Effects of tree species identity and soil origin on soil nematode communities and trophic composition in coniferous and broad-leaved forests

The effects of trees on soil nematode communities are related to nutrient cycles in forest ecosystems. We conducted greenhouse pot experiments to determine the effects of a single tree species for each of coniferous and broad-leaved tree on soil nematodes.

Soils were collected from a coniferous plantation and broad-leaved forests. Seedlings of a coniferous tree (Cryptomeria japonica) and a broad-leaved tree (Quercus serrata) were planted in soils derived from each species. After 11 months, seedling biomass, soil properties, and ectomycorrhizal fungal colonization of Q. serrata were measured. Soil nematodes were morphologically identified to the genus/family level and differentiated by community and trophic composition.

C. japonica root biomass was significantly higher than that of Q. serrata regardless of the soil and nematode community structures were significantly different between the species. The fungal: bacterial ratio and density of fungivorous nematodes were significantly higher in broad-leaved soils. Herbivorous nematodes increased significantly in C. japonica seedlings grown in broad-leaved soils. Structural equation modeling indicated that soil origin and tree species directly regulated nematode trophic compositions.

Our findings suggest that tree species modify soil micro-food webs by affecting microbial abundance and nematode trophic composition. Specifically, C. japonica, with a larger root biomass, increased the number of herbivorous nematodes, whereas Q. serrata, with ectomycorrhizal fungal symbiosis, increased the number of fungivorous nematodes. Thus, tree species are tightly involved in shaping nematode communities in forest ecosystems through root traits and mycorrhizal types.