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1.
牛尾毛中稳定性碳同位素组成变化规律研究 总被引：5，自引：1，他引：4
【目的】研究牛尾毛中稳定性碳同位素组成随饲料改变的变化规律,确证牛尾毛一旦长成,其中的稳定性碳同位素不再与其它部分的进行交换,每段毛发记录的同位素信息可反映毛发生长时的饲料信息。【方法】设计控制饲料配比的牛模型试验,利用同位素比率质谱仪测定不同段位牛尾毛中的δ13C值,分析不同段位牛尾毛的δ13C值随饲料改变的变化趋势,以及牛尾毛中的δ13C值与饲料、牛个体的关系。【结果】随着牛生育过程中饲料成分的改变,不同段位牛尾毛中碳同位素组成有极显著差异,而且饲料对牛尾毛中碳同位素组成的影响远大于个体对其的影响;分段取得的牛尾毛δ13C值与其饲料δ13C值、C4植物饲料比例呈极显著相关（P＜0.01）,而不分段的牛尾毛δ13C值与饲料碳同位素组成相关性不显著。【结论】牛尾毛一旦长成,其中的稳定性碳同位素不再与其它部分进行交换,每段毛发的同位素信息可反映牛在毛发生长时的饲料信息,牛尾毛可以看作是记录牛饲料改变信息的档案库。 相似文献
2.
Brooks JM Kennicutt MC Fisher CR Macko SA Cole K Childress JJ Bidigare RR Vetter RD 《Science (New York, N.Y.)》1987,238(4830):1138-1142
Mussels, clams, and tube worms collected in the vicinity of hydrocarbon seeps on the Louisiana slope contain mostly "dead" carbon, indicating that dietary carbon is largely derived from seeping oil and gas. Enzyme assays, elemental sulfur analysis, and carbon dioxide fixation studies demonstrate that vestimentiferan tube worms and three clam species contain intracellular, autotrophic sulfur bacterial symbionts. Carbon isotopic ratios of 246 individual animal tissues were used to differentiate heterotrophic (8(13)C = -14 to -20 per mil), sulfur-based (8(13)C = -30 to -42 per mil), and methane-based (8(13)C = <-40 per mil) energy sources. Mussels with symbiotic methanotrophic bacteria reflect the carbon isotopic composition of the methane source. Isotopically light nitrogen and sulfur confirm the chemoautotrophic nature of the seep animals. Sulfur-based chemosynthetic animals contain isotopically light sulfur, whereas methane-based symbiotic mussels more closely reflect the heavier oceanic sulfate pool. The nitrogen requirement of some seep animals may be supported by nitrogen-fixing bacteria. Some grazing neogastropods have isotopic values characteristic of chemosynthetic animals, suggesting the transfer of carbon into the background deep-sea fauna. 相似文献
3.
The insertion of an iridium complex into an N-H bond in ammonia leads to a stable monomeric amido hydride complex in solution at room temperature. This reaction advances the transition-metal coordination chemistry of ammonia beyond its role for more than a century as an ancillary ligand. The precursor for this insertion reaction is an iridium(I) olefin complex with an aliphatic ligand containing one carbon and two phosphorus donor atoms. Kinetic and isotopic labeling studies indicate that olefin dissociates to give a 14-electron iridium(I) fragment, which then reacts with ammonia. This cleavage of the N-H bond under neutral conditions provides a foundation on which to develop future mild catalytic transformations of ammonia, such as olefin hydroamination and arene oxidative amination. 相似文献
4.
Oró J Updegrove WS Gibert J McReynolds J Gil-Av E Ibanez J Zlatkis A Flory DA Levy RL Wolf C 《Science (New York, N.Y.)》1970,167(3918):765-767
Organogenic elements, mainly carbon, nitrogen, phosphorus, and sulfur are present in the particulate material and in a breccia rock from Tranquillity Base in amounts ranging from 5 to 4200 parts per million. The major compounds of carbon released by heating are carbon monoxide and carbon dioxide; the former predominates. Small amounts of other compounds of carbon have also been observed. Sulfur can be released as hydrogen sulfide by treatment with acid. The carbon isotopic delta(13L)C values are definitely nonterrestrial (+ 13 to + 18.5 per mil). 相似文献
5.
Floss C Stadermann FJ Bradley J Dai ZR Bajt S Graham G 《Science (New York, N.Y.)》2004,303(5662):1355-1358
Because hydrogen and nitrogen isotopic anomalies in interplanetary dust particles have been associated with carbonaceous material, the lack of similar anomalies in carbon has been a major conundrum. We report here the presence of a 13C depletion associated with a 15N enrichment in an anhydrous interplanetary dust particle. Our observations suggest that the anomalies are carried by heteroatomic organic compounds. Theoretical models indicate that low-temperature formation of organic compounds in cold interstellar molecular clouds can produce carbon and nitrogen fractionations, but it remains to be seen whether the specific effects observed here can be reproduced. 相似文献
6.
