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1

Long-range (1)H-(15)N heteronuclear shift correlation at natural abundance.  

PubMed

Despite the inherently low sensitivity of (15)N NMR because of its low gyromagnetic ratio (gamma(N)) and its relatively low natural abundance (0.37%), this important nuclide still has useful potential as a structural probe even at natural abundance. Inverse-detected NMR methods coupled with major advances in NMR probe designs have made it possible to acquire long-range (1)H-(15)N heteronuclear shift correlation data on samples as small as a micromole overnight. Chemical shift referencing schemes for (15)N and the range of (15)N shifts are discussed, followed by a discussion of the currently available pulse sequences, pulse calibration, parametrization and processing of long-range (1)H-(15)N data, and the implications of probe selection. These topics are followed by a review of the applications contained in the literature that have utilized (1)H-(15)N heteronuclear shift correlation experiments at natural abundance, with emphasis placed on the observed long-range coupling pathways. PMID:10785437

Martin, G E; Hadden, C E

2000-04-01

2

Atmospheric nitrogen is a reliable standard for natural 15N abundance measurements  

NASA Astrophysics Data System (ADS)

Research based on 15N stable isotope variations in natural compounds is expanding in scientific fields such as biogeochemistry (isotope fractionation effects measurements1-7), metabolic studies8,9, hydrology (research of NO3- pollution origin in aquifers10-14), agronomy (estimate of N2 symbiotic fixation by legumes15-17) and oceanography (determination of the source of sedimentary nitrogen18-21). However, intercomparison of results obtained in different laboratories is a problem due to the lack of intercalibrated standards. Atmospheric nitrogen has been chosen by many investigators as a standard20,22,23 and I present here a simple method for the preparation of atmospheric N2 as a standard for ?15N expression with excellent reproducibility. The results indicate a wide homogeneity in isotopic composition of atmospheric nitrogen which appears to be a reliable standard for 15N natural abundance measurements.

Mariotti, André

1983-06-01

3

Short-range spatial variability of soil ? 15 N natural abundance – effects on symbiotic N 2 -fixation estimates in pea  

Microsoft Academic Search

The ?15N natural abundance (‰) of the total soil N pool varies at the landscape level, but knowledge on short-range variability and\\u000a consequences for the reliability of isotopic methods are poorly understood. The short-range spatial variability of soil ?15N natural abundance as revealed by the 15N abundance in spring barley and N2-fixing pea was measured within the 0.15–4 m scale at

L. Holdensen; H. Hauggaard-Nielsen; E. S. Jensen

2007-01-01

4

15 N natural abundance in plants of the Amazon River floodplain and potential atmospheric N 2 fixation  

Microsoft Academic Search

Summary The15N natural abundance values of various Amazon floodplain (várzea) plants was investigated. Samples of young leaf tissues were collected during three different periods of the river hydrography (low water, mid rising water and high water) and during one period in the Madeira River (high water). A large variation of15N abundance was observed, both among the different plant types and

L. A. Martinelli; R. L. Victoria; P. C. O. Trivelin; A. H. Devol; J. E. Richey

1992-01-01

5

Subantarctic Macquarie Island – a model ecosystem for studying animal-derived nitrogen sources using 15 N natural abundance  

Microsoft Academic Search

Plants collected from diverse sites on subantarctic Macquarie Island varied by up to 30‰ in their leaf ?15N values. 15N natural abundance of plants, soils, animal excrement and atmospheric ammonia suggest that the majority of nitrogen utilised\\u000a by plants growing in the vicinity of animal colonies or burrows is animal-derived. Plants growing near scavengers and animal\\u000a higher in the food

Peter D. Erskine; Dana M. Bergstrom; Susanne Schmidt; George R. Stewart; Craig E. Tweedie; Justine D. Shaw

1998-01-01

6

Natural abundance of 15N and 13C in earthworms from a wheat and a wheat-clover field  

Microsoft Academic Search

The natural abundances of the stable isotopes of nitrogen (?15N) and carbon (?13C) were measured in plant shoots and in seven earthworm (Lumbricidae) species from a wheat and a wheat-clover cropping system. Variations in earthworm ?13C were generally small in these systems containing only C3 plants. Plant shoot ?15N ranged from ?2.2‰ to ?0.7‰ in white clover and from +0.9‰

O. Schmidt; C. M. Scrimgeour; L. L. Handley

1997-01-01

7

Estimates of N 2 -fixation from variation in the natural abundance of 15 N in Sonoran desert ecosystems  

Microsoft Academic Search

The 15N abundance of tissues of five Prosopis specimens at our primary study site (a Prosopis woodland at Harper's Well in the Sonoran desert of Southern California) was determined over two growing seasons 1980 and 1981. The 15N abundance of soil and of tissues of presumed non-N2-fixing (control) plants was also measured. Prosopis tissues were significantly lower in 15N than

G. Shearer; D. H. Kohl; R. A. Virginia; B. A. Bryan; J. L. Skeeters; E. T. Nilsen; M. R. Sharifi; P. W. Rundel

1983-01-01

8

Seasonal variation in nitrogen pools and 15N/13C natural abundances in different tissues of grassland plants  

NASA Astrophysics Data System (ADS)

Seasonal changes in nitrogen (N) pools, carbon (C) content and natural abundance of 13C and 15N in different tissues of ryegrass plants were investigated in two intensively managed grassland fields in order to address their ammonia (NH3) exchange potential. Green leaves generally had the largest total N concentration followed by stems and inflorescences. Senescent leaves had the lowest N concentration, indicating N re-allocation. The seasonal pattern of the ? value, i.e. the ratio between NH4+ and H+ concentrations, was similar for the various tissues of the ryegrass plants but the magnitude of ? differed considerably among the different tissues. Green leaves and stems generally had substantially lower ? values than senescent leaves and litter. Substantial peaks in ? were observed during spring and summer in response to fertilization and grazing. These peaks were associated with high NH4+ rather than with low H+ concentrations. Peaks in ? also appeared during the winter, coinciding with increasing ?15N values, indicating absorption of N derived from mineralization of soil organic matter. At the same time, ?13C values were declining, suggesting reduced photosynthesis and capacity for N assimilation. ?15N and ?13C values were more influenced by mean monthly temperature than by the accumulated monthly precipitation. In conclusion, ryegrass plants showed a clear seasonal pattern in N pools. Green leaves and stems of ryegrass plants generally seem to constitute a sink for NH3, while senescent leaves have a large potential for NH3 emission. However, management events such as fertilisation and grazing may create a high NH3 emission potential even in green plant parts. The obtained results provide input for future modelling of plant-atmosphere NH3 exchange.

Wang, L.; Schjoerring, J. K.

2012-05-01

9

Influence of mycorrhizal associations on foliar ? 15 N values of legume and non-legume shrubs and trees in the fynbos of South Africa: Implications for estimating N 2 fixation using the 15 N natural abundance method  

Microsoft Academic Search

In this study, we examined the use of the 15N natural abundance method to quantify the percentage N derived from fixation of atmospheric N2 in honeybush (Cyclopia spp.) shrubs and trees in the fynbos, South Africa. Non-fixing shrubs and trees of similar phenology to the Cyclopia species were chosen as reference plants. These reference plants were selected to cover a

Amy C. Spriggs; William D. Stock; Felix D. Dakora

2003-01-01

10

Impacts of invading N 2 -fixing Acacia species on patterns of nutrient cycling in two Cape ecosystems: evidence from soil incubation studies and 15 N natural abundance values  

Microsoft Academic Search

This study examines the impacts of woody, N2-fixing invasive Acacia spp. on the patterns of nutrient cycling in two invaded ecosystems of differing nutrient status in the Cape floristic region. Patterns of soil nutrient mineralization were measured by a field incubation method while the significance of the fixation process in altering nutrient cycling was assessed by the d15N natural abundance

W. D. Stock; K. T. Wienand; A. C. Baker

1995-01-01

11

Estimation of biological nitrogen fixation by black locust in short-rotation forests using natural 15N abundance method  

NASA Astrophysics Data System (ADS)

The importance of short rotation forests and agroforestry systems for woody biomass production for bioenergy will increase in Central Europe within the next decades. In this context, black locust (Robinia pseudoacacia) has a high growth potential especially at marginal, drought-susceptible sites such as occur in Brandenburg State (Eastern Germany). As a pioneer tree species black locust grows under a wide range of site conditions. The native range of black locust in Northern America is classified by a humid to sub-humid climate with a mean annual precipitation of 1020 to 1830 mm. In Central and Eastern Europe, this species is cultivated in a more continental climate with an annual precipitation often below 600 mm. Therefore, black locust is known to be relatively drought tolerant compared to other temperate, deciduous tree species. Because of its N2-fixation ability black locust plays generally an important role for the improvement of soil fertility. This effect is of particular interest at marginal sites in the post-mining landscapes. In order to estimate the N2-fixation potential of black locust at marginal sites leaf samples were taken from black locust trees in short rotation plantations planted between 1995 and 2007 in post-mining sites south of Cottbus (Brandenburg, NE Germany). The variation of the natural 15N abundance was measured to evaluate the biological nitrogen fixation. The nitrogen derived from the atmosphere can be calculated using a two-pool model from the quotient of the natural 15N abundances of the N2-fixing plant and the plant available soil N. Because representatively determining the plant available soil N is difficult, a non-N2-fixing reference plant growing at the same site with a similar root system and temporal N uptake pattern to the N2-fixing plant is often used. In our case we used red oak (Quercus rubra) as a reference. The average nitrogen content in the leaves of black locust ranged from 3.1% (C/N 14.8) in 15 years old trees to 3.4% (C/N 14.4) in 3 year-old trees, respectively. A higher content of nitrogen was found in leaves of re-sprouted trees with 4.3% (C/N 11.5). The estimated percentage of nitrogen derived from the atmosphere (% NdfA) in black locust was 63% - 83% compared to 56% in seabuckthorn (Hippophaë rhamnoides) and 79% in common broom (Genista scuparia). The annual leaf biomass production of black locust varied between 1325 (2 years old trees) and 2576 kg/ha a (4 years old trees). The estimated leaf nitrogen fixed by Robinia was approx. 30.5 - 59.2 kg/ha a. From the results, we can conclude that the biological nitrogen fixation by Robina is an important factor for the nitrogen balance of short-rotation plantations on nutrient poor-soils.

Veste, M.; Böhm, C.; Quinckenstein, A.; Freese, D.

2012-04-01

12

Field assessment of symbiotic N2 fixation in wild and cultivated Cyclopia species in the South African fynbos by 15N natural abundance  

Microsoft Academic Search

Summary Nitrogen (N) derived from symbiotic fixation of atmospheric N2 in wild and cultivated populations of Cyclopia, a woody endemic genus used to make honeybush tea in the Western Cape of South Africa, was quantified by the 15 N natural abundance method. Because Cyclopia species are naturally mycorrhizal, non-N2-fixing arbuscu- lar mycorrhizal shrubs of similar phenology to Cyclopia were chosen

AMY C. SPRIGGS; FELIX D. DAKORA

2008-01-01

13

Vascular plant 15 N natural abundance in heath and forest tundra ecosystems is closely correlated with presence and type of mycorrhizal fungi in roots  

Microsoft Academic Search

In this study we show that the natural abundance of the nitrogen isotope 15, ?15N, of plants in heath tundra and at the tundra-forest ecocline is closely correlated with the presence and type of mycorrhizal\\u000a association in the plant roots. A total of 56 vascular plant species, 7 moss species, 2 lichens and 6 species of fungi from\\u000a four heath

Anders Michelsen; Chris Quarmby; Darren Sleep; Sven Jonasson

1998-01-01

14

Effects of Four Different Restoration Treatments on the Natural Abundance of 15N Stable Isotopes in Plants  

PubMed Central

?15N signals in plant and soil material integrate over a number of biogeochemical processes related to nitrogen (N) and therefore provide information on net effects of multiple processes on N dynamics. In general little is known in many grassland restoration projects on soil–plant N dynamics in relation to the restoration treatments. In particular, ?15N signals may be a useful tool to assess whether abiotic restoration treatments have produced the desired result. In this study we used the range of abiotic and biotic conditions provided by a restoration experiment to assess to whether the restoration treatments and/or plant functional identity and legume neighborhood affected plant ?15N signals. The restoration treatments consisted of hay transfer and topsoil removal, thus representing increasing restoration effort, from no restoration measures, through biotic manipulation to major abiotic manipulation. We measured ?15N and %N in six different plant species (two non-legumes and four legumes) across the restoration treatments. We found that restoration treatments were clearly reflected in ?15N of the non-legume species, with very depleted ?15N associated with low soil N, and our results suggest this may be linked to uptake of ammonium (rather than nitrate). The two non-legume species differed considerably in their ?15N signals, which may be related to the two species forming different kinds of mycorrhizal symbioses. Plant ?15N signals could clearly separate legumes from non-legumes, but our results did not allow for an assessment of legume neighborhood effects on non-legume ?15N signals. We discuss our results in the light of what the ?15N signals may be telling us about plant–soil N dynamics and their potential value as an indicator for N dynamics in restoration. PMID:22645597

Temperton, Vicky M.; Märtin, Lea L. A.; Röder, Daniela; Lücke, Andreas; Kiehl, Kathrin

2012-01-01

15

Measurement of nitrogen fixation by soybean in the field using the ureide and natural sup 15 N abundance methods. [Glycine max (L. )  

SciTech Connect

Nitrogen fixation by field-grown soybean (Glycine max (L.) Merrill) was assessed by the natural {sup 15}N abundance and ureide methods. The field sites (five) and genotypes (six, plus two levels of inoculation on Bragg) were chosen to provide a range of proportions of plant N derived from nitrogen fixation (P). Genotypes K466, K468, nts 1007, and nts 1116 and Davis were included on the basis of their reported tolerance of the suppressive effects of nitrate on nodulation and nitrogen fixation. Bragg was included as a nitrate-sensitive genotype. Seeds of all genotypes were inoculated at sowing with Bradyrhizobium japonicum CB1809 (USDA 136). Amounts of nitrate in the soil profile (0-1.2 meter depth) at sowing ranged from 70 (site 3) to 278 kilograms per hectare (site 5), resulting in large effects on plant nodulation, on the {delta}{sup 15}N values of nodulated plants, on the relative abundance of ureide-N in vacuum-extracted sap (VES) and stem extracts, and finally on the estimates of P. There was no relationship between amount of soil nitrate at sowing and the {delta}{sup 15}N of the plant-available soil N. Correlation matrices of the measured and calculated parameters indicated generally weak correlations between crop growth (dry matter and N) and the parameters of symbiotic activity (nodule weight, {delta}{sup 15}N, relative ureide-N); correlations were strong and highly significant between nodulation and the measures of nitrogen fixation. Estimates of P ranged between 0 and 68% ({delta}{sup 15}N) and between 6 and 56% (ureide) and were highly correlated.

Herridge, D.F. (New South Wales Agriculture Fisheries, Tamworth (Australia)); Bergersen, F.J.; Peoples, M.B. (CSIRO Division of Plant Industry, Canberra (Australia))

1990-06-01

16

Natural 15N- and 13C-abundance as indicators of forest nitrogen status and soil carbon dynamics  

SciTech Connect

This book highlights new and emerging uses of stable isotope analysis in a variety of ecological disciplines. While the use of natural abundance isotopes in ecological research is now relatively standard, new techniques and ways of interpreting patterns are developing rapidly. The second edition of this book provides a thorough, up-to-date examination of these methods of research. As part of the Ecological Methods and Concepts series which provides the latest information on experimental techniques in ecology, this book looks at a wide range of techniques that use natural abundance isotopes to: {sm_bullet} follow whole ecosystem element cycling {sm_bullet} understand processes of soil organic matter formation {sm_bullet} follow the movement of water in whole watersheds {sm_bullet} understand the effects of pollution in both terrestrial and aquatic environments {sm_bullet} study extreme systems such as hydrothermal vents {sm_bullet}follow migrating organisms In each case, the book explains the background to the methodology, looks at the underlying principles and assumptions, and outlines the potential limitations and pitfalls. Stable Isotopes in Ecology and Environmental Science is an ideal resource for both ecologists who are new to isotopic analysis, and more experienced isotope ecologists interested in innovative techniques and pioneering new uses.

Garten Jr, Charles T [ORNL; Hanson, Paul J [ORNL; Todd Jr, Donald E [ORNL; Lu, Benwhea Bonnie [ORNL; Brice, Deanne Jane [ORNL

2007-09-01

17

Field assessment of symbiotic N2 fixation in wild and cultivated Cyclopia species in the South African fynbos by 15N natural abundance.  

PubMed

Nitrogen (N) derived from symbiotic fixation of atmospheric N(2) in wild and cultivated populations of Cyclopia, a woody endemic genus used to make honeybush tea in the Western Cape of South Africa, was quantified by the (15)N natural abundance method. Because Cyclopia species are naturally mycorrhizal, non-N(2)-fixing arbuscular mycorrhizal shrubs of similar phenology to Cyclopia were chosen as reference plants to provide the delta(15)N value of soil-derived N. Isotopic analysis showed that wild populations of Cyclopia were highly dependent on N(2) fixation for their N nutrition, ranging from 70 +/- 4% to 100 +/- 7% (mean +/- SE) at all sites, except for one. Further evidence of the high dependency of wild Cyclopia populations on symbiotic N was provided by their significantly higher foliar N concentrations compared with the non-legume reference plants. However, cultivated Cyclopia exhibited variable amounts of N(2) fixation, with Cyclopia genistoides (L.) R. Br., for example, showing low amounts of N(2) fixation at Sites P2 and P3 (0 +/- 51% and 8 +/- 46%, respectively) as a result of low D values (D is defined as the difference between the mean delta(15)N value of the reference plants and the B value of the test Cyclopia species, where B is the delta(15)N of an inoculated test legume grown in an N-free growth medium), whereas at Sites P1, P2, P5 and P6, up to 89 +/- 2%, 94 +/- 13%, 85 +/- 13% and 100 +/- 18%, respectively, plant N was derived from atmospheric fixation. The high symbiotic N nutrition observed for wild populations of Cyclopia suggests that these populations are major contributors to the N economy of the nutrient-poor soils of the South African fynbos. These data indicate that by breeding for high N(2) fixation rates in Cyclopia cultivars and selecting more efficient rhizobial strains, this legume has the potential to achieve higher N(2) fixation rates under cultivation. The low variability in Cyclopia delta(15)N values within sites, however, suggests that genetic variability is not a major factor influencing N(2) fixation rates in cultivated Cyclopia, and that more benefit may be gained from soil amelioration and the selection of improved rhizobial strains. PMID:19203949

Spriggs, Amy C; Dakora, Felix D

2009-02-01

18

Leaf allocation patterns and 13C and 15N natural abundances of tropical lianas (Passiflora sp.) as dependent on external climbing support.  

PubMed

The transformation from self-supporting lianas to host-supported climbing lianas is related to re-allocation of biomass and nutrients among plant organs. Therefore, first, variations in leaf mass per area (LMA), leaf carbon and nitrogen allocation and (13)C and (15)N natural abundances were analysed among three tropical Passiflora species (P. edulis, P. ligularis, and P. tripartita) in a greenhouse study. Second, the influence of a climbing support was considered for each species and parameter. P. ligularis leaves were most enriched in (13)C in both treatments when compared with the other two species. This enrichment was caused by a high LMA, which is related to a high internal resistance to CO(2) diffusion. For P. edulis and P. tripartita, ?(13)C was additionally increasing with nitrogen content per area. Generally, there were no differences when considering carbon and nitrogen allocation to leaves of host-supported and self-supporting lianas. The only hints towards increased investment into leaves after the transition from self-supporting to host-supported stages could be seen by a trend to increased leaf areas and masses. ?(13)C values of supported P. edulis or P. tripartita plants were significantly increasing faster than those of non-supported plants once the interactions of leaf mass or nitrogen content per area were accounted for. Hence, the offer of a climbing support had only a minor impact on ?(13)C or ?(15)N values in vitro, but this could be different with increasing age of lianas in vivo. PMID:23134439

Werth, Martin; Spiegel, Ann-Kathrin; Kazda, Marian

2013-01-01

19

The natural abundance of 15N in plant and soil-available N indicates a shift of main plant N resources to NO3(-) from NH4(+) along the N leaching gradient.  

