ALBERT

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Shrub encroachment has profound influences on regional carbon cycling. However, few studies have examined the changes in soil organic carbon (SOC) components at the molecular level along a climate gradient. In this study, we aimed to investigate the effects of biotic and abiotic factors on the patterns of SOC components in the shrub patches and the grassy matrix.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We analyzed the distribution and controlling factors of SOC components (including free lipids, bound lipids, and lignin-derived phenols) in the topsoil of shrub-encroached grasslands along natural climate gradients in Inner Mongolia, China.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉 We found that the concentrations of bound lipids and lignin-derived phenols were significantly higher and the vanillic acid to vanillin ratio ((Ad/Al)〈sub〉v〈/sub〉) was significantly lower in the shrub patches than in the grassy matrix (〈em〉p〈/em〉 〈 0.05). After excluding variables exhibiting collinearity, redundancy analysis showed that shrub patch cover and soil pH were the most important variables that influenced SOC composition in the shrub patches, while herb characteristics and shrub density were the most important in the grassy matrix. Structural equation modeling showed that shrub characteristics at the plot scale greatly contributed to the variance in all components in the grassy matrix, whereas soil properties were more important in the shrub patches.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our results highlight that although the topsoil carbon content did not change, shrub encroachment altered the SOC components and their drivers in the Inner Mongolian grasslands.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉While the coupled effects of root exudates and microbial feedbacks on soil processes are well-recognized, we still lack an understanding of differences in root exudate fluxes and the associated ecological consequences among tree growth forms.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Two deciduous tree species (i.e., 〈em〉Cercidiphyllum japonicum〈/em〉 and 〈em〉Larix kaempferi〈/em〉) and two evergreen tree species (i.e., 〈em〉Pinus armandi〈/em〉 and 〈em〉Pinus tabulaeformis〈/em〉) were selected to perform an in-situ collection of root exudates during the growing season in 2016. The net N mineralization rates and associated microbial enzyme activities were measured in rhizosphere and bulk soils to evaluate rhizosphere effects. Moreover, we compiled the dataset related to root exudation and their associated biological traits and the soil chemical properties for 21 tree species from temperate forests.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The root exudation rates and the annual root exudate carbon (C) fluxes of two deciduous tree species were significantly higher than those of the two evergreen tree species. Correspondingly, the rhizosphere effects of deciduous tree species on the microbial biomass, enzyme activity and net N mineralization rate were approximately 1.9, 1.6 and 2.4 times greater than those of the evergreen tree species, respectively. Rhizosphere effects were positively correlated with the root exudation rate. The compiled dataset also suggest that deciduous tree species tend to have higher exudation rates than evergreen tree species in temperate forests.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Collectively, these results suggest that the two tree growth forms exhibit different patterns in root exudate inputs and associated rhizosphere microbial processes. Generally, deciduous tree species tend to exude more C into the soil and consequently induce greater microbial feedback on soil N transformations during the growing season in temperate regions, implying that deciduous tree species induced a greater effect on the C and nutrient cycling in rhizosphere soil than evergreen tree species.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Culture media compositions and bioprocess conditions were studied to improve the production of cell biomass and indolic phytohormones by 〈em〉Herbaspirillum seropedicae〈/em〉 BR11471, a plant growth promoting bacterium, and different inoculant formulations were also produced and tested for their stability and shelf life.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Response surface methodology (RSM) based on central composite rotation designs (CCRD) was used to find bioprocess variables that lead to an increase in bacterial biomass and yield of indolic compounds. The major components of DYGS medium were optimized in small-scale shaken cultivations, in two sets of CCRD. High performance liquid chromatography was used to determine nutrient consumption and to correlate it with cell biomass production, and the Salkowski method was used to quantify indoles. Hydrolytic activity in the formulations was quantified with the fluorescein diacetate assay.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Glycerol (5.5 g L〈sup〉−1〈/sup〉) and yeast extract (2.8 g L〈sup〉−1〈/sup〉), as the main carbon and nitrogen sources, respectively, increased biomass production by 87.5% when compared to original DYGS medium, reaching 3.0 g L〈sup〉−1〈/sup〉 of dry cell weight (DCW). In a 2.0 L bioreactor, the optimized medium was used to enhance process conditions for DCW and indole-3-acetic acid (IAA). Biomass production reached 3.4 g L〈sup〉−1〈/sup〉 and was restrained at highest air flow levels. The conditions of 34-36 °C, 150 rpm and 4.0 L min〈sup〉−1〈/sup〉 of air flow rate resulted in 11.97 mg L〈sup〉−1〈/sup〉 of IAA, an increase of 370% over original DYGS at 30 °C. Peat can still be regarded as a good cell carrier for solid state inoculants, whilst the additives tested for liquid formulations are individually more efficient than the mixture.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The production of inoculants containing 〈em〉H. seropedicae〈/em〉 strain BR11471 can be efficiently improved with the use of the RSM approach i.e. it maximizes the production of biomass and indolic compounds, and reduces culture media components, both key factors for large-scale industrial production.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉We examined how mechanical management of invasive macrophyte, 〈em〉Typha × glauca〈/em〉 alters plant-soil interactions underlying carbon processes and nutrient cycling, which are important to wetland function but under-represented in restoration research.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉In the northern Great Lakes, we compared plant biomass, light transmittance, soil nutrient availability and carbon mineralization rates of 〈em〉Typha〈/em〉-dominated controls with 〈em〉Typha〈/em〉 stands harvested above the waterline (harvest) and at the soil surface (submerged harvest).〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Relative to controls, harvested stands had 50% less litter and twice as much light transmittance to the water surface after one year. However, 〈em〉Typha〈/em〉 stems re-grew, and soil nutrient availability rates were similar to controls. Submerged harvest eliminated 〈em〉Typha〈/em〉 litter and stems, and increased light transmittance through the water column. P and K soil availability rates were 70% greater with submerged harvest than in controls. Soil C mineralization rates were not affected by treatment (mean ± 1 SE; 40.11 ± 2.48 μg C-CO〈sub〉2〈/sub〉 and 2.44 ± 0.85 μg C-CH〈sub〉4〈/sub〉 g〈sup〉−1〈/sup〉 soil C hr.〈sup〉−1〈/sup〉), but were positively correlated with soil Fe availability.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉While submerged harvest effectively decreased invasive 〈em〉Typha〈/em〉 biomass after one year, it increased soil nutrient availability, warranting further examination of macronutrient cycling and export during invasive plant management.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉〈em〉Malus prunifolia〈/em〉 (Chinese name: Fu Ping Qiu Zi), a wild relative of cultivated apple (〈em〉Malus〈/em〉 x 〈em〉domestica〈/em〉 Borkh), is extremely resistant to drought compared with domesticated cultivars, such as ‘Golden Delicious’. However, the molecular mechanisms underlying drought resistance of 〈em〉M. prunifolia〈/em〉 have not been characterized. This study investigates a new regulatory mechanism to improve apple drought resistance.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉〈em〉M. prunifolia〈/em〉 and ‘Golden Delicious’ were each grafted on 〈em〉M. hupehensis〈/em〉 for gene expression analysis. The methylation level of the 〈em〉DREB2A〈/em〉 promoter was determined by bisulfite sequencing and ChIP-qPCR. Chromatin immunoprecipitation sequencing (ChIP-seq) was used to identify target genes of MpDREB2A in apple.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The exposure to drought stress stimulated the expression level of 〈em〉DREB2A〈/em〉 gene more than 100-fold in 〈em〉M. prunifolia,〈/em〉 but only 16-fold in ‘Golden Delicious’. This difference in gene expression could not be explained in terms of difference in leaf relative water content. Correspondingly, the methylation level of 〈em〉M. prunifolia DREB2A〈/em〉 (〈em〉MpDREB2A〈/em〉) promoter region was significantly reduced. Additionally, 〈em〉MpDREB2A〈/em〉 conferred enhanced drought resistance when ectopically expressed in 〈em〉Arabidopsis〈/em〉. Over 2800 potential downstream target genes of MpDREB2A were identified by ChIP-seq and these downstream genes have diverse potential functions related to stress resistance.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Methylation regulation in promoter of 〈em〉MpDREB2A〈/em〉 may contribute to the drought resistance of 〈em〉M. prunifolia〈/em〉.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Characterization of barley-tissue–colonization efficiency (〈em〉Hordeum vulgare〈/em〉 L.) by 〈em〉Paraburkholderia tropica〈/em〉 MTo-293 after seed inoculation was studied in two plant-growth systems: (1) in flasks with semisolid agar-containing sterile medium, as a suitable environment to study plant-bacteria interaction and also optimize molecular-biology techniques, and (2) in a pot-substrate system as an approach to understand their potential behavior as bioinput.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Culture-dependent techniques were implemented to quantify surface and endophytic bacterial populations in plant tissues. Culture-independent techniques were employed to detect and localize the inoculated bacteria in tissue samples along with evaluating the biofilm-forming capability by epifluorescent, confocal-laser-scanning, and scanning-electron microscopy. Plant-growth parameters were measured to evaluate the effects of the inoculated bacteria on the development of the barley plants.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉〈em〉Paraburkholderia tropica〈/em〉 grew as a biofilm on both abiotic and biotic surfaces and efficiently colonized barley roots and stems in plants grown in flasks in presence of other microorganisms. The bacteria was localized on root surfaces, hairs, and central-cylinder areas. 〈em〉Paraburkholderia tropica〈/em〉 also colonized the roots and stems in plants grown in the pot-substrate system. Although no endophytic root colonization occurred, the presence of the inoculated bacteria improved the aerial weight. A nested PCR detected 〈em〉P. tropica〈/em〉 in the tissue samples.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉〈em〉Paraburkholderia tropica〈/em〉 MTo-293 was characterized as an efficient biofilm-forming and barley-tissue–colonizing bacterium despite the presence of other microorganisms, but root endophytic colonization resulted dependent on the plant-growth system. Molecular-biology techniques were optimized, and also, its presence was correlated with plant-growth–promoting activity.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉In the face of problems caused by ‘intensive agriculture’ dominated by large areas of monocultures, mixed intercropping mimicking natural ecosystems has been reported to constitute a viable solution to increase and stabilize productivity. When designing such systems, root niche separation was thought to be a prerequisite to optimize production.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉This paper reviews the beneficial and adverse effects of trees and crops on water acquisition and redistribution in agroforestry ecosystems using the concepts of competition and facilitation between plants in link with root functional traits.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The results of the review showed that the reality was more complex leading agroforestry practitioners to adopt management practices to induce a separation in root activities thus avoid competition, particularly for water. Water uptake by plant roots is triggered by the water potential difference between the soil and the atmosphere when leaf stomata are open and depends largely on the root exploration capacity of the plant. Thus, root water uptake dynamics are strongly related to root-length densities and root surface areas. In addition, plants with deep roots are able to lift up or redistribute water to the upper layers through a process known as hydraulic lift, potentially acting as “bioirrigators” to adjacent plants. The redistributed water could be of importance not only in regulating plant water status, e.g. by enhancing transpiration, but also in increasing the survival and growth of associated crops in mixed systems.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Even though some more work is still needed to assess the volume of water transferred to neighbors, hydraulic lift could constitute an ecological viable mechanism to buffer against droughts and ensure productivity in regions with erratic rainfall. Giving the difficulty in measuring the above-mentioned aspects in the field, modeling of some of the most relevant parameters to quantify them might inform the design of future empirical studies.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Alpine ecosystems are important terrestrial carbon (C) pools, and microbial decomposers play a key role in cycling soil C. Microbial metabolic limitations in these ecosystems, however, have rarely been studied. The objectives of this study are to reveal the characteristics of microbial nutrient limitation, and decipher the drivers in the alpine ecosystems.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Models of extracellular enzymatic stoichiometry were applied to examine and compare the metabolic limitations of the microbial communities in bulk and rhizosphere soils along an altitudinal gradient (2800–3500 m a.s.l.) under the same type of vegetation (〈em〉Abies fabri〈/em〉) on Gongga Mountain, eastern Tibetan Plateau.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The soil microbial communities suffered from relative C and phosphorus (P) limitations in the alpine ecosystem despite of high soil nutrient contents here. Partial least squares path modelling (PLS-PM) revealed that the limitations were directly regulated by soil nutrient stoichiometry, followed by nutrient availability. The C and P limitations were higher at the high altitudes (3000–3500 m) than that at the low altitude (2800 m), which mainly attribute to changes of soil temperature and moisture along the altitudinal gradient. This suggested that global warming may relieve microbial metabolic limitation in the alpine ecosystems, and then is conducive to the retention of organic C in soil. Furthermore, the C and P limitations varied significantly between the bulk and rhizosphere soils at the high altitudes (3200–3500 m), but not at the low altitudes. This indicated the influences of vegetation on the microbial metabolisms, while the influences could decrease under the scenario of global warming.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our study suggests that the alpine ecosystems with high organic C storage harbour abundant microbial populations limited by relative C and P, which have sensitive metabolic characteristics. This could thus potentially lead to large fluctuations in the soil C turnover under climate change. The study provides important insights linking microbial metabolisms to the environmental gradients, and improves our understanding of C cycling in alpine ecosystems.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Nitrogen (N) deposition affects litter decomposition. However, how nutrients, especially deposited N are immobilized and released in decomposing litters with different qualities (C/N and C/P) remains unclear.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We conducted a laboratory microcosm experiment with four litter types and a combination of a coniferous and deciduous litter treated with N addition (6 mg 99.99% 〈sup〉15〈/sup〉N g〈sup〉−1〈/sup〉 litter) and control by measuring N-deposition effect on mass (NDEM), N (NDEN), and P remaining percentages (NDEP), deposited 〈sup〉15〈/sup〉N immobilized abundance, and microbial composition and enzyme activities in decomposing litters during two years of incubation.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The values of NDEM, NDEN, and NDEP were generally greater for the litters with intermediate C/N and C/P than those with the highest and lowest ratios after 360 days, although these parameters varied among different quality litters before 180 days. Immobilized exogenous 〈sup〉15〈/sup〉N abundance by microbes showed an increasing trend with increasing litter C/N and C/P across the whole 720-day period. Both C/N and C/P were generally correlated with decomposition rate, 〈sup〉15〈/sup〉N immobilization abundance, the microbial richness, and main enzyme activities in decomposing litters.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉N-deposition effects on N and P dynamics in decomposing litters varied with their C/N and C/P, generally exerting an unimodal curve at later decomposition stages. Lower quality litter with higher C/N and C/P favoured N immobilization in response to N addition.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉The information of nitrogen uptake by subtropical, ever-green broad-leaf plants at cold temperatures of winter is very limited. The present field experiment was conducted to investigate whether 〈sup〉15〈/sup〉N is taken up by tea (〈em〉Camellia sinensis〈/em〉 L.) plants in winter dormancy in the absence of active shoot growth and utilization in young spring shoots.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We applied 〈sup〉15〈/sup〉N-labeled urea to soil at five different times i.e. mid-January, early February, mid-February, and early and mid-March. 〈sup〉15〈/sup〉N abundance was determined in fibrous roots, twigs and mature leaves after 3, 7 and 15 days after application and in young shoots the following spring.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉〈sup〉15〈/sup〉N was taken up by fibrous roots and transported to above-ground tissues within 3 days after application under low winter temperatures. Earlier application significantly increased nitrogen derived from 〈sup〉15〈/sup〉N-urea (N〈sub〉dff〈/sub〉) and 〈sup〉15〈/sup〉N amount in young spring shoots. N〈sub〉dff〈/sub〉 values and 〈sup〉15〈/sup〉N amount in young spring shoots were described well by quadratic or linear regressions against soil growing degree days (GDD, T ≥ 8 °C, depth 20 cm) between 〈sup〉15〈/sup〉N application and harvesting dates (R〈sup〉2〈/sup〉 = 0.58–0.90, 〈em〉p〈/em〉 〈 0.001).〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Nitrogen was absorbed and translocated in dormant tea plants in the absence of active root and shoot growth throughout the late winter until early spring. Absorbed N was stored and remobilized to support shoot growth the following spring. Soil GDD between N application and harvesting could predict N〈sub〉dff〈/sub〉 and 〈sup〉15〈/sup〉N amount in young spring shoots.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉To identify the rhizobia nodulating 〈em〉Vicia sativa〈/em〉 in Northwestern China and to estimate their geographic distribution.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Rhizobia trapped with 〈em〉V. sativa〈/em〉 plants from soils at six sites in the northwest of China were classified into genotypes by PCR-based restriction fragment length polymorphism (RFLP) of 16S–23S rRNA intergenic spacer (IGS) and 16S rRNA genes, and phylogenetic analyses of housekeeping (16S rRNA, 〈em〉recA〈/em〉, 〈em〉atpD〈/em〉) and symbiotic genes were performed for the representative strains. Soil physicochemical characteristics were recorded and canonical correlation analysis was performed to examine the correlations between soil features and distribution of rhizobial genotypes.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉A total of 202 rhizobial isolates were discriminated by RFLP analyses into 15 IGS types and a single 16S rRNA type, which were identified as 〈em〉Rhizobium〈/em〉 by 16S rRNA gene phylogeny and as four clusters by multilocus sequence analysis (MLSA). Cluster 1 covering 86 strains and 7 IGS types prevalent in all sites was identified as 〈em〉Rhizobium laguerreae〈/em〉; cluster 2 was 〈em〉R. sophorae〈/em〉 with 18 strains in 2 IGS types found in the site Q-GD. Each of cluster 3 and cluster 4 contained three IGS types representing two novel 〈em〉Rhizobium〈/em〉 genospecies specific to Gansu Province and Shanxi Province, respectively. Four 〈em〉nodC〈/em〉 phylogenetic clades were defined among the isolates.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉〈em〉R. sophorae〈/em〉, 〈em〉R. laguerreae〈/em〉, and two novel 〈em〉Rhizobium〈/em〉 genospecies with diverse symbiotic genotypes are associated with 〈em〉Vicia sativa〈/em〉 L. in Northwest China. Their biogeographic patterns are mainly directed by soil pH and salinity. This is the first study on the diversity of rhizobia nodulating 〈em〉Vicia sativa〈/em〉 in China.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aim〈/h3〉 〈p〉Root-associated microbial communities influence plant phenotype, growth and local abundance, yet the factors that structure these microbial communities are still poorly understood. California landscapes contain serpentine soils, which are nutrient-poor and high in heavy metals, and distinct from neighboring soils making them ideal for studying the factors that structure root microbiomes and their functions.〈/p〉 〈/span〉 〈span〉 〈h3〉Method〈/h3〉 〈p〉Here, we surveyed the rhizoplane of serpentine-indifferent plants, which grow on and off serpentine soil, to determine the relative influence of plant identity and soil chemistry on rhizoplane microbial community structure using 16S rRNA metabarcoding. Additionally, we experimentally examined if serpentine vs. non-serpentine microorganisms differentially affected plant growth in serpentine soil.