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Soil moisture， as a key hydrological variable connecting the surface and atmospheric water and heat exchange， affects the land-air water and heat exchange and carbon cycle process.However， due to the difficulty in monitoring soil moisture in alpine mountain areas， there are some difficulties in related research.The study of time stability can reduce the difficulty of soil moisture acquisition by selecting representative points.In this study， the slope of Shangzhangfanggou grassland in Shiyang River basin of Qilian Mountain was selected to set up a high-density and high-time resolution soil moisture monitoring network to explore the temporal and spatial variation and temporal stability of soil moisture on the slope scale in alpine mountainous areas.The research results show that： （1） The surface soil moisture （10 cm， 15.90%） is significantly higher than that in the deep layer （50 cm， 11.78%）， and its temporal variability （CvT=19.46%） is also stronger than that in the deep layer （CvT=10.67%）， but its spatial variability （CvS=20.05%） is weaker than that in the deep layer （CvS=27.06%）.（2） The time stability Index of Temporal Stability （0.24） is stronger than that of the deep layer （0.34）， and the surface layer and the deep layer can represent the surface soil moisture of the slope through 3 or 5 soil moisture monitoring points respectively （R2> 0.90）.（3） Slope position and soil hydrological properties have obvious influence on time stability， and the time stability point is more likely to appear at the position with larger bulk density and smaller shape parameter n under the slope.The research results are helpful to better understand the temporal and spatial variation law， temporal stability characteristics and control function of soil moisture on slope in alpine mountain areas.

Soil organic carbon (SOC) is an important component of the global carbon pool, whose accumulation and decomposition affect the balance of the global carbon cycle and climate change. However, understanding of the responses of SOC in alpine ecosystems to climate change is quite limited, especially in the seasonal-frozen soil zone. In order to understand the impact of soil moisture changes on the carbon cycle in alpine mountain ecosystems, we established two sample plots of the semi-shady and semi-sunny slopes in the subalpine meadow zone of the eastern part of Qilian Mountains, and collected soil samples to investigate the spatial and temporal changes of SOC and soil moisture and their relationships. The study indicated that the SOC content showed significant surface aggregation during the plant growing season, and that the influence of soil moisture on SOC was different in different slope directions and soil depths. The influence of soil moisture on SOC was greater on the semi-shady slope than on the semi-sunny slope. Among different soil layer depths, the soil moisture most significantly affected SOC in the soil layer of 20-40 cm. This study provides a theoretical basis for the study of carbon stocks and carbon cycling at high altitudes. [ABSTRACT FROM AUTHOR]

The study explores the impact of mine grassland restoration on plant communities and soil properties in alpine grasslands, a subject of significant interest due to the observed relationship between grassland changes, plant communities, and soil properties. While prior research has mainly focused on the consequences of grassland degradation on plant diversity and soil characteristics, the specific effects of varying restoration degrees in alpine mining grasslands at the regional scale remain poorly understood. To address this knowledge gap, we established 15 sampling plots (0.5m×0.5m) across five different restoration degrees within alpine mining grasslands in the Qilian Mountains, China. Our objective was to assess the variations in plant diversity and soil properties along these restoration gradients. We conducted comprehensive analyses, encompassing soil properties [soil water content (SWC), available nitrogen (AN), total phosphorus (TP), nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N), total nitrogen (TN), available phosphorus (AP), soil organic carbon (SOC), nitrate nitrogen, soil pH, and electrical conductivity (EC)], plant characteristics (height, density, frequency, coverage, and aboveground biomass), and plant diversity indices (Simpson, Shannon-Wiener, Margalef, Dominance, and Evenness indexes). Our findings included the identification and collection of 18 plant species from 11 families and 16 genera across the five restoration degrees: Very Low Restoration Degree (VLRD), Low Restoration Degree (LRD), Moderate Restoration Degree (MRD), High Restoration Degree (HRD), and Natural Grassland (NGL). Notably, species like Carex duriuscula, Cyperus rotundus, and Polygonum viviparum showed signs of recovery. Principal component analysis and Pearson correlation analysis revealed that soil pH, SWC, SOC, NO3-N, and AN were the primary environmental factors influencing plant communities. Specifically, soil pH and EC decreased as restoration levels increased, while SWC, AN, TP, NH4-N, TN, AP, SOC, and NO3-N exhibited a gradual increase with greater restoration efforts. Furthermore, the HRD plant community demonstrated similarities to the NGL, indicating the most effective natural recovery. In conclusion, our study provides valuable insights into the responses of plant community characteristics, plant diversity, and soil properties across varying restoration degrees to environmental factors. It also elucidates the characteristics of plant communities along recovery gradients in alpine grasslands. [ABSTRACT FROM AUTHOR]

