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1.
Carbon isotope ratios (δ13C) of plants, litter and soil organic matter (0–5 cm, 5–10 cm and 10–20 cm) on the eastern slope of Mount Gongga were measured. The results show that δ13C values of plants, litter and soil organic matter all decrease first and then increase with altitude, i.e δ13C values gradually decrease from 1200 to 2100 m a.s.l., and increase from 2100 to 4500 m a.s.l. The δ13C altitudinal variations are related to the distribution of C3 and C4 plants on the eastern slope of Mount Gongga, because C4 plants are observed to grow only below 2100 m, while C3 plants occur at all altitudes. There are significantly positive correla-tions among δ13C of vegetation, δ13C of litter and δ13C of soil organic matter, and litter, 0–5 cm, 5–10 cm and 10–20 cm soil or-ganic matter are 0.56‰, 2.87‰, 3.04‰ and 3.49‰ greater in δ13C than vegetation, respectively. Considering the influences of rising concentration of atmospheric CO2 and decreasing δ13C of atmospheric CO2 since the industry revolution on δ13C of plants, 1.57‰ is proposed to be the smallest correction value for reconstruction of paleovegetation using δ13C of soil organic matter. 相似文献
2.
Haiping Tang 《科学通报(英文版)》1999,44(14):1316-1316
The distribution of C4 plants and the C4/C3 ratio along Northeast China transect (NECT) have been studied. A model to quantify their relation with environmental factors
has been set up. The ratio of the number of C4 plants to that of C3 plants along NECT shows two low and two high trends from east to west, and their distribution is mainly decided by annual
average temperature and precipitation. 相似文献
3.
There are many controversial issues in loess studies such as natural vegetation types on the Chinese Loess Plateau during the historical periods and the spatial and temporal evolution of C3/C4 plants. Elemental carbon isotopic composition (δ^13Cec) in the loess section may offer new evidence for these problems. Elemental carbon (EC) is produced by incomplete combustion of vegetation, and its carbon isotopic composition has a very small difference from that of the formal vegetation, then δ^13Cec can be used as a record to recover the changes of vegetation. Elemental carbon was extracted by applying the oxidation method from the Ioess-paleosol sequence in the central Chinese Loess Plateau, and its car- bon isotope composition was analyzed by the isotope mass spectrometer. The results showed that the vegetation in this region was a mixed type of C3 and C4 plants, dominated with C3 plants in most of the time. Since late Quaternary, C3/C4 plants may not follow a simple glacial-interglacial cycle mode on the Chinese Loess Plateau, but showing fluctuations. C3 plants increased gradually in L4 period, and more C3 plants occurred during $3 period, and C4 plants increased again during L3-- L2 periods, after that, Cs plants dominated again during S1 --S0 periods. During periods of paleosol development, C3 plants were abundant in S3 and S1, and there were more Ca plants in S2 and SO. During periods of loess sedimen- tation, there were more C3 plants in L4 and L1, and there were more C4 plants in L3 and L2. On the orbital timescale, the vegetation variations revealed by δ^13Cec record are consistent with the results of pollen data and also similar to the results obtained by organic carbon isotopic composition since the last glacial period. 相似文献
4.
The primary factor controlling C 3 /C 4 relative abundance in terrestrial ecosystem since the Last Glacial has been widely debated. Now more and more researchers recognize that climate, rather than atmospheric CO 2 concentration, is the dominant factor. However, for a specific area, conflicting viewpoints regarding the more influential one between temperature and precipitation still exist. As temperature and precipitation in a specific area usually not only vary within limited ranges, but also covary with each other, it is difficult to get a clear understanding of the mechanism driving C 3 /C4 relative abundance. Therefore, systematic analysis on greater spatial scales may promote our understanding of the driving force. In this paper, records of C3/C4 relative abundance since the Last Glacial on a global scale have been reviewed, and we conclude that: except the Mediterranean climate zone, C3 plants predominated the high latitudes during both the Last Glacial and the Holocene; from the Last Glacial to the Holocene, C4 relative abundances increased in the middle latitudes, but decreased in the low latitudes. Combining with studies of modern process, we propose a simplified model to explain the variations of C3 /C4 relative abundance in global ecosystem since the Last Glacial. On the background of atmospheric CO2 concentration since the Last Glacial, temperature is the primary factor controlling C3/C4 relative abundance; when temperature is high enough, precipitation then exerts more influence. In detail, in low latitudes, temperature was high enough for the growth of C4 plants during both the Last Glacial and the Holocene; but increased precipitation in the Holocene inhibited the growth of C4 plants. In middle latitudes, rising temperature in the Holocene promoted the C4 expansion. In high latitudes, temperature was too low to favor the growth of C4 plants and the biomass was predominated by C3 plants since the Last Glacial. Our review would benefit interpretation of newly gained records of C3/C4 relative abundance from different areas and different periods, and has its significance in the understanding of the driving mechanisms of C3/C4 variations on longer timescales (e.g., since the late Miocene) with reliable records of temperature and atmospheric CO2 concentration. 相似文献
5.
