Wednesday, August 8, 2007: 2:10 PM
San Carlos I, San Jose Hilton
Anthony R. Ambrose, Department of Integrative Biology, University of California, Berkeley, CA, Todd Dawson, Department of Integrative Biology, University of California Berkeley, Berkeley, CA and Stephen C. Sillett, Forest and Wildland Resources, Humboldt State University, Arcata, CA
Coast redwood (Sequoia sempervirens) and giant sequoia (Sequoiadendron giganteum) are world famous for being the tallest and largest trees on Earth. However, very little is known about the factors regulating the physiological performance, growth, and response to environmental change of these species. The water transport capacity of a trees’ vascular system has previously been shown to exert a strong influence on leaf-level water use and carbon gain. We investigated how tree height affects the functional coordination between branch hydraulic properties and leaf gas exchange in three height classes of trees. A positive correlation between maximum branch hydraulic conductivity and maximum leaf gas exchange was observed in all trees. The middle height class exhibited the highest hydraulic conductivity, stomatal conductance (g), and photosynthetic rates (A), with the tallest height class exhibiting the lowest rates and the shortest height class exhibiting intermediate rates in both species. The expected trade-off between branch hydraulic conductivity (efficiency) and vulnerability to drought-induced cavitation was not evident. Instead, both the middle and tallest height classes of trees possessed equally low vulnerabilities. Intrinsic water-use efficiency, measured as A/g, did not vary significantly among height classes in coast redwood but increased with tree height in giant sequoia. Results indicate that the maximum gas exchange rate of treetop foliage in these two tree species may be constrained by their vascular supply of water but that a component of these rates are also influenced by the environmental conditions in the forest stands where they grow.
