Drought events and nitrogen deposition are substantially modifying the stability of terrestrial ecosystems. Previous studies have mostly investigated these factors separately, with an emphasis on productivity stability, leaving their combined effects on multiple dimensions of ecosystem stability poorly understood. We conducted a four-year grassland manipulative experiment to examine how three drought scenarios-intense drought, chronic drought, and precipitation frequency reduction-interact with nitrogen addition to influence community compositional stability and productivity stability. The results showed that drought and nitrogen enrichment independently influenced grassland stability without significant interactions. Both intense and chronic drought reduced productivity stability, while reduced precipitation frequency decreased compositional stability. Nitrogen addition decreased both types of stability. Productivity stability was driven by the dominant species' productivity stability or a combination of it and species asynchrony, depending on the drought scenario. Compositional stability consistently depended on the dominant species' compositional stability. Compositional and productivity stability remained decoupled across treatments. This study provides the first empirical evidence of the divergent responses of grassland compositional and productivity stability to various drought scenarios under nitrogen enrichment. Our findings highlight the importance of prioritizing dominant species and promoting species coexistence with diverse environmental responses to maintain stable grassland composition and productivity under global change. Based on a four-year manipulative experiment, this study compared the effects of different drought scenarios and nitrogen enrichment on compositional and productivity stability in a temperate grassland. We found that these two dimensions of stability respond differently to drought types and nitrogen addition and remain persistently decoupled, highlighting the need to prioritize dominant species and promote the coexistence of species with diverse environmental response strategies to maintain grassland stability under global change. (sic)(sic):(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(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)(sic)(sic), (sic)(sic)3(sic)(sic)(sic)(sic)(sic)((sic)(sic)(sic)(sic),(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic))(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic):1)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).2)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic);(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).3)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).

Environmental changes, including nitrogen (N) enrichment and altered precipitation, significantly influence phosphorus (P) dynamics in semi-arid grassland soils. However, the long-term effects of N and water additions on microbial communities and key P cycling genes remain unclear. This study investigates how long-term nitrogen (N) and water additions affect soil phosphorus (P) fractions, microbial community composition, and the abundance of key P-cycling genes in a semi-arid grassland ecosystem of Inner Mongolia, China. Drawing on a 17-year field experiment (initiated in 2005), our findings demonstrate that combined N and water inputs significantly enhanced labile and moderately labile P fractions NaHCO3-Pi, NaHCO3-Po, NaOH-Pi, NaOH-Po, and HClD-Pi by 58.9 %, 119.5 %, 26 %, and 7.4 %, respectively. HClD-Pi, the dominant contributor to total P, was mobilized primarily in water-added treatments. Labile P followed the order WN10 > N10 > WCK > CK; moderate-labile P ranked WN10 > N10 > WCK > CK; and non-labile P ranked N10 > WN10 > CK > WCK. Water addition suppressed P-starvation-responsive genes (phoX, phnK, ppk) and enhanced mineralization and solubilization genes (phoD, gcd, pqqC). Variation Partitioning Analysis showed microbial communities explained 31 % of labile P variation, while enzyme activity accounted for 35 % of moderate-labile P. PCoA showed distinct microbial and gene composition under WN10. Random Forest, Mantel tests, and VPA confirmed shifts in microbial function and soil P dynamics. These findings demonstrate how long-term nutrient and water additions reshape P fractions and microbial P acquisition strategies. This study offers mechanistic insight into the microbial and biochemical regulation of P availability and highlights the importance of managing N and water to increase labile P, stimulate microbial activity, and reduce P fixation. These results have broad implications for improving nutrient efficiency and sustainability in semi-arid grassland ecosystems under global change.

