Poster: Stomatal Physiology

Abs # 390: A hydromechanical and biochemical model for stomatal conductance.

Presenter:	Buckley, Thomas N, tom.buckley@anu.edu.au
Authors	Buckley, Thomas N (A) (B)  Mott, Keith A (C)   Farquhar, Graham D (A) (B)
Affiliations:	(A): Environmental Biology Group, Research School of Biological Sciences, Australian National University (B): Cooperative Research Centre for Greenhouse Accounting, Research School of Biological Sciences, Australian National University (C): Biology Department, Utah State University

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 humidity, carbon dioxide, 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. By using tissue-level mechanistic constraints to integrate emergent properties of guard cell physiology with the phenomenology of whole-leaf gas exchange, our model attempts to bridge the gap between these two disparate scales.