Revealing the driving mechanism of soil respiration induced by water erosion in Ultisols landscape of southern China

Water erosion exerts a profound impact on the terrestrial C cycling and its source/sink patterns through strongly affecting soil respiration (Rs). However, the systematic mechanism of erosion-induced CO2 emissions remains inadequately elucidated. Herein, we conducted a one-year field experiment to examine the effects of erosion and deposition on Rs, as well as the relationships between different environmental factors and Rs on a typical eroded slope in southern China. Samples of the topsoil (0–20 cm), classified as Ultisols, were collected from four landscape positions (top, up, middle and toe) with different erosional and depositional characteristics along three transects. We also utilized Biolog-Eco microplates to investigate the response of soil microbial community function to water erosion. The results indicated the accumulative Rs significantly differed among different sites (P < 0.05), primarily in the order of mid-slope< up-slope< toe-slope< top-slope, with the maximum and minimum values of 18.75 and 9.75 t CO2 ha−1 yr−1, respectively. Moreover, erosion remarkably reduced the soil organic carbon (SOC), nutrients, and the average well color development (AWCD) of the carbon sources in soil microbial communities, while deposition enhanced them. The Structural Equation Modeling (SEM) elucidated the multi-factor driving mechanism of erosional site, soil temperature (Ts5), moisture (SWC10), microbial biomass carbon (MBC), SOC, and Shannon’s index on Rs (R2=84.20 %). More importantly, SEM revealed that Ts5, SWC10, MBC, SOC were the most significant predictors of Rs. In summary, Rs was regulated by the interplay of hydrothermal factors, soil properties, and microbial characteristics under erosion and deposition conditions. There is a need to incorporate additional soil properties other than the hydrothermal double-factor model. Our findings highlighted the importance of water erosion on Rs and clarified its driving mechanism, providing a theoretical basis for better predicting and managing carbon-climate feedbacks.