Greenhouse gas fluxes from soils of different land-use types in a hilly area of South China

The magnitude, temporal, and spatial patterns of greenhouse gas (hereafter referred to as GHG) fluxes from soils of plantation in the subtropical area of China are still highly uncertain. To contribute towards an improvement of actual estimates, soil CO2, CH4, and N2O fluxes were measured in two different land-use types in a hilly area of South China. This study showed 2 years continuous measurements (twice a week) of GHG fluxes from soils of a pine plantation and a longan orchard system. Impacts of environmental drivers (soil temperature and soil moisture), litter exclusion and land-use (vegetation versus orchard) were presented. Our results suggested that the plantation and orchard soils were weak sinks of atmospheric CH4 and significant sources of atmospheric CO2 and N2O. Annual mean GHG fluxes from soils of plantation and orchard were: CO2 fluxes of 4.70 and 14.72 Mg CO2–C ha−1 year−1, CH4 fluxes of −2.57 and −2.61 kg CH4–C ha−1 year−1, N2O fluxes of 3.03 and 8.64 kg N2O–N ha−1 year−1, respectively. Land use types had great impact on CO2 and N2O emissions. Annual average CO2 and N2O emissions were higher in the orchard than in the plantation, while there were no clear differences in CH4 emissions between two sites. Our results suggest that afforestation could be a potential mitigation strategy to reduce GHG emissions from agricultural soils if the observed results were representative at the regional scale. CO2 and N2O emissions were mainly affected by soil temperature and soil moisture. CH4 uptakes showed significant correlation with soil moisture. The seasonal changes in soil CO2 and N2O fluxes followed the seasonal weather pattern, with high CO2 and N2O emission rates in the rainy period and low rates in the dry period. In contrast, seasonal patterns of CH4 fluxes were not clear. Removal of surface litter reduced soil CO2 effluxes by 17–25% and N2O effluxes by 34–31% in the plantation and orchard in the second sampling year but not in the first sampling year which suggested micro-environmental heterogeneity in soils. Removal of surface litter had no significant effect on CH4 absorption rates in both years. This suggests that microbial CH4 uptake was mainly related to the mineral soil rather than in the surface litter layer.