To understand how the soil microbial community structure responds to vegetation restoration in alpine mining areas, this study specifically examines the grassland ecosystem in the Qianmalong mining area of the Qilian Mountains after five years of artificial restoration. High-throughput sequencing methods were employed to analyze soil bacteria and fungi microbial characteristics in diverse grassland communities. Combined with modifications in vegetation diversity as well as soil physicochemical properties, the impact of vegetation restoration on soil microbiome diversity in this alpine mining area was investigated. The findings indicated that the dominant plants were Cyperus rotundus, Carex spp., and Elymus nutans. As the extent of the grassland's restoration increased, the number of plant species, importance values, and plant community diversity showed an increasing trend. The plant functional groups were mainly dominated by Cyperaceae, followed by Poaceae. Plant height, density, plant cover, frequency, and aboveground biomass showed an increasing trend, and soil water content (SWC) increased. While soil pH and soil electrical conductivity (EC) exhibited a declining trend, available phosphorus (AP), total phosphorus (TP), total nitrogen (TN), nitrate nitrogen (NO3-N), soil organic carbon (SOC), and soil water content (SWC) showed an increasing trend. The dominant bacterial communities were Actinobacteriota, Proteobacteria, Acidobacteriota, Chloroflexi, Firmicutes, and Gemmatimonadota, while the dominant fungal communities were Ascomycota, Mortierellomycota, Basidiomycota, unclassified_k_Fungi, and Glomeromycota. Significant differences were detected within soil microbial community composition among different degrees of restoration grasslands, with bacteria generally dominating over fungi. SWC, TP, and TN were found to be the main soil physicochemical factors affecting the distribution of soil bacterial communities' structure; however, SOC, TN, and NO3-N were the primary factors influencing the soil distribution of fungal communities. The results of this study indicate that different degrees of vegetation restoration in alpine mining areas can significantly affect soil bacterial and fungal communities, and the degree of restoration has varying effects on the soil bacteria and fungi community structure in alpine mining areas. [ABSTRACT FROM AUTHOR]

Samples of scrub plants and soil were collected from May to October 2019 in the subalpine scrub zone of the Qilian Mountains. Based on measured oxygen isotope values (δ18O) in plant xylem water and soil water, the multivariate linear mixed model (IsoSource) and the proportional similarity index (PS index) were used to analyze the using proportion for each potential water source and the competition relationship for water use of scrub plants in different growing periods and habitats. The results showed that the soil water content gradually decreased with increasing depth of the soil layer, with the maximum value in the soil layer of 0–10 cm. Most of the scrub plants mainly used soil water in the soil layer of 0–30 cm during the different periods of growing season, but Salix sclerophylla Anderss. and Salix oritrepha Schneid. on the semi-sunny slope habitat mainly used soil water in the soil layer of 40–80 cm during the middle period of growing season (July–August), with the proportion of 59.5% and 52.1%, respectively; and Potentilla fruticosa Linn. and Salix cupularis Rehd. on the semi-shady slope habitat mainly used soil water in the soil layer of 30–60 cm during the early period of growing season (May–June), with the proportion of 61.1% and 49.7%, respectively. The competition relationships of scrub plants for water use varied during different periods of growing season (P < 0.05). On the semi-sunny slope habitat, they were fiercest for Salix cupularis Rehd. and Rhododendron thymifolium Maxim., Potentilla fruticosa Linn., and Salix sclerophylla Anderss. during the early period of growing season; Salix cupularis Rehd. and Rhododendron thymifolium Maxim. during the middle period of growing season, and Salix sclerophylla Anderss. and Salix oritrepha Schneid. during the end period of growing season (September–October). On the semi-shady slope habitat, they were fiercest for Salix oritrepha Schneid. and Caragana jubata (Pall.) Poir. during the early period of growing season; Rhododendron przewalskii Maxim. and Rhododendron thymifolium Maxim. during the middle period of growing season; and Salix cupularis Rehd. and Salix oritrepha Schneid. during the end period of growing season. This study reveals the competitive relationship of scrub plants for water use in the subalpine zone and their response to environmental changes, so as to provide theoretical references for the ecological conservation in the ecologically fragile areas of the Qilian Mountains. [ABSTRACT FROM AUTHOR]

