Compound-specific Isotope Ratio Mass Spectrometry Research Articles

Isotope applications to soil science at the University of Alberta — an historical perspective

For the past 70 yr, researchers in the Soil Science/Renewable Resources Department at the University of Alberta have used isotopes to study topics of ecological importance. This review highlights the soil isotope research conducted within our department over this time, including an historical overview of studies of interest. Analytical techniques and advances in instrumentation are discussed, focusing on the measurement of light stable isotope ratios (i.e., for C, H, N, S, and O) using isotope ratio mass spectrometry (IRMS). Early soil isotope work (1950–2000s) focused on agricultural soils and soil fertility issues. These studies included the use of radioactive isotopes such as 14C and 35S, and (or) artificially enriched stable isotopes including 15N-labelled fertilizers. More recently (2000–present), the scope of research widened to include natural-abundance stable isotope ratio studies as higher-sensitivity IRMS systems became more prevalent. Current isotope research topics include N biogeochemistry in natural and managed ecosystems, land management effects on greenhouse gas emissions, carbon cycling in northern landscapes, paleo-reconstruction in peatlands, carbon sequestration in boreal forests, and biodegradation of petroleum hydrocarbons. Further technological progress also enabled new techniques such as compound-specific IRMS analysis, including δ13C and δ2H measurements of soil n-alkanes and phospholipid fatty acids. In conclusion, current IRMS instrumentation presents unparalleled opportunities for multidisciplinary research to track carbon, plant nutrients, and pollutants as they move through soils.

Discriminating methane sources in ground gas emissions in NW England

The identification of the source of methane (CH 4 ) and carbon dioxide (CO 2 ) in gases within unconsolidated deposits outside municipal landfill sites, where there are multiple potential contributing gas inputs, is important for regulation and to inform gas management policy. Stable isotope analysis was applied to ground gas samples from boreholes close to but external to landfill cells, and landfill gas, to differentiate CH 4 from biological and abiological geological sources at sites in NW England. Landfill flare gas and landfill without external gas inputs were biogenic references. Ground gases adjacent to one landfill had potential external CH 4 inputs from underlying Coal Measures. Mineshaft vent gas and commercially-supplied North Sea gas were used as non-biological, thermogenic, source references. Ground gas samples were subjected to Compound-Specific Isotope Ratio Mass Spectrometry (GC-IRMS) and conventional IRMS examination. δ 13 C C H 4 values for landfill flare gas and landfill Site 1 were −65.0 and −61.0‰, and δ D C H 4 values were −319 and −298‰ respectively, consistent with a wholly biogenic origin. δ 13 C C H 4 values for Site 2 landfill were −55 to −48‰, and δ D C H 4 values were −173 to +55‰. Mineshaft vent gas and North Sea gas CH 4 δ 13 C C H 4 values were −46.2 and −43.5‰, and δ D C H 4 values were −214 and −203‰, respectively. Given their similarity to these data, gases in the vicinity of Site 2 landfill are considered to have a thermogenic CH 4 contribution, due to 13 C and D enrichment in CH 4 .

Archaeal and bacterial glycerol dialkyl glycerol tetraether (GDGT) lipids in environmental samples by high temperature-gas chromatography with flame ionisation and time-of-flight mass spectrometry detection

Archaeal isoprenoidal glycerol dibiphytanyl glycerol tetraether lipids (iGDGTs) and their non-isoprenoidal branched bacterial analogues (brGDGTs) have widespread applications in biogeochemistry and paleothermometry. Analysis of GDGTs usually involves separation using high performance liquid chromatography, typically coupled via atmospheric pressure chemical ionisation to mass spectrometric detection in selected ion-monitoring mode (HPLC–APCI-MS). However, reliable determination of ratios and, in particular, quantification by this technique, can be challenging due to differences in ionisation efficiencies of the various compounds. Quantification of GDGTs also relies on external calibration of the relative response to an internal standard with authenticated GDGTs, which are often not readily accessible. Here, we tested the suitability of high temperature gas chromatography with flame ionisation detection (HTGC-FID) for the determination of concentrations and tetraether lipid-based ratios in marine and terrestrial samples. For this, we identified GDGTs in environmental samples using HTGC coupled to time-of-flight mass spectrometry (HTGC–MS). Using a purified GDGT standard, we show we can quantify GDGT-0 in environmental samples by GC-FID. Some GDGT-based ratios measured by HTGC-FID exhibited a linear correlation (1:1) with ratios derived from HPLC–MS and weight-based ratios of mixtures of purified standards. However, ratios relying on minor isomers, such as TEX86 and MBT/CBT have many unresolved challenges for determination by HTGC. Detection limits were higher than for HPLC–MS. However, the advantages of employing HTGC-based methods include: (1) the independence from MS tuning-related differences in ionisation energies; (2) the potential for direct comparison with other, non-GDGT based biomarkers; and (3) a more complete insight into biomarker distributions in environmental samples by the extension of the temperature range. Quantitative elution of GDGTs from a HTGC column as demonstrated herein, will also enable their analysis by compound-specific isotope ratio mass spectrometry.

