The chemical quality of soil carbon (C) inputs is a major factor controlling litter decomposition and soil C dynamics. Mycorrhizal fungi constitute one of the dominant pools of soil microbial C, while their litter quality is understood poorly, leading to the major uncertainties in estimating soil C dynamics. For the first time, we examined chemical recalcitrance of arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungal species using fungal samples obtained from in vitro cultivation. We

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... that the chemical composition of AM and EM fungal mycelium differs significantly: EM fungi have higher concentrations of labile (water-soluble, ethanol-soluble) and recalcitrant (non-extractable) chemical components, while AM fungi have higher concentrations of acid-hydrolysable components. Our results imply that differences in chemical decomposability traits among mycorrhizal fungal guilds represent a critically important driver of the soil C cycle, which could be as vital as is recognized for differences among aboveground plant litter.