SIMULATED ACID-RAIN EFFECTS ON FINE ROOTS, ECTOMYCORRHIZAE, MICROORGANISMS, AND INVERTEBRATES IN PINE FORESTS OF THE SOUTHERN UNITED-STATES

A 2-yr study evaluated the effects of acid precipitation on the forest floor community. Throughfall was collected at weekly intervals, acidified to pH 4.3 and 3.6, and applied to throughfall excluded 1 m2 plots in a stand of loblolly pine (Pinus taeda L.) in south Mississippi, and in a longleaf pine (P. palustris Mill.) plantation in east Texas. Control plots received ambient throughfall which ranged from pH 3.7 to 6.2 in Mississippi and pH 3.8 to 6.7 in Texas. Five plots of each treatment at each location were destructively sampled after 1 yr and the 5 remaining plots were sampled after 2 yr. Chemical analyses were conducted for all collections of throughfall and litter leachate, and for the fermentation layer, rhizosphere, and mineral soil. After 2 yr, comparisons of the pH 3.6 plots with the controls indicated significant decreases in the number, length and biomass of lateral roots, and the percent and number of ectomycorrhizae. Decreases in these root characteristics for plots subjected to applications of throughfall acidified to near-ambient pH 4.3 were also significant or bordered on significance. Numbers of herbivorous mites increased significantly with decreasing pH, but the predaceous mites appeared insensitive. Treated plots had fewer numbers of some groups of the larger invertebrates, especially earthworms, but variation was generally too great to show significance. The acid treatments had little effect on numbers of nematodes, saprophytic fungi or endomycorrhizal fungi.