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Rhizoplane bacterial communities differed among plant species, soil types, and the interaction between them in both the field and experimental soils. In the experiment, soil microbial community source influenced seedling survival, but plant growth phenotypes were largely invariant to microbial community with a few exceptions.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Rhizosplane bacterial species composition differed between plant species and soil types, and Amplicon Sequence Variants (ASVs) from the phyla Acidobacteria and Proteobacteria (Genus: 〈em〉Microvirga〈/em〉) were characteristic of serpentine soils. While soil microbial community composition influenced seedling survival in the current study, further study is required to disentangle the role of microbial associations and plant tolerance to serpentine.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Plants can optimize the allocation of phosphorus (P) among their foliar P fractions to increase the P utilization efficiency (PUE). Identifying the genetic relationships between foliar P fractionation and PUE could provide opportunities to improve the P efficiency of barley (〈em〉Hordeum vulgare〈/em〉 L.).〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉The differences in the concentrations and proportions of inorganic P, ester P, nucleic acid P and insoluble P between a wild barley cultivar CN4027 and a commercial cultivar Baudin were studied, and their quantitative trait loci (QTLs) at normal P (NP) and low P (LP) fertilisations were mapped. The PUE that was determined in the previous study was used to analyze the relationship between PUE and foliar P fractionation in this research.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Both cultivars of barley could increase their metabolic P fractions as an LP stress tolerance strategy to ensure their continued metabolic activities in response to LP stress. Cultivar CN4027 showed higher nucleic acid P concentration (NPC), nucleic acid P proportion (NPP) and insoluble P proportion (IPP) than cultivar Baudin under LP stress. This abundant organic P (Po) pool of CN4027 ensured the normal functioning of its metabolic pathways under LP stress. The close relationships between the foliar P fractionation and PUE could be explained by two QTL clusters, 〈em〉Cl-3H.02〈/em〉 and 〈em〉Cl-5H.01〈/em〉. The QTL cluster 〈em〉Cl-3H.02〈/em〉 is flanked by the markers 〈em〉bPb3256099-bPb3255630〈/em〉 on chromosome 3H and controls the ester P concentration (EPC), ester P proportion (EPP), insoluble P concentration (IPC) and IPP.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The QTL cluster 〈em〉Cl-3H.02〈/em〉 might have great potential for the future genetic improvement of barley PUE and may offer clues for the genetic relationships between the foliar P fractionation and PUE.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Roots are vital organs for plants, but the assessment of root traits is difficult, particularly in deep soil layers under natural field conditions. A popular technique to investigate root growth under field or semi-field conditions is the use of minirhizotrons. However, the subsequent manual quantification process is time-consuming and prone to error.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We developed a multispectral minirhizotron imaging system and a subsequent image analysis strategy for automated root detection. Five wavelengths in the visible (VIS) and near-infrared (NIR) spectrum are used to enhance living roots by a multivariate grouping of pixels based on differences in reflectance; background noise is suppressed by a vesselness enhancement filter. The system was tested against manual analysis of grid intersections for both spring barley (〈em〉Hordeum vulgare L.〈/em〉) and perennial ryegrass (〈em〉Lolium perenne L.)〈/em〉 cultivars at two time-points. The images of living roots were captured in wet subsoil conditions with dead roots present from a previous crop.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Under the soil conditions used in the study, NIR reflectance (940 nm), provided limited ability to separate between rhizosphere components, compared to reflectance in the violet and blue light spectrum (405 nm and 450 nm). Multivariate image analysis of the spectral data, combined with vesselness enhancement and thresholding allowed for automated detection of living roots. Automated image analysis largely replicated the root intensity found during manual grid intersect analysis of the same images. Although some misclassification occurred, caused by elongated structures of dew and chalkstone with similar reflectance pattern as living root, the system provided similar or in some cases improved detection of genotypic differences in the total root length within each tube.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉The multispectral imaging system allows for automated detection of living roots in minirhizotron studies. The system requires considerably less time than traditional manual recording using grid intersections. The flexible training strategy used for root segmentation offers hope for the transfer to other rhizosphere components and other soil types of interest.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉The objective of this research was to develop a three-dimensional (3D) rhizosphere modeling capability for plant-soil interactions by integrating plant biophysics, water and ion uptake and release from individual roots, variably saturated flow, and multicomponent reactive transport in soil.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We combined open source software for simulating plant and soil interactions with parallel computing technology to address highly-resolved root system architecture (RSA) and coupled hydrobiogeochemical processes in soil. The new simulation capability was demonstrated on a model grass, 〈em〉Brachypodium distachyon〈/em〉.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉In our simulation, the availability of water and nutrients for root uptake is controlled by the interplay between 1) transpiration-driven cycles of water uptake, root zone saturation and desaturation; 2) hydraulic redistribution; 3) multicomponent competitive ion exchange; 4) buildup of ions not taken up during kinetic nutrient uptake; and 5) advection, dispersion, and diffusion of ions in the soil. The uptake of water and ions by individual roots leads to dynamic, local gradients in ion concentrations.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉By integrating the processes that control the fluxes of water and nutrients in the rhizosphere, the modeling capability we developed will enable exploration of alternative RSAs and function to advance the understanding of the coupled hydro-biogeochemical processes within the rhizosphere.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉As a major plant-derived soil organic carbon (SOC) component, lignin-derived phenolic compounds show varying biogeochemical characteristics compared to plant-derived lipid moieties. Comparing their distribution patterns can provide information on mechanisms governing SOC preservation and dynamics. However, the large-scale distribution pattern and stability of lignin versus plant-derived lipids are still poorly constrained. Here we investigated the distribution of lignin phenols versus plant-derived lipids in the surface soils across the alpine versus temperate grasslands of China and Mongolia.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Lignin phenols were isolated by cupric oxide oxidation method and compared with the previously analyzed plant-derived lipids (cutin and suberin). A comprehensive list of environmental variables was compiled to disentangle the climatic, edaphic and vegetation influences on lignin phenols’ distribution in the soil.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Lignin phenols showed similar SOC-normalized concentrations in the alpine and temperate grassland soils despite a higher plant input to the latter, suggesting better lignin preservation in the cold region. However, compared with plant-derived lipids (cutin and suberin), lignin seems to be less stabilized. The variation of lipid versus lignin components is mainly related to climate (particularly aridity) in the alpine grassland soils, while the relative abundance of plant lipids and lignin phenols is more related to reactive mineral contents in the temperate grassland soils.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Lignin contributes differentially to SOC accumulation in the alpine and temperate soils: while lignin seems to be better preserved in the cold region, lignin phenols decrease relative to other carbon components with SOC accrual in the temperate region. Overall, lignin distribution and fate may be more sensitive to carbon source variations than temperature shifts in the grasslands.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉A century of atmospheric deposition of sulfur and nitrogen has acidified soils and undermined the health and recruitment of foundational tree species in the northeastern US. However, effects of acidic deposition on the forest understory plant communities of this region are poorly documented. We investigated how forest understory plant species composition and richness varied across gradients of acidic deposition and soil acidity in the Adirondack Mountains of New York State.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We surveyed understory vegetation and soils in hardwood forests on 20 small watersheds and built models of community composition and richness as functions of soil chemistry, nitrogen and sulfur deposition, and other environmental variables.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Community composition varied significantly with gradients of acidic deposition, soil acidity, and base cation availability (63% variance explained). Several species increased with soil acidity while others decreased. Understory plant richness decreased significantly with increasing soil acidity (〈em〉r〈/em〉 = 0.60). The best multivariate regression model to predict richness (〈em〉p〈/em〉 〈 0.001, adjusted〈em〉-R〈/em〉〈sup〉〈em〉2〈/em〉〈/sup〉 = 0.60) reflected positive effects of pH and carbon-to-nitrogen ratio (C:N).〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The relationship we found between understory plant communities and a soil-chemical gradient, suggests that soil acidification can reduce diversity and alter the composition of these communities in northern hardwood forests exposed to acidic deposition.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Endophytic fungi colonization is an eco-friendly strategy to respond to environmental stresses and confer tolerance to the host plant. Here, the responses of wheat plant inoculated with an indole acetic acid (IAA) -producing endophytic fungus to drought stress and water recovery were evaluated.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉The inoculation of wheat plants with 〈em〉Alternaria alternata〈/em〉 (LQ1230) was conducted to evaluate drought resistance under adequate water, water deficit and water recovery conditions by examining the growth parameters and various physiological indicators of wheat seedlings.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The LQ1230 isolated from 〈em〉Elymus dahuricus〈/em〉 Turcz could secrete indole acetic acid (IAA) by both the tryptophan-dependent (319.24 ± 14.88 μg/mL) and independent (40.12 ± 8.59 μg/mL) pathways. LQ1230 inoculation enhanced wheat growth and drought tolerance through regulation of antioxidant enzyme activities and the content of compatible solutes such as soluble sugars and proline. Additionally, LQ1230 inoculated plants demonstrated significantly improved photosynthesis, C and N accumulation of wheat plants, leading to a positive relationship with plant dry biomass under water deficit and re-watering conditions.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉We found that the improved wheat plant growth, photosynthesis and nutrient accumulations by the inoculation of 〈em〉Alternaria alternata〈/em〉 LQ1230 might be attributed to the reprogramming of wheat plant metabolism, thus enhancing wheat drought tolerance. Inoculation with fungal endophytes such as LQ1230 has the potential to increase crop drought resistance.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Subtropical ecosystems are generally characterized by phosphorus (P)-deficient soils; however, extreme P-rich soils develop on phosphate rocks. We aimed to integrate metabolomic and ionomic analyses to survey how in situ trees adaptively respond to such contrasting P soils.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Gas (GC-MS) or liquid (LC-MS) chromatography-mass spectrometry and inductively coupled plasma-optical emission spectrometer (ICP-OES) were used to analyze leaf metabolome and ionome of 〈em〉Quercus variabilis〈/em〉, which grew at two geologic P-rich and P-deficient sites in subtropical China.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Two 〈em〉Q. variabilis〈/em〉 populations were significantly discriminated in terms of metabolome and ionome, with major contributions from 25 identified metabolites (e.g. sugars and P-containing compounds) and P and four other chemical elements. And of these 25 metabolites, orthophosphate was predominant in influencing the variation in the metabolomes of 〈em〉Q. variabilis〈/em〉 between the two P-type sites. Moreover, orthophosphate was correlated with leaf P (〈em〉r〈/em〉 = 0.85, 〈em〉p〈/em〉 〈 0.001), while leaf P was significantly influenced only by soil resident P at the P-rich site. Furthermore, the metabolic pathway analysis indicated four critical metabolic pathways: galactose metabolism, amino sugar and nucleotide sugar metabolism, glyoxylate and dicarboxylate metabolism, fructose and mannose metabolism.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉These findings suggested that there were distinct ionome-metabolome interactions in 〈em〉Q. variabilis〈/em〉 populations, between P-rich and P-deficient sites, which contributed to novel insights into how plants interactively adapt to P-limiting soils.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Although nitrogen (N) fertilization is widely used to increase rice yield, its impact on the distribution, transformation, and fates of photosynthetic carbon (C) in rice–soil systems is poorly understood. To address this, we quantified the C flows into various pools in a rice–soil system.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Rice (〈em〉Oryza sativa〈/em〉 L.) was pulse-labeled with 〈sup〉13〈/sup〉CO〈sub〉2〈/sub〉 at the tillering stage. Samples were collected six times during the 26 days following labeling. We quantified the partitioned photosynthesized C into various pools using stable isotopic techniques and estimated C flows.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Although the net distribution of assimilated C to belowground pools did not change, N fertilization promoted C assimilation in aboveground biomass. C allocation into soil was enhanced by N fertilization during early growth, but decreased during late growth. N fertilization induced higher mass-specific rhizodeposition (per unit root dry weight) and its turnover rate compared with the unfertilized system. However, with higher microbial turnover, the daily C allocation from roots to soil was similar at both fertilization levels.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Although total C input into soil is enhanced by N fertilization, its further fate is N fertilization independent, thus leading to a net accumulation of C input in rice paddy soil similar to that observed unfertilized soil.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Long-duration drought can alter ecosystem plant species composition with subsequent effects on carbon cycling. We conducted a rainfall manipulation field experiment to address the question: how does drought-induced vegetation change, specifically shrub encroachment into grasslands, regulate impacts of subsequent drought on soil CO〈sub〉2〈/sub〉 efflux (R〈sub〉s〈/sub〉) and its components (autotrophic and heterotrophic, R〈sub〉a〈/sub〉 and R〈sub〉h〈/sub〉)?〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We conducted a two-year experiment in Inner Mongolia plateau, China, using constructed steppe communities including graminoids, shrubs and their mixture (graminoid + shrub) to test the effects of extreme-duration drought (60-yr return time) on R〈sub〉s〈/sub〉, R〈sub〉h〈/sub〉 and R〈sub〉a.〈/sub〉〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Our results indicated that extreme-duration drought reduced net primary production, with subsequent effects on R〈sub〉s〈/sub〉, R〈sub〉h〈/sub〉 and R〈sub〉a〈/sub〉 in all three vegetation communities. There was a larger relative decline in R〈sub〉a〈/sub〉 (35–54%) than R〈sub〉s〈/sub〉 (30–37%) and R〈sub〉h〈/sub〉 (28–35%). Interestingly, we found R〈sub〉s〈/sub〉 in graminoids is higher than in shrubs under extreme drought. Meanwhile, R〈sub〉h〈/sub〉 declines were largest in the shrub community. Although R〈sub〉a〈/sub〉 and R〈sub〉h〈/sub〉 both decreased rapidly during drought treatment, R〈sub〉h〈/sub〉 recovered quickly after the drought, while R〈sub〉a〈/sub〉 did not, limiting the 〈em〉R〈/em〉〈sub〉〈em〉s〈/em〉〈/sub〉 recovery.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉This study suggests that plant species composition regulates several aspects of soil CO〈sub〉2〈/sub〉 efflux response to climate extremes. This regulation may be limited by above- and below-ground net primary production depending on soil water availability〈em〉.〈/em〉 The results of this experiment address a critical knowledge gap in the relationship between soil respiration and plant species composition. With shrub encroachment into grasslands, total soil respiration is reduced and can partly offset the effect of reduction in productivity under drought stress.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉The effects of root glutathione (GSH) supplementation on leaf chlorophyll, Fe concentrations and contents in leaves, stems and roots, and traits associated to Fe deficiency were studied in 〈em〉Medicago scutellata〈/em〉 plants grown in rock sand under conditions of Fe deficiency, in the presence of different concentrations of bicarbonate.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Plants were grown in acid-washed rock sand irrigated with a zero Fe solution (pH 7.8 with 0.5 g L〈sup〉−1〈/sup〉 CaCO〈sub〉3〈/sub〉) or a 45 μM Fe(III)-EDDHA solution (5 mM MES, pH 5.5), with 0, 5 or 15 mM NaHCO〈sub〉3〈/sub〉, and 250 mL of 1 mM GSH was added daily to half of the pots.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Iron deficiency caused characteristic symptoms in plants, with GSH supplementation relieving them. Glutathione supplementation led to increases in total Fe, chlorophyll and leaf total and extractable Fe, whereas root Fe concentrations decreased. Traits associated to Fe deficiency, including changes in biomass, root morphology, carboxylate contents and antioxidant parameters became less intense with GSH supplementation.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Glutathione supplementation allowed plants to take up Fe from the rock sand via a reductive solubilization mechanism. Also, the distribution of Fe within the plant changed, with more Fe being allocated to the shoot tissues and less to the roots.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Mycorrhizae and root exudates have been considered the two important pathways for nitrogen (N) transfer from legume to non-legume plants. The present study aimed to investigate contribution of the relative importance of arbuscular mycorrhizal fungi and root exudates in short-term N transfer.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉A field experiment was conducted to explore N transfer from alfalfa to maize under two different N application levels using 〈sup〉15〈/sup〉N leaf labeling.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉N transfer amount ranged from 7 to 10 mg N plant〈sup〉−1〈/sup〉 from alfalfa to maize and significantly decreased (by 11%–22%) with N fertilizer application. Intercropping of 4 rows of maize and 6 rows of alfalfa with 30 cm intra-row spacing (IMA43) was the optimal intercropping mode, which increased N transfer, total N uptake and yield by 18%, 15% and 11%, respectively. The relative importance of arbuscular mycorrhizal fungi and root exudates on N transfer was dependent on soil N availability. Under no N addition, hyphal length density (HLD) of rhizosphere soil explained the largest significant amount (50%) of the variability in N transfer and crop yield. However, root exudates explained 77% of the variability in N transfer and crop yields with N fertilizer application.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our findings highlighted that N transfer is reliant more on arbuscular mycorrhizal fungi than root exudates in N-deficient soil, whereas root exudates play a more important role in N-fertilized soil.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Magnesium (Mg) deficiency impacts many metabolic processes in 〈em〉Brassica napus〈/em〉 (〈em〉B. napus〈/em〉), leading to yield loss. However, the mechanism of Mg〈sup〉2+〈/sup〉 uptake and translocation in 〈em〉B. napus〈/em〉 remains unknown.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉After screening 39 genotypes of 〈em〉B. napus〈/em〉 under Mg-deficient conditions, the cultivars P160 and P153 were selected according to their Mg transfer factor (TF) from root to shoot. We further characterized these two genotypes under Mg-deficiency by analyzing chlorophyll concentration, malondialdehyde and peroxidase activity, and reducing sugar concentration in leaves. Additionally, we performed transcriptomics and qRT-PCR assays on P153 and P160 shoots and roots. The identified functional genes involved in Mg transport were characterized by functional assays in yeast and Arabidopsis mutants.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The physiological analysis revealed that P160 (Mg tolerance cultivar; Mg-T) is more tolerant than P153 (Mg sensitive cultivar; Mg-S) under magnesium-deficient environments. Transcriptomics and qRT-PCR assays revealed that transcript levels of 〈em〉BnMGT1–2〈/em〉 and 〈em〉BnMGT6–1〈/em〉 were more significantly up-regulated in the shoot of Mg-T cultivar than that of the Mg-S cultivar under Mg limitation. Functional assays of BnMGT1–2 and BnMGT6–1 reveals that BnMGT1–2 and BnMGT6–1 are the two main functional Mg transporters mediating Mg translocation from root to shoot under low Mg conditions.