Tibetan Alpine Meadow Research Articles

Scaling-up trait covariation: Coordination and trade-offs within and among plant species in alpine meadow communities

<p indent="0mm">Functional traits and their covariation could reflect specific ecological strategies of organisms in response and adaptation to changing environment as the basis of understanding organism-environment relations at the individual, population, and community levels. Many studies report trait coordination and trade-offs among species over broad scales, especially for the leaf economic spectrum at regional and global scales. An increasing number of studies have attempted to explain and predict the functional (trait) structure of populations, communities, and vegetation in response to environmental change, but the mechanisms underpinning trait coordination and trade-offs may differ across ecological levels. We know little about this trait coordination and trade-offs within and among species in local communities, lacking not only relevant theoretical frameworks but also experimental evidence. Merging trait covariation into theory for community assembly, we predict: (1) Significant trait coordination or trade-offs among coexisting species occur when coexisting species occupy distinct ecological niches, similar to the pattern induced by specialization of species niches on a broad scale and (2) if trait covariations are induced by functional balance and/or structural optima, then consistent trait coordination and trade-offs within and among species will occur and scale up to the community and ecosystem levels. In this study, we experimentally test these predictions in local communities and discuss the potential mechanisms underpinning trait coordination and trade-offs from the scale of individual plants to vegetation. In Tibetan alpine meadows with high plant species richness but low environmental heterogeneity, we sampled two leaf stoichiometric traits (leaf nitrogen and phosphorus content), two leaf morphological traits (specific leaf area and leaf dry matter content) and mature plant height for three to five individuals for all coexisting species within each of 36 plant communities (plots) distributed along a gradient of environmental harshness. In each plot, we averaged trait values of individual samples of each species at the population-level, and used the mean of all populations of each species to indicate the species-level traits. We assessed pairwise trait correlation within and among 29 frequent species by standardized major axis regression and trait coordination and trade-offs among multiple traits by principal component analysis. Similar to the broad-scale pattern, we found that leaf nitrogen and phosphorus contents were significantly positively correlated with specific leaf area (negatively correlated with leaf dry matter content) among 29 coexisting species, but these trade-offs were significant at a population level in only a few species. Both among species and within most species, (1) leaf nitrogen content was significantly positively correlated with phosphorus content, likely induced by functional balance, (2) specific leaf area was negatively correlated with leaf dry matter content, indicating a structural optimum, (3) neither leaf stoichiometric nor morphological traits significantly correlated with plant height. Trait coordination and trade-offs were stronger for multiple trait relationships than for bivariate correlations. These results support our predictions and provide a basis and experimental evidence for scaling up trait covariations from individuals to communities.

Climate warming promotes deterministic assembly of arbuscular mycorrhizal fungal communities.

Arbuscular mycorrhizal fungi (AMF) significantly contribute to plant resource acquisition and play important roles in mediating plant interactions and soil carbon (C) dynamics. However, it remains unclear how AMF communities respond to climate change. We assessed impacts of warming and precipitation alterations (30% increase or decrease) on soil AMF communities, and examined major ecological processes shaping the AMF community assemblage in a Tibetan alpine meadow. Our results showed that warming significantly increased root biomass, and available nitrogen (N) and phosphorus (P) in soil. While precipitation alterations increased AMF abundances, they did not significantly affect the composition or diversity of AMF communities. In contrast, warming altered the composition of AMF communities and reduced their Shannon-Wiener index and Pielou's evenness. In particular, warming shifted the AMF community composition in favor of Diversisporaceae over Glomeraceae, likely through its impact on soil N and P availability. In addition, AMF communities were phylogenetically random in the unwarmed control but clustered in warming plots, implying more deterministic community assembly under climate warming. Warming enhancement of root growth, N and P availability likely reduced plant C-allocation to AMF, imposing stronger environmental filtering on AMF communities. We further proposed a conceptual framework that integrates biological and geochemical processes into a mechanistic understanding of warming and precipitation changes' effects on AMF. Taken together, these results suggest that soil AMF communities may be more sensitive to warming than expected, highlighting the need to monitor their community structure and associated functional consequences on plant communities and soil C dynamics under the future warmer climate.

