Peatland forests, which cover vast areas of northern North America and Eurasia, represent globally important carbon sinks as well as significant sources of both timber and wildlife habitat. Despite decades of research on the vegetational structure of forested bogs and fens, comparatively little is known about the belowground structure and composition of mycorrhizal fungal communities in these habitats. To characterize these root-associated communities, we sampled roots of two dominant tree species (Picea mariana and Larix laricina) and a dominant ericaceous shrub (Ledum groenlandicum) at six locations in northern and central Minnesota. We coupled the field sampling with a greenhouse study in which the composition of these plant hosts was experimentally manipulated to further examine host-related effects on mycorrhizal diversity and composition. For both experiments, the mycorrhizal fungal communities were identified using Illumina Miseq high-throughput sequencing of the ITS1 barcoding region.
Results/Conclusions
When analyzing the mycorrhizal guilds in aggregate, there was no significant difference in OTU richness by habitat or host. However, individual guilds had notably contrasting responses to both factors; ectomycorrhizal OTU richness significantly increased in fens, while ericoid and ericoid-ectomycorrhizal guild OTU richness was significantly higher in bogs. Similarly, ectomycorrhizal abundance was significantly higher on Larix and Picea roots, while ericoid abundance peaked on Ledum roots. Mycorrhizal community composition patterns also differed by guild, with fen and bogs having significantly different ectomycorrhizal communities, but statically similar ericoid communities. In the greenhouse experiment, OTU richness was comparable when all guilds were analyzed together across the various host pairing combinations. Richness for ectomycorrhizal fungi, however, tended to rise in the Larix + Picea treatment and was not negatively influenced by the presence of Ledum. Conversely, ericoid OTU richness and abundance declined significantly between the Ledum alone and other host pairing treatments. Collectively, these results indicate that the mycorrhizal fungal communities present in bogs and fens of the Minnesota northwoods do sort along known ecological gradients and that using a guild-based approach strongly facilitates accurate characterization of mycorrhizal fungal responses.