Soil Microbial Processes Research Articles

Tree species richness and water availability interact to affect soil microbial processes

The objective of this study was to examine the interactive influence of tree diversity and water availability on microbial functioning in surface soil (0–10 cm). The study was conducted at two field experiments (ages 4.2 and 9.0 years, respectively) of the TreeDivNet platform that established plantations with a gradient of tree species richness exposed to high and low water availability treatments. Soil microbial biomass, activity, functional diversity and functional identity were estimated using the MicroResp™ method. Soil organic carbon and several other variables potentially associated with soil processes (soil moisture, soil and air temperature, soil pH, soil C:N ratio, tree biomass) were also measured. Our results indicate that tree species richness significantly increased soil microbial biomass and, to a lesser extent, soil microbial activity in the high water availability treatment, at both trial sites. However, tree species richness effects on microbial processes were not expressed in the low water availability treatment, contrary to the stress-gradient hypothesis. Tree species richness and water treatment interaction impacted microbial biomass and activity through their effects on microbial functional diversity and identity at one site and air temperature at the other site. In conclusion, the mechanisms through which tree diversity creates bottom-up effects on biological soil processes depend on environmental conditions and time following the establishment of tree communities. Future research relating diversity and water availability effects on soil microbial processes should consider functional traits of tree species and a larger range of trophic levels including herbivores and soil fauna to better understand biodiversity-soil ecosystem function relationships in forest ecosystems.

Salinity-induced changes in cadmium availability affect soil microbial and biochemical functions: Mitigating role of biochar

Biochar may improve soil microbial and biochemical functions under abiotic stresses. In this research, we studied changes in soil microbial properties and processes after sugarcane bagasse biochar (SCB) application (1% w/w) to a soil contaminated with Cd under saline conditions during an incubation experiment. SCB produced at 400 °C (B400) and 600 °C (B600) increased soil organic carbon (SOC) content by 89–127% and dissolved organic carbon content by 21–70%. NaCl salinity mobilized Cd by 16–19%, while biochar immobilized Cd by 14–18%, indicating the use of biochar would offset the increase in Cd availability induced by salinity. SCB application improved microbial and biochemical functions (up to 280%) in the soils contaminated with Cd under salinity stress. B400 biochar was often more effective in improving the soil microbial properties and functioning than B600 biochar. SCB application reduced the detrimental effects of salinity-induced Cd toxicity on soil microbial community and enzyme activity mainly through retaining Cd and supplying C substrate for microbial uptake and activity. The factor analysis and redundancy analysis results also confirmed that SOC and Cd availability was the most important factors and accounted for a large portion of the variation in soil microbial properties and enzyme activities in saline Cd-contaminated soils amended with SCB. This study indicated that B400 applied at 1% could be used in saline Cd-contaminated soils to protect the soil microbial communities from Cd toxicity, and to mitigate the potential stresses associated with the co-occurrence of Cd contamination and salinity on critical soil microbial and biochemical functions.

Spatial variation in soil microbial processes as a result of woody encroachment depends on shrub size in tallgrass prairie

As woody plants encroach into grassland ecosystems, we expect altered plant-soil interactions to change the microbial processes that affect soil carbon storage and nutrient cycling. Specifically, this research aimed to address how (1) soil chemistry, (2) microbial nutrient demand, and (3) the rate and source of potential soil C mineralization vary spatially under clonal woody shrubs of varying size within a mesic grassland. We collected soil samples from the center, the midpoint between the center and edge, the edge, and the shrub-grass ecotone of multiple Cornus drummondii shrubs across a shrub-size gradient in infrequently burned tallgrass prairie. Total soil carbon and nitrogen increased with shrub size at every sampling location but the edge. Microbial demand for nitrogen also increased as shrubs increased in size. Across all shrub sizes and sampling locations, potential soil carbon mineralization rates were higher when microbes broke down proportionally more shrub-derived (C3) organic matter than grass-derived (C4) organic matter. Our results suggest that the spatio-temporal context of woody encroachment is critical for understanding its impact on belowground microbial processes. In this ecosystem, a longer period of occupancy by woody plants increases potentially mineralizable soil carbon.

