The influence of grazing intensity on soil organic carbon storage in grassland of China: A meta-analysis

Grazing can potentially affect grassland soil carbon storage through selective feeding, trampling and fecal excretion of livestock. The numerous case studies and a few meta-analyses have focused on grazing-induced changes in soil organic carbon (SOC) storage, but the effects of grazing on SOC in major grassland types of China are not clear. In this study, we performed a comprehensive meta-analysis to identify the impact of grazing on soil carbon in China. We found that the key factors affecting the SOC content of grazing grasslands is grazing intensity. Heavy grazing (HG) significantly decreased the SOC content by 7.5 % in major grassland types of China (95 % confidence interval (CI), -11.43 % to -3.57 %, P < 0.001). The SOC content in temperate desert steppes (7.22 %), temperate meadow-steppes (10.89 %) under heavy grazing (HG) showed significantly (P < 0.05) decreased. HG resulted in significant (P < 0.01) decreases in SOC content (6.91 %) of Kastanoze. Our study highlighted that formulating rational grazing strategies according to grassland and soil types was the key to increasing SOC storage and sequestration under climate change and increased human pressure.

Interplay between Livestock Grazing and Aridity on the Ecological and Nutritional Value of Forage in Semi-arid Mediterranean Rangelands (NE Spain)

Rangeland-based livestock production constitutes a primary source of livelihood for many inhabitants of dryland regions. Their subsistence relies heavily on maintaining the productivity, biodiversity and services of these ecosystems. Harsh environmental conditions (e.g., drought) combined with land use intensification (e.g., overgrazing) make dryland ecosystems vulnerable and prone to degradation. However, the interplay between livestock grazing intensity and aridity conditions in driving the conservation and nutritional value of forage in arid and semi-arid rangelands is still not fully understood. In this study, we performed structural equation models (SEM) to assess the simultaneous direct and indirect effects of livestock grazing intensity and aridity level on community structure, diversity, biomass, forage production, forage C:N ratio and forage fiber composition in two semi-arid Mediterranean rangelands, NE Spain. Not surprisingly, we found that higher livestock grazing intensity led to lower community plant cover, especially when combined with higher aridity. However, both increasing grazing intensity and aridity were associated with higher forage production after one year of grazing exclusion. We did not find any adverse effect of livestock grazing on plant diversity, although plant species composition differed among grazing intensity levels. On the other hand, we found an aridity-driven trade-off in regard of the nutritional value of forage. Specifically, higher aridity was associated with a decrease in the least digestible fiber fraction (i.e., lignin) and an increase in forage C:N ratio. More interestingly, we found that livestock grazing modulated this trade-off by improving the overall forage nutritional value. Altogether, our results provide further insights into the management of semi-arid Mediterranean rangelands, pointing out that maintaining traditional rangeland-based livestock production may be a sustainable option as long as rangeland conservation (e.g., community plant cover) is not severely compromised.

Plant root mechanisms and their effects on carbon and nutrient accumulation in desert ecosystems under changes in land use and climate

Deserts represent key carbon reservoirs, yet as these systems are threatened this has implications for biodiversity and climate change. This review focuses on how these changes affect desert ecosystems, particularly plant root systems and their impact on carbon and mineral nutrient stocks. Desert plants have diverse root architectures shaped by water acquisition strategies, affecting plant biomass and overall carbon and nutrient stocks. Climate change can disrupt desert plant communities, with droughts impacting both shallow and deep-rooted plants as groundwater levels fluctuate. Vegetation management practices, like grazing, significantly influence plant communities, soil composition, root microorganisms, biomass, and nutrient stocks. Shallow-rooted plants are particularly susceptible to climate change and human interference. To safeguard desert ecosystems, understanding root architecture and deep soil layers is crucial. Implementing strategic management practices such as reducing grazing pressure, maintaining moderate harvesting levels, and adopting moderate fertilization can help preserve plant-soil systems. Employing socio-ecological approaches for community restoration enhances carbon and nutrient retention, limits desert expansion, and reduces CO2 emissions. This review underscores the importance of investigating belowground plant processes and their role in shaping desert landscapes, emphasizing the urgent need for a comprehensive understanding of desert ecosystems.

Large herbivore grazing accelerates litter decomposition in terrestrial ecosystems

Plant litter decomposition is critical for carbon and nutrient cycling globally. However, the effect of large herbivore grazing on litter decomposition and its mechanisms remain less explored. Here, 1203 paired observations and 381 independent experiments were analyzed to determine how litter decomposition and nutrient cycling respond to changes in grazing intensity. Grazing significantly increased litter decomposition rate by 14.08 % and litter carbon release by 5.03 %, and this effect was observed in grasslands and croplands but not in forests. The positive grazing effect was also found under sheep and cattle/yak grazing. Moderate grazing advanced the home-field advantage effect but inhibited under heavy grazing for grazed litters. The grazing effect was larger for high quality litter than for low quality litter. Litter decomposition slowed under >10 years heavy grazing but accelerated under moderate grazing. The effects of large herbivore grazing on litter decomposition were jointly influenced by grazing intensity, livestock type, climate condition, decomposition duration, litter quality, and soil properties. Our results demonstrated that large herbivore grazing accelerates litter decomposition globally and emphasized the significance and importance of grazing intensity on litter decomposition, which should be integrated into terrestrial ecosystem models.

Hotspots of biogeochemical activity linked to aridity and plant traits across global drylands

Perennial plants create productive and biodiverse hotspots, known as fertile islands, beneath their canopies. These hotspots largely determine the structure and functioning of drylands worldwide. Despite their ubiquity, the factors controlling fertile islands under conditions of contrasting grazing by livestock, the most prevalent land use in drylands, remain virtually unknown. Here we evaluated the relative importance of grazing pressure and herbivore type, climate and plant functional traits on 24 soil physical and chemical attributes that represent proxies of key ecosystem services related to decomposition, soil fertility, and soil and water conservation. To do this, we conducted a standardized global survey of 288 plots at 88 sites in 25 countries worldwide. We show that aridity and plant traits are the major factors associated with the magnitude of plant effects on fertile islands in grazed drylands worldwide. Grazing pressure had little influence on the capacity of plants to support fertile islands. Taller and wider shrubs and grasses supported stronger island effects. Stable and functional soils tended to be linked to species-rich sites with taller plants. Together, our findings dispel the notion that grazing pressure or herbivore type are linked to the formation or intensification of fertile islands in drylands. Rather, our study suggests that changes in aridity, and processes that alter island identity and therefore plant traits, will have marked effects on how perennial plants support and maintain the functioning of drylands in a more arid and grazed world.

