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• Evergreen coniferous forestlands increased the complexity of fungal networks. • Topsoil organic carbon fractions shaped complex lipid metabolism pathways. • Specific keystone taxa were potential drivers for soil water repellency. Soil water repellency (WR) is an important hydrological function in the terrestrial water cycle as it prevents water from penetrating into the soil and exacerbating soil erosion. Vegetation restoration may greatly affect WR by increasing soil organic carbon (OC) storage and altering microbial community composition in response to environmental stressors in the loess hilly areas of China. Yet, the regulating mechanisms of WR by changes in microbial functional profiles across land use types in these regions are poorly characterized. In this work, solid-state13C nuclear magnetic resonance (NMR) spectroscopy and shotgun metagenomics sequencing were applied to systematically assess the effects of land use types on the OC fractions, soil bacterial and fungal community composition, as well as microbial functional profiles. We found that artificial evergreen coniferous forestland caused more severe WR and increased the complexity of fungal networks. Besides, the artificial evergreen coniferous forestland had larger impacts on labile OC fractions, microbial communities,and lipid metabolic pathways in topsoil compared to other land use types. What's more, keystone genera (e.g., Conexibacter , Streptomyces , and Sphaerobolus) and functional genes (ACAT , atoB , ACSL , fadD , ACADM , acd , paaF , echA , and FAS2) were driven by soil properties that contributed significantly to WR. Collectively, our results indicate that topsoil OC fractions interact with keystone taxa to influence WR by regulating functional genes in lipid metabolic pathways. These findings greatly boost our understanding of assessing the SWR risk against the backdrop of climate change and lay a theoretical foundation for formulating rational vegetation restoration management strategies based on variations in SWR of forest (grassland) ecosystems on the Chinese Loess Plateau. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mixed planting of shrubs and grasses improved soil properties and permeability within 10 years. • Mechanized agricultural reclamation faced challenges like high bulk density and low permeability. • Soil pore conditions mainly controlled soil permeability in mining areas. The impacts of various reclaimed mine land use patterns on the soil properties and infiltration capacity of mine areas remain incompletely understood. This study was conducted in the northern Loess Plateau to assess the effects of reclamation patterns, specifically vegetation (shrub grassland planted for 3, 6, and 10 years) and agricultural reclamation (mechanized and non-mechanized farmland, both cultivated for 10 years), on the soil properties and permeability of an open-pit coal mine. Original grassland (OG) and farmland (OF) were used as controls. The results show that after 6 years of vegetation reclamation, the soil bulk density (BD, 1.38 g·cm−3), total porosity (TP, 47.88 %), and infiltration rates approached levels similar to those of the OG. After 10 years, the organic matter content (SOM, 8.37 g·kg−1) and average weight diameter (MWD, 0.82 mm) were restored almost to those of the OG. In comparison, after 10 years of agricultural reclamation, SOM (9.22–9.38 g·kg−1) approached the level of the OF. However, compared with the OF, the BD and MWD of mechanized farmland increased significantly by 17.37 % and 154.96 % (P < 0.05), respectively, and the infiltration rates of mechanized and non-mechanized farmland decreased significantly (P < 0.05). Soil porosity was the most important factor affecting soil permeability, accounting for 65.9 % of change in permeability. In conclusion, vegetation reclamation, particularly mixed shrub and grass, led to more pronounced improvements in soil properties and permeability in mining areas compared with agricultural reclamation over a period of 10 years. However, heavy agricultural machinery has a detrimental effect on the soil properties and infiltration capacity of mining areas and should be carefully monitored. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vegetation restoration on the Loess Plateau increased the extend and depth of infiltration. • Vegetation restoration on the Loess Plateau has altered the pattern of uniform water infiltration, resulting in a distinct preferential flow in the infiltration processes. • Mixed-mode afforestation is better than single-dominant-species afforestation to promote precipitation infiltration. • The preferential flow phenomenon was more pronounced in the natural secondary forest than that in plantation forests. In order to improve the fragile ecological environment, the Loess Plateau region of China has implemented a large number of long-term forest vegetation restoration projects. Infiltration, as an important part of the hydrological cycle, is also changing with vegetation restoration, and a comprehensive study of these changes is an essential aspect of evaluating the effectiveness of vegetation restoration. In the study, three typical forest vegetation types in the Loess Plateau were selected to investigate and analyse infiltration characteristics and infiltration patterns by staining tracer experiments. The results showed that (1) vegetation restoration increased the extend and depth of infiltration. (2) The extent of infiltration in mixed plantation forest of Pinus tabulaeformis and Robinia pseudoacacia was better than that in pure Pinus tabulaeformis plantation forest. (3) Vegetation restoration resulted in more pronounced preferential flow phenomenon in the infiltration processes. (4) The preferential flow phenomenon was more pronounced in the natural secondary forest than in plantation forests, especially if the amount of infiltrated water was low. (5) The extent of infiltration was mainly influenced by the infiltration water volume, soil water content, and total soil porosity; and the degree of preferential flow development was mainly influenced by the infiltration water volume, soil organic matter, and root distribution. At present, vegetation restoration on the Loess Plateau can play a role in promoting precipitation infiltration, and mixed-mode afforestation is better than single-dominant-species afforestation to fulfil this function of forests. [ABSTRACT FROM AUTHOR]

• Natural grasslands improve soil infiltration capacity in both plant and bare patches. • Patchy mosaic patterns make infiltration heterogeneity and redistribute water on slope scale. • Plant with tap root systems produce more effective macropores as preferential flow paths. • Fine roots have a significantly negative effect on the soil infiltration capacity. Soil infiltration capacity is an important factor affecting soil moisture, and is of great significance to plant growth and groundwater recharge in arid and semiarid areas. Patchiness of grasslands widely exist and have a crucial effect on hydrological processes in water-limited regions. This study investigated soil infiltrability under natural grasslands with patchy mosaic patterns based on a series of in-situ tests. Two dominated natural restoration vegetation communities (Bothriochloa ischaemum (B. ischaemum) with fibrous root systems and Artemisia gmelinii (A. gmelinii) with tap root systems) and abandoned land (as control) were selected in the loess hilly and gully region of the Loess Plateau, China. The results showed that natural restoration grasslands significantly improved soil infiltrability in both plant and bare patches, and the emergence of patchy mosaic patterns can result in infiltration heterogeneity to redistribute water on a hillslope scale. Compared to B. ischaemum , A. gmelinii are more likely to facilitate the formation of preferential flow, contributing to the increased soil infiltration rates. The initial, steady and average infiltration rates (IIR , SIR , and AIR , respectively) and soil infiltration capacity index (SIC) were all negatively correlated with both root length density (RLD) and root surface area density (RSAD) of fine roots (diameter < 2 mm) but positively correlated with those of coarse roots (diameter ≥ 2 mm). The main factors influencing the infiltration capacity were the mean weight diameter in the 10−20 cm layer and the RSAD of the fine roots in the 0−20 cm layer, which can explain 98.6 %, 81.7 %, 63.9 %, and 91.3 % of the total variance of IIR , SIR , AIR , and SIC , respectively. This work highlights the important roles of patchy mosaic patterns in affecting soil water redistribution and the stabilization of ecological systems, providing a scientific basis for vegetation selection in the process of vegetation restoration in water-limited regions. [ABSTRACT FROM AUTHOR]

• With increasing water temperature, the stability of aggregates decreases. • Parent material affects the sensitivity of aggregate stability to water temperature. • The soil erosion resistance decreases with the increasing water temperature. Water temperature has an important effect on soil aggregate stability. In this study, six soils derived from different parent materials in the hilly region of southern China were selected, and the mean weight diameter (MWD), geometric mean diameter (GMD), and soil erodibility (K value) were measured under different water temperature conditions. The aim of this study was to investigate the influence of water temperature on soil aggregate stability and erodibility. As the water temperature increased from 5 °C to 40 °C, the average content of >5 mm water-stable aggregates decreased by 57.13 %, while the average content of <0.25 mm water-stable aggregates increased by 214.41 %. The MWD and GMD of the six different parent soil types exhibited a decreasing trend with increasing water temperature. The trend of the K value was opposite to that of these values. The influence of water temperature on soil aggregate stability is mainly attributed to the thermal effect on the viscosity of soil water and the expansion of clay minerals. As the water temperature increases, the water viscosity coefficient, water density and water surface tension gradually decrease. Moreover, the response of soil aggregate stability and erosion resistance to water temperature varies with soil depth and parent material type. The topsoil exhibits greater sensitivity to water temperature than does the subsoil. Shale (SH) soils and quartz sandstone (QS) soils exhibited higher sensitivities, and Quaternary red clay (QRC) soils exhibited the lowest sensitivity to water temperature among the six soils. This difference is mainly attributed to differences in the contents of expansive clay minerals and organic matter. These results indicate that soil aggregate stability and erosion resistance decrease with increasing water temperature, which may be one reason for severe soil erosion under extremely high temperature and rainfall conditions in the southern red soil hilly region during summer. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vegetation restoration decreased deep soil water storage in the Loess Plateau. • Revegetation increased steady infiltration but reduced initial and mean rates. • Soil infiltration rates exhibited gradual decline trends along the slope. • The effect of vegetation type on infiltration was higher than slope position. • Soil water and clay content were key factors influencing infiltration rates. Vegetation restoration effectively mitigates soil erosion and improves soil properties, but in drylands, it can lead to soil water scarcity and disrupt ecological balance. Until now, limited research has examined the combined effects of vegetation restoration type and topography on soil water and infiltration in the Loess Plateau of China. Here, we investigated soil water content (SWC), soil water storage (SWS), soil infiltration rates and related soil properties in typical forestland, shrubland, and grassland across five slope positions on steep slopes, and compared them with cropland. The results indicated that vegetation restoration significantly decreased SWS compared to cropland. Across the entire 0–500 cm depth, reductions were observed at 30.9 %, 33.2 %, and 20.8 % for forestland, shrubland, and grassland, respectively, with forestland and shrubland demonstrating a more pronounced decrease, particularly in deeper soil layers. Shrubland had the lowest SWS on the upper, middle, and top slopes, while forestland showed the lowest SWS on the lower and foot slopes. In terms of infiltration, vegetation restoration generally increased steady infiltration rate but resulted in reduced initial and mean infiltration rates (except for shrubland). Shrubland had the highest infiltration rates, followed by forestland, while grassland had the lowest rates. Soil infiltration rates decreased gradually along the slope, indicating that the impact of vegetation restoration on soil infiltration improvement weakened with lower slope positions. Vegetation restoration type had a stronger direct and total effects on infiltration than slope position. Yet, the indirect influence of slope position through clay content and SWC outweighed that of vegetation restoration type. Our findings highlight the comprehensive assessment of the eco-hydrological effects of vegetation restoration is essential for identifying suitable species and designing optimal spatial distribution, ultimately maximizing the ecological benefits of the restoration. These insights can offer valuable guidance for ecological restoration and land management in fragile dryland ecosystems. [ABSTRACT FROM AUTHOR]

• Recurrent fire leads to degraded rainforest (DRf) and herbaceous-shrubby (HS). • Ksat and 6 years of rainfall-soil suction interactions are analyzed. • HS provide shallow soil saturation even during long dry periods. • Fire decreases Ksat in topsoil and it increases soil suction in depth at HS. • Post-fire soil changes tend to favor rapid suction loss in the unsatured zone. The role of fire in vegetation-soil–water interactions and its implications for soil stability and slope failures is poorly documented in humid tropical regions. This paper focuses on the relationships between vegetation change through recurrent fire and its effects on hydraulic conductivity and soil suction. Two monitoring sites were chosen on steep slopes in the mountainous domain of the Atlantic rainforest: the first is representative of degraded secondary rainforest (DRf) 25–30 years after slash and burn agriculture; the other represents herbaceous-shrubby vegetation (HS) resulting from wildfires in short-time intervals (<5 years). Two fires had previously occurred on the HS slope, one in December 2014 and the other in September 2019. Continuous records of rainfall and soil suction at depths of 10, 20, 50, 100, 150, and 220 cm provided a 6-year data collection from January 2015 to December 2020. Hydraulic conductivity (Ksat) field tests were conducted around the two monitoring sites before and after the September 2019 fire. The main results include: a) soil suction in the topsoil of both vegetation covers follow the rainfall inputs with high values of Ksat (DRf = 195 mm/h; HS = 203 mm/h); b) while quick rainfall-suction responses prevail within the DRf soil profile, soil suction at HS maintains a mean suction value around -27 kPa below 100 cm deep; c) field observations attest to the occurrence of hydrophobicity after the 2019 fire; d) Ksat tests just after this fire indicated a decreasing mean value from 203 mm/h to 46 mm/h; and e) by the end of the dry season after fire, there is a delayed increase in soil suction reaching -143 kPa at a depth of 100 cm and in smaller proportions at 220 cm deep. These results indicate that post-fire soil changes tend to favor the sudden loss of soil stability and slope failure during extreme rainfall events. [ABSTRACT FROM AUTHOR]

• Spatiotemporal DSL variation and associated forcings were explored at a semi-humid catchment. • Land use type was the dominant control on DSL variation at a catchment scale. • DSL response to meteorological factors differed between the semiarid and semi-humid catchments. • The mixed "forest/shrubland + grass" plantation type is recommended for the semi-humid catchment. The formation of dried soil layers (DSLs) is a broad consequence of climate change (i.e., through temperature increases and/or precipitation decreases) and poor land management practices, where these layers exist has severe negative effects (i.e., retardation of vegetation, negative water cycle balance) on the sustainability of restored ecosystems and health of agriculture. Because of the effort and time required, only sporadic in situ measurements on spatial and temporal DSL variation have been reported, particularly at a catchment scale. However, this information is essential for understanding mechanisms associated with evolutionary DSL processes as well as developing effective land management techniques. Accordingly, this study monitored soil water content to a 5 m depth over a 5-year period in a semi-humid catchment on the Loess Plateau while also investigating temporal DSL dynamics and dominant controls. In the semi-humid catchment, DSLs occurred at 90.7 % of all sampling sites. Spatially and temporally averaged DSL formation depth (DSLFD), DSL thickness (DSLT), and DSL soil water content (DSL-SWC) within the 0–5 m profile were 170 cm, 262 cm, and 9.52 %, respectively. Forest and shrubland DSL regimes were drier than those of grassland. These three DSL indices exhibited significant correlation with temperature variables, while only DSLFD variables significantly correlated to precipitation. Land use type was the predominant control of DSL variation at a catchment scale. A spatial DSLT variation comparison under different land use treatment positions determined the feasibility of planting grass at an upslope position and mixed forest/shrubland + grass at mid-slope and downslope positions in the semi-humid catchment, which provides a good case study for afforestation practices at a catchment scale. Findings from this study are intended to aid in catchment soil and water conservation, soil drought mitigation, and sustainable vegetation management practices on the Loess Plateau as well as other water-limited regions worldwide. [ABSTRACT FROM AUTHOR]

• The probability of large-scale extreme drought was higher in forest ecosystems. • Compared to natural ecosystems, soil drought was more likely to occur in farmland ecosystems during winter. • The interaction between environmental factors in farmland ecosystems was stronger than that in natural ecosystems. • The dominant factor of soil drought in farmland ecosystems was temperature, and that in forest and grassland ecosystems was vegetation. Soil drought exhibits diverse characteristics across ecosystems due to intricate interactions within the soil–plant-atmosphere continuum. However, the dynamic variability and dominant factors of soil drought in different ecosystems remain unclear. To address this knowledge gap, this study characterized soil drought according to the standardized soil moisture index (SSMI) constructed using root-soil moisture data of the Global Land Data Assimilation System. Environmental factors were classified into three categories, namely climate factors (precipitation, temperature, and potential evapotranspiration), vegetation factors (NDVI and LAI), and topographic and soil factors (elevation, slope, aspect, groundwater storage, and soil texture). On this basis, the impact of terrestrial and meteorological multi-factors and their interactive effects on soil drought variation were examined through correlation analysis. Moreover, redundancy analysis (RDA) was employed to quantify the contribution of multiple drivers to soil drought in ecosystems, as well as identify the dominant factor. The results indicated that: (i) large-scale extreme drought events are more likely to occur in forest ecosystems than in farmland and grassland ecosystems; (ii) the duration of soil drought was longer in winter, especially in forest ecosystems; (iii) in winter, soil drought is more likely to occur in farmland ecosystems than in natural ecosystems; (iv) in farmland, grassland, and forest ecosystems, environmental factors explained 71.9%, 74.0%, and 77.8% of the changes in soil drought, respectively; (v) the dominant factor controlling soil drought was temperature for farmland ecosystems (F =321.20, p <0.01), and vegetation for forest (F =212.36, p <0.01) and grassland ecosystems (F =168.00, p <0.01). [ABSTRACT FROM AUTHOR]

• Freeze-thaw cycles varied as a function of the extent of vegetation cover. • Migration of soil water was greatest with low vegetation cover. • Reallocation of soil water caused temperature in the soil complex to vary. • Freeze-thaw cycles promoted evaporation of soil water in the plant-rooting zone. Freeze-thaw events can lead to the upward migration of shallow groundwater in recharging the upper soil profile. However, their effects on soil water movement in areas of deep groundwater is not entirely known, especially in arid and semiarid regions of the world. This study analyzed the soil hydrothermal coupling at two desert sites in the Mu Us Sandy Land (northwest China), noted for their differences in surface scrub-vegetation cover, one with 80 % cover and another with 40 % (sites A and B, respectively). The work consisted of collecting soil temperature and moisture measurements at the two sites, both renowned for their deep watertable. The results showed that the freezing period at both sites was about 3–6 times longer than the thawing period, and that the duration of uniform freezing was inversely related to the degree in surface vegetation cover. During the two freezing periods of 2017–2019, as much as 3.87 (or 21.9 %) and 7.37 mm (42.2 %) of soil water was observed to have migrated upwards from the lower soil layers. Altogether, the total distance traveled by the soil water exceeded 180 cm. Also, about 33.2 (site A) and 22.9 mm of soil water (site B) were depleted because of evaporation in the first 185 cm of the soil complex during the two freeze–thaw events. Extent of vegetation cover, initial soil moisture profile, and soil texture influenced the quantity of water lost from individual soil layers due to evaporation and between soil-layer water exchanges. Soil water migration also affected changes in soil temperature in the range of −12.1 to 4.8 °C within the first 185 cm of the soil complex. Changes in soil temperature were responsible for decelerating freezing and thawing processes, prolonging soil water reallocation processes in the soil. Overall, freeze–thaw events increased the amount of shallow soil water losses due to evaporation, triggering a corresponding decline in soil water in the plant-rooting zone. This drop could conceivably lead to a reduction in sprouting and growth of spring vegetation, further degrading affected sand-dominated desertlands. This information may provide insight into the hydrological response of freeze–thaw events in arid regions, as well as provide useful information in guiding afforestation efforts in associated desertlands. [ABSTRACT FROM AUTHOR]

• Deep soil and adjacent farmland were both important water sources for apple trees. • SWD increased at a rate of 5.94 mm m−1 yr−1 in apple orchard before 30 years of age. • The migration and accumulation of NO 3 –-N confirmed the soil water exchange. • The orchard-farmland pattern can promote efficient water and nutrient use in the CLP. With the vigorous promotion of apple tree planting on the Chinese Loess Plateau (CLP), a mosaic pattern of apple orchards and traditional farmland has emerged in the region. However, the interaction between adjacent farmland and apple orchards in terms of soil water and nutrient migration remains unclear. This study aimed to investigate the spatial distribution of the soil water content (SWC) and soil nutrients, as well as their interactions, in 0–10 m soil layers of apple orchards of different stand ages and adjacent farmland under the orchard-farmland land use pattern. The results revealed a significant decrease in average-depth SWC in the orchards in the 0–10 m soil profile (R2 = 0.90) with increasing orchard age, accompanied by a significant increase in soil water deficit (SWD, R2 = 0.94). The annual growth rate of SWD was found to be as high as 5.94 mm·m−1·y−1. Deep soil and surrounding farmland were identified as important sources of soil water for apple tree growth, particularly in older orchards; a 25-year-old orchard absorbed approximately 10.8 % of soil water towards farmland with a horizontal distance of 7 m. The distribution of soil organic carbon (SOC) and total nitrogen (TN) in the 0–10 m soil profile exhibited a similar pattern, decreasing and then stabilizing with increasing depth. However, the peak depth and accumulation of soil nitrate (NO 3 –-N) significantly increased with orchard age. The migration and accumulation of NO 3 –-N in the soil provided a scientific basis for the transport of soil water, with NO 3 –-N accumulation (405.32 mg kg−1) observed in the deep soil (3–6 m) of farmland located 5 m away from a 30-year-old orchard, confirming the exchange of soil water and nutrients between the orchard and the farmland. The stand age of the orchards was identified as the main environmental factor influencing soil water transport under the orchard-farmland land use pattern. Overall, our findings provide valuable insights into the interaction between apple orchards and farmland under the mosaic pattern, which can contribute to a more rational layout of apple orchards and farmland in the future, promoting the efficient utilization of soil water and nutrients on the CLP. [ABSTRACT FROM AUTHOR]

• Land use types determined deep soil water redistribution. • Soil moisture in abandoned land was strongly affected by rainfall. • Decreased rainfall and soil drying reduced the growth of forage and shrubs. • Farmland in terraces and abandoned land on slopes were the ideal use types. The land-use change affects soil hydrological processes in semi-arid areas. Investigating the impact of precipitation change on soil moisture in different land use types (LUTs) is conducive to water resource management and ecological restoration. The volumetric water content (VWC) at 0–300 cm soil profile, meteorology data, and vegetation aboveground biomass were continuously observed from 2018 to 2022 in five terraced and three sloped LUTs. The results showed that soil moisture was affected by precipitation, vegetation, antecedent soil water, soil properties, and artificial management measures. There were significant differences in soil moisture among these land use types (P < 0.05), with the priority order of multi-year profile average VWC at 0–300 cm depth was farmland in the slope (FAS) (0.22 ± 0.01 cm3 cm−3) > bare land in the terrace (BAT) and farmland in the terrace (FAT) (0.19 ± 0.01 cm3 cm−3) > abandoned land in the slope (ABS) (0.18 ± 0.02 cm3 cm−3) > abandoned land in the terrace (ABT) (0.13 ± 0.02 cm3 cm−3) > forage land in the slope (FOS) (0.12 ± 0.02 cm3 cm−3) > forage land in the terrace (FOT) and shrubland in the terrace (SHT) (0.10 ± 0.01 cm3 cm−3). Except for BAT, soil water storage (SWS) in other LUTs decreased in 0–300 cm soil profile from 2018 to 2022. There were no or slight soil desiccations in FAS, BAT, ABS, and FAT, moderate soil desiccation in ABT, and serious soil desiccation in FOS, FOT, and SHT. The VWC, SWS, and soil desiccation index (SDI) of all LUTs were positively correlated with precipitation, especially at 0–100 cm depth. Precipitation threshold response to soil desiccation alleviation was determined to be 98–116 mm month−1. Moreover, aboveground biomass of FOT, ABT, and SHT exhibited a significant correlation with both soil moisture and precipitation (P < 0.05). Therefore, forage lands and shrublands have adverse effects on the mitigation of deep soil desiccation with decreasing rainfall. This study recommended farmland in the terrace and abandoned land in the slope for soil and water conservation and sustainable ecological restoration. [ABSTRACT FROM AUTHOR]

• Soil physical properties were strongly related to land use, slope aspect, slope position and their interactions. • 19 year old locust was the most effective at improving the BD and Ks. • Better soil physical properties were obtained on the north slope and down slope. • Soil physical properties displayed different changes with locust restoration year. • Key factor affecting forest growth and soil quality improvement varied with forest ages. Soil particle size distribution (PSD), bulk density (BD), saturated hydraulic conductivity (Ks), soil water content (SWC) and generalized soil structure index (GSSI) are key physical properties for vegetation growth and are easily affected by natural and anthropogenic factors. However, how these soil physical properties respond to land use, slope aspect, slope position, and their interactions are less clearly understood. Here, an experiment with three land uses (cropland, grassland, and black locust [ Robinia pseudoacacia L.] forests after 4, 9, 15, and 19 years of restoration), two slope aspects (south and north slope) and two slope positions (up and down slope) were conducted in the hilly loess region of China. The results showed the following: (1) The variation in different physical properties were driven by different factors of land use, slope aspect, slope position and their interactions. (2) The 9, 15 and 19 year old locust forests significantly decreased the BD by 6.75 %–19.32 % and increased the Ks by 69.96 %–195.97 % compared with grassland, while the cropland had higher SWC and GSSI values than the grassland and locust forests. (3) Soil physical properties were higher on the north slope than on the south slope and were larger on the down slope than on the up slope. (4) The BD, Ks, SWC, and GSSI of locust forests displayed different changes with the restoration year. (5) The key factor affecting forest growth and soil quality improvement varied with forest ages. Overall, 19 year old locust was the most effective at improving the BD and Ks. Furthermore, slope aspect, slope position and restoration time should be considered when evaluating the response of physical properties to land uses. [ABSTRACT FROM AUTHOR]

• The relationship between gross N turnover and temperature and moisture varies on annual and seasonal scales. • The gross N turnover under the influence of temperature and water is different between field and laboratory conditions. • Soil temperature has more influence on soil gross nitrogen turnover than moisture. Understanding how soil nitrogen (N) turnover responds to temperature and soil moisture alterations is important for accurately predicting responses of soil N availability and plant productivity to global climate change. However, few studies had explored such questions under natural conditions. We investigated effects of temperature and moisture on soil gross N turnover with an annual scale field experiment in an Inner Mongolian grassland and a laboratory incubation experiment. In the field experiment, on the annual scale both gross ammonification and nitrification rates showed a hump-shaped response to temperature, with maximum rates occurring around 10 °C and 5 °C, respectively. Gross ammonification rates did not respond to soil moisture, and gross nitrification rates decreased first and then increasing with soil moisture, which the threshold was 35% water holding capacity (WHC). Totally, soil temperature explained more variation than moisture in gross ammonification (0.30 VS 0.04) and nitrification (0.24 VS 0.14) rates. On the seasonal scale, both soil temperature and moisture showed generally significant effects on gross N turnover. Grazing had no effects on soil temperature and moisture sensitivity of gross N turnover on the annual scale, but increased the sensitivity of gross ammonification to soil moisture during the spring freeze–thaw period. In the laboratory incubation experiment, gross ammonification and nitrification rates increased with the increase of temperature, although there was no difference between 20 °C and 30 °C. Gross ammonification rates reached a maximum at 50% WHC, while gross nitrification rates did not respond to soil moisture until 100% WHC. Soil temperature explained more variation than moisture in gross ammonification (0.71 VS 0.01) and nitrification (0.37 VS 0.25) rates. Our results imply that climate warming may have greater impact on gross nitrogen turnover compared to changes in rainfall, however it remains great uncertainty due to the low explanation of soil temperature and moisture. [ABSTRACT FROM AUTHOR]

• Artificial restored shrub and grass aggravated soil deficit but they got replenished better under large rainfall. • The effects of revegetation and topography on SWS varied greatly with rainfall. • Water-intensive vegetation species should be used cautiously for revegetation. The Chinese Loess Plateau (CLP) rose to prominence for its fragmented terrain and fragile ecosystems. Large-scale revegetation was applied to control soil and water loss there. However, revegetation resulted in unexpected water shortages. In this study, we investigated the temporal-spatial distribution of soil water in the northern CLP based on 13-year soil water content (SWC) data of four different revegetation types on a loessial slope and 4-year data of a gully system to study the response of soil water to long-term revegetation, topography, and precipitation. Results showed that in the 0–400 cm soil depth under shrub, grass, natural fallow, and millet, soil water storage (SWS) was –102.8, –129.3, 54.9, and 39.3 mm higher after 13-year of restoration, respectively. Although soil water under shrubs- and grasslands became more replenished under high precipitation, planting these water-intensive vegetation types aggravated soil desiccation. The gully intensified soil water spatial heterogeneity, with mean SWS within 0–480 cm soil depth of 902, 712, and 746 mm at the gully bottom, edge, and bank, respectively. The deviation index among the four revegetation types and among gully bottom, edge, and bank were 0.43 and 0.26, respectively, which indicated that revegetation types had a more obvious effect on SWS. Given that more concentrated rainfall under global climate change, both revegetation type and topography should be considered during ecological restoration in semi-arid areas. These findings can deepen our comprehension of the hydrological processes on the CLP and provide a reference for the development of ecological restoration policies under future climate change. [ABSTRACT FROM AUTHOR]

• We addressed soil carbon fluxes in saline-alkaline grasslands. • Light grazing showed a negative effect on SR h. • Seasonal fluctuation of grazing effects resulted in unaltered seasonal mean SR. • Annual precipitation regulated the interannual variation of soil C emissions. • Soil environment explained SR more than plants and soil microorganisms. Grazing is a prevalent management strategy in grassland ecosystems that has profound effects on plants and soil microorganisms, consequently altering soil carbon (C) fluxes. However, the difference responses and regulatory mechanisms of soil autotrophic respiration (SR a) and heterotrophic respiration (SR h) to different grazing intensities remain unclear, especially in saline-alkaline grasslands. A six–year (2017–2022) field experiment involving four grazing intensities (no grazing, light grazing, moderate grazing, and heavy grazing) was conducted in a saline-alkaline grassland located in the agro-pastoral ecotone of northern China. Soil total respiration (SR tot) and its components (SR a and SR h), and the related biotic and abiotic factors (plants, soil microorganisms, and soil environment) were measured. The results showed that light grazing significantly decreased the mean SR h by 17.7% across six measuring years. The effects size of grazing on soil respiration fluctuated consistently with soil water content during the growing seasons (May–September), resulting in a neutral effect of grazing on the seasonal mean SR a. The cumulative soil C emissions of the current year varied with the seasonal precipitation in the previous year, whereas the changes in cumulative soil C emissions induced by grazing showed the same trends as annual precipitation. In addition, the key control factors for SR h and SR a differed and varied with grazing intensity and the soil environment played a critical role in regulating soil C fluxes. In conclusion, light grazing reduces soil microbial-driven C emissions and the soil environment and precipitation co-regulate the response of soil C fluxes to different grazing intensities in saline-alkaline grasslands. [ABSTRACT FROM AUTHOR]

• Soil moisture content varied with soil depth, upslope distance, vegetation type, and time. • Soil organic carbon and moisture were lowest in Robinia pseudoacacia plantations. • Grassland showed lower soil moisture loss and greater organic carbon sequestration. • On the Loess Plateau, afforestation within grassland may enhance ecosystem services. Large-scale afforestation is considered controversial as an ecosystem renewal strategy for the Loess Plateau of China, since it may increase soil organic carbon (SOC) but may also exacerbate water shortages. In our study, we aimed to clarify how afforestation and slope affect soil moisture content (SMC) and SOC and their interaction particularly for deep hillslope profiles on long hillslopes, in terms of the trade-off between soil moisture and organic carbon. This study investigated SMC and SOC density (SOCD) from 0 to 400 cm hillslope depth profiles at 20 m intervals uphill to 100 m in the May and October (the beginning and end of the growing period, respectively) from 2015 to 2017. The three sampling sites were located in Robinia pseudoacacia plantation, natural forest, and natural grassland as the control. Soil moisture deficit and SOC sequestration of plantation were compared to those of grassland, and the trade-off between SMC and SOCD was evaluated. The results showed that SMC and SOCD were the lowest in the Robinia pseudoacacia plantation, indicating that the plantation exhibited a greater soil moisture deficit and SOC loss than the grassland. In the plantation and natural forestland, the subsoil (100–400 cm) exhibited greater soil moisture deficit and SOC loss than the soil (0–100 cm). SOCD increased while SMC decreased with upslope distance for all hillslope layers in both plantation and natural forestland. The downslope sites exhibited more severe soil moisture deficit, and greater SOC loss than the upslope sites. Natural grassland exhibited low water depletion and high SOC sequestration. Further, the downslope plantation sites exhibited the lowest root mean square deviation for the relationship between SMC and SOCD. Based on these findings, a vegetation restoration strategy involving afforestation of downslope patches within a contiguous grassland matrix may achieve high-level maintenance of ecosystem services. These findings provide a theoretical basis for vegetation restoration on the Loess Plateau. [ABSTRACT FROM AUTHOR]

[Display omitted] • Afforestation has desiccated the soil in arid areas. • Soil moisture was significantly affected by plantation age. • A conceptual synthesis is proposed based on soil dry layer of Vegetation carrying capacity. In recent years, China has achieved remarkable results in curbing desertification through afforestation. However, the dry soil layer resulting from the long-term water consumption of overloaded perennial plants seriously threatens the sustainability of afforestation, and quantifying the maximum vegetation carrying capacity under certain soil moisture conditions is crucial to the sustainability of afforestation in arid areas. Therefore, we aimed to simulate soil water in Haloxylon ammodendron plantations at different growth stages using the simultaneous heat and water transfer (SHAW) model to determine the vegetation carrying capacity threshold. Field-measured soil and vegetation data for 2021 were used to calibrate the SHAW model. Good consistency in soil water content (SWC) was observed between measurements and simulations in the calibration and validation phases of the model, with considerable linear correlation and low prediction error values. Therefore, the soil water dynamics of H. ammodendron plantations in the study area could be accurately predicted using the SHAW model. The simulation results show that, with increasing forest age, the SWC at 0–400 cm gradually decreases and a dry soil layer starts to form when the forest age reaches 11 years. The dry layer thickness reaches 120 cm by 22 years, thus the optimal growth age of artificial H. ammodendron plantations in the study area should not exceed 22 years, and the maximum biomass soil water carrying capacity of vegetation is 1,650 kg/hm2. A vegetation carrying capacity threshold can be determined in this study for the sustainable management of future afforestation activities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Slope had the most significant negative effect on soil infiltration rates. • The effect of different vegetation on soil infiltration rates was significantly different. • Soil organic carbon content increases in average infiltration rates reached 47.70 %. • Non-capillary porosity increases in average infiltration rates reached 31.00 %. High Mountain Asia (HMA) surrounding the Tibetan Plateau (TP) is a critical gathering place for water resources. Investigating soil water infiltration properties in HMA is a vital component of comprehending the hydrological cycle processes in this region. Despite some experimental studies having analyzed the soil water infiltration properties under specific conditions in HMA, a systematic quantitative anlysis of this region's soil water infiltration properties remains lacking. To investigate the effect of soil water infiltration properties under different factors in HMA, we conducted a literature review and meta-analysis based on experimental data from the literature. Our study employed the initial infiltration rate (IIR), steady infiltration rate (SIR), and average infiltration rate (AIR) as response variables to quantify the variations in soil water infiltration properties under diverse conditions. Results revealed that (1) the most significant negative effect on soil water infiltration rates was due to slope (IIR: −48.31 %, SIR: −36.87 %, AIR: −51.81 %). The subgroup analysis indicated that the negative effect of slope on the three infiltration rates was more pronounced as the slope gradient increased. (2) The positive and negative effects of different vegetation types on soil water infiltration rates were significantly different. Among them, the trees + shrub group exhibited the most prominent positive effect on IIR and SIR (IIR: +206.49 %, SIR: +153.45 %). Conversely, the widely distributed alpine meadow in HMA had a significant negative effect on IIR (−39.35 %). (3) Contrary to conventional soil infiltration experiments, the increase of initial soil moisture (SM) in HMA had a positive effect on IIR and AIR (IIR: +13.88 %, AIR: +23.37 %). Considering the study of macropore flow, this may be related to soil texture and vegetation growth. (4) As the values of each soil physicochemical property increased, there was a significant positive effect of increasing non-capillary porosity (NCP) and soil organic carbon content (SOC) on AIR (NCP: +31.00 %, SOC: +47.70 %). At the same time, we found that soil water infiltration studies in HMA are subject to spatial and quantitative limitations. Considering the importance of soil water infiltration in HMA, we recommend more comprehensive studies of soil water infiltration in HMA. Such studies would provide a vital theoretical foundation for enhancing the HMA soil infiltration model and improving the terrestrial hydrological cycle process in the region. [ABSTRACT FROM AUTHOR]

• Land-use types, seasons, slope position significantly affected SOC and SWC. • Revegetation increased SWS consumption and SOC accumulation. • There was a positive linear relationship between SOC and SWC. • Planting grass and shrubs is recommended in the semi-arid hilly and gully regions. Understanding the response of soil organic carbon (SOC) and moisture to different land-use types, slope positions, seasonal variations, and their interactions has great significance for land use and management. However, the coupling effects of SOC and soil moisture in typical hilly and gully regions are still elusive. Therefore, in this study, five different land-use types, including cropland, abandoned land, grassland, shrubland, and forestland were selected in a typical Chinese loess hilly-gully region, and soil samples were collected from 0 to 200 cm profiles at the upper, middle, and lower slope positions in four seasons. The results demonstrated that the distributions of SOC and soil moisture were jointly significantly affected by land-use types, seasons, and slope positions (P < 0.01). Average SOC content was found to be highest in the shrubland, followed by grassland, abandoned land, forestland, and cropland. SOC storage at the lower slope position was 10.97% higher than that at the upper slope position. SOC storage in winter was 45.47% higher than that in summer. SOC storages of abandoned land, grassland, shrubland, and forestland were 17.38%, 33.08%, 52.52% and 1.26% more than that of cropland, respectively. Soil moisture fluctuated greatly in 0–100 cm layers and was stable beneath the 100 cm layers, which was highest in autumn, and lowest in summer. Whereas, under different land-use types, the soil moisture of cropland was the highest, especially significantly higher than all revegetated treatments in the 60–200 cm soil layers. Compared with cropland, soil water storage at other land-use types was averagely 36.45 % lower in the entire 200 cm soil profile. SOC was positively correlated with soil moisture under different factors. Thus, we recommend planting shrub and grass in watersheds with serious soil erosion in the semi-arid hilly and gully region, because they can sequestrate more SOC and retain more soil water. [ABSTRACT FROM AUTHOR]

