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1.
Many studies have documented that the δ 13C values of plants increase with altitude both on a global scale and locally in humid climates, while in semi‐arid areas the opposite trend has been found. The study reported herein was conducted in a mountainous area of China characterized by a temperate semi‐humid climate. The δ 13C values of C 3 species do not exhibit a consistent variation along an altitudinal gradient and the observations suggest that the pattern of increasing δ 13C with altitude cannot be generalized. In the study area, in addition to environmental factors such as changing air pressure and light, the interaction between temperature and plant water balance determines the δ 13C‐altitude variations in C 3 plants. The δ 13C of the leaves of C 4 plants is found to increase with altitude with a mean gradient of 0.9‰/km. The altitudinal trend of C 4 plants is attributed to the combined influences of water availability and other factors rather than temperature. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
2.
We report the first high‐precision characterization of molecular and intramolecular δ 15N of nucleosides derived from mammalian DNA. The influence of dietary protein level on brain amino acids and deoxyribonucleosides was determined to investigate whether high protein turnover would alter amino acid 15 N or 13 C values. Pregnant guinea pig dams were fed control diets, or high or low levels of dietary protein throughout gestation, and all pups were fed control diets. The cerebellar DNA of offspring was extracted at 2 and 120 days of life, nucleosides isolated and δ 15N and δ 13C values characterized. Mean diet δ 15N was 0.45 ± 0.33‰, compared with cerebellar whole tissue and DNA δ 15N = +4.1 ± 0.7‰ and ?4.5 ± 0.4‰, respectively. Cerebellar deoxythymidine (dT), deoxycytidine (dC), deoxyadenosine (dA), and deoxyguanosine (dG) δ 15N were +1.4 ± 0.4, –2.1 ± 0.9, –7.2 ± 0.3, and ?10.4 ± 0.5‰, respectively. There were no changes in amino acid or deoxyribonucleoside δ 15N values due to dietary protein level. Using known metabolic relationships, we developed equations to calculate the intramolecular δ 15N values originating from aspartate (asp) in purines (pur) or pyrimidines (pyr), glutamine (glu), and glycine (gly) to be δ 15N ASP‐PUR, δ 15N ASP‐PYR, δ 15N GLN, and δ 15N GLY +11.9 ± 2.3‰, +7.0 ± 2.0‰, –9.1 ± 2.4‰, and ?31.8 ± 8.9‰, respectively. A subset of twelve amino acids from food and brain had mean δ 15N values of 4.3 ± 3.2‰ and 13.8 ± 3.1‰, respectively, and δ 15N values for gly and asp were 12.6 ± 2.2‰ and 15.2 ± 0.8‰, respectively. A separate isotope tracer study detected no significant turnover of cerebellar DNA in the first six months of life. The large negative δ 15N difference between gly and cerebellar purine N at the gly (7) position implies either that there is a major isotope effect during DNA synthesis, or that in utero gly has a different isotope ratio during rapid growth and metabolism from that in adult life. Our data show that cerebellar nucleoside intramolecular δ 15N values vary over more than 40‰ and are not influenced by dietary protein level or age. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
3.
Fifty‐two samples of substituted benzylideneanilines XPhCH?NPhYs (XBAYs) were synthesized, and their NMR spectra were determined in this paper. Together with the NMR data of other 77 samples of XBAYs quoted from literatures, the 1H NMR chemical shifts (δ H(CH?N)) and 13C NMR chemical shifts (δ C(CH?N)) of the CH?N bridging group were investigated for total of 129 samples of XBAYs. The result shows that the δ H(CH?N) and δ C(CH?N) have no distinctive linear relationship, which is contrary to the theoretical thought that declared the δ H(CH?N) values would increase as the δ C(CH?N) values increase. With the in‐depth analysis, we found that the effects of σ F and σ R of X/Y group on the δ H(CH?N) and the δ C(CH?N) are opposite; the effects of the substituent specific cross‐interaction effect between X and Y (Δσ 2) on the δ H(CH?N) and the δ C(CH?N) are different; the contributions of parameters in the regression equations of the δ H(CH?N) and the δ C(CH?N) [Eqns 4 and 7), respectively] also have an obvious difference. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
4.
