The Detrital Input and Removal Treatment (DIRT) experiments were originally established to evaluate the relative contributions of aboveground plant litter and belowground root inputs to soil organic matter (SOM) formation. As our understanding has evolved to recognize microbes as a primary source of the stability and complexity of SOM, these original objectives can be reframed around microbial processing of these two plant carbon pools. Here, we evaluate the influence of root and leaf litter removal treatments on fungal community composition and we identify correlations with soil carbon. We sampled four litter and root manipulation treatments (control, litter removal, root removal, and litter + root removal) within a DIRT experiment at the University of Michigan Biological Station (Pellston, MI, USA). Mineral soil samples were collected from the A horizon and fungal communities were characterized by ITS2 metabarcoding. Soils were further analyzed for fungal biomass (ergosterol) and total C (%).
Results/Conclusions
Fungal biomass declined by 61% under root removal, but was unaffected by litter removal (Roots: P = 0.003; Litter: P = 0.08; RxL: P = 0.94; two-way ANOVA). Similarly, fungal community composition was significantly altered by root removal, while the effect of litter removal was only marginally significant (Roots: P = 0.004; Litter: P = 0.07; RxL: P = 0.84; PerMANOVA). Differences in fungal community composition between root manipulation treatments (roots vs. no roots) were characterized by variation in the relative abundance of basidiomycetes and ascomycetes, the majority of which were ectomycorrhizal or had unknown ecology (SIMPER, ISA). In contrast, litter treatments (litter vs. no litter) were associated with variation in the abundance of ascomycetes and mucoromycetes, which were predominantly saprotrophic or of unknown ecology. Fungal biomass was strongly positively correlated with soil carbon (P = 0.002; R2 = 0.62), and higher soil carbon was associated with treatments where roots were present. Our results suggest that root inputs and litter inputs differentially influence fungal community composition, and that overall, belowground inputs from roots may play a larger role in structuring fungal communities and ultimately soil organic matter dynamics.