Effects of ambient acidic rain on cation concentrations in leaves of Acer saccharum and Cornus florida

Are foliar concentrations of inorganic cations measurably altered by ambient acidic rain? Leaves of Acer saccharum Marsh. and Cornus florida L. were collected before and after seven rains, washed, and analyzed for concentrations of Ca2+, Mg2+, and K+. Leaf rinse water and the inorganic composition of each rain were also analyzed. All samples were collected in Indianapolis, Indiana, during June-September 1986-1987. Rain pH ranged from 3.6 to 4.6, volumes from 0.1 to 1.9 cm, and durations from 1 to 16 h. Most rains were net cleansers of leaf surfaces; concentrations of cations, SO4(-2), and NO3(-) in leaf rinse water were generally higher pre- than post-rain, or were unchanged by rain exposures, and leaf rinse water was more acidic after rains. Pre- versus post-rain changes in cation concentrations in washed leaves were generally small (+/-7%) compared with amounts present in leaves, and few differences were statistically significant (most p > 0.05). The changes in foliar cation concentrations were not correlated with rain pH, duration, volume, or date. These results suggest that short-term exposure to rain with pH typical of rain in much of the eastern United States is unlikely to have direct effects on foliar nutrient status, at least on fertile soils.