Life after death: Lignin-humic relationships reexamined

In the last decade, application of modern degradative and nondegradative analysis techniques to both lignin of living plants and humic substances of soil has demonstrated characteristic similarities in the structures of these two types of natural polymers. Recognition of the similarities resulted in a revival of an earlier hypothesis concerning the genesis of soil organic matter from the aromatic parts of wood and nonwoody plants. The hypothesis assumes functionalization and restructuring but not complete depolymerization of lignin during its biotransformation into humic and fulvic acids in the environment. The biotransformation process results in the preservation of certain structural features during the humification of dead plants. A genetic approach is useful in the analyses of structure, morphology, and chemical reactivity of humic substances.