Seed selection by earthworms: chemical seed properties matter more than morphological traits

Abstract : Aims : The passage of seeds through the earthworm gut potentially damages seeds, altering seed and seedling performances depending on seed traits. This work was conducted to study to what extent chemical and morphological seed traits determine the seed attractiveness for earthworms. Methods : We tested seed selection via the ingestion and digestion of 23 grassland plant species spanning a range of 14 morphological and chemical traits by two common earthworm species: the anecic Lumbricus terrestris and the endogeic Allolobophora chlorotica. Results : Both earthworm species ingested seeds from all plant species. A. chlorotica digested almost all ingested seeds (out of the 15 % ingested), whereas L. terrestris excreted them in varying quantities (out of the 86 % ingested), depending on plant species identity. Seed ingestion rate by L. terrestris was driven by seed oil content and earthworm initial weight. The apparent effect of seed length was explained via seed oil content. Seed digestion rate by L. terrestris was negatively impacted by seed size. Seed ingestion rate by A. chlorotica tended to be impacted by seed protein content and seed length. Conclusion : Earthworms–seed interactions depend on a variety of seed traits and earthworm identity. Thus, earthworms, via their specific feeding behavior, might facilitate or impede the regeneration of certain plant species and drive plant communities.