Utilization of a Response-Surface Technique in the Study of Plant Responses to Ozone and Sulfur Dioxide Mixtures

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Abstract
A 2nd order rotatable design was used to obtain polynomial equations describing the effects of combinations of SO2 and O3 on foliar injury and plant growth. The response surfaces derived from these equations were displayed as contour or isometric (3-dimensional) plots. The contour plots aided in the interpretation of the pollutant interactions and were judged easier to use than the isometric plots. Plants of ''Grand Rapids'' lettuce (Lactuca sativa L.), ''Cherry Belle'' radish (Raphanus sativus L.) and ''Alsweet'' pea (Pisum sativum L.) were grown in a controlled environment chamber and exposed to 7 combinations of SO2 and O3. Injury was evaluated based on visible chlorosis and necrosis and growth was evaluated as leaf area and dry weight. Covariate measurements were used to increase precision. Radish and pea had greater injury, in general, than did lettuce. All 3 spp. were sensitive to O3:pea was most sensitive and radish least sensitive to SO2. Leaf injury responses were relatively more affected by the pollutants than were plant growth responses in radish and pea but not in lettuce. In radish, hypocotyl growth was more sensitive to the pollutants than was leaf growth.