We expected seedling growth to be higher in more fertile
samples, i.e., casts that were more nutrient-rich (see Clause et al.,
2014). Casts and soil modified by earthworms are known to have a
higher content of mineral nutrients than soil with no earthworms
and to support greater plant growth (Eisenhauer and Scheu, 2008;
Laossi et al., 2010; Zhang et al., 2010). Our results showed that
seedlings grew better in the controls, independently from the soil
type. Surprisingly, seedlings in casts of L. terrestris did not grow
better than in the other samples despite their overall initial higher
nutrient-content. Seedlings of U. dioica grew better than any other
species. Poorter and Remkes (1990) also observed a higher relative
growth rate of U. dioica compared to O. vulgare, T. repens and
Festuca sp., which is common in plants that colonize fertile
secondary successional disturbed sites (Poorter and Remkes,
1990). Also, as for patterns of seed germination, we believe that
microbiological properties of casts are responsible for these
unexpected patterns.