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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]

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]

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]