Plant–soil biota interactions explain shifts in plant community composition under global change

Abstract Plant–soil biota interactions play a crucial role in the assembly of plant communities and the maintenance of plant species diversity. However, few studies have tested how the effect of soil biota on plant species and communities depends on environmental context and whether shifts in plant community composition caused by environmental change are associated with variation in plant–soil biota interactions. We combined a field experiment in a Tibetan alpine meadow and a greenhouse experiment with factorial combinations of nitrogen (N) enrichment and warming to examine the role of plant–soil biota interactions in plant community dynamics. The results showed that plant relative abundances were negatively correlated with the net effects of soil biota on plant growth but only under ambient field conditions. Warming and N enrichment alleviated the negative soil biota effects in the greenhouse, and changed plant community composition and reduced species diversity in the field. Importantly, changes in soil biota effects on plant growth were positively correlated with changes in plant relative abundances caused by warming and N enrichment in field. In a parallel field experiment, the diversity of mycorrhizal fungi increased while the diversity of fungal pathogens remained unchanged under warming and N enrichment, indicating that soil biodiversity may play a critical role in plant responses to environmental change. This study empirically demonstrates that altered plant–soil biota interactions explain shifts in plant community composition under global change, providing new insights into the mechanisms of diversity loss in a changing world. A free Plain Language Summary can be found within the Supporting Information of this article.

Moderate grazing increases the structural complexity of soil micro-food webs by promoting root quantity and quality in a Tibetan alpine meadow

Livestock grazing can affect both above- and below-ground communities, however, the effects of grazing intensity on vertical distribution of root traits and their associations with belowground food webs are still unclear. Based on a 5-year grazing intensity experiment (i.e., no grazing, moderate grazing and heavy grazing) in a Tibetan plateau meadow, we investigated how grazing-induced changes in root traits affected soil biota (microbes and nematodes) from the surface (0–10 cm) and subsurface soils (10–20 cm). Our results showed that moderate grazing increased nematode abundance and structure complexity of the soil micro-food webs compared to no and heavy grazing, and predominantly increased herbivores and fungivores regardless of soil layers. Shifts in herbivores and fungivores were mainly driven by root quantity and quality, emphasizing the stronger bottom-up effects on the lower trophic levels of nematodes. Grazing decreased the number of omnivores-predators in the surface soil compared to no grazing, which therefore weakened predation pressure on soil nematodes lower in the trophic structure, including root herbivores, while that effect was far less pronounced in the subsurface soil. Our study demonstrated that changes in root quantity and quality were highly associated with the complexity of the soil micro-food webs under grazing scenarios. These findings warranted the ideas that combined aboveground herbivore-root-soil micro-food webs as an ecological holo is essential for sustainable management of grassland.

Impact of soil degradation on plant communities in an overgrazed Tibetan alpine meadow

Predicting the impact of overgrazing on soil properties, and thus on plant succession, in the Qinghai-Tibet Plateau (QTP) is one of the primary technical bottlenecks in alpine meadow conservation. Four degradation intensities, namely D1: light degradation, D2: moderate degradation, D3: high degradation, and a non-degraded site as the control (CK), were identified. The soil properties and plant community data were analyzed. With the increase in degradation intensity, the soil pH, conductivity (EC), and bulk density (BD) values significantly increased, while the soil water content, total carbon, total nitrogen, and C/N ratio significantly decreased (p < 0.05). Plant aboveground biomass and Shannon diversity significantly decreased with the increase in degradation intensity (p < 0.05). The dominant species changed from Poa pratensis (CK) to Potentilla multifida (D1), to Iris lactea (D2), and finally to Achnatherum splendens (D3). Overgrazing can lead to changes in soil properties, and changes in soil pH and BD are the primary factors that control the changes in plant community structure and composition with grassland degradation. Soil degradation is conducive to the growth of individual species such as A. splendens, which are associated with a reduction in plant diversity in an alpine meadow of the northeastern QTP. Future research should pay more attention to the key species and soil properties in degraded grasslands.