Compound-specific δ(13)C analyses reveal sterol metabolic constraints in an aquatic invertebrate.

Dietary sterol deficiencies can have severe life history consequences for consumers. Compound-specific stable isotope analysis (CSIA) was applied to the exploration of the sterol metabolic constraints and bioconversion capacities of the amphipod Gammarus roeselii. Evaluating structural sterol requirements has great potential to improve our understanding of the ecological relevance of sterols as limiting nutrients. Juvenile G. roeselii were reared on food mixtures consisting of different ratios of the two algae Scenedesmus obliquus (cultivated with (13)C-labeled NaHCO3) and Nannochloropsis limnetica (unlabeled), which have been shown previously to differ in food quality. We measured the sterol content and composition using a gas chromatograph equipped with a flame ionization detector and the δ(13)C values of sterols using compound-specific isotope ratio mass spectrometry to examine potential sterol-mediated nutritional constraints of G. roeselii. In the food mixtures, δ(13)C values of cholesterol, synthesized by N. limnetica, were -25‰ and those of the Δ(7)-phytosterols, chondrillasterol and fungisterol, synthesized by S. obliquus, were 7 and 18‰, respectively. Although the cholesterol concentrations in G. roeselii decreased with increasing proportion of dietary S. obliquus, the δ(13)C values remained constant at -25‰. Lathosterol, which appeared in G. roeselii at high dietary proportions of S. obliquus, had a δ(13)C value of 35‰. We provide evidence that the the Δ(7)-phytosterols present in S. obliquus cannot be metabolized to cholesterol in G. roeselii, resulting in the accumulation of lathosterol in the animals and potentially in sterol-limited growth. These findings emphasize the advantage of CSIA in revealing the physiological mechanisms associated with nutritional constraints.

New insight from old bones: stable isotope analysis of fossil mammals

Stable isotope analysis of fossil materials has become an increasingly important method for gathering dietary and environmental information from extinct species in terrestrial and aquatic ecosystems. The benefits of these analyses stem from the geochemical fingerprint that an animal's environment leaves in its bones, teeth, and tissues. Ongoing study of living mammals has found the stable isotopic composition of several light (hydrogen, carbon, nitrogen, oxygen, and sulfur) and even a few heavy (calcium and strontium) elements to be useful tracers of ecological and physiological information; many of these can be similarly applied to the study of fossil mammals. For instance, the carbon isotopic composition of an animal's tissues tracks that of the food it eats, whereas the oxygen isotopic compositions of the carbonate and phosphate in an animal's bones and teeth are primarily controlled by that of the surface water it drinks or the water in the food it ingests. These stable isotope proxies for diet and habitat information are independent of inferences based on morphological characters and thus provide a means of testing ecological interpretations drawn from the fossil record. As such, when well-preserved specimens are available, any dietary study of fossil species should seriously consider including this approach. To illustrate the potential benefits associated with applying these methods to paleontological research, a review of current work on the ecological and evolutionary history of fossil mammals through geochemical analysis is presented. After a brief introduction to issues associated with the preservation of stable isotopic information in soft and mineralized tissues, a series of case studies involving the application of stable isotope analysis to fossil mammal research is discussed. These studies were selected to highlight the versatility of this analytical method to paleontological research and are complemented by a discussion of new techniques and instrumentation in stable isotope analysis (e.g., laser ablation and compound-specific isotope ratio mass spectrometry, and calcium and clumped isotopes), which represent the latest advances in the extension of these geochemical tools to the paleontology of fossil mammals.

