Effects of precipitation acidity on the chemistry and microbiology of Sitka spruce litter leachate

Simulated rain acidified with H₂SO₄ to pH 3, compared with non-acidified rain (pH 5·3) and distilled water (pH 5·5), increased the leaching of major cations from a layer of decomposing Sitka spruce litter and underlying F horizon over a 3-month incubation period at 10°C. Largest relative increases in leaching were observed for Mn²⁺ > Mg²⁺ > NH₄⁺ > Ca²⁺. Acid rain (pH 3) decreased the amount of total organic carbon, Fe³⁺ and Al³⁺ leached from the Sitka spruce litter and soil layer. Sterile litter leachates obtained from all treatments supported fungal growth equally well. Acid rain-produced leachates, however, impaired initial bacterial growth of cultures isolated from forest soil and also in mixed soil isolates. The same cultures, however, were not affected by the high Mn²⁺ concentration of the leachates, which therefore was not responsible for this observation. At the end of the raining period, the rate of respiration in the F horizon was significantly reduced in soils previously treated with acid rain, compared with the non-acid rain treated soils.