• A cosmic-ray neutron rover was introduced to observe soil moisture in the Tibetan Plateau. • Soil moisture determined by the rover, newly adjusted by vegetation effects, was within ±0.025 g/g. • The calibration parameter N 0 _NDVI was 443 cpm. • Average mesoscale soil moisture from the rover varied by ecosystem types. • Valuable mesoscale soil moisture transect data was be offered in the Tibetan Plateau. Water resources in the soil play an essential role in hydrological processes and ecosystem functions on the Tibetan Plateau. However, accurately measuring soil moisture distribution in this region presents challenges due to the diverse ecosystem types, complex terrain, and harsh environmental conditions. In this study, we introduce an approach for estimating mesoscale soil moisture in the Qilian Mountains (QLM) region of the eastern Tibetan Plateau using a cosmic-ray neutron rover. Soil moisture estimates derived from neutron count rates, newly adjusted by vegetation effects, demonstrated good agreement with soil moisture measurements obtained through soil sampling at 26 calibration sites across the region (RMSE = 0.025 g g−1). The calibration parameter N 0 _NDVI was 443 cpm in the QLM. Utilizing NDVI as vegetation correction method showed potential improvements in the accuracy of converting neutron counts to soil moisture across the diverse mountainous ecosystem types. The newly developed calibration equation provided a high-precision, high spatial resolution soil moisture transect across various landscapes measured by the rover. The average mesoscale soil moisture along the rover route varied by ecosystem types, with values of 0.10 g/g in deserts, 0.17 g/g in grasslands, 0.13 g/g in forests, 0.18 g/g in subalpine shrublands, and 0.20 g/g in croplands. Land cover types emerged as crucial determinants of mesoscale soil moisture variability in the QLM region. These findings offer valuable mesoscale soil moisture data and new insights into soil water information at the transect scale across diverse ecosystem types in the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Vegetation phenology is a commonly used indicator of ecosystem responses to climate change and plays a vital role in ecosystem carbon and hydrological cycles. Previous studies have mostly focused on the response of vegetation phenology to temperature and precipitation. Soil moisture plays an important role in maintaining vegetation growth. However, our understanding of the influences of soil moisture dynamics on vegetation phenology is sparse. In this study, using a time series of the normalized difference vegetation index (NDVI) from the moderate resolution imaging spectroradiometer (MODIS) dataset (2001–2020), the start of the growing season (SOS), the end of the growing season (EOS), and the length of the growing season (LOS) in the Qilian Mountains (QLMs) were extracted. The spatiotemporal patterns of vegetation phenology (SOS, EOS, and LOS) were explored. The partial coefficient correlations between the SOS, EOS, and seasonal climatic factors (temperature, precipitation, and soil moisture) were analyzed. The results showed that the variation trends of vegetation phenology were not significant (p > 0.05) from 2001 to 2020, the SOS was advanced by 0.510 d/year, the EOS was delayed by 0.066 d/year, and the LOS was prolonged by 0.580 d/year. The EOS was significantly advanced and the LOS significantly shortened with increasing altitude. The seasonal temperature, precipitation, and soil moisture had spatiotemporal heterogeneous effects on the vegetation phenology. Overall, compared with temperature and soil moisture, precipitation had a weaker influence on the vegetation phenology in the QLMs. For different elevation zones, the temperature and soil moisture influenced the vegetation phenology in most areas of the QLMs, and spring temperature was the key driving factor influencing SOS; the autumn soil moisture and autumn temperature made the largest contributions to the variations in EOS at lower (<3500 m a.s.l.) and higher elevations (>3500 m a.s.l.), respectively. For different vegetation types, the spring temperature was the main factor influencing the SOS for broadleaf forests, needleleaf forests, shrublands, and meadows because of the relative lower soil moisture stress. The autumn soil moisture was the main factor influencing EOS for deserts because of the strong soil moisture stress. Our results demonstrate that the soil moisture strongly influences vegetation phenology, especially at lower elevations and water-limited areas. This study provides a scientific basis for better understanding the response of vegetation phenology to climate change in arid mountainous areas and suggests that the variation in soil moisture should be considered in future studies on the influence of climate warming and environmental effects on the phenology of water-limited areas. [ABSTRACT FROM AUTHOR]

• This study examined characteristics of NEP and CUE at different ecosystems in the alpine region. • Qilian Mountains, as a climate-sensitive region, acted as an effective carbon sink. • Wetland/swamp had the highest NEP, followed by forest, while shrub had the lowest NEP in the Qilian Mountains. Warming leads to significant loss of CO 2 in high-altitude regions (HAR), posing threat to the carbon sink of terrestrial ecosystem. Additionally, the spatial distribution of environmental factors and underlying surfaces also determine the carbon sink pattern. Therefore, it is necessary to systematically explore the carbon sink of HAR. Based on it, choosing the Qilian Mountains (QLM) as the study area, the continuous observation data of 14 eddy covariance in different ecosystems was used to analyze the variation characteristics of carbon use efficiency (CUE) and net ecosystem primary productivity (NEP), which is helpful to systematically understand the response of carbon cycle to climate change in alpine ecosystem. The research results indicated that the QLM serves as an effective carbon sink (13 of the sites yielded a net carbon sink), owing to the combined influences of environmental factors and vegetation characteristics. Annual NEP varied across the 14 sites, ranging from -192.6 to 524.5 g C/m2/yr. Limited observation indicated that wetland/swamp had the highest carbon sink, followed by forest, and shrub have the lowest carbon sink in this study. Along the altitudinal gradient, both gross primary productivity (GPP) and ecosystem respiration (Re) demonstrated a declining trend (P < 0.05), while, CUE displayed an increasing trend. Soil temperature and photosynthetically active radiation dominated the variation in carbon exchange and CUE along the altitudinal gradient. However, soil moisture was the dominant factor in drought ecosystem. This study provides basis for the assessment of carbon sink of the HAR. [ABSTRACT FROM AUTHOR]

Located along the northeastern edge of the Qinghai‐Tibet Plateau in China, the Qilian Mountains are an important ecological barrier in Northwest China. Therefore, it is of great significance to study the plant water sources in subalpine habitats for understanding the ecological and hydrological processes in the Qilian Mountains. Here, based on the samples of precipitation, xylem water, soil water, river water, and spring water collected during May–October 2019 from subalpine habitats on the northern slope of the Qilian Mountains and the measured hydrogen and oxygen stable isotope values (δ2H and δ18O, respectively), the present study gained further insight into plant water sources in this region using the IsoSource model. Water absorption characteristics of shrubs were similar in subalpine habitats. Specifically, plants absorbed water primarily from the topsoil layer (0–30 cm) and rarely from the deep soil layers. Nevertheless, in the dry and growing seasons with high water demand, subalpine shrubs competed for water resources at similar depths. As a result of this competition, the utilization rate of deep soil water improved in some shrubs, expanding the differences in water sources of subalpine shrubs within the same habitat. In addition, in the dry and growing seasons, the water sources of the same subalpine shrub varied across different habitats. Compared with other subalpine shrubs, Salix cupularis Rehder, Salix oritrepha Schneid., Potentilla fruticosa L., Salix sclerophylla Anderss., Rhododendron anthopogonoides Maxim., and Rhododendron przewalskii Maxim. could alter their water use strategies with variations in water conditions, exhibiting a greater drought tolerance. These findings provide valuable information for understanding the subalpine region's eco‐hydrological processes and contribute to the selection of suitable species for the restoration of the subalpine ecological environment under the background of global change. [ABSTRACT FROM AUTHOR]

