Soil erosion accelerates carbon cycling as a response to carbon limitation in erosion-prone sloping cropland

Abstract

Soil erosion accelerates the loss of soil carbon (C) pools and then exacerbates the microbial C limitation. However, the extent to which soil microbial C limitation influences soil C cycling processes in different erosion environments remains unclear. We analyzed the differences in soil organic carbon (SOC) content, extracellular enzyme activities and C limitation between sloping cropland and adjacent forestland in a typical small watershed, and further explored the relationship between soil C limitation and the abundance of C cycling genes in different erosion environments. The results revealed that sloping cropland exhibited a 31.70 % higher soil erodibility (K_erosion) compared to forestland, making it more prone to soil erosion. Moreover, the SOC content in sloping cropland was 61.72 % lower than that in forestland. Although there was no significant difference in absolute enzyme activities between sloping cropland and forestland, the specific enzyme activities per unit of SOC (including carbon, nitrogen and phosphorus enzymes) in sloping cropland were significantly higher than those in forestland. The loss of SOC further exacerbated C limitation in sloping cropland and stimulated an increase in the abundance of C cycle genes involved in complex organic C degradation. Additionally, the C cycling genes enriched in sloping cropland demonstrated a significant positive correlation with soil CO₂ emissions (p < 0.01). Therefore, we emphasize that soil erosion stimulates an increase in the abundance of C cycle genes, particularly those involved in complex SOC degradation, as a response to C limitation in erosion-prone sloping cropland. The findings provide scientific support for developing effective soil and water conservation measures to reduce soil C loss and maintain the ecological balance of sloping cropland.