Elevated ozone affects how plants use water efficiently. By studying two different plant species, researchers found that ozone reduces the plants' ability to photosynthesize and transport electrons. They also discovered that the more ozone a plant absorbs through its stomata, the lower its photosynthesis rate becomes. By adjusting their model to include these ozone effects, the researchers were able to accurately predict how the plants' photosynthesis and water use efficiency changed under elevated ozone levels. This study provides a new method to better predict how plants will respond to ozone pollution.