Qiang Xu Lin Ding LiYun Zhang Di Yang FuLong Cai QingZhou Lai Jing Liu RenDeng Shi 《科学通报(英文版)》2010,55(1):45-54
Fossil tooth enamel from herbivores is considered one of the best proxies for paleoclimate and paleoelevation reconstructions, due to its low susceptibility to diagenetic alteration. A synthesis of oxygen and carbon isotope analyses of modern tooth enamel from herbivores such as Tibetan yaks, asses and antelopes is assessed. The average δ 13C(PDB) value of herbivore tooth enamel in the Lhasa and south Qiangtang terrains is-11.3‰± 1.1‰, whereas in the north Qiangtang and Hoh Xil terrains value is-10.2‰± 1.4‰... 相似文献
6.
Carbon isotopic records in paleosols over the Pliocene in Northern China: Implication on vegetation development and Tibetan uplift 总被引:2,自引:0,他引:2
Carbon isotopic composition of pedogenic carbonate can be used to estimate the proportion of C4 and C3 plants. Here we present carbon isotopic data of carbonate in a red earth section at Xifeng, central Loess Plateau. Results
show that C4 vegetation increased in ∼4.4 Ma B.P., stabilized between 4.0 and 3.0 Ma B.P. The character and timing of C4 expansion on the Loess Plateau are similar, but different with other localities, e.g. Pakistan and Africa, implying that
regional climate changes were main factors driving the expansion of C4 plants. This event is comparable in timing with increased aridity evidenced by Xifeng grain size and North Pacific eolian
dust records. Therefore we argue that the Pliocene expansion of C4 plants in northern China might have been caused by the increased aridity, which in turn might be related to rapid uplift
of the Tibetan Plateau. 相似文献
7.
Surface soil samples collected over a high spatial resolution in eastern China were analyzed for carbon isotope composition (δ^13C) of total organic carbon (TOC) and higher plant-derived long-chain n-alkanes, with the latter reported as weighted mean values. The two sets of δ^13C values are significantly correlated and show similar trends in spatial variation. The spatial distribution of δ^13C shows less negative values in the mid-latitudes between 31°N and 40°N and more negative ones at higher and lower latitudes. This is consistent with previously reported carbon isotope data from surface soil phytoliths in the same region and suggests that the mid-latitude area provides relatively favorable growing condi- tions for C4 plants. Furthermore, δ^13C values of both TOC and long-chain n-alkanes from 12 surface soil samples collected from a small grassland in north China displayed similar carbon isotope values and the difference between paired δ^13C of a soil samples remains relatively constant. Our data demonstrate that in eastern China, soil δ^13C composition of both TOC and long-chain n-alkanes is effective indicators of C3/C4 ratios of the prevailing vegetation. This work suggests that -22‰ and -32‰ are good es- timated end members for the weighted mean δ^13C values of long-chain n-alkanes (C27, C29 and C31 n-alkanes) from soils under dominant C4 or C3 vegetation, allowing us to reconstruct paleovegetation trends. 相似文献
8.
According to the investigations of five loess sections in Shanxi Province, China, it was found that the concentrations of the major greenhouse gases CO2, CH4 and N2O in loess-paleosol sequences are generally high, even sometimes may be several times or scores of times higher than their atmospheric concentrations respectively. Although the CO2 concentration in the same loess section shows poor regularity among different layers, it increases slowly from north to south in space. The CH4 concentration in the layers under Malan Loess is much higher than that in the atmosphere, although it is not high in Malan Loess. Most of the δ13C values of CO2 in loess are -11.14‰—15.48‰ (relative to PDB standard). Analysis of carbon isotopic compositions of CO2 indicates that the main source of CO2 in loess section is decomposition of ‘stable’ organic matters by microbes. The δ13Cg of CO2 is a little heavier than organic source for exchanging carbon isotope with carbonate in loess. The abundant carbonate in loess not only makes the loess a huge carbon reservior but also adjusts 相似文献
9.
Tian XiaoSi Zhu Cheng Sun ZhiBin Shui Tao Huang YunPing Flad Rowan Kimon Li YuMei 《科学通报(英文版)》2011,56(2):169-178
Based on AMS 14C dating data, carbon and nitrogen isotope analyses were conducted on mammal bone collagen of deer, cattle and pigs from the Zhongba site in the Three Gorges Reservoir region of the Yangtze River. These analyses were conducted to reconstruct palaeodiets of mammals, palaeoecology, palaeoenviroment and previous human activities in the study area. Results show that the collagen loss of bone did not change the in vivo isotopic composition of carbon and nitrogen stable isotopes, and most of the bone fossils were well preserved. The bone collagen of samples from deer had a mean δ13C of -23.1‰ and a mean δ15N of 4.7‰, suggesting that deer subsisted in a closed habitat and fed on branches and leaves. The bone collagen of cattle had a mean δ13C of –19.6‰ and a mean δ15N of 5.2‰, which indicates that cattle subsisted in an open habitat and fed on grasses and stems. The δ13C values show that both deer and cattle fed on C3 plants and lived in the same ecosystem, but the t-test results show that deer δ13C and δ15N values were both more negative than those of cattle, indicating that they inhabited different niches. The δ13C and δ15N values of cattle partially overlapped those of deer, suggesting some competition in diets between them. The t-tests show that the δ13C and δ15N values of pigs were more positive than those of cattle and deer, which signifies that pigs occupied a higher trophic level compared to cattle and deer. The wide range of pig δ13C values demonstrates that pig trading had been taking place from early Neolithic Age to late Bronze Age. There were no significant differences in deer δ13C and δ15N values among different archaeological periods, making it clear that climatic, ecological and environmental conditions were kept relatively stable from 2200 to 4200 a BP. This stability may have been responsible for the extensive and complete cultural layers at the Zhongba site. The minimum number of samples required to estimate the mean δ13C values of deer, pigs and cattle are 8, 73 and 16, respectively, and for mean δ15N values of deer, pigs and cattle, the minimum numbers are 4, 5 and 6, respectively. 相似文献
10.
Electronic structures and infrared spectra of C120XY molecules (X, Y=O, S) and some of the corresponding ions are investigated using PM3 semi-empirical molecular orbital calculations
with full optimization of geometrical structures. It is found that the energy penalty is about 30–42 kJ/mol due to introducing
a double bond in the fivemembered ring except for C120O2
− and triplet C120O2
2−. It is also found that the structures of neutral molecules and the corresponding ions are almost the same; for instance,
the change of bond length is less than 0.001 nm. The change of frontier orbits from oxide to sulfide is little as well. The
triplet states of C120O2
2− and C120OS2− are more stable than their singlet states, which means that C120O2
2− and C120OS2− follow the Hund’s rule. The vibration analysis showed that the infrared spectra of neutral C120O2 and C120OS molecules are in good agreement with the experimental results. Compared with the neutral molecule, vibration frequencies
of triplet C120O2
2− change little, but the vibration intensities are enhanced obviously. 相似文献
11.
RAO ZhiGuo ZHU ZhaoYu ZHANG JiaWu 《科学通报(英文版)》2007,52(2):259-266
Paleoecological records of soil δ^13Corg from three regions in the middle latitudes of the Northern Hemisphere, including the Chinese Loess Plateau (CLP), the Great Plains and adjacent areas of North America and northwestern Europe, showed different variations since the Last Glacial period. An attempt was made to evaluate the causes for the difference in δ^13Corg on the basis of the modern climatic data collected in these regions and of the modern C3 and C4 plant distributions. The analysis indicates that temperature, especially the growing season temperature, has a dominant control on the growth of C4 plants. When the mean annual or growing season temperatures are below the "threshold value", the growth of C4 plants is limited. When the temperature is above the "threshold value", C4 plants can grow under a wide range of precipitation. However, when the precipitation is high enough to favor the growth of trees, the proportions of C4 plants in local biomass will decline. The implicit control factor recovered by sedimentary records is consistent with the control factor on modern C3/C4 distribution. Pure C3 plants have been dominating the local biomass since the Last Glacial period in European loess region, mainly owing to the low local temperature. The increases in C4 plants from the late Pleistocene to the Holocene in the Chinese Loess Plateau, the Great Plains and adjacent areas, mainly reflect the influence of increasing temperature. 相似文献
12.
