Clarifying the grazing effects on the carbon sink function on the Tibetan Plateau is highly important under climate change. Based on parallel carbon flux and meteorological observations in nearby grazing and grazing-excluded alpine meadows, the effects of grazing were studied. The results indicated that gross primary productivity (GPP) was dominated by soil temperature (TS) and soil water content (SWC) in both the grazing and grazing-excluded meadows. During the whole growing season, in both meadows, TS exerted the strongest control effects on GPP, whereas the dominant factor shifted to SWC during the peak growing season. During the early and late stages of the growing season, the dominant factor for GPP shifted from SWC to TS in the grazing meadow, whereas the dominant factor remained SWC in the grazing-excluded meadow. The grazing-excluded meadow showed improved temperature conditions, resulting in a lower sensitivity of GPP to TS. In contrast, the grazing meadow showed better water conditions, leading to a lower sensitivity of GPP to SWC, which might result in stronger resistance to droughts. Proper grazing could improve GPP and shift the sensitivity of GPP to environmental factors, providing implications for the sustainable management of alpine meadows.

The CO2-fertilisation effect (CFE) on vegetation productivity is the major driver of the enhanced land carbon sink in recent decades. CFE theoretically increases with elevation due to the higher sensitivity of carboxylation to an increase of CO2 under lower CO2 partial pressure, but the elevation-dependent CFE pattern has been largely overlooked. By conducting a 6-year CO2 enrichment experiment (+100 ppm) in an alpine grassland, we show that elevated CO2 increased gross primary production (GPP) by 25.5% ± 4.6%. Water availability and plant biomass allocation modulates CFE during different seasons. A global synthesis of 10 CO2 enrichment experiments reveals that CFE increased with elevation. The satellite-based EC-LUE model also demonstrates a positive global elevation-dependent CFE pattern, albeit substantially weaker than that from experimental observations. Current terrestrial biosphere models, however, could not represent the elevation-dependent pattern, highlighting the need to improve the representations of plants' elevational physiological adaptation to rising CO2 in models.

Extensive experimental and theoretical evidence demonstrates the positive effects of plant diversity on the temporal stability of productivity, yet how the diversity-stability relationship varies across timescales and different diversity dimensions in natural ecosystems remains unclear. By integrating a comprehensive regional vegetation survey conducted in Tibetan alpine grasslands with the global plant diversity and productivity databases, we revealed a consistent temporal pattern at regional and global scales: the stabilizing effect of plant diversity on productivity strengthened over time, approaching saturation at 10 to 13 years. Notably, plant phylogenetic diversity emerged as the dominant biotic driver of long-term stability. In contrast, plant community height exerted a stronger positive influence on short-term stability. These findings highlight the critical role of timescales in shaping diversity-stability relationships and underscore the necessity of decadal-scale studies. Our results further support integrating phylogenetic diversity into conservation and management strategies to sustain ecosystem functioning under global change.

Nitrogen (N) deposition and altered precipitation co-occur under global change, yet their interaction effects on soil organic carbon (SOC) and underlying microbial mechanisms remain unclear, especially in alpine grasslands. We conducted a coordinated N × precipitation manipulation experiment at two contrasting Tibetan Plateau sites: an arid alpine steppe and a humid alpine meadow. N addition increased SOC only under elevated precipitation, with no effect under ambient or reduced precipitation. The microbial pathways driving SOC accumulation differed by site: in the water-limited steppe, SOC gains were mainly associated with suppressed microbial carbon decomposition, whereas in the humid meadow, enhanced microbial carbon use efficiency (CUE) dominated, with smaller effects on decomposition. Ecoenzymatic stoichiometry showed that N addition reduced microbial carbon and N limitation, helping explain site-specific SOC responses. Our results indicate that precipitation not only controls the magnitude but also the mechanisms of N effects on SOC, highlighting the need to incorporate site-specific hydrological context and microbial carbon processing strategies into Earth system models.

Phosphorus (P) commonly limits plant growth on strongly weathered soils in the humid subtropics. The reforestation of croplands alters soil P cycling, but the impact of reforestation on the chemical nature of soil P, mediated through climate and the alteration of soil physicochemical and microbial properties at regional scale, remain poorly understood. To address this, we quantified soil P fractions at 30 reforestation sites in Yunnan and conducted a meta-analysis including 797 records worldwide to analyze the responses of soil P fractions to reforestation. In Yunnan Province, reforestation of croplands decreased soil inorganic P (Pi), primarily in forms extracted in sodium bicarbonate (NaHCO3) and hot concentrated hydrochloric acid (cHCl-Pi), especially during conversion of maize to dawn redwood (Metasequoia glyptostroboides) forest or shrubland. However, organic P (Po) fractions were unchanged. After reforestation, total Pi, NaHCO3-Pi, cHCl-Pi, and total Po concentrations decreased from the central and southern to the northeast and northwest of Yunnan Province. Soil NaHCO3-Pi was positive correlations with soil moisture content, total nitrogen, organic carbon, and bacterial (16S rRNA) abundance. Exchangeable iron, manganese, and fungal abundance (ITS) were positively associated with cHCl-Pi, cHCl-Pi was negatively correlated with acid phosphatase activity. Total Po decreased with increasing time since reforestation. In contrast to Yunnan sites, our meta-analysis shows that reforestation reduces all soil Pi fractions (cHCl-Pi, 1 M HCl-Pi, NaOH-Pi, and NaHCO3-Pi), but does not alter other soil properties. Overall, these findings highlight that reforestation-driven decrease of soil Pi pools can inform targeted P fertilizer management in afforested agroecosystems, promoting sustainable use of soil P.

Numerous studies have demonstrated that nitrogen (N) enrichment typically reduces ecosystem stability, yet how low N addition rates influence temporal dynamics of stability remains poorly understood. Here, we examined the temporal effects of different N addition levels (0, 2.5, 5, and 10 g N m−2 year−1) on the stability of aboveground net primary production (ANPP), species richness, species stability, and species asynchrony, and how the relationships among them change with a 7-year experiment in alpine grasslands. Low N addition significantly enhanced the temporal stability of ANPP during the initial years, whereas this positive effect attenuated over time. In contrast, high N addition reduced community stability, independent of temporal changes. Across the entire experimental period, the stabilizing effect of low N addition was primarily driven by increased species asynchrony, whereas the destabilizing effect of high N addition was mainly mediated by decreased species stability. Moreover, greater interannual precipitation variability amplified the negative effect of high N addition on community stability by reducing species asynchrony, which resulted from the enhanced sensitivity of the dominant species, Stipa purpurea, to precipitation fluctuations. The low N input (≤ 2.5 g N m⁻2 year⁻1) may be prioritized to maintain alpine ecosystem stability in the short term, while attention should be paid to its potential cumulative effects over the long term.

Abstract As global warming continues, non-uniform diel warming is widely affecting terrestrial ecosystems. Because plants undergo distinct physiological processes during the day and night, daytime and nighttime warming can exert contrasting effects on ecosystem carbon uptake and release. Numerous studies have shown that alpine ecosystems are more sensitive to temperature change than low-elevation ecosystems. Owing to low-temperature constraints, alpine ecosystems may exhibit distinct responses to asymmetric diel warming compared to lowland ecosystems. However, little is known about how the differential warming intensity between day and night would affect alpine ecosystems. Here, we integrated a four-year field warming experiment (daytime warming: +1.11 ℃; nighttime warming: +2.08 ℃) with landscape-scale observations to investigate the effects of asymmetric diurnal warming on carbon cycling in alpine grasslands. We found that daytime warming reduced net ecosystem productivity (NEP) by 32.4%, whereas nighttime warming increased NEP by 14.0%. Soil moisture, the coefficient of variation of soil temperature (CVST), precipitation during phenological periods, and aboveground biomass jointly mediated these responses. Daytime warming suppressed carbon uptake primarily by intensifying soil moisture loss, while nighttime warming enhanced carbon uptake by reducing CVST and creating more favorable thermal conditions. Moreover, precipitation during phenophases modulated the effects of warming-induced phenological shifts on ecosystem carbon exchange. Our results suggest that daytime and nighttime warming influence carbon cycling in alpine grasslands through distinct ecological mechanisms, underscoring the importance of explicitly considering the regulatory roles of soil moisture and temperature variability when assessing ecosystem carbon responses to diurnally asymmetric warming.

Abstract The persistence of soil organic matter (SOM) is critical for predicting carbon-climate feedbacks, yet how increasing soil organic carbon (SOC) relates to long-term SOM persistence across environmental gradients remains unclear. Soil radiocarbon, SOM physicochemical composition, and microbial carbon use efficiency (CUE) are analyzed along a precipitation-driven gradient integrated with global datasets. Here we show, as SOC content increases, its persistence as reflected by radiocarbon signatures declines at both the transect and global scales. This pattern indicates that higher SOC soils are increasingly dominated by younger, faster-cycling carbon rather than older, stabilized pools. Plant carbon inputs strongly predict SOM persistence and are associated with younger, less persistent SOC. While microbial CUE increases with SOC, higher CUE does not necessarily enhance long-term stabilization. Our findings suggest that SOC content alone provides limited insight into long-term soil carbon persistence and highlight the importance of explicitly representing plant carbon inputs and microbially mediated persistence in Earth system models.

To better understand the dynamics of community resilience, it is crucial to examine the role of dominant species in maintaining ecosystem functions. Dominant species, due to their high abundance, are considered to maintain productivity after species loss. However, it remains unclear whether the community productivity can be maintained or restored by the remaining co-dominant species after the loss of the dominant species. Therefore, we hypothesized that after the loss of dominant species, the lost productivity would be maintained by the co-dominant species in the remaining community. This study, conducted over 13 years in an alpine grassland, investigates the compensatory responses of remaining species following the removal of each of two dominant species, Kobresia pygmaea (sedge) and Stipa purpurea (grass), both individually and in combination, under two nitrogen level scenarios. We found that while partial compensation (compensation index < 1) occurred in the remaining community, neither of the remaining dominant species effectively compensated for the loss of the removed species. Leguminous plants showed the most obvious positive response to the removal of dominant species, whereas forbs and sedges showed the most marked negative responses. In addition, fertilization does not promote the recovery of community productivity following removal of the dominant species. Our findings underscore the critical role of dominant species in sustaining productivity. In the face of the accelerating crisis of biodiversity extinction, priority should be given to protecting the dominant species and key functional groups in the region.

Anthropogenic nitrogen enrichment significantly alters plant community structure and productivity, often undermining long-term stability. However, the role of initial community structure, particularly species evenness, in mediating these stability responses remains inadequately understood. In this study, we conducted an 8-year nitrogen-addition experiment across four alpine grasslands on the Tibetan Plateau, which represent a natural gradient in initial evenness. Our results indicated that initial species evenness was crucial in mediating community stability under nitrogen enrichment. In low-evenness communities, stability exhibited a linear decline with increasing nitrogen, primarily driven by the instability of dominant species, specifically Carex parvula O. Yano in alpine meadows and Stipa purpurea Griseb. in alpine desert steppes. At lower nitrogen levels, dominant species biomass increased; however, as nitrogen levels rose, biomass variability increased, resulting in diminished overall stability. Conversely, high-evenness communities displayed nonlinear stability responses, buffered by species asynchrony. In the alpine meadow steppe, stability initially increased at low nitrogen levels but subsequently declined at higher nitrogen due to reductions in species evenness and functional redundancy. In the alpine steppe, stability first decreased at low nitrogen due to community imbalance, but compensatory dynamics among nitrogen-tolerant species, such as S. purpurea, restored stability at elevated nitrogen levels. These findings emphasize the diverse responses of alpine grasslands to nitrogen enrichment and underscore the significance of initial species evenness for ecosystem resilience. This study offers critical insights for forecasting ecosystem responses and formulating targeted management strategies in the context of global change. The long-term experiments conducted in the alpine grasslands of the Qinghai-Tibet Plateau revealed that initial species evenness plays a crucial regulatory role in community stability under nitrogen enrichment. The stability of communities with low evenness decreases linearly with nitrogen addition, driven by the instability of dominant species; while communities with high evenness exhibit a non-linear response through species asynchrony, demonstrating stronger ecological resilience. (sic)(sic): (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)4(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic) 8 (sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic);(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)((sic)(sic)(sic)(sic)(sic) Stipa purpurea Griseb.)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).

Droughts have intensified under climate change, threatening ecosystem stability. While rising atmospheric CO2 concentrations may enhance vegetation drought resistance, the net effect remains uncertain amid concurrent warming. Here we combine ecological modeling with multi-source observations to investigate how CO2 and warming jointly regulate vegetation drought responses on the Qinghai-Tibetan Plateau, a sensitive alpine region exposed to escalating drought threats under changing precipitation regimes. Using factorial scenarios to isolate individual forcings, we show that 40-year CO2 rise mitigated drought-induced productivity losses by 5.7 +/- 0.9% under constant temperature. However, in the presence of warming, rising CO2 intensifies drought stress by 5.2 +/- 0.5%, reflecting increased plant water demand and disrupted regional water supply-demand balance. Permafrost areas experienced the strongest CO2-driven drought alleviation under constant temperature, but also the greatest warming-induced reversal. These findings reveal interacting CO2-warming impacts on alpine vegetation drought responses, highlighting ecological risks for the plateau and other permafrost-dominant regions under future warming.

Grazing exclusion (GE) has been extensively implemented to alleviate grassland degradation and facilitate ecosystem restoration globally. However, how resource availability and GE duration jointly modulate the efficacy of GE remains unclear. Here, we investigated the impacts of 12 years of GE on plant productivity and species diversity across 19 long-term sites distributed along a resource gradient on the northern Qinghai-Tibetan Plateau (QTP). We found that GE consistently increased aboveground biomass, plant height and vegetation coverage. However, the magnitude of these responses was highly context-dependent. Specifically, GE resulted in significant increases in aboveground biomass in medium-resource areas (MRA) and high-resource areas (HRA) by 21.1% and 31.2%, respectively, whereas the increase observed in low-resource areas (LRA) was not statistically significant. Plant diversity responses also exhibited pronounced spatial and temporal dependence. GE significantly reduced community evenness by 40.2% and increased dominance by 34.7% in MRA but had no significant effects on either metric in LRA or HRA. Notably, prolonged GE in MRA shifted the trajectory of species richness from an initial decline to a subsequent positive response, alongside continuous increases in community dominance and reductions in community evenness. Regional-scale analyses further revealed a widespread increase in vegetation restoration potential (VRP) after GE, with the most pronounced enhancements (2.4%) observed in MRA. These findings underscore that although long-term GE can effectively enhance ecosystem productivity, it simultaneously poses a risk of disrupting community structural equilibrium, particularly under intermediate environmental conditions. By elucidating the effects of resource heterogeneity and temporal dynamics, this study provides a critical theoretical framework for developing context-dependent conservation strategies aimed at the sustainable management of alpine grassland ecosystems.

Nutrient enrichment can negatively impact the stability of various ecosystems. However, whether these impacts depend on biotic and abiotic factors, such as plant diversity and climate, remains unclear. Here, we investigated how climatic factors and plant diversity affected temporal stability of aboveground net primary production (ANPP) in responses to nitrogen (N) and phosphorus (P) additions and its biotic mechanisms over 4 years across seven Chinese grasslands spanning a climatic gradient (mean annual temperature: -0.38 to 8.75 degrees C; annual precipitation: 134.60 to 462.40 mm). We showed that N and NP additions significantly reduced temporal stability of ANPP, while P addition marginally reduced the temporal stability of ANPP across all sites. Importantly, nutrient effects at each site were inconsistent and were closely related with sites with initial richness and temperature seasonality. The structural equation modeling clarified that N and P addition alone mainly decreased community stability via decreasing dominant species stability. Notably, sites with higher species richness exhibited lower stability of dominant species and lower community stability under N or P enrichment. Taken together, our results highlight that effect of nutrient amendment on the stability of grassland ecosystems depends on local plant diversity shaped by specific climatic factors. This understanding is crucial for effective grasslands management in the context of global environmental change.

As droughts become longer and more intense, impacts on terrestrial primary productivity are expected to increase progressively. Yet, some ecosystems appear to acclimate to multiyear drought, with constant or diminishing reductions in productivity as drought duration increases. We quantified the combined effects of drought duration and intensity on aboveground productivity in 74 grasslands and shrublands distributed globally. Ecosystem acclimation with multiyear drought was observed overall, except when droughts were extreme (i.e., ≤1-in-100-year likelihood of occurrence). Productivity losses after four consecutive years of extreme drought increased by ~2.5-fold compared with those of the first year. These results portend a foundational shift in ecosystem behavior if drought duration and intensity increase, from maintenance of reduced functioning over time to progressive and profound losses of productivity when droughts are extreme.

