Mycorrhizal fungi reduce nutrient loss from model grassland ecosystems

Ectomycorrhizal fungi alter soil food webs and the functional potential of bacterial communities

Most of Earth's trees rely on critical soil nutrients that ectomycorrhizal fungi (EcMF) liberate and provide, and all of Earth's land plants associate with bacteria that help them survive in nature. Yet, our understanding of how the presence of EcMF modifies soil bacterial communities, soil food webs, and root chemistry requires direct experimental evidence to comprehend the effects that EcMF may generate in the belowground plant microbiome. To this end, we grew Pinus muricata plants in soils that were either inoculated with EcMF and native forest bacterial communities or only native bacterial communities. We then profiled the soil bacterial communities, applied metabolomics and lipidomics, and linked omics data sets to understand how the presence of EcMF modifies belowground biogeochemistry, bacterial community structure, and their functional potential. We found that the presence of EcMF (i) enriches soil bacteria linked to enhanced plant growth in nature, (ii) alters the quantity and composition of lipid and non-lipid soil metabolites, and (iii) modifies plant root chemistry toward pathogen suppression, enzymatic conservation, and reactive oxygen species scavenging. Using this multi-omic approach, we therefore show that this widespread fungal symbiosis may be a common factor for structuring soil food webs.IMPORTANCEUnderstanding how soil microbes interact with one another and their host plant will help us combat the negative effects that climate change has on terrestrial ecosystems. Unfortunately, we lack a clear understanding of how the presence of ectomycorrhizal fungi (EcMF)-one of the most dominant soil microbial groups on Earth-shapes belowground organic resources and the composition of bacterial communities. To address this knowledge gap, we profiled lipid and non-lipid metabolites in soils and plant roots, characterized soil bacterial communities, and compared soils amended either with or without EcMF. Our results show that the presence of EcMF changes soil organic resource availability, impacts the proliferation of different bacterial communities (in terms of both type and potential function), and primes plant root chemistry for pathogen suppression and energy conservation. Our findings therefore provide much-needed insight into how two of the most dominant soil microbial groups interact with one another and with their host plant.

Arbuscular mycorrhizal fungi offset NH3 emissions in temperate meadow soil under simulated warming and nitrogen deposition

Most soil ammonia (NH3) emissions originate from soil nitrogen (N) that has been in the form of exchangeable ammonium. Emitted NH3 not only induces nutrient loss but also has adverse effects on the cycling of N and accelerates global warming. There is evidence that arbuscular mycorrhizal (AM) fungi can alleviate N loss by reducing N2O emissions in N-limited ecosystems, however, some studies have also found that global changes, such as warming and N deposition, can affect the growth and development of AM fungi and alter their functionality. Up to now, the impact of AM fungi on NH3 emissions, and whether global changes reduce the AM fungi's contribution to NH3 emissions reduction, has remained unclear. In this study, we examined how warming, N addition, and AM fungi alter NH3 emissions from high pH saline soils typical of a temperate meadow through a controlled microscopic experiment. The results showed that warming significantly increased soil NH3 emissions, but N addition and combined warming plus N addition had no impact. Inoculations with AM fungi strongly reduced NH3 emissions both under warming and N addition, but AM fungi effects were more pronounced under warming than following N addition. Inoculation with AM fungi reduced soil NH4+-N content and soil pH, and increased plant N content and soil net N mineralization rate while increasing the abundance of ammonia-oxidizing bacterial (AOB) gene. Structural equation modeling (SEM) shows that the regulation of NH3 emissions by AM fungi may be related to soil NH4+-N content and soil pH. These findings highlight that AM fungi can reduce N loss in the form of NH3 by increasing N turnover and uptake under global changes; thus, AM fungi play a vital role in alleviating the aggravation of N loss caused by global changes and in mitigating environmental pollution in the future.

Improving runoff quality in vertical greenery systems: Substrate type outweighed the effect of plant growth promoting microbes

Due to limited urban green spaces and catchments, researchers are exploring the capacity of vertical greenery systems (VGSs) in stormwater management as complementary strategies. While the literature acknowledges the significant impacts of vegetated roof substrates on stormwater, comparing the stormwater management capacities of organic and non-organic substrates for VGSs remains largely unexplored. It is thus essential to gather empirical evidence to enhance the stormwater management capacity of VGSs. Here, we report on the impact of installation factors (substrate type and plant growth-promoting microbe (PGPM) inoculation) and environmental factors (simulated rainwater quantity and substrate moisture) of an innovative VGS on the concentrations and total loads of 15 elements (N, P, Al, V, Cr, Fe, Mn, Co, Ni, Cu, Zn, As, Se, Cd, and Pb) in the runoff. Results showed that substrate type was the most influential factor: concentrations and total loads were significantly higher from a reed-based substrate with high organic matter than from a sandy loam substrate. Substrate type also had profound interactive effects with other factors. For instance, PGPM inoculation significantly reduced the total loads of As, Cr, N, Ni, and Se, regardless of substrate type, and reduced the total loads of Cd, Co, Cu, Fe, Mn, and Pb in the reed-based substrate only. In addition, PGPM inoculation primarily reduced total loads, yet had little effect on concentrations. Substrate type also interacted with simulated rainwater quantity and substrate moisture: for example, in the reed-based substrate, a higher simulated rainwater quantity reduced concentrations but increased total loads, while concentrations and total loads remained constantly low from the sandy loam substrate under various simulated rainwater quantities. High antecedent substrate moisture increased both concentrations and total loads for most of the elements. We conclude that leaching from VGSs can be contained via substrate selection, maintenance of substrate moisture, and beneficial PGPM inoculation.

Simplification of soil biota communities impairs nutrient recycling and enhances above- and belowground nitrogen losses

Agriculture is a major source of nutrient pollution, posing a threat to the earth system functioning. Factors determining the nutrient use efficiency of plant-soil systems need to be identified to develop strategies to reduce nutrient losses while ensuring crop productivity. The potential of soil biota to tighten nutrient cycles by improving plant nutrition and reducing soil nutrient losses is still poorly understood. We manipulated soil biota communities in outdoor lysimeters, planted maize, continuously collected leachates, and measured N2 O- and N2 -gas emissions after a fertilization pulse to test whether differences in soil biota communities affected nutrient recycling and N losses. Lysimeters with strongly simplified soil biota communities showed reduced crop N (-20%) and P (-58%) uptake, strongly increased N leaching losses (+65%), and gaseous emissions (+97%) of N2 O and N2 . Soil metagenomic analyses revealed differences in the abundance of genes responsible for nutrient uptake, nitrate reduction, and denitrification that helped explain the observed nutrient losses. Soil biota are major drivers of nutrient cycling and reductions in the diversity or abundance of certain groups (e.g. through land-use intensification) can disrupt nutrient cycling, reduce agricultural productivity and nutrient use efficiency, and exacerbate environmental pollution and global warming.