LI XiaoDong 《科学通报(英文版)》2008,53(21):3281-3286
Configurations of three η2 models of transition-metal [60]fullerene derivatives C60M(CO)5(M=Cr, Mo and W) have been optimized at B3LYP/LanL2DZ level. On the basis of the optimized geometrical structures, their electronic spectra and the frequency dependence of third-order nonlinear optical polarizabilities γ in different optical processes of third-harmonic generation (THG), electric-field-induced second-harmonic generation (EFISHG) and degenerate four-wave mixing (DFWM) are calculated by using TDB3LYP model based on LanL2DZ level coupled with the SOS (sum-over-state) method. The obtained results show that their electronic spectra have a red shift compared with that of [60]fullerene and different transition-metal functional groups added to C60 cage may result in different spectrum properties. For the three studied species, (η^2-C60)Mo(CO)5 has the largest third-order nonlinear optical polarizability. 相似文献
13.
Pedogenic carbonate isotope record of vegetational evolution since late Miocene in Loess Plateau 总被引:2,自引:0,他引:2
Isotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai (35°N), the Loess Plateau. Stable carbon isotopic composition indicates that ( i ) C4 plants might be present at least by7.0 Ma; ( ii ) C4 plants expanded gradually between ~4.0 and ~3.2 Ma, and their biomass fraction was up to 50% ; and (Ⅲ ) the biomass of C4 vegetation since ~2.0 Ma seems to have been decreased to the level (about 20%) before 4.0 Ma. C4 plant expansion at Lingtai cannot be fully understood with the "global C4 expansion" model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C3/C4 shift except changes in atmospheric CO2 concentrations and temperature. The latitudinal zone for C3/C4 transition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N癗 is the ideal boundary for the C4 expansion. 相似文献
14.
The threshold photoelectron spectrum of the C2H3Cl molecule is studied by using synchrotron radiation light source and supersonic molecular beam. The vertical ionization
potentials of different orbital electrons and some vibrational structures are obtained. The observed Rydberg autoionization
peaks are assigned by A2A1 state of C2H3Cl+. 相似文献
15.
GAOYing ZhangZhenlong DUYinxiao DONGHua MOYujun 《科学通报(英文版)》2005,50(1):1-4
The temperature dependence of surface enhanced Raman scattering of the C70 molecule is reported. The Raman scattering of C70 molecules adsorbed on the surface of a silver mirror was measured at different temperatures. The experimental results indicate that the relative intensities of the Raman features vary with the temperature of the sample. When the temperature decreases from room temperature to 0℃, the relative intensifies of certain Raman bands decrease abruptly. If we like the strongest band 1565cm^-1 as a standard value 100, the greatest decrease approaches to 43%. However, with the further decrease in the temperature these relative intensities increase and resume the value at room temperature. And such a temperature dependence is reversible. Our results show that the adsorption state of the C70 molecules on the silver surface around 0℃ changes greatly with the temperature, resulting in a decrease in relative intensities for some main Raman features of C70 molecule. When the temperature is lower than 0℃, the adsorption state changes continually and more slowly. Synchronously, eight new Raman features, which have not ever been reported in fiterature, are observed in our experiment and this enriches the basic information of the vibrational modes for C70 molecule. 相似文献
16.
Relatively high abundance of C31 steranes has been identified from cretaceous source rocks and crude oils in the Songliao Basin, China. C31 steranes which occur as ten isomers were tentatively identified as 4, 22, 23, 24-tetrametyhlcholestane based on their retention
time and mass spectrum. They bear a lower thermal stability and occur as important components in the immature oils of Chaochang
region because they have three-methyl groups in their side chain. The relatively high abundance of C31 steranes in the samples can indicate the source input of some special algae in the brackish and saline environment. Therefore
they can be used as very useful bimarkers for organic facies analysis and oil correlation. Their biological source perhaps
related to the dinoflagellate such asG. foliaceum andP. foliaceum. The gorgostanol are considered as possible precursors for the putative C314-methyl sterane which formed in the stage of diagenesis. 相似文献
17.
YUAN Kun LU LingLing LIU YanZhi 《科学通报(英文版)》2008,53(9):1315-1323
The optimizations geometries and interaction energy corrected by BSSE of the complexes between C4H4Y (Y=O, S) and CHiLi have been calculated at the B3LYP/6-311++G^** and MP2/6-311++G^** levels. Three complexes were obtained. Abnormally, the calculations showed that all the C10--Li14 bond lengths increased obviously but the blue-shift of C10-Li14 stretching frequency occurred after formed complexes. The calculated binding energy with basis set super-position error (BSSE) and zero-point vibrational energy corrections of complexes I-III is -45.757, -35.700 and -39.107 kJ·mol^-1, respectively. The analyses on the combining interaction with the atom-in-molecules theory (AIM) also showed that a relatively strong lithium bond interaction presented in furan homologues C4H4Y-LiCH3 systems. Natural bond orbital theory (NBO) analysis has been performed, and the results revealed that the complex I is formed with n-σ type lithium bond interaction between C4H40 and LiCH3, complex II is formed with TT-s type lithium bond interaction between C4H4O and LiCH3, and complex III is formed with TT-s and n-s type lithium bond interactions between C4H4S and LiCH3, respectively. 相似文献
18.
It was found that C60Br24 transforms to C60 spontaneously in some solvents. The intermediate, C60Br8, can be separated in some cases. When the bromine trap, phenol, was added,p-bromophenol and other brominated product were obtained and identified. The influences of time, the kind of solvent, etc were
investigated. Possible mechanism was suggested.
Supported by the National Natural Science Foundation of China
Liu Ying: born in 1969, Ph. D 相似文献
19.
Pulsed laser photolysis/laser-induced fluorescence (LP-LIF) is utilized to measure rate constants for C2(a3Πu) reactions with NO, N2O, O2, H2 and NH3. Multiphoton dissociation of C2Cl4 at 266 nm is employed for the generation of C2(a3Πu) radicals. The C2(a3Πu) concentration is monitored by the fluorescence of the (0, 0) band of the (d3Πg8596;a3Πu) transition at 516.5 nm. C2(a3Πu) removal rate constants for the reactions are determined as kNO = (5.46 ± 0.10) × 10-11 cm3 molecule-1 s-1 , kN2O = (1.63 ± 0.20) × 10-13 cm3 molecule-1 s-1 , kN2O = (1.58 ± 0.16) × 10-11 cm3 molecule-1 s-1, kO2 = (5.92 ± 1.00) × 10-14 cm3 molecule-1 s-1, kH2< 1.0× 10-14 cm3 molecule-1 s-1. Based on the data analysis and theoretical calculation, we suggest that the C2(a3Πu) reactions with H2 and NH3 proceed via the hydrogen abstraction mechanism, barriers exist at the entrance channel of the reactions of C2(a3Πu) with H2 and NH3. 相似文献
20.
Surface snow samples were collected during the 14th (1997/1998) and 24th (2007/2008) Chinese National Antarctica Research Expeditions along a transect from Zhongshan Station to Dome A. The stable oxygen isotope ratios of these samples were measured to investigate their relationships with temperature and geographical parameters (latitude, longitude, altitude and distance to the coast). The results reveal a strong positive correlation (R=0.945) between δ18O and mean annual temperature, with a gradient of 0.84‰°C –1, which is a little higher than that in Terre Adelie Land. Regression analyses also show that the δ18O of surface snow is strongly correlated with distance to the coast (R=0.942), latitude (R=0.942), and altitude (R=0.941). But no significant correlation was found between δ18O and longitude in study area. Altitude should be the most important factor influencing the δ18O distribution because of distinctive topography. The δ18O-altitude and T-altitude gradients along this transect are determined to be –1.1‰/100 m and 1.31°C/100 m, respectively. 相似文献