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PubMed2003

Anomalous nitrogen isotope ratio in comets.

High-resolution spectra of the CN B2 summation operator +-X2 summation operator + (0,0) band at 390 nanometers yield isotopic ratios for comets C/1995 O1 (Hale-Bopp) and C/2000 WM1 (LINEAR) as follows: 165 +/- 40 and 115 +/- 20 for 12C/13C, 140 +/- 35 and 140 +/- 30 for 14N/15N. Our N isotopic measurements are lower than the terrestrial 14N/15N = 272 and the ratio for Hale-Bopp from measurements of HCN, the presumed parent species of CN. This isotopic anomaly suggests the existence of other parent(s) of CN, with an even lower N isotopic ratio. Organic compounds like those found in interplanetary dust particles are good candidates.

Carbon Isotopes↗
PubMed2005

The effect of dietary protein quality on nitrogen isotope discrimination in mammals and birds.

We tested the competing hypotheses that (1) nitrogen discrimination in mammals and birds increases with dietary nitrogen concentration or decreasing C:N ratios and, therefore, discrimination will increase with trophic level as carnivores ingest more protein than herbivores and omnivores or (2) nitrogen discrimination increases as dietary protein quality decreases and, therefore, discrimination will decrease with trophic level as carnivores ingest higher quality protein than do herbivores. Discrimination factors were summarized for five major diet groupings and 21 different species of birds and mammals. Discrimination did not differ between mammals and birds and decreased as protein quality (expressed as biological value) increased with trophic level (i.e., herbivores to carnivores). Relationships between discrimination factors and dietary nitrogen concentration or C:N ratios were either the opposite of what was hypothesized or non-significant. Dietary protein quality accounted for 72% of the variation in discrimination factors across diet groupings. We concluded that protein quality established the baseline for discrimination between dietary groupings, while other variables, such as dietary protein intake relative to animal requirements, created within-group variation. We caution about the care needed in developing studies to understand variation in discrimination and subsequently applying those discrimination factors to estimate assimilated diets of wild animals.

Animals↗
PubMed2002

The in vivo nitrogen isotope discrimination among organic plant compounds.

The bulk delta 15 N-value of plant (leaf) biomass is determined by that of the inorganic primary nitrogen sources NO(3)(-), NH(4)(+) and N(2), and by isotope discriminations on their uptake or assimilation. NH(4)(+) from these is transferred into "organic N" mainly by the glutamine synthetase reaction. The involved kinetic nitrogen isotope effect does not become manifest, because the turnover is quantitative. From the product glutamine any further conversion proceeds in a "closed system", where kinetic isotope effects become only efficient in connection with metabolic branching. The central and most important corresponding process is the GOGAT-reaction, involved in the de novo nitrogen binding and in recycling processes like the phenylpropanoid biosynthesis and photorespiration. The reaction yields relatively 15N-depleted glutamate and remaining glutamine, source of 15N-enriched amide-N in heteroaromatic compounds. Glutamate provides nitrogen for all amino acids and some other compounds with different 15N-abundances. An isotope equilibration is not connected to transamination; the relative delta 15 N-value of individual amino acids is determined by their metabolic tasks. Relative to the bulk delta 15 N-value of the plant cell, proteins are generally 15N-enriched, secondary products like chlorophyll, lipids, amino sugars and alkaloids are depleted in 15N. Global delta 15 N-values and 15N-patterns of compounds with several N-atoms can be calculated from those of their precursors and isotope discriminations in their biosyntheses.

Biological Transport↗
PubMed2006

Stable carbon and nitrogen isotope ratio profiling of sperm whale teeth reveals ontogenetic movements and trophic ecology.

Teeth from male sperm whales (Physeter macrocephalus) stranded in the North-eastern Atlantic were used to determine whether chronological profiles of stable isotope ratios of C (delta(13)C) and N (delta(15)N) across dentine growth layers could be used to detect known ontogenetic benchmarks in movements and trophic ecology. Profiles showed a general decrease in delta(13)C (median = 1.91 per thousand) and an increase in delta(15)N (median = 2.42 per thousand) with age. A marked decline in delta(13)C occurred for all 11 teeth around 9-10 years and again for six individuals around 20 years. After the early twenties the delta(13)C continued to decline with age for all teeth. These results are consistent with males segregating from natal groups in low latitudes with the onset of puberty between 4 and 15 years and gradually dispersing pole-ward into (13)C-depleted temperate waters. Penetration into further depleted, productive high latitudes after the age of 20 might facilitate the spurt of accelerated growth rate observed around this age. Breeding migrations back to lower latitudes were not reflected in the delta(13)C profiles possibly due to being short compared to the time spent feeding in high latitudes. The timings of marked isotopic change in the delta(15)N profiles reflect those of the delta(13)C profiles, suggesting a link between dietary changes and movements. The observed increase in delta(15)N with age is likely to be caused by a trophic level increase as males grow in size, probably feeding on larger prey. An additional explanation could be that, in the higher latitudes of the North Atlantic, the main prey source is the high trophic level squid Gonatus fabricii. Also, the lower latitudes from where males disperse are depleted in basal (15)N. Profiles of delta(13)C and delta(15)N in sperm whale teeth gathered from different regions, sexes, and periods in time, could provide a unique way to understand the ecology of this species across different oceans.

