The effect of invasive earthworm Lumbricus terrestris on the distribution of nitrogen in soil profile

Abstract

The purpose of this study was to determine if Lumbricus terrestris, an invasive earthworm in Northern Michigan, is redistributing nitrogen from the organic soil layer to the deeper, mineral soil layer. L. terrestris burrow 2 meters vertically into the ground and emerge to feed on freshly fallen leaf litter. The study included collecting of L. terrestris in 16 0.5 m square plots by method of electro-shock. Soil cores from a depth of 0-5 and 30-40 cm as well as leaf litter were taken from each plot to determine nitrogen content and nitrogen isotope ratios. Data analysis resulted in no significance between plots with earthworms and without earthworms in both nitrogen, N, isotope ratios and N content. Plots with L. terrestris showed no difference between the organic and mineral soil layer. This result suggests that L. terrestris are homogenizing soil layers. However, smaller than ideal sample sizes limit interpretive capacity of the results. Further research needs to be completed to confirm these perceived trends. The analysis of nitrogen isotope ratios suggest that there is another source of 15N other than leaf litter and L. terrestris that is contributing to soil composition and therefore the contribution of each was not conclusively determined.