Earthworms regulate the nematode community by directly enhancing the bacterial-based energy channel rather than through the effect of casts

Abstract

Earthworms and their casts act as biocatalysts and regulators of the biotic and abiotic processes in soil ecosystems. However, the relative importance of the presence of earthworms and earthworm casts in affecting other soil biota remains underexplored. In this study, we conducted a manipulative mesocosm experiment in a 30-year-old subtropical broadleaved plantation forest to determine how epi-endogeic earthworms (Amynthas corticis) and their casts affect soil nematode communities individually and additively. We found that the addition of the epi-endogeic earthworms significantly increased the proportion of the Ba1 guild nematodes and enhanced the enrichment index of the soil nematode community, but decreased the channel index. These results indicate that the soils become enriched in nutrients with a higher activity in bacterial-based decomposition pathways in the presence of earthworms. However, cast addition alone had a minor effect on soil nematodes. Results of a redundancy analysis suggest that elevated contents of soil ammonium and available phosphorous were the major influencing factors on soil nematode abundances in the presence of epi-endogeic earthworms. Our results indicate that epi-endogeic earthworms rather than through their casts contributed to the structuring of the nematode communities and enhancing of the bacterial-based energy channel. This finding contributes to our understanding of soil biodiversity maintenance mechanisms and how the relationship of the soil biota affects their functions in soil food webs.