Effects of Acidic and Neutral Sulfate Salt Solutions on Forest Floor Arthropods

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Abstract
Acidic and neutral SO42− solutions were applied to a mixed oak (Quercus spp.) forest floor on Walker Branch Watershed in eastern Tennessee to study effects of increased acid deposition on decomposer arthropods and arthropod regulation of P cycling. Treatments consisted of ambient (no applications), 2 × (low), and 10 × (high) annual atmospheric inputs of SO42− (as K2SO4) and H+ plus SO42− (as KHSO4). Arthropods were sampled monthly in litter and mineral soil. Soils were analyzed for Bray no. 2 P and for salt pH, NH4Cl exchangeable Al3+ and K+, and water‐extractable SO42−.Over a 14‐month period, the number of forest floor macroarthropods averaged 19% lower in the high SO42− salt treatment compared with the control. Macroarthropod fungivores also were adversely affected by the high SO42− salt treatment and by the high and the low KHSO4 treatments. The effects of the high SO42− treatment on macroarthropods may have resulted from a salt effect caused by the concentrated K2SO4 applications (112 mmol K+ m−2 per application). Microarthropod numbers increased significantly in response to the low K2SO4 additions and to the high and low KHSO4 treatments. Microarthropod fungivores, predators, and detritivores responded similarly. Comparison of microarthropod densities and soil K+ concentrations suggested that the response resulted from a direct fertilizer effect of K+ on arthropods or indirectly from an effect on microorganisms.Mineral soil pH, exchangeable Al3+, and Bray P were unaffected by the treatments. Soil pH (0–15 cm) was unaffected by the KHSO4 applications because most of the H+ addition was neutralized by the forest floor. Analysis of litter leachate during a single treatment interval (5 weeks) indicated that only 31% of the H+ applied in the high KHSO4 treatment reached the mineral soil.Although increased inputs of H+ appear to have little effect on decomposer arthropods, effects of nonacidic SO42− warrant further study.