Short-Term Application of Magnesium Fertilizer Affected Soil Microbial Biomass, Activity, and Community Structure

Fertilizers influence soil microbial processes and functions. The use of magnesium (Mg) fertilizer is increasing worldwide, but the effects of mineral Mg application on soil microbial biomass, activity, and diversity remain poorly understood. In this study, a 120-day experiment was conducted to evaluate the effects of magnesium sulfate (MgSO4) on soil microbial biomass, enzyme activity, and bacterial community composition. Two acidic Mg deficient soils, a high organic matter (S) and a low organic matter soil (X), were treated with MgSO4 at the dose of 0, 50, 100, and 200 mg kg−1. Results showed that MgSO4 application significantly increased microbial biomass carbon, and activities of invertase and protease of both soils, but decreased the phosphatase activity in X soil. Mg fertilizer changed the soil bacterial community structure, e.g., the relative abundance of genera Acidobacter, Mizugakiibacter, and Singulisphaera increased while the relative abundance of Acidiphilium, Bradyrhizobium, and Gemmatimonas decreased in S soil. In X soil, the abundance of genera Sphingomonas, Pseudolabrys, and Streptomyces were enhanced and the relative abundance of Anaeromyxobacter, Bradyrhizobium, and Haliangium was reduced by the application of Mg fertilizer. Redundancy analysis showed that soil bacterial community composition was shaped by exchangeable-Mg and sulfate concentrations, pH, and electrical conductivity (EC), and the exchangeable Mg was the strongest factor influencing microbial abundance and composition. Our results suggest that short-term Mg fertilizer application influenced soil microbial biomass, activity, and bacterial community composition.

The influence of tillage and fertilizer on the flux and source of nitrous oxide with reference to atmospheric variation using laser spectroscopy

Nitrous oxide (N2O) is the third most important long-lived greenhouse gas and agriculture is the largest source of N2O emissions. Curbing N2O emissions requires understanding influences on the flux and sources of N2O. We measured flux and evaluated microbial sources of N2O using site preference (SP; the intramolecular distribution of 15N in N2O) in flux chambers from a grassland tilling and agricultural fertilization experiments and atmosphere. We identified values greater than that of the average atmosphere to reflect nitrification and/or fungal denitrification and those lower than atmosphere as increased denitrification. Our spectroscopic approach was based on an extensive calibration with 18 standards that yielded SP accuracy and reproducibility of 0.7 ‰ and 1.0 ‰, respectively, without preconcentration. Chamber samples from the tilling experiment taken ~ monthly over a year showed a wide range in N2O flux (0–1.9 g N2O-N ha−1 d−1) and SP (− 1.8 to 25.1 ‰). Flux and SP were not influenced by tilling but responded to sampling date. Large fluxes occurred in October and May in no-till when soils were warm and moist and during a spring thaw, an event likely representing release of N2O accumulated under snow cover. These high fluxes could not be ascribed to a single microbial process as SP differed among chambers. However, the year-long SP and flux data for no-till showed a slight direct relationship suggesting that nitrification increased with flux. The comparative data in till showed an inverse relationship indicating that high flux events are driven by denitrification. Corn (Zea mays) showed high fluxes and SP values indicative of nitrification ~ 4 wk after fertilization with subsequent declines in SP indicating denitrification. Although there was no effect of fertilizer treatment on flux or SP in switchgrass (Panicum virgatum), high fluxes occurred ~ 1 month after fertilization. In both treatments, SP was indicative of denitrification in many instances, but evidence of nitrification/fungal denitrification also prevailed. At 2 m atmospheric N2O SP had a range of 31.1 ‰ and 14.6 ‰ in the grassland tilling and agricultural fertilization experiments, respectively. These data suggest the influence of soil microbial processes on atmospheric N2O and argue against the use of the global average atmospheric SP in isotopic modeling approaches.

Ecotoxicology of Glyphosate, Its Formulants, and Environmental Degradation Products.

The chemical and biological properties of glyphosate are key to understanding its fate in the environment and potential risks to non-target organisms. Glyphosate is polar and water soluble and therefore does not bioaccumulate, biomagnify, or accumulate to high levels in the environment. It sorbs strongly to particles in soil and sediments and this reduces bioavailability so that exposures to non-target organisms in the environment are acute and decrease with half-lives in the order of hours to a few days. The target site for glyphosate is not known to be expressed in animals, which reduces the probability of toxicity and small risks. Technical glyphosate (acid or salts) is of low to moderate toxicity; however, when mixed with some formulants such as polyoxyethylene amines (POEAs), toxicity to aquatic animals increases about 15-fold on average. However, glyphosate and the formulants have different fates in the environment and they do not necessarily co-occur. Therefore, toxicity tests on formulated products in scenarios where they would not be used are unrealistic and of limited use for assessment of risk. Concentrations of glyphosate in surface water are generally low with minimal risk to aquatic organisms, including plants. Toxicity and risks to non-target terrestrial organisms other than plants treated directly are low and risks to terrestrial invertebrates and microbial processes in soil are very small. Formulations containing POEAs are not labeled for use over water but, because POEA rapidly partitions into sediment, risks to aquatic organisms from accidental over-sprays are reduced in shallow water bodies. We conclude that use of formulations of glyphosate under good agricultural practices presents a de minimis risk of direct and indirect adverse effects in non-target organisms.

Biochar for sustainable soil management

Biochar for sustainable soil management

Effects of drought stress on soil bacteriall community in the West foot of Daxing’an Mountains

Global warming poses a serious threat to agriculture and natural systems, in part because of the change of soil moisture content, which changes soil microbial communities and ecological processes. Soil water content is the main factor limiting the growth of plants in soil. Microbial communities rely on soil water to complete their activities, and reveal the changes of underground microbial communities under different soil moisture content, which will help us to further understand the potential impact of climate change on soil ecosystem. To investigate the soil bacterial community structure, we established experiment indoor in the West foot of Daxing’an Mountains with manipulative water content treatments consisting of 20%, 15%, 10%, 5%, 0%. Results showed that bacterial community composition varied significantly with altered drought stress , but community richness did not. The relative abundance of Actinobacteria increased with the increase of drought stress, Proteobacteria, Acidobacteria and Gemmatimonadota decreased with the increase of drought stress, actinobacteria was more likely to accumulate or maintain stable under drought stress, bacterial communities can responding directly to changes in soil moisture.

Shrub encroachment affects tundra ecosystem properties through their living canopy rather than increased litter inputs

Deciduous shrub encroachment in tundra ecosystems affects the soil microclimate and, in turn, could affect soil nutrients and microbial processes. Although numerous effects of shrubs on tundra ecosystem properties have been described, there has been little focus on the mechanisms through which they impact tundra functioning. In alpine tundra of northern Canada, we examined 1) the effects of the living shrub canopy and separated them from 2) the effects of increases in litter quantity and quality. In this 4-year study we experimentally manipulated shrub presence (shrub present or removed) and litter quantity (none, natural abundance, and 2x natural abundance) in a fully factorial design. Shrub presence affected soil temperatures by increasing winter and decreased summer soil surface temperatures by about 0.8 °C and 0.6 °C respectively, and also decreased mid-summer soil moisture. Shrub presence also affected both nutrient cycling and microbial processes including decreased summer available nitrogen (N), increased N-immobilization, increased microbial biomass as well as variable effects on potential exoenzyme activity. Increased litter inputs had few significant effects on tundra ecosystems, although additional litter increased both soil C:N ratios and microbial biomass. Our results indicate that shrub encroachment is likely to affect tundra soil properties primarily through mechanisms associated with the presence of the living shrub rather than from the accompanied changing litter quality and quantity. Because of opposing effects of shrubs between seasons and years, we encourage an increased focus on the mechanisms through which shrubs may affect tundra ecosystem functions and year round assessments of these processes.