Soil phosphorus availability alters the correlations between root phosphorus-uptake rates and net photosynthesis of dominant C3 and C4 species in a typical temperate grassland of Northern China

Phosphorus (P) fertilization can alleviate a soil P deficiency in grassland ecosystems. Understanding plant functional traits that enhance P uptake can improve grassland management. We measured impacts of P addition on soil chemical and microbial properties, net photosynthetic rate (Pn ) and nonstructural carbohydrate concentrations ([NSC]), and root P-uptake rate (PUR), morphology, anatomy, and exudation of two dominant grass species: Leymus chinensis (C3 ) and Cleistogenes squarrosa (C4 ). For L. chinensis, PUR and Pn showed a nonlinear correlation. Growing more adventitious roots compensated for the decrease in P transport per unit root length, so that it maintained a high PUR. For C. squarrosa, PUR and Pn presented a linear correlation. Increased Pn was associated with modifications in root morphology, which further enhanced its PUR and a greater surplus of photosynthate and significantly stimulated root exudation (proxied by leaf [Mn]), which had a greater impact on rhizosheath micro-environment and microbial PLFAs. Our results present correlations between the PUR and the Pn of L. chinensis and C. squarrosa and reveal that NSC appeared to drive the modifications of root morphology and exudation; they provide more objective basis for more efficient P-input in grasslands to address the urgent problem of P deficiency.

The Combined Applications of Microbial Inoculants and Organic Fertilizer Improve Plant Growth under Unfavorable Soil Conditions

The performance of two bio-inoculants either in single or in combined applications with organic fertilizer was tested to determine their effect on plant growth and yield under normal and unfavorable field conditions such as low pH value and low content of P. Arbuscular Mycorrhiza Fungi (AMF; three species of Glomus) and the plant-growth-promoting bacterial strain Kosakonia radicincitans DSM16656 were applied to barley in a two-year field experiment with different soil pH levels and available nutrients. Grain yield; contents of P, N, K, and Mg; and soil microbial parameters were measured. Grain yield and the content of nutrients were significantly increased by the applications of mineral fertilizer, organic fertilizer, AMF, and K. radicincitans, and the combined application of organic fertilizer with AMF and with K. radicincitans over the control under normal growth conditions. Under low-pH and low-P conditions, only the combined application of the organic fertilizer with K. radicincitans and organic fertilizer with AMF could increase the grain yield and content of nutrients of barley over the control.

Soil microbial biodiversity promotes crop productivity and agro-ecosystem functioning in experimental microcosms

Soil biota contribute substantially to multiple ecosystem functions that are key for geochemical cycles and plant performance. However, soil biodiversity is currently threatened by land-use intensification, and a mechanistic understanding of how soil biodiversity loss interacts with the myriad of intensification elements (e.g., the application of chemical fertilizers) is still unresolved. Here we experimentally simplified soil biological communities in microcosms to test whether changes in the soil microbiome influenced soil multifunctionality including crop productivity (leek, Allium porrum). Additionally, half of microcosms were fertilized to further explore how different levels of soil biodiversity interact with nutrient additions. Our experimental manipulation achieved a significant reduction of soil alpha-diversity (45.9 % reduction in bacterial richness, 82.9 % reduction in eukaryote richness) and resulted in the complete removal of key taxa (i.e., arbuscular mycorrhizal fungi). Soil community simplification led to an overall decrease in ecosystem multifunctionality; particularly, plant productivity and soil nutrient retention capacity were reduced with reduced levels of soil biodiversity. Ecosystem multifunctionality was positively correlated with soil biodiversity (R = 0.79). Mineral fertilizer application had little effect on multifunctionality compared to soil biodiversity reduction, but it reduced leek nitrogen uptake from decomposing litter by 38.8 %. This suggests that natural processes and organic nitrogen acquisition are impaired by fertilization. Random forest analyses revealed a few members of protists (i.e., Paraflabellula), Actinobacteria (i.e., Micolunatus), and Firmicutes (i.e., Bacillus) as indicators of ecosystem multifunctionality. Our results suggest that preserving the diversity of soil bacterial and eukaryotic communities within agroecosystems is crucial to ensure the provisioning of multiple ecosystem functions, particularly those directly related to essential ecosystem services such as food provision.

Pronounced temporal changes in soil microbial community and nitrogen transformation caused by benzalkonium chloride

As one typical cationic disinfectant, quaternary ammonium compounds (QACs) were approved for surface disinfection in the coronavirus disease 2019 pandemic and then unintentionally or intentionally released into the surrounding environment. Concerningly, it is still unclear how the soil microbial community succession happens and the nitrogen (N) cycling processes alter when exposed to QACs. In this study, one common QAC (benzalkonium chloride (BAC) was selected as the target contaminant, and its effects on the temporal changes in soil microbial community structure and nitrogen transformation processes were determined by qPCR and 16S rRNA sequencing-based methods. The results showed that the aerobic microbial degradation of BAC in the two different soils followed first-order kinetics with a half-life (4.92 vs. 17.33 days) highly dependent on the properties of the soil. BAC activated the abundance of N fixation gene (nifH) and nitrification genes (AOA and AOB) in the soil and inhibited that of denitrification gene (narG). BAC exposure resulted in the decrease of the alpha diversity of soil microbial community and the enrichment of Crenarchaeota and Proteobacteria. This study demonstrates that BAC degradation is accompanied by changes in soil microbial community structure and N transformation capacity.

Positive feedback between peanut and arbuscular mycorrhizal fungi with the application of hairy vetch in Ultisol

Multiple agricultural practices are being applied to increase crop yield in order to overcome the food shortage. Green manure has emerged as an appropriate practice to improve soil fertility and crop yield. However, the potential functions of arbuscular mycorrhizal fungi (AMF) in the below-ground ecosystems following the application of green manure in Ultisols remain largely unexplored. In this study, qPCR and high-throughput sequencing were used to investigate the response of AMF abundance and communities in different treatment groups, i.e., control (without fertilization), mineral fertilization (NPK), mineral fertilization with returning peanut straw (NPKS), and with green manure (hairy vetch; NPKG). The NPKG treatment significantly increased soil fertility compared to other treatment groups. Compared with control, the NPK, NPKS, and NPKG treatments increased peanut yield by 12.3, 13.1, and 25.4%, respectively. NPKS and NPKG treatments significantly altered the AMF community composition decreased the AMF diversity and increased AMF abundance compared to the control. The AMF network of the NPKG treatment group showed the highest complexity and stability compared to other treatment groups. The structural equation modeling revealed that the application of hairy vetch improved soil nutrients and peanut yield by increasing the soil AMF abundance and network stability. Overall, the results suggested that the application of hairy vetch might trigger positive feedback between the peanut and AMF community, contributing to fertility and yield improvement in the dryland of Ultisol.

Factors Affecting the Natural Regeneration of the Larix principis-rupprechtii Mayr Plantations: Evidence from the Composition and Co-Occurrence Network Structure of Soil Bacterial Communities

Bacterial communities living in the soil can affect forests natural regeneration, but the effects of their composition and network inference on regeneration of Larix principis-rupprechtii Mayr plantations remain largely elusive. Therefore, the redundancy analysis and structure equations modeling of affecting elements for the regeneration of L. principis-rupprechtii plots including the diversity, composition and network structure of soil bacteria, topographic factors, light factors, and soil physicochemical properties have been conducted. It was found that the increased modularity of the soil bacterial community co-occurrence network and the enrichment of metabolic pathway bacteria had a significant positive effect on the successful regeneration (total effect of 0.84). The complexity of the soil bacterial community gradually decreased with the increase of stand regeneration, and the composition and structure of the flora became simpler (with standard path coefficients: −0.70). In addition, altitude also had a positive effect on regeneration with a total effect of 0.39. Soil nutrients had significantly negative effects on regeneration with total effects of −0.87. Soil bacterial communities may mediate the effects of soil nutrients, altitude, litter thickness, and herbaceous diversity on regeneration in L. principis-rupprechtii plantations. The results provide a great contribution to our understanding of regeneration-soil bacterial community interactions and the basis and important data for sustainable management of L. principis-rupprechtii plantations in the Lvliang Mountains located in northern China.

