Effect of Simulated Acid Rain on Nitrification and Nitrogen Mineralization in Forest Soils

Abstract

Abstract To determine the possible microbiological changes in soil resulting from acid rain, columns containing samples of forest soils were leached with either a continuous application of 100 cm of simulated acid rain (pH 3.2–4.1) at 5 cm/hour or an intermittent 1.5‐hour application of 1.2 cm of simulated acid rain twice weekly for 19 weeks. The upper 1.0‐ to 1.5‐cm portions of soil from treated columns were used to determine the changes in inorganic N levels in the soil. Nitrification of added ammonium (NH 4 + ) was inhibited following continuous exposure of soil to simulated acid rain of pH 4.1−3.2. The extent of the inhibition was directly related to the acidity of the simulated rain solutions. The production of inorganic N in the absence of added NH 4 + was either stimulated or unaffected following continuous treatment of soils with pH 3.2 simulated acid rain. The addition of nitrapyrin (2‐chloro‐6‐[trichloromethyl]pyridine), an inhibitor of autotrophic nitrification, caused a decrease in nitrification in water‐treated soil but had little effect on nitrification in soil treated with pH 3.2 simulated acid rain. Intermittent applications of simulated acid rain (pH 3.5–4.1) for 19 weeks partially inhibited nitrate (NO 3 − ) production in soil amended with NH 4 + following the exposure period, but NO 3 − production in unamended soil was either unaffected or stimulated.