Selective vertical seed transport by earthworms: implications for the diversity of grassland ecosystems

Summary

Earthworms are suggested to play an important role for the plant diversity of grassland ecosystems. Here we tested, whether (i) Lumbricus terrestris L. selectively feeds on seeds of grassland species, (ii) feeding patterns match with seed species present in surface casts in a permanent grassland and (iii) grassland plant seeds in different soil depths are relocated by the activity of earthworms. Food choice experiments with 10 plant species (3 grass spp., 4 non-leguminous herb spp., 3 leguminous spp.) showed that earthworms significantly selected between the offered seeds and generally favoured herbaceous species over grass species. Seed species in grassland surface casts did not correlate with seed species preferred by earthworms in the feeding experiment. Mesocosm experiments with L. terrestris in sterilized soil where 2000 seeds m-2 of Dactylis glomerata, Taraxacum officinale, Rumex obtusifolius and Trifolium repens were placed in 2, 10, 20 and 30 cm depth showed a significantly different species-specific relocation of the seeds. After 90 days on average 380 seeds m-2 of D. glomerata, 202 seeds m-2 of R. obtusifolius, 150 seeds m-2 of T. officinale and 35 seeds m-2 of the legume species were relocated. Results suggest that seed herbivory and seed transport are important mechanisms by which earthworms selectively alter the diversity of grassland ecosystems.
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