Fig. 5: Lignin structure and aromatic compound concentrations in Epsilon pool sediment incubations.

A 2D HSQC NMR spectra of initial lignin substrates showing bond types and proportions. Values for bond types and syringyl (S) and guaiacyl (G) subunits (13C NMR) are normalized per 100 aromatic units. Examples of each bond type are provided (1–3). B CO2 evolution in incubation vial headspace. Total CO2 compared with no exogenous carbon (NC) controls at 168 h using Student’s t test. C Concentrations of five monoaromatic compounds in triplicate incubations over 168 h during incubation experiments. Bars representing lignin-derived aromatic oligomers scaled to percent of max peak area. 26DMBQ 2,6-dimethoxy-1,4-benzoquinone, VAN vanillin.