ABSTRACT Mountain forests in arid regions are under long‐term water limitation, and different soil genetic horizons have distinct differences in water storage and root accessibility. Therefore, investigating the relationship between plant water uptake patterns and soil genetic horizons in arid mountain forests can help distinguish the hydrological functions of different soil horizons. In this study, we investigated Picea schrenkiana forests in the Tianshan Mountains at three elevations: 2200, 1800 and 1450 m. During the growing seasons over two consecutive years, soil water from the humus, eluvial and illuvial horizons, together with plant xylem water, was collected and the MixSIAR model was used to quantify the contributions of different soil genetic horizons to water uptake by P. schrenkiana . The results showed that during a wetter year and the early growing season, trees mainly used water from the humus horizon, whereas during a drier year or the late growing season, they increased their uptake of water from the eluvial and illuvial horizons. Along the elevational gradient, P. schrenkiana at 2200 and 1800 m mainly used water from the humus horizon. However, at 1450 m, influenced by root distribution and hydraulic connectivity, P. schrenkiana mainly used water from the eluvial horizon even when the humus horizon had relatively high soil water content. This study indicates that the humus horizon is an important water source for P. schrenkiana , and its role in maintaining forest hydrological health may exceed that of the eluvial and illuvial horizons. Higher soil water content does not necessarily indicate a higher contribution to plant water uptake, as plant water uptake is also related to root distribution, water availability and atmospheric drought stress. This study clarifies the important ecohydrological role of the humus horizon in arid mountain forests and helps improve our understanding of the mechanisms underlying tree water uptake in these ecosystems.

The rising frequency and intensity of drought, coupled with widespread nitrogen (N) fertilization, are profoundly affecting carbon cycling in typical steppes. However, how soil respiration (Rs) and its components—heterotrophic respiration (Rh) and autotrophic respiration (Ra)—respond to different drought scenarios and interact with N addition remains unclear. Based on observations conducted during the final three years of a four-year study, we investigated the effects of three drought scenarios (intense drought, chronic drought and reduced rainfall frequency) and N addition on Rs, Rh, and Ra in a typical steppe in northern China. Intense drought and chronic drought decreased Rs, whereas reduced rainfall frequency had divergent effects on Rh (stimulation) and Ra (reduction), thereby stabilizing Rs. Nitrogen addition enhanced Rs, primarily by stimulating Ra. No significant interaction between drought and N was observed. Structural equation models demonstrated that intense drought and chronic drought decreased Rh and Ra primarily by suppressing specific microbial groups and Leymus chinensis root biomass, respectively, and by reducing soil temperature, moisture, and associated soil biochemical properties. In contrast, reduced rainfall frequency stimulated Rh by lowering the fungi-to-bacteria ratio, while suppressing Ra through a reduced grass biomass-to-forb biomass ratio, resulting in no net change in Rs. Across drought scenarios, N addition stimulated Ra mainly by increasing L. chinensis root biomass and improving soil N nutrients, temperature and moisture. Our study reveals divergent responses and sophisticated mechanisms of soil respiration to different drought scenarios and nitrogen fertilization in typical steppes, providing critical insights for predicting regional carbon cycling and guiding water and N management in typical grasslands.

Atmospheric nitrogen deposition and increased precipitation are key drivers of grassland carbon cycling; however, their long-term interactive effects and mechanisms remain poorly understood. Based on a 20 year field experiment with sustained nitrogen (10 g N m-2 yr-1) and precipitation (+∼50% precipitation) addition in a temperate grassland in northern China, we found that both nitrogen deposition and precipitation addition significantly enhanced net ecosystem CO2 exchange (NEE), ecosystem respiration (ER), and gross ecosystem productivity (GEP), with additive effects of nitrogen and water addition on NEE and GEP. Structural equation modeling revealed that nitrogen deposition increased carbon fluxes by enhancing community-weighted mean leaf area (CWMLA) and chlorophyll content of dominant species, whereas precipitation addition stimulated carbon fluxes mainly through improving soil moisture (SM) and CWMLA. Notably, nitrogen deposition and precipitation addition enhanced GEP to a greater extent than ER, which led to a net ecosystem carbon sink and exhibited a significant interaction effect exclusively on ER. These findings underscore previously underexplored mechanisms linking plant trait and SM dynamics to carbon flux responses. Our results indicate that long-term increases in nitrogen deposition and precipitation may accelerate carbon cycling in temperate grasslands and enhance the carbon sequestration function of grasslands. Our study provides unique long-term evidence to demonstrate that nitrogen and precipitation additions exert progressively stronger positive effects on grassland carbon fluxes over time, providing critical insights for predicting ecosystem responses to sustained climate change and informing adaptive nitrogen and SM management strategies.

