ИСТИНА

A characteristic feature of lignin structures are their tendency to condensation reactions, which can lead to the formation of new stable C-C bonds. This lignin property with its high resistance to degradation divide it from other natural polymers and largely determines its action in biochemical processes, including the formation of humic acids. Lignin, perfoming protection function in plants, must provide different effects on the properties of humic substances, which are defined by phylogenetic origin of plants. Therefore humus substances have a different protection effect in different ecological conditions. The determination of lignin in plants, soils and humus acids involved the alkaline oxidation with copper oxide at 1700 C under pressure in nitrogen environment. 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 [1]. 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 lignin phenols and 13C-NMR spectroscopy proved that the lignin in higher plants was involved in the formation of specific compounds of soil humus, including aliphatic (peaks at 56 ppm) and aromatic ( peaks at 147 ppm) molecular fragments. In the humus acids of Greyzems Haplic and alpine Leptosols Umbric the peak areas of lignin structures are mostly in the aliphatic part of 13C-NMR spectrum. Correlation between the lignin content (VSC) in the humus horizons of humid landscapes soils and peak area of the lignin origin at 56 ppm is about 0,94 (P=0,95). In the humic acids of Chernozems, the contribution of aromatic lignin fragments to the nuclear part of the molecule is double that in the peripheral part of the molecule. In the buried horizons, the peak areas of lignin compounds in the nuclear fragments of humic acid molecules are larger than their halos for humic acids of the surface horizons by 5 times. The peak areas of lignin structures in the aromatic and aliphatic fragments are similar for the humic acids from Fe-Mn concretions and Gleysols Mollic of accumulation landscape positions. Comparison of 13C-NMR spectra of native lignin preparations, isolated from different species of tree and herbaceous plants, with a spectrum of humic acid diagnosed that, the number of peaks at 102, 115, 119, 131, 152, 166 ppm also have a lignin genesis. Secondly, heterogeneous set of peaks in the spectra of different plants and, consequently, in the molecules of humic acids of different soils, must also be different. Thirdly, lignin of southern taiga trees is the source of more advanced in space molecules of humic acid with developed aliphatic part. Cinnamilic phenols from steppe plants form a spatially compact structure of Chernozem humic acids. That is way, in Chernozem and Krasnozem, as in soils with high biochemical activity the more possible pathway of humifiation is the deep and quick fermentative degradation of high-molecular compounds to monomers. The role of humic acids abiotic condensation from simple free monomers is more considerable in lowlands hydromorphic conditions and in high mountain soils, where microbial activity is more lower and ferment amounts is also low. High-molecule compounds preserve and gradually change into humic acids by the way of biopolymer degradation. Thus the total production and composition of lignin fragments in humic acids reflects the proprieties of plant souse of lignin and biochemical conditions of humification.