Forest types matter for the community and co-occurrence network patterns of soil bacteria, fungi, and nematodes

Tree growth influences the biological, physical, and chemical properties of the soil through the input of different types of litter and various root exudates. However, our understanding of tree-mediated effects on the composition and diversity of soil biota remains limited. This study aimed to determine the effects of physically neighboring forest types (i.e., an artificial Japanese cedar (Cryptomeria japonica) plantation vs. a broadleaf (Quercus serrata) secondary forest) on individual bacterial, fungal, and nematode communities and the associations among these inter-kingdoms. Bacterial, fungal, and nematode aggregates were estimated using MiSeq high-throughput sequencing system. The amplicon sequence variant richness of fungi and nematodes was significantly greater in the cedar plantation than in the broadleaf forest, and the three soil biota community structures were significantly clustered among the forest types. Environmental factors such as soil pH, C, N, and C/N ratio significantly influenced the three soil biota community structures. The bacterial–fungal–nematode co-occurrence network of the broadleaf forest had more nodes and edges than that of the cedar plantation. Moreover, Ascomycota and Basidiomycota fungi mainly co-occurred with fungivorous nematodes in the cedar and broadleaf forests, respectively. Our results suggested that unique soil biota communities and characteristic co-occurrence network patterns were established among the tripartite inter-kingdom relationships between adjacent forest types.