Effect of components of 'acid rain' on the contribution of soil microarthropods to ecosystem function.
The consequences of stressing microarthropod assemblages (Acari and Collembola) in a Norway spruce (Picea abies) forest soil with the chronic proton and low-level nutrient input associated with 'acid rain' was evaluated. Microarthropods from the organic layer of the forest floor plots, sprayed over a 4-year period with nitric acid, sulfuric acid, ammonium sulfate (AS), ammonium nitrate (AN) and ammonium chloride (AC) were introduced into laboratory microcosms containing unpolluted litter. Assemblages from plots treated with urea and distilled water were also included. Leaching of ammonium-N, nitrate-N, sulfate-S, chloride, Ca, Mg, K and Na from the microcosms was measured over a 10-week period. Leachate pH and CO2 production (respiration) were also measured. Differences in the mean biomass of microarthropods were detected after 10 weeks. Biomass of assemblages from AN, urea and sulfuric acid plots were greater than that from nitric acid, water, AS and AC plots. The abundance of five species, Isotoma notabilis, Friesea mirabilis, Oppiella nova, Macrocheles and Cilliba cassidea differed between the assemblages. Leaching of all anions and cations measured and respiration differed between microcosms. NO3-N leaching increased over the 10 weeks whereas NH4-N decreased. Ca and Mg leaching was positively correlated with NO3-N leaching. K leaching correlated positively with NH4-N leaching. A positive relationship existed between respiration and NO3-N leaching, and a negative relationship existed with NH4-N leaching. Many of the differences between elemental losses from microcosms were elevated or diminished losses from microcosms containing animals originating in AC or AS field plots. There were no differences between assemblages derived from the two acid-treated plots but there were significant differences between disturbed and undisturbed assemblages. The results indicated that perturbation of the microarthropod assemblage, due to anthropogenic activity, may effect decomposition and local nutrient availability.