Stomatal response drives between-species difference in predicted leaf water-use efficiency under elevated ozone
2021
Xu, Yansen | Shang, Bo | Peng, Jinlong | Feng, Zhaozhong | Tarvainen, Lasse
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.
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