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Warming and N (nitrogen) deposition are the two main driving factors of global change. We examined the effects of increased N deposition (8 kg ha−1 year−1) and warming, as well as their combined effect on the leaf photosynthetic pigments of Leymus secalinus, which is one of the key alpine plants growing in different grassland habitats on Qinghai-Tibetan plateau. In 2014, the experiments were established in 12 plots (2×5m) of three types of habitats including alpine meadow (AM), alpine steppe (AS), and cultivated grassland (CG) with the following treatments: CK (control treatment), N (only N deposition), W (only warming), and W&N (warming combined with N deposition). Results showed that the effects of warming and N deposition on photosynthetic pigments of Leymus secalinus varied with different grassland habitat types. In three grassland types, warming led to no significant effects on the total chlorophyll content of L. secalinus, while N deposition alone only significantly enhanced total chlorophyll content in alpine meadow and cultivated grassland. N deposition combined with warming only significantly enhanced total chlorophyll content of L. secalinus in alpine steppe and cultivated grassland. Chla content plays an important role in determining the variation of total chlorophyll content. Chla/Chlb ratio of L. secalinus was more stable in alpine meadow compared with that of L. secalinus in the other two grassland types. Car/Chl ratio of L. secalinus was not prone to be affected by warming and N deposition in all grassland types. Leaf N content was obviously positively correlated with photosynthetic pigments, especially Chla content. Warming and N deposition all affected photosynthetic pigment dynamics and tended to increase Chla by enhancing its weight. Our results highlighted that both warming and N deposition as well as their combination can alter the trade-off of photosynthetic pigments through enhancing the Chla ratio in L. secalinus. In addition, growing habitats should be within consideration when studying alpine plants adaptation mechanism to global change in the future. [ABSTRACT FROM AUTHOR]

Global grassland degradation has prompted professionals and practitioners to critically consider about the future of grassland resources. Restoration actions related to payment for ecosystem services (PES) have been proposed as a possible approach to balancing grassland sustainable development and ecosystem service supply. Since 2005, approximately one billion U.S. dollars have been invested in the Three-River Headwater Region (TRHR) of China to restore 5.69 × 106 ha of degraded grasslands via grassland cultivation and fencing. Unfortunately, few literature has drawn valid and generalizable conclusions regarding the economic performance of these PES programs. Therefore, field data from multiple sites were collected to evaluate the economic returns of restoration actions, returns on investments (ROI), and trade-offs among ecosystem services of cultivated and fenced grasslands over different restoration years in the TRHR. The results revealed that PES-related restoration efforts in the TRHR had yielded a net profit of $14.34 billion, with $13.20 billion from the alpine meadow, $0.74 billion from the alpine steppe and $0.40 billion from the temperate steppe. These substantial economic can be attributed to the combined effects of the surge in specific ecosystem services and the synergistic improvement of all ecosystem services. The ROI of supporting service accounted for the largest proportion of ROI in total ecosystem services and exhibited drastic fluctuations with restoration years, whereas the ROI of other services either increased gradually or remained stable across different restoration periods. The trade-offs in ecosystem services varied greatly with grassland type. We observed an increasing synchronization of ecosystem services over time in the fenced alpine steppe, cultivated alpine meadow, and cultivated temperate steppe; whereas a similar trend was not detected in other grasslands. Our research underscores the importance of incorporating herders' willingness, assessing restoration performance of grasslands and adopting more targeted and adaptive restoration actions in subsequent PES programs. • PES helped balance sustainable development and ecosystem conservation. • Multiple site data was collected to explore ecological returns of restoration actions. • Restoration actions with PES programs had yielded a net profit of $14.34 billion. • Gains were owed to surge of specific ecosystem services and synergy of all services. • Herders' willingness and more targeted actions should be considered in next steps. [ABSTRACT FROM AUTHOR]