Vegetation phenology is a commonly used indicator of ecosystem responses to climate change and plays a vital role in ecosystem carbon and hydrological cycles. Previous studies have mostly focused on the response of vegetation phenology to temperature and precipitation. Soil moisture plays an important role in maintaining vegetation growth. However, our understanding of the influences of soil moisture dynamics on vegetation phenology is sparse. In this study, using a time series of the normalized difference vegetation index (NDVI) from the moderate resolution imaging spectroradiometer (MODIS) dataset (2001–2020), the start of the growing season (SOS), the end of the growing season (EOS), and the length of the growing season (LOS) in the Qilian Mountains (QLMs) were extracted. The spatiotemporal patterns of vegetation phenology (SOS, EOS, and LOS) were explored. The partial coefficient correlations between the SOS, EOS, and seasonal climatic factors (temperature, precipitation, and soil moisture) were analyzed. The results showed that the variation trends of vegetation phenology were not significant (p > 0.05) from 2001 to 2020, the SOS was advanced by 0.510 d/year, the EOS was delayed by 0.066 d/year, and the LOS was prolonged by 0.580 d/year. The EOS was significantly advanced and the LOS significantly shortened with increasing altitude. The seasonal temperature, precipitation, and soil moisture had spatiotemporal heterogeneous effects on the vegetation phenology. Overall, compared with temperature and soil moisture, precipitation had a weaker influence on the vegetation phenology in the QLMs. For different elevation zones, the temperature and soil moisture influenced the vegetation phenology in most areas of the QLMs, and spring temperature was the key driving factor influencing SOS; the autumn soil moisture and autumn temperature made the largest contributions to the variations in EOS at lower (3500 m a.s.l.), respectively. For different vegetation types, the spring temperature was the main factor influencing the SOS for broadleaf forests, needleleaf forests, shrublands, and meadows because of the relative lower soil moisture stress. The autumn soil moisture was the main factor influencing EOS for deserts because of the strong soil moisture stress. Our results demonstrate that the soil moisture strongly influences vegetation phenology, especially at lower elevations and water-limited areas. This study provides a scientific basis for better understanding the response of vegetation phenology to climate change in arid mountainous areas and suggests that the variation in soil moisture should be considered in future studies on the influence of climate warming and environmental effects on the phenology of water-limited areas.

In order to explore the characteristics of hydrogen-oxygen isotopes and ecological hydrological processes in different water bodies in the subalpine zone of Qilian Mountains, China, precipitation, soil water, plant water, groundwater and river water samples were collected from the subalpine of the Eastern of Qilian Mountains section from July to August in 2015. Qualitative analysis was used in hydrogen and oxygen isotope characteristics of different water bodies. Then, the mixing model of MixSIAR based on Bayesian theory was used to quantify the water absorption depth of shrub plant and the proportion of water source replenishment between different water bodies. The purpose is to illustrate the water migration relationship between water bodies, thereby to clarify the ecological hydrological process in the subalpine shrub area of Eastern Qilian Mountains. Results indicate that: (1) The isotopic values of various water bodies in the study area are affected by changes in the amount of precipitation, but precipitation has a smaller impact on river water. (2) Soil water of 0~20 cm is affected easily by precipitation and evaporation, while soil water of 60~80 cm is affected strongly by groundwater. (3) The water content of shrub plant in study area is mainly derived from precipitation and soil water under 0~20 cm. (4) Although the direct influence on the values of d18O in groundwater and river water by precipitation is not obvious and their variation ranges are small, there are different degrees of response to precipitation, and river water responds faster to precipitation than groundwater. [ABSTRACT FROM AUTHOR]

Knowledge of the spatial–temporal variability of soil water content is critical for water management and restoration of vegetation in semi‐arid areas. Using the temporal stability method, we investigated soil water relations and spatial–temporal variability of volumetric soil water content (VSWC) in the grassland–shrubland–forest transect at a typical semi‐arid subalpine ecosystem in the Qilian Mountains, northwestern China. The VSWC was measured on 48 occasions to a depth of 70 cm at 50 locations along a 240‐m transect during the 2016–2017 growing seasons. Results revealed that temporal variability in VSWC in the same soil layer in the three vegetation types and averaged across vegetation types tended to exhibit similar patterns of a decrease with increasing soil depth. Temporal stability in each vegetation type was stronger with an increase in soil depth. However, the results of temporal stability determined with standard deviation of relative difference (SDRD) disagreed with those based on the Spearman's rank correlation coefficient; the forest site had the highest Spearman rank correlation coefficient while the shrubland—the smallest SDRD in the 0–20 cm soil layer. Correlation analyses of VSWCs between two vegetation types indicated that soil water was related among all three vegetation types at the 0–20, and 0–70 cm soil layer, but in the 20–40 and 40–70 cm soil layers, significant correlation (p <.01) occurred only between adjacent vegetation types. In the upper soil layer (0–20 cm), soil water relations were mainly affected by surface runoff. In the lower soil layer (20–40 and 40–70 cm), soil water relations among the three vegetation types were highly complex, and probably resulting from a combination of root distribution and activity, interflow, and the impact of deep soil freeze–thaw dynamics. These results suggest that the factors affecting soil water are complex, and further research should address the relative importance of and interactions among different determining factors. [ABSTRACT FROM AUTHOR]