Kling GW Clark MA Wagner GN Compton HR Humphrey AM Devine JD Evans WC Lockwood JP Tuttle ML Koenigsberg EJ 《Science (New York, N.Y.)》1987,236(4798):169-175
The sudden, catastrophic release of gas from Lake Nyos on 21 August 1986 caused the deaths of at least 1700 people in the northwest area of Cameroon, West Africa. Chemical, isotopic, geologic, and medical evidence support the hypotheses that (i) the bulk of gas released was carbon dioxide that had been stored in the lake's hypolimnion, (ii) the victims exposed to the gas cloud died of carbon dioxide asphyxiation, (iii) the carbon dioxide was derived from magmatic sources, and (iv) there was no significant, direct volcanic activity involved. The limnological nature of the gas release suggests that hazardous lakes may be identified and monitored and that the danger of future incidents can be reduced. 相似文献
7.
Self-shielding of carbon monoxide (CO) within the nebular disk has been proposed as the source of isotopically anomalous oxygen in the solar reservoir and the source of meteoritic oxygen isotopic compositions. A series of CO photodissociation experiments at the Advanced Light Source show that vacuum ultraviolet (VUV) photodissociation of CO produces large wavelength-dependent isotopic fractionation. An anomalously enriched atomic oxygen reservoir can thus be generated through CO photodissociation without self-shielding. In the presence of optical self-shielding of VUV light, the fractionation associated with CO dissociation dominates over self-shielding. These results indicate the potential role of photochemistry in early solar system formation and may help in the understanding of oxygen isotopic variations in Genesis solar-wind samples. 相似文献
8.
GI Gellene 《Science (New York, N.Y.)》1996,274(5291):1344-1346
Application of a theory of nuclear symmetry-based reaction restrictions to the O2 + O --> O3 reaction provides a potential explanation for the symmetry-induced isotopic enrichment observed for laboratory and atmospherically produced O3. Within this theory, the rate of formation of O3 from collisions of O and isotopically homonuclear O2 depends on whether the O2 molecule is in an f (allowed) or an e (restricted) parity label state. The restriction can be relaxed by various potential energy surface coupling terms, and the assumption that approximately 78 percent of the restricted O2(e) levels produce O3 with the same efficiency as the allowed O2(f) levels can account for laboratory-observed isotopic fractionation. In particular, the theory explains the special enhanced formation of the completely asymmetric isotopomer 16O17O18O. 相似文献
9.
Strand AE Pritchard SG McCormack ML Davis MA Oren R 《Science (New York, N.Y.)》2008,319(5862):456-458
The residence time of fine-root carbon in soil is one of the least understood aspects of the global carbon cycle, and fine-root dynamics are one of the least understood aspects of plant function. Most recent studies of these belowground dynamics have used one of two methodological strategies. In one approach, based on analysis of carbon isotopes, the persistence of carbon is inferred; in the other, based on direct observations of roots with cameras, the longevity of individual roots is measured. We show that the contribution of fine roots to the global carbon cycle has been overstated because observations of root lifetimes systematically overestimate the turnover of fine-root biomass. On the other hand, isotopic techniques systematically underestimate the turnover of individual roots. These differences, by virtue of the separate processes or pools measured, are irreconcilable. 相似文献
10.
Previous studies have suggested that melting processes are responsible for the trace element variability observed in olivine-hosted basaltic melt inclusions. Melt inclusions from three individual lava samples (two from Mangaia, Cook Islands, and one from Tahaa, Society Islands) have heterogeneous Pb isotopic compositions, even though the erupted lavas are isotopically homogeneous. The range of Pb isotopic compositions from individual melt inclusions spans 50 percent of the worldwide range observed for ocean island basalts. The melt inclusion data can be explained by two-component mixing for each island. Our data imply that magmas with different isotopic compositions existed in the volcanic plumbing system before or during melt aggregation. 相似文献
11.
随着人们对名特优新农产品需求的快速增长和跨地区贸易的迅速发展,消费者对农产品原产地信息也越来越重视。近年来,国内外开展了一些应用多元素及同位素“指纹”分析技术对农产品进行原产地判定的探索性研究。研究表明利用氢、氧、碳、氮、硫、锶同位素比及多元素含量特征可对农产品进行原产地判定。综述了多元素及同位素“指纹”分析技术在肉品、乳制品、饮品原料、谷物、葡萄酒等农产品原产地判定中的研究进展,为未来相关研究的发展和农产品原产地保护工作提供理论基础。 相似文献
12.
