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

Summary

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 ($\overline {RGR}$) of seedlings grown at 21° C after fumigation were variously affected by SO₂. $\overline {RGR}$ of green ash was not inhibited by SO₂, but $\overline {RGR}$ of roots of red pine seedlings was reduced by SO₂, with greater inhibition in seedlings fumigated at 30° C. Root and shoot $\overline {RGR}$ 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.