Evapotranspiration partitioning using stable isotopes of O and H

Partitioning of evapotranspiration (ET) is a fundamental challenge in ecohydrological research, critical for advancing our understanding of the soil-plant-atmosphere continuum. This study investigates ET partitioning for spring wheat crops grown at an experimental plot at IIT Kanpur using the stable isotopes of oxygen and hydrogen. By exploiting the distinct isotopic signatures of evaporation (E) and transpiration (T), the contributions of these processes to total ET were quantified. The isotopic compositions of ET and E were determined using the Keeling plot and the Craig-Gordon model respectively, whereas the isotopic composition of the stem was taken as the isotopic composition of T. Sensitivity analysis was performed to identify and prioritize the accurate measurement of variables significantly influencing ET partitioning. Results indicated that the transpiration fraction in ET varied between 38% and 96%, depending on crop growth stage and water availability. A comparison of results from isotopic methods and hydrometric methods revealed good agreement on most days, with discrepancies on some days attributed to uncertainties in estimating key parameters such as temperature and relative humidity. To capture interannual variability, additional experiments were conducted in subsequent years, providing further insights into the dynamics of ET partitioning.