Clonal response of eastern white pine to low doses of O3, SO2, and NO2, singly and in combination

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Abstract
Eight clones of eastern white pine (Pinusstrobus L.) in three pollutant sensitivity groups (sensitive, intermediate, and tolerant) were exposed to 0.05 or 0.10 μL/L of ozone, sulfur dioxide, and (or) nitrogen dioxide 4 h daily for 35 consecutive days. Visible symptoms, length, and dry weight of 1st-year needles were determined to evaluate clonal response to these pollutants. A general response within sensitivity groups to all three pollutants, singly and in combination, was not observed. The sensitivity of the clones was dependent on the type of pollutant, its concentration, and the plant response used as the indexing factor. The amount of area injured was categorically differentiable among the three sensitivity groups but varied within the same group. Needle length was an inconclusive measure of clonal pollutant sensitivity, whereas needle dry weight was the parameter best associated with clonal pollutant sensitivity. These results demonstrate that a single response parameter is of limited value in determining plant sensitivity to air pollutants.