Nitrogen Addition in a Tibetan Alpine Meadow Increases Intraspecific Variability in Nitrogen Uptake, Leading to Increased Community-level Nitrogen Uptake

Nitrogen Addition in a Tibetan Alpine Meadow Increases Intraspecific Variability in Nitrogen Uptake, Leading to Increased Community-level Nitrogen Uptake

Grazing-to-fencing conversion affects soil microbial composition, functional profiles by altering plant functional groups in a Tibetan alpine meadow

Information on the effect of anthropogenic activities on soil microbial communities can improve our ability to formulate restoration strategies in the Tibetan Plateau, where meadow degradation has been an increasing concern. In this study, we evaluated plant functional groups, soil properties, microbial communities, and their functional groups in four types of meadows (grazed, fenced, fenced + reseeded, and intact) in the Tibetan Plateau. Based on amplicon sequencing data, both the bacterial and fungal composition, their potential functions and their possible drivers have been investigated. Fencing was the most effective approach to restore degraded alpine meadows, characterized by higher aboveground biomass, soil nutrient levels, and microbial diversity. The soil carbon, ammonium nitrogen, and the above- and below-ground biomass (mainly sedge and grass groups) were closely related to the changes in bacterial and fungal composition, while the diversity of sedge, grass, legumes, and forbs was largely associated with N cycling and fungal functional guilds. Grazing-to-fencing conversion also caused changes in the microbial community composition, specifically resulting in a shift from oligotrophs to copiotrophs, an increased abundance of diazotrophs and plant pathogens, and a decreased abundance of nitrifiers. Our results revealed the effects of grazing-to-fencing conversion on an alpine meadow and can provide significant guidance for the sustainable management of degraded grassland ecosystems.

Soil abiotic properties and plant functional diversity co-regulate the impacts of nitrogen addition on ecosystem multifunctionality in an alpine meadow.

Soil abiotic properties and plant diversity have been shown to affect ecosystem functions in alpine meadow ecosystems. However, we know little about the relative importance of these factors in driving the responses of multiple ecosystem functions simultaneously (multifunctionality) to nitrogen (N) enrichment. Here, we measured soil abiotic properties (soil pH; available nitrogen, AN; available phosphorous, AP; and dissolved organic carbon, DOC) and multiple plant diversity metrics (species diversity, SD; functional diversity, FD; and phylogenetic diversity, PD) after a 5-year N fertilization experiment (0, 5, 10, and 15gNm-2yr-1) to evaluate their roles in mediating the impacts of N addition on aboveground plant functions (APF), soil microbial functions (SMF), and ecosystem multifunctionality (EMF) in a N-limited Tibetan alpine meadow. We found that N addition decreased APF but increased SMF and EMF. Structural equation models (SEMs) showed that APF was co-driven by soil DOC and the community weighted mean for plant traits (CWMs), and SMF was driven by soil DOC, soil AN, CWMs and functional dispersion (FDis). The effects of N addition on EMF were driven by soil AN and FDis. Our results suggest that the effects of N enrichment on APF, SMF, and EMF are driven by differential mechanisms. Furthermore, the findings suggest that FD is superior to SD and PD in mediating the responses of ecosystem functions to N enrichment.

Allocation Strategies for Seed Nitrogen and Phosphorus in an Alpine Meadow Along an Altitudinal Gradient on the Tibetan Plateau.

Nitrogen (N) and phosphorus (P) play important roles in many aspects of plant biology. The allocation of N and P in plant vegetative organs (i.e., leaves, stems, and fine roots) is critical to the regulation of plant growth and development. However, how these elements are allocated in seeds is unclear. The aim of this study was to explore the N and P allocation strategies of seeds in an alpine meadow along an altitudinal gradient. We measured the seed N and P contents of 253 herbaceous species in 37 families along an altitudinal gradient (2,000–4,200 m) in the east Tibetan alpine meadow. The geometric means of seed N and P concentrations and N:P ratios were 34.81 mg g–1, 5.06 mg g–1, and 6.88, respectively. Seed N and P concentrations varied across major taxonomic groups and among different altitude zones. N:P ratios showed no significant variations among different taxonomic groups with the exception of N-fixing species. The numerical value of the scaling exponent of seed N vs. P was 0.73, thus approaching 3/4, across the entire data set, but varied significantly across major taxonomic groups. In addition, the numerical value of the scaling exponent of N vs. P declined from 0.88 in the high altitude zone to 0.63 in the low altitude zone. These results indicate that the variations in the numerical value of the scaling exponent governing the seed N vs. P scaling relationship varies as a function of major taxonomic groups and among different altitude zones. We speculate that this variation reflects different adaptive strategies for survival and germination in an alpine meadow. If true, the data presented here advance our understanding of plant seed allocation strategies, and have important implications for modeling early plant growth and development.

Nitrogen-induced acidification plays a vital role driving ecosystem functions: Insights from a 6-year nitrogen enrichment experiment in a Tibetan alpine meadow

Anthropogenic nitrogen (N) input has overtaken natural N fixation as the leading source of reactive N, and can profoundly alter the structure and functions of terrestrial ecosystems. N input impacts ecosystem functions through altering abiotic (e.g., soil nutrients and pH) and biotic (e.g., biological community composition) properties, but the relative importance of these abiotic and biotic effects remains largely unknown. We conducted a 6-year experiment of N manipulations (0, 5, 10, and 20 g N m−2 yr−1) in a Tibetan alpine meadow to assess N-induced abiotic and biotic effects on ecosystem functions. A complementary experiment with acid additions (0, 0.66, 2.65, 4.63, and 7.28 mol H+ m−2 yr−1) was also carried out to examine the direct impact of acidification. We found that N enrichment significantly increased plant productivity but decreased soil microbial respiration. While the increased productivity was associated with increased N availability, the reduction in soil microbial respiration was mainly explained by the decreased soil pH. In the acid addition experiment, enhanced soil acidity due to the increased proton concentration significantly reduced soil microbial respiration. These results indicate that N-induced changes in soil pH represent an important mechanism driving the ecosystem functions, suggesting that N-induced acidification should receive more attention for understanding and predicting ecosystem services under future N-enrichment scenarios.

Interspecific interactions between burrowing dung beetles and earthworms on yak dung removal and herbage growth in an alpine meadow

Interspecific interactions between two spatiotemporally co-occurred species sharing a single resource are considered to be either competitive or facilitative. This study examined the possible interspecific interactions between a dung-tunneling beetle species (Onthophagus yubarinus) and an earthworm species (Aporrectodea nocturna), two major detritivores responsible for dung removal in a Tibetan alpine meadow. We conducted a two-way, factorial field experiment using replicated chambers, and measured the performances of beetles and earthworms, as well as yak dung removal, soil properties and aboveground plant biomass over two months. Earthworm presence significantly decreased the body size of beetle larvae and the weight of tunnel dung that beetle larvae live on. In contrast, beetle presence did not affect the performance of earthworms. Beetles, earthworms and their interaction significantly increased dung removal and soil organic carbon concentration at the end of the experiment. Beetles alone significantly increased soil total N and P, soluble N and P concentrations, but earthworms alone had nonsignificant effects on these nutrient variables. Beetles and earthworms additively enhanced soluble N and P concentrations, and aboveground plant biomass at the end of the experiment. These results indicate 1) there was a onesided negative relationship between dung-tunneling beetles and earthworms, resulting from the consumption of earthworms on food resource of beetle larvae; and 2) the coexistence of beetles and earthworms facilitated dung removal interactively and plant growth additively by increasing nutrient availability.

