Effects of simulated acidic, metal-containing precipitation on coniferous litter decomposition

Depths of undegraded litter in hardwood and boreal forest ecosystems of Camels Hump Mountain in the Green Mountains of Vermont doubled between 1965 and 1982. Simulations of litter leaching by acidic and nonacidic snowmelt, fog water, or rain showed that hydrogen ions were retained by coniferous-needle litter and both cations and anions were leached. In vitro studies on litter degradation showed that acidic conditions reduced microbial CO2 evolution from litter. CO2 evolution was further repressed by the presence of Pb and Zn, but not by Al or Cu. Cellulose breakdown was unaffected in acidic, metal-containing soils treated with water acidified to pH 3.8. Reduction in litter decomposition, which could adversely alter the rates of mineral cycling in natural ecosystems, may be due to repression of the metabolism of litter-degrading microflora by precipitation acidity and metals present in soils and introduced by polluted rain.