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Grassland is the largest ecosystem on the Qinghai–Tibetan Plateau (QTP) and provides multiple ecosystem functions and services. Understanding the endowment of the QTP grassland and how to revitalize it have profound implications for the sustainable use and efficient conservation of these unique and globally valuable ecosystems. In this paper, we highlight the importance of the QTP grassland in regional and global settings, stress the values of the QTP grassland in ecological and socioeconomic dimensions, and emphasize the actions needed to restore degraded grassland in the QTP region. The QTP is the largest single area of alpine grassland in the world and an important gene pool of alpine biological resources. The QTP grassland covers two critical ecoregions for conserving the best and most representative habitats for alpine biodiversity on the planet. The QTP grassland is also regarded as one of the best carriers and objects of socio‐ecological systems in the world. To promote the resilience and sustainability of the QTP grassland through adaptation, different parties need to work together to find feasible options to resist shock, stresses, and disturbance and to maintain the fundamental functions and basic structures of the QTP grassland. [ABSTRACT FROM AUTHOR]

Abstract Nitrogen deposition is notable in China, even in the high altitude region of Qinghai-Tibet Plateau (QTP). To identify the effects of nitrogen deposition on soil nutrient and ecological stoichiometry of the QTP's alpine grasslands, we treated three major types of grasslands (alpine meadow, alpine steppe, and cultivated grassland) with 6 different nitrogen addition levels: 0, 8, 24, 40, 56, 72 kg N ha−1 yr−1 through the years of 2015 to 2016. We sampled the soils at two depths, 0–10 and 10–20 cm in the peak-growing season (July) of each year. Results showed that: (i) soil total carbon and phosphorus are relatively stable under nitrogen deposition. (ii) Soil total nitrogen increases under low nitrogen addition rates while decreases under higher rates, and soil available nitrogen increases under nitrogen deposition in surface soil while decreasing in deeper soil. (iii) C:N, C:P, N:P had no significant difference between different nitrogen addition levels while there were significant differences between the two years under nitrogen addition. We speculate that nitrogen addition could alter soil nutrient conditions but there were certain limit of soil nutrient under N deposition. Highlights • Soil total C and P are stable under N deposition. • Total N increase under low N addition rate while decrease under higher rate. • Available N increase under N deposition in surface soil while decrease in deep soil • Stoichiometry had no significant difference between N addition levels. [ABSTRACT FROM AUTHOR]

Fencing and grass plantation are two key interventions to preserve the degraded grassland on the Qinghai-Tibetan Plateau (QTP). Climate warming and N deposition have substantially affected the alpine grassland ecosystems. However, molecular composition of soil organic carbon (SOC), the indicator of degradation of SOC, and its responses to climate change are still largely unclear. In this study, we conducted the experiments in three types of land use on the QTP: alpine meadow (AM), alpine steppe (AS), and cultivated grassland (CG) under 2 °C climatic warming, 5 levels of nitrogen deposition rates at 8, 24, 40, 56, and 72 kg N ha − 1 year − 1 , as well as a combination of climatic warming and N deposition (8 kg N ha − 1 year − 1 ). Our findings indicate that all three types of land use were dominated by O-alkyl carbon. The alkyl/O-alkyl ratio, aromaticity and hydrophobicity index of the CG were larger than those of the AM and AS, and this difference was generally stable under different treatments. Most of the SOC in the alpine grasslands was derived from fresh plants, and the carbon in the CG was more stable than that in the AM and AS. The compositions of all the alpine ecosystems were stable under short-term climatic changes, suggesting the short-term climate warming and nitrogen deposition likely did not affect the molecular composition of the SOC in the restored grasslands. [ABSTRACT FROM AUTHOR]

