HR: 1340h
AN: B13B-1200    [Abstracts]
TI: Transition of the Isotopic Composition of Leaf Water to the Isotopic Steady State in Soybean and Corn
AU: * Kim, K
EM: kyounghee.kim@yale.edu
AF: Yale University, School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511, United States
AU: Lee, X
EM: xuhui.lee@yale.edu
AF: Yale University, School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511, United States
AU: Welp, L R
EM: lisa.welp@yale.edu
AF: Yale University, School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511, United States
AB: The isotope composition of leaf water (δ_L) plays an important role in the isotopic water and carbon fluxes between terrestrial plants and the atmosphere. The objective of this study is to improve our understanding of environmental and biological controls on the transition of δ_L to steady state through laboratory experiments. Plants (soybean, Glycine max; corn, Zea mays) were grown hydroponically with water of a known isotopic content in a greenhouse. On the day of the experiment, they were first moved to ambient environment in full sunlight for at least 6 hr and then into a dark container inside the lab for up to 48 hr in which water vapor isotope ratios, temperature, and humidity were controlled. This arrangement created a step change in the forcing on the plant isotopic exchange. Leaves were sampled prior to the transfer to the dark container and 6 more times every 4 - 12 hr over the experiment. In the first set of experiments, humidity inside the container was saturated to mimic dew events in field conditions. In the second set, humidity was controlled at approximately 95%. Water from the leaf samples was extracted by a vacuum line and was analyzed for both δD and δ¹⁸O. The dataset will allow us to evaluate leaf water isotopic theories by exploring the transitions of δ_L in response to the step change. Specifically, we are interested in whether the stomatal opening is an effective pathway for gaseous exchange in total darkness and how the transitional behaviors of δ_L differ between the C3 and C4 photosynthesis pathways.
DE: 0426 Biosphere/atmosphere interactions (0315)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting