Stomatal response drives between-species difference in predicted leaf water-use efficiency under elevated ozone.

Area of Science:

• Plant physiology
• Environmental science
• Ecosystem modeling

Background:

• Ozone (O3) affects plant photosynthesis (An) and stomatal conductance (gs), leading to variable water use efficiency (WUE) responses.
• Current vegetation models struggle to accurately simulate O3's impact on WUE due to species-specific physiological changes.

Purpose of the Study:

• To investigate O3-induced changes in the An-gs relationship and their impact on WUE in two O3-sensitive plant species.
• To improve the accuracy of vegetation models in predicting O3 effects on plant physiology and WUE.

Main Methods:

• Exposed *Cotinus coggygria* and *Magnolia denudata* to five O3 concentrations.
• Utilized a coupled An-gs model, incorporating O3-induced changes in maximum rates of Rubisco carboxylation (Vcmax), electron transport (Jmax), and minimal stomatal conductance (g0).
• Compared model simulations with observed An, gs, and WUE.

Main Results:

• Increased stomatal O3 uptake linearly reduced Vcmax and Jmax in both species.
• A negative linear correlation was found between O3-induced changes in g0 and light-saturated photosynthesis in *M. denudata*.
• The coupled model accurately simulated An under elevated O3 when O3-dependent Vcmax and Jmax were included; incorporating O3-dependent g0 further improved gs and WUE predictions for *M. denudata*.

Conclusions:

• Modified Vcmax, Jmax, and g0 parameters improve predictions of O3-induced changes in An, gs, and WUE.
• This approach provides a foundation for more accurate ecosystem modeling of O3 impacts on vegetation.
• Understanding species-specific responses to O3 is crucial for refining vegetation models and predicting ecosystem-level changes.