No abstract

Experiments were performed to show the responses of foliage of several clones of Tradescantia sp., Pteridium aquilinum, Quercus palustris, and Glycine max to simulated acid rain. These experiments were performed to (a) predict the relative sensitivities of foliage of these plants to acid rain, and (b) identify leaf surface and anatomical alterations to simulated acid rain 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) were most sensitive to simulated acid rain among the species tested. About 10% of the surface area of older leaves of P. aquilinum was injured after exposure to 10 rainfalls at pH 2.5 (a single 20‐min rainfall daily). 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 20‐min rainfall daily). The responses of soybeans (G. max) and spiderwort (Tradescantia sp.) were intermediate between these two extremes. Histological observations show that lesion development results in collapsed leaf tissue in all four species. Gall formation that resulted from both cell hypertrophy and hyperplasia occurred in lesions of Tradescantia, and Q. palustris. Limited hyperplastic and hypertrophic reactions occurred in G. max foliage after exposure to simulated acid rain but no leaf galls resulted. Sporophyte foliage of P. aquilinum exhibited a “granular” type abnormality in the cytoplasm prior to the collapse of some epidermal cells injured by simulated rain. Injury occurred most frequently near vascular tissues and trichomes in all four 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.

SUMMARYRelative rates of nutrient penetration, nutrient leaching, and cell permeability of first trifoliate leaves oi Phaseolus vulgaris L. cv. Univ. of Idaho 111 were examined after exposure to simulated acidic rain. In buffer solutions ^^804^" penetrated leaves faster at pH 27 than at 57. In contrast, •^Rb^ pervaded fastest at pH 57, and ^HgO entered foliage at similar rates at all pH levels tested. When plants were exposed to simulated rains of various pH levels, calcium, nitrate and sulphate were preferentially leached from whole leaves by rainfalls of low pH, whereas potassium and chloride leached more at pH 5 7 and 34 compared with 2 7 and 29. Isotope tests indicated that cells within leaves were more permeable to ^^804^"^ and ^HjO and less permeable to ^*Rb+ at pH 2 7 than at higher pH levels. These results suggest a wide diversity of leaf and cell permeability responses to various ions after exposure to acidic rain. In general, an increased rate of nutrient leaching at more acidic levels was correlated with a lower adaxial leaf resistance during leaf development.