Soil microbial residue carbon (MRC) represents a significant component of soil carbon pools and regulates the response of soil carbon sequestration to precipitation changes. However, the response of soil MRC to extreme drought and wetness and the underlying mechanisms in regional grassland ecosystems remain unclear. Here, we quantified the responses of soil MRC content to extreme drought and wetness and identified the key drivers using a coordinated precipitation change experiment across nine alpine and temperate grassland ecosystems in China. Extreme drought (-50% precipitation) reduced MRC content by 8% on average. In contrast, extreme wetness (+50% precipitation) unexpectedly caused a pronounced 24% average decline in MRC content. Under extreme drought, reduced plant biomass inhibited soil MRC formation, and soil microbial N enzyme activity accelerated soil MRC decomposition. Moreover, wetter ecosystems exhibited greater losses of soil MRC, whereas drier ecosystems experienced a smaller decline. Under extreme wetness, increased soil microbial N enzyme activity accelerated the decomposition and utilization of microbial residue due to intensified microbial nitrogen limitation, resulting in a reduction in MRC. Our findings challenged the conventional understanding that extreme wetness promotes MRC accumulation by revealing a stronger reduction in MRC content under extreme wetness than under extreme drought. By uncovering distinct mechanisms driving MRC responses to extreme drought and wetness, our study provides critical insights into the dynamics of microbial-derived carbon in grassland ecosystems under future climate change.

Long-term trends of vegetation spring phenology (i.e., start of season, SOS) under ongoing climate change have received widespread attention due to its implication for ecosystem carbon balance. However, the stability of SOS under short-term disturbance, such as extreme drought event, remains poorly understood. Here, we assessed the geographic patterns of SOS stability, encompassing multiple components (resistance, resilience, and temporal stability), in response to preseason extreme drought events using satellite-observed vegetation index and gridded drought index across the alpine grasslands of the Tibetan Plateau (TP). Higher resistance and temporal stability of SOS were generally observed in the meadow-dominated eastern TP, with declining westward along longitudinal gradients. Whereas, the resilience of SOS peaked in the semi-arid central plateau. The spatial coherence between resistance and temporal stability suggests that the consistency of SOS during drought periods (i.e., temporal stability) critically depends on its capacity to resist drought (i.e., resistance). The geographical detector model revealed that radiation and biodiversity were the primary drivers of the spatial distributions of SOS resistance and temporal stability, with higher resistance and temporal stability associated with lower radiation and greater biodiversity. In contrast, the contribution of environmental settings to SOS resilience was relatively lower than that of resistance, with a spatial trade-off between resistance and resilience across the TP, except in the western regions, where a distinct low resistance-low resilience pattern was observed. Overall, our findings provide novel insights into ecosystem stability under extreme droughts, and improve the representation of drought responses in alpine ecosystem within land surface models.

Climate change and human activities are increasingly influencing ecological communities. Within this context, increasing extreme snow events and persistent livestock grazing are known to pose significant challenges to alpine ecosystems on the Tibetan Plateau. However, the mechanisms driving long‐term community assembly and structural changes under these concurrent pressures remain unclear. Here, we used a 16‐year field experiment in a Tibetan alpine grassland to investigate the effects of spring snow addition and yak grazing on taxonomic, phylogenetic and functional community diversity and structure. We found that snow addition was the primary driver of community structure, while the effects of grazing were less pronounced. Specifically, snow addition shifted the phylogenetic structure from being random to overdispersed. This shift was driven by the selective loss of species with conservative resource‐use strategies (i.e. those with high leaf dry matter content [LDMC] and low‐specific leaf area), which were phylogenetically more closely related to the residents than were the gained species. In contrast, communities remained functionally clustered under all treatments. This resulted from opposing structural shifts in individual traits, where LDMC became more overdispersed, while plant height and leaf nitrogen content (LNC) became more clustered, driven by the loss of taller species and the gain of species with low LNC. This decoupling between phylogenetic and functional responses suggests that environmental filtering selects for convergent functional adaptations among phylogenetically distant species. Synthesis . Our findings highlight the importance of considering multi‐faceted diversity metrics when exploring community assembly and provide the first experimental evidence that long‐term snow addition reshapes plant phylogenetic community structure on the Tibetan Plateau. Importantly, the loss of conservative species suggests that altered snow regimes may potentially shift key ecosystem functions in alpine grasslands. Our findings also demonstrate that integrating species gain and loss is essential for a predictive understanding of long‐term community dynamics under global change.

Global warming is expected to change the diversity, composition, and functioning of plant communities. However, it remains unclear how warming alters the temporal stability of different aspects of plant communities and the extent to which these different aspects are interlinked or respond differently to warming. Here, using data from a 10-year, multi-level warming experiment in an alpine grassland, we quantified the temporal stability of three plant community aspects-species richness, composition, and cover-in response to warming scenarios that increase soil temperature by 0.4, 1.6, 2.1, and 2.5°C. We found a nonlinear concave stability response to warming for each of the three community aspects investigated. That is, moderate warming caused moderate increases in the stability of richness, composition, and cover, whereas severe warming caused strong decreases in stability. Additionally, we found that the processes contributing to stability differed among the three community aspects, with warming weakening the relationships between them. Severe warming reduced the stability of cover by reducing the stability of dominant species and species asynchrony. Compositional stability decreased due to declines in species richness, species asynchrony, and dominant species stability. Richness stability decreased due to a decline in species richness. Our results demonstrate that the stability of different community aspects responds nonlinearly to future warming scenarios, with moderate warming stabilizing but high-level warming destabilizing plant species richness, composition, and cover. Our findings emphasize the collective influence of species richness, species asynchrony, and dominant species stability as key factors modulating community stability in the context of global warming.

Evapotranspiration (ET) is a crucial component of both the water cycle and energy balance, with vegetation being a key factor influencing ET. Vegetation impacts ET primarily through two modes: vegetation growth change (VGC) and vegetation type conversion (VTC). Despite the different mechanisms by which VGC and VTC influence ET, previous studies have rarely differentiated their individual effects. This has left the relative contributions of VGC and VTC to ET changes unclear. To address this gap, this study focuses on the arid and semiarid regions of China (ASAC), where substantial vegetation changes have been observed. The spatiotemporal patterns of ET in ASAC were analyzed using remote sensing ET data from 2001 to 2018. The leaf area index (LAI) and land use/land cover (LULC) data were incorporated to perform pairwise comparison and contribution analysis to investigate the specific effects of VGC and VTC on ET. The results revealed a significant increase in mean annual ET across ASAC, with a rate of 4.5 mm/yr (p < 0.05). This increase was more pronounced in forest land and cropland compared to grasslands. ET increased across all seasons, with the largest increase occurring in summer, accounting for approximately 50 % of the annual ET increment. The pairwise comparison and contribution analysis indicated that ET in ASAC is more sensitive to vegetation greening than to VTC. VTC played a moderating role in ET changes, with relative contribution ranging from 1.3 % to 57.8 % across different LULC change types. These findings enhance our understanding of how vegetation changes influence ET. They can also provide valuable insights for land management strategies in ASAC, aiming to optimize vegetation construction and promote ecosystems sustainability.

Litter decomposition is a critical biogeochemical process for carbon and nutrient cycling in terrestrial ecosystems. Ultraviolet (UV) radiation has been recognized to accelerate litter-derived C release in arid and semi-arid ecosystems; yet its spatial controls on determining the regional pattern of litter decomposition are poorly explored. Moreover, the limited understanding of how UV radiation interacts with traditional decomposition drivers, such as climate and litter quality, significantly restricts our ability to accurately quantify the contribution of UV-driven photodegradation to large-scale carbon turnover. In this study, we established a coordinated, distributed UV-manipulation network, spanning 3500-km and covering four grassland ecosystem types, to assess the impact of UV radiation on litter decomposition across gradients of aridity, UV dose, and litter lignin/N ratio. With a modified modeling approach, we further quantified the contribution of UV radiation to litter layer decomposition across temperate grasslands in China. After more than three years in the field, we found that UV attenuation reduced litter mass loss across climatic gradients. The UV-induced facilitation effect primarily occurs in the latter stages of decomposition. The strength of photochemical degradation increased with higher cumulative UV dose, amplified by environmental aridity and litter lignin/N ratio. Across Chinese temperate grasslands, UV exposure shortens mean residence time (MRT) of litter layer by 0.40 years, representing a 16.85% reduction. Hotspots, where UV reduces MRT by over a year, are primarily located in arid and high-altitude grasslands. The sensitivity analysis indicates that the vulnerability of grassland litter decomposition to UV fluctuations intensifies as environmental aridity increases. These findings reveal the pervasiveness of UV-driven litter photodegradation across diverse grasslands and provide a comprehensive framework to improve the predictability of litter-originated C turnover in dryland ecosystems, enabling more constrained projections of terrestrial carbon-climate feedbacks in the context of global UV fluctuations and aridification.