Long-term interactive effects of increased precipitation and nitrogen deposition on grassland carbon cycling remain poorly understood, despite their individual impacts being well documented through short-term experiments. Based on a three-year investigation within a 19-year precipitation (+ 180 mm per year) and nitrogen addition (+ 10 g N m-2 yr-1) experiment in temperate grasslands of northern China, we demonstrated that while long-term increased precipitation significantly stimulated soil respiration (Rs) and its components (heterotrophic [Rh] and autotrophic respiration [Ra]), long-term N enrichment exerted suppressive effects. Crucially, N enrichment offset 86.7 % of the precipitation-induced stimulation of Rs, leaving only 13.3 % of the stimulation under combined N and precipitation addition. Furthermore, N addition also weakened the promotive effect of increased precipitation on both Rh and Ra. Mechanistic analyses revealed that Rh was mainly regulated by soil moisture, beta-glucosidase (BG) activity, and the abundance of the key carbon-degrading functional gene (apu). Whereas, Ra was primarily driven by soil moisture interacting with vegetation characteristics, including species richness, leaf area, and leaf C:N ratio. Also, by providing the first experimental evidence that long-term N deposition can counteract enhanced soil C emissions under increased precipitation in grasslands through biochemical pathways and biotic restructuring, our findings advance the predictive understanding of grassland C cycling under concurrent global change scenarios.

Several studies have explored the linkages among biodiversity, ecosystem functions, and services; however, how biodiversity affects bundles of ecosystem services through ‘ecosystem traits' remains unknown, especially in ecologically fragile drylands. In this study, species‐specific plant traits were correlated to ecosystem services at the community level through transect sampling of shrublands in Northwest China using a trait‐based approach. It revealed some biodiversity–ecosystem service (ES) relationships in drylands and how environmental pressures (sites with high aridity, precipitation seasonality, and soil total salt) and human activities affect them. We found synergistic relationships among ESs at both the species and community levels, and environmental pressures and anthropogenic activities such as cotton cultivation and grazing are important drivers of ES decline at community level. However, environmental pressure did not reduce the alpha diversity such as species richness, Simpson, Shannon–Wiener, Margalef and Pielou index of the shrublands, and the species richness of shrublands was decoupled from the ESs. Our findings highlight the vulnerability and sensitivity of drylands and show that rational human production activities are important for maintaining ESs in drylands.

The photosynthetic response of plants to drought has been widely explored, primarily through indoor cultivation or short-term physiological monitoring. However, studies linking the photosynthesis of forage with plant traits and production under various drought conditions, especially in the context of global precipitation changes, are limited. We conducted a four-year field experiment involving different precipitation treatments: ambient precipitation, intense drought (ID, precipitation exclusion during June), chronic drought (CD, reducing half precipitation amount from June to August), and reducing half precipitation frequency from June to August (RF, precipitation redistribution without changing precipitation amount). Our results showed that ID and CD significantly decreased the actual maximum photochemical quantum yield of PSII (cPSII) and maximum photochemical quantum yield (Fv/Fm), indicating a decline in photosynthetic capacity in Leymus chinensis. Meanwhile, the increase in regulatory energy dissipation quantum yield (c(NPQ)) highlighted enhanced photoprotection. Additionally, the CD increased the non-regulatory energy dissipation quantum yield (c(NO)), indicating that the photoprotection mechanism was insufficient to dissipate excess excitation energy, leading to photodamage at the reaction center. In contrast, under the RF scenario, plants effectively managed excess excitation energy by increasing c(NPQ), which prevented damage and maintained stable cPSII and Fv/Fm levels. Through regulating leaf area, drought increased c(NO) and decreased Fv/Fm. Although this strategy mitigated further photosynthetic damage, it also reduced photosynthetic efficiency and productivity of L. chinensis. This study represents the first exploration of patterns and mechanisms of plant photosynthetic processes in response to diverse drought scenarios. It underscores the crucial role of key plant traits, i.e. leaf area, in regulating photosynthetic responses amid changing precipitation patterns, and provides valuable information for grassland management and continuous forage supply.