Age Factors↗
PubMed2004

The use of carbon and nitrogen isotope ratios to identify landfill leachate contamination: Green Island Landfill, Dunedin, New Zealand.

A study was undertaken to determine whether the isotopic ratios of C and N could be used to uniquely identify municipal solid waste landfill leachate as a source of contamination in the Kaikorai Estuary, Dunedin, New Zealand. Leachate samples were taken from the adjacent Green Island Landfill (GILF), and surface water samples were collected over an 8-month period from the stream and estuary, upstream and downstream of the landfill. Samples were analysed for delta(13)C-dissolved inorganic carbon (DIC), delta(15)N-NO(3)(-), delta(15)N-NH(4)(+), and particulate organic matter (POM) delta(13)C and delta(15)N. Plant material collected along the Kaikorai Stream was analysed for POM delta(13)C and delta(15)N. Leachate was found to have a distinct isotopic signature characterised by a highly enriched delta(13)C-DIC (as much as 16.11+/-0.23 per thousand ) and highly enriched delta(15)N-NH(4)(+) (as much as 27.42+/-0.90 per thousand ). Evidence of leachate contamination was found in the isotopic signatures of downstream delta(13)C-DIC, delta(15)N-NH(4)(+), and delta(13)C and delta(15)N of plant material POM. Other potential sources of enriched delta(13)C-DIC and delta(15)N-NH(4)(+) present in the study area, such as estuarine waters and livestock effluent, were eliminated on the basis of their isotopic characteristics.

Animals↗
PubMed2002

Stable carbon and nitrogen isotope values of bone and teeth reflect weaning age at the Medieval Wharram Percy site, Yorkshire, UK.

We report on the measurements of carbon and nitrogen stable isotopes of both bone and teeth from a single site and population (Medieval Wharram Percy), undertaken to explore variations due to weaning in a past population. There have been a number of recent studies of weaning using delta(15)N values of ribs, and we indicate a number of assumptions that must be met before the results of such studies can be correctly interpreted. We found that rib collagen delta(15)N values decrease to adult levels after age 2 years, indicating that weaning occurred at or before this age. Rib collagen delta(13)C values are also more enriched than adult delta(13)C values before age 2 years, and we argue that this is due to the so-called "carnivore" effect in delta(13)C. We measured teeth and rib delta(15)N values from the same individuals and found that for individuals up to age 11 years, tooth dentine delta(15)N is higher than adult rib delta(15)N values, indicating that the dentine was formed during breast-feeding and that there was almost no turnover of dentine since. We observed some decrease in delta(13)C and delta(15)N rib values, compared to adult rib and teeth values, for the few years after weaning that may relate to a theoretically predicted physiological nitrogen imbalance during this period of rapid growth, but this is more likely due to a childhood diet (up to age 9) which was isotopically different from later diet, possibly consisting of a greater proportion of plant foods.

Adolescent↗
PubMed2006

The effects of anthropogenic organic matter inputs on stable carbon and nitrogen isotopes in organisms from different trophic levels in a southern Mediterranean coastal area.

Stable isotope ratios were used to determine the impact of anthropogenically derived organic matter from onshore and offshore fish farming and a sewage outfall on organisms at different trophic levels (primary producers and consumers) on the south-east coast of Sicily (Italy, Mediterranean). Representative macroalgae and consumers were collected in three sampling locations: "Impact" and two putative "Controls" sited to the north of the impacted location. While delta(13)C values of both organic matter sources and consumers varied little between locations, delta(15)N spatial variability was higher and delta(15)N was shown to be a good descriptor of organic enrichment and uptake of anthropogenically derived material within coastal food webs. Isotopic data were analysed using a multivariate approach. Organic matter sources and benthic components were more sensitive to pollution than nektobenthic species and revealed that the effects of anthropogenic activities seem to be detectable over a wide area. The study site is characterised by wide waste dispersal, which brings a reduction in impact in the area directly affected by organic matter inputs and enlarges the area of moderate impact.

Alismatales↗
PubMed1998

The origin of chondritic macromolecular organic matter: a carbon and nitrogen isotope study.