PubMed

To investigate which of ammonium (NH(4)(+)) or nitrate (NO(3)(-)) is used by plants at gradient sites with different nitrogen (N) availability, we measured the natural abundance of (15)N in foliage and soil extractable N. Hinoki cypress (Chamaecyparis obtusa Endlicher) planted broadly in Japan was selected for use in this study. We estimated the source proportion of foliar N (NH(4)(+) vs. NO(3)(-)) quantitatively using mass balance equations. The results showed that C. obtusa used mainly NH(4)(+) in N-limited forests, although the dependence of C. obtusa on NO(3)(-) was greater in other NO(3)(-)-rich forests. We regarded dissolved organic N (DON) as a potential N source because a previous study demonstrated that C. obtusa can take up glycine. Thus we added DON to our mass balance equations and calculated the source proportion using an isotope-mixing model (IsoSource model). The results still showed a positive correlation between the calculated plant N proportion of NO(3)(-) and the NO(3)(-) pool size in the soil, indicating that high NO(3)(-) availability increases the reliance of C. obtusa on NO(3)(-). Our data suggest the shift of the N source for C. obtusa from NH(4)(+) to NO(3)(-) according to the relative availability of NO(3)(-). They also show the potential of the foliar delta(15)N of C. obtusa as an indicator of the N status in forest ecosystems with the help of the delta(15)N values of soil inorganic and organic N. PMID:20213633

Takebayashi, Yu; Koba, Keisuke; Sasaki, Yuji; Fang, Yunting; Yoh, Muneoki

2010-04-15

20

? 15N as an integrator of the nitrogen cycle  

Microsoft Academic Search

Natural abundances of the rare stable isotope of nitrogen, 15N, are now being used widely in research on N cycling in organisms and ecosystems. 15N natural abundances are used in fundamentally different ways from traditional 15N tracers by integrating N cycle processes via N isotope fractionations and the mixing of various N-containing pools. This approach of using 15N natural abundances

David Robinson

2001-01-01

21

15 N isotope biogeochemistry and natural denitrification process in groundwater: Application to the chalk aquifer of northern France  

Microsoft Academic Search

The use of 15 N natural isotope tracing in an aquifer contained within chalk rocks in northern France indicates that, under certain hydrogeological conditions, major denitrification occurs. At the boundary where the aquifer becomes confined, the nitrate concentrations decrease in the direction of groundwater flow accompanied by an exponential increase in 15 N (expressed in 15 N ) of the

André Mariotti; Alain Landreau; Béatrice Simon

1988-01-01

22

Assessing denitrification in groundwater using natural gradient tracer tests with 15N: In situ measurement of a sequential multistep reaction  

USGS Publications Warehouse

Denitrification was measured within a nitrate-contaminated aquifer on Cape Cod, Massachusetts, using natural gradient tracer tests with 15N nitrate. The aquifer contained zones of relatively high concentrations of nitrite (up to 77 ??M) and nitrous oxide (up to 143 ??M) and has been the site of previous studies examining ground water denitrification using the acetylene block technique. Small-scale (15-24 m travel distance) tracer tests were conducted by injecting 15N nitrate and bromide as tracers into a depth interval that contained nitrate, nitrite, nitrous oxide, and excess nitrogen gas. The timing of the bromide breakthrough curves at down-gradient wells matched peaks in 15N abundance above background for nitrate, nitrite, nitrous oxide, and nitrogen gas after more than 40 days of travel. Results were simulated with a one-dimensional transport model using linked reaction kinetics for the individual steps of the denitrification reaction pathway. It was necessary to include within the model spatial variations in background concentrations of all nitrogen oxide species. The model indicated that nitrite production (0.036-0.047 ??mol N (L aquifer)-1 d -1) was faster than the subsequent denitrification steps (0.013-0.016 ??mol N (L aquifer)-1 d-1 for nitrous oxide and 0.013-0.020 ??mol N (L aquifer)-1 d-1 for nitrogen gas) and that the total rate of reaction was slower than indicated by both acetylene block tracer tests and laboratory incubations. The rate of nitrate removal by denitrification was much slower than the rate of transport, indicating that nitrate would migrate several kilometers down-gradient before being completely consumed.

Smith, R.L.; Böhlke, J.K.; Garabedian, S.P.; Revesz, K.M.; Yoshinari, T.

2004-01-01

23

The Nature of the Dietary Protein Impacts the Tissue-to-Diet 15N Discrimination Factors in Laboratory Rats  

PubMed Central

Due to the existence of isotope effects on some metabolic pathways of amino acid and protein metabolism, animal tissues are 15N-enriched relative to their dietary nitrogen sources and this 15N enrichment varies among different tissues and metabolic pools. The magnitude of the tissue-to-diet discrimination (?15N) has also been shown to depend on dietary factors. Since dietary protein sources affect amino acid and protein metabolism, we hypothesized that they would impact this discrimination factor, with selective effects at the tissue level. To test this hypothesis, we investigated in rats the influence of a milk or soy protein-based diet on ?15N in various nitrogen fractions (urea, protein and non-protein fractions) of blood and tissues, focusing on visceral tissues. Regardless of the diet, the different protein fractions of blood and tissues were generally 15N-enriched relative to their non-protein fraction and to the diet (?15N>0), with large variations in the ?15N between tissue proteins. ?15N values were markedly lower in tissue proteins of rats fed milk proteins compared to those fed soy proteins, in all sampled tissues except in the intestine, and the amplitude of ?15N differences between diets differed between tissues. Both between-tissue and between-diet ?15N differences are probably related to modulations of the relative orientation of dietary and endogenous amino acids in the different metabolic pathways. More specifically, the smaller ?15N values observed in tissue proteins with milk than soy dietary protein may be due to a slightly more direct channeling of dietary amino acids for tissue protein renewal and to a lower recycling of amino acids through fractionating pathways. In conclusion, the present data indicate that natural ?15N of tissue are sensitive markers of the specific subtle regional modifications of the protein and amino acid metabolism induced by the protein dietary source. PMID:22132207

Poupin, Nathalie; Bos, Cécile; Mariotti, François; Huneau, Jean-François; Tomé, Daniel; Fouillet, Hélène

2011-01-01

24

[Effects of intensive agricultural production on farmland soil carbon and nitrogen contents and their delta13C and delta15N isotope abundances].  

PubMed

Farmland soil carbon and nitrogen contents under intensive agricultural production are the important indices for the assessment of the soil fertility sustainability. This paper measured the soil pH, electrical conductivity (EC), organic carbon (SOC), total nitrogen (TN), and delta13C and delta15N isotope abundances of four types of farmland, i.e., conventional rice-broad bean rotation field, open vegetable field, 3-year plastic covered greenhouse field, and > 10-year plastic covered greenhouse field, aimed to understand the effects of intensive agricultural production degree on soil properties. In the open vegetable field, 3-year plastic covered greenhouse field, and > 10-year plastic covered greenhouse field, the soil (0-20 cm) pH decreased by 1.1, 0.8, and 0.7, and the soil EC was 4.2, 4.9, and 5.2 folds of that in conventional rice-broad bean rotation field, respectively. With the increasing year of plastic covered greenhouse production, the soil SOC and TN contents decreased after an initial increase. Comparing with those under rice-broad bean rotation, the SOC content in 0-20, 20-40, 40-60, 60-80 and 80-100 cm soil layers in >10-year plastic covered greenhouse decreased by 54%, 46%, 60%, 63%, and 59%, and the TN content decreased by 53%, 53%, 71%, 82%, and 85%, respectively. Intensive agricultural production degree had significant effects on the soil SOC and TN contents and delta13C and delta15N abundances. The delta13C abundance was significantly negatively correlated with the soil SOC, suggesting that the soil delta13C abundance could be regarded as an index for the assessment of carbon cycle in farmland soils under effects of human activities. PMID:22720621

Yang, Guang-Rong; Hao, Xiying; Li, Chun-Li; Wang, Zi-Lin; Li, Yong-Mei

2012-03-01

25

d 15 N constraints on long-term nitrogen balances in temperate forests  

EPA Science Inventory

Natural abundance d15N of ecosystems integrates nitrogen (N) inputs and losses, and thus reflects factors that control the long-term development of ecosystem N balances. We here report N and carbon (C) content of forest vegetation and soils, and associated d15N, across nine Doug...

26

Soil nutrient cycling in reclamation and natural boreal forest soils using 15N labeled aspen leaf litter  

NASA Astrophysics Data System (ADS)

A region of the boreal forest, located north of Fort McMurray, Alberta, is currently being disturbed by oil sands mining. Conditional to the allowance of mining is the requirement that the land be returned to an equivalent land capability. One method to determine if the equivalent capability has been met is to know if the reconstructed sites are self sustaining in terms of central ecosystem processes such as nutrient cycling. This study set out to compare nutrient cycling among the litter and live vegetation on reconstructed, harvested and undisturbed forest sites. All sites were dominated by an aspen tree canopy (Populus tremuloides Michx.). Nutrient cycling was monitored through the addition of 15N labeled aspen leaf litter to the forest floor over four sampling periods (0, 4, 12 and 16 months) and testing key soil response variables such as nutrient supply, microbial community, and organic matter composition. Over the entire collection period the soil microbial biomass for harvested and reconstructed soils was similar in quantity while the undisturbed forest soil was always three times greater in biomass. With the addition of 15N labeled leaves, the ?15N of microbial biomass increased across the incubation for all sites and the harvested site showed the greatest response. Furthermore the increased concentration of 15N in the live vegetation indicates that nutrient cycling was occurring on all sites.

Norris, Charlotte; Quideau, Sylvie; Landhäusser, Simon

2013-04-01

27

Long-range 1H-15N heteronuclear shift correlation across wide F1 spectral windows.  

PubMed

Long-range (1)H-(15)N heteronuclear shift correlation experiments at natural abundance are becoming more routinely utilized in the characterization of unknown chemical structures from a diverse range of sources including natural products and pharmaceuticals. Apart from the inherent challenges of the low gyromagnetic ratio and natural abundance of (15)N, investigators are also occasionally hampered by having to deal with the wide spectral range inherent to various nitrogen functional groups, which can exceed 500 ppm. Earlier triple resonance cryoprobe designs typically provided 90° (15)N pulses in the range of 35-40 µs, which did not allow the uniform excitation of wide F(1) spectral ranges for (1)H-(15)N GHMBC spectra. We report the results obtained with a newly designed Bruker 600 MHz triple resonance TCI Micro CryoProbe™ using methyl orange as a model compound, in which the (15)N resonances are separated by >450 ppm. PMID:21072790

Martin, Gary E; Hilton, Bruce D; Moskau, Detlef; Freytag, Nicolas; Kessler, Klemens; Colson, Kim

2010-12-01

28

¹³C NMR metabolomics: applications at natural abundance.  

PubMed

(13)C NMR has many advantages for a metabolomics study, including a large spectral dispersion, narrow singlets at natural abundance, and a direct measure of the backbone structures of metabolites. However, it has not had widespread use because of its relatively low sensitivity compounded by low natural abundance. Here we demonstrate the utility of high-quality (13)C NMR spectra obtained using a custom (13)C-optimized probe on metabolomic mixtures. A workflow was developed to use statistical correlations between replicate 1D (13)C and (1)H spectra, leading to composite spin systems that can be used to search publicly available databases for compound identification. This was developed using synthetic mixtures and then applied to two biological samples, Drosophila melanogaster extracts and mouse serum. Using the synthetic mixtures we were able to obtain useful (13)C-(13)C statistical correlations from metabolites with as little as 60 nmol of material. The lower limit of (13)C NMR detection under our experimental conditions is approximately 40 nmol, slightly lower than the requirement for statistical analysis. The (13)C and (1)H data together led to 15 matches in the database compared to just 7 using (1)H alone, and the (13)C correlated peak lists had far fewer false positives than the (1)H generated lists. In addition, the (13)C 1D data provided improved metabolite identification and separation of biologically distinct groups using multivariate statistical analysis in the D. melanogaster extracts and mouse serum. PMID:25140385

Clendinen, Chaevien S; Lee-McMullen, Brittany; Williams, Caroline M; Stupp, Gregory S; Vandenborne, Krista; Hahn, Daniel A; Walter, Glenn A; Edison, Arthur S

2014-09-16

29

Grass species influence on plant N uptake - Determination of atmospheric N deposition to a semi-natural peat bog site using a 15N labelling approach  

NASA Astrophysics Data System (ADS)

Large areas of natural peat bogs in Northwestern Germany have been converted to arable land and were subjected to draining and peat cutting in the past. The few protected peatland areas remaining are affected by high nitrogen (N) deposition. Our study site - a moderately drained raised bog - is surrounded by highly fertilized agricultural land and livestock production. In this study, we used a 15N pool dilution technique called 'Integrated Total Nitrogen Input' (ITNI) to quantify annual deposition of atmospheric N into biomonitoring pots over a two-year period. Since it considers direct N uptake by plants, it was expected to result in higher N input than conventional methods for determination of N deposition (e.g. micrometeorological approaches, bulk N samplers). Using Lolium multiflorum and Eriophorum vaginatum as monitor plants and low, medium and high levels of fertilization, we aimed to simulate increasing N deposition to planted pots and to allocate airborne N after its uptake by the soil-plant system in aboveground biomass, roots and soil. Increasing N fertilization was positively correlated with biomass production of Eriophorum vaginatum, whereas atmospheric plant N uptake decreased and highest airborne N input of 899.8 ± 67.4 µg N d-1 pot-1 was found for low N fertilization. In contrast, Lolium multiflorum showed a clear dependency of N supply on plant N uptake and was highest (688.7 ± 41.4 µg N d-1 pot-1) for highly fertilized vegetation pots. Our results suggest that grass species respond differently to increasing N input. While crop grasses such as Lolium multiflorum take up N according to N availability, species adopted to nutrient-limited conditions like Eriophorum vaginatum show N saturation effects with increasing N supply. Total airborne N input ranged from about 24 to 66 kg N ha-1 yr-1 dependent on the used indicator plant and the amount of added fertilizer. Parallel determination of atmospheric N deposition using a micrometeorological approach complemented with bulk samplers was about 24 kg N ha-1 yr-1 during both years of experiments and was thus at the lower range of results obtained by the ITNI method. The low 15N recovery rate of about 50 % during some experiments indicated an underestimation of the applied ITNI approach, resulting in a maximum possible N uptake of twice as high as the determined N input. Most likely, the intensive agricultural land management of the surrounding areas leads to this high N deposition into the protected peatland area. As a result, increasing sensitivity of ombrotrophic vegetation with a subsequent change in plant species composition and a decline in bog-specific vegetation cannot be excluded.

Hurkuck, Miriam; Brümmer, Christian; Spott, Oliver; Flessa, Heinz; Kutsch, Werner L.

2014-05-01

30

Sinks for nitrogen inputs in terrestrial ecosystems: a meta-analysis of 15N tracer field studies  

USGS Publications Warehouse

Effects of anthropogenic nitrogen (N) deposition and the ability of terrestrial ecosystems to store carbon (C) depend in part on the amount of N retained in the system and its partitioning among plant and soil pools. We conducted a meta-analysis of studies at 48 sites across four continents that used enriched 15N isotope tracers in order to synthesize information about total ecosystem N retention (i.e., total ecosystem 15N recovery in plant and soil pools) across natural systems and N partitioning among ecosystem pools. The greatest recoveries of ecosystem 15N tracer occurred in shrublands (mean, 89.5%) and wetlands (84.8%) followed by forests (74.9%) and grasslands (51.8%). In the short term (15N tracer application), total ecosystem 15N recovery was negatively correlated with fine-root and soil 15N natural abundance, and organic soil C and N concentration but was positively correlated with mean annual temperature and mineral soil C:N. In the longer term (3–18 months after 15N tracer application), total ecosystem 15N retention was negatively correlated with foliar natural-abundance 15N but was positively correlated with mineral soil C and N concentration and C: N, showing that plant and soil natural-abundance 15N and soil C:N are good indicators of total ecosystem N retention. Foliar N concentration was not significantly related to ecosystem 15N tracer recovery, suggesting that plant N status is not a good predictor of total ecosystem N retention. Because the largest ecosystem sinks for 15N tracer were below ground in forests, shrublands, and grasslands, we conclude that growth enhancement and potential for increased C storage in aboveground biomass from atmospheric N deposition is likely to be modest in these ecosystems. Total ecosystem 15N recovery decreased with N fertilization, with an apparent threshold fertilization rate of 46 kg N·ha-1·yr-1 above which most ecosystems showed net losses of applied 15N tracer in response to N fertilizer addition.

Templer, P.H.; Mack, M.C.; Chapin, F. S., III; Christenson, L.M.; Compton, J.E.; Crook, H.D.; Currie, W.S.; Curtis, C.J.; Dail, D.B.; D'Antonio, C. M.; Emmett, B.A.; Epstein, H.E.; Goodale, C.L.; Gundersen, P.; Hobbie, S.E.; Holland, K.; Hooper, D.U.; Hungate, B.A.; Lamontagne, S.; Nadelhoffer, K.J.; Osenberg, C.W.; Perakis, S.S.; Schleppi, P.; Schimel, J.; Schmidt, I.K.; Sommerkorn, M.; Spoelstra, J.; Tietema, A.; Wessel, W.W.; Zak, D.R.

2012-01-01

31

Sinks for nitrogen inputs in terrestrial ecosystems: a meta-analysis of 15N tracer field studies.  

PubMed

Effects of anthropogenic nitrogen (N) deposition and the ability of terrestrial ecosystems to store carbon (C) depend in part on the amount of N retained in the system and its partitioning among plant and soil pools. We conducted a meta-analysis of studies at 48 sites across four continents that used enriched 15N isotope tracers in order to synthesize information about total ecosystem N retention (i.e., total ecosystem 15N recovery in plant and soil pools) across natural systems and N partitioning among ecosystem pools. The greatest recoveries of ecosystem 15N tracer occurred in shrublands (mean, 89.5%) and wetlands (84.8%) followed by forests (74.9%) and grasslands (51.8%). In the short term (< 1 week after 15N tracer application), total ecosystem 15N recovery was negatively correlated with fine-root and soil 15N natural abundance, and organic soil C and N concentration but was positively correlated with mean annual temperature and mineral soil C:N. In the longer term (3-18 months after 15N tracer application), total ecosystem 15N retention was negatively correlated with foliar natural-abundance 15N but was positively correlated with mineral soil C and N concentration and C:N, showing that plant and soil natural-abundance 15N and soil C:N are good indicators of total ecosystem N retention. Foliar N concentration was not significantly related to ecosystem 15N tracer recovery, suggesting that plant N status is not a good predictor of total ecosystem N retention. Because the largest ecosystem sinks for 15N tracer were below ground in forests, shrublands, and grasslands, we conclude that growth enhancement and potential for increased C storage in aboveground biomass from atmospheric N deposition is likely to be modest in these ecosystems. Total ecosystem 15N recovery decreased with N fertilization, with an apparent threshold fertilization rate of 46 kg N x ha(-1) x yr(-1) above which most ecosystems showed net losses of applied 15N tracer in response to N fertilizer addition. PMID:22928411

Templer, P H; Mack, M C; Chapin, F S; Christenson, L M; Compton, J E; Crook, H D; Currie, W S; Curtis, C J; Dail, D B; D'Antonio, C M; Emmett, B A; Epstein, H E; Goodale, C L; Gundersen, P; Hobbie, S E; Holland, K; Hooper, D U; Hungate, B A; Lamontagne, S; Nadelhoffer, K J; Osenberg, C W; Perakis, S S; Schleppi, P; Schimel, J; Schmidt, I K; Sommerkorn, M; Spoelstra, J; Tietema, A; Wessel, W W; Zak, D R

2012-08-01

32

Fungal Functioning In A Pine Forest: Evidence From A 15N-Labeled Global Change Experiment  

NASA Astrophysics Data System (ADS)

In this study, we used tracer 15N labeling and a concurrent six-year nitrogen fertilization experiment in a Pinus taeda Free Air CO2 Enrichment (FACE) experiment to investigate the functioning of saprotrophic and ectomycorrhizal fungi in nitrogen cycling. Ectomycorrhizal fungi with hydrophobic ectomycorrhizae acquired nitrogen from deeper in the soil profile than taxa with hydrophilic ectomycorrhizae, whereas saprotrophic fungi acquired nitrogen primarily from relatively recent surface litter. By combining natural abundance and tracer measurements, we estimated the 15N enrichment of fungi relative to source nitrogen at between 4‰ and 9‰, depending on genus, with some genera sampling pools more 15N-enriched in the labeling experiment than could be measured by bulk analyses. Thus, biologically relevant nitrogen fractions may correspond poorly to what can be extracted chemically. The multiple 15N labels in this FACE experiment proved useful for tracking nitrogen into different fungal taxa from potential nitrogen sources.

Hobbie, E. A.; Hofmockel, K.; van Diepen, L.

2012-12-01

33

Characterization of Glycosaminoglycans by 15N-NMR Spectroscopy and in vivo Isotopic Labeling  

PubMed Central

Characterization of glycosaminoglycans (GAGs), including chondroitin sulfate (CS), dermatan sulfate (DS) and heparan sulfate (HS), is important in developing an understanding of cellular function and in assuring quality of preparations destined for biomedical applications. While use of 1H and 13C NMR spectroscopy has become common in characterization of these materials, spectra are complex and difficult to interpret when a more heterogeneous GAG type or a mixture of several types is present. Herein a method based on 1H-15N two dimensional NMR experiments is described. The 15N- and 1H-chemical shifts of amide signals from 15N-containing acetylgalactosamines in CSs are shown to be quite sensitive to the sites of sulfation (4-, 6- or 4,6-), and easily distinguishable from those of DS. The amide signals from residual 15N-containing acetylglucosamines in HS are shown to be diagnostic of the presence of these GAG components as well. Most data were collected at natural abundance of 15N despite its low percentage. However enrichment of the 15N-content in GAGs using metabolic incorporation from 15N-glutamine added to cell culture media is also demonstrated, and used to distinguish metabolic states in different cell types. PMID:20423049

Pomin, Vitor H.; Sharp, Joshua S.; Li, Xuanyang; Wang, Lianchun; Prestegard, James H.

2010-01-01

34

Differential incorporation of natural spawners vs. artificially planted salmon carcasses in a stream food web: Evidence from delta 15N of juvenile coho salmon  

EPA Science Inventory

Placement of salmon carcasses is a common restoration technique in Oregon and Washington streams, with the goal of improving food resources and productivity of juvenile salmon. To explore the effectiveness of this restoration technique, we measured the d15N of juvenile coho salmo...

