The aim of this study was to disentangle the effect of seed
ingestion from the effect of earthworm casts as a germination
substrate. To do so, germination and seedling growth of four plant
species were monitored in artificial casts made of soil coming from
12 treatment combinations: 3 soil types
(casts from 3 earthworm
species + no-worm control casts) (see Clause et al., 2014). The effect
of ingestion was tested through the comparison between seeds
that were ingested and excreted, and seeds that were not ingested
by earthworms. Thereby, we tested whether (i) cast substratum
obtained from various earthworm species and soil types facilitates
seedling growth when seeds have not been ingested but does not
alter germination rate, (ii) seedling growth is greater in casts
having higher nutrient contents, and (iii) seed ingestion by
earthworms increases seed germination success