The effect of earthworms and snails in a simple plant community.

Snails and earthworms affected the dynamics of a simple, three-species plant community, in the Ecotron controlled environment facility. Earthworms enhanced the establishment, growth and cover of the legume Trifolium dubium, both via the soil and interactions with other plant species. Worms increased soil phosphates, increased root nodulation in T. dubium, and enabled T. dubium seedlings to establish in the presence of grass (Poa annua) litter, by increasing soil heterogeneity. Worms also buried the seeds of Poa annua and Senecio vulgaris, reducing the germination of new seedlings. Snails reduced nitrogen-fixing Trifolium dubium and increased cover of plant litter, thereby reducing ammonia-nitrogen concentrations in the soil. These effects and their interactions demonstrate that the detritivore food chain, and earthworms in particular, cannot be ignored if we are to understand the spatial and temporal dynamics of plant communities.