Net ecosystem productivity (NEP) is a key indicator for estimating carbon sink dynamics in terrestrial ecosystems. Existing studies on carbon sink dynamics in Northwest China have uncertainties in quantifying spatiotemporal variations of NEP and their driving factors. This study estimated NEP across ecosystems in Northwest China during 2000-2020 using multi-model integration, and analyzed its spatiotemporal patterns and drivers. Results showed that the annual average NEP was 97.98 g C/(m²∙a), with higher values at eastern and western margins and lower values in central hinterland. Strong carbon sink areas included the Yili River Basin and northern slope of Tianshan Mountains, while low carbon sink areas concentrated in eastern Xinjiang Uygur Autonomous Region (Eastern Xinjiang) and Alxa-Ejin Plateau. NEP trended upward from 79.22 g C/(m²∙a) in 2000 to 109.03 g C/(m²∙a) in 2020 with low variability and strong persistence, suggesting continuous growth. NEP significantly and positively correlated with near-infrared reflectance of vegetation (NIRv), weakly with climate factors, and negatively with socio-economic density indicators. Topographically, NEP peaked at 2.0-2.4 km elevation, 15°-25° slopes, and north-facing aspects. Changes in ecosystem type significantly influenced NEP, with bare land conversion into grassland/cropland enhancing carbon sinks. Results of this study highlight the need for ecological restoration and rational land use to boost carbon sequestration in this ecologically sensitive region.

Ecological security patterns (ESPs) represent an effective way to maintain regional ecological security and promote regional sustainable development. This study investigated the spatiotemporal variations of ESPs in the West Liaohe River Basin (WLRB), China during 2000-2020 on the basis of five key ecosystem services (net primary production, soil conservation, habitat quality, water retention, and soil loss by wind). On the basis of the Geodetector model, we initially measured the explanatory rates of various natural and anthropogenic factors on the spatial differentiation of ecological sources and ecological corridors. The Geographically and Temporally Weighted Regression (GTWR) model was subsequently used to elucidate the driving mechanism of ESPs at the interannual scale. During 2000-2020, a "fan-shaped" ESP of "two zones, three belts, and many branches" formed in the WLRB. Natural factors dominated the spatial distribution of ESPs, and the average spatial explanation rate for ecological sources and ecological corridors was 23.86%, which was higher than that of anthropogenic activities (13.29%). However, anthropogenic activities amplified the spatiotemporal variations in ESPs. On this basis, this study proposed an ecological security protection and regulation strategy from three aspects, namely, regional priority, suitability analysis, and risk regulation, which might provide a working direction for regional practical management. This study extends the paradigm of ESP research and offers an important theoretical basis for regional ecological security, from "passive management" to "active management".

Drought is among the most destructive and recurrent natural disasters worldwide. In recent decades, the frequency of drought events has increased, exerting significant impacts on socioeconomic development. The propagation of meteorological drought (MD) to soil moisture drought (SMD) is a common natural process; however, its dynamics across different seasons and vegetation types on the Qinghai-Xizang Plateau, as well as the underlying meteorological driving mechanisms, remain insufficiently understood. This study utilized precipitation and soil moisture data from the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5)-Land reanalysis dataset for the period 1982-2022. The standardized precipitation index (SPI) and standardized soil moisture index (SSMI) were employed to characterize MD and SMD, respectively. By integrating run theory with an optimal parameter geographical detector (OPGD) model, this study systematically analyzed the average duration and propagation time of MD and SMD across the Qinghai-Xizang Plateau, and quantitatively evaluated the explanatory power of various meteorological and topographical factors influencing drought propagation. The results indicated that the mean duration of SMD across the Qinghai-Xizang Plateau from 1982 to 2022 was generally longer than that of MD. Significant seasonal differences in propagation time were observed, with the average propagation time ranked as winter (21 d)>spring (14 d)>autumn (10 d)>summer (8 d). Spatial variability of propagation time was more pronounced in spring and winter than in summer and autumn. Furthermore, the analysis of driving mechanisms revealed that drought propagation from MD to SMD on the Qinghai-Xizang Plateau was primarily influenced by precipitation (relative contribution proportion of 51.9%), followed by evaporation (15.1%) and snowmelt (13.6%), with the strongest interaction effects associated with precipitation. Although the dominant factors across different vegetation types were generally consistent with those for the entire plateau, solar radiation also showed a relatively high contribution (average 13.9%) across vegetation types. In summary, this study provides a scientific basis for improving drought early warning systems and optimizing water resource management strategies.

