Relative sensitivity of three species of woody plants to SO2 at high or low exposure temperature.

Seedlings of paper birch (Betula papyrifera Marsh.), green ash (Fraxinus pennsylvanica Marsh.), and red pine (Pinus resinosa Ait.) fumigated with 0.2 ppm SO2 for 30 h at 30° C had higher leaf diffusive conductances (LDC) and absorbed more sulfur than seedlings fumigated at 12° C. Comparisons among the three species fumigated at the same temperature, however, do not support the view that a plant with higher LDC should absorb more SO2 than a plant with lower LDC. Mean relative growth rates ([Formula: see text]) of seedlings grown at 21° C after fumigation were variously affected by SO2. [Formula: see text] of green ash was not inhibited by SO2, but [Formula: see text] of roots of red pine seedlings was reduced by SO2, with greater inhibition in seedlings fumigated at 30° C. Root and shoot [Formula: see text] of paper birch seedlings were lowered by SO2, and effects of SO2 were about equal at both exposure temperatures. The data indicate that temperature can affect mechanisms of SO2 avoidance, tolerance, or both to various degrees in different species. Thus generalizations on the influence of exposure temperature on resistance of plants to SO2 may be inappropriate.