TENTATIVE APPROACH TO THE MOLECULAR-STRUCTURE OF HUMIC ACIDS - SPECTRAL EVIDENCE FOR A DERIVATION OF HUMIC ACIDS FROM PLANT-BORNE ESTERS .2. INFRARED AND CHEMICAL-ANALYSES

Two questions are important in the theoretical approach to the problem of the origin of humid acids: what chemical arrangement underlies the molecular structure of the humic acids and from what substances do they originate? The discussion of humic acid formation has frequently been based on the view that all substances in fallen leaves are available to the microbes and that the humic acids originate from the waste products produced during and after this consumption. The secondary metabolism of the higher plants gives rise to products in the form of monomers which are directly polymerized into humic acids, as suggested by Bruckert and Jacquin (1971). In the secondary metabolism of microbes, there is an analogous formation of these acids via the mineralization of the assimilable substances (carbohydrates, proteins, etc.) in the litter. The following hypotheses were formulated: humic acids are polyesters; humic acids originate as monomers in the secondary metabolism of both higher and lower plants; humic acids are formed in an acid environment (including high-moor peat); the formation of humic acids is promoted by desiccation, particularly under alkaline conditions; humic acids show ketoenol tautomerism; humic acids can form semiquinones and stable radicals; and humic acids derive their color from these radicals.