Document: ROB-3-30-33

Stomatal conductance and photosynthesis are directly related to stem hydraulic conductivity in ponderosa pine seedlings.

HUBBARD, R.M.* ¹, V.STILLER ², J.S.SPERRY ² and M.G.RYAN ¹

USDA Forest Service, Fort Collins, CO 80526 USA, ¹
University of Utah, Salt Lake City, UT, 84112 USA ²

Abstract:
Plants regulate CO₂ uptake and transpirational water loss through changes in stomatal conductance. Recent work has shown that stomata are responsive to changes in the hydraulic conductivity of the soil to leaf pathway. However, there are no studies that have defined the response surface of this relationship and results from field studies can be complicated by changes in relative humidity and or light. We tested the hypothesis that changes in stem hydraulic conductivity (k) directly affect stomatal conductance and measured the response surface of k and leaf gas exchange. We systematically reduced k of six ponderosa pine seedlings using an air injection technique to induce cavitation and measured the response of leaf gas exchange in the laboratory under constant light and humidity. We found that stomatal conductance, transpiration and assimilation all declined linearly with decreasing k (R² = 0.58, 0.59, and 0.53 respectively) and that this response was independent of bulk leaf water potential. These results suggest: 1) stomatal conductance can respond directly to changes in k and that this response is linear, 2) The regulation of constant bulk leaf water potential via stomatal control of transpiration was responsible for the relationship between hydraulic conductivity and stomatal conductance, 3) changes in whole plant conductance may affect carbon gain.

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This abstract is being presented at: 4:00 PM in session:
Oral Session #34: Water Relations in Trees.