• Warming and precipitation reduction significantly affect Rs in sandy grasslands. • ST plays a dominant role in Rs during the early and whole growing seasons. • SM plays a dominant role in Rs during the middle and late growing seasons. • Rs is co-regulated by hydrothermal factors, soil properties and vegetation characteristics. • ST and SM remain the main factors determining Rs in sandy grassland. Soil respiration (Rs) is one of the largest carbon fluxes from terrestrial ecosystems to the atmosphere, and there are still a great deal of uncertainties in the estimation of soil carbon emissions from terrestrial ecosystems. Grassland ecosystems are fragile and sensitive to climate change, so it is crucial to reveal the effects of temperature and precipitation changes on Rs in sandy grasslands. Here, we examined the effects of experimental warming and precipitation reduction on Rs in the sandy grassland of Horqin and the relationships between different environmental factors and Rs. It was found that: (1) Soil temperature (ST) and soil moisture (SM) showed consistent seasonal variations with Rs during the growing season; (2) Warming increased Rs significantly in the middle of the growing season and throughout the growing season, and had no significant effect on Rs at the beginning and late of the growing season. Precipitation reduction reduced Rs significantly in the early and middle of the growing season and throughout the growing season, but had no significant effect on Rs at the late of the growing season. The interaction of warming and precipitation reduction only significantly reduced Rs in the middle and late of the growing season; (3) ST played a dominant role in Rs in the early growing season and throughout the growing season, and SM played a dominant role in Rs in the middle and late of the growing season; (4) Rs was significantly and positively correlated with ST and SM in the growing season; (5) Rs was regulated by the combination of hydrothermal factors, soil properties, and vegetation characteristics, of which hydrothermal factors are the main influencing factors in the growing season. Our results provide direct evidence to elucidate the effects of climate change on Rs in sandy grasslands. [ABSTRACT FROM AUTHOR]

• Agroforestry stand age affects soil water patterns significantly. • Over 20 years, stand age reduces soil water movement. • New and existing soil water interplay adds complexity in agroforestry. Understanding the relationship between agroforest age and soil water dynamics is crucial for effective land and water resources management. However, the complexities of these dynamics, such as soil water recharge and depletion, hamper in-depth understanding, particularly in water-scarce regions. In this study, we examined soil water recharge and depletion in relation to the stand age of apple trees, a widely planted and representative deep-rooted agroforest, over four years in a semi-arid region on China's Loess Plateau (CLP). We collected soil cores to >20 m depth from four apple orchards (referred to as 'agroforests') with variable stand ages (established in 2008, 2005, 1998, and 1994). For comparison, we selected adjacent cropland as land use prior to agroforestry practices ('control'). We measured soil water content and tritium distributions to model soil water dynamics and estimate water ages across different soil profiles. Our results show that recharge amounts (and depths) in shallow soils were 298.4 mm (7 m), 303.4 mm (6.6 m), 300.6 mm (5.4 m), and 483.1 mm (7.6 m), whereas deep soils had net depletions of 111.1 mm, 391.9 mm, 192.8 mm, and 108.9 mm for AP2008, AP2005, AP1998, and AP1994, respectively. The tritium peak depths, which indicate the 1963 bomb peak depth, significantly differed between agroforested and non-agroforested plots. In particular, agroforestation reduced the seepage velocity of soil water over 20 years. Furthermore, our tritium tracer water age model suggests that the age of transpired deep soil water exceeded 200 years in the oldest orchard. These findings highlight a complex interaction between newly infiltrated water and existing water, possibly due to variations in soil pore size distributions. The results of this study offer valuable insights into the ecohydrological impacts of agroforestation on the CLP and in similar climatic regions. [ABSTRACT FROM AUTHOR]

• Root water uptake depth increased in "S" shape with tree age and stabilized at 20 m after 20 years in an apple orchard. • Soil water deficit increased in depth of 3–21 m at a rate of 5.8 mm m−1 yr−1 from 10 to 24 years of tree age. • Apple trees could draw water horizontally up to 7 m from deeper soil layers of adjacent cropland. • Orchard-cropland mosaic structure is able to optimize the use of soil water resources in the Loess Plateau. It is of great significance to explore soil water distribution and consumptions of the agroforestry systems in water-deficient areas. In recent decades, continuous development of apple orchards in the southern Chinese Loess Plateau has formed the orchard-cropland mosaic vegetation pattern. In this study, soil water content (SWC) in two series were measured, (1) 0–21 m soil profiles of five apple orchards with different stand ages (5, 10, 15, 20 and 24 years) and one cropland; (2) 0–6 m soil profiles at different sites within the orchard-cropland border zone (with apple orchard aged 10 and 24 years old, denoted as AC10 and AC24, respectively). Results showed that (1) the water consumption depth of apple orchards increased in an "S"-shaped pattern with stand age and reached 20 m after 20 years, while the average SWC within 3–21 m layer decreased and the soil water deficits increased at a rate of 5.8 mm m−1 yr−1; and (2) the average SWC in 3–10 m layer of 15, 20 and 24-year-old orchards accounted for 69.3%, 64.2% and 57.9% of the field capacity, respectively, these proportions came to 71.2%, 67.4% and 61.1% in the 3–21 m layer, respectively; and (3) AC24 had greater influence on SWC of adjacent cropland than AC10. The soil water storage of 2–6 m layer in AC24 ranged from 713 mm to 879 mm within 7 m away from the orchard, which were significantly lower than those of 7–15 m away from the orchard (933–1042 mm). Overall, the apple tree root system can absorb soil water from a depth of 20 m in the vertical direction and up to 7 m from the adjacent cropland in the horizontal direction. Therefore, a reasonable orchard-cropland mosaic pattern should be arranged in regional agricultural planning, so as to promote the optimized utilization of regional soil water resources, and to coordinate the development of fruit industry and food security, in which the width of a cropland can't be < 14 m. [ABSTRACT FROM AUTHOR]

Abstract Soil water storage (SWS) is a critical water resource for vegetation growth in the Loess Plateau. Changes in SWS during the growing season can reflect soil water depletion or recharge conditions in different hydrological years. This study investigated the soil water in three hillslopes covered with artificial forest, natural forest and natural grass in May and October of 2015–2017. Both path analysis and stepwise multiple linear regression were used to determine the direct and indirect effects of most important variables and develop a model for predicting changes in SWS. The results showed that compared with natural forestland and grassland, artificial forestland had low soil water, but deep SWS maintained a balance of inputs and outputs. In all soil layers, during the growing season, total precipitation (X 4) was the most important variable affecting changes in SWS. The changes in SWS in surface soil layers were affected by more environmental factors than in deeper soil layers. The natural grassland (X 3) and slope position (X 12) have different degree of direct and indirect effects by means of antecedent soil water content (X 5) , even though their correlations were not significant. In addition, changes in SWS at the 0–100 cm, 100–200 cm and 0–400 cm soil layers were adequately predicted using the multiple regression equation, in which R2 reached values from 73.4–93.0%. The model simulating the changes in SWS during the growing season can improve understanding on whether rainfall infiltration can replenish soil water depletion. Highlights • Deep soil water storage (SWS) in artificial forestland can maintain a balance. • Changes in SWS in upper soil layers were affected by more major factors. • The indirect effects of some controlling factors on changes in SWS were not ignored. • Changes in SWS in upper layers were adequately estimated using the prediction model. [ABSTRACT FROM AUTHOR]

Abstract Grassland recovery from degradation is increasingly occurring worldwide. Diverse managements have been considered as effective ways to restore degraded grassland, but it remains unclear how semi-arid grasslands respond to long-term grazing exclusion and fenced mowing. Here, a study was conducted under open grazing, grazing exclusion and fenced mowing in a semi-arid grassland on the Loess Plateau. We measured plant species composition and diversity, plant production, surface litter and soil water and carbon content. Shifts in grassland management led to significant divergence in plant community composition. Long-term grazing exclusion (35 years) significantly increased plant biomass, surface litter, soil water and carbon storage, but suppressed plant diversity compared to open grazing. Conversely, fenced mowing significantly increased plant diversity accompanying with a weak effect on soil carbon. Moreover, mowing significantly reduced surface litter and soil moisture, which have strong implications for nutrient depletion and soil drying. Our results suggest that introducing disturbances are necessary to safeguard biodiversity, and continuous mowing (5 years) belongs to over exploitation of the long-term protected grassland. Therefore, it is essential to optimize management with dual objectives of biodiversity and soil carbon sequestration in the future. Highlights • Three representative management-related steppe conditions were evaluated. • Long-term grazing exclusion replenished SOC but decreased plant diversity. • Fenced mowing safeguarded plant diversity but induced soil drying. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biocrust colonization increases air permeability by up to 77% • Biocrusts significantly increase saturated water content and water retention. • Air-filled porosity of biocrusts is a key factor governing air permeability. • Biocrust relative air permeability (K ra) is well captured by the standard K ra models. Soil aeration is an important factor influencing soil biological and biochemical processes because it directly affects soil microbial activity and respiration. As an important living skin of the soil, biocrusts strongly impact various soil properties and play a vital role in maintaining surface soil structure and multifunctionality. Although there are several studies concerning the effects of biocrusts on soil respiration processes, it is still not well understood how biocrusts affect air permeability (K a) and soil aeration in drylands. In a semiarid climate region of the northern Chinese Loess Plateau, the K a and air-filled porosity (ε a) of moss-dominated biocrusts established on aeolian sand and loess soil were measured as a function of soil water content under laboratory and in situ conditions and compared to measurements of bare soils. The relative air permeability (K ra) of biocrusts and bare soils was further analyzed and estimated with commonly applied K ra models that are based on the soil water retention curve (SWRC), and the performance of these models was specifically assessed for biocrusts. The in situ measurements yielded a 51.8% and 76.7% higher K a for the biocrust-colonized aeolian sand and loess soil, respectively, when compared to the bare soils. Correspondingly, in comparison to the bare soils, the ε a of the biocrusts also increased by 38.0% for the aeolian sand and by 52.4% for the loess soil. The laboratory measurements showed an 8.5%–9.3% increase of K a for the biocrust-colonized soils from wet to dry conditions when compared to their bare counterparts, which was mainly attributed to their higher fine particle and organic matter contents as well as to the moss rhizoids. Moreover, a positive linear relationship (R 2 > 0.43) was found between the log K a and log ε a for both biocrusts and bare soils. Additionally, the biocrusts exhibited higher water content at almost all matric potentials in comparison to the bare soils. The K ra of biocrusts was 22.0% higher for aeolian sand and 42.1% higher for loess soil when compared to the bare soils. The van Genuchten-Burdine and Brooks and Corey-Burdine models performed best with regard to the estimation of K ra (RMSE ≤ 0.100, bias ≤ 0.018). In general, biocrusts may greatly increase surface soil aeration due to their higher K a and ε a , and the soil aeration status of biocrusts can be indirectly assessed through their effective degree of soil water saturation. Our findings suggest that biocrusts should be carefully considered in further studies of soil aeration related to biological processes and gas and vapor transport in dryland ecosystems. [ABSTRACT FROM AUTHOR]

