Woody plant encroachment is a phenomenon of global concern in drylands due to demonstrated reductions in livestock carrying capacity. However, shrubs are known to contribute to the development of patches of enhanced fertility that might offset any negative effects of increasing grazing. We measured soil physical and chemical characteristics within shrub and open patches across a gradient in livestock grazing to explore how the relative effect of shrubs might change with increasing grazing-induced disturbance.

Abstract Aims This study aimed to determine the responses of soil bacteria and fungi to plant species diversity and plant family composition (PFC) following secondary succession on former farmland (FL). Methods Illumina sequencing of 16S rRNA and ITS genes was used to determine soil microbial communities along a chronosequence of FL left abandoned for 0, 10, 20, 30, 40, and 50 years on the Loess Plateau. Soil properties, plant diversity, and PFC were also investigated. Results Fungal communities were dominated by Ascomycota and Basidiomycota. Fungal diversity and Ascomycota abundance increased with time, while Basidiomycota abundance decreased. The fungal diversity and dominant phyla were related to the increasing levels of plant species diversity and evenness with succession. Bacterial diversity first increased and then decreased as succession proceeded, peaking at 30 years. Bacterial communities transitioned from Actinobacteria to Proteobacteria dominance during the first 30 years, after which Actinobacteria was dominant. Plant family composition exerted indirect effects on the diversity and dominant phyla of bacterial communities, mainly through direct effects on soil organic carbon and total nitrogen content. Bacterial diversity and Proteobacteria abundance were higher at Leguminosae- and Gramineae-dominant succession stages, but lower in Compositae-dominant plots; Actinobacteria showed the opposite result. Conclusions Plant species diversity and evenness might be the key drivers for shaping fungal communities, but bacteria are influenced more by changes in PFC and abiotic soil nutrient levels during succession.

Abstract Background and aims Cadmium (Cd) is one of the heavy metal elements that are most harmful to human health, and the transmission of Cd through the food chain is a global issue. Aegilops markgrafii is a wild relative of the cultivated wheat that is tolerant of high levels of Cd. The objective of this study is to investigate the NAC transcription factors (TFs) involved in Cd tolerance in Ae. markgrafii and to verify their function in transgenic wheat. Methods We cloned NAC TFs from Ae. markgrafii plants exposed to excessive Cd treatment. The expression profiles of NAC TFs in root and shoot tissues were examined using qRT-PCR. Transgenic wheat was obtained via Agrobacterium-mediated transformation. Finally, we examined Cd concentrations in transgenic wheat under excess Cd treatment. Results We identified three NAC TFs and classified them into four subfamilies. Sequence alignments showed that the NAC TFs had conserved N-terminal domains but varied C-terminal domains. Expression profiles of NAC TFs showed about 150-fold up-regulation in the transcription of AemNAC2 and AemNAC3 under excess Cd treatment. Overexpression of AemNAC2 in the wheat cultivar ‘Bobwhite’ led to reduce Cd concentration in the root, shoot and grains. Conclusions AemNAC2 is an important TF that contributes to Cd tolerance in wheat.

To determine whether xylem sap and leaf cytokinin levels were associated with live root length density (LRLD) and leaf senescence, these variables were measured in intact (control) plants and those from which florets were removed, in hybrids of contrasting post-anthesis senescence patterns.

The causal agent of Fusarium wilt in faba bean is Fusarium oxysporum f. sp. fabae (FOF), which significantly reduces the yield in continuous cropping systems. We aimed to evaluate the role of wheat in alleviating Fusarium wilt in faba bean.

Rhizobia are soil bacteria that engage into a mutualistic symbiosis with plants and benefit the host by fixing atmospheric N. In addition, rhizobia can be considered as biocontrol agents, contributing to plant health through direct inhibition of a wide range of pathogens. More recently, it became evident that rhizobial invasion of plant roots can also trigger an increased systemic resistance state in the host, a process resembling the Induced Systemic Resistance (ISR) mechanism. However, this indirect biocontrol property of rhizobia was relatively less explored.

A potential of rare earth elements (including yttrium) (REY) accumulation in olives is increasing due to enhanced use of REY in human activities. REY transfer to extra virgin olive oil (EVOO) is little studied, and characterising the relationships between soil properties and REY concentrations in olive leaves, pomace and EVOO can enhance our understanding of soil-plant interactions.

Here we assessed N and P uptake of four grassland species grown together in response to a short-term drought event along a soil P gradient.

Plasticity of plants refers to their ability to produce different phenotypes in different environments. Plants show plasticity aboveground as well as belowground. The influence of the arbuscular mycorrhizal fungal (AMF) symbiosis on root plasticity is poorly known. This study aimed to quantify plasticity of root-system related, morphological, physiological or mycorrhizal traits along a soil phosphorus (P) supply gradient.

Abstract Background and aims The drivers of variations in leaf nutrient concentrations in cave-dwelling plants remain poorly understood. We aimed to explore the effects of light, soil chemistry and phylogeny on leaf nutrient concentrations in cave-dwelling plants. Methods We quantified light availability and sampled top-soils and leaves of the co-existing herbs and ferns in three caves. We used the traditional and phylogenetic comparative methods to determine the effects of light, soil chemistry and phylogeny on leaf nutrient concentrations and the cross-species correlations between leaf nutrients. Results Leaf nutrient concentrations differed little among caves due to the non-significant relationships of leaf nutrient concentrations with light availability and soil nutrient concentrations across caves. The phylogenetic signals in leaf nutrient concentrations were significant for Ca, Mg and N but non-significant for the remaining nutrients. The evolutionary rates of leaf nutrient concentrations tended to increase with decreasing phylogenetic signals and were faster in herbs than ferns. These contrasting degrees of phylogenetic conservatism in leaf nutrient concentrations were best generated by Ornstein-Uhlenbeck models, i.e., stabilizing selection towards an optimum across species for P, K, S, Fe, Mn and Zn or higher optimal concentrations in herbs than ferns for Ca, Mg and N. Strong cross-species correlations between leaf nutrient concentrations such as Ca vs Mg and N vs P were found. Conclusions Leaf nutrient concentrations in cave-dwelling plants showed convergent adaptations to cave environments and presented contrasting degrees of phylogenetic conservatism to produce leaf nutritional diversity for the co-existing herbs and ferns in caves.

Abstract Background In the soil ecosystem, microbial diversity exists and these diverse organisms interact with plant roots and influence the physicochemical properties of plants. Some of these diverse microorganisms can cause diseases or can provide beneficial interactions with plants. Rhizobacteria are well-known beneficial microorganism that colonize the plant root zone (rhizosphere) and are referred to as plant growth-promoting rhizobacteria (PGPR) that contribute to the promotion of plant growth either directly or indirectly. PGPRs are also known for their biocontrol abilities. Sclerotinia sclerotiorum, an Ascomycetous soil inhabiting fungus, causes white rot disease in cucumbers. This disease results in the loss of millions of dollars annually. The current study was conducted to isolate naturally occurring soil inhabiting bacteria that may promote plant growth under diseased conditions and also antagonize the pathogen. Scope The isolated LH4 strain was identified as Streptomyces sp. by 16S rRNA sequencing and phylogenetic analysis. The plant growth promoting effects and the antifungal antagonistic activities against Sclerotinia sclerotiorum were confirmed by measuring enzymatic activity of LH4 and demonstration in planta. In addition, Streptomyces sp. LH4 pure culture application exhibited significant growth inhibition of S. sclerotiorum in cucumber. Analysis of the major hormones related to pathogen defense; the jasmonic acid, and salicylic acid, showed that the modulation of these two hormones increased disease resistance in cucumber. Conclusion The present study suggests a possible dual role of Streptomyces sp. LH4 as functional material for bio-fertilizer and biocontrol against pathogens.

