FOREST SOIL RESPONSE TO ACID AND SALT ADDITIONS OF SULFATE .3. SOLUBILIZATION AND COMPOSITION OF DISSOLVED ORGANIC-CARBON

A year-long experiment, using reconstructed Spodosol and intact Alfisol soil columns, was conducted to examine the effects of various simulated throughfall solutions on soil C dynamics. Soil organic C solubilization, dissolved organic C fractions, and decomposition rates were studied using simulated acidic and salt throughfall solutions. Few effects were found on organic C solubility and movement, or on dissolved organic C fractions until after week 40. No effects were observed with acid inputs as low as pH 3.7 during weeks 21-40. When input solution pH was decreased to 3.0, organic C solubilization from the forest floor of the Spodosol columns was reduced as was adsorption in forest floor plus mineral soil columns; retention of dissolved organic C was 90 and 83% in control and acid-treated columns, respectively. Addition of sulfate salt resulted in a slight increase in dissolved organic C movement through the mineral horizons, which was due to higher solution pH and possibly competition with SO42-. No treatment effects were observed with the Alfisol column leachates which had lower concentrations of dissolved organic C compared to Spodosol leachates. Soil respiration appeared to be unaffected by simulated throughfall solutions containing either acid or salt. Based on the results of this study we propose that throughfall solutions of pH above 3.7 will have little or no influences on dissolved organic C cycling in the types of Spodosol and Alfisol forest soils used here. However, at pH 3.0 some alterations in organic C solubilization, dissolved organic C fractions, and mobility could be expected.