• Decadal changes in soil water-holding capacity were assessed using field surveys. • Soil erosion and climate change decreased soil water-holding capacity. • The decline in soil water-holding capacity could exacerbate vegetation degradation. Environmental changes on the Tibetan Plateau could affect not only the livelihoods of local people but also the food and environmental security of downstream people. Soil water-holding capacity (WHC) governs soil functioning in ecosystems, could be significantly altered by the accelerated climate change and vegetation degradation experienced by the Tibetan Plateau's alpine ecosystem. However, it remains unclear regarding the direction and magnitude of this feedback. Here, we assessed the responses of WHC to the combined impacts of climate change and vegetation degradation across the Tibetan Plateau over the past decades based on a regional resampling campaign, including 148 well-matched sampling sites, conducted in the 1980s and 2020. We observed an overall decrease in the WHC in the study area in response to a warmer climate and increased soil erosion. The decrease in the topsoil (notably 0–20 cm) was more significant than that in the subsoil (notably 20–50 cm). Average soil available water content (AWC) decreased from 0.13 to 0.10 cm3 cm−3 (p < 0.0001) for topsoil, and from 0.10 to 0.09 cm3 cm−3 (p < 0.01) for subsoil. The changes in AWC were primarily explained by soil erosion (11.3 %) and climate change (9.2 %). Furthermore, the decline in AWC results in a significant decrease in soil productivity, which may exacerbate vegetation degradation and increase the susceptibility of alpine ecosystems to disturbances. These findings suggest that soil erosion control is still an urgent task for environmental protection on the Tibetan Plateau and that increasing WHC is an important goal of adaptation measures. [ABSTRACT FROM AUTHOR]

• Provide thermal regime of uppermost soil layer on the central Tibetan Plateau. • The thermal regime of soil experienced warming during the past 20 years. • Latitude and altitude controlled the soil thermal regime at the macroscale. • Partial correlation quantified the influences of local factors on soil temperature. Permafrost degradation related to global warming has been widespread in the Tibetan Plateau (TP), manifesting prominently as variations in the soil thermal regime, an essential characteristic of permafrost. Altered soil thermal conditions can influence the energy and water balance between the atmosphere and land, leading to the release of stored carbon dioxide and methane. In this study, reanalysis and observed soil temperature data were combined to analyse the long-term changes in the thermal regime of the uppermost soil layer at six sites in the central TP. MERRA2 and ERA5-Land had the highest quality in matching the observed data at each site. The mean annual soil temperature ranged from −0.11 °C to 4.75 °C (averaging 1.73 °C) and warms at 0.059° C a - 1 . The mean annual first dates of freezing and thawing and the mean duration of freezing were 123.23 ± 10.85 d , 285.67 ± 10.34 d , and 161.44 ± 20.54 d , respectively, indicating lagged, advanced, and shortened trends with 0.54 ± 0.49 d a - 1 , 0.50 ± 1.06 d a - 1 , and 1.05 ± 1.16 d a - 1 , respectively. The mean annual freezing and thawing N-factors were 0.53 ± 0.13 and 2.43 ± 2.09, respectively. The maximum and minimum monthly average soil temperatures were 11.81 ± 2.17 °C in July and −9.54 ± 3.24 °C in January, respectively. Partial correlation analysis was used to quantify the influences of factors (including surface air temperature, snow depth, rainfall, normalised difference vegetation index [NDVI], shortwave radiation, and soil moisture) on soil temperature implicated surface air temperature as the most significant influencing factor in the increased soil temperature. Rainfall and NDVI were implicated as being likely to suppress the soil temperature warming. This study provides detailed information about the thermal regime of the uppermost soil in the central TP and facilitates validation of the land surface model. [ABSTRACT FROM AUTHOR]

• SOC higher in the permafrost region than in the non-permafrost region. • Regression-kriging method was the best upscaling approach for the prediction of SOC. • 317 Tg SOC was stored in the entire soil profile of Qinghai Lake watershed. Soil organic carbon (SOC) on the Qinghai-Tibet plateau is of global significance, due to the high carbon density and potential positive feedbacks to climate warming. Qinghai Lake watershed is an important soil pool in Qinghai-Tibet plateau, but the magnitude and characteristics of SOC stock in the high-altitude basin were not clear. To understand better how much SOC was stored and its spatial patterns in the watershed, this study analyzed the vertical variation of SOC content, quantified its influence by varied environmental factors, and further predict its storage in the entire basin. Results showed that, the SOC content decreased with the increasing depth, and was the highest in the alpine meadow in all depths, following by the alpine steppe and temperate steppe, respectively. It was generally higher in the permafrost region than that in the non-permafrost region at all depths. Soil profile depth, soil water content and NDVI could together explain about 72.6% of total variation in SOC density. The regression-kriging method was the best upscaling approach for the prediction of SOC in the study area. Approximately 317 Tg organic carbon was stored in the entire soil profile of Qinghai Lake watershed, in which 136, 140, and 41 Tg were at 0–30 cm, 30–100 cm, and below 100 cm, respectively. The higher SOC density mainly appeared on the northeast and southern region of Qinghai Lake, while the high-altitude area in the northwest of the watershed had the lower values. Moreover, it increased firstly and then decreased with the increase of altitude, with the maximum values at 3350–3400 m, which was dominated by the elevational variation of soil profile depth and NDVI. Overall, the comprehensive assessment of SOC demonstrated high storage and strong heterogenicity of soil carbon in the Qinghai Lake watershed, and it is critical for the sustainability of regional terrestrial ecosystem with future climate change. [ABSTRACT FROM AUTHOR]

Abstract: Biological soil crusts (BSCs) are extensively developed and commonly regarded as a kind of vegetation in desertification areas around the world. The natural recovery process of BSCs after disturbance and their long-term impacts on the soil water conditions are important but not well understood. In order to provide more insights into this problem, we set up two treatments including BSCs (natural BSCs without disturbance) and disturbed BSCs (the top 30mm of surface soil, including the BSC layer, was severely disturbed and completely removed) in a semi-arid environment on the Loess Plateau of China. Over the succeeding years, the natural recovery process of BSCs was qualitatively described and the soil water content at 0–90cm depth of the two treatments was consecutively monitored. The results showed the following: (1) it is possible to recover natural moss-dominated BSCs after severe disturbance under natural conditions, and the recovery process to BSC full-coverage took approximately three years; (2) the BSC disturbance greatly decreased soil water content by up to 18% and the effects gradually weakened with time; (3) the BSC disturbance decreased surface soil water content (0–70cm) by up to 24% but increased deep soil water content (80–90cm) by up to 13%; and (4) the BSC disturbance decreased soil water storage at 0–90cm by 7.8mm, 4.4mm, 8.0mm, and 4.9mm in the second, third, fourth, and seventh years, respectively. We concluded that the BSC disturbance degraded soil water conditions in the three to four years following the disturbance. Therefore, the artificial destruction of natural moss-dominated BSCs in a semi-arid region on the Loess Plateau of China should not be recommended as a land management practice for the improvement of soil water conditions. [Copyright &y& Elsevier]

• LMWOAs significantly increased soil P availability in subalpine forests. • Citric acid was more effective for the mobilization of P than other LMWOAs. • Climate did not dominate the distribution of soil available P along the altitude. • Soil moisture compensated the cold stress on soil P availability by altering citric acid and soil variables. The availability of phosphorus (P) in soils is an essential limiting factor for the development of terrestrial ecosystems; however, how root exudates affect the availability of soil P in subalpine forests remains unclear. The low molecular weight organic acids (LMWOAs) were analyzed in bulk and rhizosphere soils of Abie fabri dominated forests across four altitudes (2800–3500 m) on Gongga Mountain, eastern Tibetan Plateau, to delineate the effects of LMWOAs on the availability of soil P in response to the rhizosphere and altitude differentiation. The results showed that the concentrations of available P were markedly higher in rhizosphere soils compared to bulk soils, and the concentrations did not present a clear altitudinal trend. The increase in the concentrations of available P in rhizosphere soils was significantly related to the LMWOAs that dominated by citric acid, likely through the desorption or ligand exchange rather than acidification effect because of limited range of soil pH. Climate did not alter the distribution of soil available P along the altitude; however, citric acid and soil variables including soil moisture, ammonium nitrogen and microbial biomass P significantly contributed to soil available P. The results of this study indicate that LMWOAs can significantly promote P availability in rhizosphere soils of subalpine forests, and the compensation effect of soil moisture on soil available P for cold stress may induce the higher P availability at higher altitudes. [ABSTRACT FROM AUTHOR]

The vadose zone serves as a connection and transformation link between the atmosphere, plants, soil, surface water and groundwater. It is considered to be an important component of the geosphere and has sensitive interactions with the hydrosphere, biosphere, and atmosphere, which greatly impacts the environment and human health. This study was conducted in the Achnatherum splendens grassland of the Qinghai Lake Basin, NE Qinghai–Tibet Plateau, China, and can provide references and guidance for research on the mechanisms governing the circulation and evolution of vadose-zone water in cold arid regions. Precipitation, dustfall, and vadose zone samples were collected to investigate transport in the vadose zone water using stable isotopes of hydrogen (δ2H) and oxygen (δ18O) as well as chloride as environmental tracers. The results showed that precipitation was the main source of chloride in the research area, accounting for 86.5% of total chloride deposition. The soil water in the vadose zone was mainly recharged by local precipitation. Strong evaporation occurred before the precipitation infiltrated and recharged soil water. The soil water, chloride content, and isotope values in the soil profile varied across different depths. The annual potential recharge from precipitation to the vadose zone soil water was 9.20 mm/yr, accounting for 2.17% of the local precipitation. The actual recharge from precipitation to groundwater was 26.29 mm/yr, accounting for 6.19% of the local precipitation. The infiltration recharge from preferential and piston flow accounted for 66.40% and 33.60% of the total infiltration recharge to groundwater, respectively, indicating that preferential flow was the main source of groundwater recharge in the studied grassland. The results of this study were compared with those of other relevant studies. The recharge mechanisms of the vadose zone soil water and groundwater varied between different regions and were controlled mainly by the spatiotemporal distribution of precipitation, topographic characteristics, and soil structure. These findings provide a reference and guidance for research on the circulation and evolution of vadose-zone water in the Qinghai Lake Basin and Qinghai–Tibet Plateau. [ABSTRACT FROM AUTHOR]

