Responses of soil organic carbon components and their sensitivity to karst rocky desertification control measures in Southwest China

Adequate karst rocky desertification control measures are very important in enhancing the soil quality and soil organic carbon (SOC) sequestration in the karst regions of Southwest China. This study aims to assess the responses and sensitivity of SOC and its components to karst rocky desertification control measures in degraded karst ecosystems. Two karst rocky desertification control measures, namely, conversion of cropland to secondary forest (SF) and the Chinese prickly ash planting (CPP), were chosen with cropland (CL) as reference soil. Soils in 0–10- and 10–20-cm layers were sampled. Then, SOC, easily oxidizable organic carbon (EOC), non-liable organic carbon (NLOC), particulate organic carbon (POC), mineral-associated SOM (MOC), and the carbon pool management index (CPMI) were determined. Karst rocky desertification control measures caused SOC to increase significantly through the increase in active (EOC, POC), non-liable (NLOC), and stable carbons (MOC). Significant relationships between the changes in SOC and the changes in its components were observed in the depths of 0–20cm. The responses of POC were more sensitive than SOC and other soil C components under CPP and SF. The EOC and POC ratios to SOC were highest in SF soils, followed by CPP as compared with soils under CL. The values of the CPMI and C/N ratios in CPP were lower than those in SF. The sensitivity index (SI) value of POC was highest, followed by EOC, SOC, NLOC, and MOC. Redundancy analysis (RDA) showed the C/N, CPMI, and POC/SOC ratios had significant effects on changes in soil C components. The results indicated that karst rocky desertification control measures not only enhanced SOC quality but may also be beneficial for soil C sequestration. Conversion of cropland to natural SF could be a more suitable control measure for enhancing SOC quality and storage in the karst regions of southwestern China. POC was the most sensitive SOC fraction to karst rocky desertification control measures and can best reflect the dynamics of SOC. C/N ratio and CPMI may be considered as useful soil quality indicators for the overall C change in different karst rocky desertification control measures in degraded karst systems.