[Quantitative separation of evapotranspiration components of Platycladus orientalis ecosystem based on multiple...

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 Platycladus orientalis ecosystem during the growing season. Results showed that the ¹⁸O 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_S) > branch water and oxygen isotope composition (δ_X) > atmospheric water vapor oxygen isotopes composition (δ_V), with obvious differences due to the isotope fractionation. Oxygen isotopes composition of soil evaporated water vapor (δ_E) 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_ET) was between -15.99‰～-10.04‰. The oxygen isotopic composition of transpired water vapor under steady state(δ_T-ISS) was between -12.10‰～-9.51‰. The oxygen isotopic composition of transpired water vapor under non-steady state (δ_T-NSS) was between -13.02‰～-7.23‰. δ_ET and δ_T-NSS had the same changing trend throughout the day at the daily scale, while the trend of δ_ET, δ_T-ISS and δ_T-NSS was approximately the same during 11:00-17:00. In general, the contribution rate of plant transpiration to total evapotranspiration showed that F_T-ISS was between 79.1%-98.7%, and F_T-NSS 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.