Exotic earthworms are entering previously uninhabited soils of boreal forests, their invasion largely facilitated through human activities. As ecosystem engineers, earthworms are capable of causing dramatic changes in above- and belowground forest composition, but whether they have the same effects in all forests remains unclear. Forest compositional changes caused by earthworms may be mediated by interactions between earthworms and mycorrhizal fungi. Specifically, tree seedling growth may be altered by the presence of exotic earthworms and their subsequent impact on mycorrhizal fungi. In this study, we investigate the effects of exotic earthworms on ectomycorrhizal colonization and seedling growth of the conifer Picea glauca (white spruce) in gray luvisolic soils from the Boreal Plains. Anecic Lumbricus terrestris and epigeic Dendrobaena octaedra earthworms were added to mesocosms each containing a white spruce seedling in a greenhouse experiment. Impacts on the composition of ectomycorrhizal fungi in the mesocosms were determined using a combination of morphological and molecular techniques, and effects on seedling growth were assessed through above- and belowground measurements. The proportion of ectomycorrhizal root tips and ectomycorrhizal community composition did not vary as a function of earthworm species or density. Similarly, exotic earthworms had no significant effect on spruce seedling growth or survival.
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Vol. 19 • No. 1