the biodiversity and stability of forest ecosystems, and much of the original phosphorus (P) parent material continues to decrease in most lowland tropical forests. It remains poorly understood as to how soil microbial diversity at a molecular level responds to the addition of excess N and mitigation of soil P limitation, as well as their influencing factors, in the N-rich tropical forest ecosystems. To reach a better understanding, we conducted a six-year N〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉 and P-addition experiment consisting of three treatments: N-addition (150 kg N ha〈sup〉−1〈/sup〉 yr〈sup〉−1〈/sup〉), P-addition (150 kg P ha〈sup〉−1〈/sup〉 yr〈sup〉−1〈/sup〉), and NP-addition (150 kg N ha〈sup〉−1〈/sup〉 yr〈sup〉−1〈/sup〉 plus 150 kg P ha〈sup〉−1〈/sup〉 yr〈sup〉−1〈/sup〉), besides a control treatment in an old-growth tropical forest in southern China. We examined the snapshot responses of soil bacterial richness and community composition to the elevated N and P levels after six years using a 16S rRNA gene MiSeq sequencing method. The soil bacterial α-diversity, which is represented by Chao1 index in terms of bacterial richness, was 783 ± 87 (mean ± SD) across all samples in this study. The N addition caused a decline in soil bacterial richness, most likely through its negative effect on soil pH. The decrease in soil pH resulted from the direct N input and indirect NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 increase. However, the P treatment had no effect on soil bacterial richness. The NP treatment also reduced the soil bacterial richness as the N addition. These results suggested that the P input could not alleviate the loss of soil bacterial richness induced by excess N deposition in the old-growth N-rich tropical forest. The Acidobacteria, which comprised 31.1% of the soil bacterial community, were the most dominant bacteria across all samples. The addition of P shifted the soil bacterial community composition. The elevated P availability with P-addition and the decreased understory plant coverage in the N-input treatment altered the soil bacterial β-diversity. Our results highlight the different roles of N and P depositions in shaping the soil bacterial richness and community composition, thereby causing concomitant changes in understory plant and underground microbial communities in this ecosystem.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Jiajia Xing, Haizhen Wang, Philip C. Brookes, Joana Falcão Salles, Jianming Xu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The presence of 〈em〉Eschericia coli〈/em〉 (〈em〉E. coli〈/em〉) leads to potential outbreaks of disease, demonstrating the importance of understanding how such organisms survive in secondary environments such as soil. Biotic and abiotic soil characteristics play a role in 〈em〉E. coli〈/em〉 survival, but it remains unclear how these two aspects interact with survival and whether it is linked to toxin genes. Here we evaluated the survival of three 〈em〉E. coli〈/em〉 O157:H7strains: Shiga toxin-producing 〈em〉E. coli〈/em〉, its mutant without 〈em〉stx〈/em〉 genes and strain without virulence genes in 4 distinct Chinese soils. To further disentangle the effects of microbial diversity, soils were manipulated to generate a gradient of microbial diversity (10〈sup〉−1〈/sup〉, 10〈sup〉−6〈/sup〉, and a sterile soil [γ-irradiated control]). Overall, our results showed the 〈em〉E. coli〈/em〉 O157:H7 survival time decreased in all treatments, ranging from 8.23 ± 5.42 to 62.33 ± 35.80 days. The fastest decline was with the Shiga toxin-producing strain at 10〈sup〉−1〈/sup〉 dilution, whereas the strain without virulence genes, persisted the longest 178 days in the γ sterilized control. These results confirmed the importance of biodiversity upon 〈em〉E. coli〈/em〉 invasion and revealed virulence genes negatively influenced survival. The negative correlation between community niche or niche breadth of soil communities and survival, indicated that resource competition also was the major driver of 〈em〉E. coli〈/em〉 O157:H7 survival. Moreover, path analyses revealed that soil pH exerted a critical role on the persistence of 〈em〉E. coli〈/em〉 O157:H7, higher pH values produced longer survival time in each strain. These conclusions are of relevance for agricultural situations, where anthropogenic influences lead to decreased soil diversity, increased soil pH and resource input through manure application, which can potentially increase the survival time of 〈em〉E. coli〈/em〉 O157:H7, the expanding the window of opportunity for food contamination.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Benjamin A. Musa Bandowe, Sophia Leimer, Hannah Meusel, Andre Velescu, Sigrid Dassen, Nico Eisenhauer, Thorsten Hoffmann, Yvonne Oelmann, Wolfgang Wilcke〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Increasing plant species richness stimulates microbial activity in soil, which might favor biodegradation of polycyclic aromatic compounds (PACs). To explore the relationship between plant community composition and PACs in grassland soils (Fluvisols exposed to an urban atmosphere), we determined the concentrations of 29 polycyclic aromatic hydrocarbons (PAHs) and 15 oxygenated PAHs (OPAHs) in topsoils of 80 plots of a grassland biodiversity experiment. The plots included different levels of plant species richness (1, 2, 4, 8, 16, 60 species) and 1–4 plant functional groups (grasses, small herbs, tall herbs, and legumes) in a randomized block design. The concentrations (ng g〈sup〉−1〈/sup〉) of ∑29PAHs and ∑15OPAHs in the soils were 271–2407 and 57–329, respectively. Concentrations of 16 (out of 44) PACs and ∑29PAHs decreased significantly with increasing plant species richness, after accounting for the effects of block and initial soil organic C concentration (ANCOVA, p 〈 0.05). Microbial turnover as the mechanism underlying this relationship was supported by the findings that (i) the regression of the concentrations of PAH with 〉4 aromatic rings on plant species richness yielded slopes that were negatively correlated with their octanol-water partitioning coefficients, (ii) two OPAHs accumulated in soils with higher plant species richness, and (iii) higher plant species richness increased four OPAH/parent-PAH ratios. Accordingly, structural equation modeling indicated that the higher concentration of 1,2-acenaphthenequinone (a metabolite of acenaphthene) and the higher 1,2-acenaphthenequinone/acenaphthene and 1-indanone/fluorene ratios in plots with higher plant species richness were partly explained by higher soil microbial biomass on plots with higher plant species richness. We conclude that higher plant species richness can be used to enhance biodegradation of aged PACs in soil. We however caution that OPAHs (some of which are more toxic than their related PAHs) might accumulate in soils during such a plant-assisted remediation process.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0038071718303717-fx1.jpg" width="357" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Yuanyuan Yang, Raphael A. Viscarra Rossel, Shuo Li, Andrew Bissett, Juhwan Lee, Zhou Shi, Thorsten Behrens, Leon Court〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil bacteria play a critical role in the functioning of ecosystems but are challenging to investigate. We developed state-factor models with machine learning to understand better and to predict the abundance of 10 dominant phyla and bacterial diversities in Australian soils, the latter expressed by the Chao and Shannon indices. In the models, we used proxies for the edaphic, climatic, biotic and topographic factors, which included soil properties, environmental variables, and the absorbance at visible–near infrared (vis–NIR) wavelengths. From a cross-validation with all observations (n = 681), we found that our models explained 43–73% of the variance in bacterial phyla abundance and diversity. The vis–NIR spectra, which represent the organic and mineral composition of soil, were prominent drivers of abundance and diversity in the models, as were changes in the soil-water balance, potential evapotranspiration, and soil nutrients. From independent validations, we found that spectro-transfer functions could predict well the phyla Acidobacteria and Actinobacteria (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msup〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mo〉〉〈/mo〉〈/mrow〉〈/math〉 0.7) as well as other dominant phyla and the Chao and Shannon diversities (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msup〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mo〉〉〈/mo〉〈/mrow〉〈/math〉 0.5). Predictions of the phyla Firmicutes were the poorest (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msup〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉  = 0.42). The vis–NIR spectra markedly improved the explanatory power and predictability of the models.