31 - Hydrogen Isotopic Fractionation by Plant Roots during Water Uptake in Coastal Wetland Plants

Abstract

Hydrogen and oxygen isotope analyses of plant stem water are used to quantitatively determine the use of different water sources by various plants in different environments—such as white pines, desert plants, streamside trees, and coastal plants. There are differences in isotopic composition among possible water sources. There is no isotopic fractionation by plant roots during water uptake. The study discussed in this chapter compared δD and δ 18 Ο values between stem and source water from several plant species growing naturally in coastal wet-land habitats. Both hydrogen and oxygen isotope ratios of stem water matched those of source water under field and greenhouse conditions when there was no isotopic fractionation during water uptake. On the other hand, differences in isotopic compositions between stem and source water indicate isotopic fractionation during water uptake. The results indicate that there is a significant hydrogen isotopic fractionation during water uptake in coastal wetland plants. Oxygen isotope ratios of stem water from coastal wetland plants, however, match those of source water.