An analytical model of the hydraulic aspects of stomatal dynamics

An analytical model of the hydraulic aspects of stomatal dynamics is formulated in this paper. The model consists of a coupled system of non-linear, ordinary differential equations, written in terms of water potentials, hydrostatic pressures, osmotic potentials, water vapor resistances and water fluxes. The model is validated by comparisons with the experimental literature. Numerical solutions of the model show qualitative agreement with most known stomatal responses.Stomatal opening in the model is dependent on the interaction of the guard and subsidiary cells in the following manner. Pore opening is initiated by a rise in the guard cell hydrostatic pressure. As the stomate opens, transpiration increases, causing the cell wall water potential to drop. The drop in cell wall water potential then causes the subsidiary cell pressure to drop, opening is accelerated, and the stomate literally “pops” open. Simulated opening proceeds in two distinct phases: a stress phase and a motor phase. During the stress phase, guard cell pressure rises but the pore remains closed. The motor phase commences when the guard cell pressure has risen sufficiently to initiate pore opening, beyond which point opening progresses rapidly.Hydropassive stomatal movements are found to be insufficient to regulate water loss at low leaf water potentials. Stable, hydraulically-based oscillations in stomatal aperture are shown in the model by the existence of a stable limit cycle. The period of these oscillations is strongly influenced by the cell membrane hydraulic conductivity. An increased conductivity results in a shorter period oscillation. Environmental conditions promoting oscillatory behavior are in qualitative agreement with the experimental literature.