To assess the potential effect of the colonization of N-enriched hardwood forests by exotic earthworms, we determined the impact of Euro-Asian worms with two different feeding and burrowing modes on organic C content and N transformations in forest soils. Our study sites included adjacent control and burned forest sites. In addition, our experimental design considered two contrasting landscape positions (lower slope and ridge-tops) at each site. The worm genera we used (Lumbricus, Aporrectodea) are already present in high density in agricultural fields in the region but are absent or rare in forested areas. Worm enclosure chambers were placed in the field in August 2006 and worms were added in June 2007. Each chamber received either three Lumbricus (deep-burrowing anecic), three Aporrectodea (soil dwelling endogeic), three of each, or no worms (control). Chambers were harvested ten weeks later.
Results/Conclusions
Preliminary analysis suggests that total inorganic N (TIN) and NO3- concentrations were reduced by a factor of 2X and 5X, respectively, by Lumbricus, but not affected by either Aporrectodea or the combination of the two worm genera. NH4+ concentrations were relatively unaffected by worms. The greatest increase in NO3- occurred in lower slope position in the thin+burn plot with Aporrectodea, whereas net NO3- immobilization was observed in the lower slope position, control soils with Lumbricus. Overall, acid phosphatase activity was not affected significantly by the presence of worms, whereas b-glucosidase activity was reduced by all worm treatments. Lumbricus, but not Aporrectodea, resulted in reduced phenol oxidase activity. Integration of these data with soil organic C characteristics, dissolved organic N, microbial community-wide physiological profiles, and microbial biomass measures will be presented.