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉Mg-T is more efficient in the translocation of Mg from root to shoot than Mg-S. BnMGT1–2 and BnMGT6–1 should be the two main Mg transporters associated with Mg translocation under Mg deficiency condition, which caused the different Mg efficiency between the Mg-T and Mg-S.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Global climate change is characterized by enhanced atmospheric carbon dioxide concentration ([CO〈sub〉2〈/sub〉]) and temperature, with unknown consequences for soil nematode communities. Soil nematode in response to elevated [CO〈sub〉2〈/sub〉], warming and their interaction in paddy field remain largely unknown. Here we aimed to understand how factorial combinations of elevated [CO〈sub〉2〈/sub〉] and canopy warming affect soil nematode in a rice paddy field.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉A rice paddy field was consistently treated with elevated [CO〈sub〉2〈/sub〉] (500 ppm), canopy warming (+2 °C) or their combinations. Soil samples after a two-year treatment were collected during the rice growing season and nematode communities were extracted with a modified Baermann funnel extraction to examine the changes in nematode abundance and composition under climate change.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Soil nematode communities were altered by elevated [CO〈sub〉2〈/sub〉] and warming, but these responses were dependent on rice growing stages. When averaged over the four stages, total nematode abundances were increased by 31.5% under elevated [CO〈sub〉2〈/sub〉], and by 25.7% under warming. Elevated [CO〈sub〉2〈/sub〉] had no effect on nematode diversity, but slightly altered the composition of different trophic groups. In contrast, warming decreased nematode diversity, but increased plant parasite index, which was negative correlated with crop production. This was attributed to increases in the relative abundance of herbivores under simulated climate change conditions.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Elevated [CO〈sub〉2〈/sub〉] and warming had a positive effect on nematode abundance, but potentially reduced nematode diversity and soil health. These results suggest that multi-factors interactively affect the responses of soil nematode communities, which is important for food productivity under climate change.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Atmospheric nitrogen (N) deposition alters the priming effect (PE), which is defined as the change in native soil organic carbon (SOC) decomposition by exogenous C inputs. However, how the priming intensity varies under chemically heterogeneous N deposition, particularly with increasing labile C input, remains unclear.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We collected soils from a temperate forest in northeastern China that had received simulated organic and/or inorganic N deposition for 6 years. The soils were incubated with or without three levels of 〈sup〉13〈/sup〉C-labelled glucose solution for 152 days. CO〈sub〉2〈/sub〉 emission and its 〈sup〉13〈/sup〉C value were continuously measured to calculate the PE.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Enhanced SOC decomposition (i.e., a positive PE) was observed after glucose addition, regardless of the N deposition form. The PE intensity increased with the increase in the glucose addition level. However, organic N decreased the PE by 12.3-23.2%. The SOC-derived microbial biomass was 16.2-34.3% lower in organic N-treated soil, indicating that preferential utilization of exogenous labile C by microorganisms was responsible for the decrease in PE. The PE inhibition by organic N increased nonlinearly as a function of glucose level. Furthermore, the net annual change in SOC as a balance between the replenishment of added glucose-C and primed C was larger in organic N-treated soil due to a decrease in soil microbial metabolic quotient.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉In this study, we found that organic N deposition inhibited the PE, and the inhibition effect was intensified with increasing C inputs, favouring SOC sequestration.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Despite the high economic benefits of using an intensive agriculture system, the sustainable development of 〈em〉Lycium barbarum〈/em〉 L〈em〉.〈/em〉 cultivation in Northwest China is hindered by serious negative plant–soil feedback, which may be paralleled by the variation in the microbial rhizosphere community.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Here, we assessed the shift in the bacterial and fungal rhizosphere communities of 〈em〉L. barbarum〈/em〉 across a 20-year-old chronosequence of stands at two independent experimental sites in Ningxia, China via real-time PCR and high-throughput sequencing.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Stand age significantly influenced the α-diversity and abundance of the fungal rhizosphere community (〈em〉p〈/em〉 〈 0.05) but did not affect the bacterial community. Phytopathogenic fungi, including 〈em〉Alternaria〈/em〉, 〈em〉Fusarium〈/em〉, 〈em〉Gibberella〈/em〉, and 〈em〉Stemphylium〈/em〉, were progressively enriched in the rhizosphere as the plant aged. Structure equation model suggested that soil abiotic properties were the direct drivers for bacterial community, whereas stand age and edaphic factor coexplained the succession of the fungal rhizosphere community.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉Long-term monocropping decoupled plant–bacteria interaction and strengthened the colonization of fungal phytopathogens in 〈em〉L. barbarum〈/em〉 rhizosphere. This study presents novel assessments of the links between the shifts in microbial rhizosphere community and the negative plant–soil feedback of 〈em〉L. barbarum〈/em〉.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Twenty-four species of eucalypts were studied regarding their ability to grow under low P and their responsiveness to P inputs.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Growth and photosynthesis-related parameters were evaluated.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Growth of all species was influenced by low P availability. No significant correlation was found between leaf P concentration and biomass, indicating that P concentrations in leaves cannot be solely considered an indication of the responsiveness to P in eucalypts. Species responsive to P-input (high agronomic P efficiency values, APE) were those with low P use efficiency - PUE (here assessed as relative efficiency of P-use, REP) and low P uptake efficiency (PUpE). But, non-responsive species were related to higher P-efficiency under low soil P-availability. 〈em〉Eucalyptus tereticornis〈/em〉, 〈em〉E. cladocalyx〈/em〉, 〈em〉E. globulus〈/em〉 and 〈em〉E. camaldulensis〈/em〉 were efficient under low-P availability. Whereas, 〈em〉E. crebra〈/em〉 and 〈em〉E acmenoides〈/em〉 were the most responsive species, with high APE, suggesting that for these species P-inputs are needed to guarantee plant growth. The root:shoot ratio remained constant at different P availabilities, suggesting that biomass allocation towards the root in response to P and greater investment in roots were not correlated with greater PUE. Under limited P, 〈em〉E. robusta〈/em〉 and 〈em〉E. botryoides〈/em〉 exhibited low foliar P contents and higher root:shoot ratios than those of other species with higher P contents, indicating that greater root investment does not necessarily result in greater PUE.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉The results suggest that the divergence among species is probably related to different mechanisms, which may improve P-use efficiency.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Excessive boron (B) can pose toxicity to many plant species, and consequently restricts land utilization in B-laden regions. The purpose of this study was to identify “agretti” (〈em〉Salsola soda〈/em〉) as an alternative B-tolerant food crop.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Both pot and hydroponic experiments were conducted for measuring biomass, total phenolic content and B absorption of 〈em〉S. soda〈/em〉 exposed to varied B treatments. Mineral element accumulation in 〈em〉S. soda〈/em〉 growing in pots was also determined.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉No typical B toxicity symptoms were observed in pot experiment, and only slight B toxicity symptoms were observed in hydroponically-grown plants at 50, 100 and 200 mg B L〈sup〉−1〈/sup〉 treatments. Biomass production was not affected in either experiment. The response of total phenolic content to B exposure varied with growing medium, parts of tissues, B treatments, and exposure times. Boron predominantly accumulated in leaves and increased with increasing B treatments in both experiments. Increased exposure time increased the transport of B from root to shoot. Increasing B treatment generally reduced the accumulation of phosphorus, manganese, selenium and arsenic, but increased the accumulation of B, molybdenum and cadmium in 〈em〉S. soda〈/em〉 under specific B treatments, even the accumulation of such elements was still safe for human consumption.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉〈em〉S. soda〈/em〉 appears to be a promising alternative crop to grow in B-laden regions such as the western SJV of Central California.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Rhizosheath is known as a layer of adhering soil particle to the root surface. Despite several speculations, the positive function of rhizosheath in acquisition of water and nutrients from drying soil has not yet been experimentally proven. The objective of this study was to experimentally show whether an enhanced rhizosheath formation could help plants to better access water from drying soil.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Eight wheat cultivars were grown in a sandy-loam soil. When plants were 35 days old let dry soil to a water content at which evident wilting symptoms appeared on the plant leaves. During this drying cycle, soil water content and transpiration rate of plants were gravimetrically measured by weighing the plant pots. At the end of this drying cycle, the roots were excavated out of the soil and the rhizosheath formation was gravimetrically quantified by weighing the soil attached to the root system.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The results showed that plant cultivars with greater rhizosheath formation could sustain higher transpiration rates at dry condition (water content of 0.07 cm〈sup〉3〈/sup〉 cm〈sup〉−3〈/sup〉) while the plant cultivars with lower rhizosheath formation suffered from drought stress and reached their permanent wilting points at the same water content.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉The findings of this study gathered evidence that under severe drought condition plant cultivars with an enhanced rhizosheath formation could better survive by sustaining their transpirational and nutritional demands.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background〈/h3〉 〈p〉Agroforestry systems have enhanced diversity of cultivated plants compared to monocultures, and are expected to affect associated biodiversity. Despite a growing body of literature on the importance of soil fauna, the known effects of different agroforestry types on soil fauna communities and functions have not yet been synthesized.〈/p〉 〈/span〉 〈span〉 〈h3〉Scope〈/h3〉 〈p〉We scanned publications on soil fauna in agroforestry systems. Our aim was to give an overview of strengths and weaknesses of the existing data, in terms of spatial coverage and representation of diverse agroforestry types and soil fauna groups and functions.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our database includes sixty-seven articles, mostly focusing on tropical regions and perennial crop agroforestry systems. Soil macrofauna are the most studied fauna group. The most common question addressed is the comparison of the effect of land use types on communities. Effects on fauna abundance and diversity are mainly positive when agroforestry is compared to cropland, and neutral or negative when compared to forests. Few publications actually measure soil fauna functions, or characterize their interactions and evolution in time and space depending on system design and management. Further work on soil fauna in agroforestry should harness ecological theory and address questions of spatial structure and scale, temporal dynamics and ecological interaction networks and how they determine ecosystem functioning.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Rising atmospheric CO〈sub〉2〈/sub〉 causes an increase in dissolved inorganic carbon (DIC) availability in aquatic ecosystems, further affecting plant growth and aquatic ecosystem production. Belowground carbon input can strongly influence microbial processes (carbon or nitrogen cycling). However, changes in sediment microbial abundance and community structure have not been thoroughly assessed in freshwater ecosystems under rising atmospheric CO〈sub〉2〈/sub〉. A pot experiment was conducted using fragments of the submerged macrophyte 〈em〉Myriophyllum spicatum〈/em〉 L. to study plant and sediment microbial responses to increasing aquatic carbon availability under rising atmospheric CO〈sub〉2〈/sub〉. Three DIC levels of overlying water were set up by continuous bubbling with different concentrations of CO〈sub〉2〈/sub〉. Higher biomass accumulation, chlorophyll content, nitrate reductase activity, and leaf N content were observed in 〈em〉M. spicatum〈/em〉 under high DIC level in CO〈sub〉2〈/sub〉 treatment. The increased DIC level in CO〈sub〉2〈/sub〉 treatment reduced sediment ammonium nitrogen, dissolved organic nitrogen content, microbial biomass carbon content and phenol oxidase activity, but not microbial biomass nitrogen content, urease and N-acetyl-β-D-glucosaminidase activities. 〈em〉NifH〈/em〉 abundance significantly decreased with the increasing DIC levels in CO〈sub〉2〈/sub〉 treatment, while bacterial 16S rRNA abundance was not affected. Redundancy analysis results indicated a modest but obvious shift in sediment microbial community compositions among different levels of DIC. Variation partitioning revealed a strong interaction between plant traits and sediment properties and their regulation of sediment microbial compositions at different DIC levels. It seemed that an intensified competition for essential resources between 〈em〉M. spicatum〈/em〉 and sediment microbes occurred under increased aquatic DIC availability caused by rising atmospheric CO〈sub〉2〈/sub〉.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Aim to unveil the functions of VcLon1 in plant Fe use efficiency.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉RT-PCR was used to analyze the expression profile of 〈em〉VcLon1〈/em〉. 〈em〉VcLon1〈/em〉 was expressed in 〈em〉Nicotiana benthamiana〈/em〉, and its homologous tobacco gene was silenced using RNAi. The differences in biomass growth, oxidative stress and chloroplast ultrastructure between wild type and transgenic 〈em〉Nicotiana benthaminana〈/em〉 were analyzed after being subjected to Fe deficiency stress〈em〉.〈/em〉〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The RT-PCR showed that the expression of 〈em〉VcLon1〈/em〉 was significantly higher in young leaves than in old leaves or in leaves treated with Fe deficiency stress, indicating that VcLon1 is involved in reactive oxygen species (ROS) homeostasis induced by senescence or Fe deficiency. Compared with wild-type, overexpression of 〈em〉VcLon1〈/em〉 in 〈em〉Nicotiana benthamiana〈/em〉 reduced damage to chloroplast structure induced by Fe deficiency. Furthermore, the contents of H〈sub〉2〈/sub〉O〈sub〉2〈/sub〉, MDA and carbonylated protein in leaves were kept at a low level, and antioxidant enzyme activities in chloroplasts such as SOD and APX are also generally higher in chloroplasts with 〈em〉VcLon1〈/em〉 overexpression. In contrast, the oxidative stress levels in 〈em〉NbLon1〈/em〉 RNAi silenced 〈em〉Nicotiana benthamiana〈/em〉 leaves showed opposite trends.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Under Fe deficiency stress, VcLon1 reduces oxidative damage in plants by degrading carbonylated proteins in organelles such as chloroplasts and effectively maintains the structure and function of organelles and the activity of functional proteins, contributing to Fe use efficiency in plants.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aim〈/h3〉 〈p〉Plant-endophytic associations exist only when equilibrium is maintained between both partners. This study analyses the properties of endophytic fungi inhabiting a halophyte growing in high soil salinity and tests whether these fungi are beneficial or detrimental when non-host plants are inoculated.〈/p〉 〈/span〉 〈span〉 〈h3〉Method〈/h3〉 〈p〉Fungi were isolated from 〈em〉Salicornia europaea〈/em〉 collected from two sites differing in salinization history (anthropogenic and naturally saline) and analyzed for plant growth promoting abilities and non-host plant interactions.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Most isolated fungi belonged to Ascomycota (96%) including dematiaceous fungi and commonly known plant pathogens and saprobes. The strains were metabolically active for siderophores, polyamines and indole-3-acetic acid (mainly 〈em〉Aureobasidium〈/em〉 sp.) with very low activity for phosphatases. Many showed proteolytic, lipolytic, chitinolytic, cellulolytic and amylolytic activities but low pectolytic activity. Different activities between similar fungal species found in both sites were particularly seen for 〈em〉Epiccocum〈/em〉 sp., 〈em〉Arthrinium〈/em〉 sp. and 〈em〉Trichoderma〈/em〉 sp. Inoculating the non-host 〈em〉Lolium perenne〈/em〉 with selected fungi increased plant growth, mainly in the symbiont (〈em〉Epichloë〈/em〉)-free variety. 〈em〉Arthrinium gamsii〈/em〉 CR1-9 and 〈em〉Stereum gausapatum〈/em〉 ISK3-11 were most effective for plant growth promotion.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉This research suggests that host lifestyle and soil characteristics have a strong effect on endophytic fungi, and environmental stress could disturb the plant-fungi relations. In favourable conditions, these fungi may be effective in facilitating crop production in non-cultivable saline lands.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉To optimize assay conditions of two common methods for measuring potential free-living nitrogen-fixation (FLNF), acetylene reduction assay (ARA) and 〈sup〉15〈/sup〉N〈sub〉2〈/sub〉-incorporation (〈sup〉15〈/sup〉N〈sub〉2〈/sub〉), for use with soil/rhizosphere samples.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We tested the impact of different carbon (C) sources, oxygen concentrations (O〈sub〉2〈/sub〉), and incubation times on FLNF rates of two low-fertility Michigan soils via ARA and 〈sup〉15〈/sup〉N〈sub〉2〈/sub〉.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉FLNF rates were greatest with addition of a C cocktail, at low O〈sub〉2〈/sub〉, and with 7-day incubations for both methods. FLNF via ARA was 1700x greater with a C cocktail versus glucose only and via 〈sup〉15〈/sup〉N〈sub〉2〈/sub〉 was 17x greater with a C cocktail compared to other C sources and no-C controls. Specific O〈sub〉2〈/sub〉 optimum varied by method and site. A 7-day incubation was needed for the ARA, but a 3-day incubation was suitable for 〈sup〉15〈/sup〉N〈sub〉2〈/sub〉. Lastly, we confirm previously identified issues with the ARA of acetylene-independent ethylene production/consumption resulting in potential FLNF measurement error of 1.3–52.3 μg N g〈sup〉−1〈/sup〉 day〈sup〉−1〈/sup〉.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉We present an optimized method for measuring potential FLNF in soil/rhizosphere samples which will allow for consistent and comparable FLNF rate measurements. Researchers should account for C source, O〈sub〉2〈/sub〉, and incubation time when assessing FLNF and use the ARA method with caution.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Backgrounds〈/h3〉 〈p〉There are growing concerns regarding the restoration of karst rocky desertification (KRD) areas. However, the soil conditions and its residing microorganisms, which are essential for the plants, remain largely unclear.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We studied soil characteristics and microbial communities in natural forests (non-KRD) and shrubs with eroded soil and surface soil run-off, using Illumina Miseq sequencing.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Our results showed that despite KRD reduced soil fertility and altered microbial community structures, microbial diversity did not diminish. Interestingly, bacterial OTU richness and diversity were greater in the KRD areas than in the non-KRD areas, which had relatively greater plant density and diversity. Fungal OTU richness and diversity remained unchanged by KRD. Although the KRD areas had been clear-cut and trees were mostly absent, ectomycorrhizal fungi did not differ in diversity and relative abundance between the two land types, indicating that the KRD shrubs hosted surprisingly diverse and abundant ectomycorrhizal fungi.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our results highlight the highly diverse microbes under environmental and anthropogenic stresses in KRD areas. Despite the fact that degraded soil properties and an altered microbial community structure remain, KRD did not erode ectomycorrhizal fungal species richness, which is crucial in the revegetation of trees in KRD areas.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Initial substrate chemical characteristics are the most important factor in the regulation of fine root decomposition. However, it remains unclear how nitrogen (N) deposition changes the decomposition process by affecting initial substrate chemical characteristics with different fine root diameter sizes.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We compared the root decomposition processes across three diameter sizes (very fine roots, 〈 0.5 mm; intermediate fine roots, 0.5–1.0 mm; largest fine roots, 1.0–2.0 mm) of 〈em〉Pinus tabulaeformis〈/em〉 treated with N addition (control, low, medium, high N are 0, 3, 6, and 9 g N m〈sup〉−2〈/sup〉 y〈sup〉−1〈/sup〉 respectively) for two years.