Foliar Responses that may Determine Plant Injury by Simulated Acid Rain

Abstract

Experiments were performed to categorize the responses of foliage of several plant species after exposure to simulated acid rain in order to predict the relative sensitivities of plants to acid precipitation in nature. The present investigations were performed to (1) identify leaf indumentum responses, (2) determine histological responses, and (3) determine whole plant and individual leaf responses that may be used to diagnose acid rain injury. Plants were exposed to simulated rain at pH levels of 5.7, 3.4, 3.1, 2.9, 2.7, 2.5, and 2.3. Sporophyte leaves of bracken fern (P. aquilinum) and foliage of pinto bean, soybeans, and sunflower were most sensitive to simulated acid rain among the species tested. About 5% of the surface area of older leaves of sunflower, soybeans, and pinto beans was injured after exposure to 4 rainfalls at pH 2.5 (a single-six min rainfall every four days). Foliage of pin oak (Q. palustris) exhibited less than one-percent leaf area injury after exposure to simulated rain at pH 2.5 after 10 rainfalls (one-twenty min rainfall daily). The responses of poplar (Populus sp.) and spiderwort (Tradescantia sp.) were intermediate between these two extremes. Histological observations show that lesion development results in collapsed leaf tissue in most sensitive species. Gall formation that resulted from both cell hypertrophy (abnormal cell enlargement) and hyperplasia (abnormal cell proliferation) occurred in lesions of spiderwort, poplar, and oak. Limited hyperplastic and hypertrophic reactions occurred in soybean foliage after exposure to simulated acid rain but no leaf galls resulted, Sporophyte foliage P. aquilinum and leaves of pinto bean and sunflower exhibited neither hyperplasia nor hypertrophy after exposure to simulated acid rain. Injury occurred most frequently near vascular tissues and trichomes in all species. In general, plant species that show cell hyperplasia and hypertrophy of leaf tissues after exposure to simulated acid rain are injured less than species that do not show these responses.

Research supported in part by United States Department of Energy Contract #EY-76-C-02-0016 and in part by Associated Universities Contract #469167. By acceptance of this article, the publisher and/or recipient acknowledges the United States Government’s right to retain a non-exclusive, royalty-free license in the to any copyright covering this paper.