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Aims: Biological nitrogen fixation (BNF), a function performed by diazotrophic microbes, plays an essential role in nitrogen (N) bioavailability in terrestrial ecosystems. However, little is known about the effects of meadow degradation on soil BNF and diazotrophic communities in alpine meadows. Methods: We investigated changes in soil BNF and their potential drivers in alpine meadows along a degradation gradient on the Tibetan Plateau (non-degraded, lightly degraded, moderately degraded, and severely degraded meadows) using real-time quantitative PCR and amplicon sequencing. Results: Soil BNF rates decreased significantly along the meadow degradation gradient with a range of 17.34–79.84 nmol C2H4 g−1 dry soil d−1 across all sites. The highest BNF rate in the non-degraded meadow was 1.5–4.6-fold higher than that in the degraded meadows. The abundance and diversity of diazotrophs measured by nifH abundance and Shannon diversity was also decreased in the degraded meadows, accompanied by decreases in plant biomass, soil moisture, and nutrient content (C, N). Soil BNF rate was correlated with plant biomass, soil nutrient content, and diazotrophic abundance (including Nostoc, Scytonema, Rhodopseudomonas, and unidentified genera within the Rhizobiales and Proteobacteria). The community composition of diazotrophs differed markedly among sites with different levels of degradation, with both autotrophic (Cyanobacteria) and heterotrophic (Proteobacteria) diazotrophs contributing significantly to BNF. The plant functional groups, particularly the sedge family, were the primary drivers of soil BNF rates via mediating soil moisture, nutrient content (dissolved organic C and N), nifH gene abundance, and diazotrophic community composition. Conclusions: Our results reveal the main drivers of decreased BNF during alpine meadow degradation and emphasize the importance of plant functional groups in shaping the diazotrophic community and regulating the BNF rate. This information can be applied to the restoration of degraded meadow ecosystems. [ABSTRACT FROM AUTHOR]

Purpose: Knowledge of soil N cycling and the associated functional microbial groups of N2O production under different management measures could provide clues for the restoration of degraded meadows in alpine ecosystems. Materials and methods: We investigated soil N2O emissions, the genes related to N2O production and reduction (AOA-amoA, AOB-amoA, nirK, nirS, and nosZ), and associated microbial communities in four meadows (continuous grazing, grazing exclusion by fencing, grazing exclusion by combined fencing and reseeding, and undisturbed meadow) in the Tibetan Plateau to reveal the mechanism underlying potential N2O emissions in alpine meadows. Results and discussion: Compared to the grazing meadow, fencing and fencing + reseeding meadows had lower N2O emissions and lower abundances of AOA-amoA, AOB-amoA, nirK, nirS, and nosZ genes, suggesting that grazing exclusion could decrease the soil N-turnover potential. However, the higher N2O emissions compared to those of undisturbed meadows indicated that longer restoration periods were necessary. Seeding the fenced meadow did not alter soil N2O emission or the abundance of AOA-amoA, AOB-amoA, nirK, nirS, and nosZ genes, possibly owing to the similar soil nutrient status compared to that of the fencing meadow. Grazing exclusion also resulted in significant changes in the community diversity and composition of microbes harboring these functional genes, especially nirK and nosZ communities. N2O emissions were significantly associated with microbial communities involved in N2O production and reduction but not with the gene abundance of AOA-amoA, AOB-amoA, nirK, nirS, and nosZ. Soil dissolved organic nutrients, including C and N, and soil moisture were the controlling factors for N2O production by altering the community composition of nirK- and nosZ-type denitrifiers, such as Bradyrhizobiaceae, Rhizobiaceae, Brucellaceae, Ochrobactrum, and Proteobacteria. Conclusions: Our results indicated that grazing-induced elevation of potential N2O emissions from meadow soil could be alleviated by grazing exclusion, including sole fencing and a combination of fencing and reseeding, by changing soil dissolved organic nutrients and moisture thus regulating the microbial communities. [ABSTRACT FROM AUTHOR]

Background and aims: Afforestation is considered one important means of mitigating climate change. However, it is still controversial whether mixed-species plantations (MP) were more conducive to the soil organic carbon (SOC) stocks than monoculture plantations (PP). Methods: We conducted a meta-analysis based on 21 publications to assess the effects of different afforestation modes as well as controlling factors of SOC stocks on the Loess Plateau of China. Results: Compared with monoculture plantations, mixed-species plantations could significantly increase the response size of SOC stocks by 28%. For different species combinations, tree-shrub mixtures were more conducive to increasing the SOC stocks. In climate-limited regions (MAT <8 °C, MAP <500 mm), the response size of SOC stocks of mixed-species plantations was 34% higher than that of monoculture plantations. Furthermore, significant differences were found in the response size of SOC stocks at young (< 10 yr) and mature stages (> 20 yr). Compared with abandoned land, afforestation on cropland, especially mixed-species plantations, could increase the SOC stocks by 10%. Additionally, compared with monoculture plantations, a stronger coupling relationship was observed between the soil total nitrogen (STN) and SOC stocks in mixed-species plantations. Conclusion: Our results suggest that for the Loess Plateau of China, planting mixed-species plantations containing nitrogen-fixing plants is a more effective approach to enhancing the SOC stocks than monoculture plantations. [ABSTRACT FROM AUTHOR]

Soil ecoenzymatic stoichiometry reflects the nutrient flow of ecosystems. While knowledge exists on how the secondary succession of plants affects soil physicochemical properties and soil ecoenzymatic activity, less is known about how soil ecoenzymatics change during this process. We investigated five typical stages of the entire succession process of vegetation on the Loess Plateau, China. These stages included: (1) farmland stage (0 years), (2) grassland stage (30 years), (3) shrub land stage (60 years), (4) the pioneer forest stage (100 years), (5) the climax community stage (160 years). Soil ecoenzymatic activity, microbial biomass, and soil physicochemical properties were measured. Our research showed secondary succession significantly changed soil enzyme activity, and the metabolic activity of soil microorganisms significantly declines as secondary succession progresses. N limitation in the soil microbial community was weak initially and then gained strength. P nutrient limitation was strong initially, and then weakened. Soil ecoenzymatic C : N : P acquisition ratios deviated from 1 : 1 : 1. Thus, secondary succession on the Loess Plateau is nutrient dependent, but not homeostatic. Soil physicochemical properties and plants were important factors for soil enzyme activities. In addition, soil available nutrients were better than soil total nutrients to reveal changes in soil ecoenzymatic activities and stoichiometry. This study demonstrated the regularity of soil nutrient cycling during the secondary succession of vegetation, providing new insights on the mechanisms of nutrient flow. [ABSTRACT FROM AUTHOR]

Slope aspect is an important topographic factor for a micro-ecosystem environment that may affect macro- and micronutrients in plants and soil. The south-, northwest-, and north-facing slopes were selected to investigate the influence of slope aspect on the concentrations, storage, and allocation of macro- and micronutrients in Artemisia sacrorum on the Loess Plateau in China. The concentrations of available manganese (Mn) in both rhizosphere and non-rhizosphere soils reached their maximum on the north-facing slope. The concentrations of available iron (Fe) in rhizosphere soil and available copper (Cu) in non-rhizosphere soil reached their maximum on the south-facing slope. Slope aspect significantly affected the total concentrations of potassium (K), calcium (Ca), magnesium (Mg), Cu, and Mn in rhizosphere and non-rhizosphere soils, and all of these elements reached their maximum on the northwest-facing slope. Slope aspect significantly influenced the concentrations of aboveground K, Ca, and Mg, sodium (Na), Mn, and belowground K in A. sacrorum, and the concentrations of aboveground K, Ca, Mg, and Na and belowground Mn, Na, Fe, Ca, and Mg in weed. Most elements in A. sacrorum and the weeds reached their maximum on the south-facing slope. Slope aspect significantly changed the aboveground-to-belowground concentration ratios of K, Ca, and Na in A. sacrorum and weed. Slope aspect significantly affected the storage of macro- and micronutrients in A. sacrorum and weed but not the storage in the plants of the entire plot. Slope aspect predominantly affected the storage allocation of macro- and micronutrients in A. sacrorum but not those in weed. Slope aspect is an important topographic factor that affects the macro- and micronutrients in plants and soil in micro-ecosystem environments. [ABSTRACT FROM AUTHOR]

Aims: While the effects of destocking on soil nutrient and plant productivity are known, the effect on functional groups of fungi has received less attention. The objective of this study was to evaluate the effect of long-term destocking on fungal functional guilds and their association with plants and soil. Methods: We characterized the changes in five fungal functional guilds, including plant pathogens, animal pathogens, wood saprotrophs, dung saprotrophs, and arbuscular mycorrhizal fungi (AMF), along a 35-year chronosequence following destocking at 0–60 cm soil depths on the Chinese Loess Plateau. Fungal community composition was assigned by comparing with the FUNGuild database. Results: After 35 years of destocking, diversities of plant pathogens, wood saprotrophs, and AMF increased, while that of animal pathogens and dung saprotrophs decreased. Destocking had a greater effect in the near-surface layers (0–10 and 10–20 cm) owing to the greater influence of plant biomass and soil nutrients. Among the above- and belowground drivers, plant pathogen diversity was largely associated with plant diversity, while animal pathogens, dung saprotrophs, and wood saprotrophs were associated with aboveground biomass, AMF were responsive to soil conditions (e.g., organic C, NO3−-N, C:N ratio, and moisture). Conclusions: Long-term destocking can be considered to be an important predictor of fungal functional guilds, and changes in these microorganisms were associated with cessation-induced shifts in plants and soil by grazing. Our findings provide insights into the duration of destocking necessary to benefit fungal communities, and how this varies according to soil depth. [ABSTRACT FROM AUTHOR]

Soil water storage (SWS) is a key variable influencing hydrological processes and vegetation function in arid and semiarid regions. Although convincing evidence indicated that mixed forests have higher resistance and resilience to climate change and natural disturbance than monocultures, it is unclear how mixed-species plantations affect SWS. By conducting a meta-analysis of 1071 paired observations in mixed-species plantations and monoculture plantations from 45 studies, we showed that, on average, the SWS of mixed-species plantations at 0–500 cm was 10.81% higher than that of monoculture plantations. Importantly, these positive mixture effects increased over time, with greater positive effects in mixed tree and shrub plantations. The effects of mixed-species plantations on SWS shifted from positive to negative with increasing soil depth, and these mixing effects in the topsoil layer (0–100 cm) became more pronounced with increasing stand age. However, the mixture effects on SWS did not vary with the mean annual temperature and precipitation. Moreover, mixed-species plantations were more conducive to enhancing the SWS capacity in areas with a low initial SWS. Structural equation models demonstrated that stand age was the main factor controlling the change in SWS, and soil depth also reduced the effect size of SWS by influencing the initial SWS. Our findings highlight that protecting and promoting functionally diverse forests improves SWS capacity, thereby alleviating soil moisture stress in arid and semiarid regions. ● The soil water storage in mixed-species plantations was significantly higher than that in monoculture plantations. ● The positive effect of mixed-species plantations increased with stand age but decreased with soil depth. ● The effect of mixed-species plantations on soil water storage was not influenced by the regional background climate. ● The improvement in soil water storage was more pronounced in areas with low initial soil water storage. [ABSTRACT FROM AUTHOR]

