PARENT SESSION
Oral Session # 56: Plant Ecology IV: Plant - Water Relations II.
Presiding: D Rosenthal
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 200.
A hydromechanical and biochemical model for stomatal conductance.
Buckley, Thomas*,1, 2, Mott, Keith3, Farquhar, Graham1, 2, 1 Environmental Biology Group, Canberra, ACT, Australia2 Cooperative Research Centre for Greenhouse Accounting, Canberra, ACT, Australia3 Biology Department, Logan, UT, USA.
ABSTRACT- We present a new model for stomatal conductance in intact leaves. The model is based on principles of plant water relations, leaf gas exchange, and epidermal hydromechanics. Guard cell osmotic pressure is assumed proportional to ATP concentration, which is calculated from a popular model of photosynthesis. Unlike other stomatal models, ours accommodates the epidermal mechanical advantage, which causes the initial response to hydraulic perturbations to be in the 'wrong' direction (e.g., opening when humidity decreases), but which is overcome by hypothesizing that the sensitivity of guard cell osmotic pressure to ATP is proportional to epidermal turgor. The model accurately predicts stomatal responses to variations in ambient humidity, ambient carbon dioxide, ambient oxygen, irradiance, xylem resistance, soil water potential, and photosynthetic capacity. Most elements of the model's structure are readily interpreted in terms of reduced processes at the cellular level, but the model itself is easily expressed in a simple form that is identical to the Michaelis-Menten expression for enzyme-catalyzed reaction rates.
Key words: photosynthesis, stomata, transpiration, model