Soil aggregates reflect the stability of soil structure, soil fertility and quality, and they are closely related to the environmental quality, soil and water loss, and soil erosion. Although vegetation types, soil depths, and altitude likely have important effects on soil properties and soil aggregates, few studies have concentrated on the relationships between their interactive effects and soil aggregate stability on the regional scale. In order to study the variation characteristics of soil aggregates in the Qilian Mountains. In this study, 4 vegetation type zones (desert, steppe, meadow, and shrub) were selected in the Qilian Mountains (northwest China) as the subjects. The stability and size distribution of soil aggregates was measured by the method of wet-sieving. The characteristics of soil aggregate index were analyzed at different soil depths and different altitudes, including the percentage of water-stable aggregate (WSA), mean weight diameter (MWD), geometric mean diameter (GMD), mean weight soil specific area (MWSSA), aggregate processing damage rate ( PAD) and fractal dimension (D). The results showed that the coefficients of variation of soil aggregate index under the 4 vegetation types were high (ranging from 10.91% to 62.50%), which indicated a moderate spatial variability. Among the 4 grassland types, WSA, MWD, GMD and MWSSA all showed the same increased in order: desert < steppe or meadow 30-40 cm depth, no significant differences in aggregate stability index were found among different vegetation types (P>0.05). The reason why the aggregate stability of desert was lowest could be explained by the fact that the lower soil organic carbon (SOC) and biomass of desert, and the small aggregates couldn’t be formed. Along the vertical direction of the soil profiles from aboveground to underground, with the increase of soil depth (0-40 cm), WSA, MWD, GMD, and MWSSA gradually all decreased. Whereas PAD and D behaved opposite to them, and with the increase in soil depth, they gradually increased, which indicated that the stability and aggregation degree of soil aggregates decreased with soil depth. This could be explained as that the SOC appeared enrichment phenomenon in the 0-20 cm layer and decreased with soil depth. The soil aggregate index all tended to be significantly higher in surface layer than in lower layers only at the meadow (P<0.05), but no significant difference in MWSSA (P>0.05) were found among all soil depths. With increasing altitude, the aggregate stability (WSA, MWD, and GMD) increased gradually from 1 692 m, reached a peak at 2 800 m, and then decreased quickly. But the trends were reverse for the PAD and D, and there was no significant correlation between MWSSA and altitude under different vegetation types (P>0.05), which suggested that their distribution clearly showed unimodal patterns across all the altitude. This indicated that the stability and aggregation degree of soil aggregates first increased and then decreased with increasing altitude, and the maximum point appeared at elevation of 2 800 m. In addition, correlation analysis showed that WSA, MWD, and GMD were mainly affected by 1-4 mm, D was mainly affected by 0.038-0.25 mm, and MWSSA couldn't accurately express the characteristics of water-stable aggregates. This research will guide the practice of reducing soil erosion for the different conditions and different vegetation types, and results have great significance for controlling grassland degradation, promoting soil structure stability and the sustainable development of grassland animal husbandry. [ABSTRACT FROM AUTHOR]

Highlights • Temporal stability of soil water storage (SWS) in high-elevation forests are analyzed. • Temporal changes and spatial variation of SWS decreased with increasing soil depth. • One time-stable location (TSL) can be representative of the mean SWS. • These TSLs be with average LAI or relatively low canopy interception loss locations. • Temporal stability of SWS was mainly affected by soil and vegetation properties. Abstract Understanding soil water storage (SWS) dynamics in soil profiles is important for hydrological modeling and restoration of vegetation in semi-arid areas. Using the temporal stability method, we aimed to investigate the temporal stability of SWS at 0–40, 40–80, and 80–120 cm depth, and to identify representative sites for reliable estimates of the mean SWS in the permanent forest plot in the Qilian Mountains of China. Further, we wanted to identify correlations between temporal stability of SWS and soil, topography, and properties of the vegetation. Soil water content at soil depths 0–120 (for locations 1–40) and 0–70 cm (for locations 41–60) were measured using time-domain reflectometry (TDR) on 52 dates from 2016 to 2017. Results revealed that time-averaged mean SWS for the three layers differed significantly (P < 0.05), and the temporal changes and spatial variations of the mean SWS all decreased with increasing soil depth. Based on either the Spearman correlation coefficient or the standard deviation of relative difference (SDRD) index, the temporal stability of SWSs within the soil profiles under different soil layers were strong, and the number of time-stable locations increased with increasing soil depth, indicating that the SWS intended to be more temporally stable in deeper soil. One time-stable site can be representative of the mean SWS for multiple soil layers for the whole plot, and can accurately estimate the mean SWS for the three soil layers (R2 > 0.86, P < 0.001). Moreover, these time-stable locations should be those having average LAI, SBD or relatively low canopy interception loss compared to the corresponding field means. Soil bulk density, canopy interception rate, and aboveground biomass of mosses can significantly (P < 0.05) affect the stability of SWSs in this high-elevation forests. Such effects, however, differed among the different soil layers due to different conditions of soil characteristics, distribution of root biomass, and freeze–thawing processes. These results suggest that the influence of vegetation properties of the temporal stability of SWS should attract more attention and that both the relative importance of and interactions among different determining factors is helpful for better understanding the mechanistic determinants of SWS temporal stability in these areas. [ABSTRACT FROM AUTHOR]

