Stomatal conductance of Acer rubrum ecotypes under varying soil and atmospheric water conditions: predicting stomatal responses with an abscisic acid-based model

A multiplicative model of stomatal conductance was developed and tested in two functionally distinct ecotypes of Acer rubrum L. (red maple). The model overcomes the main limitation of the commonly used Ball-Berry model (Ball et al. 1987) by accounting for stomatal behavior under soil drying conditions. We combined the Ball-Berry model with an integrated expression of abscisic acid (ABA)-based stomatal response to ABA concentration ([ABA]) in bulk leaf tissue (g fac ), which coupled physiological changes at the leaf level with those in the root. The factor g fac = exp(-β[ABA] L ) incorporated the stomatal response to [ABA] into the Ball-Berry model by down regulating stomatal conductance (g s ) in response to physiological changes in the root. The down regulation of g s is pertinent under conditions where soil drying may modify the delivery of chemical signals to leaf stomata. Model testing indicated that the multiplicative model was capable of predicting g s in red maple under wide ranges of soil and atmospheric conditions. Concordance correlation coefficients were high (between 0.59 and 0.94) for the tested ecotypes under three environmental conditions (atmospheric, rhizospheric and minimal stress). The study supported the use of g fac as a gas exchange function that controls water stress effects on g s and aids in the prediction of g s responses.