Increases in nitrogen (N) deposition along with climate warming can change the dynamics of carbon and nitrogen in the soil, and alter greenhouse gases (GHGs) fluxes. To examine how N deposition and warming affect GHGs (CH 4 , CO 2 and N 2 O) fluxes in alpine grasslands, we conducted experiments in an alpine meadow (AM), alpine-steppe (AS), and alpine cultivated grassland (CG) on the Qinghai-Tibetan Plateau (QTP). We simulated N deposition by treating soil with ammonium nitrate (NH 4 NO 3 ) (8 kg N ha − 1 year − 1 ), a warming treatment using an open top chamber (OTC) was carried out, and a combined treatment of warming and N deposition (8 kg N ha − 1 year − 1 ) was conducted. The GHGs were collected during early, peak, and late plant growing seasons, i.e., May, August, and October of 2015, respectively, using a static chamber. We found, in general, neither N deposition nor warming solely altered CH 4 and N 2 O fluxes in the alpine grasslands. The N deposition under warming conditions reduced CO 2 emission significantly. The reduction of CO 2 emission was most significant in the alpine steppe. The effects of climatic warming and N deposition on the GHGs varied greatly across the grassland types and the growing seasons. The cultivated grasslands were much more unstable than the native grasslands in CH 4 uptake. In can be concluded the N deposition associated with human activities may buffer the CO 2 emission in the alpine grassland ecosystems in terms of climate changes on the QTP. [ABSTRACT FROM AUTHOR]

Alpine ecosystems are known to be sensitive to climate change and human disturbances. However, the knowledge about the changes of their underground microbial communities is inadequate. We explored the diversity and structure of soil bacterial and fungal communities using Ilumina MiSeq sequencing in native alpine grasslands (i.e. the alpine meadow, alpine steppe) and cultivated grassland of the Qinghai-Tibetan Plateau (QTP) under three-year treatments of overgrazing, warming and enhanced rainfall. Enhanced rainfall rather than warming significantly reduced soil microbial diversity in native alpine grasslands. Variable warming significantly reduced it in the cultivated grassland. Over 20% and 40% variations of microbial diversity could be explained by soil nutrients and moisture in the alpine meadow and cultivated grassland, separately. Soil microbial communities could be clustered into different groups according to different treatments in the alpine meadow and cultivated grassland. For the alpine steppe, with the lowest soil nutrients and moistures, < 10% variations of microbial diversity was explained by soil properties; and the soil microbial communities among different treatments were similar. The soil microbial community in the cultivated grassland was varied from it in native grasslands. Over 50% variations of soil microbial communities among different treatments were explained by soil nutrients and moisture in each grassland type. Our results suggest that climate change and human activities strongly affected soil microbial communities by changing soil nutrients and moistures in alpine grassland ecosystems. [ABSTRACT FROM AUTHOR]

The plateau pika ( Ochotona curzoniae ) is considered a keystone species on the Qinghai–Tibetan Plateau (QTP). Under a moderate burrow density condition, we investigated plant community and soil properties surrounding pika's burrows in comparison to the control sites (without pika's burrows) in an alpine meadow ecosystem. The results demonstrated that plant biomass, especially aboveground biomass around pika's burrow, was improved. The contents of available soil nutrients around the pika's burrow were improved as well. The highest aboveground biomass and highest contents of NH 4 -N, available phosphorus and available potassium was detected at the back of the burrow. The compositions of plant community were not changed significantly around the pika burrow, excluding at the front of the burrow. Our findings revealed that the activities of plateau pika can improve the production of alpine meadow and increase the soil fertility at individual burrow level when the burrow density was not out of control. [ABSTRACT FROM AUTHOR]

Massive grasslands on the Qinghai-Tibetan Plateau(QTP) provide vital ecosystems services, which have been decreased by land degradation associated with global change. Effective efforts and actions of restoration and management are required to promote the sustainable development of these grassland ecosystems with global importance. This special issue collected numerous papers to address share the innovative theoretical foundations and practical approaches for restoring and protecting QTP's grassland ecosystems in the era of global change. The findings from the collected papers of this special issue stated that the ecosystems services of the QTP's grasslands are declining due to weakened interfaces among soil, plant and grazing animals in the QTP's grassland ecosystems by climate and land use changes. Applicable actions such as climate change mitigation and adaptation, close-to-nature restoration, rotational grazing regime with moderate grazing intensity should be taken to enhance the ecosystem services through rebuilding rational soil-plant-animal interfaces. • Both climate change and human activities led to grassland degradation. • Grassland degradation have weakened the ecosystem services. • Restoration and rational grazing can enhance sustainability of grasslands. [ABSTRACT FROM AUTHOR]