The Pailugou watershed of the Qilian Mountains in the arid region of northeast China was selected for research to analyze the species, height, and biomass in typical mountain grassland with an altitude of 2,700-3,000 m and measure soil moisture, so as to explore the seasonal characteristics of grassland biomass as altitude increases and the relationship between grassland biomass and soil moisture. The results showed that: (1) with a mean value of 135.36 g/m², grassland aboveground biomass showed a unimodal distribution from rise to decline as altitude increased, and reached its maximum of 176.79 ± 28.37 g/m² at an altitude of 2,900 m; with a mean value of 946.13 g/m², grassland underground biomass showed an uptrend as altitude increased, and reached its maximum of 1,301.19 ± 68.24 g/m² at an altitude of 3,000 m; (2) the difference between aboveground biomass and underground biomass in the grassland at different altitudes was significant; (3) values of root shoot ratio of the arid mountain grassland varied between 4.14-11.95; (4) values of soil moisture content of the arid mountain grassland varied between 9.23%-31.31%; (5) there was a positive correlation between aboveground biomass and underground biomass and the mean soil moisture content (p < 0.05), with a correlation coefficient of 0.778 4 and 0.784 3 respectively, soil layers with different moisture content made different contributions to grassland biomass, and moisture content in the soil layer where over-60-cm root systems were located was of significance to grassland biomass. [ABSTRACT FROM AUTHOR]

Invasive noxious plants have important impacts on community dynamics and ecosystem functions in grasslands. Since the 1960s, the noxious plant Melica przewalskyi has spread rapidly and formed different size of patches in subalpine meadows of the Qilian Mountains, Northwest China. In this study, the species richness, vegetation structure, and soil water content are investigated from the patch edge to the center in four sizes of M. przewalskyi patches (i.e., small patch, <100 cm in canopy diameter; middle patch, 100–200 cm; large patch, 200–300 cm; and the largest patch, >300 cm). The results show that while the patches grow continuously, the dominant species changes from Stipa krylovii to M. przewalskyi with an increasing trend in plant productivity and decreasing trend in species richness and soil water content. Plant height, density, coverage, and above‐ground biomass of M. przewalskyi population increases from the patch edge to the center in small, middle, and large patches, whereas it is precisely the opposite in the largest patch. Interestingly, soil water content exhibits a decreasing trend from the patch edge to the center in all patches. The results indicate that the rapid spread of M. przewalskyi may well alter vegetation pattern and cause a severe soil moisture deficit, which would further drive the degradation of ecosystem functioning in subalpine meadows. [ABSTRACT FROM AUTHOR]

Soil moisture controls the functioning of semi-arid ecosystems. The response of soil moisture to forest stand thinning determines planting density and sustainability of forest development. However, consequences of stand thinning are poorly known in semi-arid ecosystems of the Qilian Mountains of China. We investigated long-term effects of three thinning intensities in Picea crassifolia plantations on soil hydrological responses and soil moisture dynamics at 10, 20, 40, 60, and 80 cm depths, and compared them to those of a natural Picea crassifolia forest. Results revealed that soil hydrological response may be temporarily modified by thinning according to changes in canopy structure, precipitation properties, and antecedent soil moisture conditions. Soil moisture in natural forest rapidly infiltrated into deep soil, which greatly improved the efficiency of precipitation use. Thinning significantly increased the capacity for soil infiltration, and moderate thinning intensity may be conducive to deep soil-water recharge. Soil moisture content changed drastically after thinning, with a significant decrease near-surface (10 cm), and a significant increase in sub-surface (60 and 80 cm) soil. High planting density was the main cause of severe soil moisture deficits in the long-term, but it could be mitigated by 20–40% thinning (∼3139 trees ha −1 ). Changes in precipitation patterns that include larger but less frequent rainfall events during the growing season will benefit the growth of vegetation planted at high densities in this semi-arid region. [ABSTRACT FROM AUTHOR]

• Shrub growth is limited by N but increase leaf C to resist harsh conditions. • Stoichiometric ratios of plants were not related to those of soils, but controlled by soil properties. • Soil water, bulk density and porosity drive the ecological stoichiometry. Studying the ecological stoichiometry of ecosystem would promote understanding about how plant adapt to environment changes. As a typical alpine region, the Qilian Mountain of northwest China is a good platform for this purpose, but the ecological stoichiometric of plants is largely unknown. This study selected five dominant shrub species to collect shrub leaves and soils to explored the carbon (C): nitrogen (N): and phosphorus (P) characteristics and controls of them. The mean content of C (549.39 g kg−1) in leaves of shrub plants was higher than that of global flora. N:P ratio of five shrubs leaves (7–10) were all lower than 14. The shrubs in the alpine regions resist harsh conditions by increasing leaf C content, and their growth is restricted by N. Compared with altitude and soil, shrub species have greater effects on soil stoichiometric characteristics. The Caragana tangutica shrub may be the best specie for ecological restoration. The stoichiometric ratios of shrub leaves are not related to those of soils, but controlled by soil properties, mainly including soil water content (34.2%), bulk density (32.5%) and total porosity (12.8%). This study interpreted the mechanism how shrub adapt to changing environment, and provide information for how effectively restore the ecological environment in the alpine regions. [ABSTRACT FROM AUTHOR]

