Enchytraeids and microbes in Zn polluted soil: No link between organism-level stress responses and ecosystem functioning

We studied the presence of zinc tolerance in enchytraeid worm (Cognettia sp hagnetorum, Oligochaeta) from a metal-polluted forest soil in The Netherlan ds. In a dose response experiment, we compared Zn sensitivity, measured as body growth and reproduction, of these enchytraeids with that of animals ta ken from three unpolluted sites. Because C. sphagnetorum is a keystone spec ies, regulating microbial processes in coniferous forest soil, we performed a microcosm experiment to study the interaction of enchytraeids from sever al sites with soil microbes. The idea was to study whether there is a link between metal stress response of individuals (tolerance level, life history alteration) and changes observed at higher organization levels of the biol ogical system (trophic interaction and decomposition processes). We did not find evidence for increased metal tolerance of C. sphagnetorum. Worms from the polluted site actually had reduced body growth, indicating negative fi tness effects caused by long-lasting metal stress. The density and biomass of the worm population from the polluted site was low in Zn contaminated so il. Presence of enchytraeids enhanced and Zn contamination reduced the acti vity of microbes in the soil. Enchytraeids from different sites with differ ent life histories and population development, however, had the same effect on microbes. Hence, observed stress responses of individuals and populatio ns could not be linked to density-dependent trophic interactions and ecosys tem functioning in the soil-decomposer food chain.