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Aims: Cropland revegetation is an effective measure to curb soil erosion on eroding hillslopes and increase farmers' income at depositional check dams. However, how soil microbial metabolic limitation responds to cropland revegetation in erosion and deposition landscapes remains poorly understood, which has substantial implications for carbon (C) retention and nutrient cycling in the eroding environment. Methods: We sampled 0–2 m soils in cropland and revegetated forest and grassland at upslopes and check dams in the hilly-gully region of the Loess Plateau, China. The activities of soil C-, nitrogen (N)-, and phosphorus (P)-acquiring enzymes were analyzed. The improved enzyme vector model (V-T model) based on balance points was used to quantify microbial metabolic limitations based on ecoenzymatic stoichiometry. Results: Microorganisms suffered from no energy (C) limitation, but the relative microbial C limitation was greater in revegetated forest than in cropland. At upslopes, the revegetated forest was primarily limited by P, while the revegetated grassland and cropland were limited by N, which was indicated by the VTN/P limitation values of 4.35, -2.74, and − 1.87, respectively. Microbial P limitation was greater in deep soils of revegetated forest due to the assimilation of P by the root system. At check dams, land-use change had no significant influence on microbial N/P limitations owing to abundant soil C and nutrients and a wet environment. Conclusion: Concludingly, cropland revegetation had a weaker influence on microbial metabolic limitation at the lower-lying topography, which compensates for the current understanding of resource restrictions on microorganisms at slopes or flat areas. [ABSTRACT FROM AUTHOR]

Deep soil organic carbon (SOC) plays an important role in carbon cycling. Precisely predicting deep SOC at the regional scale is crucial for the accurate assessment of carbon sequestration potential in soils but has been challenging for a century. Herein, we developed a depth distribution function-based empirical approach to predict SOC in deep soils at the regional scale. We validated this approach with a dataset from four regions of the world and examined the application of this approach in China's Loess Plateau. We found that among the reported depth distribution functions describing vertical patterns of SOC, the negative exponential function performed best in fitting SOC along the soil profile in various regions. Moreover, the parameters (i.e., Ce and k) of the negative exponential function were linearly correlated to surface SOC (0–20 cm) and the changing rates of SOC within the topsoil (0–40 cm). Based on the above relationships, the empirical equations for predicting the negative exponential parameters are established. The validation results from site-specific and regional dataset showed that combining the negative exponential function and such empirical equations can precisely predict SOC concentration in soils down to 500 cm depth. Our study provides a simple, rapid and accurate method for predicting deep soil SOC at the regional scale, which could simplify the assessment of deep soil SOC in various regions. [ABSTRACT FROM AUTHOR]

Soil erosion is a major form of land degradation, especially in agroecosystems, which has been effectively controlled by vegetation restoration. However, the interactive role of erosion and cropland revegetation on soil enzyme activities and microbial nutrient limitations is less understood. To address this issue, we examined carbon (C), nitrogen (N), and phosphorus (P) in bulk soils and microbial biomass, enzyme activities, and microbial nutrient limitations in the 0–200 cm soils in eroded and deposited landscapes occupied by cropland, revegetated forest, and grassland. The results showed that the activities of C-, N-, and P-acquiring enzymes were larger in the deposited landscape than in the eroded landscape for 0–20 cm soils in forest and grassland but not in cropland. Microbial metabolism was co-limited by N and P, and the threshold element ratio (TERL) indicated that P was the most limiting factor. Microbial N limitation was lower in the deposited than the eroded zone, especially in surface soils in revegetated forest and grassland. The TERL value was larger at the deposited than at the eroded zone, and a greater difference was found in the surface soils of forest and grassland. Microbial nutrient limitations were mostly explained by C/P and N/P. Conclusively, the deposited areas were characterized by ameliorated enzyme activities, decreased microbial N limitation but relatively strengthened microbial P limitation compared to the eroded area, and such variations existed in the revegetated forest and grassland but not in the cropland, which thus contributes to a better understanding of C and nutrient cycling for agroecosystems and revegetation ecosystems in eroded environments. [ABSTRACT FROM AUTHOR]