Growth Responses of Three European Weeds on Different AMF Species during Early Development

Arbuscular mycorrhizal fungi (AMF) have multiple functions in agroecosystems and affect many processes below- and aboveground, including plant productivity. Mycorrhizal symbiosis is not necessarily beneficial for the host plant and the growth response can be not only positive but also neutral or negative. Among other factors, the responsiveness of plants to AMF depends on the plant-fungus combination. To find out whether the AMF species or isolate is a decisive factor for growth responses of weeds, 44 AMF isolates were tested in a pot experiment for their effects on three agricultural weeds: Echinochloa crus-galli, Solanum nigrum and Papaver rhoeas. The 44 isolates cover 18 AMF species from 13 genera and all 5 orders of the Glomeromycota. The aboveground biomass of the weeds was determined after different times of growth of each weed. In most cases, the effects of AMF isolates on weed growth were negative or neutral. We conclude that some weed species do not benefit from AMF in terms of growth. AMF species can even cause negative growth responses, an effect that may be of practical interest for organic farming where the aim is to obtain a high diversity and concentration of native AMF for the benefit of the cultivated crops without increasing the labor for mechanical weeding.

Arbuscular mycorrhizal fungi reduce potassium, cadmium and ammonium losses but increases nitrate loss under high intensity leaching events

BACKGROUND

Nutrients and heavy metals can be lost from soils via leaching, and arbuscular mycorrhizal fungi (AMF) can influence these events. Soil column experiments were carried out to examine whether leaching intensity and AMF can alter nutrient and Cd uptake in white clover plants and the extent of their losses through leaching.

RESULTS

The presence of AMF significantly increased shoot and total biomass, as well as increased N, P, Cu and Zn uptake independent of water amount applied; while root P and Cu uptakes were promoted by AMF at any water amount treatments. Higher water amounts led to reductions in total N, K and Zn uptake for AMF-colonized plants in comparison to moderate water amount treatments. In the absence of AMF, white clover at low water amount treatment exhibited maximal root Cd uptake. At high water amount treatments, the presence of AMF significantly decreased leachate volumes and the amount of leached NH₄⁺, K and Cd while AMF significantly increased the amounts of leached NO₃^-.

CONCLUSIONS

Overall we found that AMF-colonized white clover plants reduced NH₄⁺, K and Cd loss from soils but increased the risk of NO₃^- loss under high intensity leaching conditions.

Agricultural Management Drive Bacterial Community Assembly in Different Compartments of Soybean Soil-Plant Continuum

Flowering stage of soybean is an important agronomic trait, which is important for soybean yield, quality and adaptability, and is the external expression of integrating external environmental factors and endogenous signals of the plant itself. Cropping system can change soil properties and fertility, which in turn determine plant growth and yield. The microbial community is the key regulator of plant health and production performance. Currently, there is limited understanding of the effects of cropping systems on microbial community composition, ecological processes controlling community assembly in different soil-plant continuum compartments of soybean. Here, we hope to clarify the structure and assembly process of different soybean compartments bacterial community at flowering stage through our work. The results showed that intercropping decreased the species diversity of rhizosphere and phyllosphere, and phylloaphere microbes mainly came from rhizosphere. FAPROTAX function prediction showed that indicator species sensitive to intercropping and crop rotation were involved in nitrogen/phosphorus cycle and degradation process, respectively. In addition, compared to the continuous cropping, intercropping increased the stochastic assembly processes of bacterial communities in plant-associated compartments, while crop rotation increased the complexity and stability of the rhizosphere network and the deterministic assembly process. Our study highlights the importance of intercropping and crop rotation, as well as rhizosphere and phyllosphere compartments for future crop management and sustainable agricultural regulation of crop microbial communities.

Arbuscular mycorrhizas increased tomato biomass and nutrition but did not affect local soil P availability or 16S bacterial community in the field

While interest in arbuscular mycorrhizal (AM) fungal effects on soil phosphorus (P) have recently increased, field experiments on this topic are lacking. While microcosm studies provided valuable insights, the lack of field studies represents a knowledge gap. Here, we present a field study in which we grew a mycorrhiza-defective tomato (Solanum lycopersicum L.) genotype (named rmc) and its mycorrhizal wild-type progenitor (named 76R) with and without additional fertiliser, using a drip-irrigation system to examine the impacts of the AM symbiosis on soil P availability and plant growth and nutrition. AM effects on fruit biomass and nutrients, soil nutrient availability, soil moisture and the soil bacterial community were examined. At the time of harvest, the AM tomato plants without fertiliser had the same early season fruit biomass and fruit nutrient concentrations as plants that received fertiliser. The presence of roots reduced the concentration of available soil P, ammonium and soil moisture in the top 10 cm soil layer. Arbuscular mycorrhizas did not significantly affect soil P availability, soil moisture, or 16S bacterial community composition. These findings suggest an indirect role for AM fungi in tomato production but not necessarily a direct role in determining soil physicochemical traits, during the one season that this experiment was conducted. While longer-term field studies may be required in the future, the present study provides new insights into impacts of AM fungi on P availability and uptake in a field soil system.

Many bee species, including rare species, are important for function of entire plant-pollinator networks

It is important to understand how biodiversity, including that of rare species, affects ecosystem function. Here, we consider this question with regard to pollination. Studies of pollination function have typically focused on pollination of single plant species, or average pollination across plants, and typically find that pollination depends on a few common species. Here, we used data from 11 plant-bee visitation networks in New Jersey, USA, to ask whether the number of functionally important bee species changes as we consider function separately for each plant species in increasingly diverse plant communities. Using rarefaction analysis, we found the number of important bee species increased with the number of plant species. Overall, 2.5 to 7.6 times more bee species were important at the community scale, relative to the average plant species in the same community. This effect did not asymptote in any of our datasets, suggesting that even greater bee biodiversity is needed in real-world systems. Lastly, on average across plant communities, 25% of bee species that were important at the community scale were also numerically rare within their network, making this study one of the strongest empirical demonstrations to date of the functional importance of rare species.

Arbuscular mycorrhizal fungi mitigate soil nitrogen and phosphorus losses: A meta-analysis

Nutrient loss from terrestrial ecosystems via leaching and gaseous emissions is increasingly threatening global environmental and human health. Although arbuscular mycorrhizal fungi (AMF) have been shown to regulate soil N and P losses, a comprehensive quantitative overview of their influences on the losses of these soil nutrients across global scales is currently lacking. This study used a meta-analysis of 322 observations from 36 studies to assess the effect of AMF inoculum on 11 variables related to the loss of soil N and P. We found that the presence of AMF significantly reduced soil N and P losses, with the most pronounced reduction occurring in soil NO₃^--N (-32%), followed by total P (-21%), available P (-16%) and N₂O (-10%). However, the mitigation effects of AMF on soil N and P loss were dependent on the identity of AMF inoculum, plant type and soil biotic and abiotic factors. Generally, the mitigation effects of AMF increased with increasing AMF root colonization rate, microbial diversity of inoculants, soil organic carbon (SOC) content and experimental duration as well as with decreasing soil sand contents and soil N and P availability. Overall, this meta-analysis highlights the importance of AMF inoculation in mitigating N and P nutrient loss and environmental pollution for terrestrial ecosystem sustainability.

