Solute concentrations and fluxes of major nutrients in potted red spruce saplings exposed to simulated acid rain treatments

Abstract

Ninety potted red spruce saplings have been enclosed in open-top fumigation chambers and exposed to simulated acid rain treatments of pH 3.1, 4.1, and 5.1 for two growing seasons as part of a 4 yr study. Original spodosol soil profiles were reconstructed in each 1 m diameter pot with tension lysimeters buried at two depths and drainage spouts installed on the bottom of each pot. All principal fluxes of the major elements are being measured in these “ecosystems” allowing calculation of precise input-output and internal nutrient budgets. During the first year of treatments, nutrient budgets were strongly affected by enhanced mineralization owing to transplant disturbances, and this masked any treatment effects. Second year budgets indicated the effects of strong acid loading on cation depletion and acidification of soils. For example, nitrate leaching from the subsoil was nearly five times higher in the pH 3.1 treatment than in others and correlated increases in base cation leaching were observed. Significant differences in soil pH among rainfall treatments were also observed. Budgetary calculations demonstrated that at present there are large exchangeable Ca pools available for tree growth, whereas for K, plant requirements were very high relative to K soil pools which may lead to growth deficiencies and/or nutrient imbalances. These results illustrate the potential for the combined effects of tree growth and strong acid loading to deplete the base status of acidic forest soils.