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Response of Chronically Ozonated Soybean Plants to an Acute Ozone Exposure. J. William Johnston, Jr., Graduate student, Department of Botany, and plant pathologist, Science and Education Administration, U.S. Department of Agriculture, Present address: Environmental Sciences Division, Oak Ridge National Laboratory (ORNL, operated by Union Carbide Corporation under contract W-7405-eng-26 with the U.S. Department of Energy), Oak Ridge, TN 37830; Allen S. Heagle, professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Phytopathology 72:387-389. Accepted for publication 13 May 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-387.

The effects of chronic ozone (O₃) exposures on the sensitivity of soybean to a subsequent acute exposure to O₃ were measured. Plants were exposed to low concentrations (≤0.10 ppm O₃) or to charcoal-filtered air (0.0 ppm O₃) for 6 hr/day on 5, 10, or 15 consecutive days (chronic dose). One day after the last chronic exposure, plants were exposed for 3 hr to 0.20 ppm of O₃ (acute dose) or to filtered air. Plants exposed to chronic doses of O₃ below the visible injury threshold (≤0.06 ppm) were more sensitive to the acute O₃ dose than were plants exposed to filtered air. Plants exposed to chronic O₃ doses above the visible injury threshold (≥0.06 ppm) were less susceptible to the acute O₃ dose than were plants exposed to filtered air. The predisposition toward greater sensitivity to the acute O₃ dose tended to be cumulative over time and was partially reversed by treatment with filtered air prior to the acute exposure.