Xiahong Feng - Current Research Interests in Stable Isotope Geochemistry

• Effect of Sea Ice on Arctic Precipitation
• Hydrogen and oxygen isotope studies of tree rings
• Oxygen and hydrogen isotopic compositions in leaf water
• Study of plants’ water used efficiency using C isotopes of tree rings
• Carbon and nitrogen cycles in plant-soil systems
• Isotope hydrology and hydrochemistry

Oxygen and Hydrogen isotopic compositions in leaf water

Understanding the isotopic variations in plants’ leaf water is important for a number of climatological and biogeochemical studies. Leaf water isotopic composition is affected by the isotopic composition of the source water, and the relative humidity of the air, both of which are related to climate. This dependency is the basis for climate reconstruction using isotopic compositions of tree-ring cellulose and leaf waxes from lake sediments. The isotopic composition of leaf water has also been used to estimate terrestrial biological productivity either by modeling d 18O of the atmospheric CO 2 or through calculating the Dole Effect.

In addition to the isotopic composition of source water and the relative humidity of the air, we have found that the oxygen and hydrogen isotopic compositions in leaf water also varie with the age and shape of the leaf. Along single pine needles, we have observed a 20‰ change in d 18O from the base to the tip. We have also observed a ~20‰ difference in d 18O between young and old leaves. In collaboration with Eric Posmentier and Leslie Sonder, we are constructing models to simulate isotopic variations along single pine needles, and using the model we are studying the pattern of isotopic enrichment of leaf water as a function of environmental and anatomical conditions.