Invasive Earthworms and N-Cycling: Do Species Matter?
Katalin Szlavecz and Peter Groffman

The ability of non-native earthworms to stimulate soil N-cycling is well established. This may result in ecosystem scale effects especially if exotics invade areas previously uninhabited by earthworms. Due to lack of data on native species we do not know what this effect might be where exotics are replacing native earthworms. In this study we compared the influence of one native (Eisenoides loennbergi) and two exotic (Lumbricus terrestris and Amynthas hilgendorfi) earthworms on soil inorganic N pools and nitrification rates. Soil samples were collected in the field and then incubated in the laboratory for three weeks. We also conducted feeding experiments using commercially available topsoil. Earthworms were kept in mesocosms at 17 0C for three weeks with tulip poplar and oak litter provided as a food source. At the end of the three weeks the earthworms were removed, and inorganic N pools and potential nitrification rates were measured. Total inorganic N was highest in the soil (both field and lab) inhabited by Amynthas, and Asian exotic. Ammonium made up more than 90% of soil inhabited by Eisenoides. All three species altered nitrification rates compared to controls. Again, Amythas had the largest impact, while there was no difference between Eisenoides and the European Lumbricus. Our results point to strong species effects, which has to be taken into account when different microhabitats are invaded by different species.

Keywords: earthworms, N-cycling, species invasion

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