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Eduardo Pérez-Valera, Marta Goberna, Miguel Verdú〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The ecosystem functions performed by soil microbial communities can be indirectly altered by ecological disturbances that deeply modify abiotic factors. Fire, a widespread disturbance in nature, is well known to alter soil abiotic properties but we still ignore how these shifts are translated into changes in the structure of soil microbial communities and the ecosystem functions they deliver. The phylogenetic structure of soil bacterial communities has been shown to be a good predictor of ecosystem functioning, and therefore we used it as a measure linking the temporal variation of soil abiotic properties and ecosystem functions caused by an experimental fire in a Mediterranean shrubland. Fire immediately favoured a basal phylogenetic clade containing lineages that are able to thrive with high temperatures and to take advantage of the post-fire nutrient release. Later changes in the phylogenetic structure of the community were dominated by phyla from another basal clade that show competitive superiority coinciding with high levels of oxidizable carbon in soil. The phylogenetic structure of the bacterial community significantly explained not only microbial biomass, respiration and specific enzymatic activities related to C, N and P cycles but also the community-weighted mean number of 16S rRNA gene copies, an integrative proxy of several functions. While most of the ecosystem functions recovered one year after the fire, this was not the case of the structure of bacterial community, suggesting that functionally equivalent communities might be recovering the pre-disturbance levels of ecosystem performance.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0038071718303821-fx1.jpg" width="256" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Sarah S. Roley, Chao Xue, Stephen K. Hamilton, James M. Tiedje, G. Philip Robertson〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Perennial grasses can assimilate nitrogen (N) fixed by non-nodulating bacteria living in the rhizosphere and the plant's own tissues, but many details of associative N fixation (ANF) remain unknown, including ANF's contribution to grass N nutrition, the exact location of fixation, and composition of the associated microbial community. We examined ANF in switchgrass (〈em〉Panicum virgatum〈/em〉 L.), a North American perennial grass, using 〈sup〉15〈/sup〉N-enriched N〈sub〉2〈/sub〉 isotopic tracer additions in a combination of 〈em〉in vitro〈/em〉, greenhouse, and field experiments to estimate how much N is assimilated, where fixation takes place, and the likely N-fixing taxa present. Using 〈em〉in vitro〈/em〉 incubations, we documented fixation in root-free rhizosphere soil and on root surfaces, with average rates of 3.8 μg N g root〈sup〉−1〈/sup〉 d〈sup〉−1〈/sup〉 on roots and 0.81 μg N g soil〈sup〉−1〈/sup〉 d〈sup〉−1〈/sup〉 in soil. In greenhouse transplants, N fixation occurred only in the early growing season, but in the field, fixation was irregularly detectable throughout the 3-month growing season. Soil, leaves, stems, and roots all contained diazotrophs and incorporated fixed N〈sub〉2〈/sub〉. Metagenomic analysis suggested that microbial communities were distinct among tissue types and influenced by N fertilizer application. A diverse array of microbes inhabiting the rhizosphere, and possibly aboveground tissues, appear to be episodically contributing fixed N to switchgrass.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Féline L. Assémien, Amélie A.M. Cantarel, Alessandro Florio, Catherine Lerondelle, Thomas Pommier, Jean Tia Gonnety, Xavier Le Roux〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Increasing attention has been paid to microorganisms able to produce nitrous oxide (N〈sub〉2〈/sub〉O), a potent greenhouse gas, or reduce it to harmless N〈sub〉2〈/sub〉. Based on previous studies, niche differentiation could exist between 〈em〉nirK〈/em〉- and 〈em〉nirS〈/em〉-nitrite reducers and 〈em〉nosZI〈/em〉- and 〈em〉nosZII〈/em〉-N〈sub〉2〈/sub〉O reducers, and 〈em〉nosZII〈/em〉-bacteria would have a key role for N〈sub〉2〈/sub〉O reduction in soils. Most previous studies have been performed for agricultural systems but never in the moist savanna zone which covers half a million km〈sup〉2〈/sup〉 in West Africa and whose soils are among the poorest in nitrogen (N) on earth. Here, we quantified potential gross and net N〈sub〉2〈/sub〉O production rates along with the abundances of 〈em〉nirK〈/em〉-, 〈em〉nirS〈/em〉-, 〈em〉nosZI〈/em〉- and 〈em〉nosZII〈/em〉-harbouring bacteria for soils under six agricultural practices with maize rotations (slash-and-burn, chemical fertilization, mulching with or without inclusion of crop legumes, and without any input) after 4 and 5 crop cycles at nine sites in Ivory Coast. Sites and practices influenced denitrifier abundances and activities, the ratio of total abundances of nitrite-to-N〈sub〉2〈/sub〉O reducers being highest and lowest for the mulching + green soya and slash-and-burn practices, respectively. Using structural equation modelling, we showed that 〈em〉nirS〈/em〉- and 〈em〉nosZI〈/em〉-bacteria both strongly depended on nitrate availability whereas 〈em〉nirK〈/em〉- and 〈em〉nosZII〈/em〉-bacteria were related to soil organic carbon and pH. Furthermore, potential gross and net N〈sub〉2〈/sub〉O production rates depended strongly and only on the abundances of 〈em〉nirS〈/em〉- and 〈em〉nosZI〈/em〉-bacteria. Our results support the view of a clear niche differentiation between these four microbial groups but invalidate the assumption of a prominent functional role of soil 〈em〉nosZII〈/em〉-N〈sub〉2〈/sub〉O reducers.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S003807171830378X-fx1.jpg" width="434" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): José A. Siles, Tomas Cajthaml, Jan Frouz, Rosa Margesin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil microbial communities involved in 〈sup〉13〈/sup〉C-labeled cellulose utilization from two contrasting (in terms of vegetation and climatic conditions) forest sites at different elevations were studied by using a laboratory microcosm experiment and a PLFA (phospholipid fatty acid)-SIP (stable isotope probing) approach considering the effects of incubation temperature (0, 10 and 20 °C) and time (1–4 weeks). The amounts of cellulose-〈sup〉13〈/sup〉C assimilated by soil microorganisms and the composition of microbial communities utilizing cellulose were site-dependent. Total, bacterial and actinobacterial biomass incorporated higher amounts of 〈sup〉13〈/sup〉C in soil from the deciduous forest site (at the lower elevation), while fungal biomass contained increased amounts of 〈sup〉13〈/sup〉C in soil from the coniferous forest site (at the higher elevation). Increasing temperatures resulted in increased amounts of 〈sup〉13〈/sup〉C assimilated by the different PLFA-based microbial groups, except fungi, and in significant changes in the community structure of cellulose utilizers. Fungi were better adapted to cold conditions than bacteria. Longer incubation times determined an increase in the amount of 〈sup〉13〈/sup〉C incorporated into total and bacterial PLFAs but had no effect on the composition of labeled microbial communities.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Ashley R. Smyth, Terrance D. Loecke, Trenton E. Franz, Amy J. Burgin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Understanding the mechanisms that lead to greenhouse gas (GHG) emissions requires knowledge of short-term fluctuations in drivers of fluxes. To better understand how variation and lags in abiotic conditions affect soil GHG fluxes, we coupled weekly methane (CH〈sub〉4〈/sub〉) and nitrous oxide (N〈sub〉2〈/sub〉O) flux measurements with time-series soil sensor data for oxygen (O〈sub〉2〈/sub〉), moisture and temperature. Including time-series data improved models for soil CH〈sub〉4〈/sub〉 and N〈sub〉2〈/sub〉O fluxes compared to models which did not contain time series data. Fluctuations in soil O〈sub〉2〈/sub〉 drove CH〈sub〉4〈/sub〉 fluxes, where rapid changes in redox conditions led to high fluxes. N〈sub〉2〈/sub〉O fluxes occurred when soils were warm and dry. Soil O〈sub〉2〈/sub〉 was the best predictor and thus sensor for understanding CH〈sub〉4〈/sub〉 fluxes, whereas soil moisture best predicted N〈sub〉2〈/sub〉O fluxes. Combining data from multiple sensors improved models for both gases, underscoring the relative importance of interactions among drivers. Overall, our top models explained 15% and 30% of the variance in N〈sub〉2〈/sub〉O and CH〈sub〉4〈/sub〉 fluxes, respectively. Fluxes predicted using linear interpolation between measured fluxes were lower than time-series model predictions for both N〈sub〉2〈/sub〉O and CH〈sub〉4〈/sub〉 fluxes. This suggests linear interpolation may fail to capture “hot moments” or episodic events which lead to high fluxes. Long-term, continuous data from sensors, which accounts for short-term variation in abiotic drivers, may improve our ability to predict the timing and intensity of GHG emissions from wetland soils.