[Spatial-temporal Evolution and Driving Factors of Soil Organic Carbon in Karst and Non-karst Areas of Guangxi Based on Random Forest].

Abstract

The difference in soil organic carbon density （SOCD） between karst and non-karst areas affects the accurate assessment of soil carbon sinks at the provincial scale， making it a hot and difficult topic in soil carbon pool research. Taking the karst and non-karst regions of Guangxi as an example， and based on soil profile and environmental variable data from 1980 and 2010， a random forest model was constructed to analyze the spatiotemporal differentiation characteristics of topsoil SOCD in karst and non-karst region. Furthermore， SHAP values and partial dependence plots were employed to reveal the response characteristics of different driving factors to topsoil SOCD in the two regions. The results show that： ① The mean SOCD in the karst region was higher than that in the non-karst region in both 1980 and 2010. The areas with a decrease in the annual mean change rate of SOCD in the karst region showed a high spatial consistency with the expansion areas of rocky desertification. ②Total nitrogen content and slope were both key driving factors affecting SOCD in the two regions. In addition， silt content， soil types， and normalized difference vegetation index significantly influenced SOCD in the karst region， while mean annual temperature， elevation， and total precipitation exerted important impacts on SOCD in the non-karst region. ③ The relationships between SOCD and the driving factors were characterized by diversity. SOCD showed a nonlinear positive correlation with total nitrogen content， silt content， normalized vegetation index， and elevation； a nonlinear negative correlation with mean annual temperature and total annual precipitation； and a nonlinear relationship with slope that was initially negative and then positive. Moreover， there were distinct thresholds in all these relationships. These research findings provide a scientific basis for systematically assessing the potential of soil carbon sinks， formulating measures for regulating soil carbon pools， and developing carbon management zoning strategies.