Effects of earthworm species on organic matter transformations

Earthworms are pivotal in improving soil health by mixing and breaking down organic matter. Earthworm species are known to have different impacts on soil structure, but only a small number of species have been studied so far, and few studies have examined how earthworms simultaneously affect soil functions. In this study, we measured the impact of different earthworm species on soil structure (bioturbation function), carbon (C) and nitrogen (N) dynamics and the microbial community (organic matter transformation function). Six earthworm species (Lumbricus terrestris, Allolobophora chlorotica, Octolasion cyaneum, Octodrilus complanatus, Aporrectodea caliginosa meridionalis and Microscolex dubius) of different ecological categories were tested. The experiment was carried out in soil cores with alfalfa litter over six weeks. Our results on the bioturbation function illustrate a great diversity of behaviors and confirm the relevance of a functional classification based on bioturbation metrics. Some species, such as Lumbricus terrestris, Microscolex dubius and Octodrilus complanatus, significantly increased soil moisture and nutrient levels, simulating the activity of microorganisms. The effects of the species studied on the function of organic matter transformation do not align to their bioturbation activities, nor to their ecological category. These results show that the contribution of earthworms to carbon and nitrogen turnover is only partially dependent on their bioturbation effects, and suggest the usefulness of developing distinct functional groups based on the specific soil functions under consideration.

This work was funded by INRAE's AgroEcoSystem division through the GloWorms project.

Contact : gwenaelle.lashermes@inrae.fr