35

Long-term 15N tracking from biological N fixation across different plant and humus components of the boreal forest  

NASA Astrophysics Data System (ADS)

Biological N2 fixation by cyanobacteria associated with feather mosses is an important cog in the nitrogen (N) cycle of boreal forests; still, our understanding of the turnover and fate of N fixed by this association remains greatly incomplete. The 15N signature of plants and soil serves as a powerful tool to explore N dynamics in forest ecosystems. In particular, in the present study we aimed to investigate the contribution of N2 fixation to ?15N signatures of plants and humus component of the boreal forest. Here we present results from a long-term (7 years) tacking of labelled 15N2 across the humus layer, seedlings of the tree species Pinus sylvestris, two common dwarf shrub species (Empetrum hermaphroditum and Vaccinium vitis-idaea) and the feather moss Pleurozium schreibery. The enriched experiment was conducted in 2005 in a natural boreal forest in northern Sweden. Two different treatments (10% 15N2 headspace enrichment and control) were setup in nine different plots (0.5 x 0.5 m) within the forest. We observed a significant reduction of ?15N signature of the 15N-enriched moss that could be explained by a growth dilution effect. Nevertheless, after 5 years since 15N2 enrichment some of the label 15N was still detected on the moss and in particular in the dead tissue. We could not detect a clear transfer of the labelled 15N2 from the moss-cyanobacteria system to other components of the ecosystem. However, we found consistence relationship through time between increments of ?15N signature of some of the forest components in plots which exhibited higher N fixation rates in the moss. In particular, changes in natural abundance ?15N that could be associated with N fixation were more apparent in the humus layer, the dwarf shrub Vaccinium vitis-idaea and the pine seedlings when comparing across plots and years.

Arroniz-Crespo, Maria; Jones, David L.; Zackrisson, Olle; Nilsson, Marie-Charlotte; DeLuca, Thomas H.

2014-05-01

36

Abundance/Productivity Comparison Populations Pre-Supplementation Natural-Origin Abundance Correlations  

E-print Network

Supplementation : Abundance and Productivity · We have achieved a significant life cycle survival advantage Spawners and Recruits #12;Program Performance Summary Life History and Spawning Characteristics Life history and spawning characteristics of hatchery salmon are not matching those of natural salmon. · Age

37

QUANTITATIVE 15N NMR SPECTROSCOPY  

EPA Science Inventory

Line intensities in 15N NMR spectra are strongly influenced by spin-lattice and spin-spin relaxation times, relaxation mechanisms and experimental conditions. Special care has to be taken in using 15N spectra for quantitative purposes. Quantitative aspects are discussed for the 1...

38

Amino-group-specific natural abundance nitrogen isotope ratio analysis in amino acids.  

PubMed

Amino acid (AA) nitrogen (N) stable isotope ratio analysis has found a wide variety of important applications including indication of the trophic level of an organism, tracing N transfer within food webs, and monitoring of AA resynthesis during heterotrophic microbial reworking of organic matter. Despite its utility, the current methodology is difficult to employ consistently for natural abundance level precision. Here, we report a new and robust method for high-precision N-compound-specific isotope analysis (N-PCIA) for single-N-containing AAs and N-position-specific isotope analysis (N-PSIA) for poly-N AAs. First the amino-N in AAs was liberated and oxidized to NO2(-) by hypochlorite at high pH. The NO2(-) produced was then quantified colorimetrically with excess hypochlorite quenched using arsenite. Subsequently, buffered azide was used to reduce NO2(-) to N2O for isotope ratio analysis using a purge-and-trap isotope ratio mass spectrometer. In the case of glycine delta15N, the average precision was SD = 0.3 per thousand. Reaction yields and labeling experiments show that this oxidation reaction is highly specific, targeting the alpha-amino group (peptide-N) of most poly-N AAs. This permits specific determination of the delta15N of peptide-N in arginine, tryptophan, and histidine. In the case of lysine, however, the side-chain amino group was found to be partially labile to hypochlorite oxidation. Using isotope fractionation factors estimated from single-N analogues of lysine, the intramolecular delta15N of lysine was calculated by mass balance, and this generally agreed with results for the same sample material analyzed by a previously published enzymatic method. Our method has the advantages of being relatively rapid, robust, and applicable to all poly-N AAs. We have also found it to work well for determining total delta15N of amino-N in complex sample matrices that have not been susceptible to previous approaches. PMID:18231965

Zhang, Lin; Altabet, Mark A

2008-01-01

39

Earthworm ? 13 C and ? 15 N analyses suggest that putative functional classifications of earthworms are site-specific and may also indicate habitat diversity  

Microsoft Academic Search

Natural abundances of the stable isotope pairs 13C\\/12C and 15N\\/14N (?13C and ?15N) were measured from earthworms sampled from six sites with contrasting habitats (deciduous and coniferous woodland, arable and permanent pasture). Knowledge about the function of earthworms is important to the understanding of their ecology. The hypothesis, that endogeic (primarily soil and organic matter feeders) and epigeic (surface litter

Roy Neilson; Brian Boag; Michael Smith

2000-01-01

40

Highly 15N-Enriched Chondritic Clasts in the Isheyevo Meteorite  

SciTech Connect

The metal-rich carbonaceous chondrites (CB and CH) have the highest whole-rock {sup 15}N enrichment ({delta}{sup 15}N up to +1500{per_thousand}), similar to {delta}{sup 15}N values reported in micron-sized regions (hotspots) of Interplanetary Dust Particles (IDPs) of possibly cometary origin and fine-grained matrices of unmetamorphosed chondrites. These {sup 15}N-rich hotspots are commonly attributed to low-temperature ion-molecule reactions in the protosolar molecular cloud or in the outer part of the protoplanetary disk. The nature of the whole-rock {sup 15}N enrichment of the metal-rich chondrites is not understood. We report a discovery of a unique type of primitive chondritic clasts in the CH/CB-like meteorite Isheyevo, which provides important constraints on the origin of {sup 15}N anomaly in metal-rich chondrites and nitrogen-isotope fractionation in the Solar System. These clasts contain tiny chondrules and refractory inclusions (5-15 {micro}m in size), and abundant ferromagnesian chondrule fragments (1-50 {micro}m in size) embedded in the partly hydrated, fine-grained matrix material composed of olivines, pyroxenes, poorly-organized aromatic organics, phyllosilicates and other hydrous phases. The mineralogy and oxygen isotope compositions of chondrules and refractory inclusions in the clasts are similar to those in the Isheyevo host, suggesting formation at similar heliocentric distances. In contrast to the previously known extraterrestrial samples, the fine-grained material in the clasts is highly and rather uniformly enriched in {sup 15}N, with bulk {delta}{sup 15}N values ranging between +1000 and +1300{per_thousand}; the {delta}{sup 15}N values in rare hotspots range from +1400 to +4000{per_thousand}. Since fine-grained matrices in the lithic clasts are the only component containing thermally unprocessed (during CAI and chondrule formation or during impact melting) materials that accreted into the metal rich chondrite parent body(ies), the {sup 15}N-enriched clasts as present in Isheyevo probably represent the major primordial carrier of {sup 15}N anomaly in these meteorites. The rather uniform and very high bulk {sup 15}N enrichment of the Isheyevo chondritic clasts, in contrast to rare hotspots of possibly molecular cloud origin in cometary IDPs, indicates that the nitrogen-isotope fractionation recorded by these clasts, containing abundant solar system materials, could have resulted from processes in the protoplanetary disk (e.g., ultraviolet photodissociation of {sup 15}N{sub 2} followed by trapping {sup 15}N atoms into NH-bearing ices) rather than solely by inheritance from the protosolar molecular cloud. If this is the case, the unique {sup 15}N-rich signature of the clasts could have resulted from nitrogen-isotope fractionation in cold and optically thin parts of the protoplanetary disk.

Bonal, L; Huss, G R; Krot, A N; Nagashima, K; Ishii, H A; Bradley, J P; Hutcheon, I D

2009-01-14

41

Cereal grain, rachis and pulse seed amino acid ?15N values as indicators of plant nitrogen metabolism.  

PubMed

Natural abundance ?(15)N values of plant tissue amino acids (AAs) reflect the cycling of N into and within plants, providing an opportunity to better understand environmental and anthropogenic effects on plant metabolism. In this study, the AA ?(15)N values of barley (Hordeum vulgare) and bread wheat (Triticum aestivum) grains and rachis and broad bean (Vicia faba) and pea (Pisum sativum) seeds, grown at the experimental farm stations of Rothamsted, UK and Bad Lauchstädt, Germany, were determined by GC-C-IRMS. It was found that the ?(15)N values of cereal grain and rachis AAs could be largely attributed to metabolic pathways involved in their biosynthesis and catabolism. The relative (15)N-enrichment of phenylalanine can be attributed to its involvement in the phenylpropanoid pathway and glutamate has a ?(15)N value which is an average of the other AAs due to its central role in AA-N cycling. The relative AA ?(15)N values of broad bean and pea seeds were very different from one another, providing evidence for differences in the metabolic routing of AAs to the developing seeds in these leguminous plants. This study has shown that AA ?(15)N values relate to known AA biosynthetic pathways in plants and thus have the potential to aid understanding of how various external factors, such as source of assimilated N, influence metabolic cycling of N within plants. PMID:23790569

Styring, Amy K; Fraser, Rebecca A; Bogaard, Amy; Evershed, Richard P

2014-01-01

42

13C/12C and 15N/14N Isotope Analysis to Characterize Natural Degradation of Atrazine: Evidence from Parent and Daughter Compound Values  

NASA Astrophysics Data System (ADS)

The mobile and still herbicidal metabolites desethylatrazine (DEA) and desisopropylatrazine (DIA) are frequently detected together with its parent compound atrazine (Atz) in the aquatic environment. Interpretation of their transformation state is often difficult with current methods, which are mainly measuring concentrations. Alternatively, compound specific isotope analyses (CSIA) has become a novel tool to detect degradation processes of contaminants in groundwater. The aim of our study was to investigate on the lab scale 13C/12C and 15N/14N isotope trends in parent and daughter compounds associated with different degradation scenarios of atrazine likely to occur in the environment. Thus atrazine was dealkylated with (i) permanganate and (ii) the bacterium Rhodococcus sp. NI86/21. In both transformations, 13C/12C ratios of atrazine increased strongly (epsilon carbon/permanganate = -4.6 ± 0.6 ‰ and epsilon carbon/Rhodoccoccus = -3.8 ± 0.2 ‰) whereas nitrogen isotope fractionation was small. 13C/12C ratios of DEA showed the following trends. (i) When DEA was formed as only product (Atz + permanganate) 13C/12C remained constant, close to the initial value of Atz. (ii) When DEA was formed together with deisopropylatrazine (biodegradation of Atz) 13C/12C increased, but only within 2‰. (iii) When DEA and DIA was further biodegraded, 13C/12C increased for both metabolites up to 9‰. Thus strong enrichment of 13C/12C in the metabolites in comparison to Atz can give strong testimony for further breakdown of the metabolite.

Elsner, Martin; Meyer, Armin

2013-04-01

43

Chlorine-36 abundance in natural and synthetic perchlorate  

SciTech Connect

Perchlorate (ClO{sub 4}{sup -}) is ubiquitous in the environment. It occurs naturally as a product of atmospheric photochemical reactions, and is synthesized for military, aerospace, and industrial applications. Nitrate-enriched soils of the Atacama Desert (Chile) contain high concentrations of natural ClO{sub 4}{sup -}; nitrate produced from these soils has been exported worldwide since the mid-1800's for use in agriculture. The widespread introduction of synthetic and agricultural ClO{sub 4}{sup -} into the environment has complicated attempts to understand the geochemical cycle of ClO{sub 4}{sup -}. Natural ClO{sub 4}{sup -} samples from the southwestern United States have relatively high {sup 36}Cl abundances ({sup 36}Cl/Cl = 3,100 x 10{sup -15} to 28,800 x 10{sup -15}), compared with samples of synthetic ({sup 36}Cl/Cl = 0.0 x 10{sup -15} to 40 x 10{sup -15}) and Atacama Desert ({sup 36}Cl/Cl = 0.9 x 10{sup -15} to 590 x 10{sup -15}) ClO{sub 4}{sup -}. These data give a lower limit for the initial {sup 36}Cl abundance of natural ClO{sub 4}{sup -} and provide temporal and other constraints on its geochemical cycle.

Heikoop, Jeffrey M [Los Alamos National Laboratory; Dale, M [NON LANL; Sturchio, Neil C [UNIV OF ILLIONOIS; Caffee, M [PURDUE UNIV; Belosa, A D [UNIV OF ILLINOIS; Heraty, Jr., L J [UNIV OF ILLINOIS; Bohike, J K [RESTON, VA; Hatzinger, P B [SHAW ENIVIORNMENTAL C0.; Jackson, W A [TEXAS TECH; Gu, B [ORNL

2009-01-01

44

Stable isotopes (?13C and ?15N) of organic matrix from coral skeleton  

PubMed Central

The evolutionary success of reef-building corals in nutrient-poor tropical waters is attributed to endosymbiotic dinoflagellates. The algae release photosynthetic products to the coral animal cells, augment nutrient flux, and enhance the rate of coral calcification. Natural abundance of stable isotopes (?13C and ?18O) provides answers to modern and paleobiological questions about the effect of photosymbiosis on sources of carbon and oxygen in coral skeletal calcium carbonate. Here we compare 17 species of symbiotic and nonsymbiotic corals to determine whether evidence for photosymbiosis appears in stable isotopes (?13C and ?15N) of an organic skeletal compartment, the coral skeletal organic matrix (OM). Mean OM ?13C in symbiotic and nonsymbiotic corals was similar (-26.08‰ vs. -24.31‰), but mean OM ?15N was significantly depleted in 15N in the former (4.09‰) relative to the latter (12.28‰), indicating an effect of the algae on OM synthesis and revealing OM ?15N as a proxy for photosymbiosis. To answer an important paleobiological question about the origin of photosymbiosis in reef-building corals, we applied this proxy test to a fossil coral (Pachythecalis major) from the Triassic (240 million years ago) in which OM is preserved. Mean OM ?15N was 4.66‰, suggesting that P. major was photosymbiotic. The results show that symbiotic algae augment coral calcification by contributing to the synthesis of skeletal OM and that they may have done so as early as the Triassic. PMID:15671164

Muscatine, Leonard; Goiran, Claire; Land, Lynton; Jaubert, Jean; Cuif, Jean-Pierre; Allemand, Denis

2005-01-01

45

N-15 NMR spectra of naturally abundant nitrogen in soil and aquatic natural organic matter samples of the International Humic Substances Society  

USGS Publications Warehouse

The naturally abundant nitrogen in soil and aquatic NOM samples from the International Humic Substances Society has been characterized by solid state CP/MAS 15N NMR. Soil samples include humic and fulvic acids from the Elliot soil, Minnesota Waskish peat and Florida Pahokee peat, as well as the Summit Hill soil humic acid and the Leonardite humic acid. Aquatic samples include Suwannee River humic, fulvic and reverse osmosis isolates, Nordic humic and fulvic acids and Pony Lake fulvic acid. Additionally, Nordic and Suwannee River XAD-4 acids and Suwannee River hydrophobic neutral fractions were analyzed. Similar to literature reports, amide/aminoquinone nitrogens comprised the major peaks in the solid state spectra of the soil humic and fulvic acids, along with heterocyclic and amino sugar/terminal amino acid nitrogens. Spectra of aquatic samples, including the XAD-4 acids, contain resolved heterocyclic nitrogen peaks in addition to the amide nitrogens. The spectrum of the nitrogen enriched, microbially derived Pony Lake, Antarctica fulvic acid, appeared to contain resonances in the region of pyrazine, imine and/or pyridine nitrogens, which have not been observed previously in soil or aquatic humic substances by 15N NMR. Liquid state 15N NMR experiments were also recorded on the Elliot soil humic acid and Pony Lake fulvic acid, both to examine the feasibility of the techniques, and to determine whether improvements in resolution over the solid state could be realized. For both samples, polarization transfer (DEPT) and indirect detection (1H-15N gHSQC) spectra revealed greater resolution among nitrogens directly bonded to protons. The amide/aminoquinone nitrogens could also be observed by direct detection experiments.

Thorn, K.A.; Cox, L.G.

2009-01-01

46

Application of stable isotopes (?(34)S-SO4, ?(18)O-SO4, ?(15)N-NO3, ?(18)O-NO3) to determine natural background and contamination sources in the Guadalhorce River Basin (southern Spain).  

PubMed

The integrated use of isotopes (?(34)S-SO4, ?(18)O-SO4, ?(15)N-NO3, ?(18)O-NO3), taking into account existing hydrogeological knowledge of the study area (mainly hydrochemical), was applied in the Guadalhorce River Basin (southern Spain) to characterise SO4(2-) and NO3(-) sources, and to quantify natural background levels (NBLs) in groundwater bodies. According to Water Framework Directive 2000/60/EC and, more recently, Groundwater Directive 2006/118/EC, it is important to determine NBLs, as their correct assessment is the first, essential step to characterising groundwater bodies, establishing threshold values, assessing chemical status and identifying trends in pollutant concentrations. In many cases, NBLs are high for some parameters and types of groundwater, making it difficult to distinguish clearly between factors of natural or human origin. The main advantages of using stable isotopes in a complex area like the Guadalhorce River Basin that exhibits widely varying hydrogeological and hydrochemical conditions and longstanding anthropogenic influences (mainly agriculture, but also many others) is accurate determination of pollution sources and precise quantification of NBLs. Since chemical analyses only provides the concentration of pollutants in water and not the source, three isotopic sampling campaigns for sulphates (?(34)S-SO4, ?(18)O-SO4) were carried out, in 2006, 2007 and 2012, and another one was conducted for nitrates (?(15)N-NO3, ?(18)O-NO3), in 2009, in groundwater bodies in order to trace the origins of each pollutant. The present study identified different pollution sources of dissolved NO3(-) in groundwater using an isotopic composition and quantified the percentage of natural (lithology, chemical and biological processes) and anthropogenic (fertilisers, manure and sewage) SO4(2-) and matched a concentration associated with the percentage in order to determine the NBLs in the basin. PMID:25460938

Urresti-Estala, Begoña; Vadillo-Pérez, Iñaki; Jiménez-Gavilán, Pablo; Soler, Albert; Sánchez-García, Damián; Carrasco-Cantos, Francisco

2015-02-15

47

Diversity and abundance of phosphonate biosynthetic genes in nature  

PubMed Central

Phosphonates, molecules containing direct carbon–phosphorus bonds, compose a structurally diverse class of natural products with interesting and useful biological properties. Although their synthesis in protozoa was discovered more than 50 y ago, the extent and diversity of phosphonate production in nature remains poorly characterized. The rearrangement of phosphoenolpyruvate (PEP) to phosphonopyruvate, catalyzed by the enzyme PEP mutase (PepM), is shared by the vast majority of known phosphonate biosynthetic pathways. Thus, the pepM gene can be used as a molecular marker to examine the occurrence and abundance of phosphonate-producing organisms. Based on the presence of this gene, phosphonate biosynthesis is common in microbes, with ?5% of sequenced bacterial genomes and 7% of genome equivalents in metagenomic datasets carrying pepM homologs. Similarly, we detected the pepM gene in ?5% of random actinomycete isolates. The pepM-containing gene neighborhoods from 25 of these isolates were cloned, sequenced, and compared with those found in sequenced genomes. PEP mutase sequence conservation is strongly correlated with conservation of other nearby genes, suggesting that the diversity of phosphonate biosynthetic pathways can be predicted by examining PEP mutase diversity. We used this approach to estimate the range of phosphonate biosynthetic pathways in nature, revealing dozens of discrete groups in pepM amplicons from local soils, whereas hundreds were observed in metagenomic datasets. Collectively, our analyses show that phosphonate biosynthesis is both diverse and relatively common in nature, suggesting that the role of phosphonate molecules in the biosphere may be more important than is often recognized. PMID:24297932

Yu, Xiaomin; Doroghazi, James R.; Janga, Sarath C.; Zhang, Jun Kai; Circello, Benjamin; Griffin, Benjamin M.; Labeda, David P.; Metcalf, William W.

2013-01-01

48

Mycorrhizal Fungi Provide Most of the Nitrogen for Symbiotic Arctic Plants: 15N Evidence  

NASA Astrophysics Data System (ADS)

When soil nitrogen is in short supply, most terrestrial plants form symbioses with fungi (mycorrhizae) in which fine hyphal threads take up soil nitrogen, transport it into plant roots, and in return receive plant sugars. Because the transfer rates are very difficult to measure in nature, ecologists need new tools by which to assess the role of mycorrhizal fungi in carbon and nitrogen cycling. Recent studies indicate that the natural abundance of 15N taken up from the soil by hyphae is changed during transfer of nitrogen to roots; the result is large differences among the natural abundance of 15N in soil, symbiotic plants, and symbiotic fungi that depend on the mass balance of nitrogen in the mycorrhizal symbiosis. Measurements were carried out in acidic tussock tundra at the Toolik Lake LTER site in Arctic Alaska (68\\deg N 149\\deg W). The \\delta15N of soil N was 1.5%, of soil ammonium was 1.5%, of ericoid and ectomycorrhizal plants was -5.0%, and of ectomycorrhizal fungi was 7.0 parts per mille%. The mass balance of the 15N shows that the plants received 61-86% of their nitrogen from the fungal hyphae. These values, when combined with known plant growth rates, reveal that the plants provided 7-16% of their photosynthetic carbon to the fungi for growth and respiration, or about 25% of all carbon allocated to belowground processes. This analytical technique could be readily applied to other nitrogen-limited ecosystems such as many temperate and boreal forests to quantify the importance for terrestrial carbon and nitrogen cycling of mycorrhizally mediated transfers at the plant-soil interface.

