Fungi stabilize multi-kingdom community in a high elevation timberline ecosystem

Microbes dominate terrestrial ecosystems via their great species diversity and vital ecosystem functions, such as biogeochemical cycling and mycorrhizal symbiosis. Fungi and other organisms form diverse association networks. However, the roles of species belonging to different kingdoms in multi-kingdom community networks have remained largely elusive. In light of the integrative microbiome initiative, we inferred multiple-kingdom biotic associations from high elevation timberline soils using the SPIEC-EASI method. Biotic interactions among plants, nematodes, fungi, bacteria, and archaea were surveyed at the community and network levels. Compared to single-kingdom networks, multi-kingdom networks and their associations increased the within-kingdom and cross-kingdom edge numbers by 1012 and 10,772, respectively, as well as mean connectivity and negative edge proportion by 15.2 and 0.8%, respectively. Fungal involvement increased network stability (i.e., resistance to node loss) and connectivity, but reduced modularity, when compared with those in the single-kingdom networks of plants, nematodes, bacteria, and archaea. In the entire multi-kingdom network, fungal nodes were characterized by significantly higher degree and betweenness than bacteria. Fungi more often played the role of connector, linking different modules. Consistently, structural equation modeling and multiple regression on matrices corroborated the "bridge" role of fungi at the community level, linking plants and other soil biota. Overall, our findings suggest that fungi can stabilize the self-organization process of multi-kingdom networks. The findings facilitate the initiation and carrying out of multi-kingdom community studies in natural ecosystems to reveal the complex above- and belowground linkages.