How microbes can, and cannot, be used to assess soil health

Healthy soils are critical to the health of ecosystems, economies, and human populations. Thus, it is widely acknowledged that soil health is important to quantify, both for assessment and as a tool to help guide management strategies. What is less clear is how soil health should actually be measured, especially considering that soil health is not exclusively a product of soil physical and chemical characteristics. Given their well-established importance to many aspects of soil health, microbes and microbial processes are often used as metrics of soil health with a range of different microbe-based metrics routinely used across the globe. Unfortunately, it is our opinion that many of these pre-existing microbial measurements are not easy to interpret and may not necessarily provide credible inferences about soil health status. Here we review the microbial indices used to assess or monitor soil health and discuss some of the broader issues associated with their use. We provide recommendations to more effectively guide and improve how microbial information could be used to yield relevant and actionable assessments of soil health.

Changes in coupled carbon\u2012nitrogen dynamics in a tundra ecosystem predate post-1950 regional warming

Arctic ecosystems are changing in response to recent rapid warming, but the synergistic effects of other environmental drivers, such as moisture and atmospheric nitrogen (N) deposition, are difficult to discern due to limited monitoring records. Here we use geochemical analyses of 210Pb-dated lake-sediment cores from the North Slope of Alaska to show that changes in landscape nutrient dynamics started over 130 years ago. Lake carbon burial doubled between 1880 and the late-1990s, while current rates (~10 g C m−2 yr−1) represent about half the CO2 emission rate for tundra lakes. Lake C burial reflects increased aquatic production, stimulated initially by nutrients from terrestrial ecosystems due to late-19th century moisture-driven changes in soil microbial processes and, more recently, by atmospheric reactive N deposition. These results highlight the integrated response of Arctic carbon cycling to global environmental stressors and the degree to which C–N linkages were altered prior to post-1950 regional warming.

Impact of natural zeolite on chemical and biochemical properties of vineyard soils

AbstractSustained tillage and continual applications of phytopharmaceutical and fertilizers using heavy machineries frequently give rise to soil erosion, loss of soil organic matter (SOM) and contamination phenomena in Mediterranean vineyards. Because of their distinctive properties, applying natural zeolites to vineyard soils can conceivably affect the efficient use of fertilizers and reduce nutrient leaching losses. This work assesses the impact of zeolite amendment at differing rates (0, 5 and 10 t/ha) on the chemical and biochemical soil properties of three vineyard soils after 6 months from initial treatments. In particular, chemical properties usually related to soil fertility were evaluated along with more sensitive indicators of soil functionality and indicators of chemical–structural characteristics of SOM. The vineyard soils amended with zeolite showed higher nutrient availability and dehydrogenase activity if compared with the control soils. In addition, even though total organic carbon (TOC) content was unchanged, a decrease in humic substances was observed in the zeolite‐treated soils. These results suggested that the stimulation of soil microbial processes by adding zeolite triggered a microbial mineralization process of soil organic carbon stocks. In addition, the modification in the chemical–structural composition of soil organic matter in zeolite‐treated soils was shown by the pyrolysis–gas chromatography (Py‐GC) results. Py‐CG of soil organic matter clearly demonstrated an increase in the labile aliphatic compound furfural and a decline in the more stable aromatic pyrolytic fragments in zeolite‐treated soils in contrast with the control soils, thus indicating the higher extent of decomposition of the SOM more stable pool.

Leaf litter of two riparian tree species has contrasting effects on nutrients leaching from soil during large rainfall events

One goal of revegetating riparian zones is to mitigate nutrient movement into waterways, however release of dissolved nutrients and organic compounds from decaying leaf litter during rainfall may partially offset these benefits. We aim to understand how litter-derived nutrients and organics affect nutrient leaching from riparian soil, and how tree species affect these processes. In the laboratory we simulated large rainfall events through the leaf litter of two riparian woody tree species, Eucalyptus tereticornis and Casuarina cunninghamiana, with and without subsequent leaching through soil, as well as soil alone. We compared the forms and loads of nitrogen and phosphorus in leachate. Litter of both tree species stimulated additional nitrate release from soil (~100–200%) compared to bare soil. More ammonium and dissolved organic nitrogen also leached from soil with E. tereticornis litter, whereas less leached with C. cunninghamiana litter. More phosphate leached from soil with either species litter compared to bare soil. Increased nitrogen releases from soil with litter were greater than inputs from litter, suggesting they are driven by positive priming of soil microbial processes, whereas litter inputs increased phosphorus leaching. This information could be combined with rates of other riparian nutrient processes (e.g. plant uptake and denitrification) to quantify the net impact of trees on nutrient retention in riparian zones.

Biological indicators of soil quality under conventional, reduced, and no-tillage systems

ABSTRACT Soil microbial processes can serve as sensitive indicators of soil quality. A 2-year field experiment was conducted to determine the combined effects of tillage (conventional, CT; reduced, RT; and no tillage, NT) and residue (with or without residue removal) on soil microbial and enzyme activities under wheat (Triticum aestivum L.)- and corn (Zea mays L.) in a rotation, using a split-plot design with three replications near Shiraz, Iran. The highest microbial biomass (660.19 and 667.00 µg MBC g−1 soil in wheat and corn, respectively) was recorded under RT. Soil respiration was affected by tillage in order NT > RT > CT. The lowest microbial quotient (qCO2) was obtained under RT (15.60 in wheat and 5.94 in corn, respectively), while NT and CT either showed similar effects or NT was superior over CT. The highest acid phosphatase enzyme was obtained under RT (442.65 and 374.17 µg PNP g−1 soil h−1 in wheat and corn, respectively). Alkaline phosphatase and urease enzymes were highest under NT. Our research has shown that replacing CT with conservation tillage (especially RT) can greatly improve soil enzymes and microbial biomass and optimize qCO2 values under wheat- and corn in a rotation in a short term.

Emergent properties of downed woody debris in canopy gaps: A response of the soil ecosystem to manipulation of forest structure

Natural forest disturbance events can influence soil biogeochemical processes in two ways - by creating downed woody debris (DWD; fallen tree boles or branches) and by creating canopy gaps that alter forest microclimate. DWD represents a substrate for microbial growth and a persistent store of carbon and nutrients, but microbial activity is also sensitive to temperature and moisture. We studied the potential interaction of DWD and canopy gaps on soil microbial processes, and wondered if microclimatic conditions resulting from the manipulation of forest structure would be enough to inhibit production, thereby altering a critical ecosystem process. Gaps and DWD (>10 cm diameter) were added to a maturing, even-aged, second-growth northern hardwood forest (the Flambeau Experiment; N Wisconsin, USA) to enhance structural complexity and promote key ecosystem processes typically associated with late-successional forests. We investigated the influence of DWD and gaps on soil microbial community composition, extracellular enzyme activity and soil characteristics. Soils were sampled near intermediately and highly decayed DWD and 2 m away from DWD (control) in gaps and closed canopy a decade after manipulation.DWD decomposition influenced the surrounding soil differentially depending on decay class and canopy condition. Mean C- and P-potential extracellular enzyme activities (BG, BX and AP) were enhanced near highly decayed DWD in gaps. The relative abundance of bacteria (actinomycete, anaerobic, gram-negative and gram-positive) remained constant in gaps but decreased from May to August in closed canopy. In gaps, soil total exchangeable cations increased by 34.6%, available phosphorus by 152% and fungal to bacterial ratios by 23.3% but temperatures decreased by 3.42% suggesting that canopy condition continues to affect soil properties and microbial processes a decade after gap creation. These results highlight the contribution of DWD to the forest floor and the influence of decaying wood characteristics on belowground ecosystems critical to future forest productivity. Retaining or adding heterogeneously distributed DWD of varying decay status may be essential to maintain ecosystem functions associated with nutrient cycling and microbial community dynamics in managed forests.

Response of Soil Microbes and Soil Enzymatic Activity to 20 Years of Fertilization

Fertilization is a worldwide agricultural practice used in agronomy to increase crop yields. Fertilizer application influences overall soil characteristics, including soil microbial community composition and metabolic processes mediated by microbial enzymatic activity. Changes in the structure of microbial communities and their metabolic activity after long-term fertilization were studied in this research. We hypothesized that the different types of fertilization regimes affect nutrient levels in the soil which subsequently influence the metabolic processes and microbial diversity and community structure. Manure (MF; 330 kg N/ha), sewage sludge at two application doses (SF; 330 kg N/ha and SF3x; 990 kg N/ha) and chemical (NPK; N-P-K nutrients in concentrations of 330-90-300 kg/ha) fertilizers have been applied regularly to an experimental field since 1996. The microbial diversity increased in all soils amended with both organic (MF, SF, SF3x) and chemical (NPK) fertilizers. The shifts in microbial communities were observed, which were mainly caused by less abundant genera that were mostly associated with one or more fertilization treatment(s). Fertilization also influenced soil chemistry and the activity of β-xylosidase, β-N-acetylglucosaminidase (NAG), acid phosphatase and FDA-hydrolases. Specifically, all fertilization treatments were associated with a higher activity of β xylosidase and lower NAG activity. Only the NPK treatment was associated with a higher activity of acid phosphatase.

Zinc-nitrogen co-fertilization influences N2O emissions and microbial communities in an irrigated maize field

Previous studies have shown that the use of zinc (Zn) chelate fertilizers combined with a nitrogen (N) fertilizer (urea) can lead to both agronomic (i.e., yields and Zn and N biofortification due to the synergies between both nutrients) and environmental (i.e., by reducing the emissions of nitrous oxide, N2O, derived from N fertilization) benefits under rainfed semi-arid conditions. However, little is known about the effect of Zn-N co-fertilization on greenhouse gas (GHG) emissions or soil microbial processes involved in N2O fluxes under non-flooded irrigated conditions (during the dry season). Under these conditions, water-filled pore space continuously fluctuates following a periodic pattern and soil temperatures are in the optimum range for soil microorganisms. In this context, a field experiment was conducted using a maize (Zea mays L.) crop treated with two N levels (no N application and 120 kg N ha−1 as urea), and three Zn sources (no Zn application, Zn sulphate, and Zn applied with a mixture of chelating compounds, DTPA-HEDTA-EDTA). Nitrous oxide, methane (CH4) and carbon dioxide (CO2) fluxes were measured using opaque chambers, as well as the total abundances of soil bacteria, archaea and nitrifier and denitrifier communities. Zn-N co-fertilization increased cumulative N2O emissions from 0.36 kg N-N2O ha−1 (for urea combined with Zn chelates) to 0.76 kg N-N2O ha−1 (for urea combined with Zn sulphate), with respect to urea without Zn application. The N2O emission factors were lower (0.34%–0.72%) than the IPCC default value of 1%. Total abundances of the nosZ denitrification gene, which is involved in the reduction in N2O to dinitrogen (N2), were reduced by 75% on average in the plots that received Zn fertilizers. This reduction may explain the higher N2O emissions in these treatments. In contrast with the case with non-irrigated crops, Zn-N co-fertilization cannot be recommended as a strategy to mitigate N2O emissions in irrigated maize under semi-arid conditions, despite of the enhancement of Zn availability in soil.

Ecosystem Recovery from Disturbance is Constrained by N Cycle Openness, Vegetation-Soil N Distribution, Form of N Losses, and the Balance Between Vegetation and Soil-Microbial Processes

We present a framework for assessing biogeochemical recovery of terrestrial ecosystems from disturbance. We identify three recovery phases. In Phase 1, nitrogen is redistributed from soil organic matter to vegetation, but the ecosystem continues to lose nitrogen because the recovering vegetation cannot take up nitrogen as fast as it is released from soil. In Phase 2, the ecosystem begins re-accumulating nitrogen and converges on a quasi-steady state in which vegetation and soil-microbial processes are in balance. In Phase 3, vegetation and soil-microbial processes remain in balance and the ecosystem slowly re-accumulates the remaining nitrogen. Phase 3 follows a balanced-accumulation trajectory along a continuum of quasi-steady states that approaches the true steady state asymptotically. We examine the effects of three ecosystem properties on recovery: openness of the nitrogen cycle, nitrogen distribution in and turnover between vegetation and soils, and the proportion of nitrogen losses that are in a refractory form. Openness exacerbates Phase 1 nitrogen losses but speeds recovery in Phases 2 and 3. A high fraction of ecosystem nitrogen in vegetation, resulting from nitrogen turnover that is slow in vegetation but fast in soil, exacerbates Phase 1 nitrogen losses but speeds recovery in Phases 2 and 3. A high proportion of nitrogen loss in refractory form mitigates Phase 1 nitrogen losses and speeds recovery in Phases 2 and 3. Application of our conceptual framework requires empirical recognition of the continuum of quasi-steady states constituting the balanced-accumulation trajectory and a distinction between the balanced-accumulation trajectory and the true steady state.

Direct and indirect influences of long-term fertilization on microbial carbon and nitrogen cycles in an alpine grassland

Beginning in the twentieth century, atmospheric deposition of N and P greatly increased in terrestrial ecosystems, including alpine grasslands. These inputs have profoundly affected soil microbial C and N cycles. Changes in the microbial environment are directly caused by changes in soil N and P availability and also indirectly through changes in vegetation in response to increased fertilization. The mechanisms involved in both the direct and indirect changes are not mutually exclusive and are poorly understood. Therefore, we investigated the responses of vegetation and soil microbes to a 9-year fertilization (N and P) experiment in an alpine grassland in the Qinghai–Tibetan Plateau in China. We found that N addition altered soil microbial community composition and processes regardless of P addition. To maintain stoichiometric homeostasis, soil microbes adjusted metabolic processes in response to changes in nutrient availability. High N availability enhanced microbial investment in C acquisition as indicated by β-1,4-Glucosidase activity. The abundance of microbial taxa that degrade labile C also increased. High N inputs also induced a proliferation of denitrifiers and increased the gaseous N loss potential. Partial least squares path modelling indicated that soil parameters (e.g., soil organic C and total N) and changes in the plant community played a key role in shaping soil microbial community structure and C and N cycling. Our results suggest that vegetation and stoichiometric differences between resource availability and soil microbial nutrient requirements collectively regulate the responses of soil microbial processes to N enrichment, which provides novel experimental insights into the mechanisms underlying the effects of nutrient inputs on microbial C and N cycles. Ultimately, our findings highlight the importance of plant traits in regulating microbial nutrient cycles, further promoting our comprehension about the mechanism of variation in the microbial nutrient cycles in an alpine grassland soils.

Higher tree diversity increases soil microbial resistance to drought

Predicted increases in drought frequency and severity may change soil microbial functioning. Microbial resistance and recovery to drought depend on plant community characteristics, among other factors, yet how changes in plant diversity modify microbial drought responses is uncertain. Here, we assessed how repeated drying-rewetting cycles affect soil microbial functioning and whether tree species diversity modifies these effects with a microcosm experiment using soils from different European forests. Our results show that microbial aerobic respiration and denitrification decline under drought but are similar in single and mixed tree species forests. However, microbial communities from mixed forests resist drought better than those from mono-specific forests. This positive tree species mixture effect is robust across forests differing in environmental conditions and species composition. Our data show that mixed forests mitigate drought effects on soil microbial processes, suggesting greater stability of biogeochemical cycling in mixed forests should drought frequency increase in the future.