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

Abstract

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 CO 2, CH 4, and N 2O 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 CH 4 and significant sources of atmospheric CO 2 and N 2O. Annual mean GHG fluxes from soils of plantation and orchard were: CO 2 fluxes of 4.70 and 14.72 Mg CO 2–C ha −1 year −1, CH 4 fluxes of −2.57 and −2.61 kg CH 4–C ha −1 year −1, N 2O fluxes of 3.03 and 8.64 kg N 2O–N ha −1 year −1, respectively. Land use types had great impact on CO 2 and N 2O emissions. Annual average CO 2 and N 2O emissions were higher in the orchard than in the plantation, while there were no clear differences in CH 4 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. CO 2 and N 2O emissions were mainly affected by soil temperature and soil moisture. CH 4 uptakes showed significant correlation with soil moisture. The seasonal changes in soil CO 2 and N 2O fluxes followed the seasonal weather pattern, with high CO 2 and N 2O emission rates in the rainy period and low rates in the dry period. In contrast, seasonal patterns of CH 4 fluxes were not clear. Removal of surface litter reduced soil CO 2 effluxes by 17–25% and N 2O 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 CH 4 absorption rates in both years. This suggests that microbial CH 4 uptake was mainly related to the mineral soil rather than in the surface litter layer.