[A new basis for the scale of atomic weights of natural elements and isotopes--carbon isotope C12].
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Carbon↗
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Enzymic Fractionation of the Stable Carbon Isotopes of Carbon Dioxide by Ribulose-1,5-bisphosphate Carboxylase.
The enzymic fractionation of the stable carbon isotopes of CO(2) (Deltaco(2)) was determined using a purified preparation of ribulose-1,5-bisphosphate (RuBP) carboxylase isolated from cotton (a C(3) plant) leaves. The bicarbonate concentration in the reaction mixture saturated the enzyme and furnished an infinite pool of (12)CO(2) and (13)CO(2) for enzyme fractionation. The RuBP was 96 to 98% pure. The phosphoglycerate synthesized in the reaction mixtures was purified free of RuBP, phosphoglycolate, and other phosphate esters by column chromatography on Dowex 1-Cl(-) resin. The average Deltaco(2) value of -27.1% was determined from five separate experiments. A discussion of the isotope fractionation associated with photosynthetic CO(2) fixation in plants shows that the enzymic fractionation of stable carbon isotopes of CO(2) by RuBP carboxylase is of major importance in determining the delta(13)C values of C(3) plants.
Journal Article↗
[Average daily values of the isotopic carbon composition in expired air and urea in human urine in normal states and in some endocrine disorders].
Daily average carbon isotope composition of CO2 of expired air and urine urea in patients being in different hormonal-metabolic states was determined. The observations were carried out under conditions of clinic to provide standard diet, and the same daily and food taking regimes. In all persons, a substantial increase enrichment in 12C of CO2 of expired air (by 3-6%) and 13C of urine urea (by 3-5%) relative to carbon of food was revealed. Marked variations in these characteristics in norm, on starvation and in endocrine pathologies were found. A relationship between the carbon isotope composition and the metabolic shifts characterizing the deviations of the studied functional states from norm was established. The changes in the isotope characteristics and their relation to the hormonal-metabolic status of the organism are interpreted in terms of the model for cell fractionation of carbon isotopes proposed earlier.
Breath Tests↗
[Short-period oscillations of isotopic carbon in CO2 from expired air in different human functional states].
The examination of diurnal variations in carbon isotope composition of CO2 under different hormonal-metabolic states in man revealed short-period inphase oscillations with a period of about 2-3 h. The oscillations occur throughout 24 h and their period is little dependent on the functional state of the organism. In endocrine pathologies, substantial differences in oscillation amplitude are observed. The relationship between the variations in carbon isotope composition of CO2 of expired air and energy exchange in cells of insulin-dependent tissues of the organism is substantiated.
Breath Tests↗
Carbon isotope ratios demonstrate carbon flux from c(4) host to c(3) parasite.
Carbon isotope ratios of mature leaves from the C(3) angiosperm root hemiparasites Striga hermonthica (Del.) Benth (-26.7 per thousand) and S. asiatica (L.) Kuntze (-25.6 per thousand) were more negative than their C(4) host, sorghum (Sorghum bicolor [L.] Moench cv CSH1), (-13.5 per thousand). However, in young photosynthetically incompetent plants of S. hermonthica this difference was reduced to less than 1 per thousand. Differences between the carbon isotope ratios of two C(3)-C(3) associations, S. gesnerioides (Willd.) Vatke-Vigna unguiculata (L.) Walp. and Oryza sativa L.-Rhamphicarpa fistulosa (Hochst.) Benth differed by less than 1 per thousand. Theoretical carbon isotope ratios for mature leaves of S. hermonthica and S. asiatica, calculated from foliar gas exchange measurements, were -31.8 and -32.0 per thousand, respectively. This difference between the measured and theoretical delta(13)C-values of 5 to 6 per thousand suggests that even in mature, photosynthetically active plants, there is substantial input of carbon from the C(4) host. We estimate this to be approximately 28% of the total carbon in S. hermonthica and 35% in S. asiatica. This level of carbon transfer contributes to the host's growth reductions observed in Striga-infected sorghum.
Journal Article↗
Effect of Varying CO(2) Partial Pressure on Photosynthesis and on Carbon Isotope Composition of Carbon-4 of Malate from the Crassulacean Acid Metabolism Plant Kalanchoë daigremontiana Hamet et Perr.
Intact leaves of Kalanchoë daigremontiana were exposed to CO(2) partial pressures of 100, 300, and 1000 microbars. Malic acid was extracted, purified, and degraded in order to obtain isotopic composition of carbon-1 and carbon-4. From these data, it is possible to calculate the carbon isotope composition of newly fixed carbon in malate. In all three treatments, the isotopic composition of newly introduced carbon is the same as that of the CO(2) source and is independent of CO(2) partial pressures over the range tested. Comparison with numerical models described previously (O'Leary 1981 Phytochemistry 20: 553-567) indicates that we would expect carbon 4 of malate to be 4 per thousand more negative than source CO(2) if diffusion is totally limiting or 7 per thousand more positive than source CO(2) if carboxylation is totally limiting. Our results demonstrate that stomatal aperture adjusts to changing CO(2) partial pressures and maintains the ratio of diffusion resistance to carboxylation resistance approximately constant. In this study, carboxylation and diffusion resistances balance so that essentially no fractionation occurs during malate synthesis. Gas exchange studies of the same leaves from which malate was extracted show that the extent of malate synthesis over the whole night is nearly independent of CO(2) partial pressure, although there are small variations in CO(2) uptake rate. Both the gas exchange and the isotope studies indicate that the ratio of external to internal CO(2) partial pressure is the same in all three treatments. Inasmuch as a constant ratio will result in constant isotope fractionation, this observation may explain why plants in general have fairly invariable (13)C contents, despite growing under a variety of environmental conditions.
Journal Article↗
Low turnover rates of carbon isotopes in tissues of two nectar-feeding bat species.
Stable isotopes of carbon are commonly used to characterize dietary preferences in animals. Because turnover rates of carbon isotopes are related to metabolic rate, we wanted to determine the rates at which carbon isotopes are exchanged in tissues of two species of nectar-feeding bats (Leptonycteris curasoae and Glossophaga soricina), both of which have relatively high mass-specific metabolic rates. To test the hypothesis that isotope turnover is higher in nectar-feeding bats, because of their high mass-specific metabolic rates, than in other eutherian mammals, we conducted diet-switching experiments and chose three target tissues (hair, wing membrane and blood) to evaluate the isotopic turnover rates. We made the following predictions: (1) isotopic composition should change towards higher delta(13)C-values due to the turnover of carbon isotopes of C(3) origin with those of C(4)/CAM origin; (2) the turnover rates of carbon isotopes would differ between the three types of tissues in the following order of decreasing turnover rates: blood>wing membrane>hair; and (3) turnover rates of nectar-feeding bats should exceed those reported for other small mammals because of the high mass-specific metabolic rate of nectar-feeding bats. Compared to the initial diet, target tissues were enriched in heavy carbon isotopes by 2.8 per thousand in L. curasoae and by 2.6 per thousand in G. soricina. After changing the diet from C(3) to C(4)/CAM origin we found an increase in abundance of (13)C in blood and wing membrane in all experimental subjects. The estimated half life of carbon isotope turnover ranged from 100 to 134 days and did not differ significantly between blood and wing membrane, nor did it differ between the two species. The low turnover rate in wing membrane may reflect its specific composition and the relatively low temperature of this tissue, and long-lived erythrocytes in bat blood may be responsible for the low turnover rate of carbon isotopes in blood. The turnover rate of stable carbon isotopes in hair was low in L. curasoae and undetectable in G. soricina, which may be explained by the seasonal growth of the hair in these two species. Because both species are small (10 and 25 g, respectively) and nectar-feeding bats have higher mass-specific metabolic rates than bats in temperate regions or similar sized terrestrial mammals, our findings of low turnover rates were unexpected.
Analysis of Variance↗
Isotopic carbon discrimination and leaf nitrogen content of Erica arborea L. along a CO(2) concentration gradient in a CO(2) spring in Italy.
We studied a Mediterranean species (Erica arborea L.) growing in a CO(2) spring in Italy that was naturally exposed for generations to a gradient of atmospheric CO(2) concentrations. The CO(2) concentration gradient to which different individual plants were exposed was determined by an indirect method based on radioisotope analysis. The stable carbon isotope ratio of sampled leaves was determined by mass spectrometry, and isotopic discrimination was then calculated. Leaf nitrogen, specific leaf area, total soil nitrogen, soil organic matter content and soil pH were also measured. In one group of plants, grown on a homogeneous soil and exposed to moderate CO(2) enrichment, isotopic discrimination was significantly reduced in response to increasing CO(2) concentrations, whereas the intercellular CO(2) concentration and leaf nitrogen content were almost unaffected. In a second group of plants, grown along a gradient of CO(2) concentration and soil nitrogen content, leaf nitrogen content was reduced when nitrogen availability was limiting. However, when soil nitrogen was available in excess, even very high CO(2) concentrations did not result in increased discrimination or reduced leaf nitrogen content in the long term. The results are discussed with respect to current theories about the long-term CO(2) response of plants based on several years of experimentation with elevated atmospheric CO(2) concentrations under controlled conditions.
Journal Article↗
Evidence of substantial carbon isotope fractionation among substrate, inorganic carbon, and biomass during aerobic mineralization of 1, 2-dichloroethane by Xanthobacter autotrophicus.
Carbon isotope fractionation during aerobic mineralization of 1, 2-dichloroethane (1,2-DCA) by Xanthobacter autotrophicus GJ10 was investigated. A strong enrichment of (13)C in residual 1,2-DCA was observed, with a mean fractionation factor alpha +/- standard deviation of 0.968 +/- 0.0013 to 0.973 +/- 0.0015. In addition, a large carbon isotope fractionation between biomass and inorganic carbon occurred. A mechanistic model that links the fractionation factor alpha to the rate constants of the first catabolic enzyme was developed. Based on the model, it was concluded that the strong enrichment of (13)C in 1,2-DCA arises because the first irreversible step of the initial enzymatic transformation of 1,2-DCA consists of an S(N)2 nucleophilic substitution. S(N)2 reactions are accompanied by a large kinetic isotope effect. The substantial carbon isotope fractionation between biomass and inorganic carbon could be explained by the kinetic isotope effect associated with the initial 1,2-DCA transformation and by the metabolic pathway of 1,2-DCA degradation. Carbon isotope fractionation during 1,2-DCA mineralization leads to 1,2-DCA, inorganic carbon, and biomass with characteristic carbon isotope compositions, which may be used to trace the process in contaminated environments.
Aerobiosis↗
Monitoring trichloroethene remediation at an iron permeable reactive barrier using stable carbon isotopic analysis.
Stable carbon isotopic analysis, in combination with compositional analysis, was used to evaluate the performance of an iron permeable reactive barrier (PRB) for the remediation of ground water contaminated with trichloroethene (TCE) at Spill Site 7 (SS7), F.E. Warren Air Force Base, Wyoming. Compositional data indicated that although the PRB appeared to be reducing TCE to concentrations below treatment goals within and immediately downgradient of the PRB, concentrations remained higher than expected at wells further downgradient (i.e. >9 m) of the PRB. At two wells downgradient of the PRB, TCE concentrations were comparable to upgradient values, and delta13C values of TCE at these wells were not significantly different than upgradient values. Since the process of sorption/desorption does not significantly fractionate carbon isotope values, this suggests that the TCE observed at these wells is desorbing from local aquifer materials and was present before the PRB was installed. In contrast, three other downgradient wells show significantly more enriched delta13C values compared to the upgradient mean. In addition, delta13C values for the degradation products of TCE, cis-dichloroethene and vinyl chloride, show fractionation patterns expected for the products of the reductive dechlorination of TCE. Since concentrations of both TCE and degradation products drop to below detection limit in wells within the PRB and directly below it, these downgradient chlorinated hydrocarbon concentrations are attributed to desorption from local aquifer material. The carbon isotope values indicate that this dissolved contaminant is subject to local degradation, likely due to in situ microbial activity.
