East Asian summer monsoon substantially affects the inter-annual variation of carbon dioxide exchange in semi-arid grassland ecosystem in Loess Plateau

Abstract The net ecosystem CO 2 exchange (NEE) of a semi-arid grassland on the boundary area of the East Asian summer monsoon (EASM) was measured continuously by eddy covariance technology in the Loess Plateau from 2007 to 2012. The grassland ecosystem was a weak carbon source with a mean of 17.1 ± 12.1 g C m −2  year -1 during the measure period. The inter-annual variability in NEE was significantly related to the annual precipitation amount. The EASM played an essential role in the CO 2 exchange of grassland at the boundary region of monsoon thought dominating climatic variables, such as the annual precipitation amount and seasonal drought. Drought stress suppressed gross primary productivity (GPP) more than ecosystem respiration (R eco ). Soil moisture reduction could result in sensitivity weaker of R eco dependence to soil temperature ( T s ), and GPP estimated by R eco - T s exponential growth function might be overestimated under severe soil drought when high T s . Additionally, warmer spring has been found to be able to enhance the grassland’s carbon uptake, and compensate for the reductions induced by the summer drought. Our results contribute to understanding of the specific driving mechanism for inter-annual variability of carbon fluxes in the Loess Plateau, and enhancing the terrestrial ecosystem model’s performance in carbon fluxes estimate under the drought stress environment.