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The composition of stable carbon isotopes in plants, plant litter, leaf litter, and soil organic matter was studied experimentally in the western part of the northern foothills of the Caucasus and mountainsides. It was found that the changes in carbon isotope composition depending on the vertical zonation do not exceed 8 per thousand and depend on the type of C3 plant communities, its presence in biogeocenosis components (living matter, plant litter, soil organic matter), and the degree of moistening of the plot studied.

Microbiological, biogeochemical, and isotopic geochemical investigation of Lake Kislo-Sladkoe (Polusolenoe in early publications) at the Kandalaksha Bay shore (White Sea) was carried out in September 2010. Lake Kislo-Sladkoe was formed in the mid-1900s out of a sea gulf due to a coastal heave. At the time of investigation, the surface layer was saturated with oxygen, while near-bottom water contained sulfide (up to 32 mg/L). Total number of microorganisms was high (12.3 x 10(6) cells/mL on average). Light CO2 fixation exhibited two pronounced peaks. In the oxic zone, the highest rates of photosynthesis were detected at 1.0 and 2.0 m. The second, more pronounced peak of light CO2 fixation was associated with activity of anoxygenic phototrophic bacteria in the anoxic layer at the depth of 2.9 m (413 μg C L(-1) day(-1)). Green-colored green sulfur bacteria (GSB) predominated in the upper anoxic layer (2.7-2.9 m), their numbers being as high as 1.12 x 10(4) cells/mL, while brown-colored GSB predominated in the lower horizons. The rates of both sulfate reduction and methanogenesis peaked in the 2.9 m horizon (1690 μg S L(-1) day(-1) and 2.9 μL CH4 L(-1) day(-1)). The isotopic composition of dissolved methane from the near-bottom water layer (δ13C (CH4) = -87.76 per thousand) was significantly lighter than in the upper horizons (δ13C (CH4) = -77.95 per thousand). The most isotopically heavy methane (δ13C (CH4) = -72.61 per thousand) was retrieved from the depth of 2.9 m. The rate of methane oxidation peaked in the same horizon. As a result of these reactions, organic matter (OM) carbon of the 2.9 m horizon became lighter (-36.36 per thousand), while carbonate carbon became heavier (-7.56 per thousand). Thus, our results demonstrated that Lake Kislo-Sladkoe is a stratified meromictic lake with active microbial cycles of carbon and sulfur. Suspended matter in the water column was mostly of autochthonous origin. Anoxygenic photosynthesis coupled to utilization of reduced sulfur compounds contributed significantly to OM production.

At ten stations of the meridian profile in the eastern Kara Sea from the Yenisei estuary through the shallow shelf and further through the St. Anna trough, total microbial numbers (TMN) determined by direct counting, total activity of the microbial community determined by dark CO2 assimilation (DCA), and the carbon isotopic composition of organic matter in suspension and upper sediment horizons (δ13C, per thousand) were investigated. Three horizons were studied in detail: (1) the near-bottom water layer (20-30 cm above the sediment); (2) the uppermost, strongly hydrated sediment horizon, further termed warp (5-10 mm); and (3) the upper sediment horizon (1-5 cm). Due to decrease in the amount of isotopically light carbon of terrigenous origin with increasing distance from the Yenisei estuary, the TMN and DCA values decreased, and the δ13C changed gradually from -29.7 to -23.9 per thousand. At most stations, a noticeable decrease in TMN and DCA values with depth was observed in the water column, while the carbon isotopic composition of suspended organic matter did not change significantly. Considerable changes of all parameters were detected in the interface zone: TMN and DCA increased in the sediments compared to their values in near-bottom water, while the 13C content increased significantly, with δ13C of organic matter in the sediments being at some stations 3.5- 4.0 per thousand higher than in the near-bottom water. Due to insufficient illumination in the near-bottom zone, newly formed isotopically heavy organic matter (δ13C(-) -20 per thousand) could not be formed by photosynthesis, active growth of chemoautotrophic microorganisms in this zone is suggested, which may use reduced sulfur, nitrogen, and carbon compounds diffusing from anaerobic sediments. High DCA values for the interface zone samples confirm this hypothesis. Moreover, neutrophilic sulfur-oxidizing bacteria were retrieved from the samples of this zone.