Highlights • Converting grassland to shrubland increased soil N availability and mineralization. • The positive effect on soil mineral N was higher in lower slope than upper slope. • The positive effect on soil mineral N was similar across soil textures. • The effect on net N mineralization varied with slope position and soil texture. Abstract Grassland afforestation, which is a major form of land-use change, has expanded considerably in the last few decades. However, the effect of conversion from grassland to shrubland on soil nitrogen (N) cycling and availability with regard to soil textures and slope positions is unclear. This lack of clarity has hindered our understanding of how grassland afforestation influences soil N availability and transformation on a larger spatial scale. In this study, we compared the net N mineralization rates and mineral N concentrations in soils from native grassland and under legume shrub (Caragana korshinskii Kom.) with contrasting soil textures (sandy-loam vs. loamy-sand) and slope positions (upper vs. lower) in the northern region of China's Loess Plateau. The objective of this study is to understand how soil texture and slope position regulate the response of soil N cycling to grassland afforestation. The results showed that the concentrations of soil nitrate and total mineral N and the rates of net nitrification and mineralization were higher in soils under shrub (0.64 ± 0.10 g N m−2, 1.01 ± 0.11 g N m−2, 23.19 ± 5.22 mg N m−2 d-1 and 22.07 ± 5.44 mg N m−2 d-1) than in grassland (0.22 ± 0.03 g N m−2, 0.56 ± 0.04 g N m−2, 1.48 ± 1.51 mg N m−2 d-1 and 1.36 ± 1.96 mg N m−2 d-1). However, soil ammonium concentration and net ammonification rate were not affected by grassland afforestation. The effect of afforestation on nitrate and total mineral N concentrations was greater in the lower slope than in the upper slope but was similar between the sandy-loam and loamy-sand soils. The effect of this land-use change on net nitrification and mineralization rates varied with soil texture and slope position, with greater effects in the upper slope than in the lower slope in more clayey soils, but with the opposite influencing pattern in more sandy soils. These results suggested that planting C. korshinskii in grassland ecosystems increased soil N mineralization and availability. More importantly, soil texture and slope position should be considered when assessing the effects of grassland afforestation in complex landscape conditions. [ABSTRACT FROM AUTHOR]

• Eroding soils and sediments were collected at 0–2 m depth across the Loess Plateau. • Sediments had higher clay than eroding soils at sites with higher erosion modulus. • Sediments had higher BD, lower Ks, FC, porosity than soils at sites with higher MAP. • Reaggregation of deposited sediments occurred, which were enriched in clay and SOC. • Spatial heterogeneity in deposition zone was not lower than that in erosion zone. Soil erosion, the most widespread form of soil degradation worldwide, has been acknowledged to cause onsite soil physical deterioration. However, the off-site impact of erosion on the soil physical and hydraulic properties of deposited sediments remains unclear, especially at catchment or larger scales. Here, we measured soil physical and hydraulic properties in erosion topography (hillslopes) and deposition topography (check dams) at 0–2 m depth in five eroding catchments across China's Loess Plateau. Results indicated that the deposition zone exhibited a higher clay content (+13%) at the southern sites with a finer texture and a higher erosion modulus, while the same zone exhibited a higher sand content (+25%) at the northern sites with a coarser texture and a higher extreme rainfall erosivity. The deposition zone exhibited a higher bulk density (+9%) and a lower saturated hydraulic conductivity (-13%), field capacity (−9%), and porosity (-5%) than those of the erosion zone, which was strengthened by a higher mean annual precipitation. Soil macroaggregate proportion and mean weight diameter of aggregates were significantly lower in the deposition zone (14.36% and 0.69 mm, respectively) than those in the erosion zone (15.71% and 0.75 mm, respectively), and the differences were larger at sites with higher rainfall erosivity levels and in surface 20 cm soils. However, sediment reaggregation occurred due to the accumulation of binding agents such as clay and organic carbon at sites with lower rainfall erosivity levels. The spatial heterogeneities of sediment physical and hydraulic properties were greater than or similar to those of soils in the erosion zone. Results of our study highlight the dependence of variations in soil physical and hydraulic properties driven by erosion and deposition on erosion factors, which contributes to a better understanding of the hydrology cycle and carbon stability in erosion and deposition topographies. [ABSTRACT FROM AUTHOR]

• WDOM parameters in erosion and deposition zone were tested across Loess Plateau. • Sediment below 20 cm had higher WEOC, aromaticity, hydrophobicity, humic components. • Eroded soils above 20 m had higher WEOC and exogenous features with plant inputs. • WEOM variations were higher in deep soils and in sites with higher erosion modulus. • WEOM variations were mostly driven by vegetation in top and by ΔSOC in deep soils. Water-extractable organic matter (WEOM) is the most active and mobile fraction of soil organic matter and responds sensitively to soil erosion. However, previous studies on the chemical nature of WEOM in the erosion and deposition landscapes were controversial at site-level studies and mainly focused on surface soils, limiting our assessment of WEOM's environmental fate at larger and deeper scales. Here, we collected eroded soils and deposited sediments from a depth of 0–200 cm in five eroding catchments with an erosion intensity gradient across the Loess Plateau. We examined the concentration, composition, and potential sources of WEOM using UV–visible absorption and fluorescence excitation-emission matrix-parallel factor analysis. Soil WEOM quantity and quality varied significantly in the erosion and deposition landscapes, with greater variations in soils below 20 cm, where WEOM in the deposition zone was characterized by higher concentration, aromaticity, hydrophobicity, and UVA and UVC humic-like components derived from terrestrial and soil organic matter. WEOM variations in deep soils increased with increasing erosion modulus among sites, and were mainly driven by changes in soil organic carbon concentration, aggregate stability, and carbon to nitrogen ratio. However, the pattern of WEOM parameters between erosion and deposition zones at 0–20 cm was opposite to that in soils below 20 cm. Vegetation inputs compensated the loss of organic matter in sites with suitable climatic status and weak erosion, and led to higher concentrations and exogenous features of WEOM in the surface erosion area. Concludingly, the WEOM concentration, components, and sources differed significantly between erosion and deposition zones, and these differences, as well as their response to erosion intensity, revealed an opposing pattern in surface and deep soils. [ABSTRACT FROM AUTHOR]

• Soil in eroding zone had higher mineral N and net mineralization rates than in depositional zone. • Vegetation removal increased soil mineral N but not affected soil net N mineralization rates. • The effects of vegetation removal on mineral N pools depended on landscape position, site, and season. • The responses of net N mineralization rates to vegetation removal were consistent across landscape positions and sites, but varied with season. The soil nitrogen (N) availability is a key limiting element of terrestrial ecosystem productivity and functioning, especially in fragile ecosystems (e.g., eroding environments). However, to date, little is known about how vegetation and erosion individually or jointly affect soil N mineralization under field conditions across a range of sites varying in soil and climate properties on a long-term observational scale. In this study, we elucidated how soil net N mineralization responds to vegetation removal (plots with vs. without vegetation) and landscape position (eroding vs. depositional zones) during a two-year manipulation experiment using an in situ incubation method on the China's Loess Plateau. The results indicated that the nitrate and total mineral N concentrations and net nitrification and mineralization rates were higher in the eroding zone (2.74 ± 0.12 mg kg−1, 4.47 ± 0.13 mg kg−1, 0.046 ± 0.005 mg kg−1 d-1 and 0.046 ± 0.006 mg kg−1 d-1) than those in the depositional zone (2.01 ± 0.10 mg kg−1, 3.80 ± 0.12 mg kg−1, 0.030 ± 0.005 mg kg−1 d-1 and 0.032 ± 0.006 mg kg−1 d-1) on the China's Loess Plateau. Vegetation removal resulted in an increase in the nitrate (2.88 ± 0.13 vs. 1.87 ± 0.09 mg kg−1) and total mineral N concentrations (4.56 ± 0.14 vs. 3.71 ± 0.11 mg kg−1), but did not affect the soil net N mineralization rates on the China's Loess Plateau. The effects of vegetation removal on soil mineral N pools depended on the site, season and landscape position, with stronger effects in the eroding zone than those in the depositional zone. However, the responses of the net N mineralization rates to vegetation removal were consistent across the various landscape positions and sites, but varied with the season. Variance partitioning revealed that soil properties rather than climate and vegetation conditions were the most dominant contributors to the variations of soil N mineralization in both the eroding and depositional zones, explaining 37.6–64.6% of the variation. These results emphasized the substantial spatial (landscape position and site) and temporal (seasonal) dependence of the effects of vegetation removal on soil N mineralization at large scale. [ABSTRACT FROM AUTHOR]

Soil erosion can dramatically alter soil nitrogen (N) cycling, but it has rarely been examined under in-situ conditions due to the complicated interaction between erosion and vegetation. Comparing the effects of vegetation presence at eroding and depositional sites would provide a direct understanding of such effects. Herein, we investigated how soil N dynamics (mineral N pools and net N mineralization rates) responded to vegetation presence (plot with vs. without vegetation), landscape position (eroding vs. depositional sites) and vegetation type (grassland vs. woodland) during a two-year manipulation experiment using an in-situ incubation method in the hilly-gully region of China's Loess Plateau. The results showed that soils on eroding site had higher concentrations of nitrate (3.820 ± 0.302 vs. 2.642 ± 0.280 mg kg-1) and mineral N (5.853 ± 0.320 vs. 4.308 ± 0.287 mg kg-1) but similar rates of net nitrification (0.057 ± 0.013 vs. 0.051 ± 0.011 mg kg-1 d-1) and mineralization (0.056 ± 0.014 vs. 0.056 ± 0.013 mg kg-1 d-1) in comparison to depositional site in all grassland plots. The concentrations of soil nitrate and mineral N and rates of net nitrification and mineralization in legume woodland were 26%, 19%, 88% and 64% higher than that in grassland in all slope plots, respectively. Although vegetation presence significantly decreased soil nitrate (−57%) and total mineral N (−27%) concentrations, it did not affect the rates of net nitrification and mineralization. The effects of vegetation presence on soil net N mineralization occurred irrespective of landscape position and vegetation type(P > 0.05), but varied with season or year, with greater effects in 2017 growing season than in the non-growing season and 2018 growing season. Redundancy analysis and hierarchical partitioning indicated that the above- and blow-ground biomass accounted for most of the variation in soil N mineralization. These results suggested that the variations in soil mineral N and net N mineralization in relation to vegetation presence in this eroding watershed were consistent across different landscape positions and vegetation types, but showed intra- and inter-annual variability. • Vegetation presence decreased soil mineral N pools because of plant uptake. • Soil mineral N concentrations in eroding site were higher than deposition site for the grassland. • Soil mineral N and mineralization rates were higher in woodland than grassland for the eroding sites. • Effects of vegetation presence on soil mineral N and mineralization rates were irrespective to landscape position and vegetation type, but varied with season or year. [ABSTRACT FROM AUTHOR]

Re-vegetation of cropland is an important measure for carbon (C) sequestration, while the combined effects of land-use change, re-vegetation type and time on soil organic C (OC) turnover and temperature sensitivity have been less studied. Here, we investigated soil cumulative OC mineralization (C min), specific OC mineralization (C min /C 0 , normalized by initial OC) and temperature sensitivity (Q 10) with an 84-d incubation experiment after the conversion of cropland to artificial grassland (6, 10, 15 and 20 yr), to natural grassland (6, 10 and 20 yr) and to pea shrub woodland (10, 20 and 40 yr) in the agro-pastoral ecotone of northern China. Results showed that re-vegetation significantly increased C min (from 38.21 to 57.79 mg kg−1 soil, +51%) at the 0–10 cm depth but not the 10–20 cm depth, with greater increases after the conversion of cropland to artificial grassland (+77%) than the other two patterns but similar among different conversion years for each pattern. Variations in C min among different re-vegetation patterns and times were mostly explained by changes in total nitrogen concentration (TN) in the macro-aggregate fraction. Across all treatments, 6.20–20.29 g kg−1 OC was mineralized during the incubation and Q 10 was 1.16–2.40. The C min /C 0 and Q 10 changed not significantly during the post-agricultural re-vegetation chronosequences for each pattern, which were mostly due to the unchanged TN concentration in silt and clay fraction. Re-vegetation also changed the dependence of C min , C min /C 0 on N availability, with significant relationships in re-vegetated artificial grassland and pea shrub woodland which may due to the influence of legumes on microbes. In conclusion, OC mineralization increased with conversion, varying by re-vegetation type, while OC decomposability and temperature sensitivity were stable regardless of re-vegetation type and time, indicating the similar biodegradability and stability in face of warming. • OC mineralization and Q 10 were tested in varied re-vegetation types and times. • Cropland re-vegetation increased C min especially for artificial grassland. • •N in macro-aggregate explained about 50% of cumulative OC mineralization. • •OC biodegradability and Q 10 were similar during the post agricultural restoration. [ABSTRACT FROM AUTHOR]

