HR: 11:35h
AN: B22B-06    [Abstracts]
TI: Variation in Leaf Physiology Along Experimental and Natural Gradients in the High Arctic: Test of a Dual Isotope Conceptual Model
AU: * Sullivan, P
EM: paddy@uaa.alaska.edu
AF: Environment and Natural Resources Institute, University of Alaska, Anchorage, Anchorage, AK 99501
AU: * Sullivan, P
EM: paddy@uaa.alaska.edu
AF: Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523
AU: Welker, J
EM: afjmw1@uaa.alaska.edu
AF: Environment and Natural Resources Institute, University of Alaska, Anchorage, Anchorage, AK 99501
AB: Stable isotopes have been used extensively to describe variation in contemporary and retrospective leaf gas exchange physiology. Leaf carbon isotope discrimination (Delta 13C) varies with the balance between photosynthetic capacity (Amax) and stomatal conductance (gs). The inferences that can be made with Delta 13C are limited in the sense that changes in Delta 13C could reflect variation in Amax and/or variation in gs. Investigators have long suggested that variation in leaf oxygen isotope enrichment above source water (Delta 18O) may enable differentiation between changes in Delta 13C driven by changes in Amax and those driven by changes in gs. This suggestion builds upon the recognition that leaf water 18O enrichment varies with transpiration rate and the vapor pressure difference. The former is closely correlated with gs, while the later is an important determinant of gs. In this study, variation in leaf gas exchange physiology of Salix arctica was examined along hill-slope gradients and in response to experimental infrared warming near Pituffik (Thule), Greenland (76 N, 38 W). Inferences made using the dual isotope approach (Delta 13C and Delta 18O) were confronted with direct measurements of leaf gas exchange. Results of the study demonstrate that variation in the slope of Delta 18O: Delta 13C faithfully reveals the relative importance of Amax and gs in determining Delta 13C. The consistency with which isotope-based inferences were confirmed by direct gas exchange measurements suggests a more quantitative dual isotope model may be a realistic goal.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: Fall Meeting 2005