Reported offsets between hydrogen isotopes in source water and that of plant xylem water

Stable isotopes of water are frequently used as a means of inferring plant source water. However, a number of studies have described the potential for fractionation of water isotopes in soil (Oerter et al., 2014), fractionation of water isotopes at the time of plant root uptake (Ellsworth & Williams, 2007; Poca et al., 2019), and fractionation of plant xylem water (Barbeta et al., 2020; Chen et al., 2020). Recently, Chen et al., (2020) compared the hydrogen isotope ratio (δ2H) of plant xylem water obtained through cryogenic vacuum distillation and the δ2H of steady-state transpiration given a known source water provided to the plants. They identified a bias attributed to some combination of isotopic exchange of hydrogen in wood tissue with water in wood tissue and/or water stored in the xylem that is not participating in transpiration. They determined the offset between source water and xylem to be -8.1‰ based on observations from 9 species. Here, we present data on δ2H offsets compiled from 6 different studies and representing 30 plant species to facilitate the calculation of offsets for any number of different purposes. We also present δ18O offsets from the studies in which they were available