• Benefit for single objective varies under different management practices. • Trade-off among multiple objectives varies under different management practices. • The overall benefit does not change due to the existence of trade-off. Developing sustainable management practices for alpine grassland on the Qinghai-Tibetan Plateau is a key challenge related to the protection of regional ecological environments, the provision of husbandry production and the improvement of pastoralist welfare. This challenge requires researchers and policymakers to seek options that optimize benefits among multiple objectives in ecological, productivity and livelihood dimensions. In this study, we developed a novel tool to value the overall benefits and trade-offs of ecological protection, livestock production and pastoral welfare from four types of grassland management practices mainly used on the Qinghai-Tibetan Plateau: individual grassland management (IGM), joint household grassland management (JHGM), shareholding cooperative grassland management (SCGM) and communal grassland management (CGM). The results showed that JHGM led to the highest ecological benefits, while CGM led to the highest benefits for livestock production and livelihood welfare. SCGM resulted in the lowest level of trade-offs as well as relatively high total benefits among multiple objectives in the ecological, productivity and livelihood dimensions. The results of this study provided empirical evidence that the effect of trade-offs among multiple objectives varied with different grassland management practices. We argue that grassland management practices may be biased if a single objective (i.e., ecological protection, livestock production provision or pastoral welfare improvement) is stressed due to the high level of trade-offs among them. The SCGM showed great potential to balance multiple objectives if properly designed. [ABSTRACT FROM AUTHOR]

• No functional traits connected both phylogeny and environmental factors. • N addition at 8 kg N ha-1year−1 filtrated the species of the gramineae. • N addition at 72 kg N ha−1 year−1 filtrated the species of non-gramineae. • Potassium in normal year and phosphorus in warm year were main factors of environmental filtering. Nitrogen (N) deposition and warming leads to environmental gradients that shape plant communities and ecological diversity, space is treated as an equally important variable as the environmental variables in the environmental gradients. The Qinghai-Tibetan Plateau (QTP) is very sensitive to large increases in N deposition rates and warming. Environmental gradients caused by N deposition and spatial factors act as environmental filtering in community assembly by affecting plant functional traits and phylogeny. To investigate the effects of environmental filtering caused by N deposition on the community assembly in alpine meadows, we randomly placed and fertilized at 6 levels of N addition (no N addition, 8 kg N ha-1year−1, 24 kg N ha−1 year−1, 40 kg N ha−1 year−1, 56 kg N ha−1 year−1 and 72 kg N ha−1 year−1) both in a normal (normal precipitation and normal temperature) year and a warm (normal precipitation and warm) year. We used the fourth-corner analysis and extended RLQ (R stands for a matrix of environmental variables by samples, L stands for a species-cover-by-samples matrix and Q stands for a species-by-traits matrix) through multiple factors (soil factors, spatial heterogeneity, species traits, phylogenetic factor) to examine the effects of environmental filtering on the community assembly in alpine meadows. The results demonstrated that all soil variables showed a clear gradient and were affected by simulated N deposition; N addition at 8 kg N ha-1year−1 can filtrate the species of the gramineae, but N addition at 72 kg N ha−1 year−1 can filtrate the species of non-gramineae, the main factors of environmental filtering were potassium in normal year and phosphorus in warm year. With the increase of N deposition rate in alpine meadow of QTP, non-gramineous plants will be favored first, but eventually gramineous plants will occupy the dominant position in the QTP. Rational mitigation strategies should be developed for different climate change scenarios of alpine grasslands on the QTP according to their responses to the N addition gradients and climate change scenarios in the future. [ABSTRACT FROM AUTHOR]

• Ecosystem fragility and human disturbances are the major causes of grassland degradations. • Revegetation of "bare land" with cultivated grasses are key restoration practices. • Soil drying lead to controversial findings about the effects of climate change on grasslands. • Predictions on the responses of plant phenology to climate changes are inconsistent. • Sustainable grazing management can promote grassland system's sustainability of the QTP. The grassland ecosystems cover above 60% of Qinghai-Tibetan Plateau (QTP) and provide important ecosystem services and functions at local and regional scales. However, both anthropogenic and non-anthropogenic disturbances are challenging the sustainability of the QTP's grassland ecosystems in the era of global change. In this review paper, we summarized the causes and effects of grassland degradation, restoration practices used on degraded grasslands, impacts of climate change and nitrogen deposition on plants and soils, adaptation strategies to climate changes, impacts of livestock grazing on plants and soils, and sustainable grazing management on the QTP. We believed that the integration of internal drivers of ecosystem fragility with external disturbances such as overgrazing are the major causes of grassland degradations on the QTP. The quantitative evaluation systems for grassland ecosystem health including plant, soil and livestock indicators are theoretically feasible and technically reliable. The major impacts of grassland degradation on the QTP are loss of biodiversity, increased water erosion, reduced carbon sequestration, decrease pastoral productivity and reduced local human well-being. The current restoration practices are mostly revegetation of "Bare Land" severely degraded grasslands using cultivated grasses. Other restoration practices such as grazing fallow and grassland fencing can be applied to restore the lightly or moderately degraded grasslands. We believed that the side effects from soil drying on plant productivity and diversity in manipulative warming experiments could be the main cause of controversial findings about the effects of climate change on plant productivity, diversity, phenology, soil physics, biochemistry and organisms. Many scholars argued the advances and delays in greening-up date, lengthening and shortening of the growth period in the phenological responses of alpine grassland plants to a warming climate. Multiple sources of remote sensing data and diverse interpretive approaches should be applied and ground-based observations and surveys should be performed to improve the accuracy and reliability of model predictions on plant phenology. Inconsistent conclusions of climate change impacts on soil biochemistry and organisms except soil acidification and eutrophication have been widely observed in most manipulated studies of nitrogen deposition. Adaptive strategies should be employed to promote grassland system's sustainability of the QTP. Rotational grazing regime with moderate grazing intensity in the warm season may retain or promote plant height, cover, productivity and biodiversity, improve soil structure, fertility and microbial biomass, enhance carbon and nitrogen storage and reduce greenhouse gas emissions in the alpine grassland ecosystems. [ABSTRACT FROM AUTHOR]

Over the last 40 years, a burrowing mammal eradication policy has been prevalent on the Qinghai–Tibetan Plateau (QTP). This policy is based on similar burrowing mammal eradication programs in other areas and is justified on the assumptions that burrowing mammals compete with livestock for forage and contribute to grassland degradation. However, there is no clear theoretical or experimental evidence supporting these assumptions.This paper synthesizes the ecological functioning of small burrowing mammals in natural grasslands and discusses the irrationality and consequences of burrowing mammal eradication for sustainable livestock grazing and grassland degradation.Past burrowing mammal eradication efforts have failed because increased food availability for the remaining rodents and reduced predator populations led to rapid population rebounds. Herbivores differ in diet, and there is clear evidence that burrowing mammals, especially plateau zokors Myospalax baileyi, have a different diet than livestock. In QTP meadows, burrowing mammal eradication induces a shift towards plant communities with fewer species preferred by livestock and more species preferred by burrowing mammals. Thus, eradicating burrowing mammals has the opposite effect, a reduction in livestock preferred vegetation. We suggest that the policy of poisoning burrowing mammals needs to be reconsidered and revoked as soon as possible.We argue that incorporating density‐dependent factors such as predation and food availability are essential for maintaining a low burrowing mammal density. For degraded grasslands, we suggest that the optimal sustainable approach is to decrease the intensity of livestock grazing. Lower grazing induces changes in vegetation structure and plant species composition that increases predation on burrowing mammals and decreases the abundance of plants preferred by burrowing mammals. Such a nature‐based grassland management system maintains the density of burrowing mammals at a low stable density while minimizing human management and interventions. [ABSTRACT FROM AUTHOR]

