Effects of watering and simulated acid rain on quantity of phyllosphere fungi of birch leaves.

The effects of simulated acid rain on the population of birch phyllosphere fungi and species/genera/group composition of fungi on birch leaves were investigated in a field study in the subarctic region of northern Finland. The acid rain treatments consisted of a mixture of H2SO4 and HNO3 with a mass ratio of 2.86∶1 (S∶N) with acidities of pH 4 (A4) and pH 3 (A3). Dry control (DC) plots received only natural precipitation; irrigated control (IC) plots received spring water (pH 6) in a volume equal to the acid treatment plots. Treatments began in 1985. Culturing of the fungi inhabiting the birch leaves was performed five times during the summer of 1988. The number of fungal colonies was significantly decreased on one of five sampling dates in the pH 4 treatment and on three of five sampling dates in the pH 3 treatment. Irrigation with spring water did not have a significant effect. The acid rain treatments affected the microflora of the upper branches (at a height of 2 m) and of the lower branches (at a height of 0.5 m) equally. The lower branches had significantly more fungi than the upper ones on three of five sampling dates. The number of phyllosphere fungi isolated from birch leaves was greater in late summer than in early summer. The most abundant taxon (∼80%) wasAureobasidium pullulons, followed byHormonema sp. and zygomycetes.