ALBERT

Description: Background and aims Soil amendments are often added to polluted soils to increase phytoremediation efficiency. Here we investigated the potential of a range of organic amendments for phytoextraction of heavy metals in a contaminated sediment. Methods Two experiments compared adsorption and phytoextraction of heavy metals by a Cd-hyperaccumulator Carpobrotus rossii grown in the contaminated sediment amended with six organic amendments. Results The adsorption capacity as measured by Langmuir adsorption maximum followed the order of Cr 〉 Zn 〉 Cu 〉 Cd, and the effect of organic amendments followed the order of chicken manure 〉 cow manure 〉 brown coal 〉 golden wattle biochar 〉 blue gum biochar 〉 radiata pine biochar. The addition of amendments increased the adsorption of heavy metals, with brown coal resulting in the lowest concentrations of water-extractable Cd, Cu and Zn. Two manures resulted in the highest concentrations of these water-extractable heavy metals in the rhizosphere soil of C. rossii. Furthermore, brown coal resulted in higher shoot accumulation of these heavy metals than three wood-derived biochars, whilst the manures generally had the lowest accumulation of Cd and Cu although they increased shoot biomass. Conclusions The addition of brown coal decreased whereas manure addition increased the mobility (water-extractable fraction) of heavy metals in rhizosphere soil. Phytoextraction of Cd and Cu was greater with brown coal than with biochars or manures. Brown coal is suitable for enhancing phytoextraction of these heavy metals because it could increase their accumulation in shoots of C. rossii and decrease the risk of leaching of these heavy metals into groundwater.

Description: Background and aims Cicer canariense has been shown to be a promiscuous legume. The symbiotic characteristics of several C. canariense mesorhizobial genospecies harbouring similar symbiotic genes are studied. Methods Comparative analysis of nodA and nifH gene phylogenies, and characterization of the symbiotic phenotypes on the basis of nodulation and nitrogen fixation was performed. Results Phylogenetic analyses of the nodulation gene nodA was in complete agreement with those previously done on nodC in grouping these mesorhizobia within symbiovar loti. In the nifH phylogeny, however, these strains were resolved into two subgroups named nifH-1 and nifH-2 . Subgroup nifH -1 contained strains from two genospecies and correlates with symbiovar loti, as it clustered with Mesorhizobium reference strains nodulating Lotus corniculatus . In contrast, subgroup nifH -2 contained strains of the other seven genospecies without reference strains and formed a distant branch on its own. Strains combining symbiovar loti genes in any chromosomal background effectively nodulated C. canariense , although with significant differences in nitrogen fixation capabilities. Conclusions Symbiovar loti genes are the most widely spread in the mesorhizobia that nodulate C. canariense in its natural habitat. They included two variants of the nifH gene and were found to be associated with nine chromosomal backgrounds (genospecies), resulting in strains showing different symbiotic effectiveness. Mesorhizobium tamadayense symbiovar loti strains were the most effective in this legume.

Description: Background and Aims Competition between intercropped species is important for yield advantage, but little attention has been given to interspecific competitive dynamics in intercropping. Methods A field experiment with five cropping systems (wheat/maize, barley/maize intercropping, wheat, maize and barley sole cropping), two N levels (0 and 225 kg N ha −1 ) and two maize mulching treatments (with and without) were performed. Sequential harvest of subplots was performed between 7 and 10 times, and the data were fitted to a logistic growth model. Results Intercropping significantly increased the maximum biomass and maximum growth rates of wheat and barley, but suppressed the early and maximum growth rate of intercropped maize. Maize growth recovered after the wheat or barley was harvested. In the presence of film mulch and/or fertilization, maximum biomass of intercropped maize was close to or significantly higher than that of maize alone. Fertilization and film mulching had much stronger effects on growth of maize than on wheat and barley. Conclusions Interspecific competitive dynamics regulated by fertilization and film mulching can be quantified by the logistic model, which is helpful to understand the yield advantage of intercropping. This has important implications for managing interspecific competition through agronomic practices at field.

Description: Background and aims Take-all, caused by the soilborne pathogen Gaeumannomyces graminis var. tritici , ( Ggt ), is an important root disease of wheat. Continuous wheat cropping has been shown to induce take-all decline (TAD). This research investigated the mechanisms of TAD in 13 New Zealand soils in two experiments and identified the associated microorganisms using denaturing gradient gel electrophoresis (DGGE). Methods In Experiment 1, a sterile sand/maize-meal mixture inoculated or not inoculated with Ggt , was added at 4 % ( w / w ) to sterilised and non-sterilised soils to determine their ability to suppress take-all, and to help identify the nature of suppression. Experiment 2 investigated the transferability of suppressive properties in five of the soils from Experiment 1. The microbial communities of these five soils were analysed using PCR-DGGE. Results Ten of the soils were able to suppress take-all but the suppression was biological in nature in only four of these soils. The suppressive properties of two of the soils were transferred to a γ-irradiated base soil amended with Ggt , indicating that suppression could be specific in nature (i.e., attributed to a specific microorganism or group of microorganisms). The suppressive properties in one soil were not transferrable, suggesting a general form of suppression, most probably because the conditions in the soil were suitable for other microorganisms to compete with Ggt . DGGE analyses of the microbial communities for five of the soils showed similar banding patterns for those with similar forms of suppression (specific, general and non-suppressive) and identified the potential microorganisms that distinguished them. Conclusion These distinguishing microorganisms are likely to independently or interactively have a function in suppressing take-all.

Description: Aims To determine the impact of long-term rabbit and sheep grazing on Salix repens N status (green and abscised leaf N content and C:N ratio), internal N dynamics and soil N supply rate in dune slacks. Methods Herbivore exclosures were erected in dune slacks at Ainsdale Sand Dunes NNR, creating three grazing treatments: rabbit grazing; rabbits excluded for 36 years; rabbit grazing followed by sheep and rabbit grazing for 18 years. Soil N supply rate was analysed using ion exchange membranes; leaf N dynamics of S. repens were measured over one summer. Results Soil N supply rate was higher in ungrazed plots. There was no difference in green leaf N MASS or C:N ratio between treatments, but N dynamics differed. Adding sheep to existing rabbit grazing reduced S. repens N resorption efficiency (R EFF ) from 67 to 37 %; excluding rabbits had no impact. Litter N MASS was lower and C:N ratio higher in ungrazed plots. Conclusions Grazing can impact significantly on leaf N resorption, but this impact depends on the grazing regime.

Description: Aims Maize ( Zea mays L.) is one of the most important crops worldwide. Despite several studies on maize roots, there is limited information on the function of different root types in extracting water from soils. Aim of this study was to investigate the location of water uptake in maize roots. Methods We used neutron radiography to image the spatial distribution of maize roots in soil and trace the transport of deuterated water (D 2 O) in soil and roots. Maize plants were grown in aluminum containers filled with a sandy soil that was kept homogeneously wet throughout the experiment. When the plants were 16 days old, we injected D 2 O into selected soil regions. The transport of D 2 O was simulated using a diffusion–convection numerical model. By fitting the observed D 2 O transport we quantified the diffusion coefficient and the water uptake of the different root segments. Results The root architecture of a 16 day-old maize consisted of a primary root, 4–5 seminal roots and many lateral roots. Laterals emerged from the proximal 15 cm of the primary and seminal roots. During both day and night measurements, D 2 O entered more quickly into lateral roots than into primary and seminal roots. The quick transport of D 2 O into laterals was caused by the small radius of lateral roots. The diffusion coefficient of lateral roots (4.68 × 10 −7  cm 2  s −1 ) was similar to that of the distal unbranched segments of seminal roots (4.72 × 10 −7  cm 2  s −1 ) and higher than that of the proximal branched segments (1.42 × 10 −7  cm 2  s −1 ). Water uptake of lateral roots (1.64 × 10 −5  cm s −1 ) was much higher than the uptake of seminal roots, which was 5.34 × 10 −10  cm s −1 in the proximal branched segments and only 1.18 × 10 −12  cm s −1 in the distal unbranched segments. Conclusions We conclude that the function of lateral roots is to absorb water from the soil, while the function of the primary and seminal roots is to axially transport water to the shoot.

Description: Aims Kin selection and resource partitioning have been proposed to explain interactions between plants growing with siblings (from the same mother). These mechanisms have been examined by measurements of fitness, phenotype or allocation traits, but have seldom been tested with N acquisition traits. Methods We determine if kin selection and resource partitioning are occurring using two annual species ( Sorghum vulgare and Glycine max ) with a short-term 15 N experiment. A mixture of ammonium, nitrate and glycine (1:1:1) was injected into soils around plants after they grew for 47 days. Only one nitrogen (N) form was 15 N labeled in each labeling solution. Results S. vulgare increased root allocation when growing with strangers (from the different mother), but not increase their N uptake. Although G. max strangers did not increase their root allocation, they significantly increased uptake of total N and the most abundant N form (nitrate) and decreased uptake of the least abundant (glycine). Conclusions G. max siblings reduced competition due to chemical resource partitioning while S. vulgare showed kin selection. We concluded that processes related to kin selection and resource partitioning can occur simultaneously, resulting in different competitive ability. These findings can improve our understanding of plants growing with siblings or strangers.

Description: Aims The aim was to devise a practical soil sampling design for oil palm plantations that takes into account tree-scale variability, thus facilitating detection of trends in soil properties over time. Methods We geometrically evaluated the ability of linear sampling transects to represent the distribution of typical management zones and radial patterns known to influence soil properties. The effect of sampling point density was tested using interpolated surfaces of soil biological, chemical and physical properties derived from values measured on a 35-point sampling grid covering the repeating tree unit in plantations with 15–25-year old palms. Results The ability of sampling transects to represent the proportion of the plantation in various zones improved with increasing transect length and sampling density. Increasing the number of sampling points from 10 to 50 (using an acceptably long transect with length 5.57 × palm spacing) decreased the maximum deviation between the overall mean and the transect-derived mean from 15.9 to 5.6 % for the most variable parameter, respiration, and 3.2 to 0.6 % for the least variable parameter, bulk density. Conclusions Transect sampling provides an efficient means of obtaining a composite soil sample that accounts for tree-scale variability in oil palm plantations. The method is readily adaptable for other tree crops.

Description: Background Botanists, ecologists and evolutionary biologists are familiar with the astonishing species richness and endemism of the fynbos of the Cape Floristic Region and the ancient and unique flora of the kwongkan of south-western Australia. These regions represent old climatically-buffered infertile landscapes (OCBILs) that are the basis of a general hypothesis to explain their richness and endemism. However, few ecologists are familiar with the campo rupestre of central and eastern Brazil, an extremely old mountaintop ecosystem that is both a museum of ancient lineages and a cradle of continuing diversification of endemic lineages. Scope Diversification of some lineages of campo rupestre pre-dates diversification of lowland cerrado , suggesting it may be the most ancient open vegetation in eastern South America. This vegetation comprises more than 5000 plant species, nearly 15 % of Brazil’s plant diversity, in an area corresponding to 0.78 % of its surface. Reviewing empirical data, we scrutinise five predictions of the OCBIL theory, and show that campo rupestre is fully comparable to and remarkably convergent with both fynbos and kwongkan , and fulfills the criteria for a classic OCBIL. Conclusions The increasing threats to campo rupestre are compromising ecosystem services and we argue for the implementation of more effective conservation and restoration strategies.

Description: Aims The colonization pattern of three grapevine endophytes (families Sphingomonadaceae and Enterobacteriaceae) and their putative metabolic signature in plants were analyzed on Vitis vinifera L. cv. Pinot noir to determine the behavior of endophytic strains inside plants as well as how plants respond to such microsymbionts. Methods Strains Enterobacter ludwigii EnVs6, Pantoea vagans PaVv7 and Sphingomonas phyllosphaerae SpVs6, were root inoculated on micropropagated grapevine plantlets and colonization was determined by double labeling of oligonucleotide probes-fluorescence in situ hybridization (DOPE-FISH) coupled with confocal microscopy. After inoculation, the metabolic signature in plants colonized by Enterobacter ludwigii EnVs6 was further studied using UPLC//tandem mass spectrometry analysis. Results E. ludwigii EnVs6 and P. vagans PaVv7 colonized the plantlets and were both observed on the root surfaces and as endophytes in the cortex and inside the central cylinder up to xylem vessels, but not in the systemic plant parts. Strain SpVs6 also efficiently colonized the root surface, but not the endorhiza and was therefore not detected as an endophyte. A metabolic signature in plants inoculated with E. ludwigii EnVs6 was depicted, resulting in a significant increase in vanillic acid and a decrease in the concentration of catechin, esculin, arbutin, astringin, pallidol, ampelopsin, D-quadrangularin and isohopeaphenol. Changes in the concentration of epicatechin, procyanidin 1, taxifolin and the sum of quercetin-3-glucoside and quercetin-3-galactoside, in roots and stems were also detected, showing that the effect of colonization of plants is most prominent in the stems. Conclusions Colonization patterns in endophytes are divergent according to the strains used. A metabolic signature suggests the activation of pathways involved in plant defense but also modulation of the production of metabolites that are keys for colonization.

Description: Background We hypothesize that invasive English ivy ( Hedera helix ) harbors endophytic microbes that promote plant growth and survival. To evaluate this hypothesis, we examined endophytic bacteria in English ivy and evaluated effects on the host plant. Methods Endophytic bacteria were isolated from multiple populations of English ivy in New Brunswick, NJ. Bacteria were identified as a single species Bacillus amyloliquefaciens . One strain of B. amyloliquefaciens , strain C6c, was characterized for indoleacetic acid (IAA) production, secretion of hydrolytic enzymes, phosphate solubilization, and antibiosis against pathogens. PCR was used to amplify lipopeptide genes and their secretion into culture media was detected by MALDI-TOF mass spectrometry. Capability to promote growth of English ivy was evaluated in greenhouse experiments. The capacity of C6c to protect plants from disease was evaluated by exposing B+ (bacterium inoculated) and B− (non-inoculated) plants to the necrotrophic pathogen Alternaria tenuissima . Results B. amyloliquefaciens C6c systemically colonized leaves, petioles, and seeds of English ivy. C6c synthesized IAA and inhibited plant pathogens. MALDI-TOF mass spectrometry analysis revealed secretion of antifungal lipopeptides surfactin, iturin, bacillomycin, and fengycin. C6c promoted the growth of English ivy in low and high soil nitrogen conditions. This endophytic bacterium efficiently controlled disease caused by Alternaria tenuissima . Conclusions This study suggests that B. amyloliquefaciens plays an important role in enhancing growth and disease protection of English ivy.