Unravelling the factors shaping microbial community structure across plant holobiont is required to promote plant health and crop productivity.

The effect of cropping regime on nitrogen (N) uptake in two coexisting plant grass species (Avena sativa and Agropyron cristatum) was investigated.

Abstract Aims Phosphorus (P) loss from paddy fields is a significant issue in sustainable rice production by threatening water environments. We aimed to examine the suitability of mycorrhiza-defective rice (non-mycorrhizal) and its mycorrhizal progenitor to evaluate P loss control via arbuscular mycorrhizal (AM) fungi. We also aimed to investigate the AM effect on P loss via runoff and leaching. Methods We grew the two rice lines in microcosms with and without AM fungi, measured P loss via runoff and leaching before and after nitrogen–phosphorus–potassium fertilization, and quantified plant P content and soil P concentration after the final harvest. Results Mycorrhizal and non-mycorrhizal rice pair systems in the absence of AM fungi had similar plant, soil, runoff, and leachate P contents (except PO43−). In the presence of AM fungi, the concentrations of all P forms in runoff water and leachate in mycorrhizal rice were lower than those in nonmycorrhizal rice regardless of their solubility in water and availability to plants. The cumulative P loss from mycorrhizal systems was 10% less than that from their nonmycorrhizal counterparts. Conclusions This mycorrhizal/non-mycorrhizal rice pair is an efficient experimental tool for research on the control of P loss from paddy fields with AM fungi. AM colonization contributes to the sustainability of rice production by decreasing P loss from paddy fields.

Abstract Background and aims Understanding the influences of environmental variation and anthropogenic disturbance on soil respiration (RS) is critical for accurate prediction of ecosystem C uptake and release. However, surprisingly, little is known about how soil respiration and its components respond to grazing in the context of global climate change (i.e., precipitation or nitrogen deposition increase). Methods We conducted a field manipulative grazing experiment with water and nitrogen addition treatments in a meadow grassland on the Songnen Plain, China, and assessed the combined influences of grazing and global change factors on RS, autotrophic respiration (RA), and heterotrophic respiration (RH). Results Compared with the control plots, RS, RA and RH all exhibited positive responses to water or nitrogen addition in the wet year, while a similar effect occurred only for RH in the dry year. The responses of RS to precipitation regimes were dominated by both frequency and amount. However, grazing significantly inhibited both soil respiration and its components in all subplots. Further analysis demonstrated that the plant root/shoot ratio, belowground biomass and microbial biomass played dominant roles in shaping these C exchange processes. Conclusion These findings suggest that changes in precipitation regimes, nitrogen deposition, and land utilization may significantly alter soil respiration and its component processes by affecting local carbon users (roots and soil microorganism) and carbon substrate supply in meadow steppe grasslands. The future soil carbon sequestration in the studied meadow steppe will be benefited more by the moderate grazing disturbance.

Abstract Aims Dimethylarsinic acid (DMA), an organic arsenic compound found in rice grain, is a causal agent of straighthead disorder, which can decimate yields. To minimize rice accumulation of DMA, we tested 9 molecules for antagonistic effects with DMA. We also tested whether the source of nitrogen is able to affect DMA uptake, as DMA is a weak acid and different nitrogen sources have differing effects on rhizospheric pH. Methods We grew rice (Oryza sativa L. cv. Lemont) hydroponically to maturity in two different experiments. First, 9 potential competitors (boric acid, calcium, glycerol, glycine, lactic acid, phosphoric acid, serine, silicic acid, and urea) were included in the hydroponic solution at a molar ratio ≥ 100:1 competitor:DMA. Second, rice receiving 5 μM DMA was grown under ammonium, nitrate, or a 1:1 mix of ammonium and nitrate. Yield metrics and plant elemental concentrations were measured after harvest. Results Of the potential competitors, only silicic acid was able to alleviate straighthead disorder and no competitors were able to reduce grain As by ≥30%. Under differing nitrogen sources, nitrate decreased plant concentrations of As relative to ammonium, but not in the grain. Conclusions While Si can alleviate DMA uptake, there remains uncertainty in how most DMA enters the plant.

As soil dries, the loss of soil hydraulic conductivity limits water supply to the leaves, which is expected to generate a nonlinear relationship between leaf water potential (ψleaf) and transpiration (E). The effect of soil drying and root properties on ψleaf and E remains elusive.

Abstract Aims The aim of the study was to evaluate the possible role of endophytic fungi (EF) on Rosa powdery mildew (PM) resistance. Methods The endophytic fungal communities of two wild Rosa varieties with different PM susceptibilities were investigated through both culture-dependent and independent methods, and the antagonistic activities of endophytes against the PM pathogen were evaluated by pot experiments. Results There were more OTUs recovered from the PM resistant variety than from the PM susceptible variety. Similarly, the culturable EF from the PM resistant variety (1333 isolates) was more than that from the PM susceptible variety (670 isolates). Consistent with this, the colonization rate of culturable EF of the PM resistant variety was significantly higher than that of the PM susceptible variety at each PM stage (p < 0.05). In addition, it was found that the dominant EF of both varieties were different using culture-dependent and independent methods. The α-diversity of both culturable and un-culturable EF were similar except at the early stage of PM infection. Pot experiments showed that the strain M7SB 41 (Seimatosporium sp.) from PM resistant variety significantly enhanced host plant PM resistance. Conclusions The results suggested that the endophytic fungal communities of two wild Rosa varieties with different PM susceptibilities were significantly different, and the PM resistant Rosa variety harbored more EF than susceptible Rosa variety, and some EF played an important role in host plant PM resistance.

Rhizobia are common members of plant microbiomes. This study aimed to evaluate if rhizobia can colonize sugarcane mini-setts and if and how they affect sprouting and morphological traits of plant development.

Cultivar mixtures can increase productivity through complementarity in resource use, but reported results are often conflicting and the role of plasticity in shaping plant-plant interactions is poorly understood. We aim to determine if individual cultivars show different phenotypic responses when grown in a mixture, whether these responses depend on the neighboring cultivar identity, and how they contribute to variations in productivity and nitrogen (N) use.

Abstract Aims In the Swedish sub-Arctic, mountain birch (Betula pubescens ssp. czerepanovii) forests mediate rapid soil C cycling relative to adjacent tundra heaths, but little is known about the role of individual trees within forests. Here we investigate the spatial extent over which trees influence soil processes. Methods We measured respiration, soil C stocks, root and mycorrhizal productivity and fungi:bacteria ratios at fine spatial scales along 3 m transects extending radially from mountain birch trees in a sub-Arctic ecotone forest. Root and mycorrhizal productivity was quantified using in-growth techniques and fungi:bacteria ratios were determined by qPCR. Results Neither respiration, nor root and mycorrhizal production, varied along transects. Fungi:bacteria ratios, soil organic C stocks and standing litter declined with increasing distance from trees. Conclusions As 3 m is half the average size of forest gaps, these findings suggest that forest soil environments are efficiently explored by roots and associated mycorrhizal networks of B. pubescens. Individual trees exert influence substantially away from their base, creating more uniform distributions of root, mycorrhizal and bacterial activity than expected. However, overall rates of soil C accumulation do vary with distance from trees, with potential implications for spatio-temporal soil organic matter dynamics and net ecosystem C sequestration.

