HR: 1340h
AN: B33D-1594    [Abstracts]
TI: Water use Efficiency in a Blue oak ( Quercus douglasii) Savanna - a Combined Analysis of Stable Isotopes and Eddy Covariance Measurements
AU: * Mambelli, S
EM: mambelli@berkeley.edu
AF: Department of Integrative Biology and Center for Stable Isotope Biogeochemistry - University of California, Valley Life Science Building, Berkeley, CA 94720, United States
AU: Tu, K P
EM: kevintu@berkeley.edu
AF: Department of Integrative Biology and Center for Stable Isotope Biogeochemistry - University of California, Valley Life Science Building, Berkeley, CA 94720, United States
AU: Knohl, A
EM: alexander.knohl@ipw.agrl.ethz.ch
AF: Institute of Plant Sciences - ETH, Universitätstrasse 2, Zurich, 8092, Switzerland
AU: Ma, S
EM: sma@nature.berkeley.edu
AF: Department of Environmental Science, Policy and Management - University of California, Hilgard Hall, Berkeley, CA 94720, United States
AU: Baldocchi, D D
EM: baldocchi@nature.berkeley.edu
AF: Department of Environmental Science, Policy and Management - University of California, Hilgard Hall, Berkeley, CA 94720, United States
AU: Dawson, T E
EM: tdawson@berkeley.edu
AF: Department of Integrative Biology and Center for Stable Isotope Biogeochemistry - University of California, Valley Life Science Building, Berkeley, CA 94720, United States
AU: Dawson, T E
EM: tdawson@berkeley.edu
AF: Department of Environmental Science, Policy and Management - University of California, Hilgard Hall, Berkeley, CA 94720, United States
AB: Understanding the relationship between carbon assimilation and water consumption by natural vegetation is needed to assess how changes in climate will affect plant carbon and water exchange as well as the energy fluxes of ecosystems. While climate change is expected to cause significant warming, most models also suggest changes in the timing and amount of precipitation received; thus implications of this type of change are particularly acute in Mediterranean regions of the world. Blue oak savannas are already exposed to broad variation in water availability and to severe droughts during the summer months. Our objective was to evaluate the trade-off between carbon gain and water loss (Water Use Efficiency) in this ecosystem at both the leaf and at the ecosystem scales. We monitored the ratio of the partial pressures of CO₂ inside the leaf (Ci) and in the outside air (Ca) or Ci/Ca, during the summer months of three subsequent years. This ratio is determined by the balance between photosynthetic capacity and stomatal conductance to water loss. Leaf-level estimates for individual trees were based on the carbon isotope composition (δ¹³C) of bulk leaf tissue and of recently fixed carbohydrates (leaf soluble sugars). These leaf and individual tree based estimates were then compared with canopy-level estimates derived from continuous eddy covariance measurements of fluxes of CO₂, water vapor and meteorological variables from two eddy covariance systems, one above (23m) and one below (2m) the tree canopy. We found that savanna Blue oak trees cope with severe drought through coordinated down-regulation of carbon and water fluxes, i.e. the ratio Ci/Ca remained stable over four summer months, despite decreasing soil water content and leaf water potentials. Stable C isotope composition of leaf soluble sugars is the most robust measure of Ci/Ca because it reflects the initial discrimination of photosynthetic products, without the confounding effects ascribed to storage, tissue chemical composition and time of tissue formation. Our findings at the leaf-level were confirmed at the ecosystem-level by using a two tower (above and below canopy) eddy covariance method.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0476 Plant ecology (1851)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting