Initial melanin and nitrogen concentrations control the decomposition of ectomycorrhizal fungal litter

Forest biogeochemical cycling is strongly influenced by the turnover of ectomycorrhizal fungal tissues. Fungal tissues may decompose differently from plant tissues due to their unique chemistry and may be important to understanding ecosystem carbon and nutrient cycles. Melanin is a recalcitrant, complex cell wall polymer commonly found in fungi. Melanin concentration varies significantly among species, which may contribute to the wide variation in their rates of decomposition previously observed. In a comparative experiment we examined decomposition of ectomycorrhizal fungi of varying melanin concentrations. In an additional experiment we examined the effect of melanin biosynthesis inhibition on decomposition of the highly melanized ectomycorrhizal fungus Cenococcum geophilum. Among species, initial melanin concentration was negatively correlated with decomposition while initial nitrogen concentration was positively correlated with decomposition. When melanin synthesis was inhibited, tissues of C.geophilum decomposed significantly faster. We conclude that melanin and nitrogen concentrations may control decomposition of ectomycorrhizal fungi as do lignin and nitrogen concentrations in plant material, and thus may have significant consequences for terrestrial carbon and nutrient cycling.