Investigating the roles of melanin and soil mineralogy in fungal derived SOM formation: 16S

Soil fungi function as both decomposers and synthesizers of soil organic matter (SOM). Despite being identified as a major source of persistent soil organic carbon (C) and nitrogen (N), we have a limited understanding of the factors that control the accumulation of fungal necromass C and N in soils. To test the hypothesis that melanin influences the persistence of fungal necromass in soils, we generated dual-labeled 13C and 15N fungal necromass of high and low melanin phenotypes of Hyaloscypha bicolor and tracked the fate of necromass derived C and N into mineral-bound SOM. We then decayed these two necromass types in forest soils differing in their physicochemical properties to compare the importance of intrinsic necromass properties versus extrinsic soil properties for predicting C and N persistence. We hypothesized that mineralogy, specifically the abundance of amorphous or poorly crystalline iron oxides (Feo), would increase the accumulation of fungal derived C & N in SOM. We found that high melanin necromass contributed more to soil C, while low melanin necromass contributed more to soil N formation. Further, we found that Feo concentrations were positively correlated with the amount of fungal derived C in SOM, but that the relationship was only significant for low melanin necromass. Collectively, these findings highlight the importance of amorphous mineral surfaces as accumulators of fungal derived C as well as the potential for fungal melanin to mediate necromass-mineral interactions.