Description: Background and aims Alkaline soils, characterized by high pH, are representative of degraded regions throughout the world. Studying germination in relation to alkalinity can contribute to understanding how species cope with such conditions. Although the effects of pH have been widely studied, it is unknown whether germination response to pH gradients created with buffer solutions is representative of the conditions experienced in alkaline soils. Our aims were to (1) determine if high pH gives an accurate assessment of the effects of alkaline soils on germination, and (2) identify the inhibitory factors for germination in alkaline soils. Methods Using Leymus chinensis seeds, germination was tested over a gradient of pH solutions prepared using Tris (50 mM and 100 mM) and H 2 O buffers and eight germination media prepared from non-alkaline and alkaline soils with different pH and electrical conductivities (EC). Additionally, solutions of 10–100 mM NaCl, Na 2 SO 4 , Na 2 CO 3 and NaHCO 3 were used to determine the main ions inhibiting seed germination. Results H 2 O-buffered pH had no effect on seed germination, and seed germination was much lower at all pH levels in 50 mM Tris–HCl solutions (pH 7.0–10.35) than in the H 2 O control (pH 7.05). No seeds germinated in 100 mM Tris–HCl buffers irrespective of the pH. In alkaline germination media (pH 10.04–10.61), high germination was obtained only at low EC. The rank order of the inhibitory effect of salts was Na 2 CO 3  〉 NaHCO 3  〉 NaCl 〉 Na 2 SO 4 . Conclusions Buffer solutions used to simulate alkaline environments did not provide a reliable indicator of the effects of alkaline soils on seed germination. High pH of alkaline soil had no negative effects, and results suggest that salt composition and concentration, especially CO 3 2− and HCO 3 − , are key inhibitors.

Description: Background and aims Exotic plant species experience conditions in their introduced ranges that differ from those in their native range. Exotic plants may experience genetic changes in traits related to resource use, abiotic stress tolerance, and biotic interactions in response to such novel biotic and abiotic environments. Methods We conducted a pot experiment in the native range to investigate how soil fertility, soil salinity and soil sterilization together determine the performances of native (China) and invasive (US) populations of the tree Triadica sebifera . Results Salinity decreased plant growth, and increased AMF colonization and root:shoot. Fertilization or an unsterilized soil biota reduced the negative effects of salinity on plant survival. Fertilization decreased AMFcolonization and root:shoot ratio. Biomass was positively related to AMF colonization in unfertilized soils only. Seedlings from invasive populations grew faster and had higher AMF colonization. Conclusions Our results suggest that this invasive plant is able to persist in more saline environments when soil fertility is high or suitable AMF is present. The importance of the soil biota appears to be greater on low fertility soils where AMF provides significant benefits. The greater AMF association of plants from invasive populations suggests that resources, abiotic stress, and biotic interactions all may play a role in successful plant invasions.

Description: Background and aims Niche complementarity arising from divergence in resource use is an important mechanism underlying species coexistence. We hypothesized fertilization with different N forms would generate plastic divergence among species with regard to their N form uptake and preference. Methods In the eighth year of a long-term N fertilization experiment in an alpine meadow on the Tibetan plateau, we labeled 11 common plant species with ammonium- 15 N or nitate- 15 N in subplots without fertilization (control) or fertilized with 7.5 g N m −2  yr −1 in the form of ammonium, nitrate, or ammonium nitrate to trace N form uptake. Results Depending on species, fertilization with nitrate or ammonium nitrate had positive, negative or neutral effects on NO 3 -N uptake rate, although ammonium fertilization showed little impact. By contrast, fertilization with any N form had little impact on NH 4 -N uptake rate. Consequently, effects of nitrate fertilization and ammonium nitrate fertilization on relative N form preference diverged among the species and the functional groups (grasses, sedges, legumes and forbs). Conclusions Alpine plant species can diverge in N form uptake and preference in response to long-term N fertilization, and such divergence may contribute to species coexistence after long-term fertilization.

Description: Aims Stomata can close to avoid cavitation under decreased soil water availability. This closure can be triggered by hydraulic (‘H’) and/or chemical signals (‘C’, ‘H + C’). By combining plant hydraulic relations with a model for stomatal conductance, including chemical signalling, our aim was to derive direct relations that link soil water availability, expressed as fraction of roots in dry soil (f dry ), to transpiration reduction. Methods We used the mechanistic soil-root water flow model R-SWMS to verify this relation. Virtual split root experiments were simulated, comparing horizontal and vertical splits with varying f dry and different strengths of stomatal regulation by chemical and hydraulic signals. Results Transpiration reduction predicted by the direct relations was in good agreement with numerical simulations. For small enough potential transpiration and large enough root hydraulic conductivity and stomatal sensitivity to chemical signalling isohydric plant behaviour originates from H + C control whereas anisohydric behaviour emerges from C control. For C control the relation between transpiration reduction and f dry becomes independent of transpiration rate whereas H + C control results in stronger reduction for higher transpiration rates. Conclusion Direct relations that link effective soil water potential and leaf water potential can describe different stomatal control resulting in contrasting behaviour.

Description: Background and Aims Interspecific differences have been clearly shown in the contribution of endogenous spatial autocorrelation (caused by dispersal) to the spatial structure of undisturbed vegetation. However, this phenomenon has not been studied in industrially polluted areas, where heavy metals’ excess is traditionally considered to be the main driver of ecosystem processes. We compare the contributions of endogenous autocorrelation and environmental parameters to the distribution of herbaceous plants in open and forested sites heavily polluted with copper smelter emissions. Methods Principal coordinates of neighbour matrices were used to create spatial predictors that were incorporated into beta regression models together with environmental predictors. Their importance for species’ spatial structure was assessed using multimodel inference and variation partitioning approach. Results Equisetum sylvaticum, Leucanthemum vulgare, Tussilago farfara, Carex rostrata, Scirpus sylvaticus and Deschampsia cespitosa responded strongly to soil toxicity, while Agrostis capillaris and Lychnis flos-cuculi , to microtopography and tree disposition. Endogenous autocorrelation was strongly pronounced in L. flos-cuculi distribution across all study sites and was substantial for A. capillaris in open areas. Conclusion Despite the extreme level of soil toxicity, the importance of other environmental parameters and endogenous autocorrelation remarkably differed among species, resulting from interspecific differences in ecological preferences and dispersal mode.

Description: Background and aims Acid leached soils developed on loessic materials in Central Belgium present homogenous edaphic characteristics and similar patterns of strontium isotopic composition ( 87 Sr/ 86 Sr), used as tracer of the origin of calcium. This was inconsistent with the large range of 87 Sr/ 86 Sr ratios measured in leaves from beech stands developed on the sites. We hypothesised that the deep carbonate-bearing horizon (〉2.5 m) with low 87 Sr/ 86 Sr ratio, could be a complementary source of Ca for tree nutrition. Methods We studied the change in foliar Sr isotopic composition and element concentrations in 12 forest sites along a soil sequence. This soil sequence was selected to include the largest range of variations in the depth at which the calcareous loess horizon occurs. In complement, root depth development was determined in six sites down to 300 cm. Results Our results reveal that Sr originating from deep carbonate influences significantly the isotopic composition of beech trees growing on loessic soils. This influence contributes from 20 to 80 % to the Ca nutrition of trees depending on their position along the soil sequence. Conclusions Despite its deep location in the soil profile, the carbonate-bearing horizon is determinant for the nutrient status of these forests.

Description: Aims Plant root traits affect soil biopore (BP) formation. Aims of this study were to measure the effects of fodder crop species with contrasting root traits and duration of cropping on BP density (BPD), and also to address the consistency of these effects over different years focusing on the effects of root decay. Methods Soil BPD was quantified after growing three perennial fodder crop species with contrasting root systems, namely, lucerne ( Medicago sativa L.), chicory ( Cichorium intybus L.) and tall fescue ( Festuca arundinacea Schreb.) for 1, 2, and 3 years with 2 years fallow in two repeated field trials from 2007 to 2014. Results Total BPD after taprooted fodder crops (421 ± 14 m −1 ) was significantly higher compared with fibrous-rooted crops (337 ± 12 m −1 ). Cropping duration did not affect soil BPD. On average, density of medium-sized BP (BP med ; 2–5 mm) increased 14 % after 2 years of fallow, whereas BPD decreased by 5 % for coarse-sized BP (BP cor ; 〉5 mm) after the fallow. Conclusions Taprooted fodder crops enhanced BP formation into subsoil. Accurate assessment of biopores (BPs) and their persistence must take account of the temporal dynamics, including effects of root decay.

Description: Background and aims Plant adaptation to waterlogged conditions requires a set of morphological and physiological/biochemical changes. The formation of aerenchyma is one of the most crucial adaptive traits for waterlogging tolerance. Enzymatic scavenging may also potentially contribute to waterlogging tolerance by providing detoxification of reactive oxygen species (ROS). Methods Changes of root porosity (as an indicator of aerenchyma formation) and activities in leaves of four major antioxidant enzymes, γ-amino butyric acid (GABA) and lactic acid contents in roots were evaluated in six barley genotypes contrasting in waterlogging tolerance. Results Soil waterlogging caused significant increases in adventitious root porosity in all genotypes. Waterlogging-tolerant genotypes showed not only significantly higher adventitious root porosity than sensitive genotypes but also much faster development of aerenchyma. The greatest difference in adventitious root porosity among genotypes was observed after 7 days of waterlogging treatment. At the same time, antioxidant enzyme activities in leaves, GABA and lactic acid contents in roots did not correlate with waterlogging tolerance. Conclusions A faster formation of aerenchyma in adventitious roots is one of the key factors for waterlogging tolerance in barley. This protocol is recommended to be applied in future studies to identify molecular markers linked to this trait using appropriate mapping populations.

Description: Aims Wildfires are important disturbances that help to shape the structure and function of forest ecosystems, and arbuscular mycorrhizal fungi (AMF) are key players in the post-fire recovery of soils and understory vegetation. We aimed to investigate the response of AMF communities to wildfire over different timescales. Methods Primer set AMV4.5NF/AMDGR was used to amplify soil 18S rRNA gene fragments for the 454 GS-FLX pyrosequencing platform to examine belowground AMF communities 1 and 11 years following low- and high-intensity wildfires in the Greater Khingan Mountains of China. Results The majority of AMF sequences detected were annotated as Glomeraceae , Claroideoglomeraceae , Diversisporaceae and Acaulosporaceae . Both AMF community composition and alpha-diversity were correlated with herbaceous and shrubby biomass, available phosphorus (AP) and NH 4 + , which were in turn altered by wildfire. AMF community composition, alpha-diversity, and phylogenetic structure were significantly altered 1-year-post-fire. However, AMF communities were indistinguishable from unburned forest soils 11-year-post-fire. Conclusions Our results indicated that AMF communities are resilient to wildfire on decadal timescales. This resilience appears to depend on the post-fire regrowth of understory vegetation and the subsequent recovery of soil chemical properties.

Description: Aims We investigated N 2 O emissions from stems of Fraxinus angustifolia and Fagus sylvatica , hypothesizing that trees emit N 2 O through the stem via diffusion out of the transpiration stream. Methods We used static chambers fixed at different heights of the stem to estimate N 2 O stem effluxes. Chambers were also used for monitoring soil N 2 O emissions. To stimulate soil N 2 O production and stem N 2 O emissions we fertilized the soil. Results Before soil fertilization, stem N 2 O emissions were at most 2 μg N 2 O-N m −2 bark h −1 . After fertilization, stem and soil emissions were linearly correlated; stem emissions decreased linearly with increasing height. Stems of Fagus sylvatica emitted up to 80 μg N 2 O-N m −2 bark h −1 at 20 cm above soil level; at 200 cm, stem N 2 O emissions were below detection limit. Fraxinus angustifolia stem N 2 O emissions reached 35 μg N 2 O-N m −2 bark h −1 after soil fertilization. Conclusions Stem N 2 O emissions in upland trees occur even without aerenchyma, associated with xylem water transport. However, stem N 2 O emissions represented only 1–3 % of total (soil + stem) N 2 O emissions at the forest level. If this holds for other forest ecosystems, stem N 2 O emissions would be a minor pathway of N 2 O loss from terrestrial ecosystems into the atmosphere.

Description: Background and Aims Epichloë endophytes inhabit aerial grass tissues but they can modify belowground processes that might affect host nutrient balance. We aimed to determine the effects of endophyte status (E+=endophyte-infected; E−=non-infected) and three Epichloë morphotypes (M1,M2,M3) on growth and nutrient content of a heterogeneous set of naturally infected asymptomatic plants of Lolium perenne . In addition, plant parameters were compared between asymptomatic E+ and plants with choke disease. Methods A field experiment was conducted with 194 plants obtained from six natural populations (97E+, 97E−). For each E+ plant, the endophyte morphotype it hosted was known. Results Endophyte-infected plants had significantly lower P, Ca, S, B, neutral detergent fiber and lignin contents, and higher Mn and digestibility than E−, independently of plant origin. Biomass production was affected by plant origin but not by endophytes. No effect of Epichloë morphotypes in any parameter was found. However, asymptomatic E+ and choke diseased plants differed in nutrients, fibers, and digestibility. Conclusions An endophyte effect was detected in nutrient and fiber content, in spite of the heterogeneous constitution of the plant and fungal material used. The results obtained indicate that Epichloë may affect above and possibly underground processes involved in nutrient absorption, as well as plant quality, what may potentially affect litter decomposition processes.

Description: Background and aims There is evidence that plant facilitation occurs in heavy metal wastelands, but the extent and mechanisms of facilitation are not known. The copper (Cu) tolerant Elsholtzia splendens is a dominant pioneer species during the secondary succession on copper mine spoils in eastern China. Species appearing later are often associated with patches of E. splendens . We hypothesize that E. splendens facilitates neighbors by modifying local soil properties. Methods We conducted a field study on a heavy metal wasteland with local variation in soil Cu level to investigate the performance of a target species, Commelina communis , growing in open gaps vs. growing with E. splendens . Soil physicochemical and biological properties, biomass, plant interaction intensity as well as heavy metal concentration in C. communis were measured to study the effects of the presence of E. splendens . Results Effects of the presence of E. splendens on C. communis were generally positive, but negative effects were sometimes observed. Positive effects of E. splendens increased with increasing soil Cu level. Soil microbial activity was higher in the presence of E. splendens . Our results are consistent with the hypothesis that facilitation occurred through enrichment of the microbial properties of the soil, especially soil respiration rate and enzyme activity. Conclusions Our study highlights the importance of soil-mediated plant-plant interactions for the establishment of C. communis on heavy metal-contaminated sites. These interactions are important for the restoration of heavy metal wastelands.

Description: Background and aims Within the last decades, considerable knowledge has been gained on the impacts of carbonaceous soil additives such as hydrochar (or HTC) and biochar (or pyrochar) on plant growth and various soil properties. However, still little is known about the effects of hydrochar and biochar on soil microorganisms, especially from field studies. Microorganisms are closely linked to nutrient dynamics in soil and therefore are tightly linked to soil fertility. As a consequence, possible changes in the microbial community structure due to HTC/biochar soil application may lead to considerable changes in soil nutrient dynamics. Methods To gain insights into HTC/biochar associated long-term effects on microorganisms, soil samples were taken from a grassland field study 2.6 years (31 months) after its initiation (April 2011), where Miscanthus × giganteus feedstock, HTC and biochar, each mixed with pig slurry had been applied as top-dressing in a randomized block design, next to a slurry-only control ( n  = 4, 16 plots). The samples were analyzed for microbial activity and biomass by substrate induced respiration (SIR). Bacterial and fungal fractions in soil microbial biomass (SMB) were determined using the inhibitors streptomycin and cycloheximide respectively. Results Total SMB in biochar-amended soils was significantly higher compared to all other treatments; fungal biomass was significantly higher compared to feedstock and control treatments. The percentage of bacterial biomass was higher in the feedstock and HTC amended soil, as compared to the control. Additionally, HTC exhibited a significantly higher percentage of fungal biomass compared to the feedstock treatment, indicating a microbial community shift. Conclusion While the uncarbonized feedstock material depleted both total SMB and especially fungi, HTC and biochar did not trigger any adverse long-term effects on SMB. Rather, the observed biochar-induced stimulation of SMB may improve soil aggregation and increase the soil organic carbon content in the long term.