Purpose: Elevated CO2 and nitrogen (N) addition both affect soil microbial communities, which significantly influence soil processes and plant growth. Here, we evaluated the combined effects of elevated CO2 and N addition on the soil–microbe–plant system of the Chinese Loess Plateau. Materials and methods: A pot cultivation experiment with two CO2 treatment levels (400 and 800 μmol mol−1) and three N addition levels (0, 2.5, and 5 g N m−2 year−1) was conducted in climate-controlled chambers to evaluate the effects of elevated CO2 and N addition on microbial community structure in the rhizosphere of Bothriochloa ischaemum using phospholipid fatty acid (PLFA) profiles and associated soil and plant properties. Structural equation modeling (SEM) was used to identify the direct and indirect effects of the experimental treatments on the structure of microbial communities. Results and discussion: Elevated CO2 and N addition both increased total and fungal PLFAs. N addition alone increased bacterial, Gram-positive, and Gram-negative PLFAs. However, elevated CO2 interacting with N addition had no significant effects on the microbial community. The SEM indicated that N addition directly affected the soil microbial community structure. Elevated CO2 and N addition both indirectly affected the microbial communities by affecting plant and soil variables. N addition exerted a stronger total effect than elevated CO2. Conclusions: The results highlighted the importance of comprehensively studying soil–microbe–plant systems to deeply reveal how characteristics of terrestrial ecosystems may respond under global change. [ABSTRACT FROM AUTHOR]

Purpose: Changes in microbial communities during natural succession in semiarid areas have been widely studied but their association with plant and soil properties remains elusive. In the present study, we investigated plant characteristics, rhizosphere soil variables, and microbial communities along a chronosequence of grasslands forming on abandoned farmland on the Chinese Loess Plateau. Materials and methods: Rhizosphere samples were collected from the early-stage dominant plant Artemisia capillaris from farmland abandoned for 5, 10, and 15 years and from the late-stage dominant plant Artemisia sacrorum from farmland abandoned for 10, 15, 20, and 30 years. Microbial community composition, including bacteria and fungi, was determined by high-throughput sequencing. Microbial succession rates represented by temporary turnover were assessed using the slope (w value) of linear regressions, based on log-transformed microbial community similarity over time. Results and discussion: Cover and aboveground biomass of A. capillaris tended to decrease, whereas those of A. sacrorum increased during the succession. Although the rhizosphere bacteria of A. capillaris transitioned from Proteobacteria-dominant to Actinobacteria-dominant, the bacteria of A. sacrorum exhibited the opposite trend. Bacterial and fungal community diversity tended to increase logarithmically with increasing plant aboveground biomass, indicating that an increase in plant biomass could lead to enhanced rhizosphere microbial diversity, but the rate of enhancement decreased gradually. A lower temporary turnover rate of bacterial and fungal communities in the rhizosphere than that in the bulk soil indicated a higher successional rate of the rhizosphere microbial community. Levels of soil nutrients, such as organic carbon, nitrate nitrogen, and ammonium nitrogen, were closely associated with the abundance and diversity of bacterial and fungal communities, indicating their critical role in shaping the rhizosphere microbial community. Conclusions: Our results indicate a close association between plant succession and rhizosphere microbial succession in a semiarid area. Plants affect the microbial communities possibly by changing the nutrient input into the rhizosphere. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) perform essential ecosystem functions in arid and semi-arid ecosystems worldwide. The formation, development, and distribution of BSCs are influenced by changes in multiple environmental factors, including changes in the vascular plant community. The influence of changes in vegetation factors on BSC cover in 8-, 12-, and 16-year-old rehabilitated grasslands were studied in the hilly area of the Chinese Loess Plateau. The rate of degradation of BSCs underneath litter ( P < 0.01) and the degradation cover of BSCs ( P < 0.05) differed significantly between the 8- and 16-year-old successions. Stepwise multiple linear regression analysis showed that the main vegetation factors influencing the dynamics of BSC cover differed among the 8-, 12-, and 16-year-old rehabilitated grasslands. Basal cover, phytomass, and litter cover were the main vegetation factors influencing the dynamics of BSC cover on 8-year-old rehabilitated grassland. Phytomass, litter thickness, and litter cover were the main factors influencing the dynamics of BSC cover on 12-year-old rehabilitated grassland. On 16-year-old rehabilitated grassland, Pielou evenness index, litter thickness, and litter biomass were the main vegetation factors influencing degradation of BSC cover underneath litter, whereas basal cover, litter thickness, and litter biomass were the main vegetation factors influencing the degradation cover of BSCs. At particular stages of herbaceous succession, vegetation factors can have a large influence on changes in the community's basal cover and litter, which are key factors influencing changes in BSC cover. The degradation of BSCs underneath litter may be a result of complicated eco-physiological processes. [ABSTRACT FROM AUTHOR]

• Afforestation consumed a substantial amounts of soil moisture, especially moisture at deep soil layers. • Mixed-species plantations had no significant effect on soil moisture after farmland abandonment. • Shrubs did not significantly reduce soil moisture in arbor-shrub mixtures. • Changes in soil moisture were controlled by climate, topography, vegetation characteristics and land use history. In recent years, the ability of mixed-species plantations to cope with environmental changes has been a focus of research. Despite compelling evidence indicating that mixed-species plantations can provide many economic, environmental and social benefits, whether they can also enhance regional stress responses to drought remains unclear. Therefore, a meta-analysis was conducted based on 457 field observations to assess the effects of different planting patterns on the soil moisture of 500 cm on the Loess Plateau. The results showed that both monoculture and mixed-species plantations consumed significant soil moisture content. However, compared with monoculture plantations, mixed-species plantations were better able to maintain the soil moisture at 0–400 cm. Soil moisture content varied by topography, climate, vegetation species and planting age. We observed that afforestation was a good choice for areas with the high precipitation (>500 mm), the middle elevation (1200–1600 m) and slope (20–30°). Furthermore, the arbors mixed with shrubs did not significantly consume the soil moisture content and was more sensitive to the change in planting ages. In addition, the response sizes of soil moisture among different vegetation species were negatively correlated with the initial soil moisture content. We therefor concluded that mixed-species plantations, especially arbors mixed with shrubs were conducive to enhancing drought resistance in arid and semiarid regions. In considering future afforestation activities, planners need to be aware that different environments support different vegetation species and patterns. This study provides a reference and guidance for the scientific planning and sustainable development of forest ecosystem in arid and semiarid regions. [ABSTRACT FROM AUTHOR]

