Comparison of nematode communities in anecic earthworm casts and adjacent soil reveal a land use-independent trophic group signature

By ingesting soil and organic matter in different soil horizons and depositing casts on soil surface, anecic earthworms have large influence on soil ecological processes. However, we still have a limited understanding of the consequences of earthworm casting activity on nematode communities, and the role played by the land use in this relationship. Therefore, the main objective of this study was to compare the effect of the anecic earthworm Amynthas adexilis (Thai, 1984) on the structure of nematode communities, in a woodland and meadow presenting different soil organic C content in northern Vietnam. Nematode population and physico-chemical properties of casts produced by the anecic earthworm A. adexilis and adjacent soil presenting no recent earthworm activity (0–10 cm deep) were characterized. A. adexilis incorporated organic matter into its casts compared to the adjacent bulk top soil horizon, reflected by a significant increase of the organic carbon and nitrogen contents (1.4 times more in the meadow and 1.8 times more in the woodland). Earthworm casts contained 2.6 and 1.7 times more nematodes than the adjacent top soil, in meadow and woodland, respectively. The effect of earthworm casting activity on nematode community structure was similar in both land uses. Compared to the soil, casts were significantly enriched in all trophic groups (between 1.9 and 11.6 times more in casts in the meadow, and between 1.6 and 23.7 times more in casts in the woodland, depending on the trophic group), except for obligate plant feeders that were under-represented (1.4 times less in casts for both land uses). The plant parasitic index decreased in the casts compared to the soil, indicating an environment less favourable for plant parasitic nematodes.