Description: Aims Root angles are widely recognized to play an important role in determining rooting depth and drought tolerance in crop plants. But there has been no report revealing any association between root angle and yield performance under drought conditions in maize. There is also no simple method available to screen root angles. The objectives of this study were to evaluate genetic variation in seminal and nodal root angles in maize in greenhouse condition and their association with drought tolerance in field condition. Methods Eighteen hybrids, of which nine were higher-yielding and nine were lower-yielding under water-stressed condition in field, were evaluated for root angle variation. Root angle was estimated as the distance between the horizontal soil surface line and slope of the root at 2 cm position from root base using a protractor. Results Significant phenotypic variation was observed among hybrids for seminal and nodal root angles and primary root diameter. These root traits showed strong positive correlations with grain yield under drought condition. All the higher-yielding hybrids had steeper root growth angle than the lower-yielding hybrids. A strong correlation between seminal and nodal root angles was observed. A strong correlation was also observed between 5th and 4th node nodal root angles. Conclusion Either seminal or nodal root angle could be used for selection for the improvement drought tolerance. The current screening system for root angle is simple and inexpensive, and could be used for screening a large number of genotypes.

Description: Background and aims We investigated the effects of silicon (Si) on chlorophyll concentration, photosynthesis, leaf chloroplast ultrastructure, and expression of genes involved in photosynthesis to elucidate the mechanisms through which Si mediated alleviation of manganese (Mn) toxicity in rice ( Oryza sativa L.). Methods Rice seedlings were grown hydroponically with normal Mn (6.7 μM) or high Mn (2 mM) concentrations, both with (1.5 mM) and without Si supplementation. Leaf chloroplast ultrastructure was observed by scanning and transmission electron microscopy. Differentially expressed genes relating to photosynthesis were identified by high-throughput sequencing, and their relative expression levels were evaluated by real-time quantitative PCR. Results Chlorophyll and carotenoid concentrations and net photosynthesis decreased with chloroplast degradation under high Mn stress. High Mn concentrations may have inhibited photosynthesis through several mechanisms, including suppressing chlorophyll and ATP synthesis, decreasing light-harvesting processes, impairing photosystem I (PSI) stability and structure, and slowing activity of phosphoribulokinase. Si enhanced Mn tolerance efficiently by increasing chlorophyll concentration, light-use efficiency, and ATP concentration as well as by stabilizing the structure of PSI and promoting CO 2 assimilation. Conclusions Our findings suggest active involvement of Si in Mn detoxification, ranging from physiological responses to gene expression.

Description: Background and aims The importance of the uptake of nitrogen in organic form by plants and mycorrhizal fungi has been demonstrated in various ecosystems including temperate forests. However, in previous experiments, isotopically labeled amino acids were often added to soils in concentrations that may be higher than those normally available to roots and mycorrhizal hyphae in situ, and these high concentrations could contribute to exaggerated uptake. Methods We used an experimental approach in which we added 13 C-labeled and 15 N-labeled whole cells to root-ingrowth cores, allowing proteolytic enzymes to release labeled organic nitrogen at a natural rate, as roots and their associated mycorrhizal fungi grew into the cores. We employed this method in four forest types representing a gradient of soil pH, nitrogen mineralization rate, and mycorrhizal type. Results Intact uptake of organic nitrogen was detected in mycorrhizal roots, and accounted for at least of 1–14 % of labeled nitrogen uptake. Forest types did not differ significantly in the importance of organic uptake. Conclusions The estimates of organic N uptake made here using 13 C-labeled and 15 N-labeled whole cells are less than those reported in other temperate forest studies using isotopically labelled amino acids, and likely represent a minimum estimate of organic N-use. The two approaches each have different assumptions, and when used in tandem should complement one another and provide upper and lower bounds of organic N use by plants.

Description: Aim To investigate how the chemical composition of native organic matter of two contrasting soils varies with inputs of biochar and fresh material (including plant roots) and how these underlying changes influence microbial community structure. Methods Corn stover (CS) and CS-derived biochars produced at 350 °C and 550 °C were applied at a dose of 7.2 t C ha −1 to two contrasting soils—an Alfisol and an Andisol. After 295 days of incubation, two undisturbed subsamples from each pot were taken: (i) in one, lucerne ( Medicago sativa L.) was seeded (plant study, P) and (ii) in the other, the incubation was continued without the plants (respiration study, R); all subsamples were incubated for an additional 215 days. Soils without amendments were used as controls. At the end of the incubation (510 days), their bacterial community profiles were characterised using ARISA and the molecular composition of soil organic matter (SOM) was investigated by pyrolysis-GC/MS. Results There were significant interactions between soil type, study type (P or R) and organic amendment. Organic amendments influenced overall SOM composition with microbial community response being mainly influenced by soil type but also strongly affected by the presence or absence of plants. For a specific soil type, ≥ 40 % of total variation in bacterial community ordination could be explained by the molecular composition of SOM. Conclusions The molecular composition of SOM is proposed as an important factor influencing the microbial response to organic amendments, including biochar.

Description: Background and aims The Karoo biomes of South Africa are major feed resources for livestock farming, yet soil nutrient depletion and degradation is a major problem. The objective of this study was to assess impacts of long-term (〉75 years) grazing during spring (SPG), summer (SUG), winter (WG) and exclosure (non-grazed control) treatments on soil nutrients, penetration resistance and infiltration tests. Methods A soil sampling campaign was carried out to collect soil to a depth of 60 cm to analyse bulk density, soil physical and chemical parameters as well as soil compaction and infiltration. Results Generally, grazing treatments reduced soil organic C (SOC) stocks and C:N ratios, and modified soil properties. There was higher SOC stock (0.128 Mg ha −1  yr −1 ) in the exclosure than in the SPG (0.096 Mg ha −1  yr −1 ), SUG (0.099 Mg ha −1  yr −1 ) and WG (0.105 Mg ha −1  yr −1 ). The C:N ratios exhibited similar pattern to that of C. From the grazing treatments, the WG demonstrated 7 to 10 % additional SOC stock over the SPG and SUG, respectively. Conclusions Short period animal exclusion could be an option to be considered to improve plant nutrients in sandy soils of South Africa. However, this may require a policy environment which supports stock exclusion from such areas vulnerable to land degradation, nutrient and C losses by grazing-induced vegetation and landscape changes.

Description: Aims Theoretical and observational studies have suggested that environmental variations would change compositional similarity between plant communities. However, this topic has rarely been examined via experiments involving direct manipulation of resources utilized by plant communities. Methods A 9-year field manipulation experiment was conducted to examine the effects of nitrogen addition and increased water on community similarity between a steppe and an old field in the semiarid region of northern China. Results Over the experimental period, nitrogen addition reduced community similarity between the steppe and the old field, whereas water addition enhanced community similarity. These treatment effects were closely related to changes in diversity characteristics as well as abundance of functional groups and dominant species of plant communities. Conclusions These results highlight the importance of resource availability in regulating the trajectory of ecosystem succession, and suggest that the increase in atmospheric nitrogen deposition in northern China will contribute to divergence between the steppe and the old field, whereas the increase in growing-season precipitation may encourage convergence between the two grasslands with respect to species composition during succession. Thus the decrease in community similarity caused by nitrogen enrichment may be counteracted, at least partially, by precipitation increase under changing atmosphere and climate.

Description: Background and Aims The Canterbury Plains of the South Island, New Zealand are being converted to intensive dairy farming; native vegetation now occupies 〈 0.5 % of the area. Reintroducing native species into nutrient-rich systems could provide economic, environmental and ecological benefits. However, native species are adapted to low nitrogen (N) environments. We aimed to determine the growth and N-uptake response of selected native species to elevated soil N loadings and elucidate the effect of these plants on the N speciation in soil. Methods Plant growth, N-uptake, and N speciation in rhizosphere soil of selected native species and Lolium perenne (ryegrass, as reference) were measured in greenhouse and field trials. Results At restoration sites, several native species had similar foliar N concentrations to ryegrass. Deciduous (and N-fixing) species had highest concentrations. There was significant inter-species variation in soil mineral N concentrations in native plant rhizospheres, differing substantially to the ryegrass root-zone. Pot trials revealed that native species tolerated high N-loadings, although there was a negligible growth response. Among the native plants, monocot species assimilated most N. However, total N assimilation by ryegrass would exceed native species at field productivity rates. Conclusions Selected native plant species could contribute to the sustainable management of N in intensive agricultural landscapes.

Description: Aims Belowground plant biomass accumulation is facilitated by the photosynthetic capacity of the canopy. We investigated the hypothesis that a precise monitoring of leaf area development provides the potential to extrapolate to belowground biomass development and to assess the timing and the degree of an inhibition of the belowground biomass generation. Sugar beet seedlings and the retarding effect of beet cyst nematodes (BCN) were used as a model system. Methods Thirty BCN infested plants and 30 non-infested plants were grown in three litre pots under greenhouse conditions. Top-view images of the plant leaf canopy were taken every two or three days. Leaf and beet biomass were measured at three different dates (32, 41 and 70 days after sowing (das)) by harvesting the plants. Results Leaf dry weight and beet fresh weight were strongly correlated 32 and 41 das. The canopy area calculated was highly correlated with both leaf and beet biomass at 32 and 41 das, and was significantly reduced in the nematode infested plants from 22 to 60 das. Conclusions Our results show the ability of canopy-imaging based approaches to evaluate plant biomass during the early developmental stages and to detect a delay in plant development caused by a below-ground stress such as nematodes.

Description: Backgrounds and aims Scotch broom is an N-fixing invasive species that has high potential to alter soil properties. We compared soil from areas of Scotch broom invasion with nearby areas that had no evidence of invasion to assess the influence of broom on soil P fractions and other chemical properties. Methods The study was conducted at two contrasting Douglas-fir sites in Oregon (OR) and Washington (WA), USA with broom invasion for 10 years. We used the Hedley sequential fractionation procedure to assess effects of Scotch broom invasion on P pools of varying bioavailability, and also measured total C, N and extractable nutrient cations. Results Total soil C and N were significantly higher with broom present at the fine-textured OR site, but there was no effect at the coarse-textured WA site. There was no difference in labile-P measures between the presence and absence of Scotch broom at either site, but there were notable reductions (25–30 %) in the intermediately-available P fraction when broom was present. Extractable nutrient cations (notably K) were lower in the presence of broom at both sites, with the effects most pronounced at the fine-textured OR site. Conclusions Lasting effects of Scotch broom invasion are likely to be associated with variable changes in soil C, N, and decreases in extractable nutrients and available P. These changes, and other documented effects of Scotch broom on soil, are likely to have lasting effects on Douglas-fir growth after Scotch broom removal that will vary depending soil nutrient status at a given site.

Description: Aims Sorghum ( Sorghum bicolor ) roots release biological nitrification inhibitors (BNIs) to suppress soil nitrification. Presence of NH 4 + in the rhizosphere stimulates BNIs release and it is hypothesized to be functionally associated with plasma membrane (PM) H + -ATPase activity. However, whether the H + -ATPase is regulated at the transcriptional level, and if so, which isoforms of the H + -ATPases are involved in BNIs release are not known. Also, it is not clear whether the stimulation on BNIs release from roots is due to NH 4 + uptake or its assimilation, which are addressed in this study. Methods Root exudates from intact sorghum plants were collected using aerated solutions of NH 4 + or methyl-ammonium (MeA); and the BNI-activity release was determined. PM vesicles were isolated from fresh roots using a two-phase partitioning system; and the hydrolytic H + -ATPase activity was determined. All genes encoding PM H + -ATPases were searched in sorghum genome, and their expression in response to NH 4 + or MeA were analyzed by quantitative RT-PCR in sorghum roots. Results BNIs release and PM H + -ATPase activity increased with NH 4 + concentration (≤1.0 mM) in the root-exudate collection solutions, but at higher concentrations, it did not respond further or declined in case of the PM H + -ATPase activity. Twelve PM H + -ATPase genes were identified in sorghum genome; and these isoforms were designated SbA1 to SbA12 . Five H + -ATPase genes were stimulated by NH 4 + in the rhizosphere, and have similar expression pattern, which is consistent with the variation in H + -ATPase activity. MeA, a non-metabolizable analogue of NH 4 + , had no significant effects on BNIs release, H + -ATPase activity, or expression of the H + -ATPase genes. Conclusions Our results suggest that the functional link between PM H + -ATPase activity and BNIs release is evident only at NH 4 + levels of ≤1.0 mM in the rhizosphere. The variation in PM H + -ATPase activity by NH 4 + is due to transcriptional regulation of five isoforms of the H + -ATPases. The stimulatory effect of NH 4 + on BNIs release is functionally associated with NH 4 + assimilation and not just with NH 4 + uptake alone.

Description: Aims We compared elemental sulphur (ES) and sulphate fertilisers in terms of yield and S uptake. Methods Two consecutive canola crops were grown on 35 S-labelled soil amended with ammonium sulphate, ES-bentonite pastilles (90 % ES), or S-fortified ammonium phosphate (NP) fertilisers containing both sulphate-S and ES (5–8 % ES). The shoot yield, S concentration and specific activity of S in the shoot were determined. Results In the first crop, the yield was significantly lower in the control (without added ES) and ES pastille treatments than in the other treatments. Sulphur uptake was highly correlated with the added sulphate rate. In the second crop, the yield and S uptake was highest for the S-fortified NP fertilizers. The contribution of ES to the S uptake was circa 20 % in the first crop and 43 % in the second crop for the S-fortified NP fertilisers, but was negligible for the ES pastilles. Modelling indicated an oxidation rate of 0.6 − 0.7 % per day for the S-fortified NP fertilisers and 0.03 % per day for the ES pastilles. Conclusions The contribution of ES pastilles to S uptake was negligible in both crops. In contrast, S-fortified NP fertilisers showed a significant contribution of ES and higher S availability than sulphate-only fertiliser in the second crop.

Description: Aim Desert herbs, a crucial component of desert ecosystems, are sensitive to water and nutrient availability and therefore to environmental change. We aimed to determine element concentrations in desert herbs and their relationships with life form, taxonomy, climate, and soil environment. Methods We measured concentrations of 11 elements in shoots and roots of 26 dominant desert herb species from 45 sites in a temperate desert. Results Shoots of desert herbs had greater concentrations of elements related to photosynthesis and water use efficiency (N, P, Mg, K) than roots. Concentrations of these elements (except N and P) were also greater in annual herbs than in perennial herbs. Greater Mg, K, and Na concentrations were observed in shoots of Chenopodiaceae (mostly C 4 species) than in Poaceae (mostly C 3 species). Soil properties and taxonomy explained 3.6–26 % and 2.8–24 % of the variation in shoot element concentrations, respectively, whereas climate factors explained only 0.05–6.5 % of the variation. Conclusions Water and nutrient availability, which are affected by environmental change, influence concentrations of mineral elements in desert plants and their biogeochemical cycles in desert ecosystems.