Fine roots and their symbionts are the key drivers of processes such as nutrient cycling and belowground productivity. Their function depends on position in a branching hierarchy, with absorptive roots (responsible for resource acquisition), and transport roots.

Abstract Aims We investigated the legacy effects of a previous ley’s legume proportion on the performance of a following grass crop in a rotation. Methods In April 2015, a pure Lolium multiflorum L. crop was sown after the removal of legume containing swards (0–100% legumes), and was harvested four times over the following one-year period (3 times in 2015 and once the following April 2016). Labeled 15N fertilizer (50 kg N ha−1) was applied during the 2nd and 3rd re-growth periods to determine N fluxes. Results Across the one-year period, a significant legume-legacy induced increase in biomass yield of L. multiflorum was observed over the entire range of previous legume proportions when compared against the non-legume ley, the effect being 2.15 and 1.73 t ha−1 (P ≤ 0.001 each) in swards with 50% and 100% previous legume proportion, respectively, or up to +31%. The legume-legacy effect on biomass yield was most pronounced at the 1st harvest (June) and persisted into the 2nd harvest in August (P ≤ 0.05 both, over the entire range of previous legume proportion), though was no longer evident at the 3rd harvest (September). Importantly, the legume-legacy effect returned in the 4th harvest in April (P ≤ 0.05). Examining the source of N contributing to N yield confirmed that more N was derived from the soil at harvest 1 and 2 for previous legume containing leys (P ≤ 0.001) compared to those which contained no legumes, with a significant increase still seen for legume mixtures at harvest 3 (P ≤ 0.01). Conclusions The results demonstrate a sustained soil-transferred performance-enhancing legacy effect on a following crop in a rotation, with previous legume proportions of 50% having a comparable effect compared with that of a previous legume monoculture.

Data on the variability of hyperaccumulation potential of the facultative serpentinophytes Noccaea kovatsii and N. praecox on different geological substrates are scarce. The aim of this study was to assess the accumulation potential of these two species from ultramafic and non-ultramafic substrates, with special emphasis on the hyperaccumulation of Ni, Zn and Cd.

Abstract Aims Arbuscular mycorrhizal (AM) fungi associate with the majority of terrestrial plants, influencing their growth, nutrient uptake and defence chemistry. Consequently, AM fungi can significantly impact plant-herbivore interactions, yet surprisingly few studies have investigated how AM fungi affect plant responses to root herbivores. This study aimed to investigate how AM fungi affect plant tolerance mechanisms to belowground herbivory. Methods We examined how AM fungi affect plant (Saccharum spp. hybrid) growth, nutrient dynamics and secondary chemistry (phenolics) in response to attack from a root-feeding insect (Dermolepida albohirtum). Results Root herbivory reduced root mass by almost 27%. In response, plants augmented investment in aboveground biomass by 25%, as well as increasing carbon concentrations. The AM fungi increased aboveground biomass, phosphorus and carbon. Meanwhile, root herbivory increased foliar phenolics by 31% in mycorrhizal plants, and increased arbuscular colonisation of roots by 75% overall. AM fungi also decreased herbivore performance, potentially via increasing root silicon concentrations. Conclusions Our results suggest that AM fungi may be able to augment plant tolerance to root herbivory via resource allocation aboveground and, at the same time, enhance plant root resistance by increasing root silicon. The ability of AM fungi to facilitate resource allocation aboveground in this way may be a more widespread strategy for plants to cope with belowground herbivory.

Abstract Background and aims Mycorrhizosphere is the interface between roots and soil where a myriad of microorganisms mediate plant growth, nutrient acquisition and tolerance to biotic and abiotic stress, and result in driving ecosystem biogeochemical cycling. Understanding the complexity and dynamics of mycorrhizosphere and its ecology and evolution are critical to enhancing forest productivity and ecosystem functioning, especially in high latitude temperate or high altitude alpine forests. However, the fungal community compositions and their driving ecological mechanisms of mycorrhizosphere during forest restoration are poorly documented. Methods In this study, we simultaneously examined the ectomycorrhizal (EM) and rhizospheric fungal communities of two dominant host tree species (Abies faxoniana and Betula albosinensis) in subalpine forest communities with distinct forest restoration stages (30- vs. 60-year) after clear-cutting. Illumina MiSeq sequencing of internal transcribed spacer 2 (ITS2) sequences was adopted. Results A total of 1222 EM and 5880 rhizosphere fungal operational taxonomic units (OTUs) were obtained at a 97% sequence similarity level, which were mainly dominated by Basidiomycota. Host identity and forest restoration stage had no significant effects on fungal species richness of both EM and rhizospheric fungi. However, the community assembly of EM and rhizospheric fungi was significantly different during forest restoration, with opposite patterns shown on ectomycorrhizae and rhizosphere. The EM fungal community assembly was significantly affected by host identity, stand age and population dynamic, while the rhizosphere fungal community was significantly structured by combinations of host trees biomass, soil properties and spatial distance. Conclusions Our data provide important insights that community assembly of EM and rhizosphere fungi may respond idiosyncratically during forest restoration, which will help us deeper understanding forest succession, stability and ecosystem functioning on the Qinghai-Tibetan Plateau.

Abstract Background and aims Phosphorus-solubilizing bacteria can colonize the surface of plant roots under natural conditions and may enter plant tissues to form endophytic symbiosis. They can convert unavailable phosphorus in the soil into available phosphorus, which can be utilized by plants. The aims of this study were to investigate the chemotaxis of Bacillus cereus YL6 and its migration and colonization sites in Chinese cabbage and to provide some technical support for the subsequent investigation of the physiological regulation mechanism of phosphate-dissolving bacteria in plants. Methods This study demonstrated that the green fluorescent protein marker did not affect the physiological and biochemical properties of YL6. Through the chemotaxis test and pot experiment, the colonization and growth promoting mechanism of YL6 in Chinese cabbage was explored. Results YL6 showed a strong positive chemotactic response to cabbage roots. The addition of organic acids to the soil promotes the colonization of YL6 in Chinese cabbage roots. Colonization of YL6 in Chinese cabbage is a dynamic process that moves from the root surface to root tissues and then up to stems and leaves. Fluorescence microscopy showed that YL6 mainly colonized cortical cells and vascular bundles of various plant tissues and was also observed in mesophyll cells. The proliferative effect of YL6 resulted from the interaction of effective phosphorus, and exuded auxin and gibberellin in the rhizosheath. Conclusion This study enhanced our understanding of the interaction mechanisms between phosphate-dissolving bacteria YL6 and Chinese cabbage. YL6 has the potential for future development into bio-fertilizer for agricultural production.

Over-grazing have significantly altered above- and belowground functions in terrestrial ecosystem. However, the influence of grazing intensity on plant-soil stoichiometric relations in alpine ecosystems remains unclear.