Although human activities have greatly increased nitrogen (N) and phosphorus (P) inputs to the alpine grassland ecosystems, how soil microbial functional genes involved in nutrient cycling respond to N and P input remains unknown. Based on a fertilization experiment established in an alpine meadow of the Qinghai-Tibetan Plateau, we investigated the response of the abundance of soil carbon (C), N, and P cycling genes to N and P addition and evaluated soil and plant factors related to the observed effects. Our results indicated that the abundance of C, N, and P cycling genes were hardly affected by N addition, while P addition significantly increased most of them, suggesting that the availability of P plays a more important role for soil microorganisms than N in this alpine meadow ecosystem. Meanwhile, when N and P were added together, the abundance of C, N, and P cycling genes did not change significantly, indicating that the promoting effects of P addition on microbial functional genes abundances were overwhelmed by N addition. The Mantel analysis and the variation partitioning analysis revealed the major role of shoot P concentration in regulating the abundance of C, N, and P cycling genes. These results suggest that soil P availability and plant traits are key in governing C, N, and P cycling genes at the functional gene level in the alpine grassland ecosystem. [ABSTRACT FROM AUTHOR]

Grassland cultivation is the key measure for restoring "Black Beach," the extremely degraded alpine meadow in the Three River Headwater Area of the Qinghai–Tibetan Plateau. In this study, we examined the inter-specific relationship in the vegetation community of cultivated grasslands with different restoration times through the network analysis method. The results showed that with the extension of restoration time, the development of cultivated grassland would lead to increasing neutral interactions among the plant species. The proportion of species with positive and negative associations in the community decreased, while the number of species-independent pairs increased significantly. The complexity of plant interspecific association (species network density) had more influence on community stability with the extension of recovery time, which can be used to quantify the characteristics of community structure. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition has been increasing for decades and has profoundly influenced the structure and function of grassland ecosystems in many regions of the world. However, the impact of N deposition on alpine grasslands is less well documented. We conducted a 3-year field experiment to determine the effects of N deposition on plant species richness, composition, and community productivity in an alpine meadow of the Qinghai-Tibetan Plateau of China. We found that 3 years of N deposition had a profound effect on these plant community parameters. Increasing N rates increased the dominance of graminoids and reduced the presence of non-graminoids. Species richness was inversely associated with aboveground biomass. The shift in plant species and functional group composition was largely responsible for the increase in productivity associated with N deposition. Climatic factors also interacted with N addition to influence productivity. Our findings suggest that short-term N deposition could increase the productivity of alpine meadows through shifts in composition toward a graminoid-dominated community. Longer-term studies are needed to determine if shifts in composition and increased productivity will be maintained. Future work must also evaluate whether decreasing plant diversity will impair the long-term stability and function of sensitive alpine grasslands. [ABSTRACT FROM AUTHOR]

The aboveground biomass (AGB) production of grazed grasslands is mediated by climate, soil nutrients, livestock and other factors. How the biotic and abiotic factors directly or indirectly regulate AGB remains unclear. To fill this gap, from 2014 to 2017, we conducted a rotational grazing experiment to examine the response of AGB to biotic and abiotic factors in Nagqu, a typical alpine meadow community on the Qinghai‐Tibetan Plateau. Six yaks were rotationally grazed among three plots from July to September, meanwhile, three plots were set up to exclude from livestock as control; climate, plant biomass, and soil nutrients were investigated during grazing experiment, and then structural equation modeling was used to analyze the regulation of environmental factors on AGB. The results showed that precipitation affected AGB via affecting soil nitrate nitrogen (NO3‐N), compensatory growth rate, and belowground biomass indirectly; temperature can directly and negatively affected AGB. In contrast grazing exclosure, rotational grazing increased both AGB and its temporal stability in alpine meadow community significantly (p <.05). The temporal stability of the AGB was positively related to the asynchrony between high‐ and low‐palatability herbages (p <.05). In conclusion, rotational grazing should be recommendable for alpine meadow management due to its benefits for community productivity and stability while current stocking rate should be reduced to a reasonable level, especially in a warm and drought year, to sustain plant compensatory growth under grazing. [ABSTRACT FROM AUTHOR]

