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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 (g_s) and mesophyll conductance of CO₂ (g_m), were used to determine the extent of the damage to plants under fumigation. Fluorescence effects were also measured using quantum yield (F_v/F_m). This study brought to light several important factors related to plant biology and pollution deposition. Cultivar and species differences were noted, especially when comparing A_max and F_v/F_m. In agreement with other studies, O₃ was shown to reduce biomass, g_s, and A_max. In contrast to O₃, the physiological effects of HNO₃ were previously unknown. This study demonstrated that HNO₃ exposure increased gm, whereas g_s and A_max were not affected. Increased g_m 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