The hydrocarbon-oxidizing potential of soil microbiota and hydrocarbon-oxidizing microorganisms introduced into soil was studied based on the quantitative and isotopic characteristics of carbon in products formed in microbial degradation of oil hydrocarbons. Comparison of CO2 production rates in native soil and that polluted with crude oil showed the intensity of microbial mineralization of soil organic matter (SOM) in the presence of oil hydrocarbons to be higher as compared with non-polluted soil, that is, revealed a priming effect ofoil. The amount of carbon of newly synthesized organic products (cell biomass and exometabolites) due to consumed petroleum was shown to significantly exceed that of SOM consumed for production of CO2. The result of microbial processes in oil-polluted soil was found to be a potent release of carbon dioxide to the atmosphere.

Six male volunteers for dry immersion (DI) modeling the microgravity effects on human organism were subjects in the GI evacuatory function investigation. The investigation was aimed to evaluate liquid food evacuation from the stomach (13C-acetate test) and time of chymus orocecal transit (H2-inulin test). The 13C-acetate test did not reveal changes in stomach evacuatory activity after 4 days in DI. The H2-inulin test demonstrated shortening of chymus transit along the small intestine and extension of chymus passage from the ileum to cecum. Subsequent reduction of inulin metabolism in the large intestine suggested inhibited passage of these GI segments. The results showed that stability of liquid evacuation from the stomach and acceleration of chymus transit along the small intestine hinder evacuation of the large intestine content which is the primary cause for inhibition of GI evacuatory activity in DI.

The stable isotope abundance of carbon in the lichens Cladina mitis, Cladonia crispata Hypogymnia physodes, Parmelia sulcata has been investigated in a study relating these values with known levels of 106Ru, 134Cs, 137Cs and 144Ce defined activity in their thalli in the pine forests of region within a 30-km radius of the Chernobyl atomic power station and beyond it (37 km). All 63 samples of the lichens were obtained from 7 different sites. Small effects on delta 13C values in the lichens Cladina mitis, Hypogymnia physodes were found to be associated with distance from CNPP, activity level of radionuclides in them thalli whereas at Cladonia crispata is observed weighting of carbon with increase in values of 134Cs and 137Cs activity in thalli. Values of delta 13C the investigated lichen species more depends on habitat conditions rather than from levels of thalli radioactivity. In our study we didn't reveal the isotope specificity of any one species as it was not possible to establish a correlation between values of delta 13C and a particular species.

Mass-spectrometric investigation of carbon isotope composition (delta13C) was carried out for suspended organic matter and dissolved mineral compounds for the water column of some meromictic water bodies differing in salinity and trophic state. As a rule, a more pronounced carbon isotope fractionation (resulting from the metabolism of phytoplankton and anoxygenic phototrophic bacteria) was revealed in the zones of enhanced oxygenic and anoxygenic photosynthesis. Carbon isotope fractionation at the border between oxidized and reduced waters depends both on the activity of microbial communities and on the dominant species of phototrophic microorganisms. Analysis of the distribution profiles of the isotopic composition of suspended organic matter and dissolved mineral carbon revealed active mineralization of the organic matter newly formed via anoxygenic photosynthesis in the monimolimnion by microbial communities, resulting in the release of isotopically light carbon dioxide. Mineral carbon in the anaerobic zones of highly productive meromictic water bodies is therefore enriched with the light 12C isotope.

Comprehensive microbiological and biogeochemical investigation of a pockmark within one of the sites of gas-saturated sediments in the Gdansk depression, Baltic Sea was carried out during the 87th voyage of the Professor Shtokman research vessel. Methane content in the near-bottom water and in the underlying sediments indicates stable methane flow from the sediment into the water. In the 10-m water layer above the pockmark, apart from methane anomalies, elevated numbers of microorganisms and enhanced rates of dark CO2 fixation (up to 1.15 micromol C/(1 day)) and methane oxidation (up to 2.14 nmol CH4/(1 day)) were revealed. Lightened isotopic composition of suspended organic matter also indicates high activity of the near-bottom microbial community. Compared to the background stations, methane content in pockmark sediments increased sharply from the surface to 40-60 ml/dm3 in the 20-30cm horizon. High rates of bacterial sulfate reduction (SR) were detected throughout the core (0-40 cm); the maximum of 74 micromol/(dm3 day) was located in subsurface horizons (15-20 cm). The highest rates of anaerobic methane oxidation (AMO), up to 80 micromol/(dm3 day), were detected in the same horizon. Good coincidence of the AMO and SR profiles with stoichiometry close to 1:1 is evidence in favor of a close relation between these processes performed by a consortium of methanotrophic archaea and sulfate-reducing bacteria. Methane isotopic composition in subsurface sediments of the pockmark (from -53.0 to -56.5% per hundred) does not rule out the presence of methane other than the biogenic methane from the deep horizons of the sedimentary cover.

The development of stable isotope techniques is one of the main methodological advances in ecology of the last decades of the 20th century. Many biogeochemical processes are accompanied by changes in the ratio between stable isotopes of carbon and nitrogen (12C/13C and 14N/15N), which allows different ecosystem components and different ecosystems to be distinguished by their isotopic composition. Analysis of isotopic composition makes it possible to trace matter and energy flows through biological systems and to evaluate the rate of many ecological processes. The main concepts and methods of stable isotope ecology and patterns of stable isotope fractionation during organic matter decomposition are considered with special emphasis on the fractionation of isotopes in food chains and the use of stable isotope studies of trophic relationships between soil animals in the field.

Microbiological and isotopic-geochemical investigations of the brackish meromictic lakes Shira and Shunet were performed in the steppe region of Khakasia in winter. Measurements made with a submersed sensor demonstrated that one-meter ice transmits light in a quantity sufficient for oxygenic and anoxygenic photosynthesis. As in the summer season, in the community of phototrophic bacteria found in Lake Shira, the purple sulfur bacteria Amoebobacter purpureus dominated, whereas, in Lake Shunet, the green sulfur bacteria Pelodictyon luteolum were predominant. Photosynthetic production, measured using the radioisotopic method, was several times lower than that in summer. The rates of sulfate reduction and production and oxidation of methane in the water column and bottom sediments were also lower than those recorded in summer. The process of anaerobic methane oxidation in the sediments was an exception, being more intense in winter than in summer. The data from radioisotopic measurements of the rates of microbial processes correlate well with the results of determination of the isotopic composition of organic and mineral carbon (delta13C) and hydrogen sulfide and sulfate (delta34S) and suggest considerable seasonal variations in the activity of the microbial community in the water bodies investigated.

The aragonite constructions of the Black Sea are formed in a stable anaerobic zone and are a perfect object to study the natural mechanism of anaerobic methane oxidation. The most probable pathway of methane oxidation is its methanogen-mediated reaction with bicarbonates, dissolved in seawater, with the formation of water and acetate, which is then consumed by other components of the anaerobic community. Comparison of the delta 13C values of carbonate minerals and organic matter once more demonstrated that the formation of the organic matter of biomass is accompanied by intense fractionation of carbon isotopes, as a result of which the total organic matter of biomass acquires an extremely light isotopic composition, characterized by delta 13C values as low as -83.8@1000.

Relationships were obtained which made possible to calculate isotope content of carbon atoms in the products and reaction compound in the course of piruvate decarboxilation. Isotope composition was determined from kinetic isotope effect accompanying the destruction of carbon bonds. Some applications of the expressions obtained are presented.

A decrease in heavy carbon isotope 13C content has been detected in atherosclerotically-altered aortic tissues. An extent of the isotope shift is increased with the intensification of sclerotic process in different regions of the aorta and depends on the patient's age. To explain the observed effect of isotope 13C content decrease in the altered aortic tissues it was suggested that the rates of biochemical conversions become considerably higher in sclerotically-altered tissues.