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Xiaoping Fan, Chang Yin, Hao Chen, Mujun Ye, Yuhua Zhao, Tingqiang Li, Steven A. Wakelin, Yongchao Liang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), can be used to reduce N〈sub〉2〈/sub〉O emissions from agricultural ecosystems. However, the effectiveness of DMPP varies among soils, and this is due to both abiotic (e.g. soil properties) and biotic factors (e.g. ammonia oxidizers and denitrifier communities). Understanding the nature of these effects is necessary to improve the efficacy of DMPP, therefore encouraging wider adoption and environmental benefits. In particular, soil microbial properties associated with variation in efficacy remain largely unknown. In this study four contrasting arable soils (a grey desert soil, an alluvial paddy soil, a loess-formed paddy soil, and a red soil), were characterized based on DMPP inhibition of N〈sub〉2〈/sub〉O emissions and associated microbial functional guilds. DMPP significantly inhibited nitrification and N〈sub〉2〈/sub〉O emissions, with an average inhibitory rate ranging from 41.7% in a red soil to 90.0% in a grey desert soil. Ammonia oxidizing bacteria (AOB) and archaea (AOA) exhibited contrasting response patterns to DMPP addition. Notably, suppression of N〈sub〉2〈/sub〉O emissions by DMPP only occurred alongside fluctuations in AOB abundance. However, when AOB were inhibited, AOA abundance increased. Soil-dependent response patterns to DMPP were observed for ammonia oxidizers and denitrifiers in terms of community structure. Partial least squares path modeling (PLS-PM) found that abiotic factors, particularly pH, and biological factors such as ammonia oxidizer communities, were closely linked to N〈sub〉2〈/sub〉O emissions. Our findings provide evidence that: (i) DMPP effectively inhibits nitrification through inhibiting the abundance of AOB across soil types; (ii) releasing AOA from the competition with AOB allows AOA to efficiently grow and multiply, even under high ammonium conditions; and (iii) abiotic factors play a more important role than biotic factors in soil N〈sub〉2〈/sub〉O emissions.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0038071718304103-fx1.jpg" width="243" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Janet Ho, Lisa G. Chambers〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Important wetland functions, including regulating soil carbon (C) storage and water quality, are linked to biogeochemical processes mediated by soil microbes. Vegetation shifts such as shrub encroachment may alter the soil microbial community and result in changes in important biogeochemical processes, although few studies have examined this in subtropical marshes. Here, we used in-situ litter decomposition experiments, quantitative polymerase chain reaction, and laboratory assays on soil respiration, extracellular enzyme activity, and denitrification potential to determine differences in C storage and nitrogen (N) cycling between willow-encroached and non-encroached plots in two subtropical marshes (Moccasin Island and Lake Apopka, FL, USA). In both regions, encroached (willow or adjacent marsh) and non-encroached plots had distinctively different microbial communities, which were correlated with soil temperature and nutrient content. Greater enzyme activity, denitrification, and CO〈sub〉2〈/sub〉 production were observed in willow and/or adjacent marsh plots compared to control marsh plots at Moccasin Island. Conversely, lower enzyme activity, denitrification, and CO〈sub〉2〈/sub〉 production were detected in willow and/or adjacent marsh plots compared to control marsh plots at Lake Apopka. Despite differences in the response of biogeochemical processes and microbial community structure in the two study regions, in-situ decomposition rates were halved in willow litter compared to herbaceous litter in both regions, which was correlated with greater recalcitrant lignin content in willow litter. Ultimately, greater short-term litter C storage was observed in both study regions, but soil N cycling changes differed by region, potentially due to unique site characteristics such as hydroperiod and nutrient availability.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): C. Buchen, D. Roobroeck, J. Augustin, U. Behrendt, P. Boeckx, A. Ulrich〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Peat soils can be strong sources of atmospheric nitrous oxide (N〈sub〉2〈/sub〉O), but at the same time act as sinks for the greenhouse gas N〈sub〉2〈/sub〉O. However, the role of N〈sub〉2〈/sub〉O reduction to dinitrogen (N〈sub〉2〈/sub〉) here is still not fully understood. In particular, this applies to pristine or weakly disturbed fen mires. These types of peatland ecosystems are characterised by anoxic soil conditions and special N dynamics restricted to ammonium (NH〈sub〉4〈/sub〉〈sup〉+〈/sup〉) turnover and very low nitrate (NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉) availability. N〈sub〉2〈/sub〉O and N〈sub〉2〈/sub〉 fluxes from intact soil cores from three weakly disturbed fen mire types and two soil habitats (tussocks and hollows) were investigated using the helium (He) incubation approach. Ambient air in headspaces were first substituted with a He-O〈sub〉2〈/sub〉 trace gas mixture to quantify N〈sub〉2〈/sub〉O and N〈sub〉2〈/sub〉 exchanges under prevailing soil oxygen (O〈sub〉2〈/sub〉) conditions, and then with an anoxic He trace gas mixture (99.9% He) for establishing the maximum possible denitrification rate. Changing from the He-O〈sub〉2〈/sub〉 mixture to a pure He trace gas mixture led to strong increase of N〈sub〉2〈/sub〉 fluxes (up to 2916 μg N m〈sup〉−2〈/sup〉 h〈sup〉−1〈/sup〉) and negative N〈sub〉2〈/sub〉O fluxes of up to −72 μg N m〈sup〉−2〈/sup〉 h〈sup〉−1〈/sup〉. Whilst small differences in N gas fluxes were found between all types of fen mires, an analysis of the denitrifier abundance based on 〈em〉nirK〈/em〉, 〈em〉nirS〈/em〉 and 〈em〉nosZ〈/em〉 genes indicated respectively more pronounced variation. The structure of denitrifier communities exhibited a strong plot specificity driven by water-filled pore space, soil organic matter and soil pH. This short-term He incubation experiment revealed that weakly disturbed fen mires act as considerable N〈sub〉2〈/sub〉O sinks under anoxic conditions and improved our knowledge of the original N dynamics in this peatland ecosystem.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Yingbin Li, T. Martijn Bezemer, Junjie Yang, Xiaotao Lü, Xinyu Li, Wenju Liang, Xingguo Han, Qi Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil microbial community composition and litter quality are important drivers of litter decomposition, but how litter quality influences the soil microbial composition largely remains unknown. We conducted a microcosm experiment to examine the effects of changes in litter quality induced by long-term N deposition on soil microbial community composition. Mixed-species litter and single-species litter were collected from a field experiment with replicate plots exposed to long-term N-addition in a semiarid grassland in northern China. The litters were decomposed in a standard live soil after which the composition of the microbial community was determined by Illumina MiSeq Sequencing. Changes in litter stoichiometry induced by N-addition increased the diversity of the fungal community. The alpha-diversity of the fungal community was more sensitive to the type of litter (mixed- or single-species) than to the N-addition effects, with higher abundance of fungal OTUs and Shannon-diversity observed in soil with mixed-species litter. Moreover, the relative abundance of saprophytic fungi increased with increasing N-addition rates, which suggests that fungi play an important role in the initial stages of the decomposition process. Litter type and N addition did not significantly change the diversity of bacterial community. The relative abundance of ammonia-oxidizing bacteria was lower in high N-addition treatments than in those with lower N input, indicating that changes in litter stoichiometry could change ecosystem functioning via its effects on bacteria. Our results presented robust evidence for the plant-mediated pathways through which N-deposition affects the soil microbial community and biogeochemical cycling.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Zhenggao Xiao, Linhui Jiang, Xiaoyun Chen, Yu Zhang, Emmanuel Defossez, Feng Hu, Manqiang Liu, Sergio Rasmann〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉How plants cope with herbivore attack is partially modulated by the biotic and abiotic environment where the plant lives. For instance, theory predicts that soil fertility should drive patterns of plant resource allocation and defensive strategies. Earthworms, by their burrowing and casting activities, modify soil physicochemical properties and soil fertility. Therefore, earthworm-mediated changes in soil properties could alter plant physiology, plant nutritional quality, and ultimately, plant resistance against insect herbivores. We tested this hypothesis by measuring the combinatorial effects of two earthworm species, an epi-endogeic earthworm (〈em〉Amynthas corticis〈/em〉) and an endo-anecic earthworm (〈em〉Metaphire guillelmi〈/em〉), on soil properties, tomato plants’ physiological traits and plant resistance against the western flower thrips (〈em〉Frankliniella occidentalis〈/em〉). We found that 〈em〉A. corticis〈/em〉 alone increased plant resistance more than 〈em〉M. guillelmi〈/em〉 alone or the combination of two species. The increased plant resistance was associated with a significant increase in the defence-related phytohormone jasmonic acid and the production of phenolic compounds. Furthermore, we observed a strong link between earthworm-mediated changes in soil properties and plant eco-physiological traits. Our results thus build toward a better predictive model of how earthworms can simultaneously influence soil parameters, plant productivity and resistance against herbivore pests.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Xiangyin Ni, Shu Liao, Fuzhong Wu, Peter M. Groffman〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉There is great uncertainty about the short- and long-term effects of precipitation increases on soil-atmosphere trace gas fluxes of carbon dioxide (CO〈sub〉2〈/sub〉), methane (CH〈sub〉4〈/sub〉) and nitrous oxide (N〈sub〉2〈/sub〉O) in temperate forests. We conducted two analyses: a field study to test whether short-term heavy precipitation events affect these fluxes as well as a meta-analysis of studies evaluating these effects in forests around the world. In the field study, four daily additions of water increased CO〈sub〉2〈/sub〉 emissions but did not alter CH〈sub〉4〈/sub〉 and N〈sub〉2〈/sub〉O fluxes. However, the meta-analysis found that long-term increases in precipitation markedly altered fluxes of all three gases. These results suggest that the influence of short-term precipitation pulses may not be as important as long-term changes in precipitation. The mechanisms underlying long-term change are likely complex.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Xiaozhe Bao, Yutao Wang, Pål Axel Olsson〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Arbuscular mycorrhizal fungi (AMF) are commonly present in wetlands, but their functional role there is not well understood. We have quantified the carbon (C) allocation from rice to AMF under different flooding regimes, using stable isotope labeling (〈sup〉13〈/sup〉CO〈sub〉2〈/sub〉), and assessed the potential phosphorus (P) delivery from AMF to rice by profiling the expression of plant and fungal P transporter genes. The results showed that the plant-assimilated C was allocated to AMF under all flooding regimes, as evidenced by the significant enrichment of 〈sup〉13〈/sup〉C in the AMF signature fatty acids. The plant C allocation to AMF declined at increased flooding intensity, and was strikingly greater at the growth stage when the rice plants had a higher nutrient requirement. The gene expression profiles and rice P levels strongly indicated that a considerable amount of P was transported to plants via the mycorrhizal pathway under wetland conditions, although AMF colonization did not improve rice growth. This work provides the first solid evidence of C‒P exchange in AM symbiosis under flooded conditions, although it is reduced compared to non-flooded conditions. Nonetheless, this means that AMF may have an important function in wetlands, which opens new perspectives on the application of symbiotic AMF in wetlands.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Antonio Rafael Sánchez-Rodríguez, Paul W. Hill, David R. Chadwick, Davey L. Jones〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soils around the world are being exposed to weather events which are unprecedented in recent history. To maintain the delivery of soil-related ecosystem services and to promote greater soil resilience it is essential to understand how plant-soil systems respond to these extreme events. In this study we replicated a recent period of extreme rainfall and prolonged spring flooding in a temperate grassland which had no previous history of flooding. Intact soil mesocosms (Eutric Cambisol) 1 kg weight were subjected to a simulated long-term spring flood (15 °C, 2 months) and maintained in the light with above ground indigenous vegetation (〈em〉Lolium perenne〈/em〉 L.) or dark with and without indigenous vegetation to simulate different flood typologies. In comparison to a no-flood control treatment, nutrient cycling, water quality, air quality (greenhouse gas emissions), habitat provision and biological population regulation shifts were evaluated. Flooding induced a rapid release of nutrients into the soil solution and overlying floodwater, resulting in potential nutrient losses up to 15 mg Fe, 16 mg NH〈sub〉4〈/sub〉〈sup〉+〈/sup〉, 360 mg DOC and 28 mg DON, per mesocosm. The presence of plants increased the rate of nutrient release (especially P), with the effects magnified when light transmission through the floodwater was restricted (1.3 mg P vs 0.2 mg P, per mesocosm). Flooding induced a rapid decline in redox potential and subsequent production of CH〈sub〉4〈/sub〉, especially in the darkened treatments (10 and between 11 and 16 times higher than the control, without and with light restrictions, respectively). Upon removal of the floodwater, the accumulated NH〈sub〉4〈/sub〉〈sup〉+〈/sup〉 was nitrified leading to a shift in greenhouse gas emissions, from CH〈sub〉4〈/sub〉 to N〈sub〉2〈/sub〉O emissions. N〈sub〉2〈/sub〉O was only significantly produced in the mesocosms kept under light restrictions (13 times higher than in other two treatments). Flooding eliminated earthworms, reduced grass production after soil recovery (from 28 g for control mesocosms to 11 g and 〈1 g for flooded mesocosms without and with light restrictions, respectively). Soil microbial biomass was also reduced (up to a 22–27% of the total PLFAs) and flooding induced shifts in microbial community structure, particularly a loss of soil fungi. The soil fungi content quickly recovered (4 weeks) when light was not restricted during the flood period, however, no such recovery was seen in the darkened treatments. Overall, we conclude that extreme flood events cause rapid and profound changes in soil function. Both the impact of the flooding and the time to recover is exacerbated when light is restricted (e.g. in sediment laden floodwater). In addition, our results suggest that the presence of flood-resilient plants can mitigate against some of the negative impacts of flooding on soil functioning.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Doreen Babin, Annette Deubel, Samuel Jacquiod, Søren J. Sørensen, Joerg Geistlinger, Rita Grosch, Kornelia Smalla〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The profound intensification of agricultural practices by increased application of agro-chemicals, short crop rotations and ploughing resulted in loss of soil fertility, erosion and accumulation of soil-borne plant pathogens. Soil microbial communities are key players in ecosystem processes and are intimately linked to crop productivity and health. Thus a better understanding of how farming practices affect soil microbiota is needed in order to promote sustainable agriculture. The long-term field trial in Bernburg (Germany) established in 1992 provides a unique opportunity to assess the effects of i) the crop (maize 〈em〉vs.〈/em〉 rapeseed) preceding the actual winter wheat culture, ii) tillage practice (mouldboard plough 〈em〉vs.〈/em〉 cultivator tillage) and iii) standard nitrogen (N)-fertilization intensity with application of growth regulators and fungicides (intensive) compared to reduced N-fertilization without growth regulators and fungicides (extensive). We hypothesized that these different farming practices affect the soil prokaryotic community structures with consequences for their functional potential. Total community-DNA was extracted directly from soils sampled at wheat harvest. Illumina sequencing of 16S rRNA genes amplified from total community-DNA revealed a significant effect of tillage practice and the preceding crop on prokaryotic community structures, whereas the influence of N-fertilization intensity was marginal. A number of differentially abundant prokaryotic genera and their predicted functions between mouldboard plough 〈em〉vs.〈/em〉 cultivator tillage as well as between different preceding crops were identified. Compared to extensive N-fertilization, intensive N-fertilization resulted in higher abundances of bacterial but not of archaeal 〈em〉amoA〈/em〉 genes, that are involved in ammonia oxidation. Our data suggest that long-term farming strategies differently shape the soil prokaryotic community structure and functions, which should be considered when evaluating agricultural management strategies regarding their sustainability, soil health and crop performance.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Lisa Noll, Shasha Zhang, Wolfgang Wanek〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Proteins comprise the largest soil N reservoir but cannot be taken up directly by microorganisms and plants due to size constraints and stabilization of proteins in organo-mineral associations. Therefore the cleavage of this high molecular weight organic N to smaller soluble compounds as amino acids is a key step in the terrestrial N cycle. In the last years two isotope pool dilution approaches have been successfully established to measure gross rates of protein depolymerization and microbial amino acid uptake in soils. However, both require laborious sample preparation and analyses, which limits sample throughput. Therefore, we here present a novel isotope pool dilution approach based on the addition of 〈sup〉15〈/sup〉N-labeled amino acids to soils and subsequent concentration and 〈sup〉15〈/sup〉N analysis by the oxidation of α-amino groups to NO〈sub〉2〈/sub〉〈sup〉−〈/sup〉 and further reduction to N〈sub〉2〈/sub〉O, followed by purge-and-trap isotope ratio mass spectrometry (PT-IRMS). We applied this method in mesocosm experiments with forest and meadow soils as well as with a cropland soil amended with either organic C (cellulose) or organic N (bovine serum albumin). To measure direct organic N mineralization to NH〈sub〉4〈/sub〉〈sup〉+〈/sup〉, the latter was captured in acid traps and analyzed by an elemental analyzer coupled to an isotope ratio mass spectrometer (EA-IRMS). Our results demonstrate that the proposed method provides fast and precise measurements of at%〈sup〉15〈/sup〉N even at low amino acid concentrations, allows high sample throughput and enables parallel estimations of instantaneous organic N mineralization rates.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Mette Vestergård, Marie Dam, Louise Hindborg Mortensen, Jens Dyckmans, Bent T. Christensen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉We determined the 〈sup〉13〈/sup〉C/〈sup〉12〈/sup〉C ratio (expressed as δ〈sup〉13〈/sup〉C ‰) of microbial biomass and nematode trophic groups in a small-plot field experiment with soil converted from C3- to C4-crop (silage maize) 20 years ago. During this period, the plots were subjected to three different organic input treatments: 1) maize stubbles and roots left after harvest (MS), 2) MS plus annual addition of aboveground maize biomass (MS + B), and 3) MS plus annual addition of faeces from sheep fed exclusively with maize (MS + F). The different δ〈sup〉13〈/sup〉C value of C3- and C4-crops allowed us to distinguish between old (〉20 years old) C3-derived C and recent (〈20 years old) C4-derived C incorporated into microbial biomass and nematodes.〈/p〉 〈p〉The δ〈sup〉13〈/sup〉C value of phytophagous nematodes closely matched that of the maize. Bacterivorous nematodes had higher δ〈sup〉13〈/sup〉C values than fungivorous nematodes and microbial biomass indicating that the C sources of bacterivorous nematodes are more recent than those of fungivorous nematodes and microbial biomass. At low abundance of fungivorous nematodes (MS and MS + F), the microbial biomass had higher δ〈sup〉13〈/sup〉C values than the fungivorous nematodes, whereas their δ〈sup〉13〈/sup〉C values were comparable at higher densities of fungivorous nematodes (MS + B). The higher C4-derived input in MS + F and MS + B treatments increased the δ〈sup〉13〈/sup〉C values of bacterivorous nematodes and microbial biomass.〈/p〉 〈p〉In MS and MS + B treatments, recent C4-derived C accounted for 50 and 70% of microbial biomass-C, respectively. Corresponding values for fungivorous and bacterivorous nematodes were 30 and 75%, and 65 and 85%, respectively.〈/p〉 〈p〉We conclude that fungal-based decomposition pathways contribute more to the turnover of old soil C than bacterial-based decomposition. A substantial fraction of the microbial biomass and fungivorous nematode C in the MS treatment (50 and 70%, respectively) was C deposited in the soil more than 20 years ago, confirming that decade-old SOC remains biologically active.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 130〈/p〉 〈p〉Author(s): Camille Cros, Gaël Alvarez, Frida Keuper, Sébastien Fontaine〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Forty years of research on the rhizosphere priming effect (RPE) has demonstrated the potentially large increase (up to a factor 3) of soil organic matter mineralization induced by plant roots, but failed to directly quantify its contribution to the carbon (C) balance. Combining continuous CO〈sub〉2〈/sub〉 flux measurements with RPE measurements has thus far been technically challenging. Here, we present an experimental platform of 40 mesocosms (volume = 88L; surface = 0.049 m〈sup〉2〈/sup〉), including a 〈sup〉13〈/sup〉C-labeled CO〈sub〉2〈/sub〉 air-production system with a maximum capacity of 4 m〈sup〉3〈/sup〉 min〈sup〉−1〈/sup〉 and customizable labeling intensity. For this study, 〈sup〉13〈/sup〉C depleted fossil C was used as source of labeled CO〈sub〉2〈/sub〉 and the experiment was run for 250 days. Continuous net CO〈sub〉2〈/sub〉-exchange measurements allowed us to estimate net ecosystem productivity, gross primary production and ecosystem respiration of the studied plant-soil systems. The RPE was regularly (bi-monthly to monthly) quantified by measuring the accumulation and isotopic composition of CO〈sub〉2〈/sub〉 in dark chambers placed over the mesocosms. Our results show a good relationship between night plant-soil respiration (from continuous CO〈sub〉2〈/sub〉-exchange measurements) and dark plant-soil respiration (from CO〈sub〉2〈/sub〉 accumulation in dark chambers). This result suggests that our estimates of RPE and plant-soil fluxes based on the different methods are comparable. Preliminary results obtained in spring with grasses cultivated under ambient or elevated CO〈sub〉2〈/sub〉 indicate that the RPE represents 1.22 ± 0.16% of gross primary production and 4.64 ± 1.12% of ecosystem respiration. The RPE estimates may have an uncertainty linked to the possible deviation in delta 〈sup〉13〈/sup〉C between C sources (soil or plant) and released CO〈sub〉2〈/sub〉 from these sources. We performed a sensitivity analysis on how the variation in intensity of isotopic labeling (difference in delta 〈sup〉13〈/sup〉C between plant and soil) affects the uncertainty of RPE estimates considering 1‰ delta 〈sup〉13〈/sup〉C deviation. Estimation of the RPE with an uncertainty lower than 10% of the estimated value requires a labeling intensity higher than 60‰. The developed platform will help to scale up the study of the RPE control on C cycling to the ecosystem level.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Johannes Friedl, Daniele De Rosa, David W. Rowlings, Peter R. Grace, Christoph Müller, Clemens Scheer〈/p〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Marcus O. Bello, Cécile Thion, Cécile Gubry-Rangin, James I. Prosser〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Microbial oxidation of ammonia controls the rate of nitrification in the majority of soils. Both nitrification rate and the composition of communities of ammonia oxidising archaea (AOA) and ammonia oxidising bacteria (AOB) are influenced by drought, with evidence that AOA are more sensitive to periods of drought than AOB. This has been explained by greater sensitivity of AOA to ammonia concentration, which will increase in soil solution during drought, but an alternative, previously unexplored explanation, is greater sensitivity of AOA to matric and/or osmotic stress. A soil microcosm experiment was designed to distinguish these different explanations in which AOA and AOB abundances (〈em〉amoA〈/em〉 abundance) and nitrification rate were measured over 28 days in nine treatments corresponding to all combinations of three soil matric potentials and three initial ammonia concentrations. Comparison of 〈em〉amoA〈/em〉 abundance dynamics suggested that AOA were more susceptible to reduced matric potential than AOB, irrespective of soil ammonia concentration. The greater sensitivity of soil AOA to osmotic stress was also tested in 10-day cultures of representative strains of AOA and AOB in liquid medium containing different concentrations of NaCl and sorbitol as osmo-inducer. AOA were significantly more sensitive to osmotic stress than AOB. These results provide evidence for greater sensitivity of AOA than AOB to both components of water stress, matric and osmotic potential, representing an additional niche differentiation between these two essential groups of ammonia oxidisers.