Description: Background and aims In order to analyse root system architectures (RSAs) from captured images, a variety of manual (e.g. Data Analysis of Root Tracings, DART), semi-automated and fully automated software packages have been developed. These tools offer complementary approaches to study RSAs and the use of the Root System Markup Language (RSML) to store RSA data makes the comparison of measurements obtained with different (semi-) automated root imaging platforms easier. The throughput of the data analysis process using exported RSA data, however, should benefit greatly from batch analysis in a generic data analysis environment (R software). Methods We developed an R package (archiDART) with five functions. It computes global RSA traits, root growth rates, root growth directions and trajectories, and lateral root distribution from DART-generated and/or RSML files. It also has specific plotting functions designed to visualise the dynamics of root system growth. Results The results demonstrated the ability of the package’s functions to compute relevant traits for three contrasted RSAs ( Brachypodium distachyon [L.] P. Beauv., Hevea brasiliensis Müll. Arg. and Solanum lycopersicum L.). Conclusions This work extends the DART software package and other image analysis tools supporting the RSML format, enabling users to easily calculate a number of RSA traits in a generic data analysis environment.

Description: Aims Little is known about why Dicranopteris dichotoma can succeed in a nutrient-limited environment. This study investigated the stoichiometric mechanisms of D. dichotoma growth and resistance to nutrient limitation in the red soil hilly region of China. Methods We examined D. dichotoma growth, soil nutrients, and stoichiometric variables in the early ecological restoration stage and across the ecological restoration chronosequence. Results Most of the D. dichotoma growth factors rapidly increased with the arbor-bush-herb mixed plantation and maintained a high level. Soil P was a main factor influencing D. dichotoma growth across the ecological restoration chronosequence, whereas its role is unclear in the early ecological restoration stage. D. dichotoma demanded low C and P and possessed high N and P utilization rates, and N and P distribution was ranked as leaf 〉 root and rhizome 〉 stem. The stoichiometry of D. dichotoma is a relatively weak stoichiometric homeostasis across the whole ecological restoration chronosequence with relatively strong stoichiometric homeostasis in the early ecological restoration stage. Conclusions Stoichiometry can be used to explore the underlying mechanisms that allow D. dichotoma to succeed to a great extent. D. dichotoma can play an important role in ecological restoration, and microtopography, especially valleys, should be created to trigger the succession of D. dichotoma in the red soil hilly region of China.

Description: Background Bacterivores, mostly represented by protists and nematodes, are a key component of soil biodiversity involved in soil fertility and plant productivity. In the current context of global change and soil biodiversity erosion, it becomes urgent to suitably recognize and quantify their ecological importance in ecosystem functioning. Scope Using meta-analysis tools, we aimed at providing a quantitative synthesis of the ecological importance of soil bacterivores on ecosystem functions. We also intended to produce an overview of the ecological factors that are expected to drive the magnitude of bacterivore effects on ecosystem functions. Conclusions Bacterivores in soil contributed significantly to numerous key ecosystem functions. We propose a new theoretical framework based on ecological stoichiometry stressing the role of C:N:P ratios in soil, microbial and plant biomass as important parameters driving bacterivore-effects on soil N and P availability for plants, immobilization of N and P in the bacterial biomass, and plant responses in nutrition and growth.

Description: Aims This study evaluated a framework for modelling the continuous exchange of carbon (C) between the atmosphere, plants, humus, and microorganisms, proposing a plant C model coupled to MOMOS, an existing microbial C model. Methods C data were collected on low fertility cereal-legume cropping systems. Plant C and microbial C were modelled simultaneously and the growth parameters of plants and nitrogen-fixing microorganisms were fitted to the data. Results All C exchanges were successfully predicted using the same weather correction for plant and microbial processes. Most of the photosynthetic production was allocated to the roots, reducing yields. The C losses were found modelled mainly by root respiration for cereals, probably as an energy source for nutrient explorings, and by root mortality for legumes as a growth source for decomposers and symbiotic nodules. The effect of root-nodule activity on shoot growth was found non-linear. The system was modelled as a sink of 4.2 Mg C ha -1 year −1 in the soil’s labile C reserve. Conclusions This paper coordinates theoretical bases for modelling the processes regulating plant productivity associated with plant C losses. The tool appears to be robust and is now available for calculating the essential parameters of agro-ecology and climate change.

Description: Aims Both aluminum (Al) toxicity and phosphorus (P) deficiency are limiting factors of crop production on acid soils. Although Al-P interaction has been extensively studied, the results are controversial. The aim of this study is to investigate the effect of in planta P on Al-induced inhibition of root elongation in wheat ( Triticum aestivum L .). Methods Roots of wheat (cv. Atlas 66) with different internal P concentrations were prepared by two methods; split-root and re-rooting in a hydroponic solution using three different P levels (0, 25 and 250 μM) to avoid direct precipitation of Al-P in the solution. Al toxicity was evaluated by root elongation inhibition and callose induction. The Al and P concentrations in the root tips were also compared among different treatments. Results Both split-root and re-rooting methods generated roots with different P concentrations in the tips when exposed to different P levels. Lower P in the root tips resulted in less Al-induced inhibition of the root elongation, less callose content and less Al accumulation, while higher root P caused a higher Al-induced inhibition of the root elongation, increased callose content and Al accumulation in the root tips. Furthermore, Al in the root cell sap was not altered by different P concentrations, but Al in the root cell wall was increased with increasing in planta P concentrations. Conclusions Al toxicity in wheat is associated with P in the root cell wall; lower root P enhanced Al tolerance, while higher root P aggravated Al toxicity in wheat.

Description: Background and aims Biochar additions may have positive impacts on phosphorus (P) availability to plants and cause down-regulation of genes associated with P starvation. Various alkaline-extracted humic substances products (HSP) also induce partial relief in plants from P starvation and, moreover, cause an increase in total cell phosphate, ATP and glucose-6-phosphate levels. As many biochars contain substances similar in structure and functioning to HSP, our goal was to examine if such products extracted from biochar (B-HSP) could affect plant responses to initial P concentration (Pi) under Pi sufficient and starvation conditions. Methods We examined the impact of B-HSP in the growing media of Arabidopsis seedlings on root hair development (length and density) in sterile systems, and evaluated whether nutrient complexation with B-HSP could account for observed differences. Results Root hair length was significantly lower in B-HSP amended Pi-sufficient growing media, and root hair density was significantly lower in both B-HSP amended Pi sufficient and starvation regimes as compared with non-amended treatments. The differences did not result from either primary (P source) or secondary (increased P availability) nutritional effects. Conclusions B-HSP appears to cause a change in plant perception of P nutrition. This may be another means by which biochar impacts growing plants.

Description: Backgrounds and aims Land use is an important factor affecting soil organic carbon (SOC) dynamics and can produce positive C climate feedback, but its effects remain unknown for Tibetan ecosystems. Methods Recent land use changes have converted the traditional winter Kobresia pastures of nomads in the northeastern Tibetan Plateau to Elymus pastures or even to cropland. Detailed SOC measurements up to 30-cm depth were combined with analysis of δ 13 C, δ 15 N, bulk density, microbial C, and N contents in three land use types. Results Bulk density was decreased by conversion from Kobresia pasture to cropland but increased by conversion to Elymus pasture. The loss of 1 % of SOC caused by land use change leads to δ 13 C increase of 0.8 ‰. Conversion to cropland significantly decreased SOC stocks (10 %) and microbial biomass C, but the C loss (1.6 %) was insignificant in Elymus pasture. Land use changes strongly increased soil δ 15 N in the top 5 cm. Conclusions Conversion to Elymus pasture did not change the C stocks, but conversion to cropland decreased C stocks by 10 % within 10 years. Soil δ 13 C and δ 15 N data indicate acceleration of C and N cycling due to the replacement of Kobresia pasture by Elymus pasture and cropland.

Description: Background and aims Contributions of legume-based catch crops (LBCCs) to succeeding cereals may be significant. We quantified biological N fixation (BNF) and residual N effects of contrasting CC tops and roots. Methods BNF of three LBCCs (red clover, winter vetch, perennial ryegrass-red clover mixture) was quantified in microplots by 15 N labelling. Their residual effects on spring barley were tested against two non-LBCCs (perennial ryegrass, fodder radish) after spring incorporation of CC tops or roots in monoliths. Results Total N accumulated in LBCCs was 153–226 kg N ha −1 , of which 62–66 % was derived from BNF in tops and 31–46 % in macro-roots (0–18 cm soil). Macro-roots represented 31–50 % of total plant N. LBCCs showed similar capacity for soil N extraction as non-LBCCs. After incorporation of LBCC residues, the dry matter and N yields of spring barley were comparable to the effect of 50 kg N fertilisation ha −1 , whereas no extra N uptake was derived from non-LBCCs. The 15 N-based N fertiliser values of LBCC tops were 34–47 % against 26–29 % for non-LBCCs. Conclusions LBCC roots contributed substantial amounts of N to the system, a source that is usually underestimated. N immobilisation after incorporation of non-LBCCs may hamper the growth of following main crops especially after removing tops.

Description: Background and aims The Shaker AKT1-like channels are considered to be involved in both high- and low-affinity K + uptake and correlated with salt tolerance in glycophytes. Suaeda salsa ( Suaeda maritima subsp. salsa ), as a typical salt-accumulating halophyte, is able to absorb K + efficiently while growing under saline conditions and taking in a large amount of Na + , thus maintaining the K + concentration in its cells. In this study, the possible functions of the inward-rectifying K + channel SsAKT1 in K + uptake and salt tolerance in the halophyte S. salsa were investigated. Methods SsAKT1 from S. salsa was isolated by RT-PCR and characterized using yeast complementation; the responses of SsAKT1 to various KCl and NaCl treatments were investigated by real-time quantitative PCR. Results SsAKT1 consisted of 879 amino acid residues and shared high homology (60–67 %) with the identified inward-rectifying K + channels AKT1 from other plants. The expression of SsAKT1 rescued the K + -uptake-defective phenotype of yeast strain CY162, and also suppressed the salt-sensitive phenotype of yeast strain G19, suggesting SsAKT1 functioned as an inward-rectifying K + channel. SsAKT1 was predominantly expressed in roots, and was induced significantly by K + starvation; transcript levels increased further on resupply of K + (0.1–10 mM for 6 h) by 62 % in 0.1 mM K + and 144–174 % in higher K + concentrations (1–10 mM). Interestingly, the expression level of SsAKT1 in roots was also induced significantly by short-term treatment (6 h) with NaCl concentrations (25–250 mM). Conclusions These results demonstrate that the inward-rectifying K + channel SsAKT1 might mediate both high- and low-affinity K + uptake in S. salsa , but play a greater role in the low-affinity system. Furthermore, SsAKT1 might also be involved in salt tolerance by participating in the maintenance of K + nutrition in S. salsa under salinity.

Description: Aims Photodegradation acts as a direct contributor to litter decomposition in arid and semi-arid ecosystems. However, its indirect effects are unclear. Does photodegradation condition litter for subsequent microbial decomposition? Methods We conditioned litter of Bromus diandrus with ambient or reduced ultraviolet (UV) radiation and three periods of exposure (summer, summer-winter, and 1 year) in a California annual grassland. We then investigated how field UV exposure affected subsequent microbial decomposition of litter using a controlled laboratory incubation. Results Surprisingly, microbial decomposition was decreased by UV radiation when the exposure occurred during summer but was unaffected by UV treatment for exposure longer than summer. Litter lignin concentrations did not explain these results, as they were not affected by UV radiation for any of the exposure periods. However, for the summer period exposure, UV radiation was associated with decreased litter N concentration, which corresponded with lowered subsequent microbial activity. Conclusions Our results suggest a new mechanism through which photodegradation interacts with litter microbial decomposition: photodegradation may decrease microbial decomposition through inhibition of microbial N immobilization. Our results imply that solar radiation can interact with litter N cycling dynamics to influence litter decomposition processes.

Description: Background and aims There is a wide variability in plant tolerance to boron (B) toxicity, which is often associated with the ability to limit B accumulation. This study was conducted on two cultivars of sweet basil ( Ocimum basilicum L.) with different B tolerance: ‘Tigullio’, less tolerant and with green leaves; ‘Red Rubin’, more tolerant and with purple leaves. The main goal was to verify whether the greater B tolerance of ‘Red Rubin’ is attributable to an exclusion mechanism. Methods In three greenhouse experiments, plants were grown hydroponically with solution B concentration ranging from 0.25 (control) to 25 mg L −1 . Results Tissue B concentration increased with increasing B supply. Boron concentrations in root and leaf tissues were comparable in ‘Tigullio’ and ‘Red Rubin’ or even higher in the purple cultivar. Boron supply did not affect the leaf concentration of total phenolic compounds and other nutrients. Leaf concentrations of total phenols and rosmarinic acid were remarkably higher in ‘Red Rubin’ than in ‘Tigullio’. Conclusions The greater B tolerance of ‘Red Rubin’ was associated with the ability to withstand higher concentrations of this element in plant tissues rather than to reduced B accumulation in the shoot. The high phenolic content was thought to contribute to the B tolerance of ‘Red Rubin’.

Description: Background and aims Positive crop yield effects from biochar are likely explained by chemical, physical and/or biological factors. However, studies describing plant allometric changes are scarcer, but may be crucial to understand the biochar effect. The main aim of the present study is to investigate the effect of biochar on root architecture under field conditions in a tropical setting. Methods The presented work describes a shovelomics (i.e., description of root traits in the field) study on the effect of biochar on maize root architecture. Four field experiments we carried out at two different locations in Zambia, exhibiting non-fertile to relatively fertile soils. Roots of maize crop ( Zea mays L. ) were sampled from treatments with fertilizer (control) and with a combination of fertilizer and 4 t.ha −1 maize biochar application incorporated in the soil. Results For the four sites, the average grain yield increase upon biochar addition was 45 ± 14 % relative to the fertilized control (from 2.1–6.0 to 3.1–9.1 ton ha −1 ). The root biomass was approximately twice as large for biochar-amended plots. More extensive root systems (especially characterized by a larger root opening angle (+14 ± 11 %) and wider root systems (+20 ± 15 %)) were observed at all biochar-amended sites. Root systems exhibited significantly higher specific surface areas (+54 ± 14 %), branching and fine roots: +70 ± 56 %) in the presence of biochar. Conclusions Biochar amendment resulted in more developed root systems and larger yields. The more extensive root systems may have contributed to the observed yield increases, e.g., by improving immobile nutrients uptake in soils that are unfertile or in areas with prolonged dry spells.

Description: Background and aims There is increasing interest and use of nitrification inhibitors (NI) in agroecosystems, yet little is known of their fate in planta . Residues of the organic, N-rich NI, dicyandiamide (DCD), have been found in milk products following commercial application to pasture. We investigated whether plant acquisition and metabolism of DCD were consistent with plant-mediated transmission from soil to agricultural food products. Methods Uptake rates, translocation to the shoot, degradation of the label within wheat tissue and availability within two soils of DCD and the structurally similar naturally occurring N-rich molecule, guanidine, were measured using 14 C labelling. Results Under sterile conditions, over 2 h wheat took up (34 and 14 μmol g −1 root DW h −1 at 1 mM: DCD and guanidine, respectively), translocated (7–15 and 19–22 %) and metabolised (0.4 and 0.9 % of uptake) DCD- and guanidine- 14 C. Both molecules were also acquired from soil by wheat despite concurrent soil sorption and microbial uptake. Conclusions Both DCD and guanidine can be acquired and metabolised by graminaceous plants. Although probably not a significant route of N acquisition, plant uptake provides a direct route of DCD entry into the food chain.

Description: Background and aims Ground-penetrating radar (GPR) has provided a non-invasive means for field root investigation. However, the horizontal cross angle ( x ) of root orientation intersecting a survey line considerably impacts the amplitude area ( A ) reflected from a root and impairs the accuracy of GPR-based root quantification. Prediction of A (90°) (the value of A scanning at x  = 90°) from multiple A ( x ) measurements could correct such impact. Previous method of A (90°) prediction focused on target roots at field point scale. The aim of this study is to develop a method to predict A (90°) at field plot scale. Methods A (90°) was predicted by a pair of A ( x ) measured at two arbitrary scanning lines together with an estimated soil background amplitude area. Three independent datasets were employed to test the proposed method. The field experiment included radar data collected for six roots of Caragana microphylla in a sandy-clay soil at four cross angles (30°, 45°, 60°, and 90°). The sand box experiment included radar data for 12 dowels at 13 cross angles (0° to 180°, in 15° steps). The simulation experiment included A ( x ) of 46 simulated roots at 13 cross angles (0° to 180°, in 15° steps). Results For all experiments, A (90°) was accurately estimated. Root orientation could also be determined. After correcting the impact of cross angle, the accuracy of root diameter estimation improved. Correlation coefficient between actual and estimated root diameters increased from 0.77 to 0.81, with RMSE declining from 9.53 to 7.05 mm. Conclusions A method of correcting the influence of root orientation on root GPR signal at the field plot scale has been established. This method enhances root quantification using GPR.

Description: Background and Aims Cover crops limit canopy growth in fruit crops to varying magnitudes but mechanisms are poorly understood. Root responses of mature grapevines to understory grass were evaluated in a temperate, humid region of USA. We hypothesized that mature grapevines competing with understory grass would show deeper root distribution with deeper use of soil water but only modest reductions in nitrogen and phosphorus uptake. Methods Root responses assessed included vertical distribution of absorptive root length, mycorrhizal fungal colonization and total vine root length. Extractable soil nitrogen and phosphorous, soil moisture, grapevine nutrient status, and grapevine depth of water uptake were also assessed. Results In response to cover crop, the well-established grapevines maintained canopy growth, had modest (17 %) reductions in fruit biomass production and exhibited little evidence of restricted uptake of water and nitrogen, despite marked shifts toward deeper grapevine root distribution and a 63 % decreased overall absorptive root length. Mycorrhizal colonization of the grapevines was unaffected by presence of a cover crop. Cover crop competition affected grapevine access to phosphorus more than water or nitrogen. Conclusions These results illustrate that grapevine root systems are capable of acclimating to understory grass competition, but specific resource limitations are strongly context dependent.

Description: Aims In the present study, the effects of Cu (2.0 and 8.0 μM) on root growth of Allium cepa var. agrogarum L. were addressed and protein abundance levels were analyzed using the technology of proteomics combined with transcriptomics, in order to go deeper into the understanding of the mechanism of Cu toxicity on plant root systems at the protein level and to provide valuable information for monitoring and forecasting the effects of exposure to Cu in real scenarios conditions. Methods Protein extraction; Two-dimensional electrophoresis (2-DE) analysis; Mass spectrometry analysis; Establishment of the in-house database; Restriction enzyme map of the in-house database and protein identification. Results Root growth was dramatically inhibited after 12 h Cu treatment. By establishing an in-house database and using mass spectrometry analysis, 27 differentially abundant proteins were identified. These 27 proteins were involved in multiple biological processes including defensive response, transcription regulation and protein synthesis, cell wall synthesis, cell cycle and DNA replication, and other important functions. Conclusions Our results provide new insights at the proteomic level into the Cu-induced responses, defensive responses and toxic effects, and provide new molecular markers of the early events of plant responses to Cu toxicity. Moreover, the establishment of an in-house database provides a big improvement for proteomics research on non-model plants.

Description: Background and aims Tree diversity is considered to influence decomposition either by changing environmental conditions or by non-additive litter mixture effects. Thus, we examined the influence of tree species richness, forest age and environmental factors on single-species decomposition, and tested the hypothesis that high litter species diversity induces predominantly positive non-additive mixture effects on decomposition processes. Methods Decomposition trials using litter bags were performed in subtropical forests in China. Plot-specific decompositions rates of the abundant species Schima superba were related to environmental factors across 27 forest stands differing in age and tree species richness. Effects of litter species diversity on decomposition and N loss was assessed based on 27 plot-specific litter mixtures comprising 7 to 17 species. Results Decomposition rate of Schima superba leaf litter was mainly affected by stand characteristics and microclimate but not tree diversity. Two thirds of plot-specific litter mixtures showed a positive non-additive mixture effect whose strength was marginally positively influenced by litter species richness. Conclusions Tree diversity at stand level does not directly influence decomposition of a common litter substrate. However, our results suggest that tree species richness in the litter layer can indirectly promote decomposition and nutrient cycling via positive non-additive mixture effects.

Description: Aims Forest-steppe and sub-taiga, two main biomes of southwestern Siberia, have been predicted to shift and spread northward with global change. However, ecological projections are still lacking a description of belowground processes in which fine roots play a significant role. We characterized regional fine root patterns in terms of length and mass comparing: 1) sites and 2) vegetation covers. Methods We assessed fine root length and mass down to one meter in aspen ( Populus tremula ) and in grassland stands on six sites located in the forest-steppe and sub-taiga zones and presenting contrasting climate and soil conditions. We distinguished fine roots over diameter classes and also between aspen and understorey in forest. Vertical fine root exploration, fine root densities and total length and mass were computed for all species. Morphological parameters were computed for aspen. Results In both forest and grassland, exploration was deeper and total length and mass were higher in forest-steppe than in sub-taiga. Exploration tended to be deeper in forest than in grassland and for trees than for understorey vegetation within forest stands. Conclusions The differences in rooting strategies are related with both pedo-climatic conditions and vegetation cover. Further investigations on nutrient and water availability and on fine root dynamics should permit a better understanding of these patterns and help predicting their future with global changes.

Description: Background and aim Although ombrotrophic peatlands are nutrient deficient, it is not clear to what extent plants will respond to changes in nutrient availability. Methods We examined the changes in foliar stoichiometry and species abundance of four shrub species and moss after a decade of nitrogen (N), phosphorus (P) and potassium (K) fertilization at the Mer Bleue bog, eastern Canada. Results Shrub abundance increased and moss cover decreased after fertilization with 6.4, 5 and 6.3 g m −2 yr −1 of N, P and K, respectively; foliar concentrations of N, P, K and calcium (Ca) and magnesium (Mg) were affected. Stoichiometry showed mainly N limitation after P and K fertilization and P (co)limitation after high levels of N addition in shrubs; moss showed consistent K or KN-co-limitation, even with PK and NPK additions. Shrubs exhibited the strongest homeostasis (the maintenance of an organism’s tissue chemical composition with changes in environmental resources) to N, with the homeostatic regulation coefficient ( H ) 〉 9.7, compared to 1.4 in moss. For P and K, shrubs showed weaker homeostasis than N, while moss had a stronger homeostasis. Conclusions The strong homeostasis of shrubs may be an adaptive strategy to limited availability of soil N and P.

Description: Aims Plants have been suggested to have significant effects on methane (CH 4 ) and nitrous oxide (N 2 O) fluxes from littoral wetlands, but it remains unclear in subtropical lakes. Methods We conducted in situ measurement of CH 4 and N 2 O fluxes for two years. To distinguish between the effects of shoots and roots, three treatments (i.e., intact plants as control, shoot clipping, and root exclusion) were used. Effects of plant biomass, temperature, and soil moisture on CH 4 and N 2 O fluxes were analyzed. Results The mean ecosystem CH 4 emission rate was 36 μg CH 4 m −2  h −1 for drying periods, but 8219 μg CH 4 m −2  h −1 for drying-wetting transition periods. CH 4 fluxes were positively correlated with below-ground and total biomass, but not with above-ground biomass. Clipping did not significantly alter CH 4 flux rate, but root exclusion decreased the CH 4 flux by 116 % as compared to the control. N 2 O emissions were similar for both the drying and drying-wetting transition periods, with a mean rate of 20 μg N 2 O m −2  h −1 . Both clipping and root exclusion significantly increased N 2 O fluxes as compared to the control. Conclusions There was no significant correlation between CH 4 and N 2 O fluxes. Roots dominated plant-mediated enhancement in CH 4 fluxes, but played almost an equal role as shoots in plant-regulated suppression on N 2 O fluxes in this Carex meadow during drawdown periods.

Description: Aims Root herbivory incurs fitness costs, but herbivory by nematodes can additionally increase nutrient availability mediated by enhanced root exudation and soil microbial activity and change plant susceptibility to aboveground herbivores due to systemic changes in plant defence. We hypothesized that such positive indirect effects may outweigh the negative direct effects of root herbivory by nematodes on plant performance. Methods We tested the effects of transient (3 weeks) and continuous (11 weeks) belowground herbivory by root-knot nematodes ( M e loidogyne incognita ) on the biomass, nitrogen levels, and reproductive output of Nicotiana attenuata , and its interaction with a specialist aboveground herbivore ( Manduca sexta ) in a greenhouse study. Results Continuous nematode herbivory caused an increase in shoot biomass and enhanced nitrogen levels in roots, shoots and seeds, but reduced the reproductive output of N. attenuata . Short-term, transient nematode herbivory had no effects. Feeding by the aboveground herbivore reduced reproductive output and increased seed nitrogen content. Nicotine levels in leaves and the plant interaction with M. sexta were not influenced by nematode herbivory. Conclusion In summary, only continuous nematode herbivory indirectly increased nitrogen availability and caused resource sequestration to the shoots; however, this effect was not strong enough to outweigh the direct fitness costs of nematode herbivory.

Description: Aims Sclerotia of Sclerotinia sclerotiorum survive in soil and germinate to produce apothecia which release airborne ascospores. Current control methods rely predominantly on the use of fungicides to kill ascospores. The aim of this research was to identify potential biofumigation treatments which suppress sclerotial germination, providing a potential alternative and long-term approach to disease management. Methods Microcosm and in vitro experiments were conducted using dried and milled plant material from six different biofumigant crop plants to determine effects on carpogenic germination of sclerotia and mycelial growth of S. sclerotiorum . Results All biofumigant plants significantly reduced germination of S. sclerotiorum sclerotia in the microcosm experiments, but were less effective against larger sclerotia. In vitro experiments showed a direct effect of biofumigant volatiles on both the mycelial growth of S. sclerotiorum , and carpogenic germination of sclerotia, where the most effective treatment was B. juncea ‘Vittasso’. Conclusions It was clear from this study that biofumigant crop plants have potential as part of an integrated disease management system for control of S. sclerotiorum . The microcosm experiments described here provide a straightforward and reliable screening method for evaluating different biofumigants for activity.

Description: Background and aims Trichoderma harzianum 6776 is a novel and beneficial tomato fungal isolate. To investigate the mechanisms underlying the T. harzianum 6776-tomato interaction, several physiological and biochemical responses were explored on dwarf tomato plants, cv . Micro-Tom. Methods Growth of treated and untreated plants was evaluated by measuring the height and biomass production of plants. The leaf pigment content and sugar partitioning in plant organs were evaluated by biochemical analysis. The photosynthetic parameters were measured by a miniaturized PAM fluorometer and a portable gas-exchange system. The hormonal analysis in root and xylem sap was performed by gas cromatography- mass spectrometry (GC-MS). Results T. harzianum 6776 positively affected plant growth, increasing the leaf pigment content and improving the photosynthetic activity at both stomatal and non-stomatal levels. Differences in pigment composition and photosynthetic performance were reflected in the carbohydrate content and their partitioning. In the absence of a pathogen, root and xylem vessel stress and growth-related hormone balance were affected by the interaction with T. harzianum 6776, with an increase in jasmonic and indoleacetic acids and a decrease in salicylic acid content. Conclusions This study shows the complex connection between increased hormone accumulation and transport, altered sugar partitioning and enhanced photosynthetic efficiency induced by T. harzianum 6776, and how growth promotion is the result of the combination of these drastic changes in Micro-Tom plants.

Description: Aims and Methods We measured changes in mass and in carbon (C), nitrogen (N) and phosphorus (P) concentrations and content of surface-placed and buried wood blocks decomposing over 12 years at 21 sites across Canada to evaluate the influence of the environment on C, N, and P dynamics. Results and Conclusions Carbon decomposition over time was best described using a sigmoidal fit, which was slightly better than a negative exponential function. Decomposition was slow at cold and wetland sites, with less than 15 % of the original C content lost after 12 years for 4 upland and 3 wetland sites. Decomposition rates were faster for buried than for surface blocks, except in wetlands and in a few upland sites that had high annual precipitation. Nitrogen was gained during the early stages of decomposition, followed by a net N loss once an average C:N mass ratio of 165 was reached for all upland surface-placed blocks, and 200 for upland buried blocks. Critical C:N values were weakly correlated with C:N ratios in the surface organic horizon, suggesting an influence of forest floor properties on decomposition dynamics with N release occurring sooner on more fertile sites. Critical values for N and P mineralization were greater than those reported for foliar litters.

Description: Background and Aims To understand the bioavailability of phosphorus (P) under different conditions, it is important to consider the P uptake by plant roots and arbuscular mycorrhizal fungi (AMF) hyphae separately. This can be done with root study containers that separate soil into root – and hyphal – zone by a layer of nylon 〈30 μm mesh, which impedes root access to parts of the soil while enabling exploration by AMF (termed the hyphal zone ). However, diffusion of P from the hyphal zone to the root zone can complicate the analysis of such experiments when a concentration gradient is created by a P–rich patch in the hyphal zone . This study tested whether a layer of tephra with high P sorption characteristics can be arranged to prevent P diffusion between the root zone and the hyphal zone . Methods A study of P sorption on tephra was conducted to determine the thickness of the tephra needed. Once this was established, the effectiveness of the “P diffusion break” in the modified root study container was tested. For this, Lotus pedunculatus cv. barsille was grown in the container having a low–P soil (Olsen P 4.3 mg kg −1 ) in the root zone and either low– or high–P soil (Olsen P 33.3 mg kg −1 ) in the hyphal zone . Results A 3–mm thick layer of tephra was shown to be adequate to prevent P diffusion for one year from the high–P soil to the low–P soil, as assessed by the absence of P accumulation in resin–P (〈 5 mg kg −1 ) and total P in the tephra layer. Plant P uptake was increased by 1.9 mg pot −1 when AMF could access the high–P soil, resulting in an increase in plant yield by 56 %. Conclusions Given that (i) P diffusion across the tephra layer was prevented; (ii) roots were confined to the root zone; and (iii) AMF hyphae were detected in the tephra layer, the additional P uptake must have been through AMF acquisition. This experimental design can then be applied to study the influence of soil amendments (e.g. fertilizers, lime, biochar) either containing P or affecting P availability in soil to cause an increasing P transfer by AMF hyphae.

Description: Aims We investigated the extent water soluble and insoluble (hexane soluble) plant residue fractions in influence the priming of soil organic carbon (SOC). Methods Carbon-13-labeled water-soluble and insoluble plant materials were added to an organic or mineral soil at three moisture levels and incubated for 57 days. Plant material decomposition and resulting priming effect (PE) was quantified. Results Water-soluble additions were not always mineralized at higher rates than insoluble material and their mineralization rates varied greatly across soil type and moisture content. Regardless of solubility, less than 33 % of the added carbon was mineralized to CO 2 by the end of the experiment, but a positive PE was observed in both soils. In general, water-soluble material caused a greater PE than insoluble organics, though the difference was not always significant throughout the experiment. Both additions induced greater PE in mineral soil than in an organic soil on a soil organic carbon basis. Moreover, the PE of soluble substrates generally increased when soil moisture increased, which was not observed for the PE of insoluble substrates. Conclusions Solubility alone is insufficient in protecting organic substrates against microbial decomposition, with soluble substrates causing only a short and pulsed response to priming of SOC, and may therefore have a less pronounced impact on soil processes and final C balance than insoluble substrates in the long-term.

Description: Aims Plant roots shape the structure of the soil microbiome by producing a wide array of phytochemicals, which in turn impact plant growth and health. The synthesis of root metabolites is a dynamic process that is modulated by interactions with soil microorganisms. This study explored the regulation of soil-borne fungal endophytes and pathogens by the production of phytochemicals in chickpea ( Cicer arietinum L.) roots colonized or not colonized by the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis . Methods Proteins and low-molecular-mass phytochemicals were extracted from chickpea roots and fractionated by flash chromatography and high pressure liquid chromatography (HPLC). The effects of these metabolites on the soil-borne fungal endophytes Trichoderma harzianum and Geomyces vinaceus and on the pathogens Fusarium oxysporum and Rhizoctonia solani were tested in 96-well plate assays. Results One protein fraction from the AM roots, which contained an apparent 34 KDa chitinase/chitin-binding domain and 24 KDa non-specific lipid transfer protein, non-selectively repressed the fungal endophytes and pathogens. By contrast to the protein fraction, the low-molecular-mass fractions were often selective. Eighteen fractions stimulated specific fungal species and seven fractions inhibited others. Conclusions Several protein and low-molecular-mass phytochemicals in chickpea roots influence fungal endophytes. The difference in the response of fungal species to the phytochemicals suggests that these metabolites could be involved in the so called host ‘preference’ of fungal endophytes or ‘resistance’ to pathogens. This research reveals that the majority of the bioactive root metabolites could be involved in the selective association of chickpea and fungal endophytes while a few compounds provided resistance by suppressing the pathogenic species.

Description: Background and Aims Plant acquisition of endogenous forms of soil phosphorus (P) could reduce external P requirements in agricultural systems. This study investigated the interaction of citrate and phytase exudation in controlling the accumulation of P and depletion of soil organic P by transgenic Nicotiana tabacum plants. Methods N. tabacum plant lines including wild-type, vector controls, transgenic plants with single-trait expression of a citrate transporter ( A. thaliana frd3 ) or fungal phytases ( phyA : A. niger , P. lycii ) and crossed plant lines expressing both traits, were characterized for citrate efflux and phytase exudation. Monocultures and intercropped combinations of single-trait plants were grown in a low available P soil (12 weeks). Plant biomass, shoot P accumulation, rhizosphere soil pH and citrate-extractable-P fractions were determined. Land Equivalent Ratio and complementarity effect was determined in intercropped treatments and multiple-linear-regression was used to predict shoot P accumulation based on plant exudation and soil P depletion. Results Crossed plant lines with co-expression of citrate and phytase accumulated more shoot P than single-trait and intercropped plant treatments. Shoot P accumulation was predicted based on phytase-labile soil P, citrate efflux, and phytase activity (Rsq=0.58, P  〈 .0001). Positive complementarity occurred between intercropped citrate- and phytase-exuding plants, with the greatest gains in shoot P occurring in plant treatments with A. niger phyA expression. Conclusions We show for the first time that trait synergism associated with the exudation of citrate and phytase by tobacco can be linked to the improved acquisition of P and the depletion of soil organic P.

Description: Background and aims Zinc (Zn) is an essential nutrient for plants, as it functions as a component and cofactor of enzymes. Metallothioneins (MTs), are known to participate in the process of metal homeostasis have been hypothesized to be partially responsible for the distribution of Zn in plants. We aimed to characterize putative MT-like genes and to analyze their expression in response to Zn supplementation in coffee. Methods Coffee seedlings were cultivated in Hoagland’s solution without Zn, and after 120 days, Zn was supplied at different concentrations. Fully expanded leaves were collected for analysis of MT relative gene expression, Zn concentrations and enzymatic activity. Results Seven putative genes were obtained in a search of the CAFEST database. Electronic Northern analysis revealed that MTs were expressed in different tissues, developmental stages and mostly under arachidonic acid treatment. Superoxide dismutase (SOD) quantification indicated that the Zn dose influenced the enzymatic activity; the lowest being at 0.6 % Zn. Quantitative expression analyses of putative MTs demonstrated that these genes are differentially expressed in response to Zn supplementation. Conclusions There is a positive correlation between MT relative expression and Zn concentration and we believe that MTs play an important role in Zn homeostasis in coffee.

Description: Background and aims The coupling of photosynthesis with belowground processes appears to be much faster than the time needed for assimilate translocation with the phloem flow. Pressure/concentration waves have been hypothesized to release belowground C already present in the phloem, resulting in a very fast feedback of rhizosphere processes to photosynthesis changes. We evaluate the speed of aboveground-rhizosphere coupling under maize by two mechanisms: pressure/concentration waves and direct phloem transport. Methods We combined two isotopic approaches: 1) the speed of direct phloem transport was evaluated by labeling shoots in 14 CO 2 and tracing 14 C in the nutrient solution and in the CO 2 flux, 2) pressure/concentration waves were evaluated by labeling the solution with [ 13 C] glucose and tracing the isotope dilution during photoassimilation. Results 14 C shoot labeling of maize plants showed that 12  h were needed for 14 C to peak in root-derived CO 2 . In contrast, in the solution labeling approach, CO 2 flux increased within 2 h after switching on the light. Pressure/concentration waves contributed 5 % to diurnal respiration efflux and affected only root respiration. Root exudation was independent of the fast mechanism of above-belowground coupling. Conclusions Photosynthesis affected root and rhizomicrobial respiration on variable time-scales: root respiration within the first 2 h by pressure/concentration waves, whereas rhizomicrobial respiration may depend on internal circadian cycles in regulating exudation rather than on light directly.

Description: Background and aims The ability of grass mulches to inhibit weed performance has been linked to their limitations on nitrogen availability to the weeds. Fungal translocation of N from the soil to the surface mulch has been confirmed in laboratories, but this mechanism has not been documented under field conditions. Methods Experiments used 15 N (NH 4 ) 2 SO 4 , 99.7 at.%, which was uniformly injected below the soil surface at a rate of 1 mg 15  N kg −1 soil. Some plots were treated with a fungicide (Captan) every 2 weeks after injection, while others were not treated. Nitrogen transfer was monitored by measuring levels in surface residue, soybean tissue, and extractable soil inorganic N pools. Results Despite the N release from the cereal rye ( Secale cereale L.) tissues ranging from 15 to 50 kg N ha −1 , there was a detectable increase in 15 N enrichment of 10–15 % in the cereal rye tissue. Six weeks after injection, tissue from the plots not treated with fungicide contained 36 % more 15  N. Conclusions The increased 15 N enrichment in the cereal rye mulch supports laboratory observations that soil inorganic N is translocated into surface mulch via fungal mechanisms. These findings illustrate microbial-mediated sinks for nitrogen in cereal rye mulches in no-till soybean production systems.

Description: Background and aims Dieback is pervasive in many populations of invasive woody weeds globally. Previous studies on dieback have focused on specific potential causative biotic agents, but most cases remain unexplained. The potential role of endophytic microbial communities in dieback, including the relative importance of endophytes with pathogenic or protective capabilities, remains poorly studied. We tested whether changes in archaeal, bacterial and fungal endophyte community structure is associated with dieback occurrence in the invasive, leguminous tree, Parkinsonia aculeata L. (parkinsonia). Methods We sampled roots, stems and stem tips from healthy and dieback-affected parkinsonia and conducted terminal restriction fragment length polymorphism (T-RFLP) analysis on DNA extracted from these samples using domain-specific primers for archaea, bacteria and higher fungi. Results Microbial community composition strongly differed with parkinsonia disease status (archaea, bacteria and fungi) and plant part (archaea and fungi). Plant part and disease status effects were strongest in archaea. We also found evidence implicating both pathogenic and potentially protective endophytes in the onset of dieback. Conclusions This is the first study that has shown significant associations between changes in endophyte community composition and dieback presence. Our results highlight the complexity of those changes and provide support for the hypothesis that diverse pathogenic and protective endophytes may be implicated in dieback.

Description: Aims Beneficial aspects of plant silicon (Si) have been identified, but little is known about how multiple abiotic conditions interact in a natural environment to influence plant Si-accumulation. Consequently, we identified abiotic correlates of soil and plant Si pools in a pristine African savanna and quantified relationships among precipitation, soil properties, and grass silicon concentration along environmental gradients. Methods Soil properties were measured at 63 sites spanning soil and precipitation gradients in the Serengeti ecosystem of northern Tanzania. Bulk and species-specific grass samples were collected at 18 of those sites and combined with soil and climate data into a structural equation model to describe landscape drivers of foliar silicon concentration. Results Soil amorphous silicon (ASi) was negatively related to precipitation but was unrelated to soil dissolved silicon (DSi). The final structural equation model included three predictor variables, each negatively associated with soil DSi: precipitation, soil percent sand, and soil pH, which, together, explained ~74 % of variation in soil DSi. Finally, soil DSi was positively related to grass Si concentration, explaining ~60 % of variation. Conclusions While evidence exists for biotic induction of silicon accumulation (e.g. herbivory), our results indicate that natural abiotic variation, which has largely been ignored, is equally important and may determine the extent to which inducibility is possible. Environmental heterogeneity, by constraining or promoting Si dissolution and availability, plays a significant role in silicon accumulation by grasses.

Description: Background and Scope Growing evidence suggests that volatile organic compounds (VOCs) play important roles in plant-plant, plant-microbe and plant-environment interactions. Demonstrating such mechanisms requires the use of innovative analytical techniques to monitor VOCs in and above soils. In this issue, Waters et al. provide experimental evidence that stolons of the woodland strawberry, Fragaria vesca , forage for nutrient-rich soil patches by a chemotropic mechanism. Conclusions These experimental results not only help clarify the means by which this clonal plant locates nutrients in a heterogeneous environment, but also demonstrate the power of using the tools of modern analytical chemistry to elucidate plant-plant and plant-environment interactions.

Description: Background and Aims Forests play a vital role in regulation of the global carbon cycle. Mechanistically understanding how their ecosystem functioning relates to biodiversity is necessary for predicting the consequences of biodiversity loss and for setting conservation priorities. Here, we test whether carbon stocks in a subtropical evergreen broad-leaved forest in China are more strongly influenced by plant functional diversity (FD), as would be predicted by the ‘niche complementarity hypothesis’, or by community-weighted mean (CWM) functional trait values, as would be predicted by the ‘mass ratio hypothesis’. Methods Using data from a 24-ha plot subdivided into 400 m 2 quadrats, we determined relationships of aboveground carbon (AGC) and topsoil (1–10 cm) organic carbon (SOC) to topographic variables, stem density, CWM and FD of six functional traits hypothesized to influence carbon stocks. Results After accounting for topographic variables and tree stem density, boosted regression tree models revealed that CWMs were the dominant driving factors for both AGC and SOC, whereas FD had negligible effects. AGC and SOC were influenced by different functional traits, with AGC responding most strongly to CWM values for wood density and maximum tree height, and SOC responding most strongly to elevation, indicating that these carbon stocks are shaped by different underlying mechanisms. Conclusions Our results support the mass ratio hypothesis but not the niche complementarity hypothesis. Our study implies that, when it comes to maximizing forest carbon storage, conservation priorities should focus on protection of species with traits associated to high carbon stocks.

Description: Aims Cover crops play an important role in soil fertility as they can accumulate large amounts of nutrients. This study aimed at understanding the nutrient uptake capacity of a wide range of cover crops and at assessing the relevance of acquisition strategies. Methods A field experiment was conducted to characterize 20 species in terms of leaf and root traits. Plant traits were related to nutrient concentration and shoot biomass production with a redundancy analysis. Acquisition strategies were identified using a cluster analysis. Results Root systems varied greatly among cover crop species. Five nutrient acquisition strategies were delineated. Significant amounts of nutrients (about 120 kg ha −1 of nitrogen, 30 kg ha −1 of phosphorus and 190 kg ha −1 of potassium) were accumulated by the species in a short period. Nutrient acquisition strategies related to high accumulations of nutrients consisted in either high shoot biomass and root mass and dense tissues, or high nutrient concentrations and root length densities. Species with high root length densities showed lower C/N ratios. Conclusions The same amounts of nutrients were accumulated by groups with different acquisition strategies. However, their nutrient concentrations offer different perspectives in terms of nutrient release for the subsequent crop and nutrient cycling improvement.

Description: Background and Aims Elevated carbon dioxide (CO 2 ) and magnesium (Mg) deficiency have contrasting influences on plant growth and performance, but disrupt carbohydrate metabolism in a similar manner. This study was aimed at characterizing interactive effects of elevated CO 2 and Mg nutrition on carbohydrate metabolism, sink strength and biomass partitioning. Methods Durum wheat was cultured in climate chambers with ambient (398 μmol mol −1 air) or elevated CO 2 (700 μmol mol −1 air) and with adequate (1000 μM) or low (75 μM) Mg supply in nutrient solution. Biomass production and partitioning, tissue Mg concentrations, photosynthetic performance and carbohydrate status of leaves and roots were determined. Results Low-Mg plants responded to elevated CO 2 with a biomass decrease rather than enhancement especially in roots. In low-Mg plants inhibition of root growth and partitioning of biomass towards shoots were enhanced by elevated CO 2 . Elevated CO 2 increased photosynthesis rate in adequate-Mg plants, but not in low-Mg plants. Leaf carbohydrate concentration was increased 2 fold by low Mg at ambient CO 2 and 3 fold at elevated CO 2 , suggesting that low Mg and elevated CO 2 decreased carbohydrate transport from source tissues. Conclusions Elevated CO 2 exacerbated adverse effects of inadequate Mg nutrition on plant growth, biomass partitioning, carbohydrate metabolism and photosynthetic performance in durum wheat. Adequate Mg nutrition was important for maintaining efficient transport of carbohydrates and thus prevent an early acclimation to elevated CO 2 .

