Dynamics of 13C natural abundance in wood decomposing fungi and their ecophysiological implications

Abstract

Factors that affect the δ 13C values of fungi need to be analyzed for the progress of isotope-based studies of food-chain or organic matter dynamics in soils. To analyze the factors that control δ 13C values of the fungal body, basidiomycete and ascomycete species were grown on a beechwood substrate (six species) and in glucose medium (nine species), and the δ 13C value of produced fungal body was compared to that of the carbon source. The 13C enrichment (Δ δ 13C) in the fungal aggregates compared to the decomposed wood varied from 1.2 to 6.3‰ among six species. In the glucose substrate experiment, the degree of 13C enrichment in the hyphal mat was relatively small and varied from −0.1 to 2.8‰ among nine basidiomycetes species depending on their growth stage. Calculated δ 13C values of the respired CO 2 were lower than those of the hyphal mat, organic metabolites and the glucose used. The degree of 13C enrichment was affected by fungal species, substrate and growth stage. Fungal internal metabolic processes are the plausible mechanism for the observed isotopic discrimination between fungal bodies and substrates. Especially, dark fixation of ambient CO 2 and kinetic isotope fractionation during assimilation and dissimilation reactions could well explain Δ δ 13C dynamics in our experiments. Through the analysis of field Δ δ 13C, we could know undisturbed fungal status about starvation, aeration and type of decomposition.