Methane uptake in global forest and grassland soils from 1981 to 2010.

Methane (CH) is one of the most potent greenhouse gases. Although forest and grassland soils generally consume atmospheric CH, the quantities and spatiotemporal changes in CH uptake remain largely uncertain for these ecosystems at the global scale. In this study, we developed an empirical model to estimate the CH uptake in global forest and grassland soils during the period 1981-2010. We estimated that the mean values of CH uptake were 9.16 (± 3.84) Tg yr in forest soils and 3.73 (± 1.41) Tg yr in grassland soils during the study period. Tropical forest and grassland soils were determined to be the largest CH sink, contributing 58% to the global total. During the 30-year period, the CH uptake in cool temperate dry and warm temperate dry soils and in polar/boreal grassland soils increased significantly (P<0.05) at rates of 0.30-2.95Ggyr owing mainly to increases in mean temperatures. However, the uptake decreased significantly (P<0.01) in tropical dry grassland soils, at 1.22Ggyr, owing mainly to increases in precipitation. Ultimately, our simulation indicated that the global CH uptake by forest and grassland soils increased significantly (P<0.05) at rates of 4.67Ggyr and 2.98Ggyr, respectively, during the period 1981-2010. The trend of increasing sinks from forest and grassland and its relationship with temperature and precipitation variability imply that forest and grassland CH sinks will play a positive role in climate change mitigation in the future.