Mycorrhizal Patterns in the Roots of Dominant Festuca rubra in a High-Natural-Value Grassland

Grassland ecosystems occupy significant areas worldwide and represent a reservoir for biodiversity. These areas are characterized by oligotrophic conditions that stimulate mycorrhizal symbiotic partnerships to meet nutritional requirements. In this study, we selected Festuca rubra for its dominance in the studied mountain grassland, based on the fact that grasses more easily accept a symbiotic partner. Quantification of the entire symbiosis process, both the degree of colonization and the presence of a fungal structure, was performed using the root mycorrhizal pattern method. Analysis of data normality indicated colonization frequency as the best parameter for assessing the entire mycorrhizal mechanism, with five equal levels, each of 20%. Most of the root samples showed an intensity of colonization between 0 and 20% and a maximum of arbuscules of about 5%. The colonization degree had an average value of 35%, which indicated a medium permissiveness of roots for mycorrhizal partners. Based on frequency regression models, the intensity of colonization presented high fluctuations at 50% frequency, while the arbuscule development potential was set to a maximum of 5% in mycorrhized areas. Arbuscules were limited due to the unbalanced and unequal root development and their colonizing hyphal networks. The general regression model indicated that only 20% of intra-radicular hyphae have the potential to form arbuscules. The colonization patterns of dominant species in mountain grasslands represent a necessary step for improved understanding of the symbiont strategies that sustain the stability and persistence of these species.

Crop diversity enriches arbuscular mycorrhizal fungal communities in an intensive agricultural landscape

Arbuscular mycorrhizal fungi (AMF) are keystone symbionts of agricultural soils but agricultural intensification has negatively impacted AMF communities. Increasing crop diversity could ameliorate some of these impacts by positively affecting AMF. However, the underlying relationship between plant diversity and AMF community composition has not been fully resolved. We examined how greater crop diversity affected AMF across farms in an intensive agricultural landscape, defined by high nutrient input, low crop diversity and high tillage frequency. We assessed AMF communities across 31 field sites that were either monocultures or polycultures (growing > 20 different crop types) in three ways: richness, diversity and composition. We also determined root colonization across these sites. We found that polycultures drive the available AMF community into richer and more diverse communities while soil properties structure AMF community composition. AMF root colonization did not vary by farm management (monocultures vs polycultures), but did vary by crop host. We demonstrate that crop diversity enriches AMF communities, counteracting the negative effects of agricultural intensification on AMF, providing the potential to increase agroecosystem functioning and sustainability.

Mycorrhizal-Bacterial Amelioration of Plant Abiotic and Biotic Stress

Soil microbiota plays an important role in the sustainable production of the different types of agrosystems. Among the members of the plant microbiota, mycorrhizal fungi (MF) and plant growth-promoting bacteria (PGPB) interact in rhizospheric environments leading to additive and/or synergistic effects on plant growth and heath. In this manuscript, the main mechanisms used by MF and PGPB to facilitate plant growth are reviewed, including the improvement of nutrient uptake, and the reduction of ethylene levels or biocontrol of potential pathogens, under both normal and stressful conditions due to abiotic or biotic factors. Finally, it is necessary to expand both research and field use of bioinoculants based on these components and take advantage of their beneficial interactions with plants to alleviate plant stress and improve plant growth and production to satisfy the demand for food for an ever-increasing human population.

Arbuscular mycorrhizal fungus-induced decrease in nitrogen concentration in pore water and nitrogen leaching loss from red soil under simulated heavy rainfall

Arbuscular mycorrhizal fungus (AMF) is generally colonized in plant roots and influences the migration of mineral elements such as nitrogen (N) in soils. However, its effect on N leaching loss in red soils is limited. In the present study, red soils were collected from wasteland, farmland, and slopeland in the Yunnan Plateau. Maize, as a host plant, was cultured in a dual-compartment cultivation system. There were mycorrhizal and hyphal compartments for the AMF inoculation treatment and root and soil compartments for the non-inoculation treatment. The N concentration and uptake in maize, N concentration in pore water within two depth (0-20 and 20-40 cm), and N leaching losses from soil under simulated heavy rainfall (40 and 80 mm/h) were analyzed. Results showed that AMF inoculation significantly enhanced the biomass and N uptake in maize. Compared with the root and soil compartments, the N concentrations in pore water and their leaching losses from the mycorrhizal and hyphal compartments were decreased by 48-77% and 51-74%, respectively. Moreover, significant or extremely significantly positive correlations were observed between the N concentrations in pore water with the N leaching losses from soil. The three-way ANOVA showed that AMF highly significantly decreased N concentrations in pore water and their leaching losses from wasteland, farmland, and slopeland; rainfall intensity had strong influences on the N concentration in pore water from farmland and N leaching losses from wasteland and farmland, whereas the maize root's effect was insignificant. The study indicated that the AMF-induced decreases in the N leaching loss from red soils were caused by increased N uptake by maize and decreased N concentrations in pore water. These results have implications for reducing nutrient leaching loss through the management of beneficial microorganisms in soils.

Potential for Mycorrhizae-Assisted Phytoremediation of Phosphorus for Improved Water Quality

During this 6th Great Extinction, freshwater quality is imperiled by upland terrestrial practices. Phosphorus, a macronutrient critical for life, can be a concerning contaminant when excessively present in waterways due to its stimulation of algal and cyanobacterial blooms, with consequences for ecosystem functioning, water use, and human and animal health. Landscape patterns from residential, industrial and agricultural practices release phosphorus at alarming rates and concentrations threaten watershed communities. In an effort to reconcile the anthropogenic effects of phosphorus pollution, several strategies are available to land managers. These include source reduction, contamination event prevention and interception. A total of 80% of terrestrial plants host mycorrhizae which facilitate increased phosphorus uptake and thus removal from soil and water. This symbiotic relationship between fungi and plants facilitates a several-fold increase in phosphorus uptake. It is surprising how little this relationship has been encouraged to mitigate phosphorus for water quality improvement. This paper explores how facilitating this symbiosis in different landscape and land-use contexts can help reduce the application of fertility amendments, prevent non-point source leaching and erosion, and intercept remineralized phosphorus before it enters surface water ecosystems. This literature survey offers promising insights into how mycorrhizae can aid ecological restoration to reconcile humans' damage to Earth's freshwater. We also identify areas where research is needed.

