Nematode communities in pine forests are shaped by environmental filtering of habitat conditions

Soil nematodes are involved in nutrient cycles through feeding on microorganisms, and the extent of their functioning is affected by subtle environmental changes and by biological interactions. Considering these features, soil nematodes can serve as bio-indicators reflecting environmental changes in a given ecosystem. However, the mechanism of shaping community structures of nematodes is not well understood due to the complex biological interactions in forest ecosystems. The aim of this study was to clarify the nematode communities and their determinant factors in both coastal and inland Pinus thunbergii forests of central Japan under contrasting environmental conditions. For this purpose, nematodes retrieved from soil samples were morphologically identified at generic levels and discriminated into trophic groups. We also determined whether nematode community structures varied with coastal or inland locations based on non-metric multidimensional scaling. Our results showed that generic richness of nematode at inland habitats (16.2 ± 0.7, mean ± SE) was significantly greater than that at coastal habitats (12.4 ± 0.4). Moreover, the non-metric multidimensional scaling scatter-plot showed nematode communities clustered significantly within their respective coastal and inland habitats. These clusterings were further significantly influenced by surrounding environmental factors; soil water content, soil temperature, litter layer thickness, pH, total both N and C concentrations and C:N ratio. For characteristic trophic groups, microbial-feeding nematodes were represented in coastal forests while predaceous ones were dominated in inland forests. Our study provided fundamental knowledge on the formation of nematode community structures that were shaped by environmental filtering.