Warming and Nitrogen (N) deposition are key global changes that may affect eco-physiological process of territorial plants. In this paper, we examined the effects of warming, N deposition, and their combination effect on the physiological performances of Leymus secalinus. Four treatments were established in an alpine meadow of Qinghai-Tibetan plateau: control (CK), warming (W), N deposition (N), and warming plus N deposition (NW). Warming significantly decreased the photosynthetic rate (Anet), stomatal conductance (gs), intercellular CO2 concentration (Ci), and transpiration rate (Tr), while N deposition and warming plus N deposition significantly increased those parameters of L. secalinus. Warming significantly increased the VPD and Ls , while N deposition and warming plus N deposition had a significant positive effect. Warming negatively reduced the leaf N content, Chla, Chlb, and total Chl content, while N deposition significantly promoted these traits. Warming, N deposition, and their combination significantly increased the activity of SOD, POD, and CAT. Besides, warming and warming plus N deposition significantly increased the MDA content, while N deposition significantly decreased the MDA content. N deposition and warming plus N deposition significantly increased the Rubisco activity, while warming showed no significant effect on Rubisco activity. N deposition and warming plus N deposition significantly increased the Fv / Fm , ΦPSII, qP , and decreased NPQ, while warming significantly decreased the Fv / Fm , ΦPSII, qP , and increased NPQ. N deposition strengthened the relations between gs , Chl, Chla, Chlb, Rubisco activity, and Anet. Under warming, only gs showed a significantly positive relation with Anet. Our findings suggested that warming could impair the photosynthetic potential of L. secalinus enhanced by N deposition. Additionally, the combination of warming and N deposition still tend to lead positive effects on L. secalinus. [ABSTRACT FROM AUTHOR]

One of the important mechanisms for the stabilization of soil organic carbon (SOC) is its spatial inaccessibility for microbial biodegradation within soil aggregates. However, little has been documented regarding soil aggregate stability with grassland degradation in the alpine region of the Qinghai‐Tibetan Plateau (QTP). In this study, we used physical and density fractions to elucidate the mechanisms of differences in SOC in non‐degraded and degraded grasslands of two grassland biomes, alpine meadow and alpine steppe in the QTP. There were considerable differences between non‐degraded and degraded grasslands for the soil physical and chemical properties, aggregate distribution and aggregate‐SOC content. The non‐degraded alpine meadow (AMND) had the largest value among all the alpine grasslands for the SOC content of the microaggregate fraction, with values of 31.83 g kg−1. The degraded grasslands showed significantly larger SOC content of macroaggregates than non‐degraded grasslands. The degraded alpine steppe (ASD) had the largest SOC content, with the value of 25.51 g kg−1. The aggregate distribution of the macroaggregate, microaggregate and free silt+clay fractions was consistent with the variation in SOC content of these three aggregate fractions. The fine intra‐aggregate particulate organic matter (fiPOM) content was significantly less in degraded grasslands, indicating that grassland degradation might have disrupted the fiPOM‐C. The increase in CO2 emissions was related to the destruction of soil aggregates in the alpine grasslands of the QTP. Highlights: Effects of alpine grassland degradation on aggregate‐associated SOC were investigated.Used soil aggregate fractions to evaluate the variation of aggregate‐associated SOC.Grassland degradation promoted the destruction of soil aggregates in the alpine grasslands of the QTP.Destruction of soil aggregates promoted CO2 emissions in the degraded alpine grasslands of the QTP. [ABSTRACT FROM AUTHOR]

