Fungal Community Composition Better Explains Variation in Wood Decomposition than Fungal Biomass in a Northern Temperate Deciduous Forest

Abstract Despite growing scientific evidence of the important role that wood-decomposing fungi serve in ecosystem function, we know little about how fungal community dynamics relate to decomposition outcomes. We deployed 42 standardized (same dimensions and source) wood stakes from sugar maple ( Acer saccharum ) and white ash ( Fraxinus americana ) on the forest floor of a northern US hardwood forest. After four years, we collected the stakes for analysis of fungal biomass (via ergosterol), community composition (DNA sequencing), and nutrient concentrations. We found large variability in mass loss (9–95% for sugar maple, 4–36% for white ash), with sugar maple stakes showing much greater mass loss than white ash. Fungal community composition, summarized by PCoA axes, was a significant predictor of mass loss for both wood species, with fungal biomass explaining additional variability in some models. As expected, lower C/nutrient ratios (higher fraction of initial nutrient remaining, $$X/X_{0}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>X</mml:mi> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>X</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:mrow> </mml:math> ) were associated with greater mass loss. We found consistently stronger correlations of fungal community composition, compared to fungal biomass, with C/nutrient ratios in sugar maple stakes. White ash stakes showed consistent correlations of both fungal community composition and fungal biomass with C/nutrient ratios. Lastly, redundancy and cluster analyses showed that fungal communities clustered into taxonomically distinct groups that also corresponded to differences in mass loss. Together, our results suggest that communities with low biomass but efficient decomposers are associated with faster decomposition, while communities with high biomass but less efficient decomposers may not necessarily correlate with high mass loss. Our results suggest that wood decomposition and forest ecosystem models could be improved by including fungal community composition and total fungal biomass.