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉(1) The root decomposition rates, which were mainly determined by initial N, phosphorus (P), cellulose and lignin concentrations, and carbon (C)/N and lignin/N ratios, increased with the root diameters. (2) The effect of N addition on fine root decomposition rate was not significant (〈em〉P〈/em〉 〉 0.05), but low N addition enhanced the correlation coefficients between initial chemical indexes and decomposition rates. (3) Low N addition increased the release rates of C and cellulose in the very fine roots but not intermediate fine and largest fine roots, while the medium and high N addition decreased the release rates of N, P, cellulose and lignin in the very fine and intermediate fine roots by affecting the initial C, N, P, starch, cellulose and lignin concentrations. (4) Release of compounds from large diameter fine roots is less responsive to N addition than that from the small ones.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The initial substrate chemistry plays an important role during the N addition affecting fine root decomposition and release of chemical compounds. Our results suggest that N deposition may change the biogeochemical processes of forest ecosystems by affecting the release of compounds from fine roots.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Root niche partitioning among trees/shrubs and grasses facilitates their coexistence in savannas, but little is known regarding root distribution patterns of co-occurring woody plants, and how they might differ on contrasting soils.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We quantified root distributions of co-occurring shrubs to 2 m on argillic and non-argillic soils.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Root biomass in the two shrub communities was 3- to 5- fold greater than that in the grassland community. 〈em〉Prosopis glandulosa〈/em〉, the dominant overstory species was deep-rooted, while the dominant understory shrub, 〈em〉Zanthoxylum fagara〈/em〉, was shallow-rooted (47% vs. 25% of root density at depths 〉0.4 m). Shrubs on argillic soils had less aboveground and greater belowground mass than those on non-argillic soils. Root biomass and density on argillic soils was elevated at shallow (〈 0.4 m) depths, whereas root density of the same species on non-argillic soils were skewed to depths 〉0.4 m. Root density decreased exponentially with increasing distance from woody patch perimeters.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Belowground biomass (carbon) pools increased markedly with grassland-to-shrubland state change. The presence/absence of a restrictive barrier had substantial effects on root distributions and above- vs. belowground biomass allocation. Differences in root distribution patterns of co-occurring woody species would facilitate their co-existence.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉In this study, we investigated the effects of reduced snow depth on plant phenology, productivity, nitrogen (N) cycling, and N use in canopy and understory vegetation. We hypothesized that decreased snow depth would hasten the timing of leaf flushing and N uptake in understory vegetation, increasing its N competitive advantage over canopy trees.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Snow removal did not directly affect the phenology of either canopy or understory vegetation. Understory vegetation took up more N in the snow removal plots than in the control plots, particularly in the mid- to late-growing season. Leaf production and N uptake in canopy trees also did not differ between the control and snow removal plots, but N resorption efficiency in the snow removal plots (57.6%) was significantly higher than those in control plots (50.0%).〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Increased N uptake by understory plants may induce N limitation in canopy trees, which in turn may cause canopy trees to increase their N use efficiency. Such competitive advantage of understory vegetation over canopy trees against snow reduction may affect N cycling via litter quality and quantity not only just after the growing season but also in subsequent seasons.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Whilst several studies have shown that edaphic variability influences species composition in nutrient-poor tropical forests, the determinants of local species distributions and, in particular, how these change from younger to mature individuals in such forests are still under debate, and have been poorly explored in tropical heath forests that are among the least fertile tropical forest ecosystems.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We investigated the influence of soil fertility and topography on a Bornean heath forest species composition, α-, β-diversity and tree size structure among size classes by recording all trees ≥1 cm DBH in 16 forest plots totalling 0.36 ha.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Tree species distributions generally followed gradients in available Al and soil depth; α- and β-diversity were linked to soil depth, and to some extent also to pH and the H:Al ratio. In contrast, forest structural attributes (basal area and stem density) were negatively correlated with both available and total P and a wider suite of soil nutrients, although trees ≥10 cm DBH were positively correlated with total P.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉Our study shows that heath forest species distribution, richness and structure is related to both edaphic and topographic characteristics and that soil acidity might have a strong influence in shaping these forests’ features. Among size classes, small trees are less influenced by soil and topography, whereas the sensitivity to these variables increases with tree size. We thus highlight that multiple edaphic factors influence different aspects of tropical forest structure, including different tree life stages, and species composition.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉The trend of soil degradation in intensive open coffee systems is well-documented. This study highlights the impact of young shade trees on soil quality only 4 years after their intercropping with coffee.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉18 young shade trees belonging to three tree species (〈em〉Cinnamomum camphora〈/em〉, 〈em〉Bishofia javanica〈/em〉 and 〈em〉Jacaranda mimosifolia〈/em〉) were selected in an intensive coffee system in Southern Yunnan. Soil samples (0–20 cm) were tested for chemical composition, soil communities and soil enzyme activities under their canopies and in open areas, both in coffee rows and inter-rows, once during the rainy and once during the dry season. Additionally, root systems were characterized using trenches. Soil water profiles and litterfall were monitored along the production cycle. Coffee yield was recorded for two consecutive years.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉We detected a positive impact of all shade tree species on soil chemical, biological and biochemical components, especially during the dry season. This positive impact included higher soil organic matter (+10%) and more abundant soil microbial communities (+64%) under shaded coffee than under open coffee. Furthermore, shaded coffee trees yielded as much as open coffee trees, except under 〈em〉C. camphora〈/em〉, probably due to high below-ground competition.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉These results demonstrate that carefully selected shade trees can rapidly contribute to preserving and/or restoring soil quality in intensive coffee systems, while maintaining high coffee yield.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Traits of the plant root system architecture (RSA) play a key role in crop performance. Therefore, architectural root traits are becoming increasingly important in plant phenotyping. In this study, we use a mathematical model to investigate the sensitivity of characteristic root system measures, obtained from different classical field root sampling schemes, to RSA parameters.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Root systems of wheat and maize were simulated and sampled virtually to mimic real field experiments using the root system architecture (RSA) model CRootBox. By means of a sensitivity analysis, we found RSA parameters that significantly influenced the virtual field sampling results. To identify correlations between sensitivities, we carried out a principal component analysis.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉We found that the parameters of zero order roots are the most sensitive, and parameters of higher order roots are less sensitive. Moreover, different characteristic root system measures showed different sensitivity to RSA parameters. RSA parameters that could be derived independently from different types of field observations were identified.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Selection of characteristic root system measures and parameters is essential to reduce the problem of parameter equifinality in inverse modeling with multi-parameter models and is an important step in the characterization of root traits from field observations.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Moso bamboo (〈em〉Phyllostachys edulis〈/em〉) invasions into adjacent forests are becoming increasingly common. Moso bamboo invasions affect litter quality, soil nutrients, and microbial community composition. Although these effects likely vary among invaded sites and forest types, this has not been investigated.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We investigated moso bamboo invasion effects on carbon (C) and other major nutrients of litter and soil, as well as soil microbial community composition determined by phospholipid fatty acids (PLFAs) in broadleaf or coniferous forests at three different sites in China.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Ordinations indicated that the effects of invasions on soil nutrients, litter nutrients, and soil microbial composition each varied among forest types and sites. Invasions consistently decreased litter C. Invasions tended to have larger effects on soil nutrients in coniferous forests. Except for bacterial groups in one coniferous forest site, invasions had positive effects on every soil group.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Variations in direction and magnitude of invasion effects on litter properties, soil properties, and soil communities among community types and sites suggest that studies of effects of invasions on soils in a single invaded community may not be able to predict effects of an invasion at other locations, even when the original community is similar or occurs in the same site.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Mine tailings are challenging substrates for ecological restoration, as the establishment of diverse native plant communities can be constrained by a range of edaphic factors. Thus, the ability to restore native vegetation communities will depend upon developing a clear evidence-base as to what types of species and communities are likely sustainably reinstated on such altered substrates. As global tailings production and the cumulative footprint of tailings storage facilities continue to grow, understanding the effect of edaphic filters on community establishment is foundational for developing effective restoration solutions for tailings.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We standardised growth rate estimates derived from nine root and shoot parameters for plants grown in magnetite tailings and natural topsoil, using crops (eight species) to characterise previously identified plant responses and native plants (40 species) to understand the impact of edaphic conditions on the species pool available for restoration.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The edaphic conditions of unweathered magnetite tailings select against the majority of native plant species and nutrient-acquisition guilds (approximately 75% of reference floristic biodiversity), with plant development on tailings compared with natural topsoil compromised in a number of variables in all but six species. Plant growth on tailings was limited by a lack of available nitrogen (N) and high alkalinity (pH 〉9), and seedling growth and development was positively associated with seed N concentration. Calcicole species and species from N〈sub〉2〈/sub〉-fixing and cluster root-producing strategies performed better on tailings than calcifuge species and species without specialised nutrient-acquisition strategy or those reliant upon mycorrhizal associations.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The return of plant communities native to highly weathered, acidic soils on magnetite tailings is likely unsuccessful, unless strategies to ameliorate substrate hostility through acidification of the soil profile and improving N availability are prioritised.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉The low phosphorus (P) fertilizer use efficiency in weathered, P deficient soils calls for better fertilizer formulations. We previously formulated nanoparticles containing P (NP-P) that were a successful fertilizer in nutrient solution. This study was set up to test the fate and the bioavailability of nanofertilizer-P and of that of native (colloid) P naturally present in soil.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉The NP-P consisted of nano-ferrihydrite (~ 10 nm) loaded with phosphate (P-〈em〉n〈/em〉Fh) and stabilized with either natural organic matter (NOM) or hexametaphosphate (HMP). Natural colloid concentrations were increased with KOH addition, as deflocculating agent, to soil; all tests used samples from P deficient, highly weathered soils.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Pot trials with rice seedlings did not reveal larger P uptake in the NP-P amended soils compared to equal doses of soluble PO〈sub〉4〈/sub〉 or soluble HMP. Total Fe concentrations in soil solutions were unaffected by NP-P addition, whereas natural colloidal Fe and P markedly increased by KOH addition. The bioavailability of native colloidal P, mobilized by KOH addition, could not be assessed due to lack of growth, likely related to collapse of the soil structure.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉This study showed that P-loaded iron oxyhydroxide NPs insufficiently enhanced soluble P in soil to offer benefits over soluble fertilizers, likely because of a combined effect of lower diffusivity of NPs compared to P〈sub〉i〈/sub〉 and lower bioavailability of NP-P than P〈sub〉i〈/sub〉. Smaller particles or small labile organic colloids might offer an improvement in both aspects.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Wetlands play vital roles as sinks for metal contaminants. Some wetland plants accumulate manganese (Mn) oxides in the black biofilm around roots and rhizomes, although the underlying mechanism is still unclear. Our aim is to determine the role of endophytic bacteria in the formation of Mn deposits in the wetland plant 〈em〉Suaeda salsa〈/em〉 Pall. as well as the underlying chemical and molecular mechanisms.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Manganese-oxidizing endophytic bacteria were isolated with leucoberbeline blue (LBB) and further identified via the phylogenetic analysis. The Mn content and black deposit characteristics of laboratory-cultivated plants before/after co-cultivation of bacteria were investigated by inductively-coupled plasma optical emission spectrometry (ICP-OES), a scanning electron microscope equipped with an energy energy-dispersive X-ray spectroscopye (SEM-EDX), and X-ray fluorescence (XRF). The chemical structures of the biogenic Mn minerals were characterized via spectra of X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and selected area electron diffraction (SAED). Proteomic analyses, coupled with the enzymic assays were performed to identify the enzymes involved in the Mn oxidation.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉We observed black deposits containing Mn oxides in the belowground and aboveground tissues of 〈em〉S. salsa〈/em〉. Three Mn-tolerant bacterial strains were isolated from the plants, and two of them possessed Mn(II) oxidation capacities, which were identified as 〈em〉Pantoea eucrina〈/em〉 SS01 and 〈em〉Pseudomonas composti〈/em〉 SS02. Co-cultivation of the two isolates with 〈em〉S. salsa〈/em〉 showed promoted plant growth and facilitated the formation of black precipitations on roots. Further results showed the different chemical compositions and cellular localizations of biogenic Mn oxides from the two strains. Hydrogen peroxide-detoxifying enzymes were involved in Mn oxidation, most likely mitigating oxidative stresses.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉We suggest a role of endophytic bacteria in Mn uptake and accumulation in the wetland plant 〈em〉S. salsa〈/em〉; our study thereby contributes to a better understanding of the plant-endophyte symbiosis in biogeochemical Mn cycling and wetland soil phytoremediation.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Northern peatlands store large amounts of soil organic carbon (C) that can be very sensitive to ongoing global warming. Recently it has been shown that temperature-enhanced growth of vascular plants in these typically moss-dominated ecosystems may promote microbial peat decomposition by increased C input via root exudates. To what extent different plant functional types (PFT) and soil temperature interact in controlling root C input is still unclear. In this study we explored how root C input is related to the presence of ericoid shrubs (shrubs) and graminoid sedges (sedges) by means of a factorial plant clipping experiment (= PFT effect) in two peatlands located at different altitude (= temperature effect).〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉By selective clipping of shrub and sedge shoots in mixed vegetation at two Alpine peatland sites we interrupted the above- to belowground translocation of C, thus temporarily inhibiting root C release. Subsequent measurements of soil respiration, dissolved organic carbon (DOC) concentration and stable isotope composition (〈sup〉13〈/sup〉C) of DOC in pore water were used as proxies to estimate the above- to belowground transfer of C by different PFT.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉We found that soil respiration rates and DOC concentrations temporarily decreased within 24 h after clipping, with the decrease in soil respiration being most pronounced at the 1.4 °C warmer peatland after clipping shrubs. The transient drop in DOC concentration coincided with a shift towards a heavier C isotope signature, indicating that the decrease was associated with inhibition of a light C source that we attribute to root exudates. Together these results imply that shrubs translocated more C into the peat than sedges, particularly at higher temperature.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉We showed that plant functional type and temperature interact in controlling root C input under field conditions in peatlands. Our results provide a mechanistic evidence that shrubs may potentially promote the release of stored soil C through root-derived C input.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Root-rot disease, a catastrophic disease of 〈em〉Panax quinquefolium〈/em〉 L. causes yield reduction and serious economic losses. However, knowledge of the relationship between rhizosphere microbial community and root-rot disease is limited. This study is aim to test whether the bacteria and fungi community differed between the soil attached to healthy and rotten roots of American ginseng. Moreover, the effects of American ginseng cultivation for 4 years on changes of soil physiochemical properties and microbial community were also investigated.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉High-throughput sequencing (Illumina MiSeq) was used to investigate the difference of microbial communities in the soils of new farmland (C) and the rhizosphere soils around healthy (H) and root rot diseased ginseng (R).〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Cultivation of American ginseng for 4 years not only changed the soil physicochemical properties, but also significantly increased the richness of the soil bacteria and decreased the fungal richness and diversity. Compared with other genera, the bacterial genera 〈em〉Nitrospira〈/em〉 and the fungal genera 〈em〉Gibberella〈/em〉 and 〈em〉Podospora〈/em〉 were strongly enriched in the soil of new farmland. However, the relative abundance of 〈em〉Janthinobacterium, Nitrospira〈/em〉 and 〈em〉Pedomicrobium〈/em〉 in bacterial community, and 〈em〉Mrakia, Paradendryphiella, Sporopachydermia, Myrothecium〈/em〉 and 〈em〉Racocetra〈/em〉 in fungal community were significantly decreased after culture of American ginseng. The results also showed that the bacteria and fungi community differs between the soil attached to healthy and rotten roots of American ginseng. The richness indices of fungal community showed a significant decrease in rhizosphere soils of R comparing with H. The bacteria 〈em〉Rhodoplanes〈/em〉 and 〈em〉Kaistobacter〈/em〉 were the dominant genera in the H sample, whereas 〈em〉Sphingobium〈/em〉 was dominant in the R sample. Notably, 〈em〉Monographella〈/em〉 was significantly higher in the R sample (23.13%) than that of H sample (2.90%). In addition, the fungi 〈em〉Melanophyllum〈/em〉 and 〈em〉Staphylotrichum〈/em〉 were the most differently abundant in the H sample, whereas 〈em〉Mortierella〈/em〉 and 〈em〉Cistella〈/em〉 were the differently abundant genera in the R sample.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our results indicate that cultivation of American ginseng changed the edaphic factors and the soil microbial community, and there are significant differences in the microbial community between the soil attached to healthy and rotten roots of American ginseng.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉 We evaluated the effect of 〈em〉Azospirillum brasilense〈/em〉 strain HM053 inoculation on maize seeds, a spontaneous mutant that excrete ammonium and fix nitrogen constitutively.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Maize was grown with different nitrogen (urea) concentration and inoculated with 〈em〉A. brasilense〈/em〉 Ab-V5 (Brazilian commercial strain) or HM053 strain in four field experiments, in three regions of Parana State, Southern Brazil. We evaluated yield components, nutrient content on leaves and grains and productivity during the crop cycle.