Vegetation and soil covariation, not grazing exclusion, control soil organic carbon and nitrogen in density fractions of alpine meadows in a Tibetan permafrost region

The accrual of soil organic carbon (SOC) and nitrogen (N) in grassland is an important management option to improve the ecosystem functions of grassland. However, how abiotic (such as grazing exclusion (GE)) and biotic factors influence SOC and N and their different fractions in Tibetan alpine meadows remains unclear. In this study, we evaluated the relative importance of abiotic and biotic factors that drive SOC and N contents in soil density fractions by performing redundancy analysis based on three long-term (10 years) fenced alpine meadows maintained in the permafrost region of the Tibetan Plateau in China. Biotic factors comprise plant aboveground biomass, cover and diversity, whereas abiotic factors include soil properties (i.e. soil moisture, pH, clay, silt, sand, total phosphorus, available phosphorus, microbial biomass carbon and N, available N, C:N ratio and C:P ratio) and GE. Site rather than GE has significant effects on the SOC and N contents. GE caused no increase in the SOC and N contents in the whole soil and fractions. Redundancy analysis showed that 96.7% of the variations in SOC and N fractions can be explained by the selected explanatory variables. Aboveground biomass, cover, soil moisture and clay contents were key factors that affected the SOC and N fractions. The SOC and N fractions were mainly explained by the interaction between vegetation and soil, followed by soil, vegetation and GE. The study highlighted the importance of considering the covariation of vegetation and soil for evaluating the SOC and N dynamics in alpine meadows. The effect of GE (such as 10 years) on the SOC and N contents in alpine meadows can be weak in the permafrost region of the Tibetan Plateau.

Beyond resource limitation: an expanded test of the niche dimension hypothesis for multiple types of niche axes.

The niche dimension hypothesis predicts that more species can coexist given a greater number of niche axes along which they partition the environment. Although this hypothesis has been broadly supported by nutrient enrichment experiments, its applicability to other ecological factors, such as natural enemies and abiotic stresses, has not been vigorously tested. Here, we examined the generality of the niche dimension hypothesis by experimentally manipulating both resource and non-resource niche dimensions-nitrogen limitation, pathogens and low-temperature stress-in a Tibetan alpine meadow. We found that decreases in niche dimensions led to a significant reduction in species richness, consistent with results from nutrient addition studies. However, different niche variables uniquely affected the plant communities. While nitrogen had largest effects on both community biomass and species richness, pathogens and low-temperature stress, in combination with nitrogen, had synergistic effects on them. Our results provide direct evidence demonstrating that both resource and non-resource niche dimensions can influence species coexistence. These findings suggest that other non-resource factors need to be taken into consideration to better predict the community assembly and control over biodiversity, particularly under the future multifaceted global change scenarios.

Harsh environmental regimes increase the functional significance of intraspecific variation in plant communities

Abstract The relative importance of intraspecific trait variation (rITV) for functional diversity (FD) in plant communities is increasingly apparent, but the influence of abiotic factors on the balance between intraspecific and interspecific effects in contrasting environments is uncertain. Drawing on a novel conceptual and analytic framework, we quantified rITV as the ratio of FD associated with between‐population ITV (Intra_FD) and the interspecific variation (Inter_FD) due to species turnover across sites. We predicted that rITV would increase with environmental harshness as a result of decreasing interspecific variation and concomitant increases in between‐population ITV. We empirically tested this prediction in a comparison of rITV for five traits (mature plant height, SLA, leaf dry matter content and the foliar concentrations of nitrogen and phosphorus (P)) characterizing species in Tibetan alpine meadow communities from contrasting environmental regimes. We found that across sites: (a) rITV for all five traits increased with environmental harshness not only through decreasing Inter_FD but also through increasing Intra_FD; (b) increases in rITV were mostly attributable to declines in soil resources, especially soil P, with lower soil P significantly associated with lower Inter_FD but higher Intra_FD for most traits; and (c) although neither Intra_FD nor Inter_FD was significantly impacted by species richness for any traits, a higher rITV for SLA was significantly associated with low species richness. Taken together, these results support our hypothesis that the functional significance of ITV in plant communities increases with environmental harshness. Moreover, in the Tibetan alpine meadows we studied, the opposing intraspecific and interspecific responses along a gradient of P availability appear to act as a buffering mechanism stabilizing the functional structure of communities on P deficient soils. Our novel conceptual and analytical framework provides a template for evaluating the generality of this favourable mismatch between intraspecific and interspecific responses in FD along environmental gradients. A free Plain Language Summary can be found within the Supporting Information of this article.

