Original article Selective vertical seed transport by earthworms: Implications for the diversity of grassland ecosystems Johann G. Zaller * , Nina Saxler Institute of Organic Agriculture, University of Bonn, 53115 Bonn, Germany Available online 21 September 2007 Abstract 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 sur- face casts in a permanent grassland, and (iii) grassland plant seeds deposited in different soil depths are transported by earthworms. Food choice experiments with 10 plant species (3 grass spp., 4 non-leguminous herb spp., 3 leguminous spp.) showed that earth- worms significantly selected between the offered seeds and generally preferred 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 ex- periments with L. terrestris in sterilized soil where 3500 seeds m 2 of Dactylis glomerata (grass), Taraxacum officinale, Rumex obtusifolius (non-leguminous herbs) and Trifolium repens (legume) were deposited in 2, 10, 20 and 30 cm depth showed a signif- icantly different species-specific transport of the seeds both downward and upward the soil profile. Dependent on the initial depo- sition depth between 26% (seeds initially at 10 cm depth) and 56% (20 cm depth) of the seeds were transported by earthworms. After 90 days on average 585 germinable seeds m 2 of D. glomerata, 94 seeds m 2 of T. officinale, 38 seeds m 2 of R. obtusifolius but no seeds of T. repens were transported from deeper soil layers to the soil surface. Results suggest that seed herbivory and seed transport are important mechanisms by which earthworms can selectively alter the diversity of grassland ecosystems. Ó 2007 Elsevier Masson SAS. All rights reserved. Keywords: Earthworm activity; Grassland diversity; Seed herbivory; Seed transport 1. Introduction Evidence is increasing that earthworm activity and grassland plant diversity are closely linked. Declining plant species diversity has been shown to reduce the size (biomass and number) of earthworm communities [13,21] most likely due to declining fine root biomass in less diverse communities [1]. Plant species have also been shown to differ in their degree of association with nutrient-rich earthworm surface casts leading to a higher growth of species more frequently associated with casts (e.g., graminoid species) than those less fre- quently associated with casts (e.g., herbaceous species; 19). These species-specific relationships between plants and casts together with the effects of earthworms on soil seedbank dynamics via seed transport [4,5,15,16], seed burial [2,4,14e16] and seed herbivory [6,12] are sug- gested to influence the structure and diversity of grass- land ecosystems. While earthworm activity in grassland * Corresponding author. Present address: Institute of Zoology, Uni- versity of Natural Resources and Applied Life Sciences Vienna, Gre- gor Mendel Strasse 33, A-1180 Vienna, Austria. Fax: þ43 1 47654 3203. E-mail address: johann.zaller@boku.ac.at (J.G. Zaller). 1164-5563/$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ejsobi.2007.08.010 Available online at www.sciencedirect.com European Journal of Soil Biology 43 (2007) S86eS91 http://www.elsevier.com/locate/ejsobi