Summary: Knowledge of soil moisture is critical to understanding many of the hydrological processes that are of interest in soil hydrology, meteorology, and ecology research. In the present study, we used rainfall and soil moisture data from 2003 to 2008 measured at grassland and meadow sites in the Qilian Mountains of northwestern China to analyze the response of soil moisture to rainfall event size during the growing season. The responses of soil moisture at the grassland and meadow sites to rainfall event size were similar, although total rainfall, the frequency of large rainfall events, and the vegetation types were different. Soil moisture at depths of 20 and 40cm increased significantly after rainfall events larger than 15 and 20mm, respectively, but the magnitude of these changes varied in response to differences in the duration of the dry interval preceding the rain. Soil moisture at depths from 60 to 80cm in the grassland increased obviously with rainfall events larger than 40mm or after two consecutive large rainfall events, but was not significantly correlated with rainfall event size in the meadow. Soil moisture at depths from 120 to 160cm did not change significantly during the growing season at either site. The soil water storage at depths from 20 to 80cm at both sites increased obviously after rainfall events larger than 20mm. The present results suggest that large rainfall events (>20mm) play a key role in increasing soil water storage in the grassland and meadow ecosystems of these semi-arid mountains. [ABSTRACT FROM AUTHOR]

[Display omitted] • Throughfall and related surface soil water content (SWC) were analyzed in a spruce forest. • Time stability of throughfall and surface SWC spatial patterns were evaluated. • Throughfall depth had a pronounced impact on surface SWC. • Litter fall biomass showed a significant negative effect. • Surface SWC is affected by precipitation, forest canopy, and soil heterogeneity factors. Throughfall (TF) is one of the most important factors affecting forest surface soil moisture. However, TF heterogeneity and its contributions to the variability in near-surface soil water-content (SWC) in a spruce forest in semiarid mountain ecosystems are poorly understood, and may determine plant survival. Here, we systematically investigated variability of TF in a Picea crassifolia stand within a protected semi-arid mountain ecosystem, and evaluated the contributions of TF to near-surface SWC variability obtained from TF gauges and SWC measurements at the plot level. Results showed that TF variability tended to decline with an increase in rainfall amount, intensity, and duration, and then tended to be stable after a value of 24.1 mm, 3.1 mm h−1 and 789.8 min, respectively. Both TF and surface SWC were highly spatially variable, but the spatial patterns appeared to be stable over time based on time-stability analysis. The mean SWC increment exhibited a strong positive power relationship with plot mean TF, and the percent of locations with SWC increments increased similarly to TF amount for individual rainfall events. TF, soil bulk density, and litter fall biomass can significantly (P < 0.05) affect the stability of SWC increments. Therefore, our research indicated that further research should consider the relative importance of, and interactions among precipitation characteristics, soil heterogeneity, and vegetation characteristics. Our results may be useful for land managers involved in enhancing the water conservation capacity of semi-arid mountain forest ecosystems, where climatic conditions, soil quality and vegetation characteristics will determine the supply of multiple forest ecosystem functions. [ABSTRACT FROM AUTHOR]

This study examined whether soil microbial composition would respond differently between alpine meadow and desert grasslands located in the Qilian mountain range in the semi-arid region of northwestern China. The measurements were carried out along a soil profile up to 40 cm. The total nitrogen (TN), total carbon (TC), soil organic carbon (SOC) and soil water content (SWC) were significantly higher (P-value < 0.05) in alpine meadow than in desert. In alpine meadows, all these properties decreased with increasing soil depth, and in desert grassland these properties – except SWC and TN - remained the same at all soil depths. The bacterial phyla Actinobacteria dominated both grasslands, significantly more so in desert grassland (P-value< 0.05). In alpine meadows Proteobacteria, Acidobacteria, Gemmatimonadetes, Planctomycetes and Rokubacteria abundance was significantly higher (P-value < 0.05). The distribution pattern of bacterial phyla along soil depth was different between the two grasslands. The abundance of Ascomycota and Basidiomycota was unaffected by grassland type or soil depth. Alpha and beta diversity analysis revealed two grasslands harbored distinct bacterial and fungal communities. We identified soil carbon, nitrogen and water as important factors that shaped the bacterial and fungal community in these semi-arid grasslands. • Alpine meadow and desert grasslands harbor distinct bacterial and fungal communities. • The bacterial phyla Actinobacteria dominated both grasslands, with significantly more so in the desert. • The fungal phyla Ascomycota and Basidiomycota dominated both grasslands, but were unaffected by grassland type and soil depth. • Carbon, nitrogen and water changes along the soil depth shaped microbial diversity. [ABSTRACT FROM AUTHOR]

