Seasonal and annual variation in fungal communities associated with epigeic springtails (Collembola spp.) in boreal forests

Soil fauna mediate nutrient cycling through engineering physical properties and altering microbial communities in soil. Collembola is one of the most abundant groups of soil fauna, which regulates microbial communities by consumption and dispersal. The spatial structure of associations between Collembola and soil microbes have been described in several studies, but temporal variation of these associations remains unclear. Using high-throughput sequencing, we studied the fungal communities on Collembola (Entomobrya nivalis, Orchesella flavescens, Pogonognathellus longicornis) body surface, gut and their immediate habitat (topsoil samples) in four seasons across three years. The soil samples were characterized by fairly uniform relative abundance of saprotrophic and mycorrhizal fungi, whereas collembolans were associated mostly with saprotrophs. The structure of fungal communities from all substrate types exhibited comparable patterns of temporal distance decay of similarity. Unlike in soil, fungal richness and composition in Collembola body and gut samples exhibited seasonal and annual variation, with a significant interaction term, indicating low predictability. These results reflect spatial and temporal plasticity of the fungal communities associated with epigeic Collembola, indicating the high adaptability of collembolans to available conditions. We found that the Collembola associations with fungi (including diet) did not vary among the studied epigeic Collembola species. The detected high diversity of fungi associated with Collembola suggests that dispersal by arthropod vectors may represent a powerful alternative to aerial dispersal of fungal propagules.