• The temporal stability of community biomass decreases with the time series. • The temporal stability of forb biomass increased with the time series. • Community asynchrony determined the temporal stability of plant community biomass. • Annual maximum and minimum temperature regulated the temporal stability of forb. Climate changes can affect the temporal stability of plant community biomass on the Qinghai-Tibet Plateau, but most studies were based on short-term field climate manipulation experiments. However, the response of biomass stability of natural alpine meadow remains largely unexplored. We conducted a 20-year experimental study monitoring aboveground biomass of plant functional groups (grass, forb and sedge) and community in eastern QTP, with linear regressions and a path analysis of: annual temperature, annual night minimum temperature, annual daytime maximum temperature, annual precipitation, annual daytime precipitation, annual night precipitation, biomass stability of grass, biomass stability of forb, plant functional groups asynchrony to assess the influence climate change and biological factors on the temporal stability of plant community biomass. We found that it was plant functional groups asynchrony rather than climate change that determined the temporal stability of plant community biomass. Our findings suggest that future climate change has a considerable uncertainty in the temporal stability of the plant community biomass in the alpine meadow and we should combine with both field climate manipulation experiments and long-term observational experiments to assess the influence of climate change on the temporal stability of plant community. [ABSTRACT FROM AUTHOR]

• A meta-analysis on the degraded grasslands of the Qinghai-Tibetan Plateau. • More severe degradation for plant growth and soil quality than plant diversity. • Fertilisation improves plant growth and soil quality but limits plant diversity. • Optimal effect is found when jointly using phosphorus and nitrogen. • Climatic factors regulate degradation degree and fertilisers' effect. Climate warming and human disturbance are supposed to have severely affected the alpine grasslands on the Qinghai-Tibetan Plateau (QTP), a region where the extremely harsh and fragile ecological environment has attracted great attention because of its sensitivity to global change. However, there is still no unified understanding of the degree and magnitude of grassland degradation and the effectiveness of nutrient addition in this vast landscape, since most previous studies have focused on short-term observations at a single site. Here, we conducted a meta-analysis of 145 published studies on degraded alpine grassland along with 90 published studies, which concerning nutrient addition (nitrogen [N], phosphorus [P], and combined N and P [NP]) to quantitatively assess the responses of plant and soil characteristics to land degradation and restoration. Our results revealed that the response ratio (RR) of above-ground biomass (AGB), below-ground biomass (BGB), soil organic carbon (SOC), and soil total N (TN) decreased significantly (−47.23 %, −43.45 %, −32.35 %, and −37.97 %, respectively) in degraded grassland compared with non-degraded grassland. The RR of AGB was correlated with mean annual precipitation (MAP), while the RR of BGB was correlated with the interaction of MAP and mean annual temperature (MAT). Severely degraded grassland required additional nutrients to aid recovery. NP addition to severely degraded sites increased plant AGB (+32.44 %), TN (+10.99 %), soil total P (+32.25 %), and soil moisture (+9.21 %), but significantly decreased species richness (−45.46 %), diversity (−30.40 % for Shannon−Wiener index) and soil pH (−3.91 %). N addition increased the RR of AGB and grass biomass significantly by 28.77 % and 36.49 %, but had no significant effect on sedge and forb biomass. MAP influenced the RR of AGB, TN, TP under NP addition, the RR of BGB and the AGB of different function groups were significantly affected by MAT. We evidenced that the QTP has endured severe vegetation and soil degradation, which cannot be completely mitigated by supplementary fertilisation. Fertilisation could yield positive effects on plant performance and soil quality, but negative effects on biodiversity. Climate warming and associated precipitation change may regulate the effects of fertiliser on plant biomass and soil nutrients. [ABSTRACT FROM AUTHOR]