• Elevation and slope aspect affected leaf stoichiometry of Oxytropis ochrocephala. • Variation of leaf stoichiometry with elevation was mainly affected by MAT, SOC and SOC:STP. • Variation of leaf stoichiometry with slope aspect was mainly affected by ST and SWC. Slope aspect and elevation gradient, important topographic factors, affect plant growth and leaf carbon:nitrogen:phosphorus (C:N:P) stoichiometry by regulating local water and energy balances. The response of leaf stoichiometry to topographic factors reflects plant adaptation strategies to different habitats. Common in various grasslands across China, Oxytropis ochrocephala Bunge. is well known in pastoral areas for its toxicity. The effects of partial or full slope sunniness (south-facing) or shadiness (north-facing) and elevation (2400 m, 2600 m, 2800 m, 3000 m, or 3200 m) on the leaf C:N:P stoichiometry of O. ochrocephala was investigated in northwest China's Qilian Mountains. While leaf C:N:P stoichiometry of O. ochrocephala changed with elevation, there was no uniform pattern of change: the greatest leaf C and P concentrations ([C] leaf , and [P] leaf) were measured at an elevation of 2800 m (417.81 g kg−1 and 1.17 g kg−1, respectively); the lowest [C] leaf was 360.43 g kg−1 at 2400 m, and the lowest [P] leaf was 0.81 g kg−1 at 2600 m. The greatest leaf N concentration ([N] leaf) was 38.29 g kg−1 at 3200 m, and the lowest was 31.94 g kg−1 at 2600 m. Leaf C:N, C:P and N:P ratios were all relatively greater at 2600 m. Across the elevation gradient, O. ochrocephala leaf nutrient concentrations and their stoichiometries were mainly determined by mean annual temperature, soil organic carbon, and soil organic carbon to soil total phosphorus ratio. The [C] leaf , [N] leaf , and [P] leaf were significantly greater on north-facing slope aspects (393.86 g kg−1, 38.04 g kg−1, and 1.16 g kg−1, respectively) than on south-facing slope aspects (365.39 g kg−1, 32.98 g kg−1, and 0.92 g kg−1, respectively). Leaf C:N, C:P, and N:P ratios were significantly lower on north-facing slope aspects (10.43, 416.49, and 39.73, respectively) than on south-facing slope aspects (11.14, 512.57, and 45.98, respectively). Differences in leaf nutrient concentrations and their stoichiometries in O. ochrocephala leaves between slope aspects were mainly determined by soil temperature and soil moisture content. In terms of leaf N:P ratios across the elevation gradient and the two slope aspects, results indicated that the growth of O. ochrocephala in the study region was mainly restricted by P. [ABSTRACT FROM AUTHOR]

Soil water is a link between different water bodies. The study of soil water evaporation is of great significance to understand the regional hydrological process, promote environmental remediation in arid areas, and rationalize ecological water use. On the basis of soil water δ2H and δ18O data from April to October 2017 in the Xiying River basin in the upper reaches of the Qilian mountains, the lc-excess and Craig-Gordon model were applied to reflect the evaporating fractionation of soil water. The results show that the change in evaporation loss drives the enrichment of soil water isotopes. The signal of evaporative fractionation of soil water isotopes at different elevations has spatiotemporal heterogeneity. From the perspective of time dynamics, the evaporation loss of the whole region during the observation period was affected by temperature before July, while after July, it was controlled jointly by temperature and humidity, evaporation was weakened. Soil salt content and vegetation played an important role in evaporation loss. In terms of spatial dynamics, the soil moisture evaporation at the Xiying (2097 m) and Huajian (2390 m) stations in the foothills area is larger than that at the Nichan station (2721 m) on the hillside and Lenglong station (3637 m) on the mountain top. The surface soil water evaporation is strong, and the evaporation becomes weak with the increase of depth. The research has guiding significance for the restoration and protection of vegetation in arid areas and the formulation of reasonable animal husbandry policies. [ABSTRACT FROM AUTHOR]

Soil moisture is a central theme in eco-hydrology. Topography, soil characteristics, and vegetation types are significant factors impacting soil moisture dynamics. However, water loss (evapotranspiration and leakage) and its factors of the self-organized vegetation pattern are not clear, which has significant ecologic functions and contributes to different hydrological ecosystem services. From an eco-hydrological point of view, we relied on the observation of rainfall, soil moisture, and soil temperature in the growing season of a drought year to compare soil moisture and temperature dynamics in terms of frequency/probability distribution and water loss among three typical vegetation types in the Qilian Mountains, China. The results indicated that shrubland (the semi-shaded slope) had the highest average soil moisture at the surface soil (0–40 cm) and soil profile during the growing season, while grassland (the south-facing slope) had the lowest daily average soil moisture and highest daily average soil temperature at the surface soil and soil profile. Spruce forest (the shaded slope) had the lowest daily average soil temperature at the surface soil and soil profile (p < 0.001). Water loss among the three vegetation types has a clear positive relationship with soil water content and a negative relationship with soil temperature. The values of water loss between values of water loss at the wilting point and maximum evapotranspiration point tend to occur in wetter soil moisture under the spruce forest and shrubland, whereas that of grassland emerges in drier soil moisture. The spruce forest and shrubland experienced higher water loss than the grassland. Although the spruce forest and shrubland had a better capacity to retain soil water, they also consumed more soil water than the grassland. Soil moisture may be the main factor controlling the difference in water loss among the three vegetation types. These findings may contribute to improving our understanding of the relationship between the soil moisture dynamics and vegetation pattern, and may offer basic insights for ecosystem management for upstream water-controlled mountainous areas. [ABSTRACT FROM AUTHOR]