Experimental warming alters potential function of the fungal community in boreal forest.

Fungal community composition often shifts in response to warmer temperatures, which might influence decomposition of recalcitrant carbon (C). We hypothesized that evolutionary trade-offs would enable recalcitrant C-using taxa to respond more positively to warming than would labile C-using taxa. Accordingly, we performed a warming experiment in an Alaskan boreal forest and examined changes in the prevalence of fungal taxa. In a complementary field trial, we characterized the ability of fungal taxa to use labile C (glucose), intermediate C (hemicellulose or cellulose), or recalcitrant C (lignin). We also assigned taxa to functional groups (e.g., free-living filamentous fungi, ectomycorrhizal fungi, and yeasts) based on taxonomic identity. We found that response to warming varied most among taxa at the order level, compared to other taxonomic ranks. Among orders, ability to use lignin was significantly related to increases in prevalence in response to warming. However, the relationship was weak, given that lignin use explained only 9% of the variability in warming responses. Functional groups also differed in warming responses. Specifically, free-living filamentous fungi and ectomycorrhizal fungi responded positively to warming, on average, but yeasts responded negatively. Overall, warming-induced shifts in fungal communities might be accompanied by an increased ability to break down recalcitrant C. This change in potential function may reduce soil C storage under global warming.