Success of seed germination and seedling establishment is potentially affected by interactions with
earthworms. Two of the possible mechanisms that might explain such impact are the selective ingestion of
seeds by earthworms that might break seed dormancy, and germination in their nutrient-rich casts. The aim
of this study was to disentangle the effect of seed passage through the earthworm gut and the effect of cast
alone, as a germination medium, on the germination and growth of four herbaceous species. We
hypothesized that the presence of seeds in casts facilitates their germination and seedling growth and that
the passage of seeds through gut favors seed germination. Non-ingested seeds were placed in artificial
earthworm casts shaped from cast material of 3 soil types
3 earthworm species combinations (plus
control). Seed germination after seed ingestion and excretion was tested in a Petri dish experiment in the
presence of each earthworm species. Contrary to our expectations, we found that passage of seeds through
the gut of Lumbricus terrestris decreased the germination of Festuca lemanii and that all seeds of Origanum
vulgare and Urtica dioica were digested. Total seed germination of non-ingested seeds placed in casts was
affected by cast properties, i.e., by the interaction between the soil type and the earthworm species.
Seedlings germinating from the control material had a higher relative growth rate than in material from
Allolobophora chlorotica cast. Our results suggest that seed ingestion alters seed germination success of
specific plant species. The cases of lower germination and seedling growth induced by cast effects are
discussed with regards to their physical, chemical and microbiological properties.