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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]

• 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]

[Display omitted] • Ca- OC and clay + silt-OC played a vital role in the stability of MAOC. • Ca- OC and clay + silt-OC contributed to the sequestration of MAOC. • MAOC persistence was positively correlated with the MAOC sequestration. Mineral associated organic carbon (MAOC) accounts for a substantial portion of soil organic carbon (SOC) due to its tendency for physicochemical bonding with mineral surfaces. However, the mechanisms controlling MAOC stability and sequestration upon erosion and deposition remain unclear. We collected samples from topsoil (0–20 cm) and subsoil (60–80 cm) in an eroding loess landscape in Northwest China. SOC was fractionated into particulate organic carbon (POC) and MAOC, and OC retained by reactive mineral phases (calcium, iron, and aluminum) were studied. Adsorption-desorption experiments were performed to quantify the OC capture capacity, and thermogravimetric techniques were used to determine the thermal stability of MAOC. Although POC dominated in the soil mass distribution (>60 %) in both sites, the MAOC in the topsoil and subsoil in the depositional sites was characterized by 1.38–3.88 times higher OC contents than the eroding sites. Furthermore, depositional sites featured 1.19–1.45, 1.43–1.72, and 1.28–1.96 times higher maximum adsorption capacity, specific mineral surface area, and silt + clay contents, respectively, than these of the eroding sites, indicating high OC sequestration capacity in the soils of depositional sites. Erosion directly transports soil materials (e.g., OC and fine particles) to the depositional sites, when coupled with the high OC capture capacity, this leads to an increase in the OC content from 0.50 to 1.37 at the eroding sites to 2.19–3.28 mg g−1 at the depositional site. The content and chemical structure of organic-metal complexes had minor differences, however, MAOC in the depositional sites was observed to have excellent thermal stability. Calcium-, and silt + clay-associated OC (Ca-OC and CS-OC) were positively correlated with the MAOC stability and content. Overall, our findings highlight the important role of Ca-OC and CS-OC in determining the stability and sequestration of MAOC in eroding loess landscapes. [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]

• 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]