Effects of plant roots and arbuscular mycorrhizas on soil phosphorus leaching

While the impact of arbuscular mycorrhizal fungi (AMF) on phosphorus (P) uptake is well understood, the mechanism(s) of how these fungi affect P leaching from soil is still unclear. Here we present results of a study in which we grew a mycorrhiza-defective tomato (Solanum lycopersicum L.) genotype (named rmc) and its mycorrhizal wild-type progenitor (named 76R) in microcosms containing non-sterile soil, to examine the influence of roots and AMF on P leaching. More P was leached from the planted microcosms as compared to the plant-free controls. Further, although there was more plant biomass and greater P uptake in the mycorrhizal plant treatments, these treatments were associated with the most leaching of total P, reactive P, and dissolved organic carbon (DOC). There was a strong correlation between the total P and DOC leached, suggesting that root and fungal exudates may have affected P leaching. These findings provide new insights into the impact of roots and AMF on nutrient leaching in soils.

Advancing an interdisciplinary framework to study seed dispersal ecology

Although dispersal is generally viewed as a crucial determinant for the fitness of any organism, our understanding of its role in the persistence and spread of plant populations remains incomplete. Generalizing and predicting dispersal processes are challenging due to context dependence of seed dispersal, environmental heterogeneity and interdependent processes occurring over multiple spatial and temporal scales. Current population models often use simple phenomenological descriptions of dispersal processes, limiting their ability to examine the role of population persistence and spread, especially under global change. To move seed dispersal ecology forward, we need to evaluate the impact of any single seed dispersal event within the full spatial and temporal context of a plant's life history and environmental variability that ultimately influences a population's ability to persist and spread. In this perspective, we provide guidance on integrating empirical and theoretical approaches that account for the context dependency of seed dispersal to improve our ability to generalize and predict the consequences of dispersal, and its anthropogenic alteration, across systems. We synthesize suitable theoretical frameworks for this work and discuss concepts, approaches and available data from diverse subdisciplines to help operationalize concepts, highlight recent breakthroughs across research areas and discuss ongoing challenges and open questions. We address knowledge gaps in the movement ecology of seeds and the integration of dispersal and demography that could benefit from such a synthesis. With an interdisciplinary perspective, we will be able to better understand how global change will impact seed dispersal processes, and potential cascading effects on plant population persistence, spread and biodiversity.

Arbuscular Mycorrhizal Fungi Mitigate Nitrogen Leaching under Poplar Seedlings

The leaching of soil nitrogen (N) has become one of the most concerning environmental threats to ecosystems. Arbuscular mycorrhizal (AM) fungi have important ecological functions, however, their influence on soil N leaching and the mechanism of action remain unclear. We conducted a two-factor (N application level × AM inoculation) experiment on poplar, and for the first time, comprehensively analyzed the mechanism by which AM fungi influence soil N leaching. The results showed that, under optimum (7.5 mM) and high (20 mM) N levels, the nitrate (NO3−) and ammonium (NH4+) concentrations of leachate in the AM inoculated treatment (+AM) were lower than in the non-inoculated treatment (−AM), with significant reductions of 20.0% and 67.5%, respectively, under high N level, indicating that AM inoculation can reduce soil N leaching and that it is more effective for NH4+. The arbuscular and total colonization rates gradually increased, and the morphology of spores and vesicles changed as the N level increased. Under optimum and high N levels, +AM treatment increased the root N concentration by 11.7% and 50.7%, respectively; the increase was significant (p < 0.05) at the high N level, which was associated with slightly increased transpiration and root activity despite reductions in root surface area and root length. Additionally, the +AM treatment increased soil cation exchange capacity (CEC), soil organic carbon (SOC), and significantly (p < 0.05) increased the proportions of macroaggregates (but without significant change in microaggregates), causing soil total nitrogen (TN) to increase by 7.2% and 4.7% under optimum and high N levels, respectively. As the N levels increased, the relative contributions of AM inoculation on N leaching increased, however, the contributions of plant physiological and soil variables decreased. Among all of the variables, SOC had important contributions to NH4+ and total N in the leachate, while root N concentration had a higher contribution to NO3−. In conclusion, AM fungi can mitigate soil N leaching and lower the risk of environmental pollution via enhancing N interception by the inoculated fungi, increasing N sequestration in plant roots, and by improving soil N retention.

Nitrogen fertilization altered arbuscular mycorrhizal fungi abundance and soil erosion of paddy fields in the Taihu Lake region of China

Arbuscular mycorrhizal (AM) fungi were of importance in mitigating soil erosion, which was highly influenced by biotic and abiotic factors, such as host plant growth and soil nutrient. To investigate the impact of nitrogen (N) fertilization on seasonal variance in AM colonization and soil erosion, we conducted a field experiment with rice cultivation under four N fertilizer levels (0 kg N ha^-1, 270 kg N ha^-1, 300 kg N ha^-1, and 375 kg N ha^-1 plus organic fertilizers) in the Taihu Lake region, China. We investigated AM colonization before rice transplantation, during rice growth, and after rice harvest. We also assessed soil splash erosion of intact soil cores sampled at tillering and after rice harvest. We found that AM colonization (indicated by percentage of root length colonization) varied from 15 to 73%, which was attributed to rice growth, N fertilization, and their interaction. Soil loss due to splash erosion was cut down by organic N fertilizer at tillering, while higher inorganic N fertilization significantly increased soil loss after rice harvest. Additionally, we found significantly negative relationships of AM colonization to soil loss but positive relationships to soil aggregate stability. We highlighted the potential role of AM fungi in decreasing soil erosion and suggested that high N fertilization should be considered carefully when seeking after high yields.

Arbuscular Mycorrhizal Fungi Alter the Community Structure of Ammonia Oxidizers at High Fertility via Competition for Soil NH4. MICROBIAL ECOLOGY 2019;78:147-158. [PMID: 30402724 DOI: 10.1007/s00248-018-1281-2]

Nitrification represents a central process in the cycling of nitrogen (N) which in high-fertility habitats can occasionally be undesirable. Here, we explore how arbuscular mycorrhiza (AM) impacts nitrification when N availability is not limiting to plant growth. We wanted to test which of the mechanisms that have been proposed in the literature best describes how AM influences nitrification. We manipulated the growth settings of Plantago lanceolata so that we could control the mycorrhizal state of our plants. AM induced no changes in the potential nitrification rates or the estimates of ammonium oxidizing (AO) bacteria. However, we could observe a moderate shift in the community of ammonia-oxidizers, which matched the shift we saw when comparing hyphosphere to rhizosphere soil samples and mirrored well changes in the availability of ammonium in soil. We interpret our results as support that it is competition for N that drives the interaction between AM and AO. Our experiment sheds light on an understudied interaction which is pertinent to typical management practices in agricultural systems.

Subsoil Arbuscular Mycorrhizal Fungi for Sustainability and Climate-Smart Agriculture: A Solution Right Under Our Feet?

With growing populations and climate change, assuring food and nutrition security is an increasingly challenging task. Climate-smart and sustainable agriculture, that is, conceiving agriculture to be resistant and resilient to a changing climate while keeping it viable in the long term, is probably the best solution. The role of soil biota and particularly arbuscular mycorrhizal (AM) fungi in this new agriculture is believed to be of paramount importance. However, the large nutrient pools and the microbiota of subsoils are rarely considered in the equation. Here we explore the potential contributions of subsoil AM fungi to a reduced and more efficient fertilization, carbon sequestration, and reduction of greenhouse gas emissions in agriculture. We discuss the use of crop rotations and cover cropping with deep rooting mycorrhizal plants, and low-disturbance management, as means of fostering subsoil AM communities. Finally, we suggest future research goals that would allow us to maximize these benefits.

