O3 and Drought Effects on Steady State Conductance and Kinetics in Pima Cotton

The degree to which ozone (O3) exposure and drought affect stomatal control of water loss and respond to environmental stimuli such as varying light is poorly characterized. To that end, we exposed Pima cotton to chronic O3 exposure (month-long daytime exposures) with and without sufficient water, as well as short term acute O3 exposure and varying light levels to understand stomatal kinetics. Chronic, month-long exposure to moderately high O3 (~114 ppb) reduced daytime steady state stomatal conductance (gs), as did water deficit. Both stomatal opening and closing displayed dose specific, “sluggish” responses to step-changes in illumination with acute, 1-day, O3 exposures of 0, 50, 100, and 125 ppb. At higher concentration (150 ppb), stomatal control of both opening and closing was degraded. Altered steady state and dynamic stomatal function suggest that elevated ambient O3, expected to increase in the future, may increasingly influence field water management and appropriate crop choices.