Subtropical plantations are large carbon sinks: evidence from two monoculture plantations in South China.

摘要

Quantifying the net carbon (C) storage of forest plantations is required to assess their potential to offset fossil fuel emissions. In this study, a biometric approach was used to estimate net ecosystem productivity (NEP) for two monoculture plantations in South China: Acacia crassicarpa and Eucalyptus urophylla. This approach was based on stand-level net primary productivity (NPP, based on direct biometric inventory) and heterotrophic respiration (R_h). In comparisons of R_h determination based on trenching vs. tree girdling, both trenching and tree girdling changed soil temperature and soil moisture relative to undisturbed control plots, and we assess the effects of corrections for disturbances of soil moisture and soil moisture on the estimation of soil CO₂ efflux partitioning. Soil microbial biomass and dissolved organic carbon were significantly lower in trenched plots than in tree girdled plots for both plantations. Annual soil CO₂ flux in trenched plots (R_h-t) was significantly lower than in tree-girdled plots (R_h-g) in both plantations. The estimates of R_h-t and R_h-g, expressed as a percentage of total soil respiration, were 58+or-4% and 74+or-6%, respectively, for A. crassicarpa, and 64+or-3% and 78+or-5%, respectively, for E. urophylla. By the end of experiment, the difference in soil CO₂ efflux between the trenched plots and tree-girdled plots had become small for both plantations. Annual R_h (mean of the annual R_h-t and R_h-g) and net primary production (NPP) were 470+or-25 and 800+or-118 g C m-2 yr-1, respectively, for A. crassicarpa, and 420+or-35 and 2380+or-187 g C m-2 yr-2, respectively, for E. urophylla. The two plantations in the developmental stage were large carbon sinks: NEP was 330+or-76 C m-2 yr-1 for A. crassicarpa and 1960+or-178 g C m-2 yr-1 for E. urophylla.