Soil carbon dynamics in different types of subtropical forests as determined by density fractionation and stable isotope analysis

摘要

Quantifying carbon (C) dynamics with forest land-use change is essential for predicting C sequestration and stabilization. Here, we combined density fractionation and stable isotope analysis to examine soil C dynamics after primary native broadleaf forests (BF) were converted to secondary forests (SF) and plantation forests (PF). The results showed that soil C stock at 0-30 cm depth decreased significantly from BF (70.8 Mg ha(-1)) to SF (60 Mg ha(-1)) and PF (53.9 Mg ha(-1)). Both soil C concentration and stock decreased, but soil delta C-13 of the light and heavy fractions increased, and these increases were more evident in the topsoil (0-10 cm) than in the subsoil (10-30 cm). The decrease of the heavy fraction C stocks accounted for 52.7% and 69.7% of the reduction of bulk soil C stocks with conversion of BF to SF and PF, respectively. Analysis of delta C-13 revealed that the input of new C into the light fraction of soil at 0-10 cm depth decreased by 13.1% with conversion of BF to SF, and by 34.0% with conversion of BF to PF. The decreases of soil C stocks in density fractions were primarily explained by soil properties (beta = 0.70) but also by vegetation biomass (beta = 0.26), and were closely correlated with soil moisture content (0.69, the highest eigenvalue among soil properties) and floor litter biomass C (0.75, the highest eigenvalue among biomass C categories). Our findings help clarify the contrasting mechanisms explaining the dynamics of light and heavy fraction of soil C, and highlight the importance of both vegetation and soil in controlling changes in soil C dynamics in response to forest conversion. Accordingly, we recommend that management policies and actions should maximize biomass C inputs of degraded forests and minimize C losses. It follows that the preservation of primary forests might increase ecosystem C sequestration and thereby mitigate climate change.