MECHANISM MODEL OF STOMATAL CONDUCTANCE

Aims The stomatal conductance model of Ball-Berry and its subsequent refinements is an important tool to evaluate performance of stomatal regulation of plant leaves. Our objective was to derive the mechanism model of stomatal conductance and provide a theoretical basis for these empirical models of stomatal conductance. Methods By means of the diffusion and collision theory of CO2 gas in physics, hydromechanics and plant physiology, we derived a relationship between stomatal conductance of leaves, net photosynthetic rate and intercellular CO2 concentration. We measured the light-response of photosynthetic rate and stomatal conductance of Triticum aestivum under different chamber CO2 concentrations and different air temperatures in North China Plain using a gas analyzer Li-6400. The measured data of stomatal conductance of T. aestivum to irradiance in North China Plain were simulated by coupling the mechanism model of stomatal conductance and non-rectangular hyperbola model, rectangular hyperbola model and modified model of light-response of photosynthesis. Important findings A mechanism model of stomatal conductance was derived without additional hypotheses. It determined that the Ball-Berry stomatal conductance model had sound theoretical basis despite the model having deficiencies. The mechanism model shows advantages over the Ball-Berry model and model of Tuzet et al. for T. aestivum. If the mechanism model of stomatal conductance is coupled with a modified model of light-response of photosynthesis, the coupled model could simulate well the light-response data of stomatal conductance of T. aestivum. The fitted results show that stomatal conductance of T. aestivum to irradiance increases with light intensity until saturation light intensity, and then decreases with light intensity. The saturation light intensity and maximum stomatal conductance of T. aestivum can be calculated directly by the coupled model. Furthermore, we can use the coupled model to study whether maximum stomatal conductance coincides with maximum net photosynthetic rate. The fitted results also show that the maximum stomatal conductance and the maximum net photosynthetic rate are not synchronous at 30 ℃ and 560 μmol·mol–1 CO2 or 32 ℃ and 370 μmol·mol–1 CO2. Additionally, the coupled model can describe not only part of the light-response curve of stomatal conductance below light saturation, but also the range of levels above the saturation light intensity under different environmental conditions.