• N deposition effects on soil C:N:P stoichiometry of ungrazed and grazed grassland varied. • Livestock grazing may weaken N deposition effects on soil C:N:P stoichiometry. • Climate variability and other environmental factors can also mediate N deposition effects. Increased nitrogen (N) deposition is expected to impact the grassland ecosystem by changing soil C:N:P stoichiometry. However, N deposition effects on soil C:N:P stoichiometry is still in debate. In addition, we still know less about how N deposition affects soil C:N:P stoichiometry in grazed grassland as most studies focus on natural grassland. Hence, it is necessary to examine N deposition effects on both ungrazed and grazed grassland and clarify the disparity. We conducted a simulated N deposition experiment in ungrazed and grazed grassland of two grassland types including alpine meadow (AM) and alpine steppe (AS) to test such effects. Results showed that N deposition effects on ungrazed and grazed grassland varied. Soil C, soil N, soil P, soil C:N, soil N:P and soil C:P were significantly affected by N deposition in ungrazed grassland while only soil N, soil P, soil C:N, soil N:P were significantly affected by N deposition in grazed grassland. Soil C and soil N:P were not sensitive to N deposition in grazed grassland. N deposition negatively affects soil P in ungrazed grassland yet positively affected soil P in grazed grassland. N deposition effects accounted for 30% in ungrazed grassland, while significantly decreased to 12% when grazing effects were considered suggesting that livestock grazing might weaken N deposition effects on soil C:N:P stoichiometry. In addition, other climate and environmental factors such as MAT, MAP, and grassland type can also mediate N deposition effects on soil C:N:P stoichiometry in both ungrazed and grazed grasslands. On the whole, our findings suggested that there existed a disparity of N deposition effects on soil C:N:P stoichiometry between ungrazed and grazed grassland, and livestock grazing may weaken N deposition effects on soil C:N:P stoichiometry in alpine grassland of the Qinghai-Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition may alter physiological process of plants in grassland ecosystem. However, little is known about the response mechanism of individual plants in alpine regions to N deposition. We conducted a field experiment, and three treatments including 0 kg Nha-1year−1 (CK), 8 kgNha-1year−1 (Low N), and 72 kg N ha-1 year−1 (High N) were established to simulate N deposition in alpine meadow of Qinghai-Tibetan plateau. Our objectives were to determine the influence of N deposition on photosynthesis of different functional types of herbage species in alpine meadow, and finally characterize the links of plant productivity and photosynthesis with soil nutrients. The results showed that responses of alpine plants were species-specific under N deposition. Compared with grass species Agropyron cristatum and forb species Thalictrum aquilegifolium , the sedge species Carex melanantha was much more sensitive to N deposition; a lower N load (8 kgNha-1year−1) can cause a negative effect on its photosynthesis and productivity. Additionally, N deposition can promote plant N uptake and significantly decreased the C (carbon)/N (nitrogen) ratio. Compared with CK and low N deposition, high N deposition inhibited the photosynthesis and growth of the forb species Thalictrum aquilegifolium and sedge species Carex melanantha. In all three functional types of herbage species, the grass species A. cristatum tended to show a much higher photosynthetic capacity and better growth potential; thus, suggesting that grass species A. cristatum will be a more adaptative alpine plants under N deposition. Our findings suggested that plant photosynthetic responses to N deposition were species-specific, low N deposition was not beneficial for all the herbage species, and N deposition may change plant composition by the differential photosynthetic responses among species in alpine grassland. Plant composition shift to grass-dorminant in alpine regions might be attributed to a much higher photosynthetic potential and N use efficiency of grass species. Image 1035 • The photosynthesis of alpine plants species-specifically response to N deposition. • The responses of the alpine plants to nitrogen deposition was closely related to soil N. • Sedge species may sensitively response to N deposition. • Grass species might have a much higher photosynthetic capacity and better growth potential. [ABSTRACT FROM AUTHOR]

• Soil total nitrogen and biodiversity were improved by restoration intervention. • The relationships of above- and belowground ecosystem services changed over time. • Economic profit of ecological restoration was insignificantly changed over time. A great number of ecological conservation and restoration projects have been implemented to prevent the deterioration of alpine grasslands on the Qinghai-Tibetan Plateau. However, few researches have documented the effects of ecological projects on the improvement of ecosystem services of alpine grasslands based on field investigations. In this study, 24 plots of alpine meadow along different succession times were investigated to estimate the impacts of ecological restoration on four key ecosystem services (i.e., soil organic carbon sequestration (SOCS), soil total nitrogen sequestration (STNS), biodiversity, and aboveground biomass) in the Glog Tibetan Autonomous Prefecture of Qinghai Province, China. The results showed that STNS and biodiversity of degraded alpine meadows were significantly improved through restoration actions, while SOCS and aboveground biomass didn't change. The relationships of above- and belowground ecosystem services changed over restoration time. Trade-offs between aboveground biomass and biodiversity, between aboveground biomass and SOCS at stage Ⅲ were significantly improved, in contrast to those at stage Ⅰ. Trade-off between STNS and biodiversity at stage Ⅱ was significantly increased, in contrast to those at stage Ⅰ. Economic profit of ecological restoration was insignificantly changed along restoration time. Our results suggested that human-induced restoration was a feasible approach to improve the ecological and economical values of "Black Beach" on the Qinghai-Tibetan Plateau, and further restoration actions and long-term research are required to enhance the ecosystem services of revegetated degraded meadow. [ABSTRACT FROM AUTHOR]

• Alpine plant and soil quality was improved by grassland cultivation. • Non-linear trajectory of plant and soil restoration existed in cultivated grassland. • Asynchrony existed between soil and plant quality along the recovery years. • Restoration of severely degraded alpine meadow took minimally 16–18 years. Resilience is crucial to promote the ecosystem sustainability and maintain ecosystem functions and services. Clarifying the variation regularity of the resilience can provide a theory foundation for the restoration and management of degraded ecosystems. Grassland cultivation has been largely used to restore extensively distributed "Black Beach", the severely degraded alpine meadow on the Qinghai-Tibetan Plateau (QTP). However, few researchers have documented the resilience of the revegetated grasslands along the succession gradients. In this study, we surveyed the revegetated grasslands on the QTP at different restoration times: 4-year, 6-year, 9-year, 12-year, 13-year, 14-year, 16-year, 18-year by using chronosequence approach to identify the resilience of the revegetated grasslands from the perspectives of plant and soil quality. We treated "Black Beach" as the baseline for restoration, and non-degraded healthy alpine meadow as the target for the restoration. We used the MDS method to identify the appropriate indicators and created an integrated assessment system that quantified the resilience of plant, soil, plant-soil system of the revegetated grasslands at different recovery years. The results showed that the non-linear resilience of revegetated grasslands were identified for the plant, soil and plant-soil systems along the temporal gradients. The plant resilience of the revegetated grasslands peaked at the 12th recovery year. The soil of the revegetated grasslands was superior to severely degraded grasslands after 13 years of revegetation. Asynchrony existed between the resilience of soil and that of the plant along the temporal gradients. The plant-soil system resilience of the revegetated grasslands peaked at the 16th recovery year. From the perspectives of plant, soil, plant-soil system, the recovery time of severely degraded grassland should be at least 16–18 years to reach a relative stable state. Revegetated grassland can be used as an effective restoration approach to improve the quality and resilience of plant and soil in the severely degraded alpine meadow on the QTP. [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]

• P addition increased N retention mainly by promoting plant N uptake. • N addition without P showed neutral effects of N retention. • N addition showed positive effects on gaseous losses of N. • N loss through NH 3 and N 2 O emissions was quite low. Nitrogen (N) and phosphorus (P) are common limiting nutrients affecting plant growth in alpine ecosystems. Anthropogenic activities significantly increase N input in ecosystems, thereby increasing P limitation when in excess. The increase of N input and P limitation may affect N retention, which is a critical ecosystem function. To understand how ecosystem N retention and N loss respond to N and P addition, this study investigated the effects of N and P addition on NH 3 volatilization, N 2 O emissions, and N pools of plants and soil in two alpine grasslands (alpine meadow and alpine steppe). The results showed that P addition (with or without N) increased N retention, mainly by promoting plant N uptake, underlining the importance of P availability in N retention in the QTP alpine grassland ecosystems while increasing N deposition. N addition without P showed neutral effects of N retention of plant, soil and microbes, and N addition (with or without P) showed positive effects on gaseous losses of N. N loss through NH 3 volatilization and N 2 O emissions was quite low (less than 1%), suggesting that N gaseous loss was not a significant pathway of N loss from the alpine grassland ecosystems. These results were meaningful for estimating the impacts of N retention and N loss under future N deposition scenarios in alpine grassland ecosystems in the QTP. [ABSTRACT FROM AUTHOR]

• Restoration actions improved community species richness, target species richness and target species aboveground biomass, not community biomass. • Community species richness was impacted by the restoration strategies. • Community biomass was impacted by the mean annual precipitation and temperature. • Recovery performance of target species was impacted by all the influencing factors. Ecological conservation and restoration projects in Three-river Headwater Region (TRHR) have been implemented to respond to the serious degradation of alpine meadow ecosystem. Compared with the substantial amount of studies on the recovery of plant communities, soil quality and ecosystem services, few studies have focused on the restoration performance of target species. Therefore, we conducted this study to analyze the dynamics and underlying mechanisms of species richness and aboveground biomass of plant communities and target species. The results showed that restoration actions (grassland cultivation and fencing) did not significantly improve the community aboveground biomass of the degraded alpine meadows, while the actions did significantly promote community species richness, target species richness and target species aboveground biomass. Community species richness (20%-45%) was significantly impacted by the restoration strategies, and community aboveground biomass (31%-53%) was impacted by the mean annual precipitation and mean annual temperature. The species richness (57%) and aboveground biomass (63%) of the target species were directly and indirectly impacted by restoration actions, climatic factors, biotic factors and soil factors. The implications of this study stress that target species should be highlighted in assessing the restoration success of degraded alpine meadows. Integrating climatic factors, target species and other biotic and abiotic indicators could help us better understand and evaluate restoration actions for degraded alpine meadows in the TRHR or other similar regions worldwide. [ABSTRACT FROM AUTHOR]

The ability of fragile ecosystems of alpine regions to adapt and thrive under warming and nitrogen deposition is a pressing conservation concern. The lack of information on how these ecosystems respond to the combined impacts of elevated levels of nitrogen and a warming climate limits the sustainable management approaches of alpine grasslands. In this study, we experimented using a completely random blocked design to examine the effects of warming and nitrogen deposition on the aboveground biomass and diversity of alpine grassland plant communities. The experiment was carried out from 2015 to 2018 in four vegetation types, e.g., alpine desert, alpine desert steppe, alpine marsh, and alpine salinised meadow, in the Aerjin Mountain Nature Reserve (AMNR) on the Qinghai–Tibetan Plateau (QTP). We found that W (warming) and WN (warming plus N deposition) treatment significantly increased the aboveground biomass of all the vegetation types (p < 0.05) in 2018. However, W and WN treatment only significantly increased the Shannon diversity of salinised meadows in 2018 and had no significant effect on the Shannon diversity of other vegetation types. Such results suggested that long-term nitrogen deposition and warming can consistently stimulate biomass accumulation of the alpine plant communities. Compared with other vegetation types, the diversity of alpine salinised meadows are generally more susceptible to long-term warming and warming combined with N deposition. Warming accounts many of such variabilities, while short-term N deposition alone may not significantly have an evident effect on the productivity and diversity of alpine grasslands. Our findings suggested that the effects of short-term (≤4 years) N deposition on alpine vegetation productivity and diversity were minimal, while long-term warming (>4 years) will be much more favourable for alpine vegetation. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibet Plateau (QTP) is experiencing increasing nitrogen (N) deposition, which may have great impacts on the physical, chemical, and biological factors that determine the stabilization of soil organic carbon (SOC). However, few studies have been conducted to quantify the relative contributions of these factors to SOC stabilization at various N addition levels in alpine habitats. We established a N manipulation experiment from 2015 to 2016 in an alpine meadow on the QTP to examine the impacts of N addition gradients on SOC stabilization under different scenarios of N deposition including 8, 24, 40, 56, and 72 kg N ha−1 yr−1. Using solid-state 13C NMR spectroscopy, we assessed the changes in the chemical composition of SOC. We measured soil aggregate size fractions, iron ions, soil microbes, and soil chemicals to investigate their contributions to SOC stabilization. We found that there were response thresholds of SOC to N addition in this alpine meadow on the QTP. The critical level of N addition for the change of SOC was close to 16 kg N ha−1 yr−1 plus the natural atmospheric N deposition (approximately 8 kg N ha−1 yr−1). N addition affected SOC stabilization in this alpine meadow mainly by affecting soil aggregates and soil microbes. These results of this study suggest that an exogenous N input lower than the critical load is beneficial for C sequestration in this alpine meadow on the QTP. This is potentially important for understanding the influences of atmospheric N deposition on soil properties, with subsequent effects on SOC stabilization on the alpine meadow of QTP and similar fragile ecosystems worldwide. • There were response thresholds of SOC to N input in alpine meadows. • The critical load of N input was close to 16 kg N ha−1 yr−1 for SOC change. • N input affected SOC stability mainly by affecting soil aggregates and microbes. [ABSTRACT FROM AUTHOR]