Research Highlights: Soil enzymes have a significant impact on the production of glomalin-related soil protein (GRSP), directly and indirectly affecting the nutrient metabolism balance, but there is little available information on ecological stoichiometry in soil aggregates. Background and Objectives: Vegetation restoration changes community structure and species composition in ecosystems, thus changing the physicochemical properties of soil. Soil aggregate is the most basic physical structure of the soil. Therefore, in order to understand dynamic changes in soil aggregate nutrients as vegetation restoration progresses, we set out to investigate the nutrient distribution and utilization in aggregates, and how enzymes respond to the nutrient changes in achieving a nutritional balance along successive stages of vegetation restoration. Materials and Methods: We collected and analyzed soil from plots representing six different stages of a vegetation restoration chronosequence (0, 30, 60, 100, 130, and 160 years) after farmland abandonment on the Loess Plateau, China. We investigated soil nutrient stoichiometry, GRSP, and enzyme stoichiometry in the different successional stages. Results: The results revealed that soil organic carbon, total nitrogen, enzyme activity, and GRSP increased with vegetation recovery age, but not total phosphorus, and not all enzymes reached their maximum in the climax forest community. The easily extractable GRSP/total GRSP ratio was the largest at the shrub community stage, indicating that glomalin degradation was the lowest at this stage. Ecological stoichiometry revealed N-limitation decreased and P-limitation increased with increasing vegetation restoration age. Soil enzymes had a significant impact on the GRSP production, directly and indirectly affecting nutrient metabolism balance. Conclusions: Further study of arbuscular mycorrhizal fungi to identify changes in their category and composition is needed for a better understanding of how soil enzymes affect their release of GRSP, in order to maintain a nutrient balance along successive stages of vegetation restoration. [ABSTRACT FROM AUTHOR]

The impact of nitrogen (N) and phosphorus (P) fertilizer inputs on soil nutrient cycling and ecological function processes has garnered significant attention. Soil multifunctionality primarily refers to the soil's ability to perform multiple functions simultaneously, particularly the functions related to the genes involved in carbon (C), nitrogen (N), and phosphorus (P) cycles, which are critical for ecosystem sustainability. Despite this, the effects of N and P fertilizers on the expression of genes involved in soil carbon (C), nitrogen (N), and phosphorus (P) cycles, and their consequent influence on soil multifunctionality, remain unclear. To investigate this, we conducted a long-term nine-year experiment. The experimental site was fenced to prevent grazing and included four treatments: Control (no fertilizer), N (10 g N m−2 y−1, urea), P (5 g P m−2 y−1, Ca(H 2 PO 4) 2), and NP (10 g N and 5 g P m−2 y−1, urea and Ca(H 2 PO 4) 2). We examined the effects of these treatments on soil microbial functional gene abundance and multifunctionality. Our findings revealed that N addition altered the composition of soil microbial functional genes but did not affect functional diversity. Both N and P inputs, as well as their combination, negatively impacted soil carbon fixation and the genes encoding enzymes for the degradation of starch, hemicellulose, cellulose, and chitin. N input also disrupted soil nitrogen and phosphorus cycling by inhibiting the expression of soil denitrification genes (nirS and nosZ), phytate hydrolase gene (cphy), and a phosphatase gene (phoD). Additionally, P input significantly inhibited functional genes involved in soil nitrification, denitrification, ammonification, nitrogen fixation, and ammonia oxidation processes. It also adversely affected phytate synthesis and degradation. The combined N and P inputs had a substantial negative impact on soil nitrification (hao), denitrification (narG , nirK , nirS , and norZ), ammonification (gdh), nitrogen fixation, annamox, and nitrogen reduction, and inhibited the expression of soil phosphorus cycle genes. Long-term phosphorus application was found to have a more detrimental effect on soil multifunctionality compared to nitrogen application. Furthermore, our study showed that vegetation diversity and abundance are crucial drivers of soil carbon, nitrogen, and phosphorus cycling functional genes and multifunctionality. We concluded that N and P inputs alter soil multifunctionality by influencing vegetation diversity; therefore, maintaining vegetation diversity is essential for sustaining soil multifunctionality. [ABSTRACT FROM AUTHOR]

Aims: Understanding the linkage between community heterogeneity (β diversity) and ecosystem functioning is crucial for uncovering complex ecological processes that impact ecosystem stability and productivity. However, our understanding of how β diversity is associated with ecosystem functioning across environmental gradients remains limited.We conducted an aridity-gradient transect survey of grassland over 3500 km across the Tibetan Plateau (a total of 80 grassland sites) to investigate the changes of plant and soil microbial diversities along a natural aridity gradient, and to evaluate the above- and belowground biomass and plant nutrient levels connected with the observed variation.Our results showed that plant richness, above- and belowground biomass, plant nutrient concentrations, and soil microbial α and β diversities (including taxonomic and functional) significantly decreased along the aridity gradient. Compared to the α diversities of plant and microbial community, their β diversities were more significantly correlated with above- and belowground biomass and plant carbon, nitrogen and phosphorus concentrations. Metagenomic functional profiles showed that β diversity of microbial functions, including genes of the carbohydrate metabolism responsible for carbon degradation, nitrification, energy production and conversion, material transport and coenzyme metabolism, had closer associations with plant biomass and nutrient concentrations than did their α diversities. These positive β biodiversity-functions association was weakened by the increasing aridity, mainly because the increasing aridity-induced lower biomass of plant functional groups (e.g., sedge and forbs), soil moisture and organic carbon content decreased both plant and soil microbial β diversities.These findings provide novel insight into the biodiversity-ecosystem functions relationship and stress the crucial roles of above- and belowground β diversity in supporting alpine grassland biomass and nutrient levels. Biodiversity conservation to prevent large-scale community homogenization should be attached in alpine ecosystem.Methods: Understanding the linkage between community heterogeneity (β diversity) and ecosystem functioning is crucial for uncovering complex ecological processes that impact ecosystem stability and productivity. However, our understanding of how β diversity is associated with ecosystem functioning across environmental gradients remains limited.We conducted an aridity-gradient transect survey of grassland over 3500 km across the Tibetan Plateau (a total of 80 grassland sites) to investigate the changes of plant and soil microbial diversities along a natural aridity gradient, and to evaluate the above- and belowground biomass and plant nutrient levels connected with the observed variation.Our results showed that plant richness, above- and belowground biomass, plant nutrient concentrations, and soil microbial α and β diversities (including taxonomic and functional) significantly decreased along the aridity gradient. Compared to the α diversities of plant and microbial community, their β diversities were more significantly correlated with above- and belowground biomass and plant carbon, nitrogen and phosphorus concentrations. Metagenomic functional profiles showed that β diversity of microbial functions, including genes of the carbohydrate metabolism responsible for carbon degradation, nitrification, energy production and conversion, material transport and coenzyme metabolism, had closer associations with plant biomass and nutrient concentrations than did their α diversities. These positive β biodiversity-functions association was weakened by the increasing aridity, mainly because the increasing aridity-induced lower biomass of plant functional groups (e.g., sedge and forbs), soil moisture and organic carbon content decreased both plant and soil microbial β diversities.These findings provide novel insight into the biodiversity-ecosystem functions relationship and stress the crucial roles of above- and belowground β diversity in supporting alpine grassland biomass and nutrient levels. Biodiversity conservation to prevent large-scale community homogenization should be attached in alpine ecosystem.Results: Understanding the linkage between community heterogeneity (β diversity) and ecosystem functioning is crucial for uncovering complex ecological processes that impact ecosystem stability and productivity. However, our understanding of how β diversity is associated with ecosystem functioning across environmental gradients remains limited.We conducted an aridity-gradient transect survey of grassland over 3500 km across the Tibetan Plateau (a total of 80 grassland sites) to investigate the changes of plant and soil microbial diversities along a natural aridity gradient, and to evaluate the above- and belowground biomass and plant nutrient levels connected with the observed variation.Our results showed that plant richness, above- and belowground biomass, plant nutrient concentrations, and soil microbial α and β diversities (including taxonomic and functional) significantly decreased along the aridity gradient. Compared to the α diversities of plant and microbial community, their β diversities were more significantly correlated with above- and belowground biomass and plant carbon, nitrogen and phosphorus concentrations. Metagenomic functional profiles showed that β diversity of microbial functions, including genes of the carbohydrate metabolism responsible for carbon degradation, nitrification, energy production and conversion, material transport and coenzyme metabolism, had closer associations with plant biomass and nutrient concentrations than did their α diversities. These positive β biodiversity-functions association was weakened by the increasing aridity, mainly because the increasing aridity-induced lower biomass of plant functional groups (e.g., sedge and forbs), soil moisture and organic carbon content decreased both plant and soil microbial β diversities.These findings provide novel insight into the biodiversity-ecosystem functions relationship and stress the crucial roles of above- and belowground β diversity in supporting alpine grassland biomass and nutrient levels. Biodiversity conservation to prevent large-scale community homogenization should be attached in alpine ecosystem.Conclusions: Understanding the linkage between community heterogeneity (β diversity) and ecosystem functioning is crucial for uncovering complex ecological processes that impact ecosystem stability and productivity. However, our understanding of how β diversity is associated with ecosystem functioning across environmental gradients remains limited.We conducted an aridity-gradient transect survey of grassland over 3500 km across the Tibetan Plateau (a total of 80 grassland sites) to investigate the changes of plant and soil microbial diversities along a natural aridity gradient, and to evaluate the above- and belowground biomass and plant nutrient levels connected with the observed variation.Our results showed that plant richness, above- and belowground biomass, plant nutrient concentrations, and soil microbial α and β diversities (including taxonomic and functional) significantly decreased along the aridity gradient. Compared to the α diversities of plant and microbial community, their β diversities were more significantly correlated with above- and belowground biomass and plant carbon, nitrogen and phosphorus concentrations. Metagenomic functional profiles showed that β diversity of microbial functions, including genes of the carbohydrate metabolism responsible for carbon degradation, nitrification, energy production and conversion, material transport and coenzyme metabolism, had closer associations with plant biomass and nutrient concentrations than did their α diversities. These positive β biodiversity-functions association was weakened by the increasing aridity, mainly because the increasing aridity-induced lower biomass of plant functional groups (e.g., sedge and forbs), soil moisture and organic carbon content decreased both plant and soil microbial β diversities.These findings provide novel insight into the biodiversity-ecosystem functions relationship and stress the crucial roles of above- and belowground β diversity in supporting alpine grassland biomass and nutrient levels. Biodiversity conservation to prevent large-scale community homogenization should be attached in alpine ecosystem. [ABSTRACT FROM AUTHOR]

Grasslands support various ecological functions, such as climate regulation, soil and water conservation, carbon turnover, and nutrient cycling. However, nearly a half of global grasslands have been degraded to varying degrees, especially on the Qinghai–Tibet Plateau (QTP), an extremely fragile ecosystem. As a primary measure of grassland restoration, fertilization largely affects soil aggregate size distribution (ASD) and particle size distribution (PSD). Fractal theory provides a powerful tool for analysis and characterization of soil ASD and PSD. However, our current understanding of soil ASD and PSD responses to fertilization remains limited. Therefore, this study investigated the response of soil structure and fertility to long-term fertilization in alpine grasslands on the QTP based on fractal theory. Long-term fertilization caused significant changes in soil ASD, which varied depending on fertilization practice, particularly in the topsoil (0–5 cm). Soil texture, which is influenced by soil parent material, exhibited a continuous vertical distribution along the depth and was not altered by fertilization. In addition, the results further confirmed that large microaggregates with specific pore structures contributed more to soil organic carbon (SOC) sequestration than did other size aggregates. The generalized dimension spectra showed varying increases (6.27–34.93 %) in the complexity or fineness (ΔD) of the soil PSD after fertilization. Capacity dimension (D 0) decreased significantly with NP addition and was correlated strongly with plant species diversity and richness, whereas the information dimension (D 1), D 1 /D 0 , and correlation dimension (D 2) exhibited significant correlations with soil nutrients. During long-term fertilization, soil texture dominated the vertical distribution of the soil erodibility factor, and characteristic microaggregates were the key factors influencing change in soil microstructural stability. Overall, the findings highlight that selection of appropriate fertilization methods (single or combined applications) is vital for regulation and improvement of soil structure and fertility in alpine grasslands. • Long-term fertilization caused significant changes in soil aggregate size distribution. • Increased complexity (ΔD) of soil particle size distribution after fertilization. • Large microaggregates (0.05–0.25 mm) contributed more to SOC sequestration. • Soil texture dominated the vertical distribution of the soil erodibility factor. • Characteristic microaggregates were the key factors for soil microstructure stability. [ABSTRACT FROM AUTHOR]

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. • Effects of grazing-to-fencing conversion on soil microbial composition, functional profiles were investigated. • Grazing-to-fencing conversion caused a shift in microbial composition that shifts from oligotrophs to copiotrophs. • Grazing-to-fencing conversion increased the abundance of diazotrophs, plant pathogens. • Changes in bacterial and fungal communities depend on the biomass and diversity of plant functional groups. [ABSTRACT FROM AUTHOR]

Increasing aridity is known to influence the diversity and function of soil microbiome. However, how it affects the microbial co-occurrence network are poorly understood, particularly in alpine ecosystem, which is one of the most vulnerable ecosystems. Here, we investigated the co-occurrence networks of soil microbiomes based on 60 sites along a natural aridity gradient across the Tibetan Plateau and evaluated their relationship with soil functionality. We hypothesized that increasing aridity could lead to a reduction in the complexity of microbial networks (e.g., the decreased number of nodes and edges, lower connectance, average degree, clustering coefficient and centralization degree), and this changed network complexity is strongly relate to microbial structure stability (network robustness and vulnerability) and soil functionality. Our results supported the hypothesis that the network complexities of bacteria, fungi and protists decreased along the aridity gradient. Microbial network complexity was significantly correlated with network robustness and vulnerability, suggesting that soil network complexity supports structure stability. Bacterial and fungal network complexities were strongly related to community functional traits (e.g., enzymes activities, carbohydrate and amino acid metabolism, C degradation genes), soil processes (e.g., CO 2 and CH 4 emission, N mineralization) and multifunctionality. This suggests a key relationship of microbial networks to alpine soil functionality, with a more significant impact observed in semi-arid and arid habitats than that in humid and semi-humid habitats. Plants played key roles in driving microbial network through altering soil organic C, with plant diversity having a greater impact in humid habitats, while plant biomass was more influential in semi-arid and arid habitats. Our results indicate that aridity-induced simplification of microbial communities can potentially weaken community stability and alpine soil functionality. Therefore, preserving the complexity of belowground communities is critical for ecosystem management and for predicting the ecological consequences of future aridification. • The network complexities of bacteria, fungi and protists decreased along a natural aridity gradient in alpine grassland. • Aridity-induced simplification of microbial communities potentially weaken community stability and alpine soil functionality. • Plants play key roles in driving microbial networks through altering soil organic C. • Preserving the complexity of microbial communities is critical for ecosystem management. [ABSTRACT FROM AUTHOR]

Global climate change is predicted to increase exogenous N input into terrestrial ecosystems, leading to significant changes in soil C-cycling. However, it remains largely unknown how these changes affect soil C-cycling, especially in semi-arid grasslands, which are one of the most vulnerable ecosystems. Here, based on a 3-year field study involving N additions (0, 25, 50, and 100 kg ha−1 yr−1 of urea) in a semi-arid grassland on the Loess Plateau, we investigated the impact of urea fertilization on plant characteristics, soil properties, CO 2 and CH 4 emissions, and microbial C cycling genes. The compositions of genes involved in C cycling, including C fixation, degradation, methanogenesis, and methane oxidation, were determined using metagenomics analysis. We found that N enrichment increased both above- and belowground biomasses and soil organic C content, but this positive effect was weakened when excessive N was input (N100). N enrichment also altered the C-cycling processes by modifying C-cycle-related genes, specifically stimulating the Calvin cycle C-fixation process, which led to an increase in the relative abundance of cbbS , prkB , and cbbL genes. However, it had no significant effect on the Reductive citrate cycle and 3-hydroxypropionate bi-cycle. N enrichment led to higher soil CO 2 and CH 4 emissions compared to treatments without added N. This increase showed significant correlations with C degradation genes (bglA , per , and lpo), methanogenesis genes (mch, ftr, and mcr), methane oxidation genes (pmoA , pmoB , and pmoC), and the abundance of microbial taxa harboring these genes. Microbial C-cycling genes were primarily influenced by N-induced changes in soil properties. Specifically, reduced soil pH largely explained the alterations in methane metabolism, while elevated available N levels were mainly responsible for the shift in C fixation and C degradation genes. Our results suggest that soil N enrichment enhances microbial C-cycling processes and soil CO 2 and CH 4 emissions in semi-arid ecosystems, which contributes to more accurate predictions of ecosystem C-cycling under future climate change. • Urea fertilization increased CO 2 and CH 4 emissions in semi-arid grasslands. • Urea fertilization enhanced microbial C-cycling by altering C-related genes. • Microbial C fixation and C degradation genes were mainly driven by available N. • Microbial methane metabolism genes were mainly driven by pH. [ABSTRACT FROM AUTHOR]

• Association between microbial diversity and soil functions was investigated. • Soil potential multifunctionality of alpine meadow decreased along the degradation. • Bacteria rather than fungi are important for soil functions in alpine meadow. • Functional redundancy of microbes may occur in alpine ecosystems. • Bacterial richness is negatively related to potential soil multifunctionality in degraded alpine meadows. Fungal richness and community composition are known to be positively associated with soil multifunctionality. However, the contributions of bacterial and fungal communities to the multiple soil functions of alpine meadow ecosystems have not been widely examined. Here, we surveyed the soil in Qinghai-Tibetan alpine meadows and classified the extent of degradation as undegraded, lightly degraded, moderately degraded, and severely degraded to clarify the associations between microbial diversity (including bacteria and fungi) and potential soil multifunctionality. Bacterial and fungal compositions were detected by sequencing of the 16S rDNA and internal transcribed spacer amplicons, respectively. Functions associated with nutrient cycling (dissolved organic nitrogen and carbon, available phosphorus, NO 3 –, NH 4 +, C, N, P-cycle enzymes) and climate regulation (CO 2 and N 2 O emissions) were also examined. Bacterial, rather than fungal, richness was negatively associated with potential soil multifunctionality, which decreased along the degradation gradient. Structural equation modeling explained 79.6% of the variation in potential soil multifunctionality and confirmed that, in addition to bacterial community richness and composition, organic carbon and moisture were important drivers of potential soil multifunctionality. These results suggest that higher bacterial richness is associated with lower potential soil multifunctionality in alpine meadow ecosystems. Among the bacterial taxa, only ~ 12% of bacterial genera were identified as predictors of multifunctionality, suggesting functional redundancy of the bacterial community in the meadow ecosystem. Rhodanobacter , Mucilaginibacter , Rhodococcus , and Bosea , belonging to the Proteobacteria and the Actinobacteria phyla were identified as critical for maintaining potential soil multifunctionality. Our results suggest that bacterial richness is negatively related to potential soil multifunctionality in alpine meadow ecosystems and there is no correlation between potential multifunctionality and fungal richness. [ABSTRACT FROM AUTHOR]

• Soil C-, N-, and P-acquiring enzyme activities and stoichiometry were investigated. • A non-homeostasis of soil ecoenzymatic activity stoichiometry exists in Tibetan alpine meadows. • Fencing can relieve nutrient limitations by increasing plant biomass. • DOC and microbial biomass N accounted for most variation in ecoenzymatic activity. • Fencing can address microbial nutrient limitations in restoration efforts. 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. [ABSTRACT FROM AUTHOR]

• Planted forest (PF) invests more carbon (C) to below-ground biomass and deep soil layer than natural forest (NF). • NF stored more than twice as much C as did PF in both biomass and soil, but exhibited much lower C sequestration rates than PF. • Afforestation promotes C accumulation without causing soil water deficit under precipitation higher than 505 mm. • Warming improves the C accumulation in PF but accelerated the soil C loss in NF. Large-scale afforestation has been widely implemented for restoring the degraded lands and mitigating climate change while naturally regenerated forests should be protected to preserve carbon (C) in land ecosystems. However, a critically needed comparison on the effectiveness of C sequestration between planted forest (PF) and natural forest (NF) in water-limited areas has rarely been conducted at a regional scale. This study synthesized 275 publications to examine the changes of C stock in above-ground biomass (AGB), below-ground biomass (BGB) and deep soils (0-200 cm) between PF and NF in the China's Loess Plateau, a typical water-limited region with extensive afforestation. We found that, NF stored more than twice as much C as did PF in both biomass and soil. But PF allocated relatively higher proportion of C stock to BGB and deep soil layer (> 100 cm) than NF. Moreover, the C sequestration rates in biomass and soil for PF were 1.42 and 1.72 Mg C ha−1 yr−1, respectively, much higher than that of NF (0.13 and -1.38 Mg C ha−1 yr−1). In addition, afforestation in areas with the mean annual precipitation (MAP) greater than 505 mm may promote both biomass and soil C accumulation without causing severe soil water deficit. Moreover, the increase in mean annual temperature (MAT) could significantly promote the C accumulation in both biomass and soil of PF but accelerated the soil C loss of NF. Overall, our results indicate that afforestation in water-limited areas may exhibit higher potential to sequester C than naturally regeneration, and afforestation is worth promoting with careful consideration of planting density and rainfall zones to avoid causing excessive water depletion. This study has important implications for the forest management in water-limited areas particularly under global climate change. [ABSTRACT FROM AUTHOR]

• Warming significantly lowered soil nematode diversity. • Warming indirectly and directly affected vegetation to lead to soil nematodes diversity being changed. • Warming and litter removal significantly reduced external resource inputs to the food web. • Warming and litter removal lead to soil food web degradation. Both climate warming and litter removal alter soil nematode communities and the structure, stability, and function of soil food webs. The soil nematode metabolic carbon footprint, based on nematode biomass and respiration, can be used to indicate ecosystem function and the response of nematodes to nutrient enrichment in the ecosystem. However, it is unclear whether or how climate warming and litter removal affect the metabolic carbon footprint of soil nematodes and soil food webs. In this study, we investigated four warming and litter removal treatments in the Qinghai-Tibet Plateau, China, to determine the effects of climate warming and litter removal on soil microbial food webs. The treatments included: (1) control (CK), (2) warming, (3) litter removal, (4) warming + litter removal. We found that warming and litter removal had significant negative effects on the diversity and richness of soil nematodes. In addition, our results showed warming indirectly and directly affected vegetation diversity, thereby altering soil nematode diversity. Vegetation played an important role in the maintenance of soil nematode community diversity. The enrichment and structural footprints reflected nematodes that could respond most rapidly to resource enrichment and those with higher trophic levels in soil food webs, respectively. Overall, warming and litter removal significantly negatively affect the enrichment metabolic footprint, indicating they could significantly reduce the external resource inputs into the food web. Both warming and litter removal reduced the structural metabolic footprint of the soil food web, although the changes were not significant, indicating that the metabolic activity of nematodes of high nutrient levels decreased and the ability to regulate the food web from top-bottom effects was weakened under warming and litter removal. The nematode functional metabolic footprints indicated that litter removal could aggravate the effect of warming on the soil food web and result in more severe degradation. The combination of warming and litter removal significantly inhibited the connectance of the bacterial channel, but had no significant effect on the fungal channel. These results suggest that the soil food web enhanced resistance to the environment by increasing the proportion of the fungal channel. It is critical to understand the responses of soil food webs to climate warming and litter removal to better predict how ecosystem functions will change in the future. [ABSTRACT FROM AUTHOR]