The Taklimakan Desert plays an important role in understanding the provenance of the iron hypothesis, which posits that iron availability limits phytoplankton growth in oceans. However, the modern processes governing iron provenance in mountain-desert transition areas remain largely unknown. To address this issue, this study systematically sampled surface sediments along an east-west transect in the Kunlun-Altun piedmont, and analyzed their grain sizes, magnetic susceptibility, total organic carbon (TOC) content, total nitrogen (TN) content, X-ray diffraction (XRD) spectra, and major elements. The grain size distributions (GSDs) at low (<2000 m a.s.l.) and high (>2000 m a.s.l.) altitudes suggested that surface sediments originated from the Kunlun-Altun Mountains, and each exhibited distinct sediment reworking and transport histories. Low chemical index of alteration (CIA) values (<65.00) confirmed that physical weathering was the predominant process and that limited chemical alteration occurred, with the preservation of provenance signatures from the Kunlun-Altun lithologies. Therefore, in the surface sediments, weakly magnetic ferrous ion (Fe²⁺)-bearing biotite served as the primary iron source. Aeolian transport (relatively fine component), TOC, and the normalized difference vegetation index (NDVI) served as key constraints on iron source dynamics. This study revealed the mineralogical form and influencing constraints of iron sources in the surface sediments derived from the northern Qinghai-Xizang Plateau, providing insights for distinguishing iron sources of the iron hypothesis in paleoclimate proxies.

Arid areas account for approximately one-quarter of the global land surface. Therefore, a comprehensive understanding of nitrogen cycling in arid watershed systems is essential for water environment protection and land use planning in dryland ecosystems. Using the Gasikule Lake Basin on the Qinghai-Xizang Plateau, China, as a representative study area, this study examined the sources, transport, and transformation mechanisms of nitrogen within a hierarchically nested hydrological system, including river water (S1R), groundwater (S2G), spring-fed river (S3R), and lake water (S4H). Dual nitrate isotopes (δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^-) were integrated with a Bayesian mixing models in R (MixSIAR) to quantify external nitrate sources. In addition, δ¹⁵N-NH₄⁺ isotopes combined with microbial techniques were applied to trace nitrogen transformation processes in water bodies, where nitrogen inputs were dominated by nitrate. The results indicated that nitrate was the primary form of nitrogen input across the study area, although overall nitrate loading remained relatively low. Atmospheric deposition and soil organic nitrogen were the dominant sources of exogenous nitrate input. Microbial genera associated with nitrate reduction generally showed low relative abundance in groundwater, whereas facultatively aerobic genera were predominant in surface water. In surface water, nitrogen transformation was mainly driven by organic nitrogen ammoniation and subsequent nitrification. In contrast, groundwater systems were characterized by stronger hydrological confinement and oxygen limitation, resulting in suppressed nitrification, incomplete denitrification, and a tendency toward ammonium accumulation. Collectively, these findings define a "low-input, low-transformation, and low-loss" nitrogen regime in the Gasikule Lake Basin. This sluggish nitrogen cycling reflects a limited ecological self-remediation capacity, highlighting the inherent biogeochemical fragility of alpine desert ecosystems. This study provides a critical theoretical basis for understanding nitrogen budgets in global dryland systems and offers scientific support for water environment protection and ecological sustainability in high-altitude areas.