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Tao Sun, Yalan Cui, Björn Berg, Quanquan Zhang, Lili Dong, Zhijie Wu, Lili Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Litter of plant origin is the main source of soil organic matter, and its physical and chemical quality and decomposition rates are key variables in the prediction and modelling of how litter-derived carbon (C) is cycling through the ecosystem. However, the biological control factors for decomposition are not well understood and often poorly represented in global C models. These are typically run using simple parameters, such as nitrogen (N) and lignin concentrations, characterizing the quality of the organic matter input to soils and its accessibility to decomposer organisms. Manganese (Mn) is a key component for the formation of manganese peroxidase (MnP), an important enzyme for lignin degradation. However, the functional role of Mn on plant litter decomposition has been rarely experimentally examined. Here, using a forest and a cropland site we studied, over 41 months, the effects of Mn fertilization on MnP activity and decomposition of eight substrates ranging in initial lignin concentrations from 9.8 to 44.6%. Asymptotic decomposition models fitted the mass loss data best and allowed us to separately compare the influence of Mn fertilization on different litter stages and pools. Across substrates, Mn fertilization stimulated decomposition rates of the late stage where lignin dominates decomposition, resulting in smaller fraction of slowly decomposing litter. The increased MnP activity caused by Mn fertilization provided the mechanism explaining the stimulated decomposition in the Mn-addition treatments.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Radomir Schmidt, Jeffrey Mitchell, Kate Scow〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Fungi are important members of soil microbial communities in row-crop and grassland soils, provide essential ecosystem services such as nutrient cycling, organic matter decomposition, and soil structure, but fungi are also more sensitive to physical disturbance than other microorganisms. Adoption of conservation management practices such as no-till and cover cropping shape the structure and function of soil fungal communities. No-till eliminates or greatly reduces the physical disturbance that re-distributes organisms and nutrients in the soil profile and disrupts fungal hyphal networks, while cover crops provide additional types and greater abundance of organic carbon sources. In a long-term, row crop field experiment in California's Central Valley we hypothesized that a more diverse and plant symbiont-enriched fungal soil community would develop in soil managed with reduced tillage practices and/or cover crops compared to standard tillage and no cover crops. We measured the interacting effects of tillage and cover cropping on fungal communities based on fungal ITS sequence assigned to ecological guilds. Functional groups within fungal communities were most sensitive to long-term tillage practices, with 45% of guild-assigned taxa responding to tillage, and a higher proportion of symbiotroph taxa under no-till. In contrast, diversity measures reflected greater sensitivity to cover crops, with higher phylogenetic diversity observed in soils managed with cover crops, though only 10% of guild-assigned taxa responded to cover crops. The relative abundance of pathotrophs did not vary across the management treatments. Cover cropping increased species diversity, while no-till shifted the symbiotroph:saprotroph ratio to favor symbiotrophs. These management-induced shifts in fungal community composition could lead to greater ecosystem resilience and provide greater access of crops to limiting resources.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Steven J. Fonte, Cesar Botero, D. Carolina Quintero, Patrick Lavelle, Chris van Kessel〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Llanos region of Colombia represents one of the last large agricultural frontiers and is undergoing a rapid conversion from naturalized savanna to intensive agriculture with high agrochemical inputs and tillage. This massive land-use conversion has considerable impact on ecosystem services and biodiversity, particularly soil macrofauna, yet the full implications of this land-use shift for long-term agroecosystem productivity are poorly understood. To better elucidate potential land-use change impacts on agricultural production we used experimental microcosms in the greenhouse to evaluate how the common earthworm, 〈em〉Pontoscolex corethrurus,〈/em〉 influences plant growth, nutrient uptake, and key soil properties relative to the application of lime and P fertilizer, both common soil fertility amendments in the region. Additionally, we aimed to explore the potential for interactions between earthworms and these amendments across distinct plant types, the grass 〈em〉Brachiaria decumbens〈/em〉 and the legume 〈em〉Phaseolus vulgaris〈/em〉, which display different rooting patterns and nutrient acquisition strategies. Earthworms increased the biomass production of 〈em〉B. decumbens〈/em〉 by 180% and N uptake by more than 240%, while P fertilizers and lime additions increased total biomass by less than 30% each for 〈em〉B. decumbens〈/em〉. Effects on 〈em〉P. vulgaris〈/em〉 were similar, but less pronounced with earthworms increasing total biomass production by 35% and total plant N content by 70%, while neither lime nor P alone significantly influenced total biomass or N uptake. However, a significant interaction between earthworms and lime enhanced total biomass N content of 〈em〉P. vulgaris〈/em〉 by more than 150% relative to microcosms without 〈em〉P. corethrurus〈/em〉, suggesting that earthworms can greatly enhance the efficacy of lime in soils. Additionally, we found that earthworms greatly improved soil aggregation, but only in the presence of plants, and that this effect was most prominent in microcosms with 〈em〉P. vulgaris〈/em〉. When testing treatment effects on soil P availability, only fertilizer P additions significantly influenced resin P, but not microbial biomass P. Our findings suggests the importance of developing management strategies that promote the activity and diversity of earthworms and other soil biota as a means to enhance crop productivity, resource use efficiency and a range of soil-based ecosystem services in the Llanos region and beyond.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Yun Chen, Siyu Li, Yajun Zhang, Tingting Li, Huimin Ge, Shiming Xia, Junfei Gu, Hao Zhang, Bing Lü, Xiaoxia Wu, Zhiqin Wang, Jianchang Yang, Jianhua Zhang, Lijun Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rice (〈em〉Oryza sativa〈/em〉 L〈em〉.〈/em〉) paddies contribute approximately 7–17% to total global methane (CH〈sub〉4〈/sub〉) emissions and are considered an important source of human-induced climate change. However, the interactive effects of rice roots and soil microbes on CH〈sub〉4〈/sub〉 emissions in paddy fields are not clearly understood. We conducted two field experiments over three years. Soil CH〈sub〉4〈/sub〉 fluxes and cumulative CH〈sub〉4〈/sub〉 emissions, rice root traits, and microbial communities and activities in soil were measured using three mid-season 〈em〉japonica〈/em〉 rice cultivars (Wuyujing 3, Zhendao 88, and Huaidao 5) that have the same growth durations and similar aboveground traits before heading. The CH〈sub〉4〈/sub〉 emissions during the mid-growing period (from panicle initiation to heading) contributed 39.0–49.7% of the total emissions during the entire growing season and differed significantly among the rice cultivars. The root morphological and physiological traits (i.e. root dry weight, root length, root oxidation activity, and root radial oxygen loss) were negatively correlated with CH〈sub〉4〈/sub〉 fluxes. Compared to the zero-N control, application rates of N fertilizer at 54 and 108 kg ha〈sup〉−1〈/sup〉 increased root biomass of cultivar Zhendao 88 by 10.1% and 17.3%, respectively, leading to corresponding decreases in CH〈sub〉4〈/sub〉 emissions by 12.7% and 22.9%. The root exudates (malic acid, succinic acid, and citric acid) promoted the abundance and activity of methanotrophs, which was the primary factors underlying the low CH〈sub〉4〈/sub〉 emissions in the paddy fields. Our findings suggested that stronger root systems, higher oxygen delivered by roots available for methanotrophs and suitable root exudates interacted in the rhizosphere, established a favourable habitat for microbial populations, and reduced CH〈sub〉4〈/sub〉 emissions in paddy fields.