Soil microarthropod contribution to forest ecosystem processes: the importance of observational scale

Investigations of the role of microarthropods (Acari and Collembola) in org anic matter decomposition and nutrient cycling have shown that they may con tribute to primary productivity in nutrient poor conditions. The potential of microarthropods to affect other ecosystem properties, such as above grou nd plant diversity or succession, lags somewhat. In this contribution we de monstrate: (1) that the effect on the mobilization of nutrients promoted by microarthropods must be measured at the microhabitat scale appropriate to the scale of the faunal activity, and (2) that small changes in the structu re of microarthropod assemblages can have significant effects on the local mobilization of nutrients. In the first of two experiments we measured the nutrients leaching from field mesocosms containing litter and mineral soil, with and without fauna. After eight months, the C:N ratios of the litter d iffered significantly indicating that the fauna were effective in altering the decomposition rate. However, the patterns of release over time and the concentration of the measured nutrients differed little between the two set s of mesocosms. In a second experiment microarthropod assemblages, which di ffered only slightly, were introduced into laboratory microcosms and the nu trient fluxes were measured over a ten week period. Significant differences were detected in the concentration of nitrogen, K and Mg leached and in CO 2 evolved. We suggest that when the potential influence of microarthropods on ecosystem properties is being assessed, specific knowledge of the releva nt details of interactions at the smallest scale must be considered. These details can be incorporated or dismissed when interactions on the next leve l of the ecological hierarchy are examined. Using such analysis we suggest that the creation of soil nutrient hot-spots by microarthropods may have im plications for maintaining plant species of lowered competitive ability in a given system.