Soil carbon (C) and nitrogen (N) combining with physical and chemical properties play important roles in terrestrial C and nutrient cycling; however, how C and N in deep soils respond to land-use change is less understood, hindering the precise evaluation of soil C dynamics and budgets. Here, we present results regarding soil C, N and related soil properties at 0–500 cm depth as affected by afforestation at two sites (Fufeng and Yongshou) with contrasting soil inorganic C (SIC) levels in China's Loess Plateau. The concentrations of SIC ranged from 12.94 to 20.17 g kg−1 in Fufeng and from 0.18 to 0.36 g kg−1 in Yongshou. The objectives of this study were to examine how soil C and N in deep soils are altered following afforestation and how these effects vary with soil depth and site. We found that the establishment of woodland on cropland increased soil porosity and saturated hydraulic conductivity but decreased the bulk density in the topsoils (0–20 cm). The conversion of cropland to woodland resulted in an increase of soil electric conductivity in the topsoils and a decrease in the deep soils in Fufeng but had an opposite influence with soil depth in Yongshou. This land-use change increased organic C and total N concentrations along the 0–500 cm soils at both sites but had divergent effects on the concentrations of SIC and soil total C (STC) between the two sites. Overall, the concentrations of SIC and STC increased in Yongshou but decreased in Fufeng after woodland establishment. The results from this study indicated the determination of the initial SIC concentration on the response of C to afforestation in semiarid soils, and such determination should be considered in biogeochemical models. • Afforestation decreased pH and increased SOC and TN regardless of sites. • Effects of afforestation on soil C were dependent on initial SIC level. • Afforestation increased SIC and STC in low SIC site and reduced them in high SIC site. [ABSTRACT FROM AUTHOR]

Background: It is widely accepted that oral health plays an important role in overall health. Both dental and medical students are expected to possess good oral health awareness and work together for public oral health promotion especially in developing countries like China. The aim of this study was to assess the oral health knowledge, behavior and status of dental and medical undergraduate students in the first (fresh) and third year (before specialized courses) study. Methods: A self-administered structured questionnaire with 13 questions was designed based on oral health knowledge, behavior and status and a cross-sectional study was conducted among the 1st, 3rd year dental students (1DS, 3DS) and medical students (1MS, 3MS) of Sichuan University in Chengdu, China, in the period of September–December 2017. The data was analyzed by chi-square test using IBM SPSS Statistics v. 21.0. Results: The oral health behavior, consciousness and status of the 1st, 3rd year medical and dental students were not optimistic. Dental freshmen were slightly superior to the medical ones in terms of the brushing methods and the awareness of oral disease-systemic disease relationship. The junior dental students showed highly significant improvement than their counterparts, mainly in the items about frequency of brushing teeth, brushing methods of vertical scrub or Bass technique (66.3%), usage of floss or mouth wash (49.7%), causes of caries, periodontal diseases and system diseases (56.9–83.4%). The rates mentioned above were 36.1, 15.8%, 26.7–43.6% among 3MS, respectively. In terms of oral health status, significant differences were only observed in junior students. The prevalence rates of bad breath, gum bleeding, and tooth discoloration among 3DS were obviously lower than those of 3MS. However, only a total of 17.2% junior students had a good oral health, including 23.8% dental students and 11.4% medical students. Conclusions: Our study provided a new understanding of oral health knowledge, behavior and status among dental and medical students, which may help to promote the reform of oral health education and establish a model for clinicians and dentists to work together for improving oral health. [ABSTRACT FROM AUTHOR]

Deforestation can lead to severe losses of soil nutrients. However, the impacts of the slope morphology and position on the spatial distributions of soil nutrients after deforestation and their relationships are unclear, thereby limiting our understanding of the mechanism of soil degradation. In this study, we aimed to identify the relationships between the changes in soil nutrients and the slope morphology (i.e., slopes with different widths or lengths) after deforestation. Soil samples were collected from forestland slopes with different morphologies after deforestation for 28 years in the hilly area of the Loess Plateau, China. We analyzed the effects of the length, width, and position of the slope on the pH, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), nitrate-N (NO 3 −), ammonium-N (NH 4 +), available phosphorus (AP), and available potassium (AK) distributions after deforestation. The spatial autocorrelation analysis indicated that the Moran's I index value for soil nutrients was larger on deforested slope than that of forest land, thereby suggesting that deforestation increased the spatial heterogeneity of the soil nutrients. After deforestation, the spatial autocorrelation distances increased for the soil pH and TP, whereas they decreased for SOC, TN, NH 4 +, NO 3 −, and AK. The TN, NH 4 +, and NO 3 − contents were significantly higher on the narrow slope than the wide slope. Among the three slope lengths, the soil nutrient losses were greater on the longer slope because of the more severe erosion of the slope after deforestation. The slope position significantly affected the distributions of the soil nutrients. In the vertical direction, the soil nutrient contents decreased continuously in the 0–10, 10–20, and 20–40 cm soil layers, but then increased in the 40–60 cm soil layers, mainly due to the eluviation of nutrients to deep soil layers. These results demonstrate that the slope morphology and position should not be overlooked when predicting the responses of soil nutrients to deforestation in the hilly loess region of China. • Deforestation changed the spatial distributions of the soil nutrients on the slope. • The nutrient contents were higher on the narrow slope than the wide and medium slopes. • Among the three slope lengths, the soil nutrient losses were greater on the longer slope. • Slope morphology and position should not be overlooked when predicting the responses of soil nutrients to reclamation. [ABSTRACT FROM AUTHOR]