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): 〈/p〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Birgit Wild, Jian Li, Johanna Pihlblad, Per Bengtson, Tobias Rütting〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil carbon (C) and nitrogen (N) availability depend on the breakdown of soil polymers such as lignin, chitin, and protein that represent the major fraction of soil C and N but are too large for immediate uptake by plants and microorganisms. Microorganisms may adjust the production of enzymes targeting different polymers to optimize the balance between C and N availability and demand, and for instance increase the depolymerization of N-rich compounds when C availability is high and N availability low (“microbial N mining”). Such a mechanism could mitigate plant N limitation but also lie behind a stimulation of soil respiration frequently observed in the vicinity of plant roots (“priming effect”). We here compared the effect of increased C and N availability on the depolymerization of native bulk soil organic matter (SOM), and of 〈sup〉13〈/sup〉C-enriched lignin, chitin, and protein added to the same soil in two complementary ten day microcosm incubation experiments. A significant reduction of chitin depolymerization (described by the recovery of chitin-derived C in the sum of dissolved organic, microbial and respired C) upon N addition indicated that chitin was degraded to serve as a microbial N source under low-N conditions and replaced in the presence of an immediately available alternative. Protein and lignin depolymerization in contrast were not affected by N addition. Carbon addition enhanced microbial N demand and SOM decomposition rates, but significantly reduced lignin, chitin, and protein depolymerization. Our findings contrast the hypothesis of increased microbial N mining as a key driver behind the priming effect and rather suggest that C addition promoted the mobilization of other soil C pools that replaced lignin, chitin, and protein as microbial C sources, for instance by releasing soil compounds from mineral bonds. We conclude that SOM decomposition is interactively controlled by multiple mechanisms including the balance between C vs N availability. Disentangling these controls will be crucial for understanding C and N cycling on an ecosystem scale.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Giuliano Bonanomi, Francesca De Filippis, Gaspare Cesarano, Antonietta La Storia, Maurizio Zotti, Stefano Mazzoleni, Guido Incerti〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Microbial succession over decomposing litter is controlled by biotic interactions, dispersal limitation, grazing pressure, and substrate chemical changes. Recent evidence suggests that the changes in litter chemistry and microbiome during decomposition are interdependent. However, most previous studies separately addressed the microbial successional dynamics or the molecular changes of decomposing litter. Here, we combined litter chemical characterization by 〈sup〉13〈/sup〉C NMR spectroscopy with next generation sequencing to compare leaf litter chemistry and microbiome dynamics using 30 litter types, either fresh or decomposed for 30 and 180 days.〈/p〉 〈p〉We observed a decrease of cellulose and C/N ratio during decomposition, while lignin content and lignin/N ratio showed the opposite pattern. 〈sup〉13〈/sup〉C NMR revealed significant chemical changes as microbial decomposition was proceeding, with a decrease in 〈em〉O〈/em〉-alkyl C and an increase in alkyl C and methoxyl C relative abundances. Overall, bacterial and eukaryotic taxonomical richness increased with litter age. Among Bacteria, Proteobacteria dominated all undecomposed litters but this group was progressively replaced by members of Actinobacteria, Bacteroidetes, and Firmicutes. Nitrogen-fixing genera such as 〈em〉Beijerinckia〈/em〉 and 〈em〉Rhizobium〈/em〉 occurred both in undecomposed as well as in aged litters. Among Eukarya, fungi belonging to the Ascomycota phylum were dominant in undecomposed litter with the typical phyllospheric genus 〈em〉Aureobasidium〈/em〉. In aged litters, phyllospheric species were replaced by zygomycetes and other ascomycetous and basidiomycetous fungi. Our analysis of decomposing litter highlighted an unprecedented, widespread occurrence of protists belonging to the Amebozoa and Cercozoa. Correlation network analysis showed that microbial communities are non-randomly structured, showing strikingly distinct composition in relation to litter chemistry. Our data demonstrate that the importance of litter chemistry in shaping microbial community structure increased during the decomposition process, being of little importance for freshly fallen leaves.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Raquel Campos-Herrera, Rubén Blanco-Pérez, Francisco Ángel Bueno-Pallero, Amílcar Duarte, Gustavo Nolasco, Ralf J. Sommer, José Antonio Rodríguez Martín〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Entomopathogenic nematodes (EPNs) are widely distributed in soils throughout the world. Their activity as biological control agents is modulated by abiotic and biotic factors (e.g. soil type, climatic fluctuation and natural enemies). We sought to identify soil properties in a Mediterranean region, which might be managed to enhance biological control agents’ services provided by EPNs. We hypothesized that responses of EPN soil food web assemblages to abiotic factors in such a Mediterranean region would be consistent with previous observations in other biomes in subtropical and temperate regions, in which pH and variables related to water content were main drivers of such association. We also expected that EPN abundance and species composition would differ between stable botanical habitats (citrus groves, palmetto areas, oaks and pines), with EPNs and associated organisms favoured in cultivated sites (citrus). In spring 2016, 50 georeferenced localities, representing four botanical habitats and two soil-ecoregions (calcareous 〈em〉versus〈/em〉 non-calcareous), were surveyed. Using published and 〈em〉de novo〈/em〉 real time qPCR tools, we evaluated the frequency and abundance of 10 EPN species and 13 organisms associated with EPNs: 6 nematophagous fungi (NF), 5 free-living nematodes (FLN), and 2 ectoparasitic bacteria. EPN activity was also assessed by traditional insect-baiting, allowing the evaluation of FLN-EPN mixed progeny. EPNs were detected by qPCR in 50% of localities, and strongly correlated with EPN activity. 〈em〉Steinernema feltiae〈/em〉 was the dominant EPN species measured by both techniques (qPCR and insect-bait), being widespread in all Algarve, while 〈em〉Heterorhabditis bacteriophora〈/em〉 was detected mainly in citrus groves. The species 〈em〉S. arenarium〈/em〉 and 〈em〉H. indica〈/em〉 were detected by qPCR for the first time in continental Portugal. The molecular analysis of insect cadaver progeny revealed novel FLN-EPN associations with 〈em〉Pristionchus maupasi〈/em〉 and 〈em〉P. pacificus〈/em〉. EPN, FLN and NF abundance differed among botanical groups, with citrus groves supporting high numbers of all trophic guilds. Oaks also favoured EPNs. Similarly, calcareous soil-ecoregion supported higher NF, FLN and EPN abundance. Two abiotic variables (pH, and clay content) explained the community variation in multivariate analysis, consistent with key abiotic variables described for other subtropical and temperate regions. The results supported the hypothesis that cultivated perennial habitats favour EPNs and soil organisms that can limit EPN activity as biological control agents.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Qingxue Guo, Lijuan Yan, Helena Korpelainen, Ülo Niinemets, Chunyang Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The impact of conspecific and heterospecific neighboring plants on soil bacterial and fungal communities has never been explored in a forest ecosystem. In the present study, we first investigated soil microbial communities in three plantations: 〈em〉Larix kaempferi〈/em〉 monoculture, 〈em〉L. olgensis〈/em〉 monoculture and their mixture. Then, a two-year growth experiment was conducted to investigate the effects of intra- and inter-specific interactions of 〈em〉L. kaempferi〈/em〉 and 〈em〉L. olgensis〈/em〉 on rhizosphere microbial communities at two different nitrogen levels. The results demonstrated clear differences in the beta-diversity and composition of bacteria and fungi among the three plantations, which implied the presence of different effects of plant-plant interactions on soil microbial communities. The results of the pot experiment showed that 〈em〉L. kaempferi〈/em〉 suffered from greater neighbor effects from its conspecific neighbor regardless of N fertilization, although the effect declined when 〈em〉L. kaempferi〈/em〉 was grown with 〈em〉L. olgensis〈/em〉 under N fertilization. Changes in intra- and inter-specific plant interactions significantly impacted the chemical and biological properties of soil under N fertilization, with lower concentrations of NH〈sub〉4〈/sub〉〈sup〉+〈/sup〉, and lower soil microbial biomass (C〈sub〉Mic〈/sub〉) and soil carbon nitrogen biomass (N〈sub〉Mic〈/sub〉) under intra-specific plant interactions of 〈em〉L. kaempferi〈/em〉 (KK) compared to inter-specific interactions of 〈em〉L. kaempferi〈/em〉 and 〈em〉L. olgensis〈/em〉 (KO). N fertilization increased bacterial and fungal alpha diversities in the rhizosphere soil of KO. For the beta diversity, the PERMANOVA results demonstrated that there was a significant impact of intra- and inter-specific plant interactions on soil microbial communities, with KK significantly differing from intra-specific plant interactions of 〈em〉L. olgensis〈/em〉 (OO) and KO. The two plant species and N fertilization showed specific effects on the soil microbial composition, particularly on the fungal community. Both 〈em〉L.