Coupling carbon and water fluxes in semiarid steppes, Inner Mongolia, China

Inner Mongolia is the area has abundant natural grassland resources and most of them locate at arid and semi-arid regions, which is more sensitive to the climatic change and human disturbance. Human disturbance (such as grazing and reclamation) has caused the dramatic changing in land use type of steppe ecosystems in the north of China and resulted in severe degradation of steppe ecosystems. To better understand the effects of human-induced land use change on carbon and water exchanges and their responses to climate changes, six eddy covariance towers were setup in Inner Mongolia grasslands since 2006. We found the steppe ecosystems acted as a carbon sink in most of years, ranging from -172.4 to 52.8 g C m-2. The cropland only showed stronger carbon uptake ability than the steppe in dry years, but the restoring degraded steppe kept a relative stable carbon sequestration potential compared with the long-term fenced steppe. Seasonal precipitation and mean air temperature were dominant factors influencing inter-annual variations of ET and ET /PPT ratio, but seasonality of precipitation and proportion of large rain events were more important for carbon sequestration of steppes.