Foliar Response and Growth of Apple Trees following Exposure to Ozone and Sulfur Dioxide1

Abstract

Abstract Three cultivars of greenhouse-grown apple trees (Malus domestica, Borkh.) were fumigated for single, 4-hour exposures with ozone (O3) and/or sulfur dioxide (SO2) at 0.40 and 0.80 ppm. Fumigations were performed in a plexiglass chamber situated within a controlled environment walk-in growth chamber. All 3 cultivars responded to treatments in a similar manner. When applied separately both gases induced characteristic foliar injury. In general, apple trees were more sensitive to 0.40 ppm O3 than to 0.40 ppm SO2; but they responded similarly to 0.80 ppm O3 or SO2. Foliar injury, leaf abscission, and shoot growth reduction were greatest when 0.80 ppm O3 and 0.80 ppm SO2 were combined. The data showed a less-than additive response when the 2 pollutants were combined; a response due, in part, to the high amount of injury induced by single pollutants at these concentrations. All O3 and/or SO2 fumigations resulted in stomatal closure.