• SOC stability in different vegetation zones was evaluated in the Loess Plateau, China. • Overall SOC stability decreased after vegetation restoration. • SOC stability was strongly affected by climate (precipitation and temperature). • A basis for the long-term monitoring of SOC stability in the Loess Plateau is provided. Vegetation restoration is considered to be an important pathway for ecosystem improvement; however, information remains limited about how the soil organic carbon (SOC) stability changes after vegetation restoration. This could be evaluated by measuring the response of SOC stability to soil physicochemical properties, soil enzyme activity, and environmental factors [recovery years, vegetation types, mean annual precipitation (MAP) and mean annual temperature (MAT)]. Here, the soils of shrub and forest land in different vegetation zones (steppe zone [SZ], forest-steppe zone [FSZ], and forest zone [FZ]) in the Loess Plateau of China were evaluated over different time periods. As the number of years increased, the active carbon fractions [very labile (C1) and labile (C2) fractions of oxidizable carbon] and carbon management index (CMI) increased, whereas the SOC stability index (SI) decreased for both vegetation types in the three vegetation zones. However, the factors driving the changes in SOC stability varied with respect to the vegetation type and zone. Specifically, the rate of change in active carbon fractions was greater in FZ, whereas the rate of change of SI was higher in FSZ, and was correlated with higher MAP and MAT. Overall, the SOC stability decreased after vegetation restoration, with MAP, MAT, vegetation type, and years of recovery representing the main factors driving the changes in SOC stability. These results are expected to facilitate future studies on SOC aimed at enhancing the management of different vegetation zones during recovery in the Loess Plateau of China, in response to global climate change. [ABSTRACT FROM AUTHOR]

The glomalin-related soil protein (GRSP) is an important fraction of soil organic carbon (SOC) and soil nitrogen (N), and is important for stabilization of SOC and soil aggregates. However, the effects of natural restoration on the concentration and allocation of GRSP differ for different soil aggregate sizes, and how size further affects SOC and soil N restoration, and stabilization of SOC and soil aggregates is not well understood. Here, we present the first characterization of the distribution of GRSP fractions and soil nutrients in soil aggregates following natural restoration by choosing fields of 0, 7, 12, 17, 22, 32 years after cropland abandonment, and a natural grassland as reference. GRSP concentration increased most in microaggregates after 32 years of natural restoration. The processes of rapid accumulation of GRSP (22 to 32 years) occurred simultaneously with the formation of macroaggregates, reduction of microaggregates, and rapid increase of mean weight diameter (22 to 32-years). The soil aggregate stability and contents of GRSP, SOC, labile carbon, total N and phosphorus in each soil aggregate fraction significantly increased in the late stage of natural restoration (22 to 32 years). The most recalcitrant carbon fraction in microaggregates significantly increased between 7 and 32 years (0.887 g kg−1). Our study suggests that abandoning farmland is effective for the restoration of GRSP, soil nutrients and structure and that microaggregates promote the accumulation of recalcitrant carbon and increase the stability of SOC largely through its ability to retain GRSP. • Natural revegetation increased the stability of SOC in aggregates < 2 mm. • Large macroaggregates played an important role in TN, SOC and labile carbon accumulation. • GRSP facilitated the accumulation of SOC and TN, and promoted the increased soil aggregation. • Microaggregates increased recalcitrant carbon and the SOC stability largely by retaining GRSP. [ABSTRACT FROM AUTHOR]

The increased use of plastic films and pesticides on agricultural soil leads to the accumulation of plastic debris and pesticide residues in soil. This accumulation has become a serious environmental issue, as it threatens life of earthworms, inhibits the enzyme activities and microbial diversity, and contributes to the loss of soil microbial carbon and nitrogen. However, little information is available regarding the effects of pesticides on soil dissolved organic matter (DOM). It is also unknown how plastic debris, especially small-sized particles called microplastics, influences the effects of pesticides on soil DOM. In this study, we performed a 30-day soil incubation experiment. Three levels of the common herbicide glyphosate were applied to soil: 0 (control, CK), 3.6 kg ha−1 (G1) and 7.2 kg ha−1 (G2). We also tested four levels of glyphosate and microplastics (homopolymer polypropylene powder) co-addition: 3.6 kg ha−1 + 7% (w/w) (M1G1), 3.6 kg ha−1 + 28% (w/w) (M2G1), 7.2 kg ha−1 + 7% (w/w) (M1G2), and 7.2 kg ha−1 + 28% (w/w) (M2G2). Glyphosate addition slightly increased soil fluorescein diacetate hydrolase (FDAse) and phenol oxidase (PO) activities. Although the glyphosate addition significantly promoted the accumulation of dissolved organic phosphorus (DOP) within the first 14 days, the M2 treatment decreased DOP at day 30. M2G1 and M2G2 increased soil FDAse activity and promoted the accumulation of DOC and DOP relative to G1 and G2 respectively while M1G1 and M1G2 benefited DON accumulation. Our results highlighted that the interaction between glyphosate and low microplastics content negatively affected DOC and DOP dynamics, leading to the loss of bioavailable C and P loss. The interaction between glyphosate and high content microplastics negatively affected DON compared with glyphosate addition, possibly decreasing DON. Unlabelled Image • Glyphosate addition transitorily increased the nutrient contents in DOM. • Interaction between glyphosate and high content microplastic enhanced FDAse. • Interaction between glyphosate and high content microplastic decreased DON. • Interaction between glyphosate and low content microplastic decreased DOC and DOP. [ABSTRACT FROM AUTHOR]