The conversion of forests to agricultural land reduced the content of soil black carbon fractions in a karst rocky desertification area of Southwest China

Understanding the effects of land use on soil black carbon (BC) is critical for correctly interpreting the role of BC in the carbon cycle of karst areas. This study investigated the distribution characteristics of organic carbon (OC), BC, char, and soot and soil physicochemical properties of the soil profiles (0-40 cm) of secondary forest, shrub, farmland, and wasteland in a rocky desertification area of Guangxi Province, a typical karst rocky desertification area in Southwest China. We used a combination of soot/char and {delta}13CBC isotope analysis to identify the source of BC of these soils. The average value of soil BC was the highest in secondary forest, followed by shrub, farmland, and wasteland in the 0-40 cm soil layer. BC had a positive correlation with OC, char, soot,soil nitrogen, phosphorus and potassium, showed a negative correlation with bulk density. In the black carbon component, char occupies a greater proportion than soot, with the heavy fraction OC exhibiting a higher concentration of BC than the light fraction OC. Conclusively, the BC content was mainly due to C3 plant burning, vehicle exhaust emissions, and fossil fuel utilization.Vegetation restoration improved the soil BC content associated with OC sequestration in the typical karst rocky desertification mountainous area of Southwest Guangxi.