Comparing model predictions and experimental data for the response of stomatal conductance and guard cell turgor to manipulations of cuticular conductance, leaf-to-air vapour pressure difference and temperature: feedback mechanisms are able to account for all observations

Stomata respond to increasing leaf-to-air vapour pressure difference (LAVPD) (D) by closing. The mechanism by which this occurs is debated. A role for feedback and peristomatal transpiration has been proposed. In this paper, we apply a recent mechanistic model of stomatal behaviour, and compare model and experimental data for the influence of increasing D on stomatal conductance. We manipulated cuticular conductance (g(c)) by three independent methods. First, we increased g(c) by using a solvent mixture applied to both leaf surfaces prior to determining stomatal responses to D; second, we increased g(c) by increasing leaf temperature at constant D; and third, we coated a small area of leaf with a light oil to decrease g(c). In all three experiments, experimental data and model outputs showed very close agreement. We conclude, from the close agreement between model and experimental data and the fact that manipulations of g(c), and hence cuticular transpiration, influenced g(s) in ways consistent with a feedback mechanism, that feedback is central in determining stomatal responses to D.