Abstract Background and aims Fires can alter the elemental stoichiometry of ecosystems, reflecting altered patterns of biogeochemical cycling in the post-fire environment. However, elements other than carbon (C), nitrogen (N), and phosphorus (P) have rarely been studied in this context. Thus, we aimed to expand the understanding of fire’s stoichiometric and biogeochemical effects to encompass a broader suite of biogenic elements. Methods We compared the stoichiometric ratios of C, N, P, potassium (K), sodium (Na), magnesium (Mg), and sulfur (S) in soil, plant litter, and beetles (Thalycrodes pulchrum) between forest plots that have been burned biennially at low intensity since 1972 and plots that have remained unburned. Results Multi-element stoichiometry differed strongly between the fire regimes. Low intensity biennial burning was associated with depletion of C, N, and S relative to P, K, and to a small extent Mg and Na, in soil and litter. The stoichiometry of T. pulchrum biomass was not significantly affected by fire regime, but fire regime-associated variation in the stoichiometry of T. pulchrum biomass was positively correlated with the fire-induced stoichiometric shifts in soil. Conclusions The effects of low intensity prescribed fire on ecological stoichiometry extend to Na, K, Mg, and S in ways consistent with the respective potentials of these elements to volatilize during fire or accumulate in the absence of fire. These effects vary among ecosystem components in a manner that reveals the importance of biological processes and constraints as factors that determine the nature, magnitude, and potential consequences of the stoichiometric signatures of fire regimes. We conclude that long-term changes in fire regime can disrupt or even decouple the biogeochemical cycles of numerous biogenic elements in the soil–plant system.

ABA plays an important role in modulating stomatal response to drought and elevated atmospheric CO2 (e [CO2]). This study aimed to investigate the effect of e[CO2] on the response of leaf gas exchange and plant water relations of barley and tomato plants with different endogenous ABA levels to progressive soil drying.

Since the 1970s, extensive croplands were converted to forest and pasture lands to control severe soil erosion on the Loess Plateau of China. We quantify the direct and indirect effects of vegetation restoration on runoff and sediment yield on hillslopes in the field to improve environmental governance.

Biological soil crusts (BSCs) are widely considered critical for soil fertility in arid ecosystems. However, how microbial communities regulate the C and N cycles during BSC succession is not well understood.

In forestry-drained peatlands, drying leads to changes in C cycling which could affect peat δ13C. Furthermore, the δ13C profile of the entire peat column may reveal effects of earlier climatic periods.

Abstract Aim To investigate the responses of different components of soil respiration to environmental factors at different timescales in a vineyard ecosystem. Methods The trenching method was used to separate total soil respiration (TSR) into autotrophic respiration (AR) and heterotrophic respiration (HR). Soil respiration rates were measured by an LI-8100 automated flux system. Results On the hourly scale, there were contrasting responses in TSR, HR and AR to soil temperature at 5 cm (ST5), with clockwise hysteresis loop responses of TSR and HR to ST5 but a counterclockwise hysteresis loop between AR and ST5. The daily TSR didn’t exponentially response to ST5 during the growing season. On the monthly scale, the relationship between TSR and ST5 showed a counterclockwise hysteresis loop. Meanwhile, the diel respiration peak lagged the peak of gross primary productivity (GPP), but the monthly peak of TSR preceded the monthly peak of GPP. The daily TSR and the daily soil water content at 5 cm (SWC5) in different months showed a quadratic relationship, but there was an exponential correlation between the monthly TSR and the monthly SWC5. Conclusions The relationship between soil respiration and environmental factors derived for a specific timescale cannot be directly applied to other timescales.

Clinoptilolite is a zeolite mineral with high cation exchange capacity used in zeoponic substrates that have been proposed as a solid medium for growing plants or as a fertilizer material. The kinetics of nitrification has not been measured for NH4+ saturated zeoponic substrate. Experiments were conducted to evaluate the production of NO2- and NO3-, and nitrifier populations in zeoponic substrates. Small columns were filled with zeoponic substrate inoculated with a commercial inoculum or soil enrichment culture of nitrifying bacteria. In addition to column studies, a growth chamber study was conducted to evaluate the kinetics of nitrification in zeoponic substrates used to grow radishes (Raphanus sativus L.). The zeoponic substrate provided a readily available source of NH4+, and nitrifying bacteria were active in the substrate. Ammonium oxidation rates in column studies ranged from 5 to 10 micrograms N g-1 substrate h-1, and NO2- oxidation rates were 2 to 9.5 micrograms N g-1 substrate h-1. Rates determined from the growth chamber study were approximately 1.2 micrograms N g-1 substrate h-1. Quantities of NH4+ oxidized to NO2- and NO3- in inoculated zeoponic substrate were in excess of plant up-take. Acidification as a result of NH4+ oxidation resulted in a pH decline, and the zeoponic substrate showed limited buffering capacity.

We analyzed the changes in growth and cell wall properties of roots of rice (Oryza sativa L. cv. Koshihikari) grown for 68.5, 91.5, and 136 h during the Space Shuttle STS-95 mission. In space, most of rice roots elongated in a direction forming a constant mean angle of about 55 degrees with the perpendicular base line away from the caryopsis in the early phase of growth, but later the roots grew in various directions, including away from the agar medium. In space, elongation growth of roots was stimulated. On the other hand, some of elasticity moduli and viscosity coefficients were higher in roots grown in space than on the ground, suggesting that the cell wall of space-grown roots has a lower capacity to expand than the controls. The levels of both cellulose and the matrix polysaccharides per unit length of roots decreased greatly, whereas the ratio of the high molecular mass polysaccharides in the hemicellulose fraction increased in space-grown roots. The prominent thinning of the cell wall could overwhelm the disadvantageous changes in the cell wall mechanical properties, leading to the stimulation of elongation growth in rice roots in space. Thus, growth and the cell wall properties of rice roots were strongly modified under microgravity conditions during spaceflight.

In the Xinjiang province of western China, conventional methods of iodine (I) supplementation (i.e, goiter pills and iodinated salt) used to mitigate I deficiencies were ineffectual. However, the recent addition of KIO3 to irrigation waters has proven effective. This study was conducted to determine the effects of I form and concentration on rice (Oryza sativa L.) growth, I partitioning within the plant, and ultimately to assist in establishing guidelines for incorporating I into the human food chain. We compared IO3- vs. I- in order to determine how these chemical species differ in their biological effects. Rice was grown in 48 L aerated tubs containing nutrient solution and IO3- or I- at 0, 1, 10, or 100 micromoles concentrations (approximately 0, 0.1, 1, and 10 mg kg-1 I). The IO3- at 1 and 10 micromoles had no effect on biomass yields, and the 100 micromole treatment had a small negative effect. The I- at 10 and 100 micromoles was detrimental to biomass yields. The IO3- treatments had more I partitioning to the roots (56%) on average than did the I- treatments (36%), suggesting differences in uptake or translocation between I forms. The data support the theory that IO3- is electrochemically or biologically reduced to I- prior to plant uptake. None of the treatments provided sufficient I in the seed to meet human dietary requirements. The I concentration found in straw at 100 micromoles IO3- was several times greater than seed, and could provide an indirect source of dietary I via livestock feeding on the straw.

We have observed that low soil phosphorus availability alters the gravitropic response of basal roots in common bean (Phaseolus vulgaris L.), resulting in a shallower root system. In this study we use a geometric model to test the hypotheses that a shallower root system is a positive adaptive response to low soil P availability by (1) concentrating root foraging in surface soil horizons, which generally have the highest P availability, and (2) reducing spatial competition for P among roots of the same plant. The growth of nine root systems contrasting in gravitropic response over 320 h was simulated in SimRoot, a dynamic three-dimensional geometric model of root growth and architecture. Phosphorus acquisition and inter-root competition were estimated with Depzone, a program that dynamically models nutrient diffusion to roots. Shallower root systems had greater P acquisition per unit carbon cost than deeper root systems, especially in older root systems. This was due to greater inter-root competition in deeper root systems, as measured by the volume of overlapping P depletion zones. Inter-root competition for P was a significant fraction of total soil P depletion, and increased with increasing values of the P diffusion coefficient (De), with root age, and with increasing root gravitropism. In heterogenous soil having greater P availability in surface horizons, shallower root systems had greater P acquisition than deeper root systems, because of less inter-root competition as well as increased root foraging in the topsoil. Root P acquisition predicted by SimRoot was validated against values for bean P uptake in the field, with an r2 between observed and predicted values of 0.75. Our results support the hypothesis that altered gravitropic sensitivity in P-stressed roots, resulting in a shallower root system, is a positive adaptive response to low P availability by reducing inter-root competition within the same plant and by concentrating root activity in soil domains with the greatest P availability.

Background and aims Carnivorous plants are sensitive to small changes in resource availability, but few previous studies have examined how differences in nutrient and prey availability affect investment in and the benefit of carnivory. We studied the impact of site-level differences in resource availability on ecophysiological traits of carnivory for Drosera rotundifolia L. Methods We measured prey availability, investment in carnivory (leaf stickiness), prey capture and diet of plants growing in two bogs with differences in N deposition and plant available N: Cors Fochno (0.62 g m-2 yr.-1, 353 μg l-1), Whixall Moss (1.37 g m-2 yr.-1, 1505 μg l-1). The total N amount per plant and the contributions of prey/root N to the plants' N budget were calculated using a single isotope natural abundance method. Results Plants at Whixall Moss invested less in carnivory, were less likely to capture prey, and were less reliant on prey-derived N (25.5% compared with 49.4%). Actual prey capture did not differ between sites. Diet composition differed - Cors Fochno plants captured 62% greater proportions of Diptera. Conclusions Our results show site-level differences in plant diet and nutrition consistent with differences in resource availability. Similarity in actual prey capture may be explained by differences in leaf stickiness and prey abundance.

Aims The pseudo-cereal quinoa has an outstanding nutritional value. Seed germination is unusually fast, and plant tolerance to salt stress exceptionally high. Seemingly all seeds harbor bacterial endophytes. This work examines mitogen-activated protein kinase (MAPK) activities during early development. It evaluates possible contribution of endophytes to rapid germination and plant robustness. Methods MAPK activities were monitored in water- and NaCl-imbibed seeds over a 4-h-period using an immunoblot-based approach. Cellulolytic and pectinolytic abilities of bacteria were assessed biochemically, and cellular movement, biofilm, elicitor and antimicrobial compound synthesis genes sequenced. GyrA-based, cultivation-independent studies provided first insight into endophyte diversity. Results Quinoa seeds and seedlings exhibit remarkably complex and dynamic MAPK activity profiles. Depending on seed origin, variances exist in MAPK patterns and probably also in endophyte assemblages. Mucilage-degrading activities enable endophytes to colonize seed surfaces of a non-host species, chia, without apparent adverse effects. Conclusions Owing to their motility, cell wall-loosening and elicitor-generating abilities, quinoa endophytes have the potential to drive cell expansion, move across cell walls, generate damage-associated molecular patterns and activate MAPKs in their host. Bacteria may thus facilitate rapid germination and confer a primed state directly upon seed rehydration. Transfer into non-native crops appears both desirable and feasible.

Aims Slow or failed tree regeneration after forest disturbance is increasingly observed in the central European Alps, potentially amplifying the carbon (C) loss from disturbance. We aimed at quantifying C dynamics of a poorly regenerating disturbance site with a special focus on the role of non-woody ground vegetation. Methods Soil CO2 efflux, fine root biomass, ground vegetation biomass, tree increment and litter input were assessed in (i) an undisturbed section of a ~ 110 years old Norway spruce stand, (ii) in a disturbed section which was clear-cut six years ago (no tree regeneration), and (iii) in a disturbed section which was clear-cut three years ago (no tree regeneration). Results Total soil CO2 efflux was similar across all stand sections (8.5 ± 0.2 to 8.9 ± 0.3 t C ha-1 yr.-1). The undisturbed forest served as atmospheric C sink (2.1 t C ha-1 yr.-1), whereas both clearings were C sources to the atmosphere. The source strength three years after disturbance (-5.5 t C ha-1 yr.-1) was almost twice as high as six years after disturbance (-2.9 t C ha-1 yr.-1), with declining heterotrophic soil respiration and the high productivity of dense graminoid ground vegetation mitigating C loss. Conclusions C loss after disturbance decreases with time and ground vegetation growth. Dense non-woody ground vegetation cover can hamper tree regeneration but simultaneously decrease the ecosystem C loss. The role of ground vegetation should be more explicitly taken into account in forest C budgets assessing disturbance effects.

BACKGROUND AND AIMS Graminaceous plants are grown worldwide as staple crops under a variety of climatic and soil conditions. They release phytosiderophores for Fe acquisition (Strategy II). Aim of the present study was to uncover how the rhizosphere pH, background electrolyte and temperature affect the mobilization of Fe and other metals from soil by phytosiderophores. METHODS For this purpose a series of kinetic batch interaction experiments with the phytosiderophore 2'-deoxymugineic acid (DMA), a calcareous clay soil and a mildly acidic sandy soil were performed. The temperature, electrolyte concentration and applied electrolyte cation were varied. The effect of pH was examined by applying two levels of lime and Cu to the acidic soil. RESULTS Fe mobilization by DMA increased by lime application, and was negatively affected by Cu amendment. Mobilization of Fe and other metals decreased with increasing ionic strength, and was lower for divalent than for monovalent electrolyte cations at equal ionic strength, due to higher adsorption of metal-DMA complexes to the soil. Metal mobilization rates increased with increasing temperature leading to a faster onset of competition; Fe was mobilized faster, but also became depleted faster at higher temperature. Temperature also affected biodegradation rates of metal-DMA complexes. CONCLUSION Rhizosphere pH, electrolyte type and concentration and temperature can have a pronounced effect on Strategy II Fe acquisition by affecting the time and concentration 'window of Fe uptake' in which plants can benefit from phytosiderophore-mediated Fe uptake.

BACKGROUND AND AIMS Elemental uptake in serpentine floras in eastern North America is largely unknown. The objective of this study was to determine major and trace element concentrations in soil and leaves of three native pseudo-metallophyte C4 grasses in situ at five sites with three very different soil types, including three serpentine sites, in eastern USA. METHODS Pseudo-total and extractible concentrations of 15 elements were measured and correlated from the soils and leaves of three species at the five sites. RESULTS Element concentrations in soils of pseudo-metallophytes varied up to five orders of magnitude. Soils from metalliferous sites exhibited higher concentrations of their characteristic elements than non-metalliferous. In metallicolous populations, elemental concentrations depended on the element. Concentrations of major elements (Ca, Mg, K) in leaves were lower than typical toxicity thresholds, whereas concentrations of Zn were higher. CONCLUSIONS In grasses, species can maintain relatively low metal concentrations in their leaves even when soil concentrations are richer. However, in highly Zn-contaminated soil, we found evidence of a threshold concentration above which Zn uptake increases drastically. Finally, absence of main characteristics of serpentine soil at one site indicated the importance of soil survey and restoration to maintain serpentinophytes communities and avoid soil encroachment.

BACKGROUND AND AIMS Picea abies, Pinus mugo and Rhododendron ferrugineum co-exist at the alpine tree line, and can have different mycorrhizal communities. The activity and diversity of mycorrhizal fungi are considered to be important factors in regulation of soil function. METHODS At a tree line site and a lower elevation site in the Austrian Alps, the community structure of ectomycorrhiza on Picea abies and Pinus mugo was determined. The activity of surface enzymes was determined on ectomycorrhizal and ericoid mycorrhizal roots. In soils, the activity of a range of enzymes, nitrogen (N) mineralization and biomass decomposition were determined. RESULTS The community structure of the ectomycorrhizal community of Picea abies and Pinus mugo differed strongly, but the average activity of surface enzymes of the ectomycorrhizal communities was similar. A lower root surface enzyme activity was determined on Rhododendron ferrugineum. Soil N-mineralization under Rhododendron ferrugineum was significantly lower than under Picea abies and Pinus mugo. In soil, the activity of a range of enzymes did not differ at the tree line but differed between the tree line and the lower elevation sites. CONCLUSION The different ectomycorrhizal communities on Picea abies and Pinus mugo and ericoid mycorrhizas on Rhododendron ferrugineum support similar ecosystem functions in soil.

Aims Dianthus caryophyllus is a commercially important ornamental flower. Plant growth promoting rhizobacteria are increasingly applied as bio-fertilisers and bio-fortifiers. We studied the effect of a rhizospheric isolate Klebsiella SGM 81 strain to promote D. caryophyllus growth under sterile and non-sterile conditions, to colonise its root system endophytically and its impact on the cultivatable microbial community. We identified the auxin indole-3-acetic acid (IAA) production of Klebsiella SGM 81 as major bacterial trait most likely to enhance growth of D. caryophyllus. Methods ipdC dependent IAA production of SGM 81 was quantified using LC-MS/MS and localised proximal to D. caryophyllus roots and correlated to root growth promotion and characteristic morphological changes. SGM 81 cells were localised on and within the plant root using 3D rendering confocal microscopy of gfp expressing SGM 81. Using Salkowski reagent IAA production was quantified and localised proximal to roots in situ. The effect of different bacterial titres on rhizosphere bacterial population was CFU enumerated on nutrient agar. The genome sequence of Klebsiella SGM 81 (accession number PRJEB21197) was determined to validate PGP traits and phylogenic relationships. Results Inoculation of D. caryophyllus roots with Klebsiella SGM 81 drastically promoted plant growth when grown in agar and soil, concomitant with a burst in root hair formation, suggesting an increase in root auxin activity. We sequenced the Klebsiella SGM 81 genome, identified the presence of a canonical ipdC gene in Klebsiella SGM 81, confirmed bacterial production and secretion of IAA in batch culture using LC-MS/MS and localised plant dependent IAA production by SGM 81 proximal to roots. We found Klebsiella SGM 81 to be a rhizoplane and endophytic coloniser of D. caryophyllus roots in a dose dependent manner. We found no adverse effects of SGM 81 on the overall rhizospheric microbial population unless supplied to soil in very high titres. Conclusion Klebsiella SGM 81 effectively improves root traits of D. caryophyllus in a dose dependent manner, likely through tryptophan dependent IAA production in the rhizoplane and potentially within the intercellular spaces of root tissue. Under optimal plant growth promoting conditions in non-sterile soil, the high total microbial titre in the rhizosphere supports a mutualistic relationship between Klebsiella SGM 81 and carnation that potentially extends to the wider rhizosphere microbiota.

Aims Drought is the major constraint to rainfed rice productivity in South Asia, but few reports provide detailed characterization of the soil properties related to drought stress severity in the region. The aim of the study was to provide a compilation of drought breeding network sites and their respective levels of drought stress, and to relate soil parameters with yield reduction by drought. Methods This study characterized levels of drought stress and soil nutrient and physical properties at 18 geographically distributed research station sites involved in rice varietal screening in Bangladesh, India, and Nepal, as well as at farmers' fields located near the research stations. Results Based on soil resistance to penetration profiles, a hardpan was surprisingly absent at about half of the sites characterized. Significant relationships of depth of compaction and yield reduction by drought indicated the effects of soil puddling on susceptibility to cracking, rather than water retention by hardpans, on plant water availability in this region. The main difference between research stations and nearby farmers' fields was in terms of soil compaction. Conclusions These results present an initiative for understanding the range of severities of reproductive-stage drought stress in drought-prone rainfed lowland rice-growing areas in South Asia.

Background In the Mediterranean climate, plants have evolved under conditions of low soil-water and nutrient availabilities and have acquired a series of adaptive traits that, in turn exert strong feedback on soil fertility, structure, and protection. As a result, plant-soil systems constitute complex interactive webs where these adaptive traits allow plants to maximize the use of scarce resources. Scope It is necessary to review the current bibliography to highlight the most know characteristic mechanisms underlying Mediterranean plant-soil feed-backs and identify the processes that merit further research in order to reach an understanding of the plant-soil feed-backs and its capacity to cope with future global change scenarios. In this review, we characterize the functional and structural plant-soil relationships and feedbacks in Mediterranean regions. We thereafter discuss the effects of global change drivers on these complex interactions between plants and soil. Conclusions The large plant diversity that characterizes Mediterranean ecosystems is associated to the success of coexisting species in avoiding competition for soil resources by differential exploitation in space (soil layers) and time (year and daily). Among plant and soil traits, high foliar nutrient re-translocation and large contents of recalcitrant compounds reduce nutrient cycling. Meanwhile increased allocation of resources to roots and soil enzymes help to protect against soil erosion and to improve soil fertility and capacity to retain water. The long-term evolutionary adaptation to drought of Mediterranean plants allows them to cope with moderate increases of drought without significant losses of production and survival in some species. However, other species have proved to be more sensitive decreasing their growth and increasing their mortality under moderate rising of drought. All these increases contribute to species composition shifts. Moreover, in more xeric sites, the desertification resulting from synergic interactions among some related process such as drought increases, torrential rainfall increases and human driven disturbances is an increasing concern. A research priority now is to discern the effects of long-term increases in atmospheric CO2 concentrations, warming, and drought on soil fertility and water availability and on the structure of soil communities (e.g. shifts from bacteria to fungi) and on patching vegetation and root-water uplift (from soil to plant and from soil deep layers to soil superficial layers) roles in desertification.

Aims Rhizodeposits collected from hydroponic solutions with roots of maize and barley, and seed mucilage washed from chia, were added to soil to measure their impact on water retention and hysteresis in a sandy loam soil at a range of concentrations. We test the hypothesis that the effect of plant exudates and mucilages on hydraulic properties of soils depends on their physicochemical characteristics and origin. Methods Surface tension and viscosity of the exudate solutions were measured using the Du Noüy ring method and a cone-plate rheometer, respectively. The contact angle of water on exudate treated soil was measured with the sessile drop method. Water retention and hysteresis were measured by equilibrating soil samples, treated with exudates and mucilages at 0.46 and 4.6 mg g-1 concentration, on dialysis tubing filled with polyethylene glycol (PEG) solution of known osmotic potential. Results Surface tension decreased and viscosity increased with increasing concentration of the exudates and mucilage in solutions. Change in surface tension and viscosity was greatest for chia seed exudate and least for barley root exudate. Contact angle increased with increasing maize root and chia seed exudate concentration in soil, but not barley root. Chia seed mucilage and maize root rhizodeposits enhanced soil water retention and increased hysteresis index, whereas barley root rhizodeposits decreased soil water retention and the hysteresis effect. The impact of exudates and mucilages on soil water retention almost ceased when approaching wilting point at -1500 kPa matric potential. Conclusions Barley rhizodeposits behaved as surfactants, drying the rhizosphere at smaller suctions. Chia seed mucilage and maize root rhizodeposits behaved as hydrogels that hold more water in the rhizosphere, but with slower rewetting and greater hysteresis.

