Changes in the Soil Labile Organic Carbon Fractions following Bedrock Exposure Rate in a Karst Context

Soil labile organic carbon fractions (SLOCFs) mainly include microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily oxidized organic carbon (EOC) and light fraction organic carbon (LFOC). The link between bedrock exposure rates with SLOCFs and the carbon pool management index under karst rocky desertification has not been well understood. We selected the bedrock exposure rate and vegetation coverage of 30–50% (light bedrock exposure, LBE), 50–70% (moderate bedrock exposure, MBE) and >70% (intense bedrock exposure, IBE) as the experimental sample plots according to the classification standard of karst rocky desertification, and then selected a sample plot of 0–30% (secondary forest, SF) as the control. This study compared the concentrations and stocks of soil organic carbon (SOC) and SLOCFs and analyzed the relevant carbon pool management index on karst landforms at Anshun, S.W. China. The aims were to determine the relationship between bedrock exposure rates and SLOCFs and to identify the most limiting factors for SLOCFs in karst rocky desertification areas. We found that (1) the concentrations and stocks of SLOCFs declined with increasing soil depth. SOC, DOC and MBC showed IBE > LBE > MBE > SF; LFOC decreased with increasing bedrock exposure rate, and EOC did not show obvious regularity. (2) The carbon pool management index and sensitivity index had significant differences under different bedrock exposure rates. Redundancy analysis and linear regression showed that the increase in bedrock exposure rate had a great impact on MBC, DOC, EOC and SOC. In conclusion, the increase of bedrock exposure rate has no side impact on the DOC, EOC and MBC of the soil, but side effects are exhibited by LFOC. Secondary forest improves the integrity of karst landscapes, and does not change the soil properties as well as the concentrations and stocks of SLOCFs in karst rocky desertification areas