RESPONSES OF LEAVES OF PHASEOLUS VULGARIS L. TO SIMULATED ACIDIC RAIN

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Abstract
SUMMARY: Relative rates of nutrient penetration, nutrient leaching, and cell permeability of first trifoliate leaves of Phaseolus vulgaris L. cv. Univ. of Idaho 111 were examined after exposure to simulated acidic rain. In buffer solutions 35SO42‐ penetrated leaves faster at pH 2·7 than at 5·7. In contrast, 86Rb+ pervaded fastest at pH 5·7, and 3H2O 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 3·4 compared with 2·7 and 2·9. Isotope tests indicated that cells within leaves were more permeable to 35SO42‐ and 3H2O and less permeable to 86Rb+ 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.
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