In recent years, China’s “greening” trend has drawn great attention. However, does this truly represent ecological improvement? This study aims to figure it out on the mountain–oasis–desert ecosystem in the rid region of Northwest China. By first exploring the vegetation changes and the influence of climate factors and human activities on these changes, we then assessed the regional ecological quality using a combination of the Remote Sensing Ecological Index (RSEI) and the InVEST Habitat Quality Model. The results revealed that the NDVI was indeed increased, but the increase was primarily driven by cropland expansion, with significant NDVI and RSEI growth confined to oases. When croplands were excluded, RSEI values dropped substantially, and 20.9% of the region shows noticeable ecological quality deterioration. Remarkably, 75% of areas with improved RSEI ratings are cultivated lands, which concealed the degradation of natural ecosystems. The InVEST model highlights intensified regional degradation, with habitat quality declining and 9.1% of grasslands converted into croplands. Hurst index projections show 47.5% of vegetation faces sustained degradation. Thus, the observed “greening” primarily reflects cropland expansion rather than ecological improvement. Natural ecosystems in mountainous and desert areas face ongoing severe degradation. This research emphasizes the urgent need for arid regions to balance agricultural expansion with ecological conservation.

Intraspecific variation (Intra-V) has played an important role in determining the responses of ecosystem functions to climate change. However, its specific role in the regulation of ecosystem functions during community assembly is less investigated. In this study, we conducted a transect survey in northwest China and determined different plant functional types, namely resource-conservative, medium, and resource-acquisitive strategies, which describe resource-use strategies of plants in multi-functional dimensions. Plant functional traits including canopy, wood density (WD), height, specific leaf area (SLA), and leaf nitrogen (N) and phosphorus (P) concentrations were determined. Ecological filters, including external filtering (assembly processes at the regional scale), internal filtering (assembly processes within a certain community), and functional redundancy, were employed to examine plant environment interactions. We found that with the decrease in environmental pressure, dominant shrub plants changed from conservative to acquisition species in drylands. Specifically, a benign environment (such as stable and adequate precipitation, loose soil, and increased acid deposition) significantly increased plant mean traits, such as SLA and WD of shrubs, especially for conservative strategy plants. In addition, a benign environment mainly reduced the functional redundancy of SLA (FRedSLA) by strengthening internal filtering and, ultimately, increased aboveground biomass but decreased species richness. Our results suggest that conservative strategy plants with stronger adaptability to the external environment may exhibit more competitive advantages and play a more important role in community construction under future climate scenarios of gradual warming and wetting in northwest China. Our results also revealed that trait-based Intra-V may be a more reasonable ecological filter than plant mean traits for predicting the structure and function of dryland ecosystems.

Soil salinization may affect biodiversity and species composition, leading to changes in the plant community structure. However, few studies have explored the spatial pattern of soil salinization and its effects on shrub community structure at the ecosystem scale. Therefore, we conducted a transect sampling of desert shrublands in Northwest China during the growing season (June-September) in 2021. Soil salinization (both the degree and type), shrub community structure (e.g., shrub density and height), and biodiversity parameters (e.g., Simpson diversity, Margalf abundance, Shannon-Wiener diversity, and Pielou evenness indices) were used to assess the effects of soil salinization on shrub community structure. The results showed that the primary degree of soil salinization in the study area was light salinization, with the area proportion of 69.8%. Whereas the main type of soil salinization was characterized as sulfate saline soil, also accounting for 69.8% of the total area. Notably, there was a significant reduction in the degree of soil salinization and a shift in the type of soil salinization from chloride saline soil to sulfate saline soil, with an increase in longitude. Regional mean annual precipitation (MAP), mean annual evapotranspiration (MAE), elevation, and slope significantly contributed to soil salinization and its geochemical differentiation. As soil salinization intensified, shrub community structure displayed increased diversity and evenness, as indicated by the increases in the Simpson diversity, Shannon-Wiener diversity, and Pielou evenness indices. Moreover, the succulent stems and leaves of Chenopodiaceae and Tamaricaceae exhibited clear advantages under these conditions. Furthermore, regional climate and topography, such as MAP, MAE, and elevation, had greater effects on the distribution of shrub plants than soil salinization. These results provide a reference for the origin and pattern of soil salinization in drylands and their effects on the community structure of halophyte shrub species.