Backgrounds and aims Negative plant-soil feedbacks (PSFs) are thought to promote species coexistence, but most evidence is derived from theoretical models and data from plant monoculture experiments. Methods We grew Anthoxanthum odoratum and Centaurea jacea in field plots in monocultures and in mixtures with three ratios (3:1, 2:2 and 1:3) for three years. We then tested in a greenhouse experiment the performance of A. odoratum and C. jacea in pots planted with monocultures and 1:1 mixtures and filled with live and sterile soils collected from the field plots. Results In the greenhouse experiment, C. jacea produced less aboveground biomass in soil conditioned by C. jacea monocultures than in soil conditioned by A. odoratum monocultures, while the aboveground biomass of A. odoratum in general did not differ between the two monospecific soils. The negative PSF effect was greater in the 1:1 plant mixture than in plant monocultures for A. odoratum but did not differ for C. jacea. In the greenhouse experiment, the performance of C. jacea relative to A. odoratum in the 1:1 plant mixture was negatively correlated to the abundance of C. jacea in the field plot where the soil was collected from. This relationship was significant both in live and sterile soils. However, there was no relationship between the performance of A. odoratum relative to C. jacea in the 1:1 plant mixture in the greenhouse experiment and the abundance of A. odoratum in the field plots. Conclusions The response of a plant to PSF depends on whether the focal species grows in monocultures or in mixtures and on the identity of the species. Interspecific competition can exacerbate the negative plant-soil feedbacks compared to intraspecific competition when a plant competes with a stronger interspecific competitor. Moreover, the abundance of a species in mixed plant communities, via plant-soil feedback, negatively influences the relative competitiveness of that species when it grows later in interspecific competition, but this effect varies between species. This phenomenon may contribute to the coexistence of competing plants under natural conditions through preventing the dominance of a particular plant species.

Background and Aims Plants affect the soil environment via litter inputs and changes in biotic communities, which feed back to subsequent plant growth. Here we investigated the individual contributions of litter and biotic communities to soil feedback effects, and plant ability to respond to spatial heterogeneity in soil legacy. Methods We tested for localised and systemic responses of Trifolium repens to soil biotic and root litter legacy of seven grassland species by exposing half of a root system to control soil and the other half to specific inoculum or root litter. Results Soil inoculation triggered a localised reduction in root length while litter locally increased root biomass independent of inoculum or litter species identity. Nodule formation was locally suppressed in response to soil conditioned by another legume (Vicia cracca) and showed a trend towards systemic reduction in response to conspecific soil. V. cracca litter also caused a systemic response with thinner roots produced in the part of the root system not directly exposed to the litter. Conclusions Spatial heterogeneity in root litter distribution and soil communities generate distinct local and systemic responses in root morphology and nodulation. These responses can influence plant-mutualist interactions and nutrient cycling, and should be included in plant co-existence models.

Aims Symbiotic nitrogen fixation (SNF) contributes to improve grain yield under nitrogen (N) deficiency. Climbing beans are known to be superior to bush beans in their potential for SNF. The main objectives of this study were to: (i) quantify genotypic differences in SNF ability of climbing beans using 15N natural abundance method; (ii) identify climbing bean genotypes that combine high SNF ability with high yield potential that could serve as parents in the breeding program; and (iii) test whether δ15N in seed can be used instead of δ15N in shoot for estimating SNF ability. Methods 98 Climbing bean genotypes were evaluated for SNF ability in terms of nitrogen derived from the atmosphere (%Ndfa). Field trials were conducted at two locations in Colombia. Results Significant genotypic differences were observed in SNF ability. Good yielding lines with 4.6 t ha-1 fixed as much as 60% of their N (up to 92 kg of N fixed ha-1) without application of N fertilizer to soil. Conclusions Based on evaluations from both locations, seven climbing bean lines (ENF 235, ENF 234, ENF 28, ENF 21, MAC 27, CGA 10 and PO07AT49) were identified as promising genotypes. Seed samples can be used to determine SNF ability, to select for genotypes with superior SNF ability.

Background and aims Understanding the structures and functions of carbon-based molecules in soils is an important goal in the context of soils as an ecosystem function of immense importance. Polysaccharides are implicated in maintaining soil aggregate status but have not been extensively dissected in terms of their structures and soil adhesion properties. This is largely because of the technical difficulties in identifying polysaccharide structures and quantifying any functional properties. Methods Here, we describe the use of a novel nitrocellulose-based adhesion assay to determine the relative capacities for soil adhesion of over twenty plant and microbial polysaccharides that are likely to be present in soil and to contribute to organic matter content and properties. Weights of soil adhered to spots of known amounts of specific polysaccharides were quantified by scanning of the nitrocellulose sheets. Results The most effective polysaccharides identified from this survey included chitosan, β-1,3-glucan, gum tragacanth, xanthan and xyloglucan. We also demonstrate that the soil adhesion assay is suitable to assess the soil-binding properties of plant exudates. Conclusions The soil adhesion assay will be useful for the functional dissection of the organic matter components of soils and also of the factors involved in soil attachment to plant roots and in rhizosheath formation.

Background and aims Bacterial Non-Specific Acid Phosphatase (NSAP) enzymes are capable of dephosphorylating diverse organic phosphoesters but are rarely studied: their distribution in natural and managed environments is poorly understood. The aim of this study was to generate new insight into the environmental distribution of NSAPs and establish their potential global relevance to cycling of organic phosphorus. Methods We employed bioinformatic tools to determine NSAP diversity and subcellular localization in microbial genomes; used the corresponding NSAP gene sequences to census metagenomes from diverse ecosystems; studied the effect of long-term land management upon NSAP diversity and abundance. Results Periplasmic class B NSAPs are poorly represented in marine and terrestrial environments, reflecting their association with enteric and pathogenic bacteria. Periplasmic class A and outer membrane-associated class C NSAPs are cosmopolitan. NSAPs are more abundant in marine than terrestrial ecosystems and class C more abundant than class A genes, except in an acidic peat where class A genes dominate. A clear effect of land management upon gene abundance was identified. Conclusions NSAP genes are cosmopolitan. Class C genes are more widely distributed: their association with the outer-membrane of cells gives them a clear role in the cycling of organic phosphorus, particularly in soils.

Aims Intercropping can improve plant yields and soil phosphorus (P) use efficiency. This study compares inter- and intra-species intercropping, and determines whether P uptake and shoot biomass accumulation in intercrops are affected by soil P availability. Methods Four barley cultivars (Hordeum vulgare L.) and three legume species (Trifolium subterreneum, Ornithopus sativus and Medicago truncatula) were selected on the basis of their contrasting root exudation and morphological responses to P deficiency. Monocultures and barley-barley and barley-legume intercrops were grown for 6 weeks in a pot trial at very limiting, slightly limiting and excess available soil P. Above-ground biomass and shoot P were measured. Results Barley-legume intercrops had 10-70% greater P accumulation and 0-40% greater biomass than monocultures, with the greatest gains occurring at or below the sub-critical P requirement for barley. No benefit of barley-barley intercropping was observed. The plant combination had no significant effect on biomass and P uptake observed in intercropped treatments. Conclusions Barley-legume intercropping shows promise for sustainable production systems, especially at low soil P. Gains in biomass and P uptake come from inter- rather than intra-species intercropping, indicating that plant diversity resulted in decreased competition between plants for P.

