HR: 11:20h
AN: B12C-05    [Abstracts]
TI: Linking carbon isotopes and carbon-water exchange of plants across different scales
AU: * Seibt, U
EM: useibt@globalecology.stanford.edu
AF: University of Cambridge, Downing Street, Cambridge, CB2 3EA, United Kingdom
AU: Rajabi, A
EM: rajabi@sbsi.ir
AF: Sugar Beet Seed Institute, P.O. Box 31585-4114, Karaj, 4114, Iran (Islamic Republic of)
AU: Griffiths, H
EM: hg230@cam.ac.uk
AF: University of Cambridge, Downing Street, Cambridge, CB2 3EA, United Kingdom
AU: Berry, J
EM: joeberry@globalecology.stanford.edu
AF: Carnegie Institution, 260 Panama Street, Stanford, CA 94305, United States
AB: The anthropogenic rise in atmospheric CO2 levels may lead to increased photosynthetic uptake while transpiration rates remain constant or are reduced. Changes in plant regulation of carbon uptake and water loss also affect the carbon isotope signatures of plant material. But environmental conditions may change in addition to CO2. The resulting combination of factors can have different effects on the carbon-water balance of plants, and their carbon isotope signatures. For example, changes in evaporative demand alter the ratio of total carbon gain to water loss of a plant, the parameter of interest from the point of view of the atmosphere. Isotope values, on the other hand, also reflect physiological properties, including C:N allocation to carboxylation and internal conductance. Here, we explore how these factors shape carbon isotope signatures as well as carbon and water fluxes from leaf to ecosystem levels, and across diurnal to decadal timescales. We present new data to illustrate that a correlation between carbon isotope signatures and carbon-water exchange at the leaf level may not be passed on to the whole plant level. We then use a simple coupled model to analyse the relationships between carbon-water fluxes and isotope values. The model calculates gas exchange and carbon isotope signatures at the leaf level (for comparison with leaf samples), and propagates both gas exchange and isotope values to long- term trends in carbon-water exchange and carbon isotope signatures at the canopy scale (for comparison with samples of annual resolution). This approach is useful for exploring the sensitivity of carbon isotope ratios and carbon-water exchange of plants to simultaneous changes in external and internal factors, for example when interpreting trends in carbon isotope signatures obtained from tree rings.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting