Effects of tree leaf litter, deer fecal pellets, and soil properties on growth of an introduced earthworm (Lumbricus terrestris): Implications for invasion dynamics

Invasive earthworm communities are expanding into previously earthworm-free forests of North America, producing profound ecosystem changes. Lumbricus terrestris is an invasive anecic earthworm that consumes a large portion of the detritus on the soil surface, eliminating forest floor organic horizons and reducing soil organic matter. Two mesocosm experiments were used to examine the individual and combined effects of litter and soil type on the growth of L. terrestris. The litter type experiment tested nine different food source treatments (7 tree leaf litters, deer fecal pellets, and a control), while the soil x litter type experiment used five different soil treatments (4 soil types and one soil type with A horizon material removed) in combination with four different food source treatments. We found that leaf litter type (p = 0.001) and soil type (p = 0.018) significantly affected earthworm growth rates, with growth rates on deer pellets similar to many high quality deciduous leaf litters. Of soil variables, exchangeable Ca (r(2) = 0.99), sum base cations (r(2) = 0.98), % organic matter (r(2) = 0.93), %N (r(2) = 0.89), %C (r(2) = 0.87), and exchangeable Mg (r(2) = 0.85) were all significant predictors of earthworm growth. Litter disappearance of all litter types was linearly related to growth, suggesting similar growth efficiency on different litter types. However, chemical properties, specifically foliar C:N and a linear combination of a suite of other chemical properties predicted growth, suggesting that consumption or gut passage rates were regulated by litter quality. This information about soil and litter characteristics that regulate L terrestris growth should improve models of their distribution, spread and abundance. Published by Elsevier Ltd.