Relationship of concentration of gaseous hydrogen fluoride to incidence and severity of foliar lesions in black spruce and white spruce

Abstract

Quantitative estimates of the variation in response to air pollutants in natural populations of trees must be considered in predicting the magnitude of an effect or the risk of an effect's occurrence. This subject was investigated in 2-year-old black spruce (Piceamariana (Mill.) B.S.P.) exposed for 78 continuous hours to gaseous hydrogen fluoride at concentrations of 2.3, 4.2, or 8.1 μg% F•m−3 and with 3-year-old white spruce (Piceaglauca (Moench) Voss) exposed for 50 continuous hours to hydrogen fluoride at 2.6, 5.2, or 11.1 μg F•m−3 in open-top, field exposure chambers. Tolerances to hydrogen fluoride induced foliar injury followed a lognormal distribution for black spruce and white spruce with, respectively, estimated median tolerances of 3.45 and 13.24 μg F•m−3 and standard deviations corresponding to 1.70- and 2.14-fold changes in concentration of hydrogen fluoride. The curves for the occurrence of moderate and severe degrees of injury in black spruce paralleled that for the occurrence of any hydrogen fluoride induced injury but were displaced towards greater exposures (1.29-fold for moderate and 1.77-fold for severe injury). The distribution of foliar injury on shoots indicated that a portion of the variation in tolerance might be attributed to phenologic differences among the trees. A knowledge of the sources of variation and their magnitudes is necessary to recognize both incidence and severity of pollutant-induced injury in dose-response relationships.