Experimental climate change modifies degradative succession in boreal peatland fungal communities

Peatlands play an important role in global climate change through sequestration of atmospheric CO2. Changes in the structure of fungal communities in boreal peatlands that favor saprotrophic fungi caused by increased temperature and reduced soil water table under future climate change scenarios will subsequently impact carbon dynamics and nutrient cycling in these crucial ecosystems. In a mesocosm study, 100 intact peat monoliths, complete with above-ground Sphagnum and vascular vegetation, were subjected to three climate change variables (increased temperature, reduced water table, elevated CO2 concentrations) over 12 months in a factorial design to assess the impacts on peat-inhabiting fungi. Changes in fungal richness, diversity and community composition were assessed from decomposition litterbags using Illumina MiSeq sequencing of rDNA. Despite an overall negative effect of warming on fungal richness, Ascomycota generally benefited from increased temperature. However, both increased temperature and lowered water table position drove shifts in fungal community composition with a strong positive effect on root-associated fungi and saprotrophs. These shifts were observed during a predicted degradative succession in the decomposer community as different carbon substrates became available. Since fungi play a central role in peatland communities, reduced fungal richness accompanied by increased saprotrophic fungi under warming may increase decomposition rates under future climate scenarios, potentially aggravating the impacts of climate change.