Drought and nitrogen enrichment could profoundly affect the productivity of semiarid ecosystems. However, how ecosystem productivity will respond to different drought scenarios, especially with a concurrent increase in nitrogen availability, is still poorly understood. Using data from a 4-year field experiment conducted in a semiarid temperate steppe, we explored the responses of aboveground net primary productivity (ANPP) to different drought scenarios and nitrogen addition, and the underlying mechanisms linking soil properties, plant species richness, functional diversity (community-weighted means of plant traits, functional dispersion) and phylogenetic diversity (net relatedness index) to ANPP. Our results showed that completely excluding precipitation in June (1-month intense drought) and reducing half the precipitation amount from June to August (season-long chronic drought) both significantly reduced ANPP, with the latter having a more negative impact on ANPP. However, reducing half of the precipitation frequency from June to August (precipitation redistribution) had no significant effect on ANPP. Nitrogen addition increased ANPP irrespective of drought scenarios. ANPP was primarily determined by soil moisture and nitrogen availability by regulating the community-weighted means of plant height, rather than other aspects of plant diversity. Our findings suggest that precipitation amount is more important than precipitation redistribution in influencing the productivity of temperate steppe, and nitrogen supply could alleviate the adverse impacts of drought on grassland productivity. Our study advances the mechanistic understanding of how the temperate grassland responds to drought stress, and implies that management strategies to protect tall species in the community would be beneficial for maintaining the productivity and carbon sequestration of grassland ecosystems under climate drought.

Background: Soil acidification caused by anthropogenic activities may affect soil biochemical cycling, biodiversity, productivity, and multiple ecosystem-related functions in drylands. However, to date, such information is lacking to support this hypothesis. Methods: Based on a transect survey of 78 naturally assembled shrub communities, we calculated acid deposition flux in Northwest China and evaluated its likely ecological effects by testing three alternative hypotheses, namely: niche complementarity, mass ratio, and vegetation quantity hypotheses. Rao's quadratic entropy and community-weighted mean traits were employed to represent the complementary aspect of niche complementarity and mass ratio effects, respectively. Results: We observed that in the past four decades, the concentrations of exchangeable base cations in soil in Northwest China have decreased significantly to the extent of having faced the risk of depletion, whereas changes in the calcium carbonate content and pH of soil were not significant. Acid deposition primarily increased the aboveground biomass and shrub density in shrublands but had no significant effect on shrub richness and ecosystem multifunctionality (EMF), indicating that acid deposition had positive but weak ecological effects on dryland ecosystems. Community weighted mean of functional traits (representing the mass ratio hypothesis) correlated negatively with EMF, whereas both Rao's quadratic entropy (representing the niche complementarity hypothesis) and aboveground biomass (representing the vegetation quantity hypothesis) correlated positively but insignificantly with EMF. These biodiversity–EMF relationships highlight the fragility and instability of drylands relative to forest ecosystems. Conclusions: The findings from this study serve as important reference points to understand the risk of soil acidification in arid regions and its impacts on biodiversity–EMF relationships.

The increasing frequency of drought events and nitrogen deposition have fundamentally changed soil microbial functions in terrestrial ecosystems. However, most studies have mainly concentrated on the impact of a single environmental factor on ecosystem functions; how drought and nitrogen enrichment interactively affect soil multifunctionality remains largely unknown. In this study, the effects of different drought scenarios [intense drought (ID), chronic drought (CD), and reduced rainfall frequency (RF)] and nitrogen addition on soil microbial biomass, and soil multifunctionality (determined using soil enzyme activity) were examined in the fourth year of a field manipulative experiment conducted in a typical steppe in northern China. The results demonstrated that both ID and CD significantly reduced soil multifunctionality, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN). The CD treatment also decreased the ratio of MBC to MBN, while RF had less impacts on soil multifunctionality and the biomass of soil microbes. In contrast, nitrogen addition enhanced soil multi- functionality, MBC and MBN. Structural equation modeling analysis demonstrated that drought decreased soil multifunctionality directly and indirectly by reducing MBN and soil water content, whereas nitrogen addition increased soil multifunctionality mainly by increasing MBN and soil inorganic nitrogen. This study provides the first experimental evidence of the opposing impacts of reduction in precipitation and nitrogen enrichment on soil microbial biomass and soil multifunctionality in a semiarid typical steppe, and suggests that nitrogen fertilization could be an effective measure to alleviate the negative effects of climate drought on soil functions in nitrogen- and water-limited grassland ecosystems.

