ABSTRACT
O ver the past 10 years, there has been an exponential increase in research addressing the impact of earthworms on terrestrial nutrient cycling processes. Earthworms have been shown to affect key soil properties and processes such as microbial biomass and activity, organic matter dynamics, nutrient availability, plant uptake and production, and soil structure significantly. Although the majority of these studies have been conducted in laboratory microcosms and/or agroecosystems, there is sufficient evidence to conclude that earthworms should be considered keystone organisms in regulat ing nutrient cycling processes in many ecosystems. Through their impact on nutrient cycling processes, earthworms may alter the balance between ecosys tem conservation and loss of nutrients, particularly C and N. We are now in a position to formulate models that integrate the effects of earthworms on soil biological, chemical, and physical properties. Both mechanistic and systemlevel models should lead to new predictions and hypotheses on how earthworms influence soil processes and fluxes of nutrients in ecosystems. Realistic models will depend upon studies at all levels of the ecological hierarchy to produce an integrated understanding of the roles of earthworms in biogeochemical cycles.