The N and C abundances and isotopic compositions of acid-insoluble carbonaceous material in thirteen primitive chondrites (five unequilibrated ordinary chondrites, three CM chondrites, three enstatite chondrites, a CI chondrite and a CR chondrite) have been measured by stepped combustion. While the range of C isotopic compositions observed is only delta 13C = 30%, the N isotopes range from delta 15N approximately -40 to 260%. After correction for metamorphism, presolar nanodiamonds appear to have made up a fairly constant 3-4 wt% of the insoluble C in all the chondrites studied. The apparently similar initial presolar nanodiamond to organic C ratios, and the correlations of elemental and isotopic compositions with metamorphic indicators in the ordinary and enstatite chondrites, suggest that the chondrites all accreted similar organic material. This original material probably most closely resembles that now found in Renazzo and Semarkona. These two meteorites have almost M-shaped N isotope release profiles that can be explained most simply by the super-position of two components, one with a composition between delta 15N = -20 and -40% and a narrow combustion interval, the other having a broader release profile and a composition of delta 15N approximately 260%. Although isotopically more subdued, the CI and the three CM chondrites all appear to show vestiges of this M-shaped profile. How and where the components in the acid-insoluble organics formed remains poorly constrained. The small variation in nanodiamond to organic C ratio between the chondrite groups limits the local synthesis of organic matter in the various chondrite formation regions to at most 30%. The most 15N-rich material probably formed in the interstellar medium, and the fraction of organic N in Renazzo in this material ranges from 40 to 70%. The isotopically light component may have formed in the solar system, but the limited range in nanodiamond to total organic C ratios in the chondrite groups is consistent with most of the organic material being, presolar.

Carbon↗
PubMed2001

Nitrogen isotope ratios in pine bark as an indicator of N emissions from anthropogenic sources.

The article describes the use of Scots pine bark to identify nitrogen sources in eastern Germany, as well as background areas in Russia and Bulgaria, by using natural isotope ratios of total nitrogen (Nt) and individual N compounds such as ammonium (NH4+), nitrate (NO3-) and amid nitrogen (amide-N). The samples collected were analysed using an elemental analyser in connection with a gas isotope mass spectrometer (EA-IRMS). Natural 15N abundances in pine bark from impact areas suggest that the ammonium accumulated on the surface of the bark is released from livestock management. Bark of Scots pines growing near agricultural land had highly depleted delta15Nt values (between -8 and -12 one thousand percent), while bark from background areas (unpolluted areas) displayed slightly negative delta15Nt values (mean 15Nt = -3.8 one thousand percent). It is assumed that part of the N adsorbed on the bark surface is mainly derived from ammonia (mean 15Nt = -40.3 one thousand percent) escaping from livestock housing and during the application of manure. This assumption is confirmed by experiments under controlled conditions in which manure samples were spread on soil. In addition, temporal and spatial variations of 15Nt abundances in pine bark from various locations in eastern Germany as well as pine stands in Nature Park Dübener Heath are discussed.

Agriculture↗
PubMed1995

Fractionation of nitrogen isotopes by mixed ruminal bacteria.

Mixed ruminal bacteria were cultured with glucose, cellulose or no carbohydrate, and ammonium bicarbonate or casein hydrolysate. Changes in amounts of bacterial ammonia and non-ammonia N were measured. Ratios of N isotopes expressed as delta 15N (delta 15N) were measured by isotope ratio mass spectrometry. When bacteria were cultured with glucose and ammonium bicarbonate, bacterial delta 15N decreased from .9 to -5.8/1000 and residual ammonia delta 15N increased from -1.4 to 12.7/1000. Fractionation of N isotope occurred during ammonia incorporation because the difference between delta 15N of ammonia and delta 15N of bacteria (delta 15N) was 18.8/1000 (P < .01). However, when casein hydrolysate was the N source, delta 15N between non-ammonia and bacteria averaged only 1.3/1000 (P > .1), indicating no fractionation of N isotopes occurred during utilization of amino acids. The amount of bacterial N was highest at 24 h of incubation when cellulose was the carbohydrate source. At that time, delta 15N between ammonia and bacteria was 8.9/1000 when ammonia was the N source, but delta 15N between non-ammonia and bacteria was 1.7/1000 when casein hydrolysate was the N source. Bacterial N decreased after 24 h when cellulose was the source of carbohydrate. Results indicate that fractionation of N isotopes occurred during ammonia incorporation, but not during incorporation of N from amino acids, deamination, and release of ammonia. Fractionation of N isotopes during incorporation of ammonia N may be used as a marker to study N metabolism by ruminal bacteria.

Amino Acids↗