Above- and belowground communities in boreal forests are tightly linked along common ecological gradients

Abstract Aims Fungal communities in boreal forest soils are highly diverse, both taxonomically and functionally, with the majority of fungi associated with living or dead plants as saprotrophs, pathogens or mycorrhizal symbionts. The aim of this study was to examine to what extent soil fungal communities are structured by the above-ground vegetation versus topographic and edaphic factors. Methods We take advantage of a vegetation survey in which plant communities have been monitored in plots located along topographic and edaphic gradients in a boreal forest area in southern Norway, spanning from mesic spruce forests to xeric pine forests. To survey the corresponding fungal communities, we applied DNA metabarcoding of soil samples collected from the same permanent plots. Results The fungal soil communities exhibited a strong structure along the same edaphic and topographic gradients as the vegetation. Plant community composition explained most of the variation in fungal community composition followed by edaphic factors and topography. The xeric pine forest was characterized by high CN ratios, ericoid vegetation, and a correspondingly higher abundance of Ascomycota, many of which form ericoid mycorrhizae or are root-associated. The submesic spruce forest was characterized by higher pH, lower CN ratios, diverse understory vegetation and high abundance of ectomycorrhizal and white-rot litter decomposer Basidiomycota. Conclusions The gradient from mesic spruce- to xeric pine-dominated forest is ubiquitous in boreal forests, and we here show a strong link between composition of vegetation and fungal communities, highlighting long-term effects influencing both plant and fungal communities in similar and predictable ways.