A Protocol to Identify the Host of Parasitoids by DNA Barcoding of Vestigial Tissues

Many parasitoid wasps parasitize herbivorous insect larvae growing within plant organs (e.g., fruits and leaves). As it is hard to identify the insect host species directly, one approach to deal with this issue is to identify it by means of molecular analysis from puparia left within plant organs after wasps emerge. Unfortunately, current barcoding methods are either too expensive or too inefficient for mass species identification. Here, we present a protocol that is comparatively inexpensive and rapid. It includes two major modifications in the barcoding process. One is to use a modified Chelex DNA extraction method, which performed best in PCR amplification and was the least costly and time-consuming among four candidate methods. The other is to use general PCR primers for the host taxon, which had the highest sequencing success rate when coupled with the Chelex DNA extraction method. Our protocol proved to be successful in identifying the hosts (i.e., tephritid fly species) of parasitoid wasps in a Tibetan alpine meadow. The protocol can be widely used for mass identification of insect host species from puparia tissues to facilitate the studies on host–parasitoid interactions.

Simulated warming enhances the responses of microbial N transformations to reactive N input in a Tibetan alpine meadow

Alpine ecosystems worldwide are characterized with high soil organic carbon (C) and low mineral nitrogen (N). Climate warming has been predicted to stimulate microbial decomposition and N mineralization in these systems. However, experimental results are highly variable, and the underlying mechanisms remain unclear. We examined the effects of warming, N input, and their combination on soil N pools and N-cycling microbes in a field manipulation experiment. Special attention was directed to the ammonia-oxidizing bacteria and archaea, and their mediated N-cycling processes (transformation rates and N2O emissions) in the third plant growing season after the treatments were initiated. Nitrogen input (12 g m−2 y−1) alone significantly increased soil mineral N pools and plant N uptake, and stimulated the growth of AOB and N2O emissions in the late growing season. While warming (by 1.4 °C air temperature) alone did not have significant effects on most parameters, it amplified the effects of N input on soil N concentrations and AOB abundance, eliciting a chain reaction that increased nitrification potential (+83%), soil NO3−-N (+200%), and N2O emissions (+412%) across the whole season. Also, N input reduced AOB diversity but increased the dominance of genus Nitrosospira within the AOB community, corresponding to the increased N2O emissions. These results showed that a small temperature increase in soil may significantly enhance N losses through NO3− leaching and N2O emissions when mineral N becomes available. These findings suggest that interactions among global change factors may predominantly affect ammonia-oxidizing microbes and their mediated N-cycling processes in alpine ecosystems under future climate change scenarios.

Increased litter input significantly changed the total and active microbial communities in degraded grassland soils

Increasing organic matter input and phosphorus fertilization are employed extensively to restore degraded grasslands. Nevertheless, little is known about their effects on microbes, especially on active microbial populations. Therefore, this study is aimed at examining the short-term influences of litter and phosphorus addition on microbes in degraded grassland soils. A microcosm experiment was established using soils sampled from a heavily degraded Tibetan alpine meadow. The experiment used a two-way factorial design with grass litter and phosphorus addition as the main factors. Microbial abundance and rDNA transcriptional activity were assessed through quantitative PCR. Total and active microbial community profiles were measured using DNA- and RNA-based MiSeq sequencing, respectively. As shown in this study, litter addition significantly increased microbial rDNA transcriptional activity and fungal abundance, but it decreased microbial α-diversity. However, prokaryote abundance was unaffected by the litter addition. Total and active soil microbial community profiles and interaction patterns were also significantly altered by litter addition. The relative abundance of copiotrophic and oligotrophic microbial lineages significantly increased and decreased, respectively, in the soils with litter addition. Functional predictions suggested that litter addition might significantly increase the abundance of pathogens, as well as microbes related to nitrogen fixation, denitrification, and chitinolysis, while decreasing nitrifier abundance. In contrast, no significant effects of the phosphorus addition on soil microbes were observed. These findings highlight the significant effects of increasing litter input on total and active soil microbial communities and suggest that microbial responses should be considered when restoring degraded grasslands by increasing organic matter input.