〈/em〉〈em〉olgensis〈/em〉 and N fertilization increased the abundance of 〈em〉Ascomycota〈/em〉 but reduced that of 〈em〉Basidiomycota〈/em〉, and even shifted the dominance from 〈em〉Basidiomycota〈/em〉 to 〈em〉Ascomycota〈/em〉 under KO combined with N fertilization.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Raquel Campos-Herrera, Robin J. Stuart, Ekta Pathak, Fahiem E. El-Borai, Larry W. Duncan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The abundance of three entomopathogenic nematode (EPN) species, seven species of nematophagous fungi, free living nematode competitors of EPNs and a bacterial ectoparasite of EPNs were monitored during approximately two years in four Florida citrus orchards. The objective of the surveys was to identify natural enemies that potentially regulate the temporal abundance of naturally occurring EPNs by using molecular tools. Nematodes were extracted from two soil depths at ∼ monthly intervals, DNA extracted, and target organisms were measured using qPCR. Potentially causal relationships between the temporal patterns of EPNs and their natural enemies were assessed primarily with stepwise regression of variables at various time lags. 〈em〉Drechslerella dactyloides〈/em〉 was the only nematophagous fungus species exhibiting evidence of top-down regulation, being inversely related to population change of 〈em〉Heterorhabditis indica〈/em〉 at two of three sites. 〈em〉Acrobeloides〈/em〉 spp. (EPN competitors) were associated with reduced population growth of 〈em〉Steinernema diaprepesi〈/em〉 at two sites and 〈em〉H. indica〈/em〉 was associated with reduced abundance of 〈em〉H. zealandica〈/em〉 and 〈em〉S. diaprepesi〈/em〉 at one site each. A 〈em〉Paenibacillus〈/em〉 sp. exhibited significant phase-space, predator-prey dynamics at two of three sites with abundant 〈em〉S. diaprepesi〈/em〉, a species-specific host of the bacterium. The initial abundance of both 〈em〉S. diaprepesi〈/em〉 and 〈em〉Paenibacillus〈/em〉 sp. explained significant variability in population changes of 〈em〉S. diaprepesi〈/em〉 in a multiple regression model at a lag of three months. Controlled experiments showed that pH is directly related to adherence of the bacterial endospores to the 〈em〉S. diaprepesi〈/em〉 cuticle. Soil pH in these surveys was directly related to the infestation rate (encumbrance) by 〈em〉Paenibacillus〈/em〉 and inversely related to the abundance of 〈em〉S. diaprepesi〈/em〉. Vertical distribution patterns reflected potential routes for avoiding competition and predation between species. Nematode-trapping fungi tended to inhabit shallower soil horizons than did several other nematophagous fungal species and 〈em〉S. diaprepesi〈/em〉 and 〈em〉H. indica〈/em〉. The nematophagous fungus 〈em〉Purpureocillium lilacinum〈/em〉 was especially abundant in deeper soil horizons and in the flatwoods sites. Depth distribution among EPNs also differed significantly with 〈em〉H. indica〈/em〉 〉 〈em〉S. diaprepesi〈/em〉 〉 than 〈em〉H. zealandica〈/em〉. These results support soil pH management to conserve the demonstrated services of 〈em〉S. diaprepesi〈/em〉. They also suggest a need to better understand potential non-target effects of practices favorable to nematophagous fungi and bactivorous nematode competitors of EPNs.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0038071718303602-fx1.jpg" width="259" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 129〈/p〉 〈p〉Author(s): Roser Matamala, Julie D. Jastrow, Francisco J. Calderón, Chao Liang, Zhaosheng Fan, Gary J. Michaelson, Chien-Lu Ping〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Vast amounts of soil organic matter (SOM) have been preserved in arctic soils over millennia time scales due to the limiting effects of cold and wet environments on decomposer activity. With the increase in high latitude warming due to climate change, the potential decomposability of this SOM needs to be assessed. In this study, we investigated the capability of mid infrared (MIR) spectroscopy to quickly predict soil carbon and nitrogen concentrations and carbon (C) mineralized during short-term incubations of tundra soils. Active layer and upper permafrost soils collected from four tundra sites on the North Slope of Alaska were incubated at 1, 4, 8 and 16 °C for 60 days. All incubated soils were scanned to obtain the MIR spectra and analyzed for total organic carbon (TOC) and total nitrogen (TN) concentrations, and salt-extractable organic matter carbon (SEOM). Partial least square regression (PLSR) models, constructed using the MIR spectral data for all soils, were excellent predictors of soil TOC and TN concentrations and good predictors of mineralized C for these tundra soils. We explored whether we could improve the prediction of mineralized C by splitting the soils into the groups defined by the influential factors and thresholds identified in a principal components analysis: (1) TOC 〉10%, (2) TOC 〈 10%, (3) TN 〈 0.6%, (4) TN 〉 0.6%, (5) acidic tundra, and (6) non-acidic tundra. The best PLSR mineralization models were found for soils with TOC 〈 10% and TN 〈 0.6%. Analysis of the PLSR loadings and beta coefficients from these models indicated a small number of influential spectral bands. These bands were associated with clay content, phenolics, aliphatics, silicates, carboxylic acids, and amides. Our results suggest that MIR could serve as a useful tool for quickly and reasonably estimating the initial decomposability of tundra soils, particularly for mineral soils and the mixed organic-mineral horizons of cryoturbated soils.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 127〈/p〉 〈p〉Author(s): 〈/p〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 128〈/p〉 〈p〉Author(s): Zongzhuan Shen, Chao Xue, C. Ryan Penton, Linda S. Thomashow, Na Zhang, Beibei Wang, Yunze Ruan, Rong Li, Qirong Shen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉〈em〉Fusarium〈/em〉 wilt disease of banana, caused by the fungus 〈em〉Fusarium oxysporum〈/em〉 f. sp. 〈em〉cubense〈/em〉 race 4, is a serious soil-borne fungal disease that currently threatens worldwide banana production. No single agricultural practice has yet been developed to effectively manage this disease. In the present study, greenhouse experiments were conducted to evaluate the effect of an integrated biofertilizer application after ammonia fumigation to enhance control of 〈em〉Fusarium〈/em〉 wilt disease in severely infected banana mono-cropped soils. Quantitative PCR and high-throughput sequencing were used to characterise soil microbial community structure and the results from both two-season experimental studies showed that biofertilizer application after ammonia fumigation significantly reduced the incidence of banana Panama disease by approximately 55% and promoted the plant biomass, compared to the control application of cow manure to non-fumigated soil. Ammonia fumigation significantly reduced total fungal and 〈em〉F. oxysporum〈/em〉 abundances and bacterial and fungal diversities. Biofertilizer application after fumigation further depleted the abundance of the pathogen. Biofertilizer application and fumigation altered the soil microbial community composition with the bacterial community responding first to fumigation, while the fungal community responded first to fertilization. Although 〈em〉Bacillus〈/em〉, including our inoculated strain, was not enriched after biofertilization, putative beneficial microbes such as 〈em〉Paenibacillus〈/em〉, 〈em〉Virgibacillus〈/em〉, 〈em〉Nitrosomonas〈/em〉, and 〈em〉Nitrobacter〈/em〉, were significantly enriched by ammonia fumigation and biofertilizer application, and were significantly correlated with disease suppression or increased plant biomass. Furthermore, fumigation and biofertilization significantly increased the soil pH and nutrient contents, with concomitant effects on the microbial community. Overall, the observed disease suppression and increased plant biomass resulting from both soil fumigation and biofertilization after banana cropping can be attributed to the reduced abundance of 〈em〉F. oxysporum〈/em〉 and general suppression from altered soil properties that may enable the establishment of a beneficial soil microbiome.〈/p〉〈/div〉 〈/div〉