Physiological effects of direct impact of acidic deposition on foliage

Abstract

Numerous studies have examined the direct effects of acidic deposition on physiological processes or morphological indicators at the foliar level. Cuticular features, nutrient dynamics, photosynthesis and water relations have been studied intensively using a variety of crop and forest species. The evidence suggests that extreme pH values (less than pH 3.0) can affect cuticular structure, increase leaching of foliar cations, reduce photosynthesis and transpiration, and increase cuticular water loss. In addition, studies have demonstrated that there is variation among species in the magnitude of the response and the effective pH at which a response is observed. Most of the evidence for forest species, however, suggests that these indicators showed little response until the pH of acidic deposition was in the range pH 3.0–3.5. This suggests that the possibility of direct injury to forest vegetation from ambient rainfall is slight. Acidic deposition, however, is only part of the continuum of stresses to which our forests are exposed. Further research is required to understand the interaction between acidic deposition, gaseous pollutants and other abiotic stresses.