Carbon dynamics in mycorrhizal symbioses is linked to carbon costs and phosphorus benefits

The nutrient and carbon (C) allocation dynamics in mycorrhizal hyphal networks cause variation in costs and benefits for individual plants and fungi and influence the productivity, diversity and C cycling in ecosystems. We manipulated light and phosphorus (P) availability in a pot experiment with Trifolium subterraneum colonised by the arbuscular mycorrhizal (AM) fungus Glomus intraradices. Stable (13)C-labelling was used to trace assimilated CO(2) to the mycorrhizal fungus in roots and soil using compound-specific isotope ratio mass spectrometry. We used the neutral lipid fatty acid 16:1omega5 as a signature for AM fungal storage lipids. Both P and shading reduced the AM fungal lipid accumulation in the intraradical mycelium, while only P reduced the amount of lipids in the extraradical mycelium. Recently assimilated plant C was only allocated to the mycorrhizal fungus to a small extent when plant mycorrhizal benefit was reduced by P fertilization, while increasing the plant C cost by shading did not reduce the C flow to the fungus. These results are of importance for our conception of mycorrhizal dynamics during periods of shade in nature.

Introduction to a Virtual Special Issue: probing the carbon cycle with 13C

Introduction to a <i>Virtual Special Issue</i>: probing the carbon cycle with ¹³C

Microbial biosyntheses of individual neutral sugars among sets of substrates and soils

The presence of neutral carbohydrates in soil organic matter (SOM) in significant amount is apparently in contradiction with their lability. It may result either from stabilization or from continuous recycling of SOM by micro-organisms and biosynthesis of microbial sugars. To address this question, it was necessary to precisely determine the average yield of sugar biosyntheses and the distribution of individual sugars. We performed incubations of 13C labelled substrates and quantified biosyntheses of neutral carbohydrates using compound-specific isotope ratio mass spectrometry. To investigate the natural variation of the microbial biotransformations, we varied the soil characteristics on the one hand and the substrate on the other. Incubation kinetics reflected the existence of two pools of carbohydrate metabolites. One pool was characterized by its lability with a mean residence time of about two weeks, whereas the second was preserved from biodegradation. The yield of sugar production by soil micro-organisms was poorly affected by the quality of the substrates glucose, cellulose and glycine, and very similar distributions of individual sugars were observed (Glc > Gal = Man = Rham > Xyl = Ara = Fuc). Soil type affected sugar biosyntheses slightly more, reflecting some diversity of either microbial communities or ecophysiology among soils. These results provided important indications to further calibrate a comprehensive model of carbohydrate dynamics in soils.

Rhizodeposition shapes rhizosphere microbial community structure in organic soil

The aims of the study were to determine group specificity in microbial utilization of root-exudate compounds and whole rhizodeposition; quantify the proportions of carbon acquired by microbial groups from soil organic matter and rhizodeposition, respectively; and assess the importance of root-derived C as a driver of soil microbial community structure. Additions of 13C-labelled root-exudate compounds to organic soil and steady-state labelling of Lolium perenne, coupled to compound-specific isotope ratio mass spectrometry, were used to quantify group-specific microbial utilization of rhizodeposition. Microbial utilization of glucose and fumaric acid was widespread through the microbial community, but glycine was utilized by a narrower range of populations, as indicated by the enrichment of phospholipid fatty acid (PLFA) analysis fractions. In L. perenne rhizospheres, high rates of rhizodeposit utilization by microbial groups showed good correspondence with increased abundance of these groups in the rhizosphere. Although rhizodeposition was not the quantitatively dominant C source for microbes in L. perenne rhizospheres, relative utilization of this C source was an important driver of microbial group abundance in organic soil.

Flow cytometric detection of phosphatase activity combined with 13C-CO2 tracer-based growth rate assessment in phytoplankton populations from a shallow lake

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 37:159-169 (2004) - doi:10.3354/ame037159 Flow cytometric detection of phosphatase activity combined with 13C-CO2 tracer-based growth rate assessment in phytoplankton populations from a shallow lake Marco Dignum1,2,*, Hans L. Hoogveld1, Virgilio Floris1, Herman J. Gons1, Hans C. P. Matthijs2, Roel Pel1 1Netherlands Institute of Ecology (NIOO-KNAW), Centre for Limnology, Rijksstraatweg 6, 3631 AC Nieuwersluis, The Netherlands 2University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Department of Aquatic Microbiology, Nieuwe Achtergracht 127, 1018 WS Amsterdam, The Netherlands *Email: m.dignum@nioo.knaw.nl ABSTRACT: To determine nutrient availability and growth rates of phytoplankton on a population level, improvement of discriminative power in fluorescence-activated cell sorting is required. We have combined fluorescence of the endogenous photosynthetic pigments chlorophyll a and phycocyanin with a phosphate deficiency (P-deficiency) related stain (enzyme-labelled fluorescence, ELF-97) that yields green fluorescent precipitates at the site of phosphatase activity, referred to as ELF alcohol (ELFA) fluorescence, to sort phytoplankton from Lake Loosdrecht (The Netherlands). Stable isotope labelling with 13C-enriched CO2 enabled assessment of specific growth rates of sorted populations by pyrolytic methylation-gas chromatography and in-line compound specific isotope-ratio mass spectrometry. The dominant population in the lake, the filamentous cyanobacterium Limnothrix sp., was growing under P-deficiency in spring, but the availability of phosphate increased in summer. Continuous flow of phosphate-rich medium into a laboratory-scale enclosure of lake water resulted in washout of the cells with ELFA fluorescence, and increased growth rates. In addition, this study revealed population heterogeneity within the cluster of phycocyanin-containing cyanobacteria. ELFA fluorescence thus reflects the level of P-deficiency of freshwater cyanobacteria and micro-algae, but is modulated by metabolic activity of cells within the population. KEY WORDS: Alkaline phosphatase · Enzyme-labelled fluorescence · Filamentous cyanobacteria · Fluorescence-activated cell sorting · Population-specific growth rate · Phytoplankton · Stable isotope labelling Full article in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 37, No. 2. Online publication date: November 11, 2004 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2004 Inter-Research.

Stable carbon isotope variation of n-alkanes in Central Graben oils

While isotope analysis of bulk fractions is a well-tried and useful tool in oil correlation, use of compound specific isotope ratio mass spectrometry (CS-IRMS) of individual hydrocarbons is still in its infancy. This technique has been developed over the past few years as a useful research tool, but its potential in petroleum exploration has yet to be demonstrated. In this paper both bulk fraction and individual hydrocarbon isotopic data were acquired. Their use was evaluated and compared with traditional geochemical measurements such as gas chromatography and GC-MS. Data on 72 oils from the Norwegian sector of the Central Graben were acquired. Data include δ 13C isotope composition of whole oil and topped oil, as well as saturated and aromatic hydrocarbon, NSO and asphaltene fractions, and δ 13C isotopic composition of individual n-alkanes in the range nC 4 to nC 35. The same samples were also analysed by capillary GC and GC-MS. GC, GC-MS and bulk fraction isotope data suggest that many of the analysed Greater Ekofisk oils (e.g. Valhall, Edlfisk), i.e. within the Lindesnes Ridge Inversion zone have more than one source facies. Outside of this area, particularly towards the northwest, oils are probably mainly from a single source facies. The isotopic compositions of individual hydrocarbon compounds also reveal the same divisions. In addition, several further features were observed. The normal alkanes of many of the Greater Ekofisk oils are more depleted in 12C between nC 20– nC 25 than at higher or lower molecular weight (possibly representative of the original microbial precursors). Other oils have relatively uniform n-alkane isotope profiles, with n-alkanes which are enriched in 12C relative to the n-alkanes of oils with the other type of profile. The two different isotope profiles are interpreted as being separate source facies. The least mature Greater Ekofisk oils also become more enriched in 12C with decreasing molecular weight. Mature oils from this area tend to have very similar n-alkane isotope values throughout the measured n-alkane range. The higher maturity oils and condensates have n-alkanes < nC 8, which are more depleted in 12C than the n-alkanes > nC 8. The tentative interpretation of this is that the highly mature oils/condensates are sourced only from highly mature source rocks, i.e. of a condensate window maturity and are not products of thermal alteration in the reservoir.