Global climate change has markedly intensified environmental heterogeneity across plateau ecosystems, thereby imposing stronger environmental stresses on the structure and function of plant communities. Alpine herbaceous plant communities, as a climate-sensitive component, can rapidly reflect ecosystem responses to external environmental fluctuations. Their resource-use strategies, interspecific interactions, and mechanisms maintaining community stability are fundamental to understanding the adaptive processes of alpine ecosystems. Therefore, we selected the alpine desert of northwestern Qinghai-Xizang Plateau, China as the study area and conducted vegetation surveys from June to August 2024, encompassing 7 counties, 173 plots, and 519 quadrats. We analyzed patterns of niche overlap and differentiation, interspecific association types, and assessed the current state of community stability under extremely cold and arid conditions. The results revealed significant differentiation in niche breadth among dominant species, with Stipa purpurea Griseb identified as a broad-niche dominant species, whereas species such as Kobresia pygmaea (C. B. Clarke) C. B. Clarke exhibited narrow-niche specialization strategies. The mean community niche overlap index was 0.06, and the mean niche similarity index was 0.03, indicating a high degree of resource-use differentiation among species. Interspecific associations were predominantly weakly positive, and the community as a whole exhibited a significantly positive network structure, with a significant positive:negative associations ratio of 2.2:1.0. This pattern indicated that a community structure was dominated by facilitative interactions with markedly weakened competitive interactions. The intersection point in the stability model suggests that the system is currently in a stable state, characterized by low niche overlap, low similarity, and overall positive associations. Considering the high sensitivity of alpine desert ecosystems on the Qinghai-Xizang Plateau to climate change and anthropogenic disturbance, we recommend prioritizing the introduction of broad-niche dominant species such as S. purpurea to enhance resource-use diversity and structural resilience, thereby proactively strengthening the ecosystem's resistance to disturbance while maintaining its existing stability. These findings provide a scientific basis for elucidating the adaptive strategies of alpine desert ecosystems to climate change and for optimizing ecological conservation and restoration frameworks.

The formation of desert shrub sand piles (nebkhas) is attributed to the obstruction and subsequent deposition of migrating sand by the shrub itself. However, the relationship between sediment particle size distribution and shrub branch architecture remains inadequately understood. In August 2020, field investigations were conducted on Tetraena mongolica Maxim. shrubs in the Bayan Engger Desert Nature Reserve, located on the Ordos Plateau in Inner Mongolia Autonomous Region, China. Crown morphological parameters of T. mongolica shrubs and associated nebkhas were systematically measured alongside branch architectures. A one-way analysis of variance (ANOVA) was used to identify differences in branch architectures among various levels, while correlation analysis and model fitting were applied to establish the relationship between crown and nebkha morphological parameters. Path analysis was utilized to identify the key branch architectures that influence crown development. Furthermore, sediment redistribution characteristics of nebkhas were quantified, and principal component analysis combined with regression models was utilized to elucidate the contributions of key branch architectures and sensitive particle size fractions to nebkha deposition. Results indicated that the step-by-step branch ratio (SBR) initially increased from the lower branches to the outermost branches before subsequently decreasing. Additionally, branch angle significantly increased (P<0.0500), whereas both the branch length and the ratio of branch diameters (RBD) significantly decreased toward the exterior of the shrub (P<0.0500). Expansion of crown area significantly enhanced nebkha volume, demonstrating a strong linear relationship (P<0.0010). As the primary contact surface for trapping wind-blown sand, the silhouette area of the shrub initially increased and then decreased from bottom to top. Notably, the silhouette area of the 10-30 cm height layer played a crucial role in promoting nebkha volume expansion (P<0.0100). Path analysis further revealed that the key branch architectures promoting crown area expansion were the step-by-step branch ratio between the third-level and fourth-level branches (SBR_3:4), followed by the fourth-level branch length (BL_L4), the third-level branch angle (BA_L3), and the ratio of branch diameters between the fourth-level and third-level branches (RBD_4:3). Under the continuous interception of sediments by branches and leaves, the proportion of surface sediment with a particle size of 100.00-250.00 μm reached 51.07%, indicating a significant increase in fine-sized particles. Further analysis confirmed that SBR_3:4, BL_L4, BA_L3, and sediments within the 50.00-100.00 μm particle size range were the primary contributors to nebkha deposition. These results demonstrate that the branch characteristics of T. mongolica shrubs near the ground surface promote fine sediment accumulation and nebkha development by regulating crown expansion. The findings reveal the unique adaptation mechanisms of rare and endangered plants in nebkha microhabitats and provide a scientific basis for ecological windbreak and sand-fixation projects in the desert transition zones of arid and semi-arid regions.