• Water use pattern was investigated for Caragana korshinskii on sunny and shady slopes. • Caragana korshinskii seasonally switched its water sources from different soil layers. • Caragana korshinskii on sunny slope used shallower soil water than that on shady slope. • Root distribution and soil moisture affect water use pattern of Caragana korshinskii. Flexible water use patterns are of great importance for the survival of vegetation in dryland regions. Our study aimed to investigate the influences of season and slope aspect on the water use patterns of Caragana korshinskii on typical shady and sunny slopes on the Loess Plateau in China. We collected xylem water, soil water from the 0–200 cm soil layers, and precipitation in May, July, September and November 2018 and measured their hydrogen (δD) and oxygen (δ18O) isotope compositions. The root distribution of C. korshinskii in the 0–200 cm soil layer on both slopes was also investigated. The 0–20, 20–80, and 80–200 cm soil layers were identified as three potential water sources for C. korshinskii , and their proportional contributions to the plant water supply were calculated using a linear mixed model. The results showed that C. korshinskii on the sunny slope absorbed 89.3% of their water from the 0–20 cm soil layer in May but mainly utilized water from the 0–20 and 20–80 cm soil layers in both July and September, and the total contribution percentages of these layers were 84.5% and 89.2%, respectively. However, C. korshinskii on the shady slope extracted water evenly from all three soil layers in May. Thereafter, the plants absorbed water from the 20–80 and 80–200 cm soil layers in both July and September, and the total contribution percentages of these layers were 96.0% and 91.8%, respectively. In November, C. korshinskii absorbed 84.8% and 78.0% of their water from the 80–200 cm soil layer on the shady and sunny slopes, respectively. The generally shallower soil water use of C. korshinskii on the sunny slope than on the shady slope may be due to the larger fine-root (d < 2 mm) length density in the 0–80 cm soil layer on the sunny slope (1.12 ± 0.28 mm/cm3) than on the shady slope (0.57 ± 0.16 mm/mm3) (P < 0.05). This study indicates that C. korshinskii on both shady and sunny slopes seasonally switched their water sources from different soil water layers during the growing season. However, due to their reliance on soil water at the 0–20 cm depth, which is supplied by unstable rainfall, C. korshinskii on sunny slopes may be more vulnerable to future climatic warming and drying on the Loess Plateau. Our findings provide valuable information related to optimal water management in the afforested shrublands in this region. [ABSTRACT FROM AUTHOR]

• Lakes in the endorheic basin exhibited a rapid expansion since 2000. • The significant lake expansion was observed in the Hoh Xil region. • Lake expansion was closely related to precipitation and permafrost degradation. • Meltwater from permafrost thawing contributes to 21% of lake volume change. • Glacier retreat contributed to expansion of several large lakes. The QTP (Qinghai-Tibet Plateau) holds the greatest concentration of high-elevation inland lakes in the world, and most of these lakes are located in the QTP endorheic basin. Accelerated lake expansion in the endorheic basin since 2000 has been confirmed by many studies, but there is disagreement as to which components of the water balance explain most of the lake expansion. In this paper, based on Landsat images, meteorological data, glacier data and permafrost monitoring data, we analyzed the spatial–temporal changes in lake area and further explored the driving factors behind rapid lake expansion in different zones in the endorheic basin. The results suggested that the spatial pattern of trends in lake area in the endorheic basin from 2000 to 2017 showed a southwest-northeast transition from contracting to slightly expanding to rapidly expanding. More importantly, the dramatic lake expansion observed in most regions was statistically significant (0.01 ~ 26.29 km2/yr). Although retreating glaciers may have contributed to lake growth, this can not fully explain the recent lake expansion. We find that increasing precipitation was the primary driver behind lake expansion, and that permafrost degradation accelerated lake expansion. Lakes on the northern slope of the Gangdise Mountains, fed by the most rapidly retreating glaciers, were relatively stable or even contracted. In contrast, most of the non-glacier-fed lakes in the Hoh Xil region and the central endorheic basin nevertheless experienced significant expansion and slight expansion, respectively, which were mainly attributed to the greatest increase in AP (annual precipitation). Remarkable lake expansion was found in the continuous permafrost zone. The increasing ALT (active layer thickness) and soil temperature of permafrost resulted in an increase in meltwater from ground ice, the partial release of soil moisture and an amount of unfrozen water content, which has contributed to supply lakes and accelerated lake expansion. [ABSTRACT FROM AUTHOR]

• Precipitation had the strongest effect on SMC. • AGB was controlled more by vegetation restoration type and elevation. • BGB was controlled more by vegetation restoration age and elevation. • SMC had a higher relative benefit than AGB and BGB in most precipitation areas. • Understanding the trade-offs is important to better restore and manage vegetation. Plant biomass is a crucial parameter for terrestrial ecosystem carbon cycling. Water plays a crucial role in biomass production, especially in arid and semi-arid regions. However, the trade-off relationships between the plant biomass and soil moisture have not been well investigated on the Loess Plateau. In our study, we synthesized 615 pairs of data to evaluate the trade-off between the plant biomass and soil moisture in different precipitation areas and vegetation restoration ages on the Loess Plateau using the quantitative trade-off method. The results showed that precipitation had the strongest effect on soil moisture content (SMC), and aboveground biomass (AGB) was controlled more by vegetation restoration type and elevation, whereas belowground biomass (BGB) was controlled more by vegetation restoration age and elevation. SMC had a higher relative benefit than AGB and BGB in most precipitation areas. In addition, vegetation restoration age is another critical variable to determine the trade-offs between AGB and SMC and between BGB and SMC. For forest, the minimum trade-off of restoration years was > 10 years, but it was < 10 years for shrubland and grassland. Because the trade-offs between AGB and SMC and between BGB and SMC revealed a large spatial change on the whole Loess Plateau, the vegetation in different precipitation areas should identify suitable management strategy to maintain benefits. Understanding the relationship between the plant biomass and soil moisture will improve our ability to sustainably manage vegetation construction and water resources. [ABSTRACT FROM AUTHOR]

• Effect of vegetation type on soil LOC fractions is greater than that of topography. • Soil LOC fractions increased with litter stock, coverage and thickness. • Soil LOC fractions are directly influenced by soil basic properties. • Soil LOC fractions are indirectly affected by litter stock, coverage and thickness. • Multiple factors explained over 50% of the variation in SOC and soil LOC fractions. Vegetation type and topographic characteristics are important factors that affect the amount and spatial distribution of the forest floor and the soil carbon cycling. However, the relationships among vegetation type, topographic characteristics, forest floor properties, soil properties and soil labile organic carbon (LOC) fractions remain to be elucidated. Here, we conducted a field observational study to explore the relationships between the soil LOC fractions (microbial biomass carbon (MBC), extractable organic carbon (EOC) and permanganate oxidizable carbon (Pox-C)) and forest floor characteristics under various vegetation types (forest, forest-steppe and steppe) and topographic features (slope position and aspect). Our results showed that the vegetation type and topography are both important factors that significantly influence the forest floor properties (i.e., stock, thickness and coverage). The soil total nitrogen and phosphorus were significantly increased, and the soil pH and bulk density were decreased, with an increase in litter stock, coverage and thickness. Simultaneously, the SOC and soil LOC fractions were increased significantly with the increase in litter stock, coverage and thickness. Over 50% of the variation in the SOC and soil LOC fractions was jointly explained by environmental factors, litter properties and soil properties. Our results demonstrated that the SOC and soil LOC fractions are directly influenced by soil physical and chemical properties (e.g., pH, bulk density and soil total nitrogen) and indirectly affected by external environmental factors. Changes in vegetation and topography lead to increases in the litter stock, coverage, thickness and water content in the backslope position and northern slope, which could create favorable soil nutrient and environmental conditions (e.g., higher soil moisture and lower bulk density) to further enhance SOC and soil LOC fraction sequestration. The forest floor potentially links environmental factors and soil properties and serves as an important factor for soil C cycling. [ABSTRACT FROM AUTHOR]

• Vegetation degradation could decrease CH 4 emissions and increase Re fluxes. • Soil temperatures at 5 and 10 cm were the main controls on Re variability. • Soil temperature and water content were the main controls on CH4 emission. • Less CH 4 flux in vegetation degradation peatland was due to low soil water content. Vegetation plays a critical role in regulating ecosystem carbon (C) processes in peatlands, but vegetation faces serious degradation on the Tibetan Plateau, China. However, how vegetation degradation affects on carbon processes of peatlands remains unclear. Using the static chamber technique, we compared ecosystem respiration (Re) and methane (CH 4) fluxes for healthy vegetation (HV) and degraded vegetation (DV) during two growing seasons (2013 and 2014) on peatlands of the Tibetan Plateau. We also determined the dominant factors controlling Re and CH 4 fluxes. The average Re flux for DV (218.04 ± 95.08 mg C m-2h−1 in 2013 and 219.03 ± 140.96 mg C m-2h−1 in 2014) was considerably larger than that at the HV(163.78 ± 87.51 mg C m-2h−1 in 2013 and143.91 ± 84.44 mg C m-2h−1 in 2014), whereas the average CH 4 fluxes for DV (0.06 ± 0.20 mg C m-2h−1 in 2013 and 0.04 ± 0.07 mg C m-2h−1 in 2014) were significantly lower than the corresponding fluxes for HV (2.19 ± 2.05 mg C m-2h−1 in 2013 and 0.85 ± 0.95 mg C m-2h−1 in 2014). The Re fluxes for the two vegetative treatments had the same temporal trends, with the peaking flux observed in July 2014. The temporal patterns of CH 4 fluxes were similar to Re for two vegetation treatments where fluxes peaked in July 2014. Soil temperatures were found to be the primary factors influencing temporal Re fluxes. Soil temperatures and soil water content (SWC) were found to be the dominant factors influencing temporal CH 4 flux for HV, while the main control for CH 4 emission was the SWC for DV. Therefore, vegetative condition must be considered when estimating Re and CH 4 flux from peatlands, particularly under the current situation of climate warming. [ABSTRACT FROM AUTHOR]

