Labile organic carbon pools and enzyme activities of Pinus massoniana plantation soil as affected by understory vegetation removal and thinning

The effects of forest management on carbon (C) sequestration are poorly understood, particularly in the Three Gorges Reservoir area. We aimed to identify the effects of forest management on C sequestration in Pinus massoniana plantations. An intact control forest (CK), a site undergoing regular shrub cutting with the simultaneous removal of residues (SC), a site under low-intensity thinning (LIT), and a site under high-intensity thinning (HIT) were compared for soil labile organic carbon (LOC), related enzyme activities, and soil characteristics. Soil organic carbon (SOC) significantly decreased in the HIT treatment as compared with that in the CK treatment. Soil EOC, DOC, MBC contents in treated plots were higher than those in the CK treatment; particularly, the HIT treatment significantly increased those values in 0–10 cm layer. Thinning resulted in a decrease in cellulase and amylase activities, but an increase in invertase activity. In addition, the SOC content was significantly correlated with four enzymes activities and LOC components, which suggested that the soil LOC components and enzymes activities were sensitive to the changes of SOC. Our results suggest that high-intensity thinning treatment in Pinus massoniana plantation could significantly decrease the SOC content and lead to an increase of LOC components.