Analysis of the Physiological Effects of Ozone and Nitric Acid on Two Cultivars of Tobacco and Snapbean with Differing Sensitivities to Ozone

Cara M.Stripe1, Pamela E. Padgett2 and Louis S. Santiago1

Damage done to plants due to air pollution deposition decreases overall productivity and reduces the profitability and sustainability of crops near urban centers. Increasing population and urbanization in areas surrounding agriculture makes an understanding of possible pollutant effects increasingly important. Physiological effects of two photochemical pollutants, ozone (O3) and nitric acid (HNO3), were examined on Phaseolus vulgaris (snapbean) and Nicotiana tobaccum (tobacco), crops with cultivars known to differ in sensitivity to O3. Measurements based on photosynthetic gas exchange, including, photosynthetic CO2 assimilation (A), stomatal conductance to water vapor (gs) and mesophyll conductance of CO2 (gm), were used to determine the extent of the damage to plants under fumigation. Fluorescence effects were also measured using quantum yield (Fv/Fm). This study brought to light several important factors related to plant biology and pollution deposition. Cultivar and species differences were noted, especially when comparing Amax and Fv/Fm. In agreement with other studies, O3 was shown to reduce biomass, gs, and Amax. In contrast to O3, the physiological effects of HNO3 were previously unknown. This study demonstrated that HNO3 exposure increased gm, whereas gs and Amax were not affected. Increased gm in response to HNO3 exposure may be tied to other physiological processes that depend on conductance of CO2 through the mesophyll, such as photosynthetic gas exchange and Rubisco activity.

1Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA
2USDA Forest Service, Pacific Southwest Research Station, Riverside, CA 92507, USA