Limited inorganic N niche partitioning by nine alpine plant species after long-term nitrogen addition

1.Nitrogen (N) is a major nutrient limiting plant growth in most terrestrial ecosystems. Both niche partitioning and fitness equalizing mechanisms related to N acquisition have been proposed to explain the maintenance of biodiversity and ecosystem functioning. However, their relative importance remains controversial and unclear, especially in worldwide terrestrial ecosystems increasingly threatened by N deposition.2.We added NH4NO3 at four levels over 7 years in an alpine meadow on Qinghai-Tibetan Plateau to simulate the effects of N deposition. Nine species that all occurred along an N addition gradient were selected for in-situ15N labeling experiment to quantify their uptake of ammonium verse nitrate.3.Plants absorbed more ammonium and nitrate with increased N addition. We found limited inorganic N niche partitioning along the N addition gradient. Instead, species tended to prefer the most abundant form of inorganic N in soil, i.e. ammonium. Of all possible linear mixed effects models constructed to explain variation in either ammonium or nitrate uptake, the most parsimonious one included soil available N. That means plant' N uptake is influenced by habitat qualities, instead of the amount of added N itself.4.Our findings suggest that inorganic N niche partitioning may play limited role in the maintenance of high diversity in this alpine meadow. Instead, species coexistence might be promoted by minimizing their fitness differences through preferring the most abundant form of inorganic N in the soil. This provides important insights into species coexistence under future N addition in Tibetan alpine meadows.

Fencing as an effective approach for restoration of alpine meadows: Evidence from nutrient limitation of soil microbes

The effects of restoration on plant communities and soil nutrients have been extensively studied but knowledge of the metabolic requirements of microbial communities is limited, especially in fragile alpine meadow ecosystems. Here, vegetation and soil from four meadows (grazed meadow, fenced meadow, fenced + reseeded meadow, and undegraded meadow) on the Tibetan Plateau were investigated. The nutrient requirements of microbes represented by stoichiometry of extracellular enzyme activities related to soil C, N, and P acquisition (β-1,4-glucosidase, BG; β-1,4-N-acetylglucosaminidase, NAG; leucine aminopeptidase, LAP; and alkaline phosphatase, AP) and their possible environmental drivers were determined. Our results showed that enzymatic C:N:P acquisition in all the meadows deviated from 1:1:1, suggesting that soil enzymatic activity stoichiometry in Tibetan alpine meadows is not homeostatic. Microbial communities in grazed meadows were co-limited by soil N and P levels, and this limitation was closely associated with the stoichiometry of soil nutrients. Activities of BG, NAG + LAP, AP, and their stoichiometry (C:N, C:P, and N:P) in fenced meadows were 38.2%, 32.9%, 51.2%, 16.8%, 19.5% and 2.3% higher than those in grazed meadows. These results indicate that fencing can relieve the N and P limitations for microbial communities in alpine meadows. Seeding the fenced meadow did not increase the soil nutrient content, microbial biomass, or enzyme activity compared with the fenced meadow, possibly owing to the low competition of the seeded species for resources. Changes in extracellular enzyme activity and stoichiometry were better explained by dissolved organic C and microbial biomass N than by plant or other soil properties. Our results demonstrate the effectiveness of fencing on the restoration of degraded alpine meadows from the perspective of alleviating microbial nutrient limitations.

Effect of soil environment on functional diversity of soil nematodes in Tibetan alpine meadows

Effect of soil environment on functional diversity of soil nematodes in Tibetan alpine meadows