Hobbie, J. E.; Hobbie, E. A.

2004-12-01

49

THE EFFECTS OF PARAMAGNETIC RELAXATION REAGENTS ON 15N SPIN RELAXATION AND THE USE OF GD(DPM)3 AS A NITROGEN-15 NUCLEAR MAGNETIC RESONANCE SPIN LABEL  

EPA Science Inventory

Electron-nuclear relaxation times (T(1) sup e's) for (15)N and (13)C in natural abundance are measured for a series of amines of a wide range of pK(a)s using four paramagnetic relaxation reagents that are soluable in organic solutions. Cr(acac)3 and Cr(dpm)3 are seen to affect th...

50

Associative N 2 -fixation in plants growing in saline sodic soils and its relative quantification based on 15 N natural abundance  

Microsoft Academic Search

Saline-sodie soils are characterized by a very low nitrogen and organic matter content and thus are practically non fertile. However under these conditions, certain plants have been found to grow luxuriantly. One of such plants,Leptochloa fusca (Kallar grass) has exhibited nitrogenase activity associated with its roots as determined by acetylene reduction assay (ARA). Quantification of such nitrogen fixation was also

K. A. Malik; Rakhshanda Bilal; G. Rasul; K. Mahmood; M. I. Sajjad

1991-01-01

51

Novel labeling technique illustrates transfer of 15N2 from Sphagnum moss to vascular plants via diazotrophic nitrogen fixation  

NASA Astrophysics Data System (ADS)

We used 15N2 gas to trace nitrogen (N) from biological N2-fixation to vascular plant uptake in an Alberta bog in order to determine if neighboring bog plants acquire recently fixed N from diazotrophs associating with Sphagnum mosses. Recent evidence indicates high rates of N2-fixation in Sphagnum mosses of Alberta bogs (Vile et al. 2013). Our previous work has shown that mosses can assimilate fixed N from associated diazotrophs as evidenced by the high N content of mosses despite minimal inputs from atmospheric deposition, retranslocation, and N mineralization. Therefore, the potential exists for vascular plants to obtain N from ';leaky' tissues of live mosses, however, this phenomenon has not been tested previously. Here we document the potential for relatively rapid transfer to vascular plants of N fixed by Sphagnum moss-associated diazotrophs. We utilized the novel approach of incubating mosses in 15N2 to allow the process of diazotrophic N2-fixation to mechanistically provide the 15N label, which is subsequently transferred to Sphagnum mosses. The potential for vascular bog natives to tap this N was assessed by planting the vascular plants in the labeled moss. Sphagnum mosses (upper 3 cm of live plants) were incubated in the presence of 98 atom % 15N2 gas for 48 hours. Two vascular plants common to Alberta bogs; Picea mariana and Vaccinium oxycoccus were then placed in the labeled mosses, where the mosses served as the substrate. Tissue samples from these plants were collected at three time points during the incubation; prior to 15N2 exposure (to determine natural abundance 15N), and at one and two months after 15N2 exposure. Roots and leaves were separated and run separately on a mass spectrometer to determine 15N concentrations. Sphagnum moss capitula obtained N from N2-fixation (?15N of -2.43 × 0.40, 122.76 × 23.78, 224.92 × 68.37, 143.74 × 54.38 prior to, immediately after, and at 1 and 2 months after exposure to 15N2, respectively). Nitrogen was transferred to P. mariana roots (mean ?15N at 1 and 2 months of 15.26 × 3.30 and 16.19 × 1.21) more than shoots (mean ?15N at 1 and 2 months of 6.57 × 0.52 and 4.67×0.17) (initial ?15N values of roots and shoots of 2.16 × 0.37 and 5.54 × 0.35, respectively). Nitrogen also was transferred to V. oxycoccos roots (?15N at 2 months of 21.46 × 3.61) more than shoots (?15N 2 months of -2.17 × 0.23) (initial ?15N values of roots and shoots of -6.41 × 0.21 and -6.85 × 0.15, respectively). A two-way ANOVA and Tukey's HSD verified that both vascular plants' roots were significantly enriched with 15N (P. mariana roots; p < 0.0001, V. oxycoccus roots; p < 0.0001) after 1 month. These results indicate that bog vascular plants may derive considerable nitrogen from biological N2-fixation taking place in Sphagnum moss capitula. The experiment was subsequently repeated in-situ.

Thorp, N. R.; Vile, M. A.; Wieder, R.

2013-12-01

52

Stable isotopes (delta13C and delta15N) of organic matrix from coral skeleton.  

PubMed

The evolutionary success of reef-building corals in nutrient-poor tropical waters is attributed to endosymbiotic dinoflagellates. The algae release photosynthetic products to the coral animal cells, augment nutrient flux, and enhance the rate of coral calcification. Natural abundance of stable isotopes (delta13C and delta18O) provides answers to modern and paleobiological questions about the effect of photosymbiosis on sources of carbon and oxygen in coral skeletal calcium carbonate. Here we compare 17 species of symbiotic and nonsymbiotic corals to determine whether evidence for photosymbiosis appears in stable isotopes (delta13C and delta15N) of an organic skeletal compartment, the coral skeletal organic matrix (OM). Mean OM delta13C in symbiotic and nonsymbiotic corals was similar (-26.08 per thousand vs. -24.31 per thousand), but mean OM delta15N was significantly depleted in 15N in the former (4.09 per thousand) relative to the latter (12.28 per thousand), indicating an effect of the algae on OM synthesis and revealing OM delta15N as a proxy for photosymbiosis. To answer an important paleobiological question about the origin of photosymbiosis in reef-building corals, we applied this proxy test to a fossil coral (Pachythecalis major) from the Triassic (240 million years ago) in which OM is preserved. Mean OM delta15N was 4.66 per thousand, suggesting that P. major was photosymbiotic. The results show that symbiotic algae augment coral calcification by contributing to the synthesis of skeletal OM and that they may have done so as early as the Triassic. PMID:15671164

Muscatine, Leonard; Goiran, Claire; Land, Lynton; Jaubert, Jean; Cuif, Jean-Pierre; Allemand, Denis

2005-02-01

53

(13)C natural abundance in the British diet: implications for (13)C breath tests.  

PubMed

Surprisingly little information is available on the natural abundance of the minor isotope of carbon, (13)C, in common foodstuffs in the British diet. This study therefore aimed to examine the (13)C natural abundance of foodstuffs from a small cross-section of the British diet. The isotopic abundance, delta per mil, was calculated by measurement of the isotope ratio (13)C:(12)C by isotope ratio mass spectrometry. Results from this study were also compared with results from a North American study to highlight the difference in isotopic abundance between Northern European foodstuffs and North American foodstuffs. Such data should prove useful to those planning tracer studies using the stable isotope (13)C where enrichment is measured against a large and variable natural abundance in the body. Minimisation of this basal variation, for example in breath CO(2), can be achieved by controlling dietary intake of foods naturally abundant in (13)C. PMID:10920349

Morrison, D J; Dodson, B; Slater, C; Preston, T

2000-01-01

54

Protein Retention Assessment of Four Levels of Poultry By-Product Substitution of Fishmeal in Rainbow Trout (Oncorhynchus mykiss) Diets Using Stable Isotopes of Nitrogen (?15N) as Natural Tracers  

PubMed Central

This is second part from an experiment where the nitrogen retention of poultry by-product meal (PBM) compared to fishmeal (FM) was evaluated using traditional indices. Here a quantitative method using stable isotope ratios of nitrogen (?15N values) as natural tracers of nitrogen incorporation into fish biomass is assessed. Juvenile rainbow trout (Oncorhynchus mykiss) were fed for 80 days on isotopically distinct diets in which 0, 33, 66 and 100% of FM as main protein source was replaced by PBM. The diets were isonitrogenous, isolipidic and similar in gross energy content. Fish in all treatments reached isotopic equilibrium by the end of the experiment. Two-source isotope mixing models that incorporated the isotopic composition of FM and PBM as well as that of formulated feeds, empirically derived trophic discrimination factors and the isotopic composition of fish that had reached isotopic equilibrium to the diets were used to obtain a quantitative estimate of the retention of each source of nitrogen. Fish fed the diets with 33 and 66% replacement of FM by PBM retained poultry by-product meal roughly in proportion to its level of inclusion in the diets, whereas no differences were detected in the protein efficiency ratio. Coupled with the similar biomass gain of fishes fed the different diets, our results support the inclusion of PBM as replacement for fishmeal in aquaculture feeds. A re-feeding experiment in which all fish were fed a diet of 100% FM for 28 days indicated isotopic turnover occurred very fast, providing further support for the potential of isotopic ratios as tracers of the retention of specific protein sources into fish tissues. Stable isotope analysis is a useful tool for studies that seek to obtain quantitative estimates of the retention of different protein sources. PMID:25226392

Badillo, Daniel; Herzka, Sharon Z.; Viana, Maria Teresa

2014-01-01

55

Diversity and abundance of phosphonate biosynthetic genes in nature  

Technology Transfer Automated Retrieval System (TEKTRAN)

Phosphonates, molecules containing direct C-P bonds, comprise a structurally diverse class of natural products with interesting and useful biological properties. Although their synthesis in protozoa was discovered more than fifty years ago, the extent and diversity of phosphonate production in natur...

56

?15N as a Potential Paleoenvironmental Proxy for Nitrogen Loading in Chesapeake Bay  

NASA Astrophysics Data System (ADS)

Stable isotope analysis of Eastern Oyster (Crassostrea virginica) and other mollusk shells from archaeological sites is a useful means of acquiring paleoenvironmental data. Recently, nitrogen isotopes have been identified as a potential new proxy in these shells. ?15N content in mollusk shells is affected by numerous anthropogenic and natural influences and may be used as an environmental proxy for nitrogen loading conditions. Chesapeake Bay is well known for both historic and modern pollution problems from numerous anthropogenic sources, such as fertilizer runoff, sewage discharge, and densely populated land use and serves as an ideal study location for long-term nitrogen loading processes. Longer records of these processes may be recorded in abundant archaeological remains around the bay, however, little is known about the stability of ?15N and %N in shell material over recent geologic time. In this study, 90 archaeological C. virginica shells were collected by the Smithsonian Institution from the Rhode River Estuary within Chesapeake Bay and range in age from ~150 to 3200 years old. Twenty-two modern C. virginica shells were also collected from nearby beds in the bay. All shell samples were subsampled from the resilifer region of the calcitic shell using a hand-held micro drill and were analyzed using EA-IRMS analysis to determine the potential temporal variability of ?15N and %N as well as creating a baseline for ancient nitrogen conditions in the bay area. Modern POM water samples and C. virginica soft tissues were also analyzed in this study to determine the degree of seasonal variation of ?15N and %N in Chesapeake Bay.

Black, H. D.; Andrus, C. F.; Rick, T.; Hines, A.

2013-12-01

57

Mechanisms of laser nitriding in 14N and 15N atmospheres studied with RNRA  

NASA Astrophysics Data System (ADS)

Armco iron samples were irradiated successively in an atmosphere containing natural nitrogen and in a nitrogen atmosphere enriched with 15N. Resonant nuclear reaction analysis showed characteristic differences between samples irradiated with different numbers of pulses in natural N 2 and in 15N2. Based on these differences conclusions are drawn concerning the importance of nitrogen diffusion and layer ablation.

Illgner, C.; Schaaf, P.; Lieb, K.-P.; Queitsch, R.; Schutte, K.; Bergmann, H.-W.

1997-02-01

58

Natural variability in abundance of prevalent soybean proteins.  

PubMed

Soybean is an inexpensive source of protein for humans and animals. Genetic modifications (GMO) to soybean have become inevitable on two fronts, both quality and yield will need to improve to meet increasing global demand. To ensure the safety of the crop for consumers it is important to determine the natural variation in seed protein constituents as well as any unintended changes that may occur in the GMO as a result of genetic modification. Understanding the natural variation of seed proteins in wild and cultivated soybeans that have been used in conventional soybean breeding programs is critical for determining unintended protein expression in GMO soybeans. In recent years, proteomic technologies have been used as an effective analytical tool for examining modifications of protein profiles. We have standardized and applied these technologies to determine and quantify the spectrum of proteins present in soybean seed. We used two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS), and liquid chromatography mass spectrometry (LC-MS) for the separation, quantification, and identification of different classes of soybean seed proteins. We have observed significant variations in different classes of proteins, including storage, allergen and anti-nutritional protein profiles, between non-GMO cultivated and wild soybean varieties. This information is useful for scientists and regulatory agencies to determine whether the unintended expression of proteins found in transgenic soybean is within the range of natural variation. PMID:20709130

Natarajan, Savithiry S

2010-12-01

59

Transposases are the most abundant, most ubiquitous genes in nature  

PubMed Central

Genes, like organisms, struggle for existence, and the most successful genes persist and widely disseminate in nature. The unbiased determination of the most successful genes requires access to sequence data from a wide range of phylogenetic taxa and ecosystems, which has finally become achievable thanks to the deluge of genomic and metagenomic sequences. Here, we analyzed 10 million protein-encoding genes and gene tags in sequenced bacterial, archaeal, eukaryotic and viral genomes and metagenomes, and our analysis demonstrates that genes encoding transposases are the most prevalent genes in nature. The finding that these genes, classically considered as selfish genes, outnumber essential or housekeeping genes suggests that they offer selective advantage to the genomes and ecosystems they inhabit, a hypothesis in agreement with an emerging body of literature. Their mobile nature not only promotes dissemination of transposable elements within and between genomes but also leads to mutations and rearrangements that can accelerate biological diversification and—consequently—evolution. By securing their own replication and dissemination, transposases guarantee to thrive so long as nucleic acid-based life forms exist. PMID:20215432

Aziz, Ramy K.; Breitbart, Mya; Edwards, Robert A.

2010-01-01

60

A 115-year ?15N record of cumulative nitrogen pollution in California serpentine grasslands  

NASA Astrophysics Data System (ADS)

Until the 1980s, California’s biodiverse serpentine grasslands were threatened primarily by development and protected by reserve creation. However, nitrogen (N) fertilization due to increasing fossil fuel emissions in the expanding Bay Area is thought to be contributing to rapid, recent invasion of these ecosystems by exotic annual grasses that are displacing rare and endemic serpentine species. Documenting the cumulative effects of N deposition in this ecosystem can direct policy and management actions to mitigate the role of N deposition in its transformation. Natural abundance stable isotopes of N in vegetation have been increasingly used as bio-indicators of N deposition patterns and subsequent changes to plant N cycling and assimilation. However, the long-term record of atmospheric reactive N enrichment and the resulting changes in ecosystem N dynamics have yet to be adequately reconstructed in many ecosystems. Museum archives of vascular plant tissue are valuable sources of materials to reconstruct temporal and spatial isotopic patterns of N inputs to ecosystems. Here, we present N stable isotope data from archived and current specimens of an endemic California serpentine grassland species, leather oak (Quercus durata), since 1895 across the greater San Francisco Bay region. We measured spatial and temporal trends in stable isotope composition (?15N and ?13C) and concentration (%N and %C) of historical and current samples of leather oak leaves from sites within the Bay Area, impacted by increasing development, and sites northeast of the Bay Area, with significantly lower rates of urbanization and industrialization. Specifically, we sampled dry museum and fresh leaf specimens from serpentine sites within Lake (n=27) and Santa Clara (n=30) counties dating from 1895 to 2010. Leaf ?15N values were stable from 1895 to the 1950s and then decreased strongly throughout the last 50 years as fossil fuel emissions rapidly increased in the Bay Area, indicating that N pollution is being retained in serpentine grassland ecosystems. Leaf ?15N values in the high-deposition region declined at a rate of -0.041‰ yr-1, while leaf ?15N values in the low-deposition region did not show a strong pattern. In both regions, leaf ?13C values declined through time as atmospheric CO2 concentrations increased in response to fossil fuel combustion (the Suess effect). Leaf %N and %C values did not present any clear patterns at sites within or outside of the Bay Area. We conclude that using natural abundance stable isotope values in leaves can indicate variation in N pollution inputs across wide spatial and temporal scales and that archived plant samples can provide valuable baselines against which to assess changes in regional N cycling and subsequent ecological impacts on vegetation.

Vallano, D.; Zavaleta, E. S.

2010-12-01

61

ABUNDANCE OF MACROCRUSTACEANS IN A NATURAL MARSH AND A MARSH ALTERED BY DREDGING, BULKHEADING, AND FILLINGl  

E-print Network

ABUNDANCE OF MACROCRUSTACEANS IN A NATURAL MARSH AND A MARSH ALTERED BY DREDGING, BULKHEADING compared between 1) a natural marsh area, 2) upland and bayward canal areas ofa housing development, and 3,P. duorarum, were significantly greater at night than during the day at one or more stations in the marsh

62

Untersuchungen mit (15)n im dauerdüngungsfeldversuch.  

PubMed

Abstract Long-term static fertilizer experiments are important for the soil fertility research, particular for using nitrogen problems. There are several possibilities for (15)N-traces in such experiments. One example is the International Organic Nitrogen Long-Term Experiment at Berlin-Dahlem in which (15)N-tracers are used, involving organic and inorganic fertilizers. By analyzing the soil and the plant biomass, it was possible to distinguish between nitrogen originating from the soil and that from the fertilizer. Some results are published. PMID:22088106

Peschke, H; Mollenhauer, S

1996-08-01

63

Seasonal variation in nitrogen pools and 15N/13C natural abundances in different tissues of grassland plants  

NASA Astrophysics Data System (ADS)

Seasonal changes in nitrogen (N) pools, carbon (C) content and natural abundance of 13C and 15N in different tissues of ryegrass plants were investigated in two intensively managed grassland fields in order to address their ammonia (NH3) exchange potential. Green leaves generally had the largest total N concentration followed by stems and inflorescences. Senescent leaves had the lowest N concentration, indicating N re-allocation. The seasonal pattern of the ? value, i.e. the ratio between NH4+ and H+ concentrations, was similar for the various tissues of the ryegrass plants but the magnitude of ? differed considerably among the different tissues. Green leaves and stems generally had substantially lower ? values than senescent leaves and litter. Substantial peaks in ? were observed during spring and summer in response to fertilization and grazing. These peaks were associated with high NH4+ rather than with low H+ concentrations. Peaks in ? also appeared during the winter, coinciding with increasing ?15N values, indicating absorption of N derived from mineralization of soil organic matter. At the same time, ?13C values were declining, suggesting reduced photosynthesis and capacity for N assimilation. ?15N and ?13C values were more influenced by mean monthly temperature than by the accumulated monthly precipitation. In conclusion, ryegrass plants showed a clear seasonal pattern in N pools. Green leaves and stems of ryegrass plants generally seem to constitute a sink for NH3, while senescent leaves have a large potential for NH3 emission. However, management events such as fertilisation and grazing may create a high NH3 emission potential even in green plant parts. The obtained results provide input for future modelling of plant-atmosphere NH3 exchange.

Wang, L.; Schjoerring, J. K.

2011-12-01

64

Plantation vs. natural forest: Matrix quality determines pollinator abundance in crop fields  

PubMed Central

In terrestrial ecosystems, ecological processes and patterns within focal patches frequently depend on their matrix. Crop fields (focal patches) are often surrounded by a mosaic of other land-use types (matrix), which may act as habitats for organisms and differ in terms of the immigration activities of organisms to the fields. We examined whether matrix quality affects wild pollinator abundance in crop fields, given that the species (Apis cerana) generally nest in the cavities of natural trees. We examined fields of a pollination-dependent crop surrounded by plantations and natural forests, which comprised the matrix. Our analysis revealed a clear positive effect of the natural forest on the pollinator abundance, but the plantation forest had little effects. These indicate that agricultural patches are influenced by their matrix quality and the resulting crop pollinator abundance, suggesting the importance of matrix management initiatives such as forest restoration surrounding agricultural fields to improve crop production. PMID:22355649

Taki, Hisatomo; Yamaura, Yuichi; Okabe, Kimiko; Maeto, Kaoru

2011-01-01

65

Correlation between modern plant ? 15N values and activity areas of Medieval Norse farms  

Microsoft Academic Search

This further nitrogen isotopic study of Greenlandic Norse archaeological sites provides new evidence of the affect of past human activity on modern plant ?15N values. Grass samples were taken from a number of spatially defined features at four Norse farms and one site interpreted to be a seasonally occupied herding station (sæter). At the farms, un-naturally high ?15N values were

R. G. Commisso; D. E. Nelson

2008-01-01

66

Natural Abundance 17O NMR Spectroscopy of Rat Brain In Vivo  

PubMed Central

Oxygen is an abundant element that is present in almost all biologically relevant molecules. NMR observation of oxygen has been relatively limited since the NMR-active isotope, oxygen-17, is only present at a 0.037% natural abundance. Furthermore, as a spin 5/2 nucleus oxygen-17 has a moderately strong quadrupole moment which leads to fairly broad resonances (T2* = 1 - 4 ms). However, the similarly short T1 relaxation constants allow substantial signal averaging, whereas the large chemical shift range (> 300 ppm) improves the spectral resolution of 17O NMR. Here it is shown that high-quality, natural abundance 17O NMR spectra can be obtained from rat brain in vivo at 11.74 T. The chemical shifts and line widths of more than 20 oxygen-containing metabolites are established and the sensitivity and potential for 17O-enriched NMR studies are estimated. PMID:18456525

de Graaf, Robin A.; Brown, Peter B.; Rothman, Douglas L.; Behar, Kevin L.

2008-01-01