A COMPARISON OF THE ABILITY OF LEAF SURFACES OF THREE SPECIES TO NEUTRALIZE ACIDIC RAIN DROPS

Abstract

In order to compare the ability of leaf surfaces of different species to neutralize acidic rain, acidic droplets of identical size were placed on leaves of Artemisia tilesii, Spinacea oleracea and Phaseolus vulgaris. The pH values over time were measured using a micro‐pH electrode. The pH of rain droplets initially of pH 3.0, 3.5 and 5.6 increased after contact with leaves of these species. However, for droplets of pH 2.5 the pH of droplets actually decreased with time on leaves as the drops evaporated, despite the very large quantity of hydrogen ions neutralized by the leaf surface. Neutralization of acidic droplets was greatest in A. tilesii plants, which also showed the lowest sensitivity to foliar injury from simulated acid rain, Spinacea oleracea leaves were the least able to neutralize acid droplets and also were most sensitive to foliar damage. In each species the more acidic the rain, the greater the quantity of hydrogen ions neutralized by the leaf surface. This ability to neutralize acidic droplets on the leaf surface may be an effective means of reducing damage by acid rain, especially since rain events with a pH < 3.0 are very rare. Neutralization of acidic droplets may be brought about when cations are leached from exchangeable pools or by dissolution of salts deposited on the leaf surface through guttation. Large increases in Ca especially, but also in Mg and K in droplets collected from leaves of A. tilesii, suggest that these cations may play an important role in increasing the pH of acidic droplets. Copyright © 1984, Wiley Blackwell. All rights reserved