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824 Ergebnisse:

Compound‐specific amino acid 15N stable isotope probing of nitrogen assimilation by the soil microbial biomass using gas chromatography/combustion/isotope ratio mass spectrometry
Rapid Communications in Mass Spectrometry (2016)
A. F. Charteris, T. D. J. Knowles, K. Michaelides, R. P. Evershed

Rationale Organic nitrogen (N) greatly exceeds inorganic N in soils, but the complexity and heterogeneity of this important soil N pool make investigations into the fate of N-containing additions and soil organic N cycling challenging. This paper details a novel approach to investigate the fate of applied N in soils, generating quantitative measures of microbial assimilation and of newly synthesized soil protein. Methods Laboratory incubation experiments applying 15N-ammonium, 15N-nitrate and 15N-glutamate were carried out and the high sensitivity and selectivity of gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) exploited for compound-specific 15N stable isotope probing (15N-SIP) of extracted incubation soil amino acids (AAs; as N-acetyl, O-isopropyl derivatives). We then describe the interpretation of these data to obtain a measure of the assimilation of the applied 15N-labelled substrate by the soil microbial biomass and an estimate of newly synthesised soil protein. Results The cycling of agriculturally relevant N additions is undetectable via bulk soil N content and δ15N values and AA concentrations. The assimilation pathways of the three substrates were revealed via patterns in AA δ15N values with time, reflecting known biosynthetic pathways (e.g. ammonium uptake occurs first via glutamate) and these data were used to expose differences in the rates and fluxes of the applied N substrates into the soil protein pool (glutamate > ammonium > nitrate). Conclusions Our compound-specific 15N-SIP approach using GC/C/IRMS offers a number of insights, inaccessible via existing techniques, into the fate of applied 15N in soils and is potentially widely applicable to the study of N cycling in any soil, or indeed, in any complex ecosystem.
Schlagworte: N , soi , EA

Carbon isotope analyses of n -alkanes released from rapid pyrolysis of oil asphaltenes in a closed system
Rapid Communications in Mass Spectrometry (2016)
Shasha Chen, Wanglu Jia, Ping'an Peng

Rationale Carbon isotope analysis of n-alkanes produced by the pyrolysis of oil asphaltenes is a useful tool for characterizing and correlating oil sources. Low-temperature (320–350°C) pyrolysis lasting 2–3 days is usually employed in such studies. Establishing a rapid pyrolysis method is necessary to reduce the time taken for the pretreatment process in isotope analyses. Methods One asphaltene sample was pyrolyzed in sealed ampoules for different durations (60–120 s) at 610°C. The δ13C values of the pyrolysates were determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). The molecular characteristics and isotopic signatures of the pyrolysates were investigated for the different pyrolysis durations and compared with results obtained using the normal pyrolysis method, to determine the optimum time interval. Several asphaltene samples derived from various sources were analyzed using this method. Results The asphaltene pyrolysates of each sample were similar to those obtained by the flash pyrolysis method on similar samples. However, the molecular characteristics of the pyrolysates obtained over durations longer than 90 s showed intensified secondary reactions. The carbon isotopic signatures of individual compounds obtained at pyrolysis durations less than 90 s were consistent with those obtained from typical low-temperature pyrolysis. Several asphaltene samples from various sources released n-alkanes with distinct carbon isotopic signatures. Conclusions This easy-to-use pyrolysis method, combined with a subsequent purification procedure, can be used to rapidly obtain clean n-alkanes from oil asphaltenes. Carbon isotopic signatures of n-alkanes released from oil asphaltenes from different sources demonstrate the potential application of this method in ‘oil–oil’ and ‘oil–source’ correlations.
Schlagworte: C , oi , GC

Carbon isotope analyses of n -alkanes released from rapid pyrolysis of oil asphaltenes in a closed system
Rapid Communications in Mass Spectrometry (2016)
Shasha Chen, Wanglu Jia, Ping'an Peng

