Soil grit influences the effects of earthworms (Lumbricus terrestris) on seed damage

Ingested soil grit is thought to enhance the grinding action of the earthworm gizzard but its role in earthworm -seed interactions is unknown. This study used feeding trials to investigate how different levels of supplemental soil grit (+0 %, +25 %, and +50 % sand additions by weight) influenced the impacts of the cosmopolitan anecic earthworm Lumbricus terrestris L. on seed ingestion, egestion, seed coat damage, and germination of garlic mustard (Alliaria petiolata). Added grit increased the amount of seed coat damage on garlic mustard seeds egested by L. terrestris. Earthworm egestion also increased the speed of garlic mustard germination (similar to 20 days control, similar to 14 days with L. terrestris and +0 % grit, similar to 11 days with L. terrestris and +25-50 % grit). The results demonstrate how earthworm ingestion and soil grit can modify the impacts of earthworms on seeds and highlight the importance of considering soil texture in field and laboratory earthworm experiments.