Quantitative separation of evapotranspiration components of Platycladus orientalis ecosystem based on multiple isotope models

doi:10.13287/j.1001-9332.202106.023

Abstract

Abstract: 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.

Key words: stable isotope, plant transpiration, soil evaporation, non-steady-state assumption, quantitative partitioning

WU Yu-xin, ZHANG Yong-e, JIA Guo-dong, WANG Yu-song, YU Xin-xiao. Quantitative separation of evapotranspiration components of Platycladus orientalis ecosystem based on multiple isotope models[J]. Chinese Journal of Applied Ecology, 2021, 32(6): 1971-1979.

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