Comparison of two isotope-based methods used in determining forest evapotranspiration partitioning

Abstract

A comprehensive understanding of the changing patterns and the contribution of each component of the forest ecosystem to evapotranspiration is necessary for an accurate assessment of biological quality, terrestrial ecosystem production, energy exchange, and water use efficiency. In this study, two methods (i.e., the sap-flow and lysimeter methods) were used to partition evapotranspiration (ET) into evaporation(E) and transpiration(T) components using stable isotope techniques. The factors affecting the contribution of T to ET (FT) were evaluated. The results showed that FT presents seasonal variation patterns throughout the year. Both methods accurately simulated the ET partitioning and its seasonal variation. The ET value estimated by the sap-flow method was less than that estimated by the lysimeter method. In contrast, the simulated value of T calculated using the lysimeter method was higher than that calculated by the sap-flow method. However, this was within allowable limits. The lysimeter method is more accurate and suitable for monitoring forest ecosystem evapotranspiration in practical experiments. This study provides a technical reference for the optimal calculation method of ET partitioning using a stable isotope-based technique. It provides baseline information to better understand water vapour exchange in forest ecosystems in China.