Possible decline of the carbon sink in the Mongolian Plateau during the 21st century

The Mongolian Plateau is dominated by grassland ecosystems. It frequently experiences drought and is underlain by permafrost in the north. Its complex responses of plant carbon uptake and soil carbon release to climate change are considered to have affected the global carbon cycle during the 21st century. Here we combine spatially explicit information on vegetation, soils, topography and climate with a process-based biogeochemistry model to assess the carbon responses for the 20th and 21st centuries. We estimate the region acted as a C sink of 31 Tg C yr−1 in the 1990s, but that this sink will likely decline in both magnitude and extent under future climate conditions. This change is due to the relatively larger enhancement of soil organic matter decomposition, which releases carbon to the atmosphere, than the corresponding enhancement of plant C uptake, by rising temperatures and atmospheric CO2 concentrations. Future plant C uptake rates are expected to become more limited due to drier soils caused by increasing evapotranspiration rates. Complex soil thermal and moisture dynamics result in large interannual and spatial variability as a consequence of the different rates of change of air temperature and precipitation in this region.