[Quantitative separation of evapotranspiration components of ecosystem based on multiple isotope models].

To fully understand the changes in the evapotranspiration components in forest ecosystem and their contribution to evapotranspiration at daily scale, we used the hypothesis theory of isotopic steady state and non-steady state combined with the water isotope analyzer system to quantitatively split and compare the evapotranspiration components of ecosystem during the growing season. Results showed that the O of water from different sources during the four mea-surement days (August 5, 8, 10, 11, 2016) all showed surface soil water and oxygen isotope composition (δ) > branch water and oxygen isotope composition (δ) > atmospheric water vapor oxygen isotopes composition (δ), with obvious differences due to the isotope fractionation. Oxygen isotopes composition of soil evaporated water vapor (δ) was between -26.89‰～-59.68‰ at the daily scale, showing a pattern of first rising and then decreasing. The oxygen isotopic composition of evapotranspiration water vapor in forest ecosystem (δ) was between -15.99‰～-10.04‰. The oxygen isotopic composition of transpired water vapor under steady state(δ) was between -12.10‰～-9.51‰. The oxygen isotopic composition of transpired water vapor under non-steady state (δ) was between -13.02‰～-7.23‰. δ and δ had the same changing trend throughout the day at the daily scale, while the trend of δ, δ and δ was approximately the same during 11:00-17:00. In general, the contribution rate of plant transpiration to total evapotranspiration showed that was between 79.1%-98.7%, and was between 88.7%-93.7%. Our results suggested that water consumption through soil evaporation was far less than that of vegetation transpiration in the study area, and that vegetation transpiration dominated forest evapotranspiration.