Effect of simulated environmental change on alpine soil arthropods

The effects of environmental change on soil animal communities are poorly known. Norwegian mountains are subject to both atmospheric nitrogen deposition and increased temperature. In a nutrient poor alpine Dryas heath in south Norway, soil arthropods were studied after 4 years of simulated environmental change by warming and/or nutrient addition. Warming alone only affected three low-density Collembola species, while nutrient addition, with or without warming, greatly changed the dominance hierarchy of the microarthropod community. Certain Collembola species with a short (1 year) life cycle and predatory Gamasina mites increased markedly in density. These groups may have been favored by increased litter production, as plant biomass and litter producing graminoids and forbs increased significantly in plots with nutrient addition and nutrient addition combined with warming. Microarthropods with a longer life cycle, such as Oribatida and certain Collembola, were generally unaffected by nutrient addition and probably need more time to respond. The number of Oribatida taxa was, however, reduced in plots with nutrient addition, both with and without warming. A groundliving species of Coccoidea (Homoptera) declined in plots with nutrient addition and warming compared with only warming, probably due to reduced cover of its host plant Dryas. The density of Diptera larvae (Sciaridae and Chironomidae) was unaffected by the treatments. Our results show that increased nutrient availability in nutrient poor alpine soils may have large but different effects on different taxa of soil animals. Species with short life cycles reacted first. Nutrient addition and nutrient addition combined with warming resulted in several effects below ground on microarthropods as previously shown above ground on plants: Increased biomass, high dominance of a few rapidgrowing species, contrasting responses of closely related species, and a reduction in species numbers. These short-term responses may have profound long-term effects in this alpine ecosystem.