α-cellulose is widely used as a target substance for isotope ratio analysis in environmental reconstructions. Its preparation includes three basic steps: organic solvent extraction, delignification and alkaline hydrolysis. Recent works have suggested omission of the first step. We have made a detailed comparison in carbon isotope ratio of α-cellulose with or without organic solvent extraction using 32 consecutive tree ring and 30 subfossil peat samples. These samples were exposed to three different chemical treatments: with organic solvent extraction as the first step (Cell OE), without organic solvent extraction (Cell NOE), and with organic solvent extraction as the final step (Cell NOE/OE). The third treatment is used to test if organic extractives can be completely removed or if their solubility in organic solvents has been altered by delignification and alkaline hydrolysis. In tree rings and peat, δ 13C C ell NOE was always significantly different from δ 13C C ell OE, but the trends were not the same. In tree rings, δ 13C C ell NOE was always more negative than δ 13C C ell OE by ?0.31 ~ ?0.01‰. In contrast, δ 13C C ell NOE in peat could be more negative or more positive than δ 13C C ell OE by ?3.08 ~ 0.27‰. The third chemical treatment resulted in different patterns. For tree rings, δ 13C C ell NOE/OE was still more negative than δ 13C C ell OE by ?0.36 ~ ?0.08‰. However, the differences between δ 13C C ell NOE/OE and δ 13C C ell OE for peat varied in a more narrow range from ?0.58 to 0.61‰, compared to the differences between δ 13C C ell NOE and δ 13C C ell OE. These results exposed a complex chemical evolution behaviour and an incomplete removal of lipids during delignification and alkaline hydrolysis. The mean value, long-term trend and seesaw patterns for a tree ring or peat Cell NOE series were significantly different from those for a Cell OE series, indicating that omission of organic solvent extraction will lead to a biased inference of past environmental conditions. 相似文献
5.
A recent literature review reported negative relationships between diet discrimination factors (DDFs = X fish – X food; X = δ 15N or δ 13C) and the values of δ 15N and δ 13C in the food of wild organisms but there has been no laboratory‐based confirmation of these relationships to date. Laboratory reared guppies ( Poecilia reticulata) fed a series of diets with a range of δ 13C (?22.9 to ?6.6‰) and δ 15N (6.5 to 1586‰) values were used to magnify diet‐tissue dynamics in order to calculate DDFs once the fish had achieved equilibrium with each of the diets. Values of DDFs range widely for δ 15N (7.1 to ?849‰) and δ 13C (1.1 to ?7.0‰) and showed a strong negative correlation with the stable isotope value in the food for δ 15N (slope = ?0.59 ± 0.02, r 2 = 0.95) and δ 13C (slope = ?0.56 ± 0.02, r 2 = 0.94). Based on these relationships, the magnitude of DDF change over environmentally relevant values of δ 15N or δ 13C would be significant and could confound the interpretation of stable isotopes in the environment. Using highly enriched experimental diets, our study adds to a growing number of studies that undermine the consistent trophic enrichment paradigm with results that demonstrate the currently poor mechanistic understanding of how DDFs arise. The results of our study highlight that the magnitude of the stable isotope values in prey must be considered when choosing DDF values. Future laboratory studies should therefore be directed at uncovering the mechanistic basis of DDFs and, like others before, we recommend the determination of diet‐dependent DDFs under laboratory conditions before modeling dietary proportions or calculating trophic positions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
6.
Currently, bacterial denitrification is becoming the accepted method for δ 15N‐ and δ 18O‐NO determination. However, proper correction methods with international references (USGS32, USGS34 and USGS35) are needed. As a consequence, it is important to realize that the corrected isotope values are derived from a combination of several other measurements with associated uncertainties. Therefore, it is necessary to consider the propagated uncertainty on the final isotope value. This study demonstrates how to correctly estimate the uncertainty on corrected δ 15N‐ and δ 18O‐NO values using a first‐order Taylor series approximation. The bacterial denitrification method errors from 33 batches of 561 surface water samples varied from 0.2 to 2.1‰ for δ 15N‐NO and from 0.7 to 2.3‰ for δ 18O‐NO, which is slightly wider than the machine error, which varied from 0.2 to 0.6‰ for δ 15N‐N 2O and from 0.4 to 1.0‰ for δ 18O‐N 2O. The overall uncertainties, which are composed of the machine error and the method error, for the 33 batches ranged from 0.3 to 2.2‰ for δ 15N‐NO and from 0.8 to 2.5‰ for δ 18O‐NO. In addition, the mean corrected δ 15N and δ 18O values of 132 KNO 3‐IWS (internal working standard) measurements were computed as 8.4 ± 1.0‰ and 25.1 ± 2.0‰, which is a slight underestimation for δ 15N and overestimation for δ 18O compared with the accepted values (δ 15N = 9.9 ± 0.3‰ and δ 18O = 24.0 ± 0.3‰). The overall uncertainty of the bacterial denitrification method allows the use of this method for source identification of NO. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
7.
The present study was aimed to investigate the variation of stable isotopic ratios of carbon, nitrogen, hydrogen, and oxygen in wheat kernel along with different processed fractions from three geographical origins across 5 years using isotope ratio mass spectrometry (IRMS). Multiway ANOVA revealed significant differences among region, harvest year, processing, and their interactions for all isotopes. The region contributed the major variability in the δ 13C ‰, δ 2H ‰, δ 15N ‰, and δ 18O‰ values of wheat. Variation of δ 13C ‰, δ 15N ‰, and δ 18O ‰ between wheat whole kernel and its products (break, reduction, noodles, and cooked noodles) were ?0.7‰, and no significant difference was observed, suggesting the reliability of these isotope fingerprints in geographical traceability of wheat‐processed fractions and foods. A significant influence of wheat processing was observed for δ 2H values. By applying linear discriminant analysis (LDA) to the whole dataset, the generated model correctly classified over 91% of the samples according to the geographical origin. The application of these parameters will assist in the development of an analytical control procedure that can be utilized to control the mislabeling regarding geographical origin of wheat kernel and its products. 相似文献
8.
1H, 13C, 15N and 195Pt NMR studies of gold(III) and platinum(II) chloride organometallics with N(1),C(2′)‐chelated, deprotonated 2‐phenylpyridine (2ppy*) of the formulae [Au(2ppy*)Cl 2], trans( N, N)‐[Pt(2ppy*)(2ppy)Cl] and trans(S,N)‐[Pt(2ppy*)(DMSO‐ d6)Cl] (formed in situ upon dissolving [Pt(2ppy*)(µ‐Cl)] 2 in DMSO‐ d6) were performed. All signals were unambiguously assigned by HMBC/HSQC methods and the respective 1H, 13C and 15N coordination shifts (i.e. differences between chemical shifts of the same atom in the complex and ligand molecules: Δ 1Hcoord = δ 1Hcomplex ? δ 1Hligand, Δ 13Ccoord = δ 13Ccomplex ? δ 13Cligand, Δ 15Ncoord = δ 15Ncomplex ? δ 15Nligand), as well as 195Pt chemical shifts and 1H‐ 195Pt coupling constants discussed in relation to the known molecular structures. Characteristic deshielding of nitrogen‐adjacent H(6) protons and metallated C(2′) atoms as well as significant shielding of coordinated N(1) nitrogens is discussed in respect to a large set of literature NMR data available for related cyclometallated compounds. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
9.
By combining Hartree–Fock results for nonrelativistic ground-state energies of N-electron atoms with analytic expressions for the large-dimension limit, we have obtained a simple renormalization procedure. For neutral atoms, this yields energies typically threefold more accurate than the Hartree–Fock approximation. Here, we examine the dependence on Z and N of the renormalized energies E(N, Z) for atoms and cations over the range Z, N = 2 → 290. We find that this gives for large Z = N an expansion of the same form as the Thomas–Fermi statistical model, E → Z 7/2(C 0 + C 1Z ?1/3 + C 2Z ?2/3 + C 3Z ?3/3 + ?), with similar values of the coefficients for the three leading terms. Use of the renormalized large- D limit enables us to derive three further terms. This provides an analogous expansion for the correlation energy of the form δ E δ Z4/3(δC 3 + δC 5Z ?2/3 + δC 6Z ?3/3 + ?); comparison with accurate values of δ E available for the range Z ? 36 indicates the mean error is only about 10%. Oscillatory terms in E and δ E are also evaluated. © 1994 John Wiley & Sons, Inc. 相似文献
10.
Individual free amino acid δ15N values in plant tissue reflect the metabolic pathways involved in their biosynthesis and catabolism and could thus aid understanding of environmental stress and anthropogenic effects on plant metabolism. In this study, compound-specific nitrogen isotope analysis of amino acid by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) was carried out to determine individual free amino acid δ15N values. High correlations were observed between the δ15N values obtained by GC-C-IRMS and elemental analyzer-isotope ratio mass spectrometry (EA-IRMS) determinations, and the mean precision measured was better than 1 ‰. Cation-exchange chromatography was employed to purify the sample, and the difference between prior to and following passage through the resin was within 1 ‰. The amino acid δ15N values of plant leave samples following incubation in 15N-nitrate at different time points were determined. A typical foliar free amino acid 15N-enrichment pattern was found, and glutamine was the most rapidly labeled amino acid; other amino acids derived from the GS-GOGAT cycle were also enriched. The pyruvate family amino acids were labeled less quickly followed by the aromatic amino acids. This study highlighted that amino acid metabolism pathways had a major effect on the δ15N values. With the known amino acid metabolism pathways and δ15N values determined by the presented method, the influence of various external factors on the metabolic cycling of amino acid can be understood well. 相似文献
11.
We examined an applicability of an improved urea adduction technique for the determination of hydrogen isotopic composition (δD) of homologous series of n-alkanes present in polluted urban aerosols using GC/TC/IRMS. Unresolved complex mixture (UCM) of hydrocarbons that interferes with accurate isotope measurements of n-alkanes was removed from n-alkane fraction by a urea adduction method. Recoveries of C 20 to C 30 n-alkanes during the urea adduction procedure were greater than 90% when the concentrations of total n-alkanes exceed 6.1?µg?mL ?1. Our compound-specific D/H ratios confirm the absence of significant hydrogen isotope fractionation in n-alkanes during urea adduction and recovery of the purified n-alkane fraction. We applied this technique to the urban aerosols that contain a large quantity of UCM to measure δD of C 20 to C 35 n-alkanes in urban aerosols from Tokyo and Sapporo with an accuracy less than 10‰. We found that the δD values widely ranged from ?38 to ?179‰. Based on the δD values of individual n-alkanes in aerosol samples, we can obtain further information on the sources of aerosol n-alkanes and their source regions, and the atmospheric processes such as long-range transport and atmospheric mixing of air masses of different origin. 相似文献
12.
The nitrogen (δ 15N) and oxygen isotope (δ 18O) analysis of nitrate (NO 3–) from aqueous samples can be used to determine nitrate sources and to study N transformation processes. For these purposes, several methods have been developed; however, none of them allows an accurate, fast and inexpensive analysis. Here, we present a new simple method for the isolation of nitrate, which is based on the different solubilities of inorganic salts in an acetone/hexane/water mixture. In this solvent, all major nitrate salts are soluble, whereas all other oxygen‐bearing compounds such as most inorganic carbonates, sulfates, and phosphates are not. Nitrate is first concentrated by freeze‐drying, dissolved in the ternary solvent and separated from insoluble compounds by centrifugation. Anhydrous barium nitrate is then precipitated in the supernatant solution by adding barium iodide. For δ 18O analysis, dried Ba(NO 3) 2 samples are directly reduced in a high‐temperature conversion system to CO and measured on‐line using isotope ratio mass spectrometry (IRMS). For δ 15N analysis, samples are combusted in an elemental analyzer (EA) coupled to an IRMS system. The method has been tested down to 20 µmol NO 3– with a reproducibility (1SD) of 0.1‰ for nitrogen and 0.2–0.4‰ for oxygen isotopes. For nitrogen we observed a small consistent 15N enrichment of +0.2‰, probably due to an incomplete precipitation process and, for oxygen, a correction for the incorporation of water in the precipitated Ba(NO 3) 2 has to be applied. Apart from being robust, this method is highly efficient and low in cost. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
13.
The stable isotopes of water (hydrogen and oxygen isotopes) are of utmost interest in ecology and the geosciences. In many cases water has to be extracted directly from a matrix such as soil or plant tissue before isotopes can be analyzed by mass spectrometry. Currently, the most widely used technique for water is cryogenic vacuum extraction. We present a simple and inexpensive modification of this method and document tests conducted with soils of various grain size and tree core replicates taken on four occasions during 2010. The accuracies for sandy soils are between 0.4‰ and 3‰ over a range of 21‰ and 165‰ for δ 18O and δ 2H, respectively. Spiking tests with water of known isotope composition were conducted with soil and tree core samples; they indicate reliable precision after an extraction time of 15 min for sandy soils. For clayey soils and tree cores, the deviations were up to 0.63‰ and 4.7‰ for δ 18O and δ 2H, respectively. This indicates either that the extraction time should be extended or that mechanisms different from Rayleigh fractionation play a role. The modified protocol allows a fast and reliable extraction of large numbers of water samples from soil and plant material in preparation for stable isotope analyses. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
14.