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Inoculation with 〈em〉A. brasilense〈/em〉 strain Ab-V5 and HM053 associated with base fertilization (30 kg ha〈sup〉−1〈/sup〉 N) improved crop yield in all trials. Ab-V5 increased production between 2.2 to 10.4%, or 178.0 to 759.9 kg ha〈sup〉−1〈/sup〉, respectively. HM053, by itself, increased production between 4.7 to 29%, or 460.5 to 1769.3 kg ha〈sup〉−1〈/sup〉, respectively.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉The new strain HM053 showed to be a great biofertilizer for maize seeds and a new alternative for a more sustainable agriculture.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉X-ray computed tomography (CT) is widely recognized as a powerful tool for in-situ quantification of root system architecture (RSA) in soil. However, employing X-ray CT to identify the spatio-temporal dynamics of RSA still remains a challenge due to non-automatic, time-consuming image processing protocols and their poor recovery of fine roots in soil.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Here we present a new protocol (Rootine) to segment roots rapidly and precisely down to fine roots with two voxels in diameter (90 μm in pots with 70 mm in diameter). This is facilitated by feature detection of the tubular shape of roots, an approach that was originally developed for detecting blood vessels in medical imaging.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉In comparison to established root segmentation methods, Rootine produced a more accurate root network, i.e. more roots and less over-segmentation. Root length quantified by X-ray CT showed high correlation with results by root washing combined with 2D light scanning (R〈sup〉2〈/sup〉 = 0.92). Tests with different soil materials showed that the recovery of roots depends on signal-to-noise ratio but can be up to 99% for a favorable contrast between fine roots and background.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉This new protocol provides great efficiency to study RSA in undisturbed soil. As it is fully automated it has the potential for high-throughput root phenotyping and related modelling.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Litter inputs are closely related to both forest productivity and nutrient cycling under climate change and local management. This study investigated the effect of litter inputs on litter decomposition, changes in litter chemistry and nitrogen (N) dynamics during eucalyptus leaf litter decomposition.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Two parallel in situ litter decomposition experiments were conducted at two sites with high-quality (HQ) and low-quality (LQ) litters in a eucalyptus-dominated forest of southeast Queensland, Australia. At each site, leaf litters with either a single (SL) or double mass load (DL) of litter inputs were decomposed for 15 months. Litter mass loss, chemical composition and N content of decomposing litters were measured seasonally during the decomposition period. The chemical composition of the collected litters was determined by solid-state 〈sup〉13〈/sup〉C nuclear magnetic resonance (NMR) spectroscopy.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The HQ litters decomposed faster than the LQ litter, with a decomposition constant of 0.53 and 0.33 y〈sup〉−1〈/sup〉 at the HQ and LQ site, respectively. Litter addition rates had no effect on litter decomposition, changes in chemical composition and N content during decomposition regardless of differences in initial litter quality. The HQ and LQ litters showed the same pattern of chemical changes during decomposition, with an increase in alkyl C and a decrease in di-O-alkyl C and aryl C. The relative intensity of O-aryl C and carboxyl C converged, while the relative intensity of di-O-alkyl C and 〈em〉δ〈/em〉〈sup〉15〈/sup〉N diverged as the decomposition progressed. N immobilization during decomposition depended on litter quality, with N consistently immobilized in LQ litters over the whole decomposition period.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉In subtropical eucalyptus-dominated forests, the dynamics of organic C and N during litter decomposition were resistant to the increased inputs of aboveground litters. Litter chemistry of different initial qualities converged at the early stages of decomposition, and the implications of chemical convergence on the formation and stabilization of soil organic matter need to be assessed in the future.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Previous studies suggest that organic carbon (C) and nitrogen (N) can stimulate soil nitrification, but whether autotrophic or heterotrophic nitrification is stimulated and who are active nitrifiers for the nitrification activity is still in debate. We elucidated which nitrification dominated and the active nitrifiers during the decomposition of rice callus.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉〈sup〉15〈/sup〉N-labeled callus and acetylene (C〈sub〉2〈/sub〉H〈sub〉2〈/sub〉) inhibition were used to explore the autotrophic or heterotrophic nitrification during the decomposition of callus and DNA-based stable isotope probing (SIP) and high-throughput sequencing were used to investigate the active nitrifiers.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Autotrophic nitrification dominated the nitrification activity, driven by oxidation of ammonia (NH〈sub〉3〈/sub〉) produced from mineralization of the callus-derived organic N. Callus significantly stimulated nitrification activity, which was paralleled by changes in the abundance and community composition of AOA. DNA-SIP further demonstrated that the active AOA outnumbered their bacterial counterparts in the 〈sup〉13〈/sup〉C-DNA from the soil with callus amendment. Phylogenetic analysis revealed the functional importance of soil fosmid 29i4-like and 54d9-like AOA within soil group 1.1b during the active nitrification with callus cells.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉NH〈sub〉3〈/sub〉 released from the mineralization of callus was the main substrate for autotrophic nitrification and preferentially stimulated the growth of AOA within group 1.1b in the paddy soil.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and Aims〈/h3〉 〈p〉Rare earth elements (REE) are a group of the periodic table formed by 17 chemical elements (lanthanoids plus yttrium and scandium). They have been used in different field applications. In agriculture, they can be found in some phosphate fertilizers at levels one or two orders of magnitude higher than those found in normal agricultural soils. Citrus plants are known to present high levels of REE when compared to most other species, however, there is little information about bioavailability of REE in phosphate fertilizers for citrus plants. This work focuses on the study of REE behavior by the application of increasing doses of single superphosphate fertilizer in Rangpur lime (〈em〉Citrus limonia〈/em〉 Osbeck) plants in a greenhouse study.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉The technique used was instrumental neutron activation analysis (INAA).〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The results showed that the fertilizer has caused significant increases in the content of REE in the citrus plant tissues, with higher concentrations in leaves than in branches. The highest substrate-leaf transfer factor was observed for La (0.0047), though the concentrations in the plants followed the same order found in the substrate, i.e. Ce 〉 La 〉 Sm 〉 Eu 〉 Sc.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉There was an increase of rare earth elements concentrations in Rangpur lime plants by superphosphate fertilizer application.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Soil alkalization imposes severe ion toxicity, osmotic stress, and high pH stress to plants, inhibiting their growth and productivity. NaHCO〈sub〉3〈/sub〉 is a main component of alkaline soil. However, knowledge of the NaHCO〈sub〉3〈/sub〉-responsive proteomic pattern of alkaligrass is still lacking. Alkaligrass (〈em〉Puccinellia tenuiflora〈/em〉) is a monocotyledonous halophyte pasture widely distributed in the Songnen Plain in Northeastern China. This study aims to investigate the NaHCO〈sub〉3〈/sub〉-responsive molecular mechanisms in the alkaligrass plants.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉An integrative approach including photosynthetic and redox physiology, and comparative proteomics was used.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉NaHCO〈sub〉3〈/sub〉 decreased photosynthesis, but increased nonphotochemical quenching, increased membrane electrolyte leakage of alkaligrass, and increased proline and glycine betaine concentrations in leaves. In addition, the NaHCO〈sub〉3〈/sub〉 stress increased Na〈sup〉+〈/sup〉 concentration and decreased K〈sup〉+〈/sup〉/Na〈sup〉+〈/sup〉 ratio in leaves, while Ca〈sup〉2+〈/sup〉 and Mg〈sup〉2+〈/sup〉 concentrations were maintained, contributing to signaling and homeostasis of ion and enzyme activity. Furthermore, O〈sub〉2〈/sub〉〈sup〉−〈/sup〉 generation rate and H〈sub〉2〈/sub〉O〈sub〉2〈/sub〉 concentration were increased, and the activities of ten antioxidant enzymes and antioxidant concentrations were changed in response to the NaHCO〈sub〉3〈/sub〉 stress. Proteomics revealed 90 NaHCO〈sub〉3〈/sub〉-responsive proteins, 54% of which were localized in chloroplasts. They were mainly involved in signaling, photosynthesis, stress and defense, carbohydrate and energy metabolism, as well as protein synthesis, processing and turnover. Some protein abundances did not correlate well with their activities, implying that the enzyme activities were affected by NaHCO〈sub〉3〈/sub〉-induced post-translational modifications.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉To cope with the NaHCO〈sub〉3〈/sub〉 stress, alkaligrass deployed multiple strategies, including triggering phospholipase D (PLD)-mediated Ca〈sup〉2+〈/sup〉 signaling pathways, enhancing diverse reactive oxygen species (ROS) scavenging pathways, and regulating chloroplast protein synthesis and processing.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉The selection and breeding of low grain-cadmium (Cd)-accumulating rices is a promising approach for reducing the Cd concentration in grains. A cadmium-safe rice line designated D62B (〈em〉Oryza Sative〈/em〉 L.) accumulated a low Cd concentration in brown rice for safe consumption (〈 0.2 mg kg〈sup〉−1〈/sup〉). D62B was a great potential breeding material with a weaker translocation capacity of Cd to shoot compared with common rice lines. A prior understanding of the Cd translocation mechanisms in D62B offered theoretical basis for breeding new low-Cd-accumulating rice cultivars in the future.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉A pot experiment was conducted to investigate the changes of non-protein thiols in shoot and root of D62B in comparison with a common rice line (Luhui17), and then the relationship between the Cd translocation via xylem and organic acids in xylem sap of two rice lines was explored by a hydroponic experiment.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉D62B showed lower Cd translocated to shoot in comparison with Luhui17. The translocation factor (TF) of D62B varied from 0.11 to 0.15. Cd exposure promoted the synthesis of non-protein thiols in two rice lines, particularly in roots. Syntheses of glutathione (GSH) and phytochelatins (PCs) in root of D62B were greater than those of Luhui17. Cd concentration in xylem sap of D62B was significant positively correlated with the malic acid, citric acid and tartaric acid concentrations. The citric acid and tartaric acid concentrations in xylem sap of D62B were significantly lower than those of Luhui17. There was no significant difference for malic acid between two rice lines.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉More GSH and PCs in root of D62B was beneficial to Cd retention in root. Furthermore, the involvement of lower citric acid and tartaric acid in Cd translocated in xylem sap of D62B resulted in lower Cd accumulation in shoot.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Microbial denitrification is the primary driver of nitrogen losses from the plant-soil system and the key process for the closure of the global N cycle. All major controls of denitrification might be directly or indirectly affected by plants. However, there is a lack of research of the direct effects of plants on soil denitrification and how this effect might be mediated by soil properties. This study assesses the effect of three common crop species and two agricultural soils on denitrification potentials.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We conducted a factorial experiment under controlled conditions to analyze the effects of (1) different plant species (barley, wheat or ryegrass), (2) two different soils (texture/ SOC) and (3) two different soil moisture levels on Denitrification Enzyme Activity (DEA) in bulk and rhizosphere soil.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The SOC richer clay loam soil showed on average higher DEA (+81%) compared to the SOC poorer silty loam soil. All three plants were found to stimulate denitrification with significant differences between certain species: rye grass (+92% ± 14%) ≥ barley (+75% ± 26%) ≥ wheat (+50% ± 19%).〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉DEA in agricultural soils is interactively controlled by plant species and soil type with an overall stimulating effect of plants on the denitrification potential. Future research should focus on disentangling single mechanisms of plant control on actual denitrification rates and N gas product ratios.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background〈/h3〉 〈p〉Biocrusts are important functional units in dryland ecosystems. Regarded as ecosystem engineers, cyanobacteria in biocrusts contribute several major physico-chemical and biological processes. However, the role of cyanobacteria in the process of loess formation has been underestimated. Recently, their contribution to sediment development was presented in the BLOCDUST model of loess formation.〈/p〉 〈/span〉 〈span〉 〈h3〉Scope〈/h3〉 〈p〉This 〈em〉perspective paper〈/em〉 features the environmental impact of cyanobacteria and biocrusts with a focus on processes involved in the formation of loess sediments. We propose that the formation of loess can be mediated by cyanobacteria, including initial trapping, and the accumulation and preservation of loess-forming particles. Moreover, the initial structure may be further altered by weak mineral weathering, dissolution and mineral re-precipitation due to cyanobacterial metabolic processes. Possible negative aspects of environmental impact related to the potential toxicity of cyanobacterial biocrusts are also discussed. We highlight specific biotic-abiotic interactions between biocrusts and loess (e.g. exudation of organic polymers, carbonate dissolution and re-precipitation, and dust-dependent metabolic activities of cyanobacteria) which are essential for the formation of stabilized loess and propose the term “synergosis” to comprise these interactions.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉The role of cyanobacteria in loess formation has only recently been recognized and the possible biogenic nature of loessification is underestimated as compared to their eolian nature. Mineral weathering and mineral precipitation processes as well as mineral dust flux between litho- and atmosphere mediated by cyanobacteria and biocrusts require more attention due to their significant contribution to ecosystem properties.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉The objective of this paper was to develop a method based on infrared spectroscopy to compare mineral content in soils and apply it to evaluate soil mineralogical variations in pairs of inter-patch and patch soils in a semi-arid area.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Mixtures of several minerals were analyzed by infrared spectroscopy, the second derivative of the spectra was calculated and the spectra normalized respect to calcite or quartz signals (711 cm〈sup〉−1〈/sup〉 or 800 cm〈sup〉−1〈/sup〉 respectively). The intensities of representative signals of each mineral were related to their concentration in the mixtures. Pairs of patch and inter-patch soils from five different sites were analyzed by this method. Elemental analysis and total lime analysis were performed in some soil pairs.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Soils were dominated by calcite and quartz, or by montmorillonite and kaolinite. Inter-patch soils were richer in calcite and poorer in quartz or clays than patch soils. Calcite losses in patch soils might be related to soil acidification by CO〈sub〉2〈/sub〉 from respiration and/or organic matter. Elemental analysis showed high values of S, Cl, and K in patch soils with respect to inter-patch soils.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The proposed FTIR method was useful to compare soil mineralogy in specific areas. Fertile spots by accumulation of water, soluble salts and sediments may favor plant growth in semi-arid regions and these plants may increase the fertility of the spot. Changes in soil mineral composition could be used to monitor the biological activity of soil in arid and semi-arid zones.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Waterlogging is a common natural disturbance that has negative impacts on dry-land plant species. However, few studies have focused on how waterlogging influences the invasiveness of non-native plant species on dry lands. 〈em〉Bidens pilosa〈/em〉 is an invasive dry-land plant of the Asteraceae family that causes serious damage to biodiversity and agricultural production in southern China. To date, it remains unclear how waterlogging affects the competitiveness and growth of 〈em〉B. pilosa〈/em〉. The goal of this study is to determine whether waterlogging promotes the competitiveness of invasive 〈em〉B. pilosa〈/em〉.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉The growth and physiological responses of invasive 〈em〉B. pilosa〈/em〉 and native 〈em〉B. biternata〈/em〉 and the competition effects between them were studied after 0 (control), 5, 10, 15, and 20 days of waterlogging stress (wherein the water level was maintained at the soil surface level).〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉After short-term waterlogging stress, the competitive balance index of invasive 〈em〉B. pilosa〈/em〉 significantly increased, indicating that short-term waterlogging on dry lands could significantly improve the competitiveness of invasive 〈em〉B. pilosa〈/em〉. Invasive 〈em〉B. pilosa〈/em〉 maintained more rapid adventitious root generating capacity and higher root dehydrogenase activity under waterlogging conditions than native 〈em〉B. biternata〈/em〉, which allowed 〈em〉B. pilosa〈/em〉 to adapt to the anoxic conditions much more rapidly. The smaller reductions in net photosynthetic rate, actual quantum yield of photosystem II and relative growth rate in 〈em〉B. pilosa〈/em〉 than in 〈em〉B. biternata〈/em〉 showed that invasive 〈em〉B. pilosa〈/em〉 had stronger tolerance to waterlogging than native 〈em〉B. biternata〈/em〉.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉Our results indicate that invasive 〈em〉B. pilosa〈/em〉 has stronger tolerance to waterlogging than native 〈em〉B. biternata〈/em〉 and that short-term waterlogging on dry lands can significantly improve the competitiveness of invasive 〈em〉B. pilosa〈/em〉. Short-term waterlogging on dry lands caused by extreme precipitation during the rainy season is expected to promote the invasive potential of exotic 〈em〉B. pilosa〈/em〉.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Endophytes benefit host plants by increasing biotic and abiotic stress tolerance. The aims of this study were to evaluate endophytic community (EC) of 〈em〉Arabis alpina〈/em〉, a Pb-Zn hyperaccumulator and investigate role of EC in host plants metal tolerance.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉EC of 〈em〉A. alpina〈/em〉 growing at Pb–Zn mining area was evaluated by Illumina MiSeq sequencing. Pot experiments were conducted for the role of EC in metal accumulation and tolerance of host.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Fungal EC of shoots showed greater similarity to roots than to seeds; and Chao1 and Shannon indices for shoots and roots were significantly higher than for seeds. Inoculation of EC significantly improved host plants growth under multi-metal stress (〈em〉p〈/em〉 〈 0.05, T test). The shoot length, root length and dry biomass of the treatment were improved when compared with the control. EC inoculation significantly altered accumulation of Pb, Cd and Zn in plant tissues. Particularly decreased the accumulation of Pb (〈em〉p〈/em〉 〈 0.05) and Cd (〈em〉p〈/em〉 〉 0.05) in the shoots of the treatment.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Hyperaccumulator 〈em〉A. alpina〈/em〉 growing in metals contaminated soils was colonized by a diverse assemblage of endophytic fungi, and the EC played a key role in increasing host plants metal tolerance.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉The incidence of extreme weather events, particularly drought is predicted to increase in the future and alter the ecosystem process. Despite that the interplay between plant species play a critical role in reducing the vulnerability of soil ecosystem to drought, whether the presence of legumes in plant community could maintain nutrient uptake of focal species by stabilizing soil biota and ecosystem processes under drought conditions remains essentially unexplored.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉In a field experiment, the soil biota community and ecosystem processes were studied using four planting systems contain monoculture of focal species 〈em〉Zanthoxylum bungeanum〈/em〉, mixed cultures of 〈em〉Z. bungeanum〈/em〉 and 〈em〉Capsicum annuum〈/em〉, 〈em〉Z〈/em〉. 〈em〉bungeanum〈/em〉 and 〈em〉Medicago sativa,〈/em〉 and 〈em〉Z. bungeanum〈/em〉 and 〈em〉Glycine max〈/em〉 subjected to drought.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Drought had no significant effects on soil microbial biomass in monoculture and mixed cultures, but significantly increased microbial stress indices. Drought significantly increased the densities of total nematodes, herbivores, bacterivores and fungivores in 〈em〉Z〈/em〉. 〈em〉bungeanum〈/em〉 and 〈em〉M. sativa〈/em〉 mixed culture, but significantly decreased the total nematodes, bacterivores and fungivores in 〈em〉Z. bungeanum〈/em〉 and 〈em〉G. max〈/em〉 mixed culture. Under drought stress, leaf nitrogen concentrations of 〈em〉Z. bungeanum〈/em〉 were significantly higher in 〈em〉Z. bungeanum〈/em〉 and 〈em〉M. sativa〈/em〉 mixed culture than 〈em〉Z. bungeanum〈/em〉 monoculture and the other mixed cultures, this is mainly due to higher microbial activity and net nitrogen mineralization rate.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉Differences in resistance traits of neighbors had additive effects and rapidly reflected in different soil ecosystem processes and nutrient uptake of focal species. Our results revealed that specific legume species intercropping management could stabilize focal species by maintaining soil ecosystem processes under drought condition.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Although aluminum (Al) exclusion via root exudation of organic matters is a common resistance mechanism adopted by many plant species, whether root exudation of benzoxazinoids, such as hydroxamic acids (HAs), confers Al resistance remains unclear.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We performed physiological characterization for an Al-resistant maize cultivar TY and a sensitive maize cultivar ZD.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉First, Al exposure induced HA exudation from the root tip of TY, but not from ZD. Second, HAs formed non-toxic Al chelation complexes in vitro and exogenous HAs alleviated root damage and improved root growth under Al stresses. Third, both Al and exogenous salicylic acid (SA) treatments induced accumulation of endogenous SAs in the root apices of TY, which in turn enhanced root HA exudation and Al resistance in TY. Furthermore, an SA biosynthesis inhibitor significantly decreased Al resistance in TY and abolished the beneficial effects of exogenous SA on Al resistance, suggesting a key role of the endogenous SAs in induction of Al resistance. Finally, it was the root-tip HA exudation but not the root-tip HA contents that determined Al resistance in maize.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉We have revealed a unique Al exclusion mechanism underlying Al resistance via Al and SA-mediated root HA efflux in maize.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉〈em〉Dicranopteris linearis〈/em〉 is a fern that accumulates unusually high concentrations (up to 0.3% dry weight) of rare earth elements (REEs) in China. Previously, we reported that 〈em〉D. linearis〈/em〉 accumulates high concentrations of aluminium (Al) and silicon (Si) in the fronds, but the interactions between these elements and REEs were unknown.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉In this study, a range of analytical techniques, including chemical extractions, Scanning-Electron Microscopy with Energy-Dispersive Spectroscopy (SEM-EDS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) were used to study the association of REEs with Al and Si.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The results show that 〈em〉D. linearis〈/em〉 accumulates high concentrations of REEs (up to 3830 mg kg〈sup〉−1〈/sup〉), Al (up to 9660 mg kg〈sup〉−1〈/sup〉) and Si (up to 20,300 mg kg〈sup〉−1〈/sup〉), with concentrations increasing with age and frond order of pinna. The extraction patterns suggest the existence of REEs-Si and Al-Si complexes. The SEM-EDS analysis confirmed the existence of phytoliths (Al) deposits in the protoplast and apoplast of the pinna cells. The upper epidermis of the pinnule and the pericycle of the midvein are more concentrated in phytoliths (Al) particles. The LA-ICP-MS analysis revealed that REEs and Al are preferentially compartmentalized within bio-inactive tissues of the pinnules, e.g. necrotic tissues (REEs) and in the margins (Al).〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Co-deposition of Si with REEs and Al may be a mechanism for dealing with the high concentrations of REEs and Al in 〈em〉D. linearis〈/em〉 fronds.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aim〈/h3〉 〈p〉Entomopathogenic nematodes (EPN) use odor cues to locate and infect their insect hosts in the soil, making them an important tool in sustainable management of agricultural insect pests. However, very little information is available on the role of soil bacteria in mediating belowground interactions between plants, herbivores and the EPN. In this study, a maize-herbivore-entomopathogenic nematode complex was used to investigate the effect of plant root colonization by a soil bacterium on belowground tritrophic interactions.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉The impact of maize root colonization by 〈em〉Bacillus pumilus〈/em〉 strain INR-7 on the preference of the EPN, 〈em〉Heterorhabditis bacteriophora〈/em〉 was tested in four arm olfactometer bioassays in the presence or absence of the root herbivore 〈em〉Diabrotica virgifera〈/em〉 LeConte (Coleoptera: Chrysomelidae). Plant volatiles were collected for profile characterization. Further preference assays were performed using plant volatile extracts and synthetic volatiles.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉In the absence of the root herbivore, the nematodes were attracted to maize roots whose seeds were coated with dead and living bacteria. In the presence of the herbivore, the nematodes selectively oriented towards infested plants whose seeds were treated with 〈em〉B. pumilus〈/em〉 strain INR-7 than dead bacteria treated, untreated plants or sunshine sand mix. In contrast, plant volatile extracts or pure compounds did not reproduce the observed behavior.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The study showed that bacterial coating of maize seeds with the tested strain may play an important role in shaping belowground tritrophic interactions through mechanisms that would require further investigations. The potential of 〈em〉B. pumilus〈/em〉 strain INR-7 integration in maize rootworm management program is discussed.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Increasing cadmium (Cd) contamination of agricultural soils is a serious problem. Identification of the mechanisms that control Cd uptake by roots is essential if we wish to improve the efficiency of plants in removing Cd from contaminated soils.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We dissected the role and the mechanism of 〈em〉S〈/em〉-nitrosoglutathione reductase (GSNOR) in regulating root Cd uptake in 〈em〉Arabidopsis〈/em〉 plants using GSNOR-related mutants and pharmacological methods.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Exposure to Cd stimulated the activity of GSNOR in roots. Both treatment with 〈em〉S〈/em〉-nitrosoglutathione (substrate of GSNOR) in wild-type plants and loss of GSNOR function in 〈em〉gsnor〈/em〉 mutants improved expression of 〈em〉IRON-REGULATED TRANSPORTER 1〈/em〉 (〈em〉IRT1〈/em〉) and increased root Cd uptake, thereby elevating the Cd levels in plants. The opposite patterns were observed in the 〈em〉GSNOR〈/em〉 over-expression transgenic plant 〈em〉GSNOR〈/em〉〈sup〉〈em〉OE〈/em〉〈/sup〉, suggesting a negative regulation of 〈em〉IRT1〈/em〉 expression and Cd uptake by GSNOR. However, both the improvement of Cd uptake owing to 〈em〉S〈/em〉-nitrosoglutathione treatment or 〈em〉GSNOR〈/em〉 mutation and the inhibition of Cd uptake due to 〈em〉GSNOR〈/em〉 over-expression, could be blocked by loss of function of IRT1 in plants.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉We concluded that induction of GSNOR reduced Cd uptake because of its negative regulation of IRT1 in roots, which lowered Cd accumulation in plants.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Increasing atmospheric carbon dioxide concentration ([CO〈sub〉2〈/sub〉]) stimulates the leaf-level (intrinsic) water use efficiency (iWUE), which may mitigate the adverse effects of drought by lowering water use in plants. This study investigated the interactive effect of [CO〈sub〉2〈/sub〉] and soil type on growth, yield and water use of canola (〈em〉Brassica napus〈/em〉 L.) in a dryland environment.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Two canola cultivars (vigorous hybrid cv. ‘Hyola 50’ and non-hybrid cv. ‘Thumper’) were grown in large intact soil cores containing either a sandy Calcarosol or clay Vertosol under current ambient (a[CO〈sub〉2〈/sub〉]) and future elevated [CO〈sub〉2〈/sub〉] (e[CO〈sub〉2〈/sub〉]), ∼550 μmol mol〈sup〉−1〈/sup〉). Net assimilation rates (〈em〉A〈/em〉〈sub〉〈em〉net〈/em〉〈/sub〉), stomatal conductance (g〈sub〉s〈/sub〉) and leaf area were measured throughout the growing season. Seed yield and yield components were recorded at final harvest. Water use was monitored by lysimeter balances.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Elevated [CO〈sub〉2〈/sub〉]-stimulation of iWUE was greater than the effect on leaf area, therefore, water use was lower under e[CO〈sub〉2〈/sub〉] than a[CO〈sub〉2〈/sub〉], but this was further modified by soil type and cultivar. The dynamics of water use throughout the growing season were different between the studied cultivars and in line with their leaf development. The effect of e[CO〈sub〉2〈/sub〉] on seed yield was dependent on cultivar; the non-hybrid cultivar benefitted more from increased [CO〈sub〉2〈/sub〉]. Although textural differences between soil types influenced the water use under e[CO〈sub〉2〈/sub〉], this did not affect the ‘CO〈sub〉2〈/sub〉 fertilisation effect’ on the studied canola cultivars.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉Elevated [CO〈sub〉2〈/sub〉]-induced water savings observed in the present study is a potential mechanism of ameliorating drought effects in high CO〈sub〉2〈/sub〉 environment. Better understanding of genotypic variability in response to water use dynamics with traits affecting assimilate supply and use can help breeders to improve crop germplasm for future climates.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Supplying phytolith-rich biochar in agrosystems increases soil pH, CEC and nutrient availability, adding to the impact of Si uptake on plant growth. Here we studied this specific impact as influenced by soil properties, and assessed the role of phytoliths to provide plant available Si.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We used a young Cambisol and a highly weathered, poorly buffered, desilicated Nitisol. The biochars were produced from rice plants respectively enriched (Si+) and depleted (Si-) in Si. They had identical pH and nutrient contents, but largely differed in Si content (51.3 g Si kg〈sup〉−1〈/sup〉 in Si + vs 0.3 g Si kg〈sup〉−1〈/sup〉 in Si-). We compared their effects to that of wollastonite (CaSiO〈sub〉3〈/sub〉) on the biomass and mineralomass of wheat plants in a soil:solution:plant device. The contents of soil bioavailable Si and biogenic Si were assessed through an original CaCl〈sub〉2〈/sub〉 kinetic extraction and the 〈em〉DeMaster〈/em〉 Na〈sub〉2〈/sub〉CO〈sub〉3〈/sub〉 alkaline dissolution, respectively.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The 〈em〉DeMaster〈/em〉 technique dissolved Si from phytolith as well as from wollastonite. The soil buffering capacity (cmol〈sub〉c〈/sub〉 kg〈sup〉−1〈/sup〉) was 31 in the Cambisol and 0.2 in the Nitisol. An identical supply of phytolithic biochar increased pH from 4.5 to 4.8 in the Cambisol, and from 4.8 to 7.4 in NI. It further increased the content of bioavailable Si (from 55 to 97 mg kg〈sup〉−1〈/sup〉 in the Cambisol, and 36 to 209 mg kg〈sup〉−1〈/sup〉 in the Nitisol), as well as plant Si uptake, biomass and Si mineralomass. That increase was largest in the Nitisol.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The 〈em〉DeMaster〈/em〉 technique did not specifically quantify the phytolith pool. This pool was the main source of plant available Si in both the Cambisol and Nitisol amended with phytolithic biochar. At identical phytolithic Si supply, however, soil pH and soil buffering capacity controlled the transfer of Si in the soil-plant system, which was largest in the poorly buffered Nitisol. The effect of phytolithic biochar on Si bioavailability was depending on soil constituents and properties, and thus on soil type.〈/p〉 〈/span〉

Description: 〈p〉In the published version, the article title was presented incorrectly. The word “cycling” was inadvertently deleted. The correct title is shown here.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Given that environmental factors like atmospheric CO〈sub〉2〈/sub〉, temperature, and water availability will likely change simultaneously, it is difficult to make accurate predictions about future crop production. Effects of elevated CO〈sub〉2〈/sub〉 or drought on aboveground plant growth are relatively well studied, while effects on the rhizosphere are rarely dealt with. The present work investigates the root exudation pattern of different osmotic protectants such as ions and sugars of two cultivars of barley grown under different water and CO〈sub〉2〈/sub〉 levels.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Barley (〈em〉Hordeum vulgare〈/em〉 L.) plants were grown in plant containers in climate chambers with an optimal and reduced water supply and two CO〈sub〉2〈/sub〉 concentrations (380 and 550 ppm) and harvested at the stem elongation growth stage and when the inflorescences emerged.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The responses of root exudation to CO〈sub〉2〈/sub〉 enrichment, watering level, and cultivar and their interactions varied with the developmental stage. While K〈sup〉+〈/sup〉/Na〈sup〉+〈/sup〉 ratio in root exudates remained stable at the stem elongation stage (DC30), it was higher at the booting stage (DC49) in the cv. “Bambina” than in cv. “Golden Promise”. At DC30, in general the exudation of sugars, dissolved organic carbon (DOC) and their ratio (SUG/DOC) were lower at e[CO〈sub〉2〈/sub〉] compared to ambient CO〈sub〉2〈/sub〉 at normal watering conditions. Under reduced watering conditions, plants exuded on average 55% more sucrose than under well-watered conditions. The modern cv. BA exuded on average 53% more fructose than the older cv.GP. In contrast, at DC49, sucrose, DOC and SUG/DOC exudation were not affected by any factor. At e[CO〈sub〉2〈/sub〉] plants exuded on average 39% less fructose than under ambient CO〈sub〉2〈/sub〉. A water and CO〈sub〉2〈/sub〉 interaction on glucose exudation was found at this stage. Under reduced water conditions, plants growing at ambient CO〈sub〉2〈/sub〉 exuded less glucose but at e[CO〈sub〉2〈/sub〉] exuded similar (GP) or even higher (BA) glucose levels than under normal water supply. Although drought and cultivar factors affected the root exudation of barley, the strongest effects in the exudation pattern were caused by CO〈sub〉2〈/sub〉.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉This study presents a non-destructive percolation method for the collection of root exudates which can be used to give an insight into the complex interaction between global warming-associated environmental factors that cause yield losses and changes in crop quality and components of the belowground plant metabolism.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background & aims〈/h3〉 〈p〉Endophytic 〈em〉Bacillus〈/em〉 species with plant growth promoting activities have been used in the last decade. The mechanism of their activities has been partially elucidated recently. Plant growth regulatory hormones that interact with volatiles emitted by endophytic 〈em〉Bacillus siamensis〈/em〉 YC7012 have not been well defined yet. To elucidate the mechanism involved in the promoting effect of endophytic 〈em〉Bacillus siamensis〈/em〉 YC7012 on root development of plants, the objective of this study was to investigate potential factors involved in interaction between 〈em〉Arabidopsis〈/em〉 and strain YC7012.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Bioassay was conducted by co-cultivating 〈em〉Arabidopsis〈/em〉 mutants of auxin (〈em〉axr4–2〈/em〉, 〈em〉aux1–7〈/em〉 and 〈em〉eir1–1〈/em〉), ethylene (〈em〉etr1〈/em〉), and jasmonic acid (〈em〉jar1, coi1–1〈/em〉) with strain YC7012 in petri dishes compared to exogenous MeJA treatment. Auxin response was further determined by using transgenic line 〈em〉DR5::GUS〈/em〉. Volatile experiments were conducted in central partition plates (I-plates). Cell wall modification genes were investigated using qRT-PCR.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉All tested mutants showed significantly increased biomass with more lateral roots in the treated seedlings compared with the untreated mutants. Moreover, the co-cultivation of the strain YC7012 with the auxin response transgenic 〈em〉AtDR5::GUS〈/em〉 did not distinctly show any visualized 〈em〉GUS〈/em〉 signalling. Co-treatment of YC7012 with MeJA increased the number of lateral roots and biomass of 〈em〉Arabidopsis jar1〈/em〉. However, application of MeJA only failed to promote the growth of lateral root or biomass. Expression levels of cell wall modification genes 〈em〉EXPANSIN〈/em〉, 〈em〉EXPA5,〈/em〉 and 〈em〉EXPB1〈/em〉, 〈em〉CHLOROPLAST LUMEN PROTIEN〈/em〉 (〈em〉CLP〈/em〉), and carbohydrate and cell wall biosynthesis gene 〈em〉REB1〈/em〉 were significantly up regulated by co-cultivation with strain YC7012. Strain YC7012 significantly increased plant biomass. Its effect was similar to volatile producing strains 〈em〉B. subtilis〈/em〉 GBO3 and 〈em〉B. siamensis〈/em〉 (KACC 15859〈sup〉T〈/sup〉).〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Strain YC7012 can promote the growth of 〈em〉Arabidopsis〈/em〉 by producing volatile organic compounds independent of auxin, ethylene, or jasmonic acid signalling pathway.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Changes in root functional traits reveal important nutrient acquisition strategies, with well documented patterns in root trait expression within complex communities or along gradients of singular nutrients. In this field study, we investigate intra-root functional trait expression with six soil macro- and micro-nutrients in 〈em〉Theobroma cacao〈/em〉 agroforestry systems.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Using image, chemical, and spatial analysis, the fine root distribution, architecture, and morphology of 〈em〉T. cacao〈/em〉 were compared to localized soil nutrients on two-dimensional soil profiles with conspecific and heterospecific neighbours.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Fine-scale variation in soil nutrients was observed within the range of 〈em〉T. cacao〈/em〉 root systems. Higher NH〈sub〉4〈/sub〉〈sup〉+〈/sup〉 and Ca〈sup〉2+〈/sup〉 was associated with greater root length and biomass densities, coupled with greater investment to individual roots, expressed as increased fine root tissue density and diameter and lower specific root length. Conversely, NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 had the opposite effect. Overall, roots tended towards higher acquisitive trait values when next to a shade tree.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Plants generally employ several concomitant and at times opposing strategies for nutrient acquisition in heterogeneous soils. We show that fine-scale root plasticity is highly linked to localized nutrient-specific and neighbour-specific effects, driving patterns of nutrient acquisition in agroforestry systems.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉If and how eutrophication influences the persistent soil seed bank is poorly understood. Here, we hypothesized that eutrophication alters the composition of the persistent seed bank indirectly through changes in the soil characteristics and aboveground plant community and productivity. We also hypothesized that changes in the persistent seed bank will consequently impact the aboveground vegetative composition.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We tested these hypotheses using data from a 9-year nitrogen and phosphorus fertilization experiment in an alpine meadow ecosystem on the eastern Qinghai-Tibet plateau.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉We found that long-term nitrogen and phosphorus fertilization indirectly impacted the composition of the persistent seed bank through changes in soil pH, aboveground vegetation composition and annual net primary productivity (ANPP). Changes in the composition of the persistent seed bank, however, were relatively minor in comparison to changes in aboveground vegetation composition. Finally, changes in the persistent seed bank did not feedback on aboveground vegetation composition.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉Our findings demonstrate the importance of soil pH, ANPP and vegetation composition in regulating the persistent seed bank under eutrophication. Our results also highlight the relative stability of the persistent seed bank to long-term eutrophication and their important contribution to the sustainability of grassland ecosystems.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Plant growth promoting bacteria (PGPB) are associated with plant roots and augment plant productivity and immunity; however, recent work by several groups has shown that PGPB also elicit the so-called “induced systemic tolerance” to drought stress. This work aimed to evaluate the effect of 〈em〉Gluconacetobacter diazotrophicus〈/em〉 Pal5 inoculation on the mitigation of drought stress in red rice (〈em〉Oryza sativa〈/em〉 L.).〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉The experiment treatments of the red rice cultivar inoculated and uninoculated with 〈em〉G. diazotrophicus〈/em〉, and cultivated with and without water restriction. Physiological, biochemical, and molecular analyses of plant tissues were carried out, along with measurements of biomass and seed yield components.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The plants showed a positive response to inoculation with 〈em〉G. diazotrophicus〈/em〉, with promotion of growth and induction of tolerance to drought. Increase in plant biomass and higher levels of gas exchange and osmoprotectant solutes were observed in shoots. The bacterial inoculation increased the yield and positively regulated some defense genes against the water deficit in plants.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉〈em〉G. diazotrophicus〈/em〉 Pal5 strain inoculation was beneficial for red rice plants, suppressing the various deleterious effects of drought stress and increasing the biomass and seed yield components.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉This study defines key genes involved in Fe homeostasis and reveals cultivar differences in Fe deficiency responses in peanuts.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉A comparative transcriptome analysis was conducted on two peanut cultivars, Silihong and Fenghua 1, under Fe-sufficient and -deficient conditions. Plant growth and metal contents were measured.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Silihong is more tolerant to Fe-deficiency than Fenghua 1. Fe deficiency increased the uptake of Zn, Mn, Mg, Ca and Cu in peanut plants. A total of 56 and 19 transporter genes were identified to be differentially expressed genes in Silihong and Fenghua 1 respectively. Two cultivars shared twelve common differentially expressed genes encoding OPT3, FRO2, Nramp3, YSL3, IRT1, FER3 and FRO7. Silihong showed higher expressions of 〈em〉AHA4〈/em〉, 〈em〉COPT1〈/em〉, 〈em〉FRO2〈/em〉, 〈em〉IRT1〈/em〉, 〈em〉MTP4〈/em〉, 〈em〉MTP9〈/em〉, 〈em〉Nramp5〈/em〉, 〈em〉OPT3〈/em〉 and 〈em〉VITH4〈/em〉, while Fenghua 1 exhibited higher expressions of 〈em〉ATX1〈/em〉, 〈em〉HMA5〈/em〉, 〈em〉MPT1〈/em〉, 〈em〉OPT6〈/em〉, 〈em〉YSL3〈/em〉, 〈em〉YSL7〈/em〉, 〈em〉ZIP1〈/em〉, 〈em〉ZIP4〈/em〉, 〈em〉ZIP5〈/em〉 and 〈em〉ZIP11〈/em〉 under Fe deficiency.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Peanuts overcome Fe deficiency by increasing Fe uptake and altering its transport pathway, in which 〈em〉FRO2〈/em〉, 〈em〉IRT1〈/em〉, 〈em〉Nramp3〈/em〉, 〈em〉YSL3〈/em〉 and 〈em〉OPT3〈/em〉 are involved. Higher expression of 〈em〉AHA4〈/em〉, 〈em〉FRO2〈/em〉, 〈em〉IRT1〈/em〉 and 〈em〉Nramp5〈/em〉 might be responsible for higher Fe-deficiency tolerance in Silihong. Induction of 〈em〉IRT1〈/em〉, 〈em〉Nramp5〈/em〉 and 〈em〉COPT1〈/em〉 by Fe deficiency contribute to increased metal uptake in peanut plants.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Photodegradation of senescent plant material has been identified as an important vector of aboveground carbon (C) loss in aridland ecosystems, but the consequences for biotic activity and soil C in the field are not well understood.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We established an experiment in a semiarid woodland in Patagonia, Argentina with attenuation of solar radiation and additions of leaf litter to evaluate impacts of photodegradation on changes in labile C and biotic activity in aboveground litter and surface soils.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Litter decomposition was significantly accelerated by exposure to solar radiation. Moreover, labile sugars (hexoses and pentoses), microbial enzymatic activity (β-glucosidase activity) and available carbohydrates for cellulase degradation (saccharification) all significantly increased in sunlight-exposed litter. None of these stimulatory effects were observed in the surface soils exposed to sunlight. On the contrary, soil microbial biomass and β-glucosidase activity in surface soils were significantly greater only with litter addition and attenuated sunlight.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our results suggest that photodegradation of plant litter (production of volatile compounds through photochemical mineralization) and photofacilitation (stimulation of biotic activity due to change in litter chemistry with exposure to sunlight) generate rapid turnover of C in aboveground litter. The consequences of this accelerated C turnover may be that a fraction of leaf litter decomposes and is directly released back to the atmosphere as CO〈sub〉2〈/sub〉 and never enters soil organic matter pool. Taken together, these results highlight the functional importance of solar radiation in determining the C balance in semiarid ecosystems.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Visible and near-infrared spectral reflectance can be used to determine the chemical composition of soil and plant organs. However, previous research has not used this for fresh fine root systems of tree species. We aimed to explore the predictive ability of spectral reflectance relationships among fine-root morphological, anatomical, and chemical traits for 12 tree species in a temperate forest in Japan.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Intact fresh systems of fine root were imaged at 478–978 nm wavelengths (153 bands, 3.6 nm interval). Relationships between spectral reflectance and specific root length, root tissue density, branching intensity, stele/cortex ratio, and Ca concentration were analyzed at each spectral band.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Reflectance peaked at around 920 nm across all species; however, reflectance magnitude at spectral regions of blue (478 nm), green (546 nm), red (648 nm), and near-infrared (847 nm) significantly differed among species. All variables measuring traits were significantly correlated with spectral reflectance only at specific wavelengths, but the strength of the correlation differed among wavelengths.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉Spectral reflectance in visible–near-infrared regions for fresh intact root systems can evaluate the species-differences in fine root traits, and can predict fine root traits across species. Our findings facilitate a general assessment of root traits across tree species and will allow more accurate estimation of fine root functions.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Jasmonic acid (JA), a plant hormone and signal molecule, is known to enhance plant tolerance to various biotic and abiotic stresses. Our purpose is to determine the effect of JA on boron (B) toxicity in a B-tolerant species, 〈em〉Puccinellia tenuiflora〈/em〉, especially on seed germination and seedling growth.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉In a germination trial, we germinated 〈em〉P. tenuiflora〈/em〉 seeds using Petri dishes under 300 mg L〈sup〉−1〈/sup〉 B with JA treatment in the concentration range of 0.1–10 μM. In a hydroponic experiment, 〈em〉P. tenuiflora〈/em〉 seedlings were grown under 250 mg L〈sup〉−1〈/sup〉 B with JA treatment at a concentration of 0.1 and 1.0 mM, respectively.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The germination trial shows that JA has an alleviatory effect on the inhibition of germination induced by excess B. The hydroponic experiment shows that JA is able to mitigate the inhibition of plant growth caused by excess B. The effect of JA was dose dependent, and only appropriate concentrations of JA were found to alleviate B toxicity in 〈em〉P. tenuiflora〈/em〉.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our findings suggest that the application of exogenous JA is able to help plants tolerate high levels of B at both the germination and seedling stages, which also indicates that JA is a promising growth regulator for 〈em〉P. tenuiflora〈/em〉 under excess B.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉This study investigated the detailed mechanism underlying the alleviation of osmotic stress by exogenous hydrogen (H〈sub〉2〈/sub〉) in 〈em〉Medicago sativa〈/em〉.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉By using biochemical and molecular approaches, the experiments were performed with the analyses of biomass, relative water content (RWC), lipid peroxidation, abscisic acid (ABA) content, antioxidant activities, and related gene expression profiles.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉H〈sub〉2〈/sub〉 application stimulated ABA production, which was accompanied by the regulation of ABA biosynthesis and deactivation/activation genes. Elevated H〈sub〉2〈/sub〉-induced ABA synthesis was sensitive to tungstate, an inhibitor of ABA synthesis. Meanwhile, H〈sub〉2〈/sub〉-alleviated osmotic stress, which was supported by the increases in biomass and RWC, and the reduction of lipid peroxidation, was impaired by the inhibition of ABA synthesis. Consistently, tungstate blocked H〈sub〉2〈/sub〉-induced antioxidant defense. Molecular evidence revealed that 〈em〉miR528〈/em〉 was down-regulated by H〈sub〉2〈/sub〉, showing a negative correlation with its target gene 〈em〉POD2〈/em〉. When tungstate was added together, the decreased 〈em〉miR528〈/em〉 and increased 〈em〉POD2〈/em〉 transcripts were respectively blocked. Transcriptional factor genes involved in ABA signaling, including 〈em〉MYB102〈/em〉, 〈em〉MYC2〈/em〉, and 〈em〉ABF/AREB2〈/em〉, were differentially upregulated by H〈sub〉2〈/sub〉, but further impaired by the co-incubation with tungstate.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Collectively, our results suggested the possible role of ABA signaling in exogenous H〈sub〉2〈/sub〉-mediated tolerance against osmotic stress in alfalfa.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉The aim of this study was to examine whether differences in the provenances of canopy tree species affect the community of soil invertebrates.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We used a common garden, where 〈em〉Cryptomeria japonica〈/em〉 trees (Yoshino, Yanase, Itoshiro and Yaku) from four provenances were planted separately in each plot. In these plots, we measured the concentration of nutrients in leaves, litter and roots; Sr isotope ratio (〈sup〉87〈/sup〉Sr/〈sup〉86〈/sup〉Sr) of leaves; root exudation rate of organic acids; exchangeable nutrients in soil and soil parameters such as soil pH; and abundance and composition of soil invertebrates.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Some parameters that may affect nutrient dynamics (concentration of nitrogen in roots, root exudation rate of organic acids, tree growth) and concentrations of calcium and phosphorus in leaves and soil were significantly higher in the Yoshino plot than in the other plots. The 〈sup〉87〈/sup〉Sr/〈sup〉86〈/sup〉Sr of leaves suggested that the cycling of nutrients such as calcium differed significantly between the plots. Furthermore, the abundances of soil invertebrates that are likely to be affected by nutrient concentrations (e.g. soil crustaceans) were significantly higher in the Yoshino plot than in the other plots.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The effects of the provenance of a canopy tree species shape the soil invertebrate abundances and composition by altering the concentration of nutrients in the soil.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Understanding seed-soil dynamics is important for improving plant emergence and growth. The objectives of this study were to develop a Seed-Soil model to simulate the dynamic process of seed expansion in soil, and a Cotyledon-Soil model to simulate the dynamic process of cotyledon movement in soil.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉To obtain model inputs, a soybean emergence experiment was conducted to measure the expansion rates of seed and the translational and rotational velocities of cotyledon movement. After being calibrated and validated, the models were used to simulate the contact and force characteristics of seed-soil and cotyledon-soil as well as the resultant kinetic energy of soil particles in the seedbed.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Results from the Seed-Soil model showed that during the germination phase (0–48 h), the number of contacts between the seed and soil increased from the initial 40 counts to about 80. Results from the Cotyledon-Soil model demonstrated that the vertical movement and rotation of cotyledon during the emergence phase (48–120 h) caused a linear increase in the kinetic energy of the soil particles, and a decrease in the number of contacts between the cotyledon and soil. The maximum soil impedance to the cotyledon was 0.123 N, which occurred at 54 h after planting.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The two models developed were capable of simulating the dynamic processes of seed expansion and cotyledon movement in soybean emergence.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉The study investigated the growth and metal accumulation over time of young forest vegetation growing on metal-contaminated topsoil above either acidic or calcareous subsoil.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉A 4-year model ecosystem experiment was performed under quasi-natural conditions. The heavy metal (HM) contaminated topsoil contained around 3000 mg/kg Zn, 600 Cu, 100 Pb, 9 Cd.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Total biomass was 25.7% lower on the acidic than on the calcareous subsoil. The HM topsoil did not affect total understorey and 〈em〉Salix〈/em〉 biomass, but decreased the growth of 〈em〉Populus, Betula〈/em〉 and on the acidic subsoil also that of 〈em〉Picea〈/em〉. Leaf Cd and Zn concentrations were around 6 and 1000 mg/kg, respectively, in 〈em〉Populus〈/em〉 and 〈em〉Salix〈/em〉 on the HM topsoil, and 0.6 and 200 mg/kg in 〈em〉Picea〈/em〉 and understorey. Leaf and wood HM concentrations, were lower in 〈em〉Populus〈/em〉 and 〈em〉Salix〈/em〉 on the calcareous than on the acidic subsoil. Temporal trends differed among the investigated metals. The HM-induced relative increases in leaf and wood metal concentrations were lower by at least an order of magnitude than in the respective soluble topsoil metal concentrations. Over the four years, Zn was increasingly accumulated in older twigs in 〈em〉Picea〈/em〉.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The selected native trees are suited for phytomanagement of HM-contaminated topsoils. Subsoil acidity is a relevant factor.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉In forest ecosystems, trees may have genetically distinct patterns in leaf decomposition. Trees also can have genetically distinct canopy environments which modify temperature, moisture, and microbial communities on the forest floor. The interaction between these factors may result in underexplored interactions between microenvironment and leaf decomposition at the genotype level.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We compare litter decomposition rates for distinct genotypes of Fremont cottonwood (〈em〉Populus fremontii〈/em〉) grown in a common garden environment under three different riparian conditions: 1) under a 16-tree stand of the same genotype, 2) under a 16-tree stand of another genotype, and 3) under a 16-tree stand of 16 different genotypes. Genotypes differed in canopy size and phenology.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉While genotype exerted a strong effect on decomposition, this effect was most pronounced when litter was decomposed under a self-similar (“home”) canopy. The strongest driver of decomposition rates across all factors (including litter quality and environmental factors) was spring (leaf-out) and fall (leaf-drop) phenology, but responses were variable by genotype.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The influence of genetics on litter decomposition, canopy environment, and tree phenology provides justification for the inclusion of stand-level traits like canopy cover into models of decomposition and complicates the results of studies that rely on litter quality traits alone.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Microbial communities are the primary drivers of organic matter decomposition in peatlands. However, limited knowledge is available regarding depth-dependent microbial community structure and function in East Asian peatlands, using cultivation independent approaches.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We investigated the vertical stratification of prokaryote and fungal communities in a moderately rich fen in northeast China (Hani) and a rich fen in southwest China (Riganqiao).〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Fungal and prokaryotic operational taxonomic unit (OTU) composition exhibited strong site and/or depth responses. Prokaryotic OTUs exhibited the greatest alpha diversity at the mesotelm ‘hot spot’, whereas the predicted metagenomic metabolic functions did not align with the pattern of prokaryote alpha diversity. The large cover of shrubs contributed to a greater relative abundance of ericoid- and ecto-mycorrhizal fungi at Hani, whereas Riganqiao showed more arbuscular mycorrhizal fungi. Soil pH and water table depth were among the predominant abiotic factors associated with microbial community composition.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Projected shifts in hydrology and/or vegetation with global change may cause substantial impacts on peatland microorganisms and thus the associated biogeochemistry. It is critical to better understand the mechanism of the discrepancy between microbial community structure and the functions at the mesotelm ‘hot spot’ when evaluating the ecosystem functions in peatlands.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Biological fixation of atmospheric nitrogen (N〈sub〉2〈/sub〉) is the main pathway for introducing N into unmanaged ecosystems. While recent estimates suggest that free-living N fixation (FLNF) accounts for the majority of N fixed in mature tropical forests, the controls governing this process are not completely understood. The aim of this study was to quantify FLNF rates and determine its drivers in two tropical pristine forests of French Guiana.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We used the acetylene reduction assay to measure FLNF rates at two sites, in two seasons and along three topographical positions, and used regression analyses to identify which edaphic explanatory variables, including carbon (C), nitrogen (N), phosphorus (P) and molybdenum (Mo) content, pH, water and available N and P, explained most of the variation in FLNF rates.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Overall, FLNF rates were lower than measured in tropical systems elsewhere. In soils seasonal variability was small and FLNF rates differed among topographies at only one site. Water, P and pH explained 24% of the variation. In leaf litter, FLNF rates differed seasonally, without site or topographical differences. Water, C, N and P explained 46% of the observed variation. We found no regulatory role of Mo at our sites.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Rates of FLNF were low in primary rainforest on poor soils on the Guiana shield. Water was the most important rate-regulating factor and FLNF increased with increasing P, but decreased with increasing N. Our results support the general assumption that N fixation in tropical lowland forests is limited by P availability.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Global warming is predicted to alter the timing and magnitude of biogeochemical nitrogen cycling in paddy soils. However, little is known about its effect on active nitrifying populations. Here we investigated the responses of nitrification activity and active nitrifiers to elevated temperature in an acidic paddy soil.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉〈sup〉13〈/sup〉CO〈sub〉2〈/sub〉-DNA-stable isotope probing (SIP), qPCR and high-throughput sequencing were used to determine active nitrifying phylotypes as well as difference in their abundance and community composition incubated at field temperature (15 °C) and elevated temperature (20 °C).〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Urea application led to significant production of nitrate and growth of ammonia-oxidizing bacteria (AOB) at both temperatures. Nitrification activity at elevated temperature was 148.3% and 18.5% higher than that of low temperature at day 28 and 56, respectively, accompanied by an increase in the extent of 〈sup〉13〈/sup〉C-label incorporation by AOB. 〈sup〉13〈/sup〉CO〈sub〉2〈/sub〉-based SIP experiment indicated that both AOB and ammonia-oxidizing archaea (AOA) were involved in the nitrification activity and the active ammonia oxidizers changed from AOA to AOB with elevated temperature. Significant variation of AOA communities was observed under different temperatures. Dominant 〈sup〉13〈/sup〉C-labeled nitrite-oxidizing bacteria (NOB) shifted from 〈em〉Nitrospira moscoviensis〈/em〉 to 〈em〉Nitrospira japonica〈/em〉 with higher temperature.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our findings emphasized that elevated temperature had pronounced effects on autotrophic nitrification which was mediated by altering relative abundance of active AOB and AOA, as well as the community composition of AOA and NOB. AOB were more adaptable than AOA with increasing abundance but no alteration of composition at elevated temperature.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉To restore species-rich grasslands on former agricultural land, typically phosphorus-poor soil conditions need to be re-established. Here we assess the potential of phosphorus extraction by biomass production, i.e. phytomining. We compare two techniques: (i) ‘mowing’, i.e. cutting and removing hay two or three times a year, and (ii) ‘P-mining’, i.e. mowing with yield maximization by adding growth-limiting nutrients other than phosphorus (i.e. nitrogen and potassium).〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉In a five-year field experiment at three fields situated along a soil phosphorus gradient, we studied phosphorus removal through both biomass assessment and changes in two soil phosphorus pools: bioavailable phosphorus (P〈sub〉Olsen〈/sub〉) and slowly cycling phosphorus (P〈sub〉Oxalate〈/sub〉).〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Phosphorus-mining doubled the phosphorus removal with biomass compared to mowing, and phosphorus removal with biomass was lower at fields with an initially lower concentration of P〈sub〉Olsen〈/sub〉 in the soil. The P〈sub〉Olsen〈/sub〉 concentrations decreased significantly during the experiment with the largest decreases in phosphorus-rich plots. Changes in the P〈sub〉Olsen〈/sub〉 and P〈sub〉Oxalate〈/sub〉 stocks were correlated with the amount of phosphorus removed with biomass.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Phosphorus-mining effectively increases phosphorus removal compared to mowing, but becomes less efficient with decreasing soil phosphorus concentrations. Restoring phosphorus-poor soil conditions on formerly fertilized land remains a challenge: phytomining most often needs a long-term commitment.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Pseudo-metallophyte 〈em〉Silene vulgaris〈/em〉 frequently colonizes polluted areas. We investigated whether plants obtained under in vitro conditions can be used to form long-term communities on zinc-lead tailings rich in cadmium. To this end, we checked the species stabilization capacity and biochemical properties of the area subjected to long-term cultivation of a local 〈em〉S vulgaris〈/em〉 ecotype. We focused on evaluation of its ability to accumulate trace metals (TMs) after 10-year cultivation period.