Background Phosphorus (P) fertilizer is usually applied in excess of plant requirement and accumulates in soils due to its strong adsorption, rapid precipitation and immobilisation into unavailable forms including organic moieties. As soils are complex and diverse chemical, biochemical and biological systems, strategies to access recalcitrant soil P are often inefficient, case specific and inconsistently applicable in different soils. Finding a near-universal or at least widely applicable solution to the inefficiency in agricultural P use by plants is an important unsolved problem that has been under investigation for more than half a century. Scope In this paper we critically review the strategies proposed for the remobilization of recalcitrant soil phosphorus for crops and pastures worldwide. We have additionally performed a meta-analysis of available soil 31P-NMR data to establish the potential agronomic value of different stored P forms in agricultural soils. Conclusions Soil inorganic P stocks accounted on average for 1006 ± 115 kg ha-1 (57 ± 7%), while the monoester P pool accounted for 587 ± 32 kg ha-1 (33 ± 2%), indicating the huge potential for the future agronomic use of the soil legacy P. New impact driven research is needed in order to create solutions for the sustainable management of soil P stocks.

Background and aims Plants influence the soil they grow in, and this can alter the performance of other, later growing plants in the same soil. This is called plant-soil feedback and is usually tested with monospecific soils, i.e. soils that are conditioned by one plant species. Here, we test if plant-soil feedbacks of inocula consisting of mixtures of monospecific soils can be predicted from the effects of the component inocula. Methods Chrysanthemum plants were grown in sterile soil inoculated with eight monospecific conditioned soils and with mixtures consisting of all pairwise combinations. Plant biomass and leaf yellowness were measured and the additivity was calculated. Results On average, plant biomass in the mixed inocula was slightly but significantly (6%) lower than predicted. In contrast, when growing in mixed inocula, plants showed 38% less disease symptoms than predicted. Moreover, the larger the difference between the effects of the two monospecific soils on plant growth, the higher the observed effect in the mixture exceeded the predicted effects. Conclusions We show that mixed monospecific soils interact antagonistically in terms of plant growth, but synergistically for disease symptoms. Our study further advances our understanding of plant-soil feedbacks, and suggests that mixing soils can be a powerful tool to steer soil microbiomes to improve plant-soil feedback effects.

Aims Root characteristics are important for predicting plant and ecosystem responses to resource scarcity. Simple, categorical traits for roots could be broadly applied to ecosystem function and restoration experiments, but they need to be evaluated for their role and behaviour under various stresses, including water limitation. We hypothesised that more complex root architectures allow more plastic responses to limited water than do tap roots. Methods We carried out two greenhouse experiments: one with a range of grassland plant species; the other with only species of Asteraceae to test the responsiveness of root architectural classes to location of limited water in the soil column. Using trait screening techniques and X-ray tomography, we measured the plasticity of the roots in response to water location. Results Plasticity of root biomass was lowest in tap rooted species, while fibrous and rhizomatous roots allocated biomass preferentially to where the soil was wettest. X-ray tomography indicated that root morphology was least plastic in rhizomatous species. Conclusions Our results provide a starting point to effective categorisation of plants in terms of rooting architecture that could aid in understanding drought tolerance of grassland species. They also demonstrate the utility of X-ray tomography in root analyses.

Background and aims Soil inoculation is a powerful tool for the restoration of terrestrial ecosystems. However, the origin of the donor material may differentially influence early- and late-successional plant species. Donor soil from late-succession stages may benefit target plant species due to a higher abundance of soil-borne mutualists. Arable soils, on the other hand, may suppress ruderals as they support more root herbivores that preferentially attack ruderal plant species, while mid-succession soils may be intermediate in their effects on ruderals and target species performance. We hypothesized that a mixture of arable and late-succession inocula may outperform pure late-successional inocula for restoration, by promoting late-successional target plants, while simultaneously reducing ruderal species' performance. Methods We conducted a glasshouse experiment and tested the growth of ruderal and target plant species on pure and mixed inocula. The inocula were derived from arable fields, mid-succession grasslands and late-succession heathlands and we created a replacement series testing different pairwise mixitures for each of these inocula types (ratios: 100:0, 75:25, 50:50, 25:75, 0:100 of inoculum A and B respectively). Results In general, we found that a higher proportion of heathland material led to a higher aboveground biomass of target plant species, while responses of ruderal species were variable. We found synergistic effects when specific inocula were mixed. In particular, a 50:50 mixture of heathland and arable soil in the inoculum led to a significant reduction in ruderal species biomass relative to the two respective pure inocula. The overall response was driven by Myosotis arvensis, since the other two ruderal species were not significantly affected. Conclusions Mixing inocula from different successional stages can lead to synergistic effects on restoration, but this highly depends on the specific combination of inocula, the mixing ratio and plant species. This suggest that specific inocula may need to be developed in order to rapidly restore different plant communities.

Background and aims We lack studies evaluating how the identity of plant, lichen and moss species relates to microbial abundance and soil functioning on Antarctica. If species identity is associated with soil functioning, distributional changes of key species, linked to climate change, could significantly affect Antarctic soil functioning. Methods We evaluated how the identity of six Antarctic plant, lichen and moss species relates to a range of soil attributes (C, N and P cycling), microbial abundance and structure in Livingston Island, Maritime Antarctica. We used an effect size metric to predict the association between species (vs. bare soil) and the measured soil attributes. Results We observed species-specific effects of the plant and biocrust species on soil attributes and microbial abundance. Phenols, phosphatase and β-D-cellobiosidase activities were the most important attributes characterizing the observed patterns. We found that the evaluated species positively correlated with soil nutrient availability and microbial abundance vs. bare soil. Conclusions We provide evidence, from a comparative study, that plant and biocrust identity is associated with different levels of soil functioning and microbial abundance in Maritime Antarctica. Our results suggest that changes in the spatial distribution of these species linked to climate change could potentially entail changes in the functioning of Antarctic terrestrial ecosystems.

BACKGROUND AND AIMS Plant-derived phenols are a major input to the terrestrial carbon cycle that might be expected to contribute substantially to dissolved organic carbon (DOC) losses from soils. This study investigated changes in DOC and phenols in leachates from soil treated with individual plant litter types under seasonal temperature change. METHODS Senescing grass, buttercup, ash and oak litters were applied to soil lysimeters. Leachates were collected over 22 months and analysed for DOC and phenols. Phenols in litter and DOC were analysed using on-line thermally assisted hydrolysis and methylation with tetramethylammonium hydroxide (TMAH). RESULTS Mass loss differed between litter type (buttercup>ash>grass>oak). Phenol concentrations in the senescing litters (<2 % TOC) were small, resulting in minor losses to water. Seasonal soil temperature positively correlated with DOC loss from litter-free soils. An initial correlation between temperature change and total phenol concentration in grass and ash litter treatment leachates diminished with time. Dissolved phenol variety in all litter-amended soil leachates increased with time. CONCLUSIONS Plant-derived phenols from senescing litter made a minor contribution to DOC loss from soils. The strength of the relationship between seasonal temperature change and phenol type and abundance in DOC changed with time and was influenced by litter type.