The effect of land use change and soil redistribution on soil organic carbon dynamics in karst graben basin of China

Abstract

Ascertaining soil and associated soil organic carbon (SOC) redistribution induced by erosion and deposition processes is of critical importance to explore SOC dynamics on the landscape. The relationship between landscape scale erosion and deposition and SOC dynamics still has to be clearly described in fragile karst region. The soil profiles of 40-cm depth in relation to different land use types (e.g., grassland, forests, shrubland, and farmland) at the eroding and depositional landform positions were chosen. The profile patterns of SOC and its isotopic signatures were analyzed. The source and decomposition of SOC in profiles were investigated subsequently. The mean SOC concentration in soil profiles decreased in the following order: shrubland > grassland > artificial forest > farmland at the eroding sites and grassland > artificial forest > shrubland > farmland at the depositional sites. The main sources of SOC in profiles at both landform positions were from C3 plants, while the proportional contribution of C4 plants increased along the depth. Although a higher concentration of SOC at the depositional sites was found relative to upland soils, there was higher decomposition rate of SOC at the depositional sites than that at the eroding sites, particularly under the farmlands. Our findings imply that the conversion of farmland to natural forests or grassland could be feasible for enhancing SOC sequestration potential; meanwhile, the soil redistribution process has significant effect on dynamics of eroded SOC in fragile systems, especially in the karst region.