Nitrogen (N) and phosphorus (P) are essential nutrients regulating plant growth, yet their long-term impacts on grassland ecosystems in Tajikistan remain poorly understood. This study conducted a five-year (2018-2022) field experiment across four grassland sites (Tabakqi, Balkhi, Luchob, and Ziddi) along an elevation gradient in central and southwestern Tajikistan to explore the effects of varying N (0, 30, and 90 kg N/(hm²∙a)) and P (0 and 30 kg P/(hm²∙a)) additions on aboveground biomass (AGB) and plant species diversity. Nutrient addition significantly increased AGB across all sites. Compared with the control (without N or P addition), AGB increased by 20%-80% under moderate N treatment (adding 30 kg N/(hm²∙a)) and by up to 190%-200% under high N and P addition treatment (adding 90 kg N/(hm²∙a) and 30 kg P/(hm²∙a)). In 2022, AGB at the low-elevation site (Tabakqi) increased from 494 g/m² under the control to 650 g/m² under high N and P treatment, while at the high-elevation site (Ziddi), it rose from 552 to 1614 g/m². In contrast, biodiversity responses were elevation-dependent: species richness declined at mid-elevation grassland sites (Balkhi and Luchob) but showed little change at low-elevation (Tabakqi) and high-elevation (Ziddi) sites. Shannon-Wiener index, Simpson's dominance index, and Pielou's equitability index also varied, reflecting complex interactions among nutrient addition, precipitation, and temperature. The structural equation model (SEM) confirmed that nutrient addition directly enhance AGB but generally suppress plant species diversity, while precipitation promotes AGB, and temperature effects are inconsistent across sites. Overall, our findings demonstrate that nutrient enrichment can increase productivity but reduce biodiversity, with responses strongly mediated by elevation and climate. These results provide the first long-term experimental evidence from Tajikistan's grasslands and underscore the need to balance productivity gains with biodiversity conservation in sustainable grassland management.

Fruit trees are typically organized at the orchard level, where the tree-based ecosystem is characterized by high homogeneity, leading to clustered distributions with distinct boundaries. While remote sensing-based classification techniques are well established, most studies have not treated fruit orchards as a distinct category. Whether remote sensing can effectively address orchard classification and distribution remains uncertain. This study focused on the Guanzhong Plain on the southern part of the Loess Plateau as a representative drought-vulnerable region in China, characterized by mixed orchard-cropland landscapes. Sentinel-2 imagery was used as the primary classification feature, supplemented by topographic characteristics. A Random Forest classifier was trained and validated using 1980 ground samples across major planting regions in May 2024. The final classification results were satisfactory, with an overall accuracy of 0.86. Meanwhile, a comparison against statistical data demonstrated the reasonableness of fruit orchard area: the correlation coefficients for three major fruit types (apple, grape, and kiwi) are greater than 0.75. Compared with existing land cover products, which often misclassify fruit trees as cropland or forestland, our results demonstrated that combining band reflectance time series, vegetation index time series, and topographic features can effectively differentiate fruit orchards from spectrally similar cropland and forestland. This study facilitates precise fruit orchard mapping, supporting targeted production management and ecological carbon sequestration estimation in similar regions with drought-vulnerable agroforestry systems.