Ozone-induced changes in the relationship between photosynthesis (An) and stomatal conductance (gs) vary among species, leading to inconsistent water use efficiency (WUE) responses to elevated ozone (O3). Thus, few vegetation models can accurately simulate the effects of O3 on WUE. Here, we conducted an experiment exposing two differently O3-sensitive species (Cotinus coggygria and Magnolia denudata) to five O3 concentrations and investigated the impact of O3 exposure on predicted WUE using a coupled An-gs model. We found that increases in stomatal O3 uptake caused linear reductions in the maximum rates of Rubisco carboxylation (Vcmax) and electron transport (Jmax) in both species. In addition, a negative linear correlation between O3-induced changes in the minimal gs of the stomatal model (g0) derived from the theory of optimal stomatal behavior and light-saturated photosynthesis was found in the O3-sensitive M. denudata. When the O3 dose-based responses of Vcmax and Jmax were included in a coupled An-gs model, simulated An under elevated O3 were in good agreement with observations in both species. For M. denudata, incorporating the O3 response of g0 into the coupled model further improved the accuracy of the simulated gs and WUE. In conclusion, the modified Vcmax, Jmax and g0 method presented here provides a foundation for improving the prediction for O3-induced changes in An, gs and WUE.
Keywords: Leaf photosynthetic model; Ozone; Photosynthesis; Stomatal conductance; Water use efficiency.
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