• Responses of different functional groups to overgrazing and overgrazing with N deposition varied. • Overgrazing and overgrazing with N deposition provided a favorable living environment for forbs. • Overgrazing with N deposition obviously promoted forbs dominance both directly and indirectly. Alpine grasslands are sensitive to grazing and atmospheric nitrogen (N) deposition. Despite increases in N deposition, few field studies have assessed the effects of grazing in conjunction with increased N deposition on alpine grassland vegetation. In this two-year field study, we examined the effects of overgrazing and overgrazing plus N deposition on eco-physiological processes of alpine grassland plants at the functional group level. We found that both overgrazing and overgrazing plus N deposition altered species composition and the dominance of three plant functional groups (grasses, sedges, and forbs) in an alpine meadow and alpine steppe. In the overgrazing and overgrazing plus N deposition treatments, forbs dominated the plant community. Grass and sedge dominance decreased substantially, relative to a ungrazed treatment. The underlying eco-physiological processes that led to the forb-dominated plant community differed between the overgrazing and overgrazing plus N deposition treatments. Overgrazing plus N deposition increased forb dominance both directly by selective herbivory and indirectly by enhancing forb photosynthetic rates. Our results suggest that overgrazing concomitant with increases in N deposition will likely shift the plant community composition of alpine grasslands on the Qinghai-Tibetan Plateau from grass/sedge communities to forb-dominated communities in the future. [ABSTRACT FROM AUTHOR]

• The effect of grazing regime on functional genes were different at distinct grazing period. • Grazing regime affected the temporal variation of soil microbial functional genes. • Grazing rather than exclosure promote C fixation and decomposition and N cycling. • There existed trade-offs between plant and soil nutrients along the grazing time. • Continuous grazing promoted CH 4 metabolism. Microbial functional genes can reflect the nutrient cycle activities in soil, because they encode various enzymes involved in the material cycle. Therefore, the gene abundance variation can reveal the impact of interference on the material cycle of grassland. To study the cycle of carbon (C), nitrogen (N) and phosphorus (P) between plant and soil in grassland under different grazing regimes, we investigated the soil microbial functional genes related to C, N, and P cycling by high-throughput quantitative PCR and 16S rRNA-based Illumina sequencing analysis under grazing exclusion (GE), rotational grazing (RG), and continuous grazing (CG) in alpine meadow of the Qinghai-Tibetan Plateau, where climate is characterized by little rain and low temperature, and grassland is very sensitive to grazing. The results showed at the early grazing period, C fixtion (rbcL , korA , and frdA) and lignin degradation (abfA , xylA , exg , lig , exoPG , chiA , and glx) processes were slower under GE; CH 4 metabolism (mcrA) was faster under CG; RG and CG improved the denitrification process (narG); RG slowed down organic-P mineralization (phoD). At the late grazing period, C fixation (accA and frdA) and degradation (mnp , apu , and amyA) processes were slower under GE; CH 4 metabolism (pmoA and mxa) was faster under CG; RG and CG improved the ammonia-oxidizing (amoA2), nitrification (hao), and denitrification (nirS3 and nirK1) processes. The majority of the genes involved in C, N, and P cycling decreased, the C, N and P content in plant leaf decreased, while that of soil increased from early to late grazing period. No matter grazing or not, there were negative relationships between genes and soil nutrients, and positive relationships between genes and plant nutrients, implying a trade-off between plant nutrients and soil nutrients along the grazing time. The genes responsible for regulating C and N cycling were increased under grazing, implying that reasonable grazing is beneficial to the nutrients cycling of grassland. [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]

