Response of soil labile organic carbon fractions to forest conversions in subtropical China

In order to determine the impact of forest conversions on labile organic carbon fractions, soils at depths of 0 - 10, 10 - 30 and 30 - 50 cm were collected from three types of forest: secondary monsoon evergreen broadleaved forest (BF), mixed pine and broadleaved forest (MF) and Masson pine forest (PF) in subtropical China. The light fraction organic carbon (LFOC), particulate organic carbon (POC) and microbial biomass carbon (MBC) in the soils were determined. The results showed that soils, the top soils (at depths of 0 - 10 cm) in particular, in BF had significantly higher LFOC, POC and MBC than those in MF and PF, indicating that forest conversions influenced the labile organic carbon fractions in subtropical China, and this influence mainly occurred in the top soils. The significantly higher ratios of labile organic carbon to soil organic carbon in BF than those in MF and PF confirmed that forest conversions from BF to MF could lead to a considerable reduction in soil labile organic carbon. In all three types of forest, the reduction of soil organic carbon in the rainy season was higher than that in the dry season.