Growth effects of SO₂ and/or NO₂ on woody plants and grasses during spring and summer

Abstract

The two most widespread air pollutants in Britain are SO₂ and NO₂ (refs 1, 2). These not only contribute to acidity in rain³, which may seriously affect plant growth, but also cause substantial effects by their direct action as gaseous pollutants. Research into the effects of the gaseous pollutants on grasses has shown that the combination of SO₂ and NO₂ may be particularly toxic to plant growth^4,5. Further research in this laboratory showed that Phleum pratense L. was more sensitive to SO₂ when growth was slow and it was suggested that exposures during winter may be particularly phytotoxic⁶. Here we present the results of experiments in which serious effects on plant growth were detected even during the summer months. Autumn-sown smooth stalked meadow grass (Poa pratensis L.) exposed to SO₂ or SO₂ plus NO₂ showed marked growth reductions during the winter and spring, and although the plants recovered during the summer, flowering was inhibited. Moreover, four broad-leaved tree species showed substantial decreases in growth when exposed to SO₂ plus NO₂ between March and August.