Mining is well-known as one of the most aggressive human disturbances leading to massive and irreversible damages to natural ecosystems. However, the influence mechanisms of open-pit mining on plant communities and soil properties of alpine meadow on the Qinghai-Tibetan plateau are not well understood. In this study, we used structural equation modeling (SEM) to study the influence mechanisms in the disturbed areas of the Qulong copper mine. Our results revealed that the soil parameters of alpine meadow have been significantly changed by mining activities. SEM results showed that Plantago depressa Willd. was more suitable for growing in current soil conditions due to its tolerance to heavy metals than other dominant species, which meant that it would substitute the current two dominant species (Kobresia myosuroides (Villars) Fiori and Blysmus sinocompressus Tang et Wang) in the future and become the most important dominant species in the study area. Unfortunately, the Shannon-Wiener index, Alatalo evenness index and M-Gordon stability index are relatively low in the plot with Plantago depressa Willd. as the dominant species. In a word, the fragile alpine meadow ecosystem may degenerate in the future due to plants and soil disturbed by mining activities. Further, eight targeted recommendations were proposed to protect alpine meadow on the Qinghai-Tibetan plateau. Image 1 • Soil parameters had been significantly changed by mining activities. • Plantago depressa Willd. will become the most important dominant species. • The fragile alpine meadow ecosystem may degenerate in the future. • Eight targeted recommendations were proposed to protect alpine meadow. We confirmed the degradation trend of dominant species and plant communities in alpine meadow of the Qinghai-Tibetan Plateau under the disturbance of mining activities. [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]

• We monitored the dynamics of seedling recruitment of 303 grassland species. • Seed size indirectly and positively affected seedling survival via biomass growth. • The direct effect of seed size on seedling survival was negative. • This study has a reference for breeding of new herbage varieties on Tibetan plateau. Theoretical models of life-history strategies assume a positive relationship between seed size and subsequent offspring survival (seed size–survival relationship). There is limited empirical evidence, however, on how this relationship changes across environments or in relationship to seedling traits. Moreover, characterizing the dynamics of seedling recruitment under natural conditions is central to understanding how seedling recruitment may in turn affect large-scale ecological processes. Here, first-year seedling survival was monitored from emergence for 303 angiosperms species originated from alpine and sub-alpine meadows of the eastern Tibetan Plateau grasslands, across an experimental light gradient consisting of four treatments. We used linear models (LM) and phylogenetic generalized linear models (PGLM) to test for the seed size–survival relationship, and how this relationship differed across light treatments. We also used path analysis (PA) and phylogenetic confirmatory path analysis (PPA) to assess how seed size interacted with other seedling traits (seedling emergence time, specific leaf area, root: shoot biomass ratio, and biomass growth) to either directly or indirectly affect seedling survival. We found seed size to be positively associated with seedling survival only under low to medium light treatments only in LM (not in PGLM). PA and PPA revealed that the positive effect of seed size on seedling survival was indirect, mainly acting via biomass growth. Under low light, larger seeds exhibited greater biomass growth, which in turn increased seedling survival. In contrast, the direct effect of seed size on seedling survival is negative. In sum, the seed size–survival relationship appears to be both environmentally and phylogenetically dependent. The survival advantage of large seeds appears to be the result of their ability of higher biomass growth after emergence in low resource environments. However, our results also suggest there may be an underlying trade-off with larger seeds facing a lesser, but direct risk of increased mortality. The influence of environment on seedling traits, the interaction among traits, and phylogeny should be taking into consideration when modeling the dynamics of seedling recruitment. [ABSTRACT FROM AUTHOR]