Stomatal Response and Leaf Injury of Pisum sativum L. with SO(2) and O(3) Exposures : II. INFLUENCE OF MOISTURE STRESS AND TIME OF EXPOSURE.

Stomatal response during exposure to SO(2) and O(3) and subsequent leaf injury were examined in plants of Pisum sativum L. ;Alsweet' grown in a peat-vermiculite medium in controlled environment chambers. Plants developing under moisture stress, induced by drying the medium to 50% of field capacity, exhibited greater stomatal closure during exposures and less than one-fourth the necrosis compared to plants developing in a medium maintained at field capacity. Plants under moisture stress had only a slightly more negative plant water potential ( approximately -4.0 bars) than at field capacity ( approximately -3.4 bars). Plants exposed to pollutants for 2 hours near the beginning or end of a 16-hour light period had greater stomatal closure during exposures and less leaf necrosis than plants exposed during the middle of the light period.