oa Non-Pyrogenic Pathways for Black Carbon and Nitrogen in Soils

This study identifies a nonpyrogenic pathway for the formation of black carbon (BC) and black nitrogen (BN) in soils through ambient iron driven oxidation. By examining pine wood weathered for 12 years in contact with iron nails, we simulated natural Fenton-like conditions that produced condensed aromatic carbon (ConAC) and nitrogen (ConAN) compounds without fire. High resolution spectroscopy and mass spectrometry revealed increasing aromaticity and molecular condensation with oxidation, and up to 18 wt% ConAC in the most altered samples, chemically resembling wildfire derived BC. Atmospheric and rain derived nitrogen was abiotically incorporated into organic matter, forming lignin-N complexes and pyrrolic nitrogen structures. These findings challenge the assumption that BC and BN are exclusively fire derived and suggest that nonpyrogenic pathways could contribute significantly, up to 1.3 Pg C yr-1, to global BC pools. This overlooked mechanism has major implications for carbon and nitrogen accounting in Earth system models.