• Soil CO 2 emissions decreased exponentially with slope gradients. • Erosion-distributed water and nutrient responsible for slope dependent CO 2 emissions. • First study to parameterize the dependency of soil CO 2 emissions to slope gradients. Slope induced runoff and erosion processes redistribute water, soil and nutrients, thus potentially influence soil CO 2 emissions and perturb the carbon balances on sloping land. However, most of the previous studies on soil CO 2 emissions were conducted on flat land. In regions with complex terrains and fragmented fields with terraces, such as the Chinese Loess Plateau, it is particularly important to understand slope dependent soil CO 2 emissions. This requires investigations to unravel the relationship between soil erosional responses and CO 2 emissions on different slopes. In this study, erosion plots, set at angles of 0.5°, 5°, 10°, and 20°, were refilled with loess soils from local farmland on the Chinese Loess Plateau. Changes of soil properties and CO 2 emission rates were measured at three positions (upper, middle, lower) on each plot from October 2014 to September 2015. Our results show that greater runoff from the steeper slopes evidently depleted soil water and nutrients, directly responsible for the less soil CO 2 emissions. Furthermore, the average yearly soil CO 2 emissions decreased exponentially with slope gradients, from approximately 832.7 g m−2 yr−1 on the 0.5° slope, to 380.9 g m−2 yr−1 when the slope gradient was 20°. This not only proves the dependency of soil CO 2 emission to slope gradients, but also provides the fundamental dataset to develop an empirical model between slope gradients and soil CO 2 emissions. A coefficient β has been parameterized for the first time in this study to represent the sensitivity of soil CO 2 emissions to slope gradients. The model of slope-dependent CO 2 emissions identified in this study tentatively demonstrate non-negligible implications for global carbon fluxes from sloped and terraced field to the atmosphere. Further investigations on slope-scale carbon balances should test and integrate topography specific CO 2 emissions. [ABSTRACT FROM AUTHOR]

• SWC in 0–21 m under four land uses was monitored and simulated from 2011 to 2015. • Different factors controlled the spatiotemporal variations of SWC in 0–2 m layer. • Soil texture (soil texture and root biomass) adjusted SWC in space (time) in 2–21 m. • Shifting shallow-rooted plants to deep-rooted plants consume more SWC in 3.4–4.8 m. • Appropriate plants should be considered based on local climatic and SWC regimes. Soil water content (SWC) with a deep profile is crucial to land use management, soil and water conservation, and ecological restoration worldwide, including the wind–water erosion crisscross region in the Critical Zone of the Chinese Loess Plateau. To ascertain the spatiotemporal variation of deep SWC and its response to land-use shifts in the region, the SWC was monitored at four representative land uses (farmland, shrubland, natural grassland, and planted grassland) to a depth of 21 m. Monitoring occurred between 2011 and 2015 in the Liudaogou watershed of the Chinese Loess Plateau. The Hydrus-1D model was then applied to simulate the SWC dynamics for the different land-use types and scenarios of land-use shifts. The SWC exhibited a high spatial variability in the vertical direction both within a given soil profile and among the different land uses. In the 0–2 m layer, the soil texture and root biomass controlled the spatial-temporal variability of the SWC. The temporal variability was also controlled by meteorological factors. In the 2–21 m layer, spatial variability was controlled by the soil texture, while soil texture and root biomass influenced the temporal variability of the SWC. The Hydrus-1D model accurately simulated spatiotemporal variations of SWC in the 0–21 m layer and was more effective on layers minimally influenced by weather. Land-use shifts from farmland with shallow-rooted plants to those with deep-rooted plants intensified soil water consumption in the 3.5–5 m layer. For best-management practices, appropriate plant species should be considered based on climatic conditions and SWC regimes. A better understanding of this information is useful for plant species selection, soil water resource utilization, and land use policymaking in the wind–water erosion crisscross region of the Critical Zone and other similar regions around the world. [ABSTRACT FROM AUTHOR]

• We measured the organic carbon associated with iron in slump deformation landscapes. • Slump deformation changed soil variables and decreased organic carbon and nitrogen. • Changes of the carbon associated with iron varied among vegetation types. • Organic carbon stabilization processes can be affected by slump deformation features. Soil organic carbon (SOC) associated with iron (Fe-OC) can be recognized as an important component of the stabilized carbon pool. In permafrost regions, slump deformation can expose soil organic carbon and alter moisture conditions, which change the Fe-OC distribution. We measured the top 30 cm of soils in five slump deformation landscapes under three vegetation types on the middle and eastern Qinghai-Tibetan Plateau. Three stages of slump deformation were defined according to their microtopography. In the slump deformation areas, the SOC and total nitrogen (TN) contents in the surface 30 cm of soils were all lower than the soils without slump deformation in wet meadow (22% and 26%), meadow (16% and 29%), and steppe (14% and 20%) areas. The contents of Fe-OC in wet meadow were 4.1% and 12.5% in the soils without and with slump deformation, respectively, whereas these contents in the meadow and steppe soils were 25.6% and 17.2%, respectively. Slump deformation greatly changed the physiochemical soil variables and affected the Fe-OC% based on different vegetation types. Fe-OC was correlated with factors such as soil moisture, pH and C/Fe ratio. The study shows that slump deformation greatly affected the SOC and TN distribution and SOC stabilization processes in areas with slump deformation features. [ABSTRACT FROM AUTHOR]

• SOC increased with increasing precipitation, but the reverse for SIC in alpine steppe. • SOC density decreased with soil depth, but SIC density increased with depth. • Biological processes drive SOC profiles, while abiotic factors determine SIC patterns. • SIC comprises about 10% of C storage in alpine steppe soils of the Tibetan Plateau. Both soil organic carbon (SOC) and inorganic carbon (SIC) are important components of soil carbon storage. However, few studies have attempted to estimate the magnitude and patterns of SIC in arid areas. We measured the concentrations of SOC and SIC in alpine steppe grasslands along a climate gradient in the Tibetan Plateau. At all sites, an opposing trend was found in the distribution of SOC compared with SIC. SOC increased with increasing precipitation, while SIC decreased. Within sites, SOC decreased with soil depth, while SIC increased. Among the variables considered, soil total nitrogen (TN) and soil water content explained the most variability in SOC (r2 = 0.95 for TN, r2 = 0.93 for soil water content), and soil pH had the highest correlation with SIC (r2 = 0.90). This finding indicates that SOC is closely related to biological processes, such as biomass input and litter accumulation, while SIC is determined by abiotic factors such as chemical and physical processes of soil formation. SOC and SIC densities showed that the SOC pool comprised 91% of total carbon (TC) storage in these alpine steppe soils. A decrease in SOC density occurred with depth, but this pattern was the opposite for SIC density in all soil profiles. These findings help to characterize the C cycle in the alpine steppe of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The cropland-to-apple orchard conversion is expanding in the semiarid Loess Plateau, yet its impacts on deep soil moisture and nitrate are poorly documented. This study was conducted in Luochuan, typically the best area for apple planting in China, where fifteen 6-m-deep soil profiles were sampled from each cropland (as the control), as well as 8-, 17- and 25-yr apple orchards, to investigate the vertical distributions of soil moisture and nitrate and their storage. Results showed that the 8-yr apple orchards were comparable to cropland in soil moisture content (SMC), soil water storage (SWS), soil nitrate concentration (SNC) and residual soil nitrate (RSN). In contrast, 17- and 25-yr apple orchards, caused serious SWS deficits, of 140 mm and 150 mm, and substantially increased RSN, by 4270 and 7250 kg N ha−1, respectively, when compared with cropland. Notably, RSN in deep soils was strongly enhanced by the stand age of apple orchard, which was primarily associated with accumulated N fertilizer inputs. Similar SNCs in the 540–600 cm layer among land use types implied a 6-m-deep soil profile might be robust for evaluating NO 3 − dynamics following cropland-to-orchard conversion in the study region. Regression relationships between RSN and SWS were significantly positive in the 100–300 cm soil layer under cropland but significantly negative in the 0–100 cm and 100–300 cm layers under 8-yr apple orchards, indicating distinct hydrological processes of NO 3 − under differing land uses. In conclusion, converting cropland to apple orchards could result in soil moisture decline and nitrate accumulation in the 6-m profile that may threaten the Loess Plateau's sustainability. Therefore, integrated water and N management should be practiced to mitigate the unfavorable impacts and develop sustainable apple production in China and other semiarid areas of the world. • The 17- and 25-yr apple orchards decreased soil moisture in soils deeper than 3 m. • NO 3 − accumulation in deep soil layers increased with stand age of apple orchard. • A 6-m-deep soil profile was robust for evaluating vertical patterns of soil NO 3 −. • 8-yr orchard may be an optimal age avoiding soil water decline and NO 3 − accumulation. • Converting cropland to apple orchard may threaten the Loess Plateau's sustainability. [ABSTRACT FROM AUTHOR]