HR: 1340h
AN: B13B-1201    [Abstracts]
TI: Discovering the Importance of Bi-directional Water Fluxes in Leaves
AU: * Kayler, Z E
EM: zachary.kayler@oregonstate.edu
AF: Department of Forest Science, Oregon State University, 321 Richardson Hall, Corvallis, OR 97330, United States
AU: Saurer, M
EM: matthias.saurer@psi.ch
AF: Paul Scherrrer Institute, PSI, Villigen, 5232, Switzerland
AU: Siegwolf, R
EM: rolf.siegwolf@psi.ch
AF: Paul Scherrrer Institute, PSI, Villigen, 5232, Switzerland
AB: The stable isotope ratio ¹⁸O/¹⁶O is used for constraining climate change models, partitioning ecosystem water fluxes and for studies of plant ecophysiology. Leaf water enrichment is an essential starting point for each of these applications. In order to obtain a complete picture of the role leaf water plays, not only the ¹⁸O values from leaf water but also the signature of transpired water must be accurately predicted for plants under varying environmental conditions. We used a novel chamber approach using highly depleted water (-330 ‰) as a vapor source to leaves of the velvet bean (Mucuna pruriens). We used a Walz gas exchange system consisting of a chamber that is controlled for humidity, light, and temperature. Water and carbon dioxide fluxes were measured by an infrared gas analyzer and chamber vapor was collected in cold traps chilled to - 60°C. Three leaves were collected after 2 hours to insure isotopic steady-state followed by leaf water extraction and isotope analysis. From this experiment we were able to measure the outward flux of soil source water and the inward flux of ambient vapor over a range of environments that varied in relative humidity (80%, 45%, 20%), light (50, 1000 μmolm^-2s^-1) and CO2 (50, 800 ppm). Leaf water isotopic values were below the source water values reflecting the influx of the labeled vapor. The degree to which leaf water values were depleted was strongly related to the relative humidity. The Craig-Gordon model overestimated depletion of leaf water under high relative humidity and predictions were improved with the Péclet correction. However, our initial analysis indicates that these models may not fully account for stomatal conductance in predicting leaf water isotopic values.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting