Interactions among earthworms species affect soil functioning

Earthworms are involved in the regulation of many soil ecosystem services. Their communities are often composed of several species but the role of each species and the potential interactions among these species on soil functioning is still poorly understood. The aim of this study was to test the hypothesis that the higher the earthworm diversity, the stronger the effect on soil processes and plant growth. A second assumption relied on the fact that earthworm effects depend on soil texture. To test our hypotheses, a laboratory controlled experiment was conducted on 5L mesocosms filled with 3 grassland soils with different textures (from sandy to loamy), covered by a layer of green waste compost. In each soil, 8 combinations of 3 different species of earthworms (Lumbricus terrestris, Lumbricus castaneus, and Allolobophora chlorotica) were tested. The experiment lasted about 14 months during which the CO₂ and the water holding capacity were recorded. Then, Lolium perenne were grown during 6 months. At the end of the experiment, analyses of soil porosity and aggregation were performed by X-ray-tomography followed by dry sieving. Results obtained shows that the assembly of the 3 species had the strongest effects on compost mineralization and hydric properties, depending on the soil texture. The analyses of the soil physical structure revealed that interactions between earthworm species lead to significant changes in the soil porosity and aggregation profiles. The ongoing analyses of plant biomass will determine whether the demonstrated changes in soil properties will result in changes in plant growth and physiology.