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

Methane (CH₄) is one of the most potent greenhouse gases. Although forest and grassland soils generally consume atmospheric CH₄, the quantities and spatiotemporal changes in CH₄ uptake remain largely uncertain for these ecosystems at the global scale. In this study, we developed an empirical model to estimate the CH₄ uptake in global forest and grassland soils during the period 1981-2010. We estimated that the mean values of CH₄ uptake were 9.16 (± 3.84) Tg yr^-1 in forest soils and 3.73 (± 1.41) Tg yr^-1 in grassland soils during the study period. Tropical forest and grassland soils were determined to be the largest CH₄ sink, contributing 58% to the global total. During the 30-year period, the CH₄ 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^-1 owing mainly to increases in mean temperatures. However, the uptake decreased significantly (P<0.01) in tropical dry grassland soils, at 1.22Ggyr^-1, owing mainly to increases in precipitation. Ultimately, our simulation indicated that the global CH₄ uptake by forest and grassland soils increased significantly (P<0.05) at rates of 4.67Ggyr^-1 and 2.98Ggyr^-1, 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 CH₄ sinks will play a positive role in climate change mitigation in the future.