Significant Difference in Hydrogen Isotope Composition Between Xylem and Tissue Water in Populus Euphratica

Abstract

Deuterium depletions between stem water and source water have been observed in coastal halophyte plants and in multiple species under greenhouse conditions. However, the location(s) of the isotope fractionation is not clear yet and it is uncertain whether deuterium fractionation appears in other natural environments. In this study, through two extensive field campaigns utilizing a common dryland riparian tree species Populus euphratica Oliv., we showed that no significant δ(18) O differences were found between water source and various plant components, in accord with previous studies. We also found that no deuterium fractionation occurred during P. euphratica water uptake by comparing the deuterium composition (δD) of groundwater and xylem sap. However, remarkable δD differences (up to 26.4‰) between xylem sap and twig water, root water and core water provided direct evidence that deuterium fractionation occurred between xylem sap and root or stem tissue water. This study indicates that deuterium fractionation could be a common phenomenon in drylands, which has important implications in plant water source identification, palaeoclimate reconstruction based on wood cellulose and evapotranspiration partitioning using δD of stem water.

Cryogenic vacuum artifacts do not affect plant water‐uptake studies using stable isotope analysis

“…Consistent with previous research, we found that xylem waters extracted from S. viminalis followed a Rayleigh distillation curve taking 2 hr to flatten the typical benchmark for complete extraction (West et al, ). Although we thus conclude that we can successfully recover xylem water in our cryogenic extraction line, recent research (Zhao et al, ) has identified possible difficulties with this method where significant differences between water passively removed from the xylem via needle and syringe was found to be significantly different from water removed from cores and twigs via cryogenic vacuum extraction. It has been hypothesized that cryogenic vacuum extraction removes water from all cells within the plant tissues, including parenchyma cells, which could contain isotopically enriched organics capable of exchange (Zhao et al, ).…”

“…Although we thus conclude that we can successfully recover xylem water in our cryogenic extraction line, recent research (Zhao et al, ) has identified possible difficulties with this method where significant differences between water passively removed from the xylem via needle and syringe was found to be significantly different from water removed from cores and twigs via cryogenic vacuum extraction. It has been hypothesized that cryogenic vacuum extraction removes water from all cells within the plant tissues, including parenchyma cells, which could contain isotopically enriched organics capable of exchange (Zhao et al, ). In contrast, passive extraction from living xylem tissue via needle and syringe may give a more representative isotope value of plant source waters.…”

Reviews and syntheses: on the roles trees play in building and plumbing the critical zone

“…There have been a number of recent papers building upon the early work in Graham Allisons' laboratory exploring water isotope fractionation in subsurface pools (Allison et al, 1983). This new work investigates methodologies of extraction, isotope fractionation during water uptake by plants, and interpretation of isotope data (Oerter et al, 2014;Orlowski et al, 2016a, b;Oshun et al, 2016;Zhao et al, 2016;Gaj et al, 2017;Johnson et al, 2017;Vargas et al, 2017). These papers provide new insights at the same time that they add to the ongoing controversy about what explains water isotope variation in the many possible subsurface pools, highlighting the need for research.…”

Multiple Methods to Partition Evapotranspiration in a Maize Field

“…However, there are many sensitive parameters in this model (e.g., the kinetic fractionation factor and the isotopic composition of liquid water at the soil evap orating front) that can result in a large uncertainty if those parameters could not be determined accurately (Cappa et al 2003;Dubbert et al 2013;Majoube 1971;Wei et al 2015). For the isotopic composition of transpiration 8r, it is typically measured using stem or xylem water under the assumption that it is equal to that of root uptake, maintaining a condition referred as isotopic steady state (ISS; Flanagan and Ehleringer 1991;Zhang et al 2011;Zhao et al 2016). However, the ISS is typically only met for short time frames during a day (Lee et al 2007;Peters and Yakir 2010;Welp et al 2008) with stable vapor pressure deficit and high transpiration rate (Harwood et al 1998).…”