The conversion of croplands to shrublands is a common approach used to control soil erosion in the drylands of the Loess Plateau in China and affects the soil, water, and carbon cycles. Knowledge of the soil water content (SWC) and soil organic carbon (SOC) content in response to land-use change is essential for optimizing revegetation strategies and improving ecosystem services. This study investigated the distribution characteristics of the SWC and SOC content for the 0–500 cm soil layer in 11 croplands and 39 shrublands planted on a former cropland over 50 years ago. The coupled and trade-off relationship between soil water consumption and carbon fixation in the shrubland soil was also analyzed. The results showed that the SOC content and SWC of the shrublands and croplands varied with soil depth, but their distribution patterns were similar under both land-use types. Planting shrubs on slopes reduced the SWC but did not significantly enhance the SOC content, indicating that cropland-to-shrubland conversion results in excessive soil water depletion without increasing carbon fixation in the soil. Additionally, both the SOC content and SWC of the shrublands varied significantly with slope positions (p < 0.05) and showed intermediate coordination levels across the entire slope. Moreover, the SOC content provided higher benefits than SWC, where the foot slope showing a relatively higher coupling coordination degree and a lower trade-off than other slope positions. These results suggest that shrubs provide a limited contribution to improve SOC stocks in the drylands of the Loess Plateau and that reductions in deep soil water under cropland-to-shrubland conversion require consideration when planning future ecological restoration measures. To improve ecosystem services (carbon sequestration and soil conservation) without compromising water resources in the drylands of the Loess Plateau or similar regions worldwide, it is necessary to fully consider the slope position and the trade-off between the SWC and SOC content. • Cropland-to-shrubland conversion induces soil moisture decline on the Loess Plateau. • Planting shrubs on slope land does not sequester large amounts of carbon. • SOC content has a higher relative benefit than SWC for the entire shrubland slope. • Afforestation measures in dryland areas should consider slope position. [ABSTRACT FROM AUTHOR]

Soil erosion is continually overlooked in the hilly red soil region of southern China, and there is a substantial lack of knowledge about the effects of soil and water conservation measures (SWCMs) on erosion prevention and soil carbon and nitrogen accumulation for the eroded sloping arable land in this region. Herein, based on a long-term experiment in the red soil hilly region in China, we investigated the effects of 17 years of SWCMs on soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon and nitrogen (MBC and MBN, respectively) as well as soil erodibility (K factor) at soil depths of 0–100 cm in the top, middle and bottom parts of the slope. The SWCMs included straw mulching (SM), downslope ridge cultivation (DC), downslope ridge cultivation + contour hedgerow planting (DCH), and contour ridge cultivation tillage (CC). A bare land treatment without any crops was used as a control (CK). We found that SWCMs increased SOC, TN, MBC, and MBN by 8–57%, 1–14%, 25–68%, and 17–35%, respectively, with greater increases in these variables in the CC and SM treatments and smaller increase in the DC treatment. Additionally, the effects of the SWCMs were greater at the top and middle of the slope than at the bottom of the slope, and the effects varied with soil depth. Moreover, the SWCMs decreased soil erodibility, with a lower K factor in the SWCMs treatments (0.018–0.049 t ha h ha−1 MJ−1 mm−1) than in the CK (0.042–0.068 t ha h ha−1 MJ−1 mm−1) and a greater decrease in the CC treatment. The effects of the SWCMs on soil erodibility mainly occurred through the regulation of SOC according to structural equation modeling. Overall, this study suggested that straw mulching and contour ridge cultivation tillage were the most effective strategies for restoring soil carbon and nitrogen and preventing soil erosion. • The SWCMs improved soil carbon and nitrogen levels but reduced erodibility. • The effects of the SWCMs on soil erodibility mainly through the regulation of SOC. • Straw mulching and contour ridge cultivation tillage prevent soil erosion conspicuously. [ABSTRACT FROM AUTHOR]