Rationale Carbon isotope analysis of n-alkanes produced by the pyrolysis of oil asphaltenes is a useful tool for characterizing and correlating oil sources. Low-temperature (320–350°C) pyrolysis lasting 2–3 days is usually employed in such studies. Establishing a rapid pyrolysis method is necessary to reduce the time taken for the pretreatment process in isotope analyses. Methods One asphaltene sample was pyrolyzed in sealed ampoules for different durations (60–120 s) at 610°C. The δ13C values of the pyrolysates were determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). The molecular characteristics and isotopic signatures of the pyrolysates were investigated for the different pyrolysis durations and compared with results obtained using the normal pyrolysis method, to determine the optimum time interval. Several asphaltene samples derived from various sources were analyzed using this method. Results The asphaltene pyrolysates of each sample were similar to those obtained by the flash pyrolysis method on similar samples. However, the molecular characteristics of the pyrolysates obtained over durations longer than 90 s showed intensified secondary reactions. The carbon isotopic signatures of individual compounds obtained at pyrolysis durations less than 90 s were consistent with those obtained from typical low-temperature pyrolysis. Several asphaltene samples from various sources released n-alkanes with distinct carbon isotopic signatures. Conclusions This easy-to-use pyrolysis method, combined with a subsequent purification procedure, can be used to rapidly obtain clean n-alkanes from oil asphaltenes. Carbon isotopic signatures of n-alkanes released from oil asphaltenes from different sources demonstrate the potential application of this method in ‘oil–oil’ and ‘oil–source’ correlations
Schlagworte: C , oi , GC

Compound-Specific Isotope Analyses to Assess TCE Biodegradation in a Fractured Dolomitic Aquifer
Groundwater (2016)
Justin A. Clark, Randy L. Stotler, Shaun K. Frape, Walter A. Illman

The potential for trichloroethene (TCE) biodegradation in a fractured dolomite aquifer at a former chemical disposal site in Smithville, Ontario, Canada, is assessed using chemical analysis and TCE and cis-DCE compound-specific isotope analysis of carbon and chlorine collected over a 16-month period. Groundwater redox conditions change from suboxic to much more reducing environments within and around the plume, indicating that oxidation of organic contaminants and degradation products is occurring at the study site. TCE and cis-DCE were observed in 13 of 14 wells sampled. VC, ethene, and/or ethane were also observed in ten wells, indicating that partial/full dechlorination has occurred. Chlorine isotopic values (δ37Cl) range between 1.39 to 4.69‰ SMOC for TCE, and 3.57 to 13.86‰ SMOC for cis-DCE. Carbon isotopic values range between −28.9 and −20.7‰ VPDB for TCE, and −26.5 and −11.8‰ VPDB for cis-DCE. In most wells, isotopic values remained steady over the 15-month study. Isotopic enrichment from TCE to cis-DCE varied between 0 and 13‰ for carbon and 1 and 4‰ for chlorine. Calculated chlorine-carbon isotopic enrichment ratios (ϵCl/ϵC) were 0.18 for TCE and 0.69 for cis-DCE. Combined, isotopic and chemical data indicate very little dechlorination is occurring near the source zone, but suggest bacterially mediated degradation is occurring closer to the edges of the plume.
Schlagworte: C , po , GC , Col

Dynamic anoxic ferruginous conditions during the end-Permian mass extinction and recovery
Nature Communications (2016)
M. O. Clarkson, R. A. Wood, S. W. Poulton, S. Richoz, R. J. Newton, S. A. Kasemann, F. Bowyer, L. Krystyn

The end-Permian mass extinction, ~252 million years ago, is notable for a complex recovery period of ~5 Myr. Widespread euxinic (anoxic and sulfidic) oceanic conditions have been proposed as both extinction mechanism and explanation for the protracted recovery period, yet the vertical distribution of anoxia in the water column and its temporal dynamics through this time period are poorly constrained. Here we utilize Fe–S–C systematics integrated with palaeontological observations to reconstruct a complete ocean redox history for the Late Permian to Early Triassic, using multiple sections across a shelf-to-basin transect on the Arabian Margin (Neo-Tethyan Ocean). In contrast to elsewhere, we show that anoxic non-sulfidic (ferruginous), rather than euxinic, conditions were prevalent in the Neo-Tethys. The Arabian Margin record demonstrates the repeated expansion of ferruginous conditions with the distal slope being the focus of anoxia at these times, as well as short-lived episodes of oxia that supported diverse biota.

Characterization of the water chemistry, sediment 13C and 18O compositions of Kolleru Lake—a Ramsar wetland in Andhra Pradesh, India
Environmental Monitoring and Assessment (2016)
Subrata Das Sharma, D. Sujatha

Specialized morphology corresponds to a generalist diet: linking form and function in smashing mantis shrimp crustaceans
Oecologia (2016)
Maya S. deVries, Brian C. Stock, John H. Christy, Gregory R. Goldsmith, Todd E. Dawson

A Southern Hemisphere record of global trace-metal drawdown and orbital modulation of organic-matter burial across the Cenomanian-Turonian boundary (Ocean Drilling Program Site 1138, Kerguelen Plateau)
Sedimentology (2016)
Alexander J. Dickson, Matthew Saker-Clark, Hugh C. Jenkyns, Cinzia Bottini, Elisabetta Erba, Fabio Russo, Olga Gorbanenko, B. David A. Naafs, Richard D. Pancost, Stuart A. Robinson, Sander van den Boorn, Erdem Idiz

Schlagworte: C , ge , oc , GC

Effects of lipid extraction and ultrafiltration on stable carbon and nitrogen isotopic compositions of fish bone collagen
Rapid Communications in Mass Spectrometry (2016)
Eric J. Guiry, Paul Szpak, Michael P. Richards

Rationale Fish bone collagen isotopic measurements are increasingly important in palaeodietary and paleoenvironmental studies yet differences in the chemical and physical properties of fish relative to other vertebrate bones are rarely considered. Lipid content in fish bone, which can exceed 50%, may underlie the poor collagen integrity criteria typically observed in archaeological studies. Methods We compare stable carbon and nitrogen isotopic and elemental compositions of bone collagen prepared using four different methods from a wide range of modern fish species to: (1) assess the extent to which lipid content influences bone collagen δ13C and δ15N values, and (2) evaluate the relative efficacy of chemical (2:1 chloroform/methanol) and physical (30 kDa ultrafilters) methods for removing lipids from bones. Results Lower δ13C values were observed when the lipid content exceeded 5% of the initial bone mass. The lipid content did not influence the δ15N values. 30 kDa ultrafiltration, a common pretreatment for purifying archaeological collagen, removed fewer lipids and was associated with reduced collagen yields (37% loss) as well as altered amino acid compositions. In contrast, collagen prepared using a 2:1 chloroform/methanol lipid extraction step resulted in significantly improved collagen yields, elemental compositions, and isotopic measurements relative to a control treatment. Conclusions The chemical lipid extraction method (2:1 chloroform/methanol) performed significantly better than the physical lipid extraction method (30 kDa ultrafilters). Given the high quantities of lipids in fish bones we recommend the inclusion of a chemical lipid extraction step when isolating collagen from modern and archaeological fish bones.
Schlagworte: C , N , ar , ec , EA

Plant-mediated rhizospheric interactions in maize-pigeon pea intercropping enhance soil aggregation and organic phosphorus storage
Plant and Soil (2016)
Gina Garland, E. K. Bünemann, A. Oberson, E. Frossard, J. Six

Background and aims In Malawi, strategies are being sought to boost maize production through improvements in soil fertility. This study assessed the impact of intercropping maize (Zea mays) with pigeon pea (Cajanus cajan) in Lixisols of Malawi on yield, biological N fixation, soil aggregation, and P forms within soil aggregates. Methods Maize and pigeon pea were grown intercropped in pots, with varying degrees of root interaction in order to understand the relative importance of biochemical versus physical rhizospheric interactions. Following harvest, soils were separated into aggregate fractions using wet-sieving, and the nutrient content of all fractions was assessed. Results The proportion of macroaggregates and microaggregates increased by 52 and 111%, respectively, in the intercropping treatment compared to sole maize, which significantly increased organic P storage in the microaggregates of intercropped compared to sole maize (84 versus 29 mg P kg−1, respectively). Biologically fixed N increased from 89% in the sole pigeon pea to 96% in the intercropped system. Conclusions Intercropping maize with pigeon pea can have a significant and positive impact on soil structure as well as nutrient storage in these high P-sorbing soils. This is caused primarily by physical root contact and to a lesser degree by biochemical activities.