Estimation and decomposition pattern of the lignin component in forest humus layers

Lignin is one of the most abundant polymeric organic constituents of forest litter. Due to its molecular structure and heterogeneity the isolation of lignin in an unchanged form and its exact determination in forest humus have not proved possible. The oxidative degradation with CuO provides a specific method for the characterization of intact lignin structures in forest humus layers. The sum of phenolic CuO oxidation products gives an overall pattern of lignin decomposition. The degree of alteration of the remnant lignin is described by the acid-to-aldehyde ratio (Ac:Al) of syringyl and vanillyl units for angiosperm and gymnosperm lignin and the ratio of syringyl-to-vanillyl units (S:V) for angiosperm lignin. The lignin component of three different forest humus layers investigated was partly decomposed. The residual lignin fraction had undergone extensive modification during microbial decomposition. The chemical changes occurring in the lignin molecule during decomposition in forest humus layers suggest similar mechanisms of lignin degradation (“white-rot”) are shared by wood and forest litter.