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉The calamine 〈em〉S. vulgaris〈/em〉 ecotype was propagated in vitro and acclimatized to ex vitro conditions in a greenhouse. The plants were then replanted on plots created on the flotation settler heavily polluted with Zn, Pb and Cd. The capacity of trace metal accumulation in plant material was checked based on translocation (TF) and bio-concentration (BCF) factors. Nutrient, TMs content, and enzyme activity of substrate were determined after 1 and 10 years of cultivation and compared with the properties of bare flotation waste.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Numerous plants obtained through vegetative in vitro propagation were planted in the field after a short hardening period. Cultivation of plant material obtained this way increased microbial activity, C concentration, and reduced TM contents in the substrate. TF calculated after the first season of 〈em〉S. vulgaris〈/em〉 cultivation was similar for all metals and amounted to about 40%. After 10 years, it was the highest for Cd (50%). Independently of the experiment duration, BCF for Zn and Pb was 〈1, while for Cd it reached about 1.4 after 10 years for both shoots and roots.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The calamine 〈em〉S. vulgaris〈/em〉 ecotype cloned in tissue culture proved useful material for stabilization of trace metal contaminated post-flotation wastes. Ten years of its cultivation in tailings rich in Zn, Pb and Cd contributed to humus layer formation and increase in microbial activity in the substrate. Thus, the beginning of soil formation was noticed in heavily polluted tailings.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉A reliable root architectural model is required to study tree anchorage, including secondary root growth, from seed to the mature stage.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We calibrated the generic RootTyp model for the seven root types of 〈em〉Pinus pinaster〈/em〉. We determined most parameter distributions from the means and standard deviations of corresponding features in 92 excavated root systems of various ages. We set the remaining parameters using the literature or an optimisation method. The simulated root systems were compared to 22 additional root systems for validation.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Branching varies as a function of the distance from the root base, and the growth capacity decreases with branching order. These damping properties had to be implemented in the model to yield realistic outputs beyond the juvenile phase. Diameter growth was satisfactorily modelled from the apex diameter and a tapering-by-branching coefficient. Nevertheless, the diameters of the simulated roots were underestimated near the stump. Growth alterations due to soil constraints were accurately reproduced using the calibrated soil module.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Root architecture of large-size and long-living plants can be appropriately modelled with the modified RootTyp model. We suppose that diameter underestimation was due to selective acclimation to the prevailing wind, a facet not taken into account at this calibration step.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉To assess the effects of potato-legume intercropping on selected soil physical and chemical properties after four consecutive growing seasons (from the short rains in 2014 to long rains 2016).〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉The experiment was laid out in a randomised complete block design with four replicates. The treatments were potato-dolichos (PD); potato-garden pea (PG); potato-bean (PB) intercropping systems, and a pure stand of potato (PS). After every harvest, crop residues were ploughed back and selected soil physico-chemical properties were assessed after two years of cultivation.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Potato-legume intercropping resulted in a significant increase down the slope for clay and silt under PS, PG and PB whereas, an opposite observation was made for sand and bulk density. Nonetheless, under PD, slope position had no significant effect on soil physical properties. In all cropping systems, a significant increase was observed down the slope for pH and cation exchange capacity. Similar observations were made for phosphorous, nitrogen and organic carbon under all the cropping systems except PD.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉This study has established PD as a viable intercropping system, which could be adopted by farmers for improved soil fertility.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Continuous cropping of watermelon is known to result in the disruption of the rhizospheric bacteria and fungi that contribute to the occurrence of Fusarium wilt disease. However, the underlying changes in microbial composition and function as a response to mono-cropping are less studied.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉In this study, differences in composition and potential function of the microbiome between healthy and diseased soils were investigated using MiSeq targeted sequencing and the functional GeoChip array, respectively.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Twenty years of continuous watermelon monoculture was found to significantly alter the soil microbial communities by increasing bacterial diversity but decreasing fungal diversity. Compare to bacterial network, fungal co-occurrence networks were less robust and less connected in the monoculture diseased soil. Identified keystone species, belonging to the Proteobacteria, Bacteroidetesand Acidobacteria, were present in both the diseased and healthy soils. Key fungal species from the healthy soil belonged solely within the Ascomycete, while in the diseased soil Basidiomycota were dominant. As such, overall variations in the composition of the soil microbiome are accompanied by changes in the identities of the keystone species when comparing healthy versus diseased soils, further suggesting that soil function may also be altered. Relative abundances of genes associated with the degradation of hemicelluloses and chitin, the Calvin circle, ammonification, stress responses, iron uptake, and nitrogen fixation were significantly higher under long-term monoculture. Particularly, Fusarium spp. relative abundance was positively correlated with the relative abundances of genes involved in adherence, cellular metabolism, and immune evasion which may facilitate pathogen infection of plant roots.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉In conclusion, these results highlight the significant compositional and functional differences in microbial communities between Fusarium wilt diseased soils and healthy soils under watermelon cultivation. This provides insight into the complex array of microorganisms in soils that suffer from Fusarium disease and illustrates potential directions towards the manipulation of the soil microbiome for suppression of this disease.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉In tropical rainforests, seedling performance at fine ecological scales has traditionally been explained by seed dispersal limitation and negative density dependence. Soil properties have strong patch structures at fine scales, and we investigated whether such heterogeneity contributes to seedling coexistence.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉From January 2011 to January 2014, in a one-hectare area of tropical rainforest in Southwest China, we sampled seedlings from ninety-nine 2-m〈sup〉2〈/sup〉 quadrats, and measured light condition (canopy openness), and the height (〉10 cm) of seedlings at bi-monthly intervals. In addition, we measured soil pH, total nitrogen, ammonium, nitrate, and available phosphorus and potassium three times during the survey period. These data were used to examine the effects of soil properties and light on seedling spatial distribution, survival, and growth.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Seedling spatial distribution was significantly associated with light and spatial heterogeneity in all the examined soil properties except available K. These fine scale soil properties and light heterogeneity also promoted seedling growth, whereas they had no discernible effects on seedling survival.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusion〈/h3〉 〈p〉This study highlights the effects of fine scale soil property heterogeneity on seedling spatial distribution and growth, and indicates their importance in the maintenance of seedling biodiversity.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Litter decomposition patterns, non-additive effects, and spectral data of abundant alpine leaf litters were assessed in litterbag experiments containing single species and mixtures. We tested if low-quality shrub litter decomposes faster in mixtures with high-quality litter and if predictions on decomposed litter using spectral data are feasible.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Chemical and physical traits and near-infrared reflectance (NIR) spectra of six alpine freshly fallen litter types were measured. A litterbag experiment (0.1 mm mesh size) with single and 2- and 3-species mixtures was conducted with three species from three functional groups (shrub, grass, forb). Decomposition rates, litter mass loss, non-additive effects, and NIR spectra were recorded after 6, 12, and 24 months.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉The six freshly fallen litter types differed significantly in leaf litter traits and NIR spectra. Decomposition rates steadily slowed during the 24 months, with shrub litter having the lowest on all sampling dates. In litter mixtures, shrub and grass litter showed higher decomposition rates after 12 and 24 months compared with the single-species treatments.〈/p〉 〈/span〉 〈span〉 〈h3〉Discussion〈/h3〉 〈p〉The accelerated decomposition in litter mixtures indicates stimulating interactions between low- and high-quality litter types, most probably mediated by their associated microbiomes. By using NIR spectra, we successfully predicted all initial litter traits, but only total carbon content along the entire decomposition period.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Repeated applications of glyphosate in short timeframes can lead to periodic accumulation of soilborne glyphosate residues. This study aimed to determine whether typical glyphosate residues observed in fields affect growth, plant metabolite composition and fungal root endophyte colonisation of wheat (〈em〉Triticum aestivum〈/em〉).〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Glyphosate was applied to a sandy soil at 0, 0.33, 1, 3, 9 and 27 times a recommended label rate (LR) to establish soil glyphosate concentrations of 0, 0.1, 0.4, 1, 4.7 and 14.8 mg kg〈sup〉〈strong〉−〈/strong〉1〈/sup〉 in topsoil (0–100 mm) after a 28 d plant-free incubation. Wheat plants were then grown to establish thresholds of soilborne glyphosate on seedling emergence, major alterations to plant metabolic responses and fungal root endophyte colonisation.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Seedling emergence was unaffected by soil residual glyphosate treatments. Shoot biomass was significantly higher at 1 mg kg〈sup〉〈strong〉−〈/strong〉1〈/sup〉 compared to the control treatments (〈em〉P〈/em〉 〈 0.05) and root biomass followed a similar trend. Leaf metabolite profiles of plants growing in soil containing 4.7–14.8 mg kg〈sup〉〈strong〉−〈/strong〉1〈/sup〉 glyphosate could be discriminated from the 0–0.4 mg kg〈sup〉〈strong〉−〈/strong〉1〈/sup〉 treatments due to significant (〈em〉P〈/em〉 〈 0.05) effects on the relative concentrations of metabolites. Fungal root endophyte colonisation was significantly reduced to 10% at 14.8 mg kg〈sup〉〈strong〉−〈/strong〉1〈/sup〉 (〈em〉P〈/em〉 〈 0.05) whereas shoot and root biomass remained unaffected.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our study highlights differences in glyphosate sensitivity thresholds between plants and fungal symbionts. Sub-lethal concentrations of residual soilborne glyphosate can alter wheat metabolism and impair fungal root endophyte colonisation. Effect thresholds for glyphosate may be lower for fungal symbionts than for host plants. However, the soil glyphosate residue levels required to reach such thresholds are high and would only be approached in commercial fields with a history of repeated glyphosate application.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉It has been well demonstrated that several interacting endogenous and exogenous factors influence decomposition. However, teasing apart the direct and indirect effects of these factors to predict decomposition patterns in heterogenous landscapes remains a key challenge.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉At 157 locations in a temperate forest, we measured decomposition of a standard substrate (filter paper) over two years, the landscape context in which decomposition took place, and the functional composition of the woody species that contributed leaf litter to the forest floor where litter bags were placed. We tested for direct and indirect effects of landscape context and direct effects of forest functional composition on decay using structural equation modelling.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉We found that landscape context had direct effects on decay and indirect effects on decay via its influence on the functional composition of the surrounding forest. Forest functional composition also had direct effects on decay, but these effects decreased or disappeared completely over time. Moreover, community weighted mean trait values were better predictors of decay than functional dispersion of leaf traits, and leaf nitrogen content and carbon content were better predictors of decay than leaf dry matter content or leaf toughness.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our results highlight the importance of an integrative approach that examines the direct and indirect effects of multiple factors for understanding and predicting decomposition patterns across heterogenous landscapes.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉Roots contribute greatly to carbon cycling in agriculture. Measuring aboveground litter decomposition could approximate belowground turn-over if drivers of decomposition, f.e. litter traits and plant presence, influence shoot and root decomposition in a comparable manner. We tested coordination of above- and belowground litter traits and decomposition rates for six pairs of crops and closely related wild plants and studied the influence of plant presence on decomposition.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Above- and belowground traits were measured, compared and related to decomposition rates. Shoot and root litters were incubated in presence of the same plant species as the litter species (own) or in presence of two other plant species (a grass or forb).〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Shoots decomposed 1.43–1.98 times faster than (resp.) wild plant and crop roots. Decomposition correlated negatively with litter carbon and lignin concentrations, except crop root decomposition which correlated negatively with nitrogen concentration. Unexpectedly, plant presence reduced litter decomposition, with strongest effects for root litters in presence of forbs.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Carbon cycling might be slower than predicted solely based on shoots decomposition rates, especially in presence of growing plants. While root decomposition of wild plants can be approximated by shoot decomposition, crop shoots are a poor proxy for crop root decomposition.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Previous studies showed that the competition-recovery principle is one of the mechanisms underpinning overyielding in wheat/maize intercropping. However, few studies have focused on the effects of root morphological and physiological changes during the recovery growth of late-maturing species. The present study aimed to determine the mechanism underlying the recovery growth in terms of root distribution and nitrogen (N) uptake in response to different N supplies.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉The roots of maize were sampled three times by auger after wheat harvest in the intercropping system with six levels of N application and sole crops at one N-application rate under field condition.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Intercropped maize adjusted its root length density (RLD) and root distribution and enhanced its N absorption per unit root length with increasing soil N concentration. Soil inorganic N concentration had a direct influence on RLD of intercropped maize which was related to shoot N concentration. In addition, maize took up 93% more N per unit root length when intercropped with maize compared with sole cropping.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Our findings show that the recovery growth of late-maturing species involves phenotypic plasticity of maize root architecture, and the enhanced N uptake resulted from extra soil N acquired from the area where wheat was growing before its harvest.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Bark contains a substantial fraction of the nutrients stored in woody biomass, however the degree of functional coordination of bark, wood, and foliar nutrient pools, and its relationship to soil nutrient availability remains poorly understood.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Bark thickness and nitrogen, phosphorus, potassium, calcium, and magnesium concentrations were measured in 23 tree species present in two premontane wet tropical forests in western Panama differing in soil nutrient availability. Bark data were combined with existing wood and leaf data from the same species.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Bark nutrients were positively correlated with leaf and wood nutrients for all elements. The low fertility site had both lower bark nutrient concentrations and thicker bark, driven primarily by species compositional differences between sites, and secondarily by intraspecific variation. Across species, bark nutrient concentration varied 4 to 25 fold, with the highest variation for calcium. Overall, bark accounted for the largest percent of Ca in above-ground biomass nutrient pools (22–82%) and a large fraction of the other nutrients studied (N: 6–53%, P: 5–50%, K: 4–40%, and Mg: 2–35%).〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉Bark represents a substantial, and highly variable, pool of biomass nutrients. The functional role of bark nutrients, the causes and consequences of this variation, and its relation to other bark traits, including bark thickness, deserve further study.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Background and aims〈/h3〉 〈p〉Autotoxicity is a serious problem for continuous cropping of cucumber, it can limit its own growth and that of nearby cucumber plants and decrease yield and quality. Cinnamic acid (CA) derivatives are a class of autotoxins that can mimic autotoxic effects in cucumber.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉We screened an Arabidopsis long hairpin RNA (lhRNA) library under CA-mimicked autotoxicity stress to obtain autotoxicity-resistant mutant lines. The 〈em〉glycerol-3-phosphate 2-O-acyltransferase 6〈/em〉 (〈em〉GPAT6〈/em〉) gene was found to be silenced in one resistant mutant line, and 〈em〉GPAT6〈/em〉 homologous gene in cucumber was cloned and named 〈em〉CuGPAT6.〈/em〉 To test gene function quickly, a new tobacco rattle virus (TRV)-mediated virus-induced gene silencing (VIGS) system was established in cucumber using a special agroinfiltration solution and whole cotyledonary nodes.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉〈em〉Cucumber phytoene desaturase〈/em〉 gene (〈em〉CuPDS〈/em〉) and 〈em〉CuGPAT6〈/em〉 gene were successfully silenced with a newly established tobacco rattle virus (TRV)-mediated virus-induced gene silencing (VIGS) system in cucumber showing photobleaching and decreased 〈em〉CuPDS〈/em〉 expression in leaves; and silencing of 〈em〉CuGPAT6〈/em〉 enhanced the tolerance to the autotoxin stress mimicked by CA in cucumber.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉It indicated that the alleviation of the damage caused by CA treatment was probably through maintaining the integrity of cellular structure, supporting cell vitality and promoting growth in roots, and increasing the integrate chloroplast and thylakoid numbers in leaves, which restored the growth and net photosynthesis rate of CA treated 〈em〉CuGPAT6〈/em〉 silenced plants to the similar level to those of control plants. The results also demonstrated that the newly established TRV mediated VIGS system is functional, rapid, convenient and highly efficient in cucumber.〈/p〉 〈/span〉

Description: 〈h3〉Abstract〈/h3〉 〈span〉 〈h3〉Aims〈/h3〉 〈p〉The contribution of plant mucilage and microbial biofilms in the rhizosphere to the physical behaviour of roots, and therefore on geotechnical performance, is not fully understood. We explore the impact of biopolymers on the ability of fibrous inclusions in soil to resist shear loading, to test the hypothesis that biopolymer-enhanced cohesion will be most significant at shallow depths where frictional effects are less, whilst exploring the response of biopolymer to changes in the moisture regime.〈/p〉 〈/span〉 〈span〉 〈h3〉Methods〈/h3〉 〈p〉Artificial root/biopolymer systems comprising 3D-printed fibres and xanthan gum biopolymer in sand have been tested under direct shear at low vertical normal stress (1–30 kPa). The impact of drying and wetting on the ability of the reinforced sand to resist shear was assessed.〈/p〉 〈/span〉 〈span〉 〈h3〉Results〈/h3〉 〈p〉Fibres combined with fresh biopolymer caused an increase in mobilisable shear stress, which is proportionally more significant at lower normal stress and so shallower depth (up to 30% increase at 1 kPa). Increased shear resistance and sand aggregation were observed with progressive drying. A cyclic shear response was observed over wetting and drying cycles with considerable strengthening after drying, which was enhanced by preceding wetting increasing the biopolymer zone of influence around the fibre.〈/p〉 〈/span〉 〈span〉 〈h3〉Conclusions〈/h3〉 〈p〉The behaviour of this idealised system attests that root-associated biopolymers contribute significantly to the stabilisation of shallow soil by creating bonds between the root and soil grains, but the response is dependent on the soil moisture regime.〈/p〉 〈/span〉