Biodegradation, Environmental↗
Seasonal, daily and diurnal variations in the stable carbon isotope composition of carbon dioxide respired by tree trunks in a deciduous oak forest.
The stable C isotope composition (delta13C) of CO2 respired by trunks was examined in a mature temperate deciduous oak forest (Quercus petraea). Month-to-month, day-to-day and diurnal, measurements were made to determine the range of variations at different temporal scales. Trunk growth and respiration rates were assessed. Phloem tissue was sampled and was analysed for total organic matter and soluble sugar 13C composition. The CO2 respired by trunk was always enriched in 13C relative to the total organic matter, sometimes by as much as 5 per thousand. The delta13C of respired CO2 exhibited a large seasonal variation (3.3 per thousand), with a relative maximum at the beginning of the growth period. The lowest values occurred in summer when the respiration rates were maximal. After the cessation of radial trunk growth, the respired CO2 delta13C values showed a progressive increase, which was linked to a parallel increase in soluble sugar content in the phloem tissue (R=0.95; P<0.01). At the same time, the respiration rates declined. This limited use of the substrate pool might allow the discrimination during respiration to be more strongly expressed. The late-season increase in CO2 delta13C might also be linked to a shift from recently assimilated C to reserves. At the seasonal scale, CO2 delta13C was negatively correlated with air temperature (R=-0.80; P<0.01). The diurnal variation sometimes reached 3 per thousand, but the range and the pattern depended on the period within the growing season. Contrary to expectations, diurnal variations were maximal in winter and spring when the leaves were missing or not totally functional. By contrast to the seasonal scale, these diurnal variations were not related to air temperature or sugar content. Our study shows that seasonal and diurnal variations of respired 13C exhibited a similar large range but were probably explained by different mechanisms.
Analysis of Variance↗
Microbial influences on local carbon isotopic ratios and their preservation in carbonate.
Analysis of the carbon isotopic composition of carbonates is a valuable tool for studying microbial processes and looking for evidence of life. Microbial fixation of CO2 and conversion of organic carbon to CO2 can produce measurable delta 13C shifts in a microbial mat environment. Diffusion modeling demonstrates that substantial isotopic shifts can develop within the mat and in the diffusion boundary layer in the fluid when CO2 fixation is rapid and prolonged for several hours. Carbonates that precipitate during rapid CO2 fixation can preserve these microbially produced isotopic shifts. However, continued precipitation during intervals when respiration dominates or after the cessation of active microbial growth commonly dilutes autotrophic isotopic signatures. Thus, preserved isotopic signatures rarely reflect the magnitude of isotopic shifts within the mat. Interpretation of observed isotopic shifts in microbial mat carbonate depends on fully characterizing ambient delta 13C and eliminating other origins for isotopic shifts. The carbon isotopic composition of reservoirs can vary substantially, both on Earth and on other planets. Characterizing the reservoir composition and any changes through time is critical to evaluating microbially induced shifts. In addition, careful evaluation of non-microbial causes for shifts in isotopic composition is essential for a reliable interpretation. Complicating processes include recrystallization, calcite precipitation over extended periods of time, variable precipitation rates and water chemistry, and mixing of carbonates having different isotopic signatures.
Carbon Dioxide↗
Stable carbon isotope discrimination: an indicator of cumulative salinity and boron stress in Eucalyptus camaldulensis.
