Dilute permanganate oxidizes organic functional groups typically associated with polyphenolic compounds

An attempt was made to resolve the apparent contradiction between molecular properties of permanganate oxidizable carbon (PoxC) as measured according to the Weil et al. 2003 protocol and its empirical relationship with many soil functions. While PoxC measured with dilute permanganate has been demonstrated to be a strong indicator for some beneficial properties of soil organic matter, its chemistry as demonstrated by Christy et al. 2021 and others (Tirol-Padre et al., 2004) clearly disagrees with traditional perceptions of the molecular nature of so called "active carbon." The major groups of biomolecules (Carbohydrates, lignin, lipids, proteinaceous compounds) were screened for the prevalence and abundance of the functional groups identified as being particularly responsive to permanganate oxidation and tested for their reactivity. Corroborating the results presented by Christy et al. 2021, we found that high permanganate reactivity is a specific property of polyphenolic compounds. Our findings suggest that the POXC method of Weil et al (2003) is particularly sensitive to the presence of polyphenols. These molecules are frequently aromatic and hence do not fall into the traditional bracket of "labile" or "active" carbon. However, polyphenols have abundant beneficial functions in soil ecosystems. They are, for instance, involved in nitrogen cycling, disease suppression and in the stimulation of extracellular enzyme activities. This leads us to conclude that PoxC is indeed a promising indicator of soil health. The realization that PoxC targets polyphenolic carbon hence provides an answer to the question posed by Wade et al 2020: What molecular fraction of soil C does the permanganate actually oxidize? and, at the same time, explains why there are abundant correlations between PoxC data and soil health indicators as well as the sensitivity of PoxC to changes in management practices.