Fig. 1: Experimental framework using a model polyphenol to interrogate soil microbial metabolism.

a Schematic summarizing the polyphenol lock paradigm^9,10, demonstrating the ways these compounds may control microbial carbon transformations in anoxic soils. The green solid line indicates that in anoxic soils, polyphenols promote the lock on dissolved organic carbon (DOC). The dotted-red lines show the three proposed mechanisms by which polyphenols restrict the activity of soil microorganisms to lock soil carbon, including (1) toxicity to microorganisms, (2) inhibiting microbial extracellular enzymes, and (3) binding and depriving microorganisms of nutrients. b A purified condensed tannin (CT) was selected as the model polyphenol in this study due to its inferred lack of microbial degradation in anoxic soils⁷. This model compound is well characterized chemically²¹ and has an average degree of polymerization of 16, where interflavan bonds (red arrow) connect monomers of epicatechin with a single catechin monomer cap. c The experimental design included soil reactors from three treatments (i) Biologically-active CT amended (dark purple), (ii) Biologically-active unamended control (green), and (iii) CT-amended autoclaved control (light purple). Autoclaved soils only included metabolite analyses, while microbially-active soils were analyzed with the suite of multi-omics approaches. The timepoints of each type of analysis are shown, with the total number (n) of samples across treatments denoted on the right in gray.