Background and aims: The stomata are a key channel of the water cycle in ecosystems, and are constrained by both physiological and environmental elements. The aim of this study was to parameterize stomatal conductance by extending a previous empirical model and a revised Ball-Berry model.
Methods: Light and CO(2) responses of stomatal conductance and photosynthesis of winter wheat in the North China Plain were investigated under ambient and free-air CO(2) enrichment conditions. The photosynthetic photon flux density and CO(2) concentration ranged from 0 to 2000 micro mol m(-2) s(-1) and from 0 to 1400 micro mol mol(-1), respectively. The model was validated with data from a light, temperature and CO(2) response experiment.
Results: By using previously published hyperbolic equations of photosynthetic responses to light and CO(2), the number of parameters in the model was reduced. These response curves were observed diurnally with large variations of temperature and vapour pressure deficit. The model interpreted stomatal response under wide variations in environmental factors.
Conclusions: Most of the model parameters, such as initial photon efficiency and maximum photosynthetic rate (P(max)), have physiological meanings. The model can be expanded to include influences of other physiological elements, such as leaf ageing and nutrient conditions, especially leaf nitrogen content.