The exogenic sulfur cycle is tightly coupled with the carbon and oxygen cycles, and therefore a central component of Earth's biogeochemistry. Here we present a high-resolution record of the sulfur isotopic composition of seawater sulfate for the Cretaceous. The general enrichment of isotopically light sulfur that prevailed during the Cretaceous may have been due to increased volcanic and hydrothermal activity. Two excursions toward isotopically lighter sulfur represent periods of lower rates of pyrite burial, implying a shift in the location of organic carbon burial to terrestrial or open-ocean settings. The concurrent changes in seawater sulfur and inorganic carbon isotopic compositions imply short-term variability in atmospheric oxygen partial pressure. 相似文献
13.
Significant variations in the isotopic composition of marine calcium have occurred over the last 80 million years. These variations reflect deviations in the balance between inputs of calcium to the ocean from weathering and outputs due to carbonate sedimentation, processes that are important in controlling the concentration of carbon dioxide in the atmosphere and, hence, global climate. The calcium isotopic ratio of paleo-seawater is an indicator of past changes in atmospheric carbon dioxide when coupled with determinations of paleo-pH. 相似文献
14.
Polycrystalline diamonds (framesites) from the Venetia kimberlite in South Africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption. Chemical variations within the garnets correlate with carbon isotopes in the diamonds, indicating contemporaneous formation. Trace element, radiogenic, and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt, derived by remobilization of material that had been stored for a considerable time in the lithosphere. These results indicate more recent formation of diamonds from older materials within the cratonic lithosphere. 相似文献
15.
Measures of growth and skeletal isotopic ratios in the Caribbean coral Montastraea annularis are fundamental to many studies of paleoceanography, environmental degradation, and global climate change. This taxon is shown to consist of at least three sibling species in shallow waters. The two most commonly studied of these show highly significant differences in growth rate and oxygen isotopic ratios, parameters routinely used to estimate past climatic conditions; unusual coloration in the third may have confused research on coral bleaching. Interpretation or comparison of past and current studies can be jeopardized by ignoring these species boundaries. 相似文献
16.
Based on the boron isotopic composition of coral from the southwestern Pacific, Pelejero et al. (Reports, 30 September 2005, p. 2204) suggested that natural variations in pH can modulate the impact of ocean acidification on coral reef ecosystems. We show that this claim cannot be reconciled with other marine carbon chemistry constraints and highlight problems with the authors' interpretation of the paleontologic data. 相似文献
17.
Stable carbon isotope ratios of organic matter in rock varnishes of Holocene age from western North America and the Middle East show a strong association with the environment. This isotopic variability reflects the abundance of plants with different photosynthetic pathways in adjacent vegetation. Analyses of different layers of varnish on late Pleistocene desert landforms indicate that the carbon isotopic composition of varnish organic matter is a paleoenvironmental indicator. 相似文献
18.
Chang S Kvenvolden K Lawless J Ponnamperuma C Kaplan IR 《Science (New York, N.Y.)》1971,171(3970):474-477
Total carbon in the Apollo 12 sample 12023 fines was 110 micrograms per gram of sample with a carbon isotopic abundance delta(13)C (relative to the Pee Dee belemnite standard) of +12 per mil. Hydrolysis of the fines with deuterium chloride yielded undeuterated methane along with deuterated hydrocarbons, thus confirming the presence of 7 to 21 micrograms of carbon per gram of sample as carbide and about 2 micrograms of carbon per gram of sample as indigenous methane. After vacuum pyrolysis of the fines to 1100 degrees C the following gases were detected in the relative abundance: carbon monoxide carbon dioxide methane. Variations of the delta(13)C value with the pyrolysis temperature indicated the presence of carbon with more than one range of isotopic values. The observed delta(13)C value of +14 per mil for lunar carbide is much higher than that of carbide in meteorites. These results suggest that lunar carbide is either indigenous to the moon or a meteoritic contribution that has been highly fractionated isotopically. 相似文献
19.
Oxygen isotopes were equilibrated between carbon dioxide and calcite at four temperatures in the range 350 degrees to 610 degrees C and between carbon dioxide and dolomite at 350 degrees and 400 degrees C. Carbon of unusual isotopic composition was used as a tracer to demonstrate the nature and extent of the exchange process. Extrapolation of these data at lower temperatures indicates that at 25 degrees C dolomite is enriched in oxygen-18 by 6.8 per mil with respect to calcite. This result indicates that those natural dolomite-calcite assemblages which show very small fractionations were not formed in isotopic equilibrium. 相似文献
20.
Acetic acid is an important petrochemical that is currently produced from methane (or coal) in a three-step process based on carbonylation of methanol. We report a direct, selective, oxidative condensation of two methane molecules to acetic acid at 180 degrees C in liquid sulfuric acid. Carbon-13 isotopic labeling studies show that both carbons of acetic acid originate from methane. The reaction is catalyzed by palladium, and the results are consistent with the reaction occurring by tandem catalysis, involving methane C-H activation to generate Pd-CH3 species, followed by efficient oxidative carbonylation with methanol, generated in situ from methane, to produce acetic acid. 相似文献