Effects of Ambient and Acute Partial Pressures of Ozone on Leaf Net CO2 Assimilation of Field-Grown Vitis vinifera L.

Mature, field-grown Vitis vinifera L. grapevines grown in open-top chambers were exposed to either charcoal-filtered air or ambient ozone partial pressures throughout the growing season. Individual leaves also were exposed to ozone partial pressures of 0.2, 0.4, or 0.6 micropascals per pascal for 5 hours. No visual ozone damage was found on leaves exposed to any of the treatments. Chronic exposure to ambient O(3) partial pressures reduced net CO(2) assimilation rate (A) between 5 and 13% at various times throughout the season when compared to the filtered treatment. Exposure of leaves to 0.2 micropascals per pascal O(3) for 5 hours had no significant effect on A; however, A was reduced 84% for leaves exposed to 0.6 micropascals per pascal O(3) when compared to the controls after 5 hours. Intercellular CO(2) partial pressure (c(i)) was lower for leaves exposed to 0.2 micropascals per pascal O(3) when compared to the controls, while c(i) of the leaves treated with 0.6 micropascals per pascal of 0(3) increased during the fumigation. The long-term effects of ambient O(3) and short-term exposure to acute levels of O(3) reduced grape leaf photosynthesis due to a reduction in both stomatal and mesophyll conductances.