Influence of mist pH and acid anion on cation efflux from pinto bean foliage

The cation content of droplets collected from Phaseolus vulgaris (pinto bean) leaf surfaces during misting was more strongly influenced by mist pH (2.5, 4.0, or deionized water) than by source of acidity (HCI or H₂SO₄ + HNO₃). Concentrations of Ca²⁺, Mg²⁺, and K⁺ were highest in droplets from leaves treated with the pH 2.5 mists, but there were often no differences between the pH 4.0 and deionized water treatments. Cation content and pH of droplets from leaves treated with pH 2.5 mists increased across the three days of treatment, while those from leaves treated with less acidic mists decreased or did not change across the days of treatment. Source of acidity often affected foliar concentrations of Mg²⁺, K⁺, and Na⁺, but in inconsistent directions, and foliar concentrations of Mg²⁺ and K⁺ were unaffected by mist pH. Foliar Ca ²⁺ concentrations were often highest in leaves treated with pH 2.5 mists, in contrast to expectation, perhaps because of effects of acidic mist on foliar carbohydrate status. Despite the large efflux of cations from leaves treated with pH 2.5 mists, foliar cation concentrations in nonmisted foliage were sometimes lower than in misted foliage (Ca²⁺), but were higher in other cases (Na⁺) or indistinguishable in still others (K^?). While exposure of plants to highly acidic mists appeared to cause accelerated efflux of foliar cations, effects on foliar chemistry are probably dependent on soil nutrient status and on other aspects of plant vigor.