The impending rise in drought events in grasslands of northern China over the next few decades, coupled with escalating nitrogen (N) deposition, will have an important impact on nutrient resorption. Previous research has mostly focused on examining the individual effect of specific drought scenario or N enrichment on nutrient resorption. Nonetheless, the impacts of different drought regimes on the resorption of nutrients have rarely been distinguished, especially under the scenario of N enrichment in temperate typical steppe in Inner Mongolia, we studied how intense drought (excluding 100 % rainfall in June), chronic drought (excluding 50 % rainfall during June-August), reduced rainfall frequency (reducing half rainfall events without changing rainfall amount in June-August), and N deposition (0 and 10 g N m(-2) yr(-1)) affected the efficiency of plants in reabsorbing N and phosphorus (P). Both intense and chronic drought significantly reduced N (by 9.41 % and 9.53 %, respectively) and P resorption efficiency (by 6.71 % and 6.62 %, respectively) in plant communities (defined as the proportion of N and P nutrient resorption from senescing leaves), however reducing rainfall frequency had less effects on plant community N and P resorption efficiency. Nitrogen deposition had no effects on N and P resorption efficiency. Drought and N addition interacted to affect plant community P resorption efficiency. Structural equation modeling (SEM) showed that drought reduced N and P resorption efficiencies in plant communities by directly decreasing soil moisture, suppressing nutrient concentrations in green leaves, and enhancing soil nutrient content. Nitrogen deposition reduced P resorption efficiency by reducing P concentration in green leaves, but this effect was offset by the reduction of soil P availability. These results imply that rainfall amount is more important than rainfall frequency in determining the nutrient resorption efficiency of plant communities in the typical steppe. This study highlights the importance of soil water and N availabilities as well as nutrient concentrations in green leaves in modulating the responses of plant nutrient resorption to global change in the typical steppe.

Haloxylon ammodendron and Haloxylon persicum are the dominant species in the deserts of Central Asia. As groundwater exploration has resulted in a decline in groundwater depth in this region, the impact on the regeneration of these two Haloxylon populations calls for urgent attention. Therefore, we conducted an intensive vegetation survey, including population density, age structure and seed production and seed characteristics, along a groundwater depth gradient in the Gurbantunggut Desert of Central Asia. The result shows that for H. ammodendron, groundwater depth of 15m is its survival and regeneration limit, beyond which this species cannot grow. However, for H. persicum, this limit does not apply. Instead, declined groundwater depth promotes a reproduction strategy with low seed quantity, high quality, and a high germination rate for H. ammodendron. Ultimately, H. ammodendron exhibits a tighter regeneration trait coordination, with a reasonable age structure being crucial for its population continuation and environmental adaptation. In contrast, H. persicum demonstrates higher resource acquisition and reproductive ability, along with tolerance to groundwater depth decline. In conclusion, if the groundwater depth decline continues, the continuation of H. ammodendron will be seriously threatened but H. persicum will not be. This study is beneficial for evaluating the future trend of vegetation cover in desert region and planning water resources management in Central Asia.

The increases in extent and frequency of extreme drought events and increased nitrogen (N) deposition due to global change are expected to have profound impacts on carbon cycling in semi-arid grasslands. However, how ecosystem CO2 exchange processes respond to different drought scenarios individually and interactively with N addition remains uncertain. In this study, we experimentally explored the effects of different drought scenarios (early season extreme drought, 50 % reduction in precipitation amount, and 50 % reduction in precipitation events) and N addition on net ecosystem CO2 exchange (NEE), ecosystem respiration (ER), and gross ecosystem productivity (GEP) over three growing seasons (2019-2021) in a semi-arid grassland in northern China. The growing-season ecosystem carbon fluxes in response to drought and N addition were influenced by inter-annual precipitation changes, with 2019 as a normal precipitation year, and 2020 and 2021 as wet years. Early season extreme drought stimulated NEE by reducing ER. 50 % reduction in precipitation amount decreased ER and GEP consistently in three years, but only significantly suppressed NEE in 2019. 50 % reduction in precipitation events stimulated NEE. Nitrogen addition stimulated NEE, ER, and GEP, but only significantly in wet years. The structural equation models showed that changes in carbon fluxes were regulated by soil moisture, soil temperature, microbial biomass nitrogen (MBN), and the key plant functional traits. Decreased community-weighted means of specific leaf area (CWMSLA) was closely related to the reduced ER and GEP under early season extreme drought and 50 % reduction in precipitation amount. While increased community-weighted means of