Saplings of Eucalyptus camaldulensis Dehn. Clone 4544, irrigated with water of differing salinities (2 to 28 dS m-1) and boron concentrations (1 to 30 mg l-1), integrated the history of these stresses through the discrimination of stable isotopes of carbon in leaf and woody tissues. Carbon isotope discrimination (delta) was reduced primarily by salinity. Decreases in discrimination in response to boron stress were detected in the absence of salinity stress, but the decreases were significant only in leaf tissues with visible boron injury. Sapwood core samples indicated that salinity- and boron-induced reductions in delta increased with increasing tree age. Absolute values of delta varied with location of leaf or wood tissue, but relative effects of salinity on the relationship between delta and transpiration efficiency (W) were similar. In response to increasing salinity stress, relative decreases in delta paralleled relative decreases in biomass and both indices yielded similar salt tolerance model parameters. The strong correlations between delta, tree fresh weight, leaf area and W suggest that delta is a useful parameter for evaluating salt tolerance of eucalyptus
Boron↗
Decarboxylation of glycine contributes to carbon isotope fractionation in photosynthetic organisms.
Carbon isotope effects were investigated for the reaction catalyzed by the glycine decarboxylase complex (GDC; EC 2.1.2.10). Mitochondria isolated from leaves of pea (Pisum sativum L.) and spinach (Spinacia oleracea L.) were incubated with glycine, and the CO(2) evolved was analyzed for the carbon isotope ratio (delta(13)C). Within the range of parameters tested (temperature, pH, combination of cofactors NAD(+), ADP, pyridoxal 5-phosphate), carbon isotope shifts of CO(2) relative to the C(1)-carboxyl carbon of glycine varied from +14 per thousand to -7 per thousand. The maximum effect of cofactors was observed for NAD(+), the removal of which resulted in a strong (12)C enrichment of the CO(2) evolved. This indicates the possibility of isotope effects with both positive and negative signs in the GDC reaction. The measurement of delta(13)C in the leaves of the GDC-deficient barley (Hordeum vulgare L.) mutant (LaPr 87/30) plants indicated that photorespiratory carbon isotope fractionation, opposite in sign when compared to the carbon isotope effect during CO(2) photoassimilation, takes place in vivo. Thus the key reaction of photorespiration catalyzed by GDC, together with the key reaction of CO(2) fixation catalyzed by ribulose-1,5-bisphosphate carboxylase, both contribute to carbon isotope fractionation in photosynthesis.
Journal Article↗
[Terrestrial plant stable carbon isotope composition and global change].
Stable carbon isotope analysis is a rapid and reliable technique developed in recent years, and has been widely applied to reconstruct the sequences of atmospheric CO2 concentration changes, clarify the hysteresis effect and junior effect of temperature and precipitation on tree growth, and distinguish the distributions of plants with different photosynthetic pathways. The water use efficiency (WUE) of different plant functional groups and the variations of plant WUE with tempo-spatial and climatic changes can be also indicated by determining plant carbon isotope composition. In this paper, the effects of environmental factors, e.g., atmospheric CO2 concentration, air temperature, precipitation, and altitude on terrestrial plant carbon isotope composition were discussed, and the advances and applications of carbon isotope technique in global change research were summarized. Furthermore, the existing and disputed problems in carbon isotope analysis were discussed, and the future trends of carbon isotope technique in global change research were prospected, aimed to widen people's knowledge and promote the development of this technique.
Air↗
On-line measurement of intramolecular carbon isotope distribution of acetic acid by continuous-flow isotope ratio mass spectrometry.
Molecular and intramolecular carbon isotope measurements of acetic acid present in natural environments have been performed by off-line procedures. The off-line method is complicated and time-consuming and requires micromolar to millimolar amounts of sample. This limits geochemical isotopic studies, especially at the intramolecular level, on acetic acid present in natural samples. Here, we examine an on-line measurement of intramolecular carbon isotope distribution of acetic acid using continuous-flow isotope ratio mass spectrometry (CF-IRMS) coupled with an on-line pyrolysis system. This is achieved by measurement of the respective carbon isotope ratios of CH4 and CO2 produced by on-line pyrolysis of acetic acid. Results for authentic standards of pure acetic acid demonstrated the practicality of this on-line method, although the carbon isotope ratio of the methyl group could not be determined directly. The precision of the carbon isotope measurements was 0.4 per thousand (1sigma). The carbon isotope distribution determined by the on-line method was identical to that determined by the conventional off-line method within analytical error. The advantages of the on-line method compared with the conventional off-line method are that it is less laborious, requires less analytical time (less than one hour per sample) and, most importantly, uses smaller sample sizes (ca. 10 nanomole). An application of this on-line method to natural geochemical samples will provide an insight into the geochemical cycle of acetic acid.
Acetic Acid↗
Heavy and light beer: a carbon isotope approach to detect C(4) carbon in beers of different origins, styles, and prices.
The carbon isotope ratios (delta(13)C) of 160 beers from around the world ranged from -27.3 to -14.9 per thousand, primarily due to variation in the percentage of C(3) or C(4) plant carbon in the final product. Thirty-one percent of beers had a carbon signature of C(3) plants (barley, rice, etc.), whereas the remaining 69% contained some C(3)-C(4) mixture (mean of mixtures, 39 +/- 11% C(4) carbon). Use of C(4) carbon (corn, cane sugar, etc.) was not confined to beers from any particular region (Pacific Rim, Mexico, Brazil, Europe, Canada, and the United States). However, the delta(13)C of European beers indicated mostly C(3) plant carbon. In contrast, U.S. and Canadian beers contained either only C(3) or C(3)-C(4) mixtures; Brazilian, Mexican, and Pacific Rim beers were mostly C(3)-C(4) mixtures. Among different lagers, U.S.-style lagers generally contained more C(4) carbon than did imported pilsners. Among different ales, those brewed by large high-production breweries contained significant proportions of C(4) carbon, while C(4) carbon was not detected in microbrewery or home-brew ales. Furthermore, inexpensive beers generally contained more C(4) carbon than expensive beers.
Beer↗
The carbon-isotopic composition of Proterozoic carbonates: Riphean successions from northwestern Siberia (Anabar Massif, Turukhansk Uplift).
Thick carbonate-dominated successions in northwestern Siberia document secular variations in the C-isotopic composition of seawater through Mesoproterozoic and early Neoproterozoic (Early to early Late Riphean) time. Mesoproterozoic dolomites of the Billyakh Group, Anabar Massif, have delta 13C values that fall between 0 and -1.9 permil versus PDB, with values in the upper part of the succession (Yusmastakh Formation) consistently higher than those of the lower (Ust'-Il'ya and Kotuikan formations). Consistent with available biostratigraphic and radiometric data, delta 13C values for Billyakh carbonates compare closely with those characterizing early Mesoproterozoic carbonates (about 1600-1200 Ma) worldwide. In contrast, late Mesoproterozoic to early Neoproterozoic limestones and dolomites in the Turukhansk Uplift exhibit moderate levels of secular variation. Only the lowermost carbonates in the Turukhansk succession (Linok Formation) have delta 13C values that approximate Billyakh values. Higher in the Turukhansk succession, delta 13C values vary from -2.7 to +4.6 permil (with outliers as low as -5.0 permil interpreted as diagentically altered). Again, consistent with paleontological and radiometric data, these values compare well with isotopic values from 1200 to 850 Ma successions elsewhere. Five sections measured in different parts of the Turukhansk basin show nearly identical patterns of variation, confirming that carbonate delta 13C correlates primarily with time and not facies. The Siberian sections illustrate the potential of integrated biostratigraphic and chemostratigraphic data in the intra- and interbasinal correlation of Mesoproterozoic and early Neoproterozoic rocks.
Calcium Carbonate↗