• Up-slope runoff and sediment increased most nutrient contents on the wide slope. • Up-slope runoff and sediment decreased most nutrient contents on the narrow slope. • Up-slope runoff and sediment reduced random spatial heterogeneity of soil nutrients. Upslope runoff and sediment critically influence soil erosion, while their impact on the subsequent downslope nutrient distribution has not been examined, consequently hindering the exact assessment of the effects of erosion on soil biogeochemical cycles. Herein we selected two groups of wide and narrow slopes on the middle Loess Plateau, with each slope group including slopes with and without upslope runoff and sediment. For each slope, we collected soil samples from topsoil along the slope at different distances from the upper slope to the lower slope, and collected samples from depths of 0–60 cm at the upper, middle and lower positions of the slope. The contents of soil organic matter and nutrients were analysed. The purpose of this study was to disentangle the effects of upslope runoff and sediment on spatial distribution of soil nutrients on slopes of different widths. We showed that compared with slopes without upslope runoff and sediment, upslope runoff and sediment increased the content of most nutrients in topsoil on the wide slope, but had a contrasting effect on the narrow slope. Upslope runoff and sediment reduced the random spatial heterogeneity of soil nutrients on both the wide and narrow slopes, with greater effects observed on the narrow slope. The influence of upslope runoff and sediment on the profile distribution of soil nutrients varied with slope position and slope width, and was nutrient type-dependent. These results indicated that slope topographical conditions interact with upslope runoff and sediment in influencing vertical and horizontal patterns of soil nutrients on slopes. [ABSTRACT FROM AUTHOR]

• Higher erosion intensity and smaller size of check dam resulted in greater variation in soil particles. • Soil OC and N in check dams decreased with the distance from the dam body to the gully head. • Silt content was more important than clay content in influencing the distribution of OC and N in check dam soils. Check dams are effective soil and water conservation structures worldwide that play an important role in preserving sediments containing carbon (C) and nitrogen (N). However, in terms of the depositional characteristics of C and N in check dams, research on the relative effects of erosion intensity and depositional area is limited, hindering our understanding of the fates of eroded C and N. This study compared the horizontal and vertical distributions of soil particles, organic C (OC), and total N (TN) in check dams of various sizes and erosion intensities in the Loess Plateau. The results showed greater variations in the horizontal and vertical patterns of soil particles of smaller check dams and highly serious erosion (erosion modulus = 15040 t km-2 a-1) than those that of larger check dams and strong erosion regions (erosion modulus = 5151 t km-2 a-1). Soil OC and TN contents decreased from the dam body to the gully head, especially in the highly serious erosion region. Notably, the effect of smaller check dam on the vertical distributions of soil OC and TN was more intense than that of the larger check dam in the strong erosion region. In contrast, a minor effect of check dam size was observed in the highly serious erosion region. Moreover, a closer relationship between the distribution of OC and TN with silt content rather than with clay content in check dams was observed, and this relationship was enhanced by an increase in erosion intensity. Overall, the synergistic effects of erosion intensity and check dam size affected the spatial patterns of OC and TN in sediments on the Loess Plateau. Careful consideration of these two factors is beneficial for accurately assessing the C and N fates in depositional areas. [ABSTRACT FROM AUTHOR]

Soil nitrogen (N) mineralization is an important ecological process influencing N availability and ecosystem functionality, and is sensitive to vegetation presence and soil erosion. However, how vegetation presence affects N mineralization and its response to erosion has not been directly examined, hindering our ability to predict N cycling in eroding environments. Herein, we compared the effect of vegetation presence on N mineralization and mineral N dynamics in two growing seasons between erosion vs. deposition sites in three sub-watersheds in the transition zone between water erosion and wind erosion of North China. We aim to examine how soil N cycling responds to erosion and vegetation presence at temporal and spatial scales. The mineral N concentration in the soil solution and mineralization rates between May 2017 and October 2018 in plots with and without vegetation were measured to assess the effects of vegetation presence. We showed that N mineralization rates did not significantly vary among the three sub-watersheds or between erosion and deposition sites. The concentrations of mineral N in the soil solution were higher in relatively larger sub-watersheds for the erosion sites and in smaller sub-watersheds for the deposition sites. Vegetation decreased soil NO 3 --N and total mineral N and increased NH 4 +-N concentrations in the early and middle periods of the growing season. The effects of vegetation presence on net N mineralization rates varied with size of sub-watersheds, with increased rates of net nitrification and mineralization at both deposition and erosion sites in relatively larger sub-watershed, but reduced rates of net nitrification and mineralization in smaller sub-watersheds. Moreover, the presence of vegetation shifted the seasonal pattern of N mineralization. Therefore, vegetation presence had important ecological regulation on soil N cycling at spatial and temporal scales in the transition zone between water erosion and wind erosion. • Soil mineral N varied with sub-watershed scales and landscape positions. • Vegetation decreased nitrate and total mineral N but increased ammonium. • The effects of vegetation on N mineralization varied with sub-watershed scales. • Vegetation presence shifted the seasonal pattern of N mineralization. [ABSTRACT FROM AUTHOR]

