Effects of sulfuric acid rain on decomposition rate and chemical element content of hardwood leaf litter

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Abstract
Simulated sulfuric acid rain (pH 3.0, 3.5, or 4.0) or control rain (pH 5.6) was applied to decomposing leaf packs of 10 hardwood species. Changes in weight and chemical element concentrations were followed for 408 days. Leaf-pack weight decreased most rapidly under the intermediate acid treatments, especially at pH 3.5. The ratio of the decomposition rate of leaves at pH 3.5 to the decomposition rate of the control leaves varied from 1.10 for Quercus garryana to 12.57 for Quercus palustris. As expected, control decomposition rates tended to be higher for species with low C:N ratios and high base content. However, there was no apparent relationship between sulfuric acid rain effect on decomposition rate and initial chemical element content. The lack of a relationship to either S concentration or S:N ratio suggests that the sulfuric acid rain did not enhance decomposition by supplying S; however, the rain S was undoubtedly more available than organic S. For all treatments except pH 3.0, Mn concentrations tended to increase during decomposition; at pH 3.0, Mn concentrations increased initially and then decreased. After 408 days, Mn concentrations were considerably lower at pH 3.0 than under any other treatment. Manganese was the only element whose concentration was found to depend on sulfuric acid rain treatment.