Effects of crop species richness on the community of soil nematodes in an experimental agro-ecosystem

• Crop species diversity did not affect the abundance and community structures of soil nematodes.
• Trophic group abundance and community compositions of soil nematodes were changed by crop biomass.
• The variations in soil nematodes largely attributed to crop biomass.

Biodiversity losses in terrestrial ecosystems may negatively affect the functioning of underground ecosystems, especially in trophic interaction networks. These effects have mainly been found in grassland ecosystems. The responses of underground agro-ecosystems to biodiversity loss are largely unknown. Here, the relationships between crop species diversity and the abundance, diversity and functional indices of soil nematodes were examined in a 4-yr field experiment across five crop species richness levels (1, 2, 4, 8, and 16). The relationships between crop biomass and nematode abundance or ecological indices were also tested. Crop species richness had no significant effects on either total abundance nematode, nematode abundance within each trophic group, or nematode ecological indices. However, the plant parasitic nematodes, Psilenchus and Partylenchus, significantly differed among crop species diversity. Crop biomass significantly increased the abundances of total nematodes, plant parasites and omnivores/predators, and decreased that of fungivores. Furthermore, the responses of PPI (Maturity index of plant-parasitic nematode), EI (Enrichment index), and SI (Structure index) to crop biomass were positive, although CI (Channel index) was negatively affected. Redundancy analysis (RDA) further showed that crop species diversity and crop biomass account for 0.7% and 1.9% of the variation in nematode abundance, respectively. Our results clearly indicate that soil nematode abundance and community composition was more affected by crop biomass than by crop species diversity in agricultural systems.