In recent years,with frequent changes in land use and extensive reclamation of farmlands,soil saliniza-tion has become an environmental factor leading to the degradation of cultivated land quality and hindering the development of oasis-based agriculture on the northern slopes of the Tianshan Mountains.However,an objective understanding of the current status of soil salinization in cultivated lands and its evolution is lacking.This study,based on detailed survey data,actual soil measurements,and the China Land Cover Dataset,compares the advan-tages and disadvantages of traditional interpolation models and random forest interpolation models for estimating the salt content in the topsoil layer(0-30 cm).The most accurate quantitative prediction model was selected to quantitatively predict as well as obtain the distribution and change characteristics of the salt content in the plow layer soil of the northern slope of the Tianshan Mountains.By using space for time,the salt content in the plow layer soil of newly reclaimed farmland over 30 years was compared to understand the impact of cultivation dura-tion.The results showed that:(1)Compared to traditional interpolation methods,the random forest algorithm could more accurately predict the soil salt distribution of salinized land.(2)In the northern Tianshan region,there was significant spatial heterogeneity in the salt content of the topsoil,with salt concentrations in the higher alti-tude areas leaching with runoff and accumulating in the lower altitude areas near rivers or in depressions close to the deserts.(3)With the extension of cultivation years,the overall salt content in the plow layer soil of the north-ern slope of the Tianshan Mountains decreased,and the degree of soil salinization converged at a moderate level,trending toward equilibrium or"centralization."This study has enhanced the understanding of the current salini-zation status of cultivated land and the alterations in soil salinity from the reclamation of virgin wastelands to cul-tivated lands.It provides theoretical support for the development,management,and effective use of reserve land resources in arid areas,and offers a scientific basis for the sustainable development of agriculture.

IntroductionDryland ecosystems face serious threats from climate change. Establishing the spatial pattern of ecosystem multifunctionality, maximum height and the correlation of biodiversity patterns with climate change is important for understanding changes in complex ecosystem processes. However, the understanding of their relationships across large spatial areas remains limited in drylands.MethodsAccordingly, this study examined the spatial patterns of ecosystem multifunctionality, maximum height and considered a set of potential environmental drivers by investigating natural shrub communities in Northwest China.ResultsWe found that the ecosystem multifunctionality (EMF) and maximum height of shrub communities were both affected by longitude, which was positively correlated with the precipitation gradient. Specifically, the EMF was driven by high precipitation seasonality, and the maximum height was driven by high precipitation stability during the growing season. Among the multiple biodiversity predictors, species beta diversity (SD-beta) is the most common in determining EMF, although this relationship is weak.DiscussionUnlike tree life form, we did not observe biodiversity-maximum height relationships in shrub communities. Based on these results, we suggest that more attention should be paid to the climatical fluctuations mediated biodiversity mechanisms, which are tightly correlated with ecosystem’s service capacity and resistance capacity under a rapid climate change scenario in the future.

Enzyme activity plays an important role in soil biochemical processes and is a key factor driving nutrient cycling. Although a great number of studies examined the effects of nitrogen (N) enrichment and water (W) addition on soil enzyme activity, most of them focused on the effect of only one resource and are based on short-term investigations. The separate and interactive effects of long-term changes in nitrogen and water on soil enzyme activity remain largely unexplored. In this study, we demonstrated the responses of two types of soil enzyme, β-1,4-glucosidase (BG) and acid phosphatase (APA), to increased nitrogen and water based on a 16-year experiment conducted in a typical grassland in northern China. The results show that: (1) nitrogen addition inhibited BG and APA in 2019 and 2020; (2) water addition had no significant effect on BG activity, but significantly reduced APA activity in 2020; and (3) redundancy analysis (RDA) showed that nitrogen and water addition affected soil enzyme activity mainly by affecting soil microbial biomass carbon (MBC). The present research offers a comprehensive explanation of how atmospheric nitrogen deposition and precipitation patterns affect the characteristics of microorganisms and the cycling of nutrients in grassland ecosystems.