• Afforestation increased significantly soil OC and N mineralization. • The increase of OC and N mineralization were larger in sites with high clay content. • The temperature sensitivity decreased in sites with relative high clay content. • Soil texture regulated OC and N mineralization and their temperature sensitivity. Afforestation on abandoned cropland has great potential to increase soil organic carbon (OC) and nitrogen (N). Identifying the effect of afforestation on mineralization of OC and N as well as their temperature sensitivity at large spatial and temporal scales is essential to understand soil OC and N dynamics. In this study, we measured mineralization of soil OC and N at standard temperatures (15 and 25 °C) by laboratory incubation, and calculated their temperature sensitivity (Q 10). Soil samples were collected from cropland (0 years, selected as a control) and adjacent woodlands with different afforestation age (10, 20 and 30 years) at five sites from north to south on China's Loess Plateau. The objectives were to understand how long-term afforestation affects OC and N mineralization and their Q 10 and whether such effects depend on afforestation age and soil texture. The results showed that afforestation increased OC and N mineralization, but this effect was not affected by afforestation age (10–30 years). The Q 10 of OC and N mineralization increased in the first 10 years of afforestation but decreased in the late stage. Furthermore, the increases of OC and N mineralization by afforestation were higher at sites with fine-textured soils than those at sites with coarse-textured soils. However, the Q 10 increased at sites with a relatively high sand content but decreased or remained unchanged at sites with a relatively high clay content. The changes in OC and N mineralization and their Q 10 were related to soil OC and N contents, pH and clay content. Overall, we concluded that long-term afforestation would contribute to the stability of soil OC and N in afforested ecosystems. Soil texture is an important factor controlling OC and N mineralization and their Q 10 , and should be considered when predicting soil OC and N dynamics in response to temperature change in different landscapes. [ABSTRACT FROM AUTHOR]

• Simulated erosion decreased mineralization of OC and N in soils • Decrease in OC and N mineralization was mainly occurred in small aggregate sizes • Changes in OC and N availability determined decrease in OC and N mineralization • The OC and N mineralization increased with OC and N contents but texture independent Soil erosion has important influence on soil processes and particularly soil nutrient dynamics, which in turn affects the terrestrial C and N cycling and greenhouse gases emission. However, the responses of carbon (C) and nitrogen (N) cycling in soils and soil fractions to erosion remain largely unclear, hindering the precise prediction of the fate of C and N in the terrestrial ecosystem. Herein, we compared the mineralization of organic carbon (OC) and N at two different temperatures (15 and 25 °C) in bulk soils and aggregate fractions of 19 soils before and after a simulated rainstorm. The temperature sensitivity (Q 10) of OC and N mineralization was calculated. Soil samples were collected from 9 sites across China, with soil types of Alfisols, Inceptisols, Mollisols, Ultisols, and land uses of croplands, grasslands, and woodlands. The soil aggregate fractions were >2, 2-1, 1-0.25 and <0.25 mm, respectively. We hypothesized that erosion will decrease OC and N mineralization due to the loss of labile organic matter from soils and that the effects of erosion would decrease with clay content and vary with different aggregate fractions. In support of these hypotheses, the cumulative mineralized OC and N (C m and N m) in the soils and aggregate fractions were decreased of 78-85% and 37-52% after erosion, and the temperature sensitivities of OC and N mineralization were decreased of 80-84% and 4-43%, respectively. The effects of erosion varied with site where the soil was collected. The decreases in C m and N m mainly occurred in small aggregate sizes (1-0.25 and <0.25 mm fractions). The C m and N m in bulk soils and aggregates increased significantly with the contents of OC, N, labile OC and mineral N but were texture independent. These results highlighted significantly reduction of OC and N mineralization at eroding sites, which should be carefully considered when assessing emissions of greenhouse gases in eroding environments. [ABSTRACT FROM AUTHOR]