Exotic earthworm community composition interacts with soil texture to affect redistribution and retention of litter-derived C and N in northern temperate forest soils

Exotic earthworm impacts on temperate forest soils are influenced by earthworm community composition and are likely constrained by the degree of organic matter redistribution following earthworm introductions across different soil types; however, the relative importance of these factors remains unknown. We examined how exotic earthworm communities affected leaf litter carbon (C) and nitrogen (N) mineralization and transport in two Spodosols with contrasting textures and organic matter contents. In reconstructed soil mesocosms, we measured organic C pools, quantified C-13 and N-15 transport from isotopically labeled red maple (Acer rubrum) leaf litter, and linked leaf litter redistribution to sub-surface burrow system structures following 150-day incubations. Transport of C and N from surface litter into soil was greatest with multi-species earthworm communities, and A-horizon and burrow pools functioned as dominant sinks for this material. Litter-derived C:N recovery ratios of soil pools revealed higher retention of litter-derived N over litter-derived C; recovery of litter N (mg N-15 m(-2)) transported from surface litter was greater in the sandy loam (98.2 +/- A 2.73 %) than in the sandy soil (66.2 +/- A 4.92 %) following earthworm community additions. Earthworm biomass was as a minor sink for litter C (mg C-13 m(-2)) and N transported from surface litter (0.56 +/- A 0.13 and 2.26 +/- A 0.31 %, respectively). Recovery of litter-derived C and N in earthworm biomass increased with the degree of direct leaf litter consumption (A. trapezoides < E. fetida < L. terrestris). Surface-dwelling epigeic and mineral-soil dwelling endogeic species produced burrow systems with the highest volume, surface connectivity, and density in the A-horizon; these properties were associated with greater CO2 losses and with greater litter C and N transport into A-horizons and burrows. Burrow systems with high continuity and large burrows produced by vertical-burrowing anecic species were associated with greater litter C and N transport into B-horizons, and greater dissolved organic C leaching losses. This study shows that the degree of organic matter redistribution in temperate forest soils following earthworm introductions is directly related to earthworm community composition, while the preferential retention of N over C and the potential stabilization of this material is determined by soil type.