Earthworms (Lumbricus terrestris) affect plant seedling recruitment and microhabitat heterogeneity

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Abstract
Summary: The effects of the anecic earthwormLumbricus terrestrisL. on plant seedling recruitment and spatial aggregation were investigated in a microcosm glasshouse experiment by varying plant seed size (small and large); functional groups (grasses, legumes, herbs); plant species diversity (1, 3, 6); and plant functional group diversity (1, 3). Generally, earthworms buried seeds quickly irrespective of seed size and species. Secondary seed dispersal (phase II dispersal) by earthworms affected plant community composition depending mainly on seed size but less on plant functional group identity and diversity: small‐seeded species were repressed whereas large‐seeded were promoted. Although, in general, recruitment of seedlings was less in the presence ofL. terrestris, recruited seedlings benefited from establishing in the vicinity of earthworm burrows. The strong aggregation of plants in the vicinity of earthworm burrows resulted in plant communities with a more heterogeneous small‐scale architecture. Earthworm burrows and middens acted as an important regeneration niche for emergent seedlings by reducing microsite and nutrient limitations. In conclusion, seed dispersal, seed burial, seedling recruitment, and the spatial distribution of seedlings of plant species of different functional groups and with a wide range of seed size are strongly affected byL. terrestris, and this probably affects plant community composition.