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

Area of Science:

• Plant physiology
• Stable isotope geochemistry
• Ecology

Background:

• Deuterium depletions between plant stem water and source water are documented in some plants.
• The precise location of this isotope fractionation within the plant remains unclear.
• Its occurrence in diverse natural environments, like drylands, is uncertain.

Purpose of the Study:

• To investigate deuterium fractionation in the dryland riparian tree Populus euphratica Oliv.
• To determine if fractionation occurs during water uptake or within plant tissues.
• To assess the prevalence of deuterium fractionation in dryland ecosystems.

Main Methods:

• Conducted two extensive field campaigns on Populus euphratica.
• Analyzed oxygen-18 (δ18O) and deuterium (δD) isotope compositions.
• Compared isotope ratios in groundwater, xylem sap, twig water, root water, and core water.

Main Results:

• No significant differences in δ18O were found between water sources and plant components.
• No deuterium fractionation was detected during water uptake (groundwater vs. xylem sap).
• Significant δD differences (up to 26.4‰) were observed between xylem sap and twig, root, and core water, indicating fractionation within the plant.

Conclusions:

• Deuterium fractionation occurs between xylem sap and root/stem tissues in Populus euphratica.
• This fractionation is likely a common phenomenon in dryland environments.
• Findings have implications for plant water source identification, paleoclimate reconstruction, and evapotranspiration partitioning.