Feeding behavior of epi-anecic earthworm species and their impact on soil microbial communities

International audienceOrganic matter decomposition is a key ecosystem function due to its importance for carbon and nutrient cycling (Bardgett et al., 2005), soil structure (Soane, 1990), and water storage (Soane, 1990). Roughly 90 % of the global terrestrial plant production enters the dead organic matter pool (Cebrian, 1999), making decomposition of plant material one of the most crucial processes in terrestrial ecosystems (Tiessen et al., 1994). Plant litter decomposition is governed by environmental conditions (e.g. humidity and temperature), litter quality (i.e. its physical and chemical characteristics), and the decomposer communities (i.e. abundance, diversity and activity) (Stout and Goh, 1980; Coûteaux et al., 1995). Given their impact on soil functioning and their interactions with soil organisms, earthworms contribute to the recycling of organic matter and participate significantly in the numerous ecosystem services provided by soils. Most of the studies focusing on the role of earthworms on litter decomposition were conducted by comparing distinct ecological categories (epigeic, epi-anecic, anecic strict and endogeic), whereas their specific contribution within a given ecological category remains largely unknown. In this context, the aim of this study was to determine the contribution of four epi-anecic earthworm’ species to (i) the decomposition of plant litters with contrasted chemical and physical proprieties and (ii) the effect of these interactions on fungal and bacterial communities inhabiting their burrows.We selected four epi anecic taxa (Lumbricus rubellus, L. festivus, L. centralis and L. terrestris). Each taxon was exposed separately to leaves of three different plants (Holcus lanatus, Lolium perenne and Corylus avellana). A 5 × 3 factorial design was performed with 4 replicates and for two incubation times (10 or 20 days): with or without (control accounting for the litter mass loss due to microbial decomposition or leaching) one of the four epi-anecic species; with one of the three litter types placed at the soil surface and at 10 cm deep. The effect of these interactions on fungal and bacterial communities inhabiting epi-anecic burrows were assessed using T-RFLP analysis.Epi-anecic species improved the litter mass loss solely at the soil surface, while, at 10 cm deep, litter mass loss was mainly due to microbial activity. Litter mass loss was correlated to the initial mass of epi-anecic species and its intensity depended on litter quality as the four epi-anecic species displayed a similar sensitivity to the quality of the litter added. Interestingly, L. festivus seemed to have a higher efficiency in surface litter mass loss that was linked to a stimulation of the fungal communities in its burrows. Fungal communities were thus impacted by both the litter type and the epi-anecic species whereas soil bacterial diversity and richness were stimulated in the earthworm burrows whatever the epi-anecic species. Overall, epi-anecic species contribute to enhance the diversity of the drilospheric microbiota. Our results indicate that grouping earthworms within ecological categories can give an indication of their global effect on soil litter decomposition, however, to take this analysis further, species-level studies are needed and advised