Transformation of lignin in surface and buried soils of mountainous landscapes

Abstract

The content and composition of the lignin phenols in plants and soils of vertical natural zones were studied in the Northern
Caucasus region and Northwestern Tien Shan. Three types of lignin transformation were revealed: steppe, forest, and meadow
ones. It was shown that the degree of oxidation of the biopolymer during the transformation of organic matter increased when
going from the living plant tissues to humic acids in surface and buried soils. The portion of lignin fragments remained unchanged
during the biopolymer transformation in the following series: plant tissues-falloff-litter-soil-humic acids-buried humic acids.
It was also shown that the biochemical composition of the plants had a decisive effect on the structure of the humic acids
in the soils. The quantitative analysis of the lignin phenols and the 13C NMR spectroscopy proved that the lignin in higher plants was involved in the formation of specific compounds of soil humus,
including aliphatic and aromatic molecular fragments. The first analysis of the lignin content and composition in buried soils
of different ages was performed, and an increase in the degree of oxidation of the lignin structures was revealed in the soil
chronoseries. It was proposed to use the proportions of lignin phenols in surface and buried soils as diagnostic criteria
of the vegetation types in different epochs.