Soil‐atmospheric exchange of CO2, CH4, and N2O in three subtropical forest ecosystems in southern China

Abstract The magnitude, temporal, and spatial patterns of soil‐atmospheric greenhouse gas (hereafter referred to as GHG) exchanges in forests near the Tropic of Cancer are still highly uncertain. To contribute towards an improvement of actual estimates, soil‐atmospheric CO 2 , CH 4 , and N 2 O fluxes were measured in three successional subtropical forests at the Dinghushan Nature Reserve (hereafter referred to as DNR) in southern China. Soils in DNR forests behaved as N 2 O sources and CH 4 sinks. Annual mean CO 2 , N 2 O, and CH 4 fluxes (mean±SD) were 7.7±4.6 Mg CO 2 ‐C ha −1 yr −1 , 3.2±1.2 kg N 2 O‐N ha −1 yr −1 , and 3.4±0.9 kg CH 4 ‐C ha −1 yr −1 , respectively. The climate was warm and wet from April through September 2003 (the hot‐humid season) and became cool and dry from October 2003 through March 2004 (the cool‐dry season). The seasonality of soil CO 2 emission coincided with the seasonal climate pattern, with high CO 2 emission rates in the hot‐humid season and low rates in the cool‐dry season. In contrast, seasonal patterns of CH 4 and N 2 O fluxes were not clear, although higher CH 4 uptake rates were often observed in the cool‐dry season and higher N 2 O emission rates were often observed in the hot‐humid season. GHG fluxes measured at these three sites showed a clear increasing trend with the progressive succession. If this trend is representative at the regional scale, CO 2 and N 2 O emissions and CH 4 uptake in southern China may increase in the future in light of the projected change in forest age structure. Removal of surface litter reduced soil CO 2 effluxes by 17–44% in the three forests but had no significant effect on CH 4 absorption and N 2 O emission rates. This suggests that microbial CH 4 uptake and N 2 O production was mainly related to the mineral soil rather than in the surface litter layer.