Description: Background and aims Lower concentrations of REEs promote plant growth, whereas higher concentrations of REEs negatively affect plant growth, soil accumulation, and environmental pollution. To clarify the mechanism of cerium (Ce) toxicity on Allium sativum , the effects of Ce(IV) on mitosis in root tip cells and physiological responses were studied. Methods Roots growth, mitosis, chlorophyll and malondialdehyde contents, and activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase were measured after treatments with Ce(IV). Results Lower Ce concentrations (0.4 and 4 μM) increased leaf chlorophyll content and enhanced SOD and catalase activities. Higher Ce concentrations (40 and 100 μM) decreased chlorophyll content and inhibited root growth, but enhanced malondialdehyde contents and catalase and APX activity in roots and leaves. SOD activity was inhibited after 12 days of treatment with 100 μM Ce. Treatment with 〉100 μM Ce caused chromosomal aberrations (e.g., sticky chromosomes, chromosomal fragments, and bridges) in root tip cells. Conclusions Chromosomal aberrations in root cells induced by high Ce concentrations might be associated with inhibition of root growth. Changes in antioxidant enzyme activities suggested that Ce(IV) induced antioxidative stress responses and that Ce(IV) treatment first damaged root cells and subsequently affected physiological processes in leaves.

Description: Background and aims Planted forests, established on non-forest lands, play an important role in enhancing terrestrial carbon (C) sequestration. Understanding the changes in soil C, nutrients and stoichiometry in planted forests is important for forest management. Methods We conducted a global meta-analysis of changes in C, nitrogen (N), phosphorus (P) and sulfur (S) and their stoichiometry in mineral soils of planted forest across broad climatic zones from 139 papers. Results Soil C and N are slightly decreased after forestation on grassland, moderately increased after forestation on cropland, and substantially increased after forestation on barren land. Forestation does not affect total soil P, but the available P is significantly depleted after the forestation of grassland and cropland with N-fixers. Changes in soil nutrients (N, P and S) and shifts in stoichiometry (ratios of C:N, C:P and N:P) are significantly related to soil C dynamics ( p  〈 0.05). Soil C sequestration is the lowest in the boreal zone, and greater under plantation with N-fixing species than under non-fixing species. Conclusion Changes in soil C and nutrients after forestation mainly differ to prior land use. Compared with forestation of grassland, forestation of barren land is a more effective approach to enhancing C sequestration.

Description: Aims The study aimed to find soil parameters that are best related to Se plant uptake for low Se soils with predominantly organic Se, and to explore the mechanisms that control Se bioavailability in the soils under study. Methods A pot experiment using nineteen soil samples taken from different fields of arable land (potato fields) in the Netherlands was conducted on summer wheat ( Triticum aestivum L.). Selenium in wheat shoots and soil parameters, including basic soil properties, C:N ratio, inorganic selenite content, and Se and organic C in different soil extractions (0.01 M CaCl 2 , 0.43 M HNO 3 , hot water, ammonium oxalate, aqua regia) were analysed. Regression analysis was performed to identify soil parameters that determine Se content in wheat shoots. Results The regression model shows that Se:DOC ratio in 0.01 M CaCl 2 soil extraction explained about 88 % of the variability of Se uptake in wheat shoots. Selenium uptake increased with Se:DOC ratio in CaCl 2 extraction, which can be interpreted as a measure of the content of soluble Se-rich organic molecules. Selenium:DOC ratio in CaCl 2 extraction and Se uptake increased towards higher soil pH and lower soil C:N ratio. The soil C:N ratio is also negatively correlated to Se:organic C ratio in other extractions (0.43 M HNO 3 , hot water, ammonium oxalate, aqua regia), indicating that at low soil C:N ratio soil organic matter is richer in Se. Contrarily, the soil pH is positively and strongly correlated to Se:organic C ratio in CaCl 2 and hot water extractions, but only weakly correlated to Se:organic C ratio in other extractions. Conclusions Selenium-rich dissolved organic matter is the source of bioavailable Se in low Se soils with predominantly organic Se. The soil pH and quality of soil organic matter (i.e. soil C:N ratio) are the main soil properties determining Se bioavailability in these soil types.

Description: Aims The plant-beneficial bacterium Pseudomonas fluorescens F113 harbours an acdS gene, which enables deamination of 1-aminocyclopropane-1-carboxylate. The impact of abiotic and biotic factors on the expression of this gene was assessed, as well as the plant-beneficial properties of F113 under different soil moistures. Methods An acdS - egfp biosensor was constructed in F113, validated in vitro and used to analyse, by microscopy, its expression on roots of Zea mays comparatively to Beta vulgaris . An acdS mutant was constructed and compared with the wild-type to characterize plant-beneficial effects of F113 on maize lines EP1 and FV2, under well-watered and water deficit conditions. Results Different patterns of root colonization and acdS expression were observed according to plant genotype. acdS rhizoplane expression was higher on Beta vulgaris , and on maize line FV2 and hybrid PR37Y15 than on maize line EP1 and teosinte. Strain F113 but not its acdS mutant promoted root growth of EP1 under well-watered conditions and germination of FV2 under water deficit conditions. Conclusions Maize lines differed in their ability to induce acdS expression and to respond to P. fluorescens F113. The maize line leading to higher acdS expression, FV2, was the one benefiting from inoculation under water deficit.

Description: Background and Aims Phosphorus (P) is an essential nutrient for plants but its low availability often necessitates amendments for agronomical issues. Objectives were to determine P spatial distribution and speciation that remain poorly understood in cultivated soils. Methods Aquic Argiudoll soil samples developed on a calcareous loam glacial till were collected from experimental plots submitted to contrasting crop rotations and amendments. Micro-X-ray fluorescence (μ-XRF) maps were collected on undisturbed samples. X-ray absorption near edge structure (XANES) spectra were collected on bulk samples and on fractions thereof, and on points of interests selected from μ-XRF maps. Results were compared with chemical analyses and extraction techniques results. Results Chemical analyses show variations in total and exchangeable P contents depending on the samples but no significant difference is observed in terms of P distribution and speciation. P distribution is dominated by a low-concentration diffuse background with a minor contribution from minute hot spots. P speciation is dominated by phosphate groups bound to clay-humic complexes. No modification of P distribution and speciation is observed close to roots. Conclusions This study evidenced minor effect of cropping and fertilizing practices on P speciation in cultivated soils. Despite analytical challenges, the combined use of μ-XRF and XANES provides relevant information on P speciation in heterogeneous soil media.

Description: Aims The readily available global rock phosphate (P) reserves may be depleted within the next 50–130 years warranting careful use of this finite resource. We develop a model that allows us to assess a range of P fertiliser and soil management strategies for Barley in order to find which one maximises plant P uptake under certain climate conditions. Methods Our model describes the development of the P and water profiles within the soil. Current cultivation techniques such as ploughing and reduced till gradient are simulated along with fertiliser options to feed the top soil or the soil right below the seed. Results Our model was able to fit data from two barley field trials, achieving a good fit at early growth stages but a poor fit at late growth stages, where the model underestimated plant P uptake. A well-mixed soil (inverted and 25 cm ploughing) is important for optimal plant P uptake and provides the best environment for the root system. Conclusions The model is sensitive to the initial state of P and its distribution within the soil profile; experimental parameters which are sparsely measured. The combination of modelling and experimental data provides useful agricultural predictions for site specific locations.

Description: Aims Progress in improving the internal phosphorus utilisation efficiency of crops has been limited, which may be due to poor screening methods that allow differences in P uptake among genotypes grown in soil to mask genotypic differences in shoot biomass produced per unit of shoot P (PUE). We investigated alternative soil and hydroponic screening methods for their capacity to produce a consensus ranking of genotypes with regard to PUE. Methods Six rice genotypes previously identified in hydroponic screening studies as being high, intermediate or low in PUE were screened using multi P rate hydroponic and soil-based experiments. Results Comparisons made at each rate of soil-P supply produced estimates of PUE strongly biased by P uptake differences among genotypes. Using multiple-rate data to derive response functions per genotype showed that similar P content was achieved at different rates of P supply but that high-PUE genotypes clearly separated from intermediate- and low-PUE genotypes if equal P content was used. Ranking analysis suggested that results obtained from soil agreed well with those from the hydroponic study. Conclusions PUE was significantly influenced by genotype and P supply, but there was no significant genotype x P supply interaction. Hence, we conclude that screening genotypes using hydroponics at one or two P supply levels is the most cost- and time effective means to screen large numbers of rice genotypes for PUE.

Description: Background and aims Plant growth is frequently limited by the availability of inorganic phosphorus (P) in the soil. In most soils, a considerable amount of the soil P is bound to organic molecules. Of these, phytate is the most abundant identifiable organic P form, but is not readily available to plants. In contrast, microorganisms have been shown to degrade phytate with high efficiency. The current study aims to characterize the members of the phytate-hydrolysing bacterial community in rhizosphere, and the molecular and enzymatic ability of these bacteria to degrade phytate. Methods and results The phytate-hydrolysing bacterial community was characterized from the rhizosphere of plants cultivated in the presence or absence of phytate supplementation. Major changes in the bacterial community structure were observed with both culture-dependent and -independent methods, which highlighted the predominance of Proteobacteria and Actinobacteria . Phytase activity was detected for a range of rhizobacterial isolates as well as the presence of, β -propeller phytases (BPP) for both isolates and directly in a soil sample. Conclusion A wide taxonomic range of functional phytate utilizers have been discovered, in soil bacterial taxa that were previously not well known for their ability to utilise phytate as P or C sources. This study provides new insights into microbial carbon and phosphorus cycling in soil.

Description: Background and aims Measures of phosphorus (P) in roots recovered from soil underestimate total P accumulation below-ground by crop species since they do not account for P in unrecovered (e.g., fine) root materials. 33 P-labelling of plant root systems may allow more accurate estimation of below-ground P input by plants. Methods Using a stem wick-feeding technique 33 P-labelled phosphoric acid was fed in situ to canola ( Brassica napus ) and lupin ( Lupinus angustifolius ) grown in sand or loam soils in sealed pots. Results Recovery of 33 P was 93 % in the plant-soil system and 7 % was sorbed to the wick. Significantly more 33 P was allocated below-ground than to shoots for both species with 59–90 % of 33 P measured in recovered roots plus bulk and rhizosphere soil. 33 P in recovered roots was higher in canola than lupin regardless of soil type. The proportion of 33 P detected in soil was greater for lupin than canola grown in sand and loam (37 and 73 % lupin, 20 and 23 % canola, respectively). Estimated total below-ground P accumulation by both species was at least twice that of recovered root P and was a greater proportion of total plant P for lupin than canola. Conclusion Labelling roots using 33 P via stem feeding can empower quantitative estimates of total below-ground plant P and root dry matter accumulation which can improve our understanding of P distribution in soil-plant systems.

Description: Background and aims Use of zinc (Zn) fertilisers may be cost-effective in increasing crop yields and in alleviating dietary Zn deficiency. However, Zn fertilisers are underutilised in many countries despite the widespread occurrence of Zn-deficient soils. Here, increased Zn fertiliser-use scenarios were simulated for wheat production in Punjab and Sindh Provinces, Pakistan. Inputs and outputs were valued in terms of both potential yield gains as well as health gains in the population. Methods The current dietary Zn deficiency risk of 23.9 % in Pakistan was based on food supply and wheat grain surveys. “Disability-adjusted life years (DALYs) lost” are a common metric of disease burden; an estimated 245,000 DALYs y −1 are lost in Punjab and Sindh due to Zn deficiency. Baseline Zn fertiliser-use of 7.3 kt y −1 ZnSO 4 .H2O was obtained from published and industry sources. The wheat area currently receiving Zn fertilisers, and grain yield responses of 8 and 14 % in Punjab and Sindh, respectively, were based on a recent survey of 〉2500 farmers. Increased grain Zn concentrations under Zn fertilisation were estimated from literature data and converted to improved Zn intake in humans and ultimately a reduction in DALYs lost. Results Application of Zn fertilisers to the area currently under wheat production in Punjab and Sindh, at current soil: foliar usage ratios, could increase dietary Zn supply from ~12.6 to 14.6 mg capita −1 d −1 , and almost halve the prevalence of Zn deficiency, assuming no other changes to food consumption. Gross wheat yield could increase by 2.0 and 0.6 Mt. grain y −1 in Punjab and Sindh, respectively, representing an additional return of US$ 〉800 M and an annual increased grain supply of 19 kg capita −1 . Conclusions There are potential market- and subsidy-based incentives to increase Zn fertiliser-use in Pakistan. Benefit-Cost Ratios (BCRs) for yield alone are 13.3 and 17.5 for Punjab and Sindh, respectively. If each DALY is monetised at one to three fold Gross National Income per capita on purchasing power parity (GNI PPP ), full adoption of Zn fertiliser for wheat provides an additional annual return of 405–1216 M International Dollars (I$) in Punjab alone, at a cost per DALY saved of I$ 461–619.

Description: Background and aims Nitrogen (N) deposition is currently widespread in many ecosystems and often promotes shifts in plant composition towards invasive species. In this study we evaluated how soil N availability affects the competitive interactions between a native Cerrado grass ( Aristida riparia ) and an invasive African grass ( Melinis minutiflora ). Methods We evaluated the effects of increased soil N and the presence of another species on the relative growth rate (RGR), relative competition intensity (RCI), shoot N concentration and δ 15 N, intrinsic water-use efficiency (iWUE) and N productivity ( A ) of the two grasses in a glasshouse experiment. Results We found that the presence of M. minutiflora reduces the RGR of A. riparia by 52 % under high N availability, and by 29 % under low N availability. The shoot N and δ 15 N patterns of A. riparia when grown together with M. minutiflora indicate that the exotic species interferes with the native species’ N acquisition. However, the lower RGR and iWUE of A. riparia observed only when grown together with M. minutiflora under high N availability suggests that other mechanisms might also limit A. riparia growth. Conclusions We predict that the global trend of N deposition in ecosystems might facilitate the spread of M. minituflora in Cerrado areas.

Description: Background and aims Elevated CO 2 (C E ) and temperature (T E ) can not only affect crop physiology and growth but also soil nutrient availability, which could in turn influence crop response to C E and T E . However, such indirect impacts of C E and T E on crop productivity are often unexplored, potentially underestimating the impact of C E and T E at a system level. Methods To explore the possible role of soil nutrient availability in mediating crop responses to C E and T E , we examined the effects of C E and T E on cotton productivity and soil nutrient availability in two soils. Results Early vegetative growth response was dominated by the interaction between C E and T E ; T E accelerated vegetative growth while C E enhanced photosynthesis and vegetative growth at ambient temperature. When soil nitrogen availability became low during the reproductive phase, altered soil nitrogen availability at C E and T E and differences in soil characteristics influenced resource allocation and yield response, resulting in a doubling of cotton yield at T E but only a marginal increase at C E . Conclusions Changes in soil nutrient availability induced by C E and T E during crop development can enhance or limit yield responses to C E and T E . Thus, soil responses should also be considered when developing adaptation strategy for climate change.

Description: Aims To describe the chickpea rhizobial diversity in Gansu Province of China, so far uninvestigated. Methods Nodule bacteria were isolated from chickpea grown in Gansu and characterized by phylogenetic analysis of 16S rRNA gene, housekeeping genes ( atpD , recA , and glnII ), and symbiotic genes ( nodC and nifH ). The genetic differentiation and gene flow among the chickpea microsymbionts were estimated and considered in view of soil characteristics. Results A total of nineteen new isolates originating from alkaline-saline (pH 7.9–8.1) soils in Gansu formed two clades by housekeeping gene analyses; clade I (16 isolates) was identified as Mesorhizobium muleiense (97.7–98.7 % of similarities with the type strain CCBAU 83963 T ) and clade II (3 isolates) formed a separate group within Mesorhizobium branch, displaying 97.0 and 96.6 % similarities with the most related type strains M. temperatum SDW 018 T and M. muleiense CCBAU 83963 T , respectively. Their symbiotic genes ( nodC and nifH ) were highly similar (〉98.0 %) with those described for chickpea microsymbionts in literature, i.e., M. muleiense , M. ciceri , and M. mediterraneum . The genetic differentiation and gene flow between the chickpea rhizobial groups supported our conclusions for species affiliation. Conclusions M. muleiense and a novel Mesorhizobium genospecies, sharing similar symbiotic genes, are distributed in the alkaline-saline soils of Gansu and may be considered as the main and specific chickpea symbionts in the Northwest of China.

Description: Background and aims Tillage system and crop rotation influences soil organic carbon (SOC) and total N (TN), but there remains considerable uncertainty in the response of C and N dynamics to fertilizer N inputs. A long-term (11-yr) experiment on a clay loam Orthic Humic Gleysol at Ridgetown, Ontario, Canada was used to evaluate the impact of fertilizer N applications (in-season zero N (−N) compared to (+N) 100 and 80 kg N ha -1  yr. -1 to corn ( Zea mays L.) and wheat ( Triticum aestivum L.), respectively) on soil attributes. Methods The cropping systems consisted of continuous corn (CC), corn-soybean ( Glycine max L.) (C-S) and corn-soybean-wheat (C-S-W) rotations using conventional moldboard plough and no-till systems. Soil was collected from the 0–120 cm profile in 5, 10, and 20 cm increments and analyzed for SOC and TN. Results The effect and interaction of N fertilization on soil attributes was highly dependent on crop rotation and tillage system. The gain in SOC and TN contents due to +N fertilizer was greatest (up to 31 and 57 % relative to the -N control, respectively) in the 0–20 cm depth with the C-S-W rotation, and lowest under CC, which showed no N fertilizer effect. However, differences in SOC and TN were not confined to the surface 20 cm, as N fertilizer treatments significantly influenced the contents at 20–60 and 60–120 cm in certain rotation and tillage systems; C-S-W was the most responsive to N fertilizer-induced SOC and TN gains. Conclusions Using regression analysis, we found that higher SOC contents corresponded to lower variability in the 5-yr. mean corn yield, which suggests that the inclusion of winter wheat in a C-S rotation may have important implications for sustainable and resilient agroecosystems in humid, temperate climates.

Description: Aims Struvite (MgNH 4 PO 4 .6H 2 O) recovered from wastewater can be used as fertilizer. The agronomic effectiveness of struvite has mostly been evaluated using ground fertilizer mixed through soil. However, fertilizers are most commonly applied in granular form in the field. In this study, we assessed the dissolution and effectiveness of different struvites when applied in granular or powdered form. Methods Phosphorus (P) diffusion in soil, determined using a visualization technique and chemical analyses, and P uptake by 6-week old wheat was compared for soluble fertilizer (monoammonium phosphate, MAP), a commercial struvite and three synthesized struvites with different excess MgO, in both granular and ground form. Results Ground struvite mixed through soil quickly dissolved and its agronomic effectiveness was similar to that of MAP. For pure granular struvite, the granule dissolution rate ranged from circa 0.03 mg d −1 in alkaline soil to 0.43 mg d −1 in acidic soil. Excess base in the struvite fertilizer reduced its dissolution rate. The P uptake by wheat followed the order MAP 〉 〉 struvite ≥ control (no P), with no significant difference between the control and the struvite treatment in alkaline soil. Conclusions Both fertilizer characteristics (particle size, excess base) and soil pH strongly affect the dissolution rate of struvite and hence its agronomic effectiveness.

Description: Background and aims Plants often establish multiple simultaneous symbiotic associations with different micro-organisms; however, the way in which each symbiont affects the other symbionts and the effects of these multiple interactions on plant performance are not well understood. The aim of this study was to evaluate how two different asexual Epichloë species modulate the establishment of arbuscular mycorrhizal fungi (AMF) in a wild forage grass under different soil fertilization levels. Methods We performed a completely randomized 12-month-long field experiment to evaluate the effect of two B. auleticus -endophyte ecotypes and two soil fertilization levels on the colonization of AMF, in seedlings and adult plants. Plant biomass and reproductive tillers production were also measured. Results The symbiosis, measured as the total extent of AM fungal colonization and frequency of arbuscules was significantly higher in Epichloë -infected plants and was not affected by fertilization either in seedlings or in adult plants. Plant biomass was increased by fertilization but no differences were observed due to the endophytic status. However, E+ plants produced more panicles than their E− counterparts. Conclusions Our findings strongly support the hypothesis of positive association between Epichloë endophytes and AMF in wild grasses, making this model important for agronomic improvement.

Description: Background Biological control is an environmentally sound and effective means of reducing pathogen-induced damage to agriculture using natural antagonists. Paenibacillus is a cosmopolitan and ubiquitously occurring bacterial genus with antagonistic activity against phytopathogens. Many species and strains with promising potential for plant growth promotion and biocontrol of pathogens have been identified since Paenibacillus was first described 20 years ago. Nevertheless, important questions regarding the colonization of plants, and the mode of action of Paenibacillus remain unanswered. Scope This review focuses on the occurrence of Paenibacillus in microbial metagenomes, the endophytic lifestyle of Paenibacillus, and the function of Paenibacillus -derived volatile organic compounds (VOCs) combining actual literature with our own results. Conclusions This review provides new insights into the endophytic lifestyle of Paenibacillus and discusses strain-specific and system-dependent growth promotion effects on plants. VOCs, in particular pyrazine derivatives emitted by Paenibacillus, showed high activity against other organisms. This suggests that VOCs play an important role in communication and interaction. Overall, Paenibacillus strains demonstrate promising potential not only for sustainable agriculture and biological control, but also as a source for novel bioactive volatiles.

Description: Background and aims Infection of tall fescue with the common toxic fungal endophyte Epichloë coenophiala harms livestock via toxic alkaloid production; therefore, non-toxic ‘novel’ strains of the endophyte have been developed and released. How different endophyte strains impact biological nitrogen fixation (BNF) in mixed species pastures is unknown. We asked whether novel endophyte or common toxic endophyte-infected (NE+; CTE+) tall fescue affects symbiotic and non-symbiotic BNF, and utilization of biologically-fixed nitrogen in tall fescue. Methods Tall fescue was planted either endophyte-free (E-), infected with CTE, two non-toxic strains AR542 NE, AR584 NE, or a blend of endophyte treatments. We measured natural abundance of 15  N in plant and soil samples, and conducted soil acetylene reduction assays. Results Endophyte presence and strain significantly affected the δ 15 N of tall fescue. Near red clover, CTE+ and AR584 NE+ tall fescue were most 15  N-depleted; but away, E- tall fescue was most 15  N-depleted. Endophyte strain significantly influenced N concentration in red clover, but not symbiotic or non-symbiotic BNF. Conclusions Endophyte strains produce different effects on tall fescue’s competitive ability and nitrogen utilization. In mixed pastures, deployment of NE strains for decreased alkaloid toxicity will differentially impact use of biologically fixed nitrogen in tall fescue and nitrogen concentration in red clover.

Description: Background and aims It is proposed that Epichloë endophytes have a role protecting host grasses against pathogens. However, it is unclear whether this protection is extended to other non-symbiotic plants. Here we explored the effect of the asexual fungal symbiont, Epichloë occultans , on the interaction between Lolium multiflorum host plants and soil pathogens, and its potential positive side-effect on neighbouring plants. Methods We conducted two microcosm experiments to assess the endophyte effect on seedling establishment of the host grass and other non-symbiotic grasses in the presence of soil pathogens. With an in-vitro experiment, we tested whether the endophyte inhibits, during seed germination, the growth of these pathogens. Results Independently of pathogen identity, the endophyte improved host establishment (6 %). The endophyte also enhanced the establishment of the neighbouring grass Bromus catharticus (≈20 %) only in soil with Rhizoctonia solani . The endophyte in seed reduced the growth (≈20 %) of two out of four pathogens ( Fusarium acuminatum and R. solani ). Conclusions We conclude that asexual endophytes could protect host grasses against pathogens but most importantly, that they can have protective effects beyond their hosts. Since effects depended on pathogen and plant identity, more experiments are needed in order understand the ecological meaning of these positive side-effects.

Description: Aims Afforestation causes important alterations in SOM content and composition that affect the soil functions and C balance. The aim of this study was to identify the mechanisms that determine the changes in SOM composition following afforestation of grasslands. Methods The study included 4 chronosequences and 5 paired plots comprising pastures and land afforested with Pinus radiata . The SOM was characterized by 13 C CP-MAS NMR spectroscopy and differential scanning calorimetry. Results During the first 10–20 year after afforestation, the changes in SOM content varied from slight gains to large losses (〉40 %). The analyses revealed that even SOM compounds considered resistant to decomposition were degraded during this time. The SOM gains, observed 20 year after stand establishment, were favoured by the higher recalcitrance of pine litter and possibly by soil acidification. The concentrations of most SOM compounds, particularly the stable compounds, were higher at the end of the rotation. The low degree of protection, along with the favourable climatic conditions, may also explain the rapid decomposition of SOM, including resistant compounds, in these soils. DSC analysis complemented the information about SOM composition provided by other techniques. Conclusions The accumulation of stable SOM compounds at the end of the rotation suggests a longer soil C turnover in these afforested soils, which may alleviate the gradual loss of SOC in intensively managed forest soils.

Description: Background and aims Plant nutrient uptake from coarse soil (2–4 mm diameter) has been demonstrated for only a limited number of nutrients, and the nutritional contribution of coarse soil when present with fine soil (material 〈2 mm diameter) in realistic ratios is unknown. We conducted a seedling pot trial to investigate the functional relevance of this soil fraction to plant nutrition. Methods Fine soil was mixed with either coarse soil, or the equivalent volume of inert glass chips, in ratios identical to those occurring naturally in soil sampled from two depths at each of two sites. Seedlings of Nothofagus solandri var. cliffortioides and Weinmannia racemosa were planted in the soil mixtures and harvested after 9 months. Results The content of nitrogen, phosphorous, potassium, magnesium and other elements in the above ground seedling tissue was significantly increased by the presence of coarse soil. The coarse soil fraction also contributed proportionally much more to plant nutrient uptake than fine soil on a mass per mass basis. Conclusions Coarse soil is excluded from conventional soil analysis, so is possible that soil nutrient capital is systematically underestimated. This has implications for land management and studies of plant dynamics in relation to nutrient supply.

Description: Background and aims Lateral tree-scale variability in plantations should be taken into account when scaling up from point samples, but appropriate methods for sampling and calculation have not been defined. Our aim was to define and evaluate such methods. Methods We evaluated several existing and new methods, using data for throughfall, root biomass and soil respiration in mature oil palm plantations with equilateral triangular spacing. Results Three ways of accounting for spatial variation within the repeating tree unit (a hexagon) were deduced. For visible patch patterns, patches can be delineated and sampled separately. For radial patterns, measurements can be made in radial transects or a triangular portion of the tree unit. For any type of pattern, including unknown patterns, a triangular sampling grid is appropriate. In the case studies examined, throughfall was 79 % of rainfall, with 95 % confidence limits being 62 and 96 % of rainfall. Root biomass and soil respiration, measured on a 35-point grid, varied by an order of magnitude. In zones with steep gradients in parameters, sampling density has a large influence on calculated mean values. Conclusions The methods defined here provide a basis for representative sampling and calculation procedures in studies requiring scaling up from point sampling, but more efficient methods are needed.

Description: Background Plants must acquire at least 14 mineral nutrients from the soil to complete their life cycles. Insufficient availability or extreme high levels of the nutrients significantly affect plant growth and development. Plants have evolved a series of mechanisms to adapt to unsuitable growth conditions where nutrient levels are too low or too high. microRNAs (miRNAs), a class of small RNAs, are known to mediate post-transcriptional regulation by transcript cleavage or translational inhibition. Besides regulating plant growth and development, miRNAs are well documented to regulate plant adaptation to adverse environmental conditions including nutrient stresses. Scope In this review, we focus on recent progress in our understanding of how miRNAs are involved in plant response to stresses resulting from deficiency in nutrients, such as nitrogen, phosphorus, sulfur, copper and iron, as well as toxicities from heavy metal ions. Conclusions Accumulated evidence indicates that miRNAs play critical roles in sensing the abundance of nutrients, controlling nutrient uptake and phloem-mediated long-distance transport, and nutrient homeostasis. miRNAs act as systemic signals to coordinate these physiological activities helping plants respond to and survive nutrient stresses and toxicities. Knowledge about how miRNAs are involved in plant responses to nutrient stresses promise to provide novel strategies to develop crops with improved nutrient use efficiency which could be grown in soils with either excessive or insufficient availability of nutrients.

Description: Background and aims (i) compare the concentrations of total polyphenols (TP) and condensed tannins (CT), and CT profiles in different organs of mature trees and seedlings of eight true mangrove species in Hong Kong; (ii) examine the antioxidant activities of CT and (iii) relate the non-enzymatic antioxidative defence system with the vertical zonation pattern of mangrove species. Methods Mature trees and seedlings of eight species were collected from a Hong Kong mangrove swamp to determine TP and CT concentrations and the antioxidant activities of CT. Results According to TP concentrations, the true mangrove species could be broadly classified into three groups, (i) Lumnitzera racemosa and Aegiceras corniculatum 〉 (ii) Heritiera littoralis , Excoecaria agallocha , Bruguiera gymnorrhiza and Kandelia obovata 〉 (iii) Acanthus ilicifolius and Avicennia marina . The last two are pioneer species in the most foreshore location. They also had significantly lower antioxidant activities, CT concentrations and different CT profiles than the other six species in mid- and low-tides. Conclusions Classification of the eight true mangrove species into three groups based on polyphenols was similar to their vertical zonation from land to sea. The relationships between these antioxidants and zonation should be further verified by transplantation studies.