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PECULIARITIES OF DECOMPOSITION OF ORGANIC SUBSTRATES OF DIFFERENT NATURE IN SOIL: IMPLICATION FOR ARCHAEOLOGICAL RECONSTRUCTIONS

T. E. Khomutova

Abstract

For reasoned reconstruction of initial presence of various organic substrates in the soil-ground material of archaeological sites, a model experiment was performed, where the dynamics of decomposition of organic substrates of protein, lipid and polysaccharide composition by soil microbial communities was studied. The experiment was carried out on gray forest soil under optimal conditions (60% WHC, 25oC). Soil samples were enriched by one of the substrates of protein (gelatin, casein, and sheep wool), lipid (sheep fat, sunflower oil) and polysaccharide (starch) nature, dried plant residues; control soil was without any substrate. The dynamics of decomposition of organic substrates was analyzed by measuring the respiratory activity of microbial communities and losses of organic carbon. Catabolic diversity of microbial communities was assessed by multi-substrate respiration testing using a spectrum of amino acids, carbohydrates, and sodium salts of carboxylic acids. The dynamics of the respiratory activity of microorganisms in the soils and the magnitude of organic carbon losses showed that the protein substrates were mineralized by microorganisms within first 3 months. In other variants of experiment the decomposition of substrates was less active. As a result of the succession of microbial communities during the experiment the ratio of carbon to nitrogen had changed from 20-40 to 6-11 in the lipid and polysaccharide variants that favored the substrates decomposition. Differences in functional diversity of microbial communities in the experiment were manifested in the intensity of respiratory response to introduction of a variety of low molecular compounds: the magnitude of the response of microbial communities to carbohydrates correlated with biomass, and that to amino acids was specific: 1.5 ? 2.7 times exceeding the control response was in variants with lipid and polysaccharide substrates, and very low one was in those with protein substrates. The ratio of the responses of microbial communities to carboxylic and amino acids seems to be promising for indicating of the initial presence of various organic materials in soil-ground archaeological material.

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