A method quantifying soil melanin to understand fungal impacts on soil carbon stability

Fungal necromass, particularly dead microbial cells rich in melanin, is an important contributor to long-term soil carbon stabilization. Progress in understanding the role of soil melanin is limited by the lack of validated analytical methods. DNA-based approaches estimate only the genetic potential for melanin production and therefore provide indirect evidence of melanin occurrence. To directly assess soil melanin, we evaluated spectroscopic and spectrophotometric assays; however, both approaches proved insufficiently specific due to interference from chemically related compounds. Here, we introduce a liquid chromatography method that enables quantification of major fungal melanin types in soils. By enabling direct quantification of fungal melanin in soil, this framework allows longstanding hypotheses regarding melanized fungal necromass and soil carbon stabilization to be tested mechanistically. Here, we show with the proposed method that soil melanin concentrations are strongly correlated with total soil carbon, supporting a central role for fungal melanin in long-term soil carbon stabilization.