Accurate determinations of stable isotope ratios require a calibration using at least two reference materials with different isotopic compositions to anchor the isotopic scale and compensate for differences in machine slope. Ideally, the δ values of these reference materials should bracket the isotopic range of samples with unknown δ values. While the practice of analyzing two isotopically distinct reference materials is common for water (VSMOW‐SLAP) and carbonates (NBS 19 and L‐SVEC), the lack of widely available organic reference materials with distinct isotopic composition has hindered the practice when analyzing organic materials by elemental analysis/isotope ratio mass spectrometry (EA‐IRMS). At present only L‐glutamic acids USGS40 and USGS41 satisfy these requirements for δ13C and δ15N, with the limitation that L‐glutamic acid is not suitable for analysis by gas chromatography (GC). We describe the development and quality testing of (i) four nicotine laboratory reference materials for on‐line (i.e. continuous flow) hydrogen reductive gas chromatography‐isotope ratio mass‐spectrometry (GC‐IRMS), (ii) five nicotines for oxidative C, N gas chromatography‐combustion‐isotope ratio mass‐spectrometry (GC‐C‐IRMS, or GC‐IRMS), and (iii) also three acetanilide and three urea reference materials for on‐line oxidative EA‐IRMS for C and N. Isotopic off‐line calibration against international stable isotope measurement standards at Indiana University adhered to the ‘principle of identical treatment’. The new reference materials cover the following isotopic ranges: δ2H nicotine ?162 to ?45‰, δ13C nicotine ?30.05 to +7.72‰, δ15N nicotine ?6.03 to +33.62‰; δ15N acetanilide +1.18 to +40.57‰; δ13C urea ?34.13 to +11.71‰, δ15N urea +0.26 to +40.61‰ (recommended δ values refer to calibration with NBS 19, L‐SVEC, IAEA‐N‐1, and IAEA‐N‐2). Nicotines fill a gap as the first organic nitrogen stable isotope reference materials for GC‐IRMS that are available with different δ15N values. Comparative δ13C and δ15N on‐line EA‐IRMS data from 14 volunteering laboratories document the usefulness and reliability of acetanilides and ureas as EA‐IRMS reference materials. Published in 2009 by John Wiley & Sons, Ltd. 相似文献
15.
A new analytical method is presented for the compound-specific carbon and nitrogen isotope ratio analysis of a thermo-labile nitramine explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by gas chromatograph coupled to an isotope ratio mass spectrometer (GC-IRMS). Two main approaches were used to minimise thermal decomposition of the compound during gas chromatographic separation: programmed temperature vaporisation (PTV) as an injection technique and a high-temperature ramp rate during the GC run. δ 15N and δ 13C values of RDX measured by GC-IRMS and elemental analyser (EA)-IRMS were in good agreement within a standard deviation of 0.3‰ and 0.4‰ for nitrogen and carbon, respectively. Application of the method for the isotope analysis of RDX during alkaline hydrolysis at 50°C revealed isotope fractionation factors ε carbon?=??7.8‰ and ε nitrogen?=??5.3‰. 相似文献
16.
The composition and molecular residence time of soil organic matter (SOM) in four particle‐size fractions (POM >200 µm, POM 63–200 µm, silt and clay) were determined using Curie‐point pyrolysis/gas chromatography coupled on‐line to mass spectrometry. The fractions were isolated from soils, either continuously with a C 3 wheat (soil 13C value = ?26.4‰), or transferred to a C 4 maize (soil 13C value = ?20.2‰) cropping system 23 years ago. Pyrograms contained up to 45 different pyrolysis peaks; 37 (ca. 85%) were identifiable compounds. Lignins and carbohydrates dominated the POM fractions, proteins were abundant, but lignin was (nearly) absent in the silt and clay fractions. The mean turnover time (MRT) for the pyrolysis products in particulate organic matter (POM) was generally <15 years (fast C pool) and 20–300 years (medium or slow C pools) in silt and clay fractions. Methylcyclopentenone (carbohydrate) in the clay fraction and benzene (mixed source) in the silt fraction exhibited the longest MRTs, 297 and 159 years, respectively. Plant‐derived organic matter was not stored in soils, but was transformed to microbial remains, mainly in the form of carbohydrates and proteins and held in soil by organo‐mineral interactions. Selective preservation of plant‐derived OM (i.e. lignin) based on chemical recalcitrance was not observed in these arable soils. Association/presence of C with silt or clays in soils clearly increased MRT values, but in an as yet unresolved manner (i.e. ‘truly’ stabilized, or potentially still ‘labile’ but just not accessible C). Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
17.
Using molecular and isotopic mass spectrometry, we investigated the toxic effect of naphthalene as a representative of polycyclic aromatic hydrocarbons (PAHs) on plants growing under sterile conditions and plants inoculated with microorganisms capable and incapable of naphthalene degradation. Tobacco plants of the Samsun variety were grown in a closed gas-nutrient system on a mineral medium with sucrose as a carbon source. Naphthalene used as a toxicant at a concentration of 5.2 × 10 ?4% contained 13C isotope whose amount was characterized by the value δ 13C = +281.4 ± 0.6‰ relative to the PDB standard and differed from that of sucrose, the main source of carbon (δ 13C = ?12.0 ± 0.1‰). Degradation of naphthalene was determined by the inclusion of its carbon in metabolic CO 2 and plant tissues (the root, stem, leaves). The effect of naphthalene on plants was indicated by the rates of O 2 production and CO 2 uptake during the light period as compared with the dark period of exposure. A decrease of the toxic effect of naphthalene on plants was observed only at the inoculation of plants with Pseudomonas aureofaciens BS1393 rhizosphere bacteria bearing plasmid pBS216, which controls the naphthalene biodegradation ability. The occurrence of other heterotrophic microorganisms incapable of naphthalene degradation had no similar protective effect. 相似文献
18.
Natural 15N abundances (δ 15N values) of different soil nitrogen pools deliver crucial information on the soil N cycle for the analysis of biogeochemical processes. Here we report on a complete suite of methods for sensitive δ 15N analysis in soil extracts. A combined chemical reaction of vanadium(III) chloride (VCl 3) and sodium azide under acidic conditions is used to convert nitrate into N 2O, which is subsequently analyzed by purge‐and‐trap isotope ratio mass spectrometry (PTIRMS) with a cryo‐focusing unit. Coupled with preparation steps (microdiffusion for collection of ammonium, alkaline persulfate oxidation to convert total dissolved N (TDN) or ammonium into nitrate) this allows the determination of the δ 15N values of nitrate, ammonium and total dissolved N (dissolved organic N, microbial biomass N) in soil extracts with the same basic protocol. The limits of quantification for δ 15N analysis with a precision of 0.5‰ were 12.4 µM for ammonium, 23.7 µM for TDN, 16.5 µM for nitrate and 22.7 µM for nitrite. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
19.
We investigated the δ 15N profile of N (extractable NH, NO, and organic N (EON)) in the soil of a N‐saturated subtropical forest. The order of δ 15N in the soil was EON > NH > NO. Although the δ 15N of EON had been expected to be similar to that of bulk soil N, it was higher than that of bulk soil N by 5‰. The difference in δ 15N between bulk soil N and EON (Δ 15N bulk‐EON) was correlated significantly with the soil C/N ratio. This correlation implies that carbon availability, which determines the balance between N assimilation and dissimilation of soil microbes, is responsible for the high δ 15N of EON, as in the case of soil microbial biomass δ 15N. A thorough δ 15N survey of available N (NH, NO, and EON) in the soil profiles from the organic layer to 100 cm depth revealed that the δ 15N of the available N forms did not fully overlap with the δ 15N of plants. This mismatch in δ 15N between that of available N and that of plants reflects apparent isotopic fractionation during N uptake by plants, emphasizing the high N availability in this N‐saturated forest. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
20.
NMR Spectroscopic Studies of 15N Labelled N-Methyl-imidodiphosphoric Acid Derivatives 15N labelled compounds (EtO) mCl 2?m(O)P? NMe? P(O)(OEt) nCl 2?n (m = 0–2, n = 0–2) were prepared as a mixture and investigated by means of 31P and 15N NMR spectroscopy. The chemical shift values δ P and δ N, and the coupling constants 1J PN and 2J PP are discussed and interpreted qualitatively by semiempirical quantumchemical calculations (CNDO/2) using POPLE 'S ΔE-model. 相似文献
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