Nitrogen transfer from one plant to another depends on plant biomass production between conspecific and heterospecific species via a common arbuscular mycorrhizal network

The formation of a common mycorrhizal network (CMN) between roots of different plant species enables nutrient transfers from one plant to another and their coexistence. However, almost all studies on nutrient transfers between CMN-connected plants have separately, but not simultaneously, been demonstrated under the same experimentation. Both conspecific and heterospecific seedlings of Cinnamomum camphora, Bidens pilosa, and Broussonetia papyrifera native to a karst habitat in southwest China were concurrently grown in a growth microcosm that had seven hollowed compartments (six around one in the center) being covered by 35.0-μm and/or 0.45-μm nylon mesh. The Ci. camphora in the central compartment was supplied with or without Glomus etunicatum and ¹⁵N to track N transfers between CMN-connected conspecific and heterospecific seedlings. The results showed as follows: significant greater nitrogen accumulations, biomass productions, ¹⁵N content, % N_transfer, and the N_transfer amount between receiver plant species ranked as Br. papyrifera≈Bi. pilosa > Ci. camphora under both M⁺ and M^-, and as under M⁺ than under M^- for Ci. camphora but not for both Bi. Pilosa and Br. papyrifera; the CMN transferred more nitrogen (¹⁵N content, % N_transfer, and N_transfer amount) from the donor Ci. camphora to the heterospecific Br. papyrifera and Bi. pilosa, with a lower percentage of nitrogen derived from transfer (%NDFT). These findings suggest that the CMN may potentially regulate the nitrogen transfer from a donor plant to individual heterospecific receiver plants, where the ratio of nitrogen derived from transfer depends on the biomass strength of the individual plants.

Arbuscular Mycorrhizal Fungi Alter Plant and Soil C:N:P Stoichiometries Under Warming and Nitrogen Input in a Semiarid Meadow of China

Ecological stoichiometry has been widely used to determine how plant-soil systems respond to global change and to reveal which factors limit plant growth. Arbuscular mycorrhizal fungi (AMF) can increase plants' uptake of nutrients such as nitrogen (N) and phosphorus (P), thereby altering plant and soil stoichiometries. To understand the regulatory effect of AMF feedback on plants and soil stoichiometry under global change, a microcosm experiment was conducted with warming and N input. The C₄ grass Setaria viridis, C₃ grass Leymus chinensis, and Chenopodiaceae species Suaeda corniculata were studied. The results showed that the mycorrhizal benefits for the C₄ grass S. viridis were greater than those for the C₃ grass L. chinensis, whereas for the Chenopodiaceae species S. corniculata, AMF symbiosis was antagonistic. Under N input and a combination of warming and N input, AMF significantly decreased the N:P ratios of all three species. Under N input, the soil N content and the N:P ratio were decreased significantly in the presence of AMF, whereas the soil C:N ratio was increased. These results showed that AMF can reduce the P limitation caused by N input and improve the efficiency of nutrient utilization, slow the negative influence of global change on plant growth, and promote grassland sustainability.

Biodiversity of arbuscular mycorrhizal fungi and ecosystem function

Contents Summary 1059 I. Introduction: pathways of influence and pervasiveness of effects 1060 II. AM fungal richness effects on ecosystem functions 1062 III. Other dimensions of biodiversity 1062 IV. Back to basics - primary axes of niche differentiation by AM fungi 1066 V. Functional diversity of AM fungi - a role for biological stoichiometry? 1067 VI. Past, novel and future ecosystems 1068 VII. Opportunities and the way forward 1071 Acknowledgements 1072 References 1072 SUMMARY: Arbuscular mycorrhizal (AM) fungi play important functional roles in ecosystems, including the uptake and transfer of nutrients, modification of the physical soil environment and alteration of plant interactions with other biota. Several studies have demonstrated the potential for variation in AM fungal diversity to also affect ecosystem functioning, mainly via effects on primary productivity. Diversity in these studies is usually characterized in terms of the number of species, unique evolutionary lineages or complementary mycorrhizal traits, as well as the ability of plants to discriminate among AM fungi in space and time. However, the emergent outcomes of these relationships are usually indirect, and thus context dependent, and difficult to predict with certainty. Here, we advocate a fungal-centric view of AM fungal biodiversity-ecosystem function relationships that focuses on the direct and specific links between AM fungal fitness and consequences for their roles in ecosystems, especially highlighting functional diversity in hyphal resource economics. We conclude by arguing that an understanding of AM fungal functional diversity is fundamental to determine whether AM fungi have a role in the exploitation of marginal/novel environments (whether past, present or future) and highlight avenues for future research.

Poor plant performance under simulated climate change is linked to mycorrhizal responses in a semiarid shrubland

Warmer and drier conditions associated with ongoing climate change will increase abiotic stress for plants and mycorrhizal fungi in drylands worldwide, thereby potentially reducing vegetation cover and productivity and increasing the risk of land degradation and desertification. Rhizosphere microbial interactions and feedbacks are critical processes that could either mitigate or aggravate the vulnerability of dryland vegetation to forecasted climate change.We conducted a four-year manipulative study in a semiarid shrubland in the Iberian Peninsula to assess the effects of warming (~2.5ºC; W), rainfall reduction (~30%; RR) and their combination (W+RR) on the performance of native shrubs (Helianthemum squamatum) and their associated mycorrhizal fungi.Warming (W and W+RR) decreased the net photosynthetic rates of H. squamatum shrubs by ~31% despite concurrent increases in stomatal conductance (~33%), leading to sharp decreases (~50%) in water use efficiency. Warming also advanced growth phenology, decreased leaf nitrogen and phosphorus contents per unit area, reduced shoot biomass production by ~36% and decreased survival during a dry year in both W and W+RR plants. Plants under RR showed more moderate decreases (~10-20%) in photosynthesis, stomatal conductance and shoot growth.Warming, RR and W+RR altered ectomycorrhizal fungal (EMF) community structure and drastically reduced the relative abundance of EMF sequences obtained by high-throughput sequencing, a response associated with decreases in the leaf nitrogen, phosphorus and dry matter contents of their host plants. In contrast to EMF, the community structure and relative sequence abundances of other non-mycorrhizal fungal guilds were not significantly affected by the climate manipulation treatments.Synthesis: Our findings highlight the vulnerability of both native plants and their symbiotic mycorrhizal fungi to climate warming and drying in semiarid shrublands, and point to the importance of a deeper understanding of plant-soil feedbacks to predict dryland vegetation responses to forecasted aridification. The interdependent responses of plants and ectomycorrhizal fungi to warming and rainfall reduction may lead to a detrimental feedback loop on vegetation productivity and nutrient pool size, which could amplify the adverse impacts of forecasted climate change on ecosystem functioning in EMF-dominated drylands.

Mycorrhizal fungi enhance plant nutrient acquisition and modulate nitrogen loss with variable water regimes

Climate change will alter both the amount and pattern of precipitation and soil water availability, which will directly affect plant growth and nutrient acquisition, and potentially, ecosystem functions like nutrient cycling and losses as well. Given their role in facilitating plant nutrient acquisition and water stress resistance, arbuscular mycorrhizal (AM) fungi may modulate the effects of changing water availability on plants and ecosystem functions. The well-characterized mycorrhizal tomato (Solanum lycopersicum L.) genotype 76R (referred to as MYC+) and the mutant mycorrhiza-defective tomato genotype rmc were grown in microcosms in a glasshouse experiment manipulating both the pattern and amount of water supply in unsterilized field soil. Following 4 weeks of differing water regimes, we tested how AM fungi affected plant productivity and nutrient acquisition, short-term interception of a 15NH4+ pulse, and inorganic nitrogen (N) leaching from microcosms. AM fungi enhanced plant nutrient acquisition with both lower and more variable water availability, for instance increasing plant P uptake more with a pulsed water supply compared to a regular supply and increasing shoot N concentration more when lower water amounts were applied. Although uptake of the short-term 15NH4+ pulse was higher in rmc plants, possibly due to higher N demand, AM fungi subtly modulated NO3- leaching, decreasing losses by 54% at low and high water levels in the regular water regime, with small absolute amounts of NO3- leached (<1 kg N/ha). Since this study shows that AM fungi will likely be an important moderator of plant and ecosystem responses to adverse effects of more variable precipitation, management strategies that bolster AM fungal communities may in turn create systems that are more resilient to these changes.

Symbiotic soil fungi enhance ecosystem resilience to climate change

Substantial amounts of nutrients are lost from soils through leaching. These losses can be environmentally damaging, causing groundwater eutrophication and also comprise an economic burden in terms of lost agricultural production. More intense precipitation events caused by climate change will likely aggravate this problem. So far it is unresolved to which extent soil biota can make ecosystems more resilient to climate change and reduce nutrient leaching losses when rainfall intensity increases. In this study, we focused on arbuscular mycorrhizal (AM) fungi, common soil fungi that form symbiotic associations with most land plants and which increase plant nutrient uptake. We hypothesized that AM fungi mitigate nutrient losses following intensive precipitation events (higher amount of precipitation and rain events frequency). To test this, we manipulated the presence of AM fungi in model grassland communities subjected to two rainfall scenarios: moderate and high rainfall intensity. The total amount of nutrients lost through leaching increased substantially with higher rainfall intensity. The presence of AM fungi reduced phosphorus losses by 50% under both rainfall scenarios and nitrogen losses by 40% under high rainfall intensity. Thus, the presence of AM fungi enhanced the nutrient interception ability of soils, and AM fungi reduced the nutrient leaching risk when rainfall intensity increases. These findings are especially relevant in areas with high rainfall intensity (e.g., such as the tropics) and for ecosystems that will experience increased rainfall due to climate change. Overall, this work demonstrates that soil biota such as AM fungi can enhance ecosystem resilience and reduce the negative impact of increased precipitation on nutrient losses.

Response of AM fungi spore population to elevated temperature and nitrogen addition and their influence on the plant community composition and productivity

To examine the influence of elevated temperature and nitrogen (N) addition on species composition and development of arbuscular mycorrhizal fungi (AMF) and the effect of AMF on plant community structure and aboveground productivity, we conducted a 5-year field experiment in a temperate meadow in northeast China and a subsequent greenhouse experiment. In the field experiment, N addition reduced spore population diversity and richness of AMF and suppressed the spore density and the hyphal length density (HLD). Elevated temperature decreased spore density and diameter and increased the HLD, but did not affect AMF spore population composition. In the greenhouse experiment, AMF altered plant community composition and increased total aboveground biomass in both elevated temperature and N addition treatments; additionally, AMF also increased the relative abundance and aboveground biomass of the grasses Leymus chinensis (Poaceae) and Setaria viridis (Gramineae) and significantly reduced the relative abundance and aboveground biomass of the Suaeda corniculata (Chenopodiaceae). Although elevated temperature and N addition can affect species composition or suppress the development of AMF, AMF are likely to play a vital role in increasing plant diversity and productivity. Notably, AMF might reduce the threat of climate change induced degradation of temperate meadow ecosystems.

Using mycorrhiza-defective mutant genotypes of non-legume plant species to study the formation and functioning of arbuscular mycorrhiza: a review

A significant challenge facing the study of arbuscular mycorrhiza is the establishment of suitable non-mycorrhizal treatments that can be compared with mycorrhizal treatments. A number of options are available, including soil disinfection or sterilisation, comparison of constitutively mycorrhizal and non-mycorrhizal plant species, comparison of plants grown in soils with different inoculum potential and the comparison of mycorrhiza-defective mutant genotypes with their mycorrhizal wild-type progenitors. Each option has its inherent advantages and limitations. Here, the potential to use mycorrhiza-defective mutant and wild-type genotype plant pairs as tools to study the functioning of mycorrhiza is reviewed. The emphasis of this review is placed on non-legume plant species, as mycorrhiza-defective plant genotypes in legumes have recently been extensively reviewed. It is concluded that non-legume mycorrhiza-defective mutant and wild-type pairs are useful tools in the study of mycorrhiza. However, the mutant genotypes should be well characterised and, ideally, meet a number of key criteria. The generation of more mycorrhiza-defective mutant genotypes in agronomically important plant species would be of benefit, as would be more research using these genotype pairs, especially under field conditions.

The role of arbuscular mycorrhizas in reducing soil nutrient loss

Substantial amounts of nutrients are lost from soils via leaching and as gaseous emissions. These losses can be environmentally damaging and expensive in terms of lost agricultural production. Plants have evolved many traits to optimize nutrient acquisition, including the formation of arbuscular mycorrhizas (AM), associations of plant roots with fungi that acquire soil nutrients. There is emerging evidence that AM have the ability to reduce nutrient loss from soils by enlarging the nutrient interception zone and preventing nutrient loss after rain-induced leaching events. Until recently, this important ecosystem service of AM had been largely overlooked. Here we review the role of AM in reducing nutrient loss and conclude that this role cannot be ignored if we are to increase global food production in an environmentally sustainable manner.

Mycorrhizal ecology and evolution: the past, the present, and the future

Almost all land plants form symbiotic associations with mycorrhizal fungi. These below-ground fungi play a key role in terrestrial ecosystems as they regulate nutrient and carbon cycles, and influence soil structure and ecosystem multifunctionality. Up to 80% of plant N and P is provided by mycorrhizal fungi and many plant species depend on these symbionts for growth and survival. Estimates suggest that there are c. 50 000 fungal species that form mycorrhizal associations with c. 250 000 plant species. The development of high-throughput molecular tools has helped us to better understand the biology, evolution, and biodiversity of mycorrhizal associations. Nuclear genome assemblies and gene annotations of 33 mycorrhizal fungal species are now available providing fascinating opportunities to deepen our understanding of the mycorrhizal lifestyle, the metabolic capabilities of these plant symbionts, the molecular dialogue between symbionts, and evolutionary adaptations across a range of mycorrhizal associations. Large-scale molecular surveys have provided novel insights into the diversity, spatial and temporal dynamics of mycorrhizal fungal communities. At the ecological level, network theory makes it possible to analyze interactions between plant-fungal partners as complex underground multi-species networks. Our analysis suggests that nestedness, modularity and specificity of mycorrhizal networks vary and depend on mycorrhizal type. Mechanistic models explaining partner choice, resource exchange, and coevolution in mycorrhizal associations have been developed and are being tested. This review ends with major frontiers for further research.

Is nitrogen transfer among plants enhanced by contrasting nutrient-acquisition strategies?

Nitrogen (N) transfer among plants has been found where at least one plant can fix N2 . In nutrient-poor soils, where plants with contrasting nutrient-acquisition strategies (without N2 fixation) co-occur, it is unclear if N transfer exists and what promotes it. A novel multi-species microcosm pot experiment was conducted to quantify N transfer between arbuscular mycorrhizal (AM), ectomycorrhizal (EM), dual AM/EM, and non-mycorrhizal cluster-rooted plants in nutrient-poor soils with mycorrhizal mesh barriers. We foliar-fed plants with a K(15) NO3 solution to quantify one-way N transfer from 'donor' to 'receiver' plants. We also quantified mycorrhizal colonization and root intermingling. Transfer of N between plants with contrasting nutrient-acquisition strategies occurred at both low and high soil nutrient levels with or without root intermingling. The magnitude of N transfer was relatively high (representing 4% of donor plant N) given the lack of N2 fixation. Receiver plants forming ectomycorrhizas or cluster roots were more enriched compared with AM-only plants. We demonstrate N transfer between plants of contrasting nutrient-acquisition strategies, and a preferential enrichment of cluster-rooted and EM plants compared with AM plants. Nutrient exchanges among plants are potentially important in promoting plant coexistence in nutrient-poor soils.

Spatiotemporal changes in arbuscular mycorrhizal fungal communities under different nitrogen inputs over a 5-year period in intensive agricultural ecosystems on the North China Plain

Appropriate nitrogen (N) management is important to minimize N losses from intensively managed agricultural ecosystems. Understanding the community structure of arbuscular mycorrhizal fungi (AMF) in response to N management can be of great ecological significance, particularly with the recent emphasis on the role of AMF in N cycling. A comprehensive study of both the vertical distribution of AMF in the soil profile and the temporal changes in community structure in maize roots was conducted over a 5-year period at a field site on the North China Plain. The N treatments consisted of zero N, conventional farming practice, and optimum N based on an in-season soil Nmin test. Terminal restriction fragment length polymorphism and clone sequencing were used to analyse the AMF community. Optimum N mitigated the decline in richness of AMF in the conventional N treatment in the surface soil. Diverse and species-rich AMF communities occurred deep in the soil profile. A significant difference in AMF community structure was observed between the control and fertilizer N treatments but not between the two N application strategies. AMF communities deeper in the soil profile were subsets of those richer communities in the surface soil and the loss of AMF taxa was mostly due to the absence of rare taxa. Soil pH and Nmin contents were major soil properties affecting the soil AMF communities among the N treatments while vertical distribution was influenced mainly by soil electrical conductivity. Crop phenology had a stronger influence than N treatment on the temporal shifts in AMF communities in maize roots. Our results provide evidence for the importance of N management in maintaining AMF diversity. Changes in soil chemical properties due to N fertilization, in particular declining soil pH, should be integrated in N management strategies to reduce the negative impacts on AMF communities induced by N fertilization. Excessive N inputs induced significant changes in soil physicochemical properties, especially soil acidification, and may have negative impacts on AMF communities.

Soil biodiversity and soil community composition determine ecosystem multifunctionality

Biodiversity loss has become a global concern as evidence accumulates that it will negatively affect ecosystem services on which society depends. So far, most studies have focused on the ecological consequences of above-ground biodiversity loss; yet a large part of Earth's biodiversity is literally hidden below ground. Whether reductions of biodiversity in soil communities below ground have consequences for the overall performance of an ecosystem remains unresolved. It is important to investigate this in view of recent observations that soil biodiversity is declining and that soil communities are changing upon land use intensification. We established soil communities differing in composition and diversity and tested their impact on eight ecosystem functions in model grassland communities. We show that soil biodiversity loss and simplification of soil community composition impair multiple ecosystem functions, including plant diversity, decomposition, nutrient retention, and nutrient cycling. The average response of all measured ecosystem functions (ecosystem multifunctionality) exhibited a strong positive linear relationship to indicators of soil biodiversity, suggesting that soil community composition is a key factor in regulating ecosystem functioning. Our results indicate that changes in soil communities and the loss of soil biodiversity threaten ecosystem multifunctionality and sustainability.

Agricultural practices indirectly influence plant productivity and ecosystem services through effects on soil biota

It is well established that agricultural practices alter the composition and diversity of soil microbial communities. However, the impact of changing soil microbial communities on the functioning of the agroecosystems is still poorly understood. Earlier work showed that soil tillage drastically altered microbial community composition. Here we tested, using an experimental grassland (Lolium, Trifolium, Plantago) as a model system, whether soil microbial communities from conventionally tilled (CT) and non-tilled (NT) soils have different influences on plant productivity and nutrient acquisition. We specifically focus on arbuscular mycorrhizal fungi (AMF), as they are a group of beneficial soil fungi that can promote plant productivity and ecosystem functioning and are also strongly affected by tillage management. Soil microbial communities from CT and NT soils varied greatly in their effects on the grassland communities. Communities from CT soil increased overall biomass production more than soil communities from NT soil. This effect was mainly due to a significant growth promotion of Trifolium by CT microorganisms. In contrast to CT soil inoculum, NT soil inoculum increased plant phosphorus concentration and total plant P content, demonstrating that the soil microbial communities from NT fields enhance P uptake. Differences in AM fungal community composition resulting, for instance, in twofold greater hyphal length in NT soil communities when compared to CT, are the most likely explanation for the different plant responses to CT and NT soil inocula. A range of field studies have shown that plant P uptake increases when farmers change to conservation tillage or direct seeding. Our results indicate that this enhanced P uptake results from enhanced hyphal length and an altered AM fungal community. Our results further demonstrate that agricultural management practices indirectly influence ecosystem services and plant community structure through effects on soil biota.

Symbiotic relationships between soil fungi and plants reduce N2O emissions from soil

N2O is a potent greenhouse gas involved in the destruction of the protective ozone layer in the stratosphere and contributing to global warming. The ecological processes regulating its emissions from soil are still poorly understood. Here, we show that the presence of arbuscular mycorrhizal fungi (AMF), a dominant group of soil fungi, which form symbiotic associations with the majority of land plants and which influence a range of important ecosystem functions, can induce a reduction in N2O emissions from soil. To test for a functional relationship between AMF and N2O emissions, we manipulated the abundance of AMF in two independent greenhouse experiments using two different approaches (sterilized and re-inoculated soil and non-mycorrhizal tomato mutants) and two different soils. N2O emissions were increased by 42 and 33% in microcosms with reduced AMF abundance compared to microcosms with a well-established AMF community, suggesting that AMF regulate N2O emissions. This could partly be explained by increased N immobilization into microbial or plant biomass, reduced concentrations of mineral soil N as a substrate for N2O emission and altered water relations. Moreover, the abundance of key genes responsible for N2O production (nirK) was negatively and for N2O consumption (nosZ) positively correlated to AMF abundance, indicating that the regulation of N2O emissions is transmitted by AMF-induced changes in the soil microbial community. Our results suggest that the disruption of the AMF symbiosis through intensification of agricultural practices may further contribute to increased N2O emissions.