Partitioning of evapotranspiration and its relation to carbon dioxide fluxes in Inner Mongolia steppe

A process-based model (VIP model) was used to partition evapotranspiration (ET) into transpiration (T) and evaporation (E). Gross ecosystem productivity (GEP) and ecosystem respiration (R_e) were calculated based on CO₂ fluxes measured by eddy covariance in a typical steppe. The results revealed that the water and CO₂ fluxes were low before the growth of vegetation in the spring. During the growth period, plant transpiration was found to account for 33-74% of the total ET. Additionally, the variations in daily net ecosystem exchange (NEE) and GEP were found to be correlated with precipitation and T, but not ET during the study periods. The peak responses of R_e to rain events lagged by 1-2 days when compared to the evaporation peak. The leaf area index (LAI) primarily regulated the changes in water use efficiency (WUE). Taken together, the results of this study indicated that the development of vegetation and the pattern of precipitation worked in concert to regulate the components of water and carbon fluxes and their coupling.