A critical appraisal of a combined stomatal‐photosynthesis model for C₃ plants

TLDR

The model extends the Ball‑Woodrow‑Berry stomatal conductance formulation to include CO₂ concentration and humidity effects. The authors tested a semi‑empirical stomatal conductance model with gas‑exchange data from *Eucalyptus grandis* and coupled it to a C3 photosynthesis biochemical model to simulate leaf responses to light, humidity, temperature, and CO₂. Adding the CO₂ compensation point and a hyperbolic humidity term improved low‑CO₂ performance, matched observed stomatal and intercellular CO₂ responses, and allowed the revised model to accurately reproduce responses across species and conditions, especially for well‑watered plants.

Abstract

ABSTRACT Gas‐exchange measurements on Eucalyptus grandis leaves and data extracted from the literature were used to test a semi‐empirical model of stomatal conductance for CO 2 g Sc =g o +a 1 A/(c s ‐I) (1+D s /D o )] where A is the assimilation rate; D s and c s are the humidity deficit and the CO 2 concentration at the leaf surface, respectively; g 0 is the conductance as A → 0 when leaf irradiance → 0; and D 0 and a 1 are empirical coefficients. This model is a modified version of g sc =a 1 A h s /c s first proposed by Ball, Woodrow & Berry (1987, in Progress in Photosynthesis Research , Martinus Mijhoff, Publ., pp. 221–224), in which h s is relative humidity. Inclusion of the CO 2 compensation point, τ, improved the behaviour of the model at low values of c s , while a hyperbolic function of D s for humidity response correctly accounted for the observed hyperbolic and linear variation of g sc and c i /c s as a function of D s , where C i is the intercellular CO 2 concentration. In contrast, use of relative humidity as the humidity variable led to predictions of a linear decrease in g sc and a hyperbolic variation in c i /c s as a function of D s , contrary to data from E. grandis leaves. The revised model also successfully described the response of stomata to variations in A, D s and c s for published responses of the leaves of several other species. Coupling of the revised stomatal model with a biochemical model for photosynthesis of C 3 plants synthesizes many of the observed responses of leaves to light, humidity deficit, leaf temperature and CO 2 concentration. Best results are obtained for well‐watered plants.