Leaf trait plasticity reveals interactive effects of temporally disjunct grazing and warming on plant communities

Changes in climate and grazing intensity influence plant-community compositions and their functional structure. Yet, little is known about their possible interactive effects when climate change mainly has consequences during the growing season and grazing occurs off growing season (dormant season grazing). We examined the contribution of trait plasticity to the immediate responses in the functional structure of plant community due to the interplay between these two temporally disjunct drivers. We conducted a field experiment in the northern Mongolian steppe, where climate was manipulated by open-top chambers (OTCs) for two growing seasons, increasing temperature and decreasing soil moisture (i.e., increased aridity), and grazing was excluded for one dormant season between these two growing seasons. We calculated the community-weighted mean (CWM) and the functional diversity (FD) of six leaf traits. Based on a variance partitioning approach, we evaluated how much of the responses in CWM and FD to OTCs and dormant season grazing occur through plasticity. The interactive effect of OTCs and the dormant season grazing were detected only after considering the role of trait plasticity. Overall, OTCs influenced the responses in CWM more than in FD, but the effects of OTCs were much less pronounced where dormant season grazing occurred. Thus, warming (together with decreased soil moisture) and the elimination of dormant season grazing could interact to impact the functional trait structure of plant communities through trait plasticity. Climate change effects should be considered in the context of altered land use, even if temporally disjunct.

Cross-scale analysis reveals interacting predictors of annual and perennial cover in Northern Great Basin rangelands

Exotic annual grass invasion is a widespread threat to the integrity of sagebrush ecosystems in Western North America. Although many predictors of annual grass prevalence and native perennial vegetation have been identified, there remains substantial uncertainty about how regional-scale and local-scale predictors interact to determine vegetation heterogeneity, and how associations between vegetation and cattle grazing vary with environmental context. Here, we conducted a regionally extensive, one-season field survey across burned and unburned, grazed, public lands in Oregon and Idaho, with plots stratified by aspect and distance to water within pastures to capture variation in environmental context and grazing intensity. We analyzed regional-scale and local-scale patterns of annual grass, perennial grass, and shrub cover, and examined to what extent plot-level variation was contingent on pasture-level predictions of site favorability. Annual grasses were widespread at burned and unburned sites alike, contrary to assumptions of annual grasses depending on fire, and more common at lower elevations and higher temperatures regionally, as well as on warmer slopes locally. Pasture-level grazing pressure interacted with temperature such that annual grass cover was associated positively with grazing pressure at higher temperatures but associated negatively with grazing pressure at lower temperatures. This suggests that pasture-level temperature and grazing relationships with annual grass abundance are complex and context dependent, although the causality of this relationship deserves further examination. At the plot-level within pastures, annual grass cover did not vary with grazing metrics, but perennial cover did; perennial grasses, for example, had lower cover closer to water sources, but higher cover at higher dung counts within a pasture, suggesting contrasting interpretations of these two grazing proxies. Importantly for predictions of ecosystem response to temperature change, we found that pasture-level and plot-level favorability interacted: perennial grasses had a higher plot-level cover on cooler slopes, and this difference across topography was starkest in pastures that were less favorable for perennial grasses regionally. Understanding the mechanisms behind cross-scale interactions and contingent responses of vegetation to grazing in these increasingly invaded ecosystems will be critical to land management in a changing world.

The effect of livestock grazing on plant diversity and productivity of mountainous grasslands in South America - A meta-analysis

Mountainous grasslands in South America, characterized by their high diversity, provide a wide range of contributions to people, including water regulation, soil erosion prevention, livestock feed provision, and preservation of cultural heritage. Prior research has highlighted the significant role of grazing in shaping the diversity and productivity of grassland ecosystems, especially in highly productive, eutrophic systems. In such environments, grazing has been demonstrated to restore grassland plant diversity by reducing primary productivity. However, it remains unclear whether these findings are applicable to South American mountainous grasslands, where plants are adapted to different environmental conditions. To address this uncertainty, we conducted a meta-analysis of experiments excluding livestock grazing to assess its impact on plant diversity and productivity across mountainous grasslands in South America. In alignment with studies in temperate grasslands, our findings indicated that herbivore exclusion resulted in increased aboveground biomass but reduced species richness and Shannon diversity. The effects of grazing exclusion became more pronounced with longer durations of exclusion; nevertheless, they remained resilient to various climatic conditions, including mean annual precipitation and mean annual temperature, as well as the evolutionary history of grazing. In contrast to results observed in temperate grasslands, the reduction in species richness due to herbivore exclusion was not associated with increased aboveground biomass. This suggests that the processes governing (sub)tropical grassland plant diversity may differ from those in temperate grasslands. Consequently, further research is necessary to better understand the specific factors influencing plant diversity and productivity in South American montane grasslands and to elucidate the ecological implications of herbivore exclusion in these unique ecosystems.

Meta-analysis reveals that vertebrates enhance plant litter decomposition at the global scale

Evidence is mounting that vertebrate defaunation greatly impacts global biogeochemical cycling. Yet, there is no comprehensive assessment of the potential vertebrate influence over plant decomposition, despite litter decay being one of the largest global carbon fluxes. We therefore conducted a global meta-analysis to evaluate vertebrate effects on litter mass loss and associated element release across terrestrial and aquatic ecosystems. Here we show that vertebrates affected litter decomposition by various direct and indirect pathways, increasing litter mass loss by 6.7% on average, and up to 34.4% via physical breakdown. This positive vertebrate impact on litter mass loss was consistent across contrasting litter types (woody and non-woody), climatic regions (boreal, temperate and tropical), ecosystem types (aquatic and terrestrial) and vertebrate taxa, but disappeared when evaluating litter nitrogen and phosphorus release. Moreover, we found evidence of interactive effects between vertebrates and non-vertebrate decomposers on litter mass loss, and a larger influence of vertebrates at mid-to-late decomposition stages, contrasting with the invertebrate effect known to be strongest at early decomposition stage. Our synthesis demonstrates a global vertebrate control over litter mass loss, and further stresses the need to account for vertebrates when assessing the impacts of biodiversity loss on biogeochemical cycles.

Vitamin E: An assistant for black soldier fly to reduce cadmium accumulation and toxicity

Cadmium (Cd) is a toxic heavy metal associated with osteoporosis, liver, and kidney disease. The black soldier fly (BSF) Hermetia illucens may be exposed to Cd during the transformation of livestock manure. The BSF has a high tolerance to Cd. In the previous work of the laboratory, we found that vitamin E (VE) may play a role in the tolerance of BSF to Cd exposure. The main findings are as follows: The BSF larvae pretreated with exogenous VE had heavier body weight, lower content and toxicity of Cd under similar Cd exposure. Even in high Cd exposure at the concentrations of 300 and 700 mg/kg, the BSF larvae pretreated with exogenous VE at a concentration of 100 mg/kg still reduced the Cd toxicity to 85.33 % and 84.43 %, respectively. The best-fitting models showed that metallothionein (MT) content, oxidative damage (8-hydroxydeoxyguanosine content, malondialdehyde content), antioxidant power (total antioxidant power, peroxidase activity) had a great influence on content and toxicity of Cd bioaccumulated in the larvae. The degree of oxidative damage was reduced in the larvae with exogenous VE pretreatments. This variation can be explained by their changed MT content and increased antioxidant power because of exogenous VE. These results reveal the roles of VE in insects defense against Cd exposure and provide a new option for the prevention and therapy of damage caused by Cd exposure.

A 10-m annual grazing intensity dataset in 2015-2021 for the largest temperate meadow steppe in China

Mapping grazing intensity (GI) using satellites is crucial for developing adaptive utilization strategies according to grassland conditions. Here we developed a monitoring framework based on a paired sampling strategy and the classification probability of random forest algorithm to produce annual grazing probability (GP) and GI maps at 10-m spatial resolution from 2015 to 2021 for the largest temperate meadow in China (Hulun Buir grasslands), by harmonized Landsat 7/8 and Sentinel-2 images. The GP maps used values of 0-1 to present detailed grazing gradient information. To match widely used grazing gradients, annual GI maps with ungrazed, moderately grazed, and heavily grazed levels were generated from the GP dataset with a decision tree. The GI maps for 2015-2021 had an overall accuracy of more than 0.97 having significant correlations with the statistical data at city (r = 0.51) and county (r = 0.75) scales. They also effectively captured the GI gradients at site scale (r = 0.94). Our study proposed a monitoring approach and presented annual 10-m grazing information maps for sustainable grassland management.

Livestock grazing modifies soil nematode body size structure in mosaic grassland habitats

Body size is closely related to the trophic level and abundance of soil fauna, particularly nematodes. Therefore, size-based analyses are increasingly prominent in unveiling soil food web structure and its responses to anthropogenic disturbances, such as livestock grazing. Yet, little is known about the effects of different livestock on the body size structure of soil nematodes, especially in grasslands characterized by local habitat heterogeneity. A four-year field grazing experiment from 2017 to 2020 was conducted in a meadow steppe characterized by typical mosaics of degraded hypersaline patches and undegraded hyposaline patches to assess the impacts of cattle and sheep grazing on the body size structure of soil nematodes within and across trophic groups. Without grazing, the hypersaline patches harbored higher abundance of large-bodied nematodes in the community compared to the hyposaline patches. Livestock grazing decreased large-bodied nematodes within and across trophic groups mainly by reducing soil microbial biomass in the hypersaline patches, with sheep grazing resulting in more substantial reductions compared to cattle grazing. The reduction in large-bodied nematode individuals correspondingly resulted in decreases in nematode community-weighted mean (CWM) body size, nematode biomass, and size spectra slopes. However, both cattle and sheep grazing had minimal impacts on the CWM body size and size spectra of total nematodes in the hyposaline patches. Our findings suggest that livestock grazing, especially sheep grazing, has the potential to simplify soil food webs by reducing large-bodied nematodes in degraded habitats, which may aggravate soil degradation by weakening the bioturbation activities of soil fauna. In light of the widespread land use of grasslands by herbivores of various species and the ongoing global grassland degradation of mosaic patches, the recognition of the trends revealed by our findings is critical for developing appropriate strategies for grassland grazing management.

Is Joint Management between Conservationists and Farmers Sustainable and Biodiversity-friendly? A Ten-year Study in Residual Grasslands of a Protected Area

In recent decades, there has been a discernible reduction in temperate and Mediterranean grasslands with consequences on the decline of biodiversity and landscape heterogeneity. When this decline is due to agricultural abandonment, a renewed joint management, combining bush clearing by conservationists and grazing by farmers, should favor the maintenance of grasslands, their protected habitats and species and forage production. Rainfall irregularity explains part of the variation of these parameters. To verify these hypotheses, we conduct a comprehensive, multi-scale, multi-taxa study over a ten-year period in a Mediterranean protected area. At the regional scale, experimental plots in which this joint management was implemented are representative of residual managed grasslands of the protected area. At the mesoscale, rainfall irregularity is the main factor explaining inter-annual differences in the biomass of open landscapes, while fauna depends on management, tree cover and trophic resources. At the local scale, in a representative experimental plot, clearing had an immediate negative impact on plant richness and bird and positive on forage. Over a decade, plant biodiversity increased while forage, specialist plants and bird maintained, despite the regrowth of bush. Drought had a negative impact on richness, plant and forage abundance and phenological asynchrony on butterflies. In conclusion, joint management has positive, neutral and negative impacts to be considered before implementing this strategy. This long-term monitoring study draws important lessons for designing a sustainable management of grasslands under abandonment and irregular climate, that should be applied in temperate and Mediterranean regions that are increasingly vulnerable to these trends.

Dryland microbiomes reveal community adaptations to desertification and climate change

Drylands account for 45% of the Earth's land area, supporting ~40% of the global population. These regions support some of the most extreme environments on Earth, characterized by extreme temperatures, low and variable rainfall, and low soil fertility. In these biomes, microorganisms provide vital ecosystem services and have evolved distinctive adaptation strategies to endure and flourish in the extreme. However, dryland microbiomes and the ecosystem services they provide are under threat due to intensifying desertification and climate change. In this review, we provide a synthesis of our current understanding of microbial life in drylands, emphasizing the remarkable diversity and adaptations of these communities. We then discuss anthropogenic threats, including the influence of climate change on dryland microbiomes and outline current knowledge gaps. Finally, we propose research priorities to address those gaps and safeguard the sustainability of these fragile biomes.

New perspectives on microbiome and nutrient sequestration in soil aggregates during long-term grazing exclusion

Grazing exclusion alters grassland soil aggregation, microbiome composition, and biogeochemical processes. However, the long-term effects of grazing exclusion on the microbial communities and nutrient dynamics within soil aggregates remain unclear. We conducted a 36-year exclusion experiment to investigate how grazing exclusion affects the soil microbial community and the associated soil functions within soil aggregates in a semiarid grassland. Long-term (36 years) grazing exclusion induced a shift in microbial communities, especially in the <2 mm aggregates, from high to low diversity compared to the grazing control. The reduced microbial diversity was accompanied by instability of fungal communities, extended distribution of fungal pathogens to >2 mm aggregates, and reduced carbon (C) sequestration potential thus revealing a negative impact of long-term GE. In contrast, 11-26 years of grazing exclusion greatly increased C sequestration and promoted nutrient cycling in soil aggregates and associated microbial functional genes. Moreover, the environmental characteristics of microhabitats (e.g., soil pH) altered the soil microbiome and strongly contributed to C sequestration. Our findings reveal new evidence from soil microbiology for optimizing grazing exclusion duration to maintain multiple belowground ecosystem functions, providing promising suggestions for climate-smart and resource-efficient grasslands.

Benefits, potential and risks of China's grassland ecosystem conservation and restoration

Severe threats from ongoing degradation undermine the grasslands to support ecosystem services, biodiversity, and human well-being. Unfortunately, grasslands are often underappreciated and ignored in sustainable development agendas. Despite a series of projects for Grassland Ecosystem Conservation and Restoration (GECR) been implemented in China, the effects and cost-effectiveness of these efforts remain uncertain and untested. Therefore, we developed an integrated assessment framework to evaluate the benefits of GECR, considering ecological value accounting and input-output efficiency estimation. Additionally, we projected potential and risk areas for GECR in the future. The results showed that in 2020, the annual ecological value of China's grassland ecosystem was CNY 246 trillion. The investment in GECR exceeded CNY 7 billion, leading to an ecological benefit of CNY 3478 billion, with an input-output ratio of 1:446. Over the past 20 years, GECR positively impacted nearly 90 % of China's grassland. Furthermore, grasslands in southern provinces with favorable hydrothermal conditions exhibited significantly higher GECR efficiency, boasting an input-output ratio of >1:2000. The arid and semi-arid northern grasslands and the alpine grasslands on the Tibetan Plateau, despite being the main regions for animal husbandry development and GECR, exhibited comparatively lower efficiency and input-output ratio in GECR. Moreover, the central and northwest parts of Tibet showed higher potential and lower risk, indicating their greatest likelihood of benefiting from GECR in the future. Meanwhile, Hulunbeier and Inner Mongolia deserve more special attention to reverse degradation and mitigate climate change due to their lower potential and higher risks. Our study provides an important basis for prioritizing and implementing effective and sustainable GECR treatment methods.

Light grazing intensity enhances ecosystem services in semi-arid grasslands through plant trait associations

Grasslands provide multiple ecosystem services (ESs) including provisioning, regulating, supporting, and cultural services that are largely affected by livestock grazing. Linking plant functional traits (PFTs) to ecosystem processes and functions has attracted extensive ecological research to explore the responses and inter-relations of ecosystem services to environmental and management changes. However, little information is available on the links between PFTs and ESs in most ecosystems. We conducted a grazing experiment to investigate the response of PFTs at different levels, including in plant organs (leaves and stems), individual plants, and the overall community in a typical steppe region of Inner Mongolia. Additionally, we examined the effect of animal grazing at four intensities (nil, light, moderate, and heavy) and explored the dynamic interconnections between PFTs and ecosystem services in grasslands. Our analysis revealed that the highest total ecosystem service and provisioning service were achieved under light- and moderate-grazing treatments, respectively. Heavy grazing also increased provisioning service but with a large decline in regulating and total ecosystem services. These changes in ESs were closely associated with grazing-induced variations in PFTs. Compared to no grazing, light grazing increased plant size-related functional traits, such as height, leaf length, leaf area, stem length, and the ratio of stem length to diameter. In contrast, heavy grazing decreased these PFTs. Provisioning and regulating services were determined by plant above-ground community function and structural properties, while supporting service was jointly affected by the below-ground community and soil properties. Our results indicate that light grazing should be recommended for the best total ESs, although moderate grazing may lead to high short-term economic benefits. Moreover, PFTs are powerful indicators for provisioning and regulating services. These findings provide a valuable reference for developing effective management practices to achieve targeted ESs using PFTs as indicators.

Dung removal increases under higher dung beetle functional diversity regardless of grazing intensification

Dung removal by macrofauna such as dung beetles is an important process for nutrient cycling in pasturelands. Intensification of farming practices generally reduces species and functional diversity of terrestrial invertebrates, which may negatively affect ecosystem services. Here, we investigate the effects of cattle-grazing intensification on dung removal by dung beetles in field experiments replicated in 38 pastures around the world. Within each study site, we measured dung removal in pastures managed with low- and high-intensity regimes to assess between-regime differences in dung beetle diversity and dung removal, whilst also considering climate and regional variations. The impacts of intensification were heterogeneous, either diminishing or increasing dung beetle species richness, functional diversity, and dung removal rates. The effects of beetle diversity on dung removal were more variable across sites than within sites. Dung removal increased with species richness across sites, while functional diversity consistently enhanced dung removal within sites, independently of cattle grazing intensity or climate. Our findings indicate that, despite intensified cattle stocking rates, ecosystem services related to decomposition and nutrient cycling can be maintained when a functionally diverse dung beetle community inhabits the human-modified landscape.

C:N:P stoichiometry of plants, soils, and microorganisms: Response to altered precipitation

Precipitation changes modify C, N, and P cycles, which regulate the functions and structure of terrestrial ecosystems. Although altered precipitation affects above- and belowground C:N:P stoichiometry, considerable uncertainties remain regarding plant-microbial nutrient allocation strategies under increased (IPPT) and decreased (DPPT) precipitation. We meta-analyzed 827 observations from 235 field studies to investigate the effects of IPPT and DPPT on the C:N:P stoichiometry of plants, soils, and microorganisms. DPPT reduced leaf C:N ratio, but increased the leaf and root N:P ratios reflecting stronger decrease of P compared with N mobility in soil under drought. IPPT increased microbial biomass C (+13%), N (+15%), P (26%), and the C:N ratio, whereas DPPT decreased microbial biomass N (-12%) and the N:P ratio. The C:N and N:P ratios of plant leaves were more sensitive to medium DPPT than to IPPT because drought increased plant N content, particularly in humid areas. The responses of plant and soil C:N:P stoichiometry to altered precipitation did not fit the double asymmetry model with a positive asymmetry under IPPT and a negative asymmetry under extreme DPPT. Soil microorganisms were more sensitive to IPPT than to DPPT, but they were more sensitive to extreme DPPT than extreme IPPT, consistent with the double asymmetry model. Soil microorganisms maintained stoichiometric homeostasis, whereas N:P ratios of plants follow that of the soils under altered precipitation. In conclusion, specific N allocation strategies of plants and microbial communities as well as N and P availability in soil critically mediate C:N:P stoichiometry by altered precipitation that need to be considered by prediction of ecosystem functions and C cycling under future climate change scenarios.

Accounting for herbaceous communities in process-based models will advance our understanding of "grassy" ecosystems

Grassland and other herbaceous communities cover significant portions of Earth's terrestrial surface and provide many critical services, such as carbon sequestration, wildlife habitat, and food production. Forecasts of global change impacts on these services will require predictive tools, such as process-based dynamic vegetation models. Yet, model representation of herbaceous communities and ecosystems lags substantially behind that of tree communities and forests. The limited representation of herbaceous communities within models arises from two important knowledge gaps: first, our empirical understanding of the principles governing herbaceous vegetation dynamics is either incomplete or does not provide mechanistic information necessary to drive herbaceous community processes with models; second, current model structure and parameterization of grass and other herbaceous plant functional types limits the ability of models to predict outcomes of competition and growth for herbaceous vegetation. In this review, we provide direction for addressing these gaps by: (1) presenting a brief history of how vegetation dynamics have been developed and incorporated into earth system models, (2) reporting on a model simulation activity to evaluate current model capability to represent herbaceous vegetation dynamics and ecosystem function, and (3) detailing several ecological properties and phenomena that should be a focus for both empiricists and modelers to improve representation of herbaceous vegetation in models. Together, empiricists and modelers can improve representation of herbaceous ecosystem processes within models. In so doing, we will greatly enhance our ability to forecast future states of the earth system, which is of high importance given the rapid rate of environmental change on our planet.

Long-term livestock exclusion increases plant richness and reproductive capacity in arid woodlands

Herbivore exclusion is implemented globally to recover ecosystems from grazing by introduced and native herbivores, but evidence for large-scale biodiversity benefits is inconsistent in arid ecosystems. We examined the effects of livestock exclusion on dryland plant richness and reproductive capacity. We collected data on plant species richness and seeding (reproductive capacity), rainfall, vegetation productivity and cover, soil strength and herbivore grazing intensity from 68 sites across 6500 km2 of arid Georgina gidgee (Acacia georginae) woodlands in central Australia between 2018 and 2020. Sites were on an actively grazed cattle station and two destocked conservation reserves. We used structural equation modeling to examine indirect (via soil or vegetation modification) versus direct (herbivory) effects of grazing intensity by two introduced herbivores (cattle, camels) and a native herbivore (red kangaroo), on seasonal plant species richness and seeding of all plants, and the richness and seeding of four plant groups (native grasses, forbs, annual chenopod shrubs, and palatable perennial shrubs). Non-native herbivores had a strong indirect effect on plant richness and seeding by reducing vegetative ground cover, resulting in decreased richness and seeding of native grasses and forbs. Herbivores also had small but negative direct impacts on plant richness and seeding. This direct effect was explained by reductions in annual chenopod and palatable perennial shrub richness under grazing activity. Responses to grazing were herbivore-dependent; introduced herbivore grazing reduced native plant richness and seeding, while native herbivore grazing had no significant effect on richness or seeding of different plant functional groups. Soil strength decreased under grazing by cattle but not camels or kangaroos. Cattle had direct effects on palatable perennial shrub richness and seeding, whereas camels had indirect effects, reducing richness and seeding by reducing the abundance of shrubs. We show that considering indirect pathways improves evaluations of the effects of disturbances on biodiversity, as focusing only on direct effects can mask critical mechanisms of change. Our results indicate substantial biodiversity benefits from excluding livestock and controlling camels in drylands. Reducing introduced herbivore impacts will improve soil and vegetation condition, ensure reproduction and seasonal persistence of species, and protect native plant diversity.

Connecting the multiple dimensions of global soil fungal diversity

How the multiple facets of soil fungal diversity vary worldwide remains virtually unknown, hindering the management of this essential species-rich group. By sequencing high-resolution DNA markers in over 4000 topsoil samples from natural and human-altered ecosystems across all continents, we illustrate the distributions and drivers of different levels of taxonomic and phylogenetic diversity of fungi and their ecological groups. We show the impact of precipitation and temperature interactions on local fungal species richness (alpha diversity) across different climates. Our findings reveal how temperature drives fungal compositional turnover (beta diversity) and phylogenetic diversity, linking them with regional species richness (gamma diversity). We integrate fungi into the principles of global biodiversity distribution and present detailed maps for biodiversity conservation and modeling of global ecological processes.

Seedling responses to moderate and severe herbivory: a field-clipping experiment with a keystone Mediterranean palm

Plant-ungulate interactions are critical in shaping the structure of Mediterranean plant communities. Nevertheless, there is a dearth of knowledge on how plant intrinsic and extrinsic factors mediate the sign and strength of plant-ungulate interactions. This is most relevant when addressing natural or assisted restoration of plant communities in human-disturbed areas. We conducted field-clipping experiments simulating how different intensities of ungulate herbivory may affect the natural regeneration and establishment of the Mediterranean dwarf palm (Chamaerops humilis), a keystone species in Mediterranean ecosystems. We quantified seedling survival and size in two human-disturbed sites (SW Spain) where wild and domestic ungulates exert high herbivory pressure on vegetation. Severe clipping and seedling aging reduced rates of seedling survival. In contrast, moderate clipping did not affect seedling survival, suggesting a certain degree of C. humilis tolerance to herbivory. Severe clipping reduced seedling height strongly but not seedling diameter, and these effects seem to have decreased seedling survival. Nurse shrubs increased seedling size, which likely improved seedling survival. We also found seedling compensatory growth which varied between study sites. Field-clipping experiments can help disentangle effects of plant extrinsic and intrinsic factors on the sign and strength of plant-ungulate interactions and their ecological consequences on the dynamics of human-disturbed ecosystems. We call attention to the importance of appropriately managing scenarios of severe herbivory and summer droughts, particularly frequent in Mediterranean ecosystems, as synergic effects of such key drivers can negatively affect the structure and dynamics of plant communities and endanger their conservation.

Fertilization can accelerate the pace of soil microbial community response to rest-grazing duration in the three-river source region of China

Overgrazing leads to grassland degradation and productivity decline. Rest-grazing during the regreen-up period can quickly restore grassland and fertilization is a common restoration strategy. However, the effects of rest-grazing time and fertilization on soil microorganisms are unclear in the alpine grasslands. Therefore, the experiment of rest-grazing time and fertilization was carried out to explore the response of soil microorganisms to rest-grazing time and fertilization measures. A field control experiment with rest-grazing time and fertilization as factors have been conducted from the time when grass returned to green till the livestock moved to the summer pasture in Dawu Town of Maqin County of China. The primary treatment we established was the five rest-grazing time, including rest-grazing time of 20 days, 30 days, 40 days, 50 days, and traditional grazing was used as a check group. At the same time, the secondary treatment was nitrogen addition of 300 kg·hm-2 in each primary treatment. The results showed that the total phospholipid fatty acid (total PLFA), actinomyces (Act), and arbuscular mycorrhizal fungi (AMF) showed an ever-increasing biomass with the increase of rest-grazing time and the highest was at 50 days of rest-grazing, and they were all significantly higher than CK. In addition, soil microbial biomass carbon-nitrogen ratio (MBC/MBN) had great influence on the change of microbial community. Applying nitrogen fertilizer can increase the maximum value of biomass of all PLFA groups and the biomass of all PLFA groups changed in an "inverted V" shape with the increase of rest-grazing time. Besides, instead of MBC/MBN, NO3 --N was positively correlated with the biomass of all PLFA groups, which actively regulated the trend of microbial functions. The longer rest-grazing time is more conducive to the biomass of all PLFA groups. However, applying nitrogen fertilizer could break this pattern, namely, the 30 days rest-grazing would be beneficial to the biomass of all PLFA groups. These findings provide key information that rest-grazing during the regreen-up period is benefiscial to the all PLFA groups and fertilization could change the response of microorganisms to rest-grazing, which provide reference measures for the restoration of degraded alpine meadows.

Dryland sensitivity to climate change and variability using nonlinear dynamics

Primary productivity response to climatic drivers varies temporally, indicating state-dependent interactions between climate and productivity. Previous studies primarily employed equation-based approaches to clarify this relationship, ignoring the state-dependent nature of ecological dynamics. Here, using 40 y of climate and productivity data from 48 grassland sites across Mongolia, we applied an equation-free, nonlinear time-series analysis to reveal sensitivity patterns of productivity to climate change and variability and clarify underlying mechanisms. We showed that productivity responded positively to annual precipitation in mesic regions but negatively in arid regions, with the opposite pattern observed for annual mean temperature. Furthermore, productivity responded negatively to decreasing annual aridity that integrated precipitation and temperature across Mongolia. Productivity responded negatively to interannual variability in precipitation and aridity in mesic regions but positively in arid regions. Overall, interannual temperature variability enhanced productivity. These response patterns are largely unrecognized; however, two mechanisms are inferable. First, time-delayed climate effects modify annual productivity responses to annual climate conditions. Notably, our results suggest that the sensitivity of annual productivity to increasing annual precipitation and decreasing annual aridity can even be negative when the negative time-delayed effects of annual precipitation and aridity on productivity prevail across time. Second, the proportion of plant species resistant to water and temperature stresses at a site determines the sensitivity of productivity to climate variability. Thus, we highlight the importance of nonlinear, state-dependent sensitivity of productivity to climate change and variability, accurately forecasting potential biosphere feedback to the climate system.

Experimental impacts of grazing on grassland biodiversity and function are explained by aridity

Grazing by domestic herbivores is the most widespread land use on the planet, and also a major global change driver in grasslands. Yet, experimental evidence on the long-term impacts of livestock grazing on biodiversity and function is largely lacking. Here, we report results from a network of 10 experimental sites from paired grazed and ungrazed grasslands across an aridity gradient, including some of the largest remaining native grasslands on the planet. We show that aridity partly explains the responses of biodiversity and multifunctionality to long-term livestock grazing. Grazing greatly reduced biodiversity and multifunctionality in steppes with higher aridity, while had no effects in steppes with relatively lower aridity. Moreover, we found that long-term grazing further changed the capacity of above- and below-ground biodiversity to explain multifunctionality. Thus, while plant diversity was positively correlated with multifunctionality across grasslands with excluded livestock, soil biodiversity was positively correlated with multifunctionality across grazed grasslands. Together, our cross-site experiment reveals that the impacts of long-term grazing on biodiversity and function depend on aridity levels, with the more arid sites experiencing more negative impacts on biodiversity and ecosystem multifunctionality. We also highlight the fundamental importance of conserving soil biodiversity for protecting multifunctionality in widespread grazed grasslands.

Negative effects of phosphorus addition outweigh effects of arbuscular mycorrhizal fungi and nitrogen addition on grassland temporal stability in the eastern Eurasian desert steppe

The temporal stability of grassland plant communities is substantially affected by soil nutrient enrichment. However, the potential main and interactive effects of arbuscular mycorrhizal fungi (AMF) and soil nitrogen (N) and phosphorus (P) enrichment on the stability of plant productivity have not yet been clarified. We combined a three-year in situ field experiment to assess the impacts of soil fertilization and AMF on the stability of plant productivity. P addition decreased the stability of plant productivity by increasing the standard deviation relative to the mean of plant productivity. However, compared to species richness, the stability of C3 grasses and other functional groups asynchrony were the most important drivers changing the stability of plant productivity. The negative impacts of P addition overrode the impacts of AMF on the stability of plant productivity. Overall, our study suggests the importance of soil nutrient availability over AMF in terms of shaping the stability of plant productivity. Our results also suggest that three-year anthropogenic soil nutrient enrichment could reduce the stability of plant communities in grassland regardless of AMF in the P-limited grassland ecosystem.

Grassland biodiversity and ecosystem functions benefit more from cattle than sheep in mixed grazing: A meta-analysis

Grasslands have been widely grazed for livestock production by cattle and sheep. However, previous studies have mainly focused on the impacts of single-species grazing on grassland biodiversity and ecosystem functions; the effects of mixed grazing of cattle and sheep remain largely unknown. We conducted a meta-analysis to examine the impacts of mixed grazing and analyzed the relative roles of cattle and sheep on grassland biodiversity and multiple ecosystem functions. Mixed grazing studies mainly originated from Europe, the USA, and China. Generally, cattle and sheep exhibited distinctive impacts on grassland biodiversity and functions in single-species and mixed grazing regimes. Cattle grazing alone increased plant diversity and soil organic carbon content (SOC), while sheep grazing alone had little impact. Compared to single-species grazing, mixed grazing generally increased plant density and richness of insect herbivores and decreased soil nematode richness, but did not alter plant biomass, soil nitrogen, or nematode abundance. Cattle in the mixed grazing regime increased plant diversity, biomasses of forbs and legumes, SOC, and liveweight gains of livestock. The mixed grazing impacts were further regulated by climate conditions, grazing intensity, and grazing duration. Our findings provide compelling evidence that mixed grazing benefits biodiversity, soil carbon sequestration, livestock production, and community structure of grasslands, and cattle are more influential than sheep in creating the benefits of mixed grazing for sustainable management of grasslands.

Water availability creates global thresholds in multidimensional soil biodiversity and functions

Soils support an immense portion of Earth's biodiversity and maintain multiple ecosystem functions which are essential for human well-being. Environmental thresholds are known to govern global vegetation patterns, but it is still unknown whether they can be used to predict the distribution of soil organisms and functions across global biomes. Using a global field survey of 383 sites across contrasting climatic and vegetation conditions, here we showed that soil biodiversity and functions exhibited pervasive nonlinear patterns worldwide and are mainly governed by water availability (precipitation and potential evapotranspiration). Changes in water availability resulted in drastic shifts in soil biodiversity (bacteria, fungi, protists and invertebrates) and soil functions including plant-microbe interactions, plant productivity, soil biogeochemical cycles and soil carbon sequestration. Our findings highlight that crossing specific water availability thresholds can have critical consequences for the provision of essential ecosystem services needed to sustain our planet.

Human activities modulate reciprocal effects of a subterranean ecological engineer rodent, Tachyoryctes macrocephalus, on Afroalpine vegetation cover

Human activities, directly and indirectly, impact ecological engineering activities of subterranean rodents. As engineering activities of burrowing rodents are affected by, and reciprocally affect vegetation cover via feeding, burrowing and mound building, human influence such as settlements and livestock grazing, could have cascading effects on biodiversity and ecosystem processes such as bioturbation. However, there is limited understanding of the relationship between human activities and burrowing rodents. The aim of this study was therefore to understand how human activities influence the ecological engineering activity of the giant root-rat (Tachyoryctes macrocephalus), a subterranean rodent species endemic to the Afroalpine ecosystem of the Bale Mountains of Ethiopia. We collected data on human impact, burrowing activity and vegetation during February and March of 2021. Using path analysis, we tested (1) direct effects of human settlement on the patterns of livestock grazing intensity, (2) direct and indirect impacts of humans and livestock grazing intensity on the root-rat burrow density and (3) whether human settlement and livestock grazing influence the effects of giant root-rat burrow density on vegetation and vice versa. We found lower levels of livestock grazing intensity further from human settlement than in its proximity. We also found a significantly increased giant root-rat burrow density with increasing livestock grazing intensity. Seasonal settlement and livestock grazing intensity had an indirect negative and positive effect on giant root-rat burrow density, respectively, both via vegetation cover. Analysing the reciprocal effects of giant root-rat on vegetation, we found a significantly decreased vegetation cover with increasing density of giant root-rat burrows, and indirectly with increasing livestock grazing intensity via giant root-rat burrow density. Our results demonstrate that giant root-rats play a synanthropic engineering role that affects vegetation structure and ecosystem processes.

Impacts of large herbivores on terrestrial ecosystems

Large herbivores play unique ecological roles and are disproportionately imperiled by human activity. As many wild populations dwindle towards extinction, and as interest grows in restoring lost biodiversity, research on large herbivores and their ecological impacts has intensified. Yet, results are often conflicting or contingent on local conditions, and new findings have challenged conventional wisdom, making it hard to discern general principles. Here, we review what is known about the ecosystem impacts of large herbivores globally, identify key uncertainties, and suggest priorities to guide research. Many findings are generalizable across ecosystems: large herbivores consistently exert top-down control of plant demography, species composition, and biomass, thereby suppressing fires and the abundance of smaller animals. Other general patterns do not have clearly defined impacts: large herbivores respond to predation risk but the strength of trophic cascades is variable; large herbivores move vast quantities of seeds and nutrients but with poorly understood effects on vegetation and biogeochemistry. Questions of the greatest relevance for conservation and management are among the least certain, including effects on carbon storage and other ecosystem functions and the ability to predict outcomes of extinctions and reintroductions. A unifying theme is the role of body size in regulating ecological impact. Small herbivores cannot fully substitute for large ones, and large-herbivore species are not functionally redundant - losing any, especially the largest, will alter net impact, helping to explain why livestock are poor surrogates for wild species. We advocate leveraging a broad spectrum of techniques to mechanistically explain how large-herbivore traits and environmental context interactively govern the ecological impacts of these animals.

Moderate precipitation reduction enhances nitrogen cycling and soil nitrous oxide emissions in a semi-arid grassland

The ongoing climate change is predicted to induce more weather extremes such as frequent drought and high-intensity precipitation events, causing more severe drying-rewetting cycles in soil. However, it remains largely unknown how these changes will affect soil nitrogen (N)-cycling microbes and the emissions of potent greenhouse gas nitrous oxide (N₂ O). Utilizing a field precipitation manipulation in a semi-arid grassland on the Loess Plateau, we examined how precipitation reduction (ca. -30%) influenced soil N₂ O and carbon dioxide (CO₂ ) emissions in field, and in a complementary lab-incubation with simulated drying-rewetting cycles. Results obtained showed that precipitation reduction stimulated plant root turnover and N-cycling processes, enhancing soil N₂ O and CO₂ emissions in field, particularly after each rainfall event. Also, high-resolution isotopic analyses revealed that field soil N₂ O emissions primarily originated from nitrification process. The incubation experiment further showed that in field soils under precipitation reduction, drying-rewetting stimulated N mineralization and ammonia-oxidizing bacteria in favor of genera Nitrosospira and Nitrosovibrio, increasing nitrification and N₂ O emissions. These findings suggest that moderate precipitation reduction, accompanied with changes in drying-rewetting cycles under future precipitation scenarios, may enhance N cycling processes and soil N₂ O emissions in semi-arid ecosystems, feeding positively back to the ongoing climate change.

Consumption in Non-Pastoral Regions Drove Three-Quarters of Forage-Livestock Conflicts in China

Forage-livestock conflict (FLC) is a major anthropogenic cause of rangeland degradation. It poses tremendous threats to the environment owing to its adverse impacts on carbon sequestration, water supply and regulation, and biodiversity conservation. Existing policy interventions focus on the in situ FLCs induced by local production activities but overlook the role of consumption activities in driving FLCs. Here, we investigate the spatiotemporal variations in China's FLCs and the domestic final consumers at the county level by combining remote sensing data and multi-regional input-output model. Results show that during 2005-2015, China's pastoralism induced an average of 82 million tons of FLCs per year. Domestic final demand was responsible for 85-93% of the FLCs in China. There was spatiotemporal heterogeneity in domestic consumption driving China's FLCs. In particular, the final demand of non-pastoral regions was responsible for around three-quarters (74-79%) of the total FLCs throughout the decade. The rangeland-based livestock raising, agricultural and sideline product processing, and catering sectors are important demand-side drivers. These findings can support targeted demand-side strategies and interregional cooperation to reduce China's FLCs, thus mitigating rangeland degradation.

Steps to operationalize a rewilding decision: Focus on functional types

If transparent and inclusive stakeholder discussion delivers a consensus for active rewilding, then five steps are recommended for operationalizing that decision, focused initially on the large herbivore assemblage. Consideration of large predators could follow, contingent upon the establishment of prey populations. First, determine the potential biomass density (kg/km2) of large mammalian herbivores in the target landscape. Regression models based on rainfall or primary productivity are helpful if applicable, otherwise comparative studies are needed. Second, use empirical data from reference ecosystems to apportion biomass density among functional types, crudely defined by body size and feeding type (grazer, browser, mixed feeder). Third, identify specific functional traits (coarse grazing, endozoochory, etc.) of particular local importance. Fourth, identify species within each functional type that are already present, estimate their potential biomass densities, and thus identify the shortfall within each cell of the body size x feeding type matrix. A candidate set of native and non-native (surrogate) species is then identified to make up the shortfalls. This is followed by an iterative process of estimating equilibrium population sizes, stakeholder acceptance, and viability of each potential population. Fifth, stakeholders must be inclusively re-engaged to visualize the potential assemblage, its expected functional interactions, the ecosystem services to be delivered, and the long-term costs (including opportunity costs) and benefits. When a plan is supported, local stakeholders should be integrated as active participants in the implementation, monitoring, and championing of their rewilding project.

Distinct response patterns of plants and soil microorganisms to agronomic practices and seasonal variation in a floodplain ecosystem

Introduction

Climate change and anthropogenic activities are the greatest threats to floodplain ecosystems. A growing body of literature shows that floodplain ecosystems have experienced increased chemical fertilizer and pesticide loads, which will disturb the above and belowground ecosystems. However, we lack knowledge regarding the effects of such human activities on the vegetation and soil microbiomes in these ecosystems.

Methods

In the present study, plant functional traits and Illumina Mi-Seq sequencing were to assess the impact of nitrogen fertilizer and glyphosate addition on the structure and function of the vegetation and soil microbiomes (bacteria, fungi, and protists) in a floodplain ecosystem, and to assess the influence of seasonal variation.

Results

We identified distinct response mechanisms of plant and microbial communities to the addition of nitrogen fertilizer and glyphosate, and seasonal variation. Nitrogen fertilizer and glyphosate significantly affected plant diversity, aboveground and underground biomass, and C and N content and significantly changed the leaf area and plant stature of dominant plants. However, the addition of nitrogen fertilizer and glyphosate did not significantly affect the diversity and structure of bacterial, fungal, and protist communities. The application of nitrogen fertilizer could improve the negative effects of glyphosate on the functional traits of plant communities. The seasonal variation of floodplain has significantly changed the soil's physical, chemical, and biological properties. Our results showed that compared with that in summer, the soil ecosystem multifunctionality of the floodplain ecosystem in autumn was significantly lower. Seasonal variation had a significant effect on plant diversity and functional traits. Moreover, seasonal variation significantly affected the community compositions, diversity, and structure of bacteria, fungi, and protists. Seasonal variation had a stronger impact on fungal community assembly than on that of bacteria and protists. In summer, the assembly of the fungal community was dominated by a deterministic process, while in autumn, it is dominated by a stochastic process. In addition, the negative association among bacteria, fungi, and protists has been strengthened in autumn and formed a more robust network to cope with external changes.

Discussion

These results extended our understanding of the ecological patterns of soil microbiomes in floodplain ecosystems and provided support for enhancing the ecological barrier function and the service potential of floodplain ecosystems.

Diamonds in the rough: Dryland microorganisms are ecological engineers to restore degraded land and mitigate desertification

Our planet teeters on the brink of massive ecosystem collapses, and arid regions experience manifold environmental and climatic challenges that increase the magnitude of selective pressures on already stressed ecosystems. Ultimately, this leads to their aridification and desertification, that is, to simplified and barren ecosystems (with proportionally less microbial load and diversity) with altered functions and food webs and modification of microbial community network. Thus, preserving and restoring soil health in such a fragile biome could help buffer climate change's effects. We argue that microorganisms and the protection of their functional properties and networks are key to fight desertification. Specifically, we claim that it is rational, possible and certainly practical to rely on native dryland edaphic microorganisms and microbial communities as well as dryland plants and their associated microbiota to conserve and restore soil health and mitigate soil depletion in newly aridified lands. Furthermore, this will meet the objective of protecting/stabilizing (and even enhancing) soil biodiversity globally. Without urgent conservation and restoration actions that take into account microbial diversity, we will ultimately, and simply, not have anything to protect anymore.

How vulnerable are rangelands to grazing?

Assessing multiple site conditions and climate reveals the impacts of livestock pressure