Cross-Site: Earthworms and Soil Processes In North American Ecosystems

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Influences of earthworms on soil processes in agricultural and pastoral systems are well recognized but there is considerably less information about their importance in wildland ecosystems such as forests, grasslands and savannas. Furthermore, very little is known about the ecology of native earthworm species in North America, even though they are prevalent in a number of areas unaffected by Pleistocene glaciations. The few existing studies indicate that where they are abundant, these organisms can have significant effects on soil structural properties and on nutrient transformations. However. the relative importance of native versus invasive exotic earthworm species remain virtually unknown. This proposal requests funding for a cross-site investigation of native and exotic earthworms, to determine if native species are more efficient than exotic species in nutrient processing in undisturbed ecosystems. They also will determine if disturbance sets the stage for invasion by exotic earthworms, which may be more competitive than natives but less effective in nutrient cycling. Th ese ideas will be tested in two phases over a three year period at three LTER sites (Coweeta Hydrologic Laboratory, Konza prairie Research Natural Area and Luquillo Experimental Forest) and one non-LTER site (Apalachicola National Forest). They will undertake field surveys and collections in a variety of habitats, and will initiate field enclosure experiments using 13C- and 14N- enriched substrates. Together, these two phases of work optimize the use of stable isotopes in field studies--first, as survey tools to characterize and identify important species and patterns of resource utilization across sites; and then as biogeochemical tracers to elaborate earthworm-microbial interactions and to quantify influences of various earthworm species on C and N dynamics. Results from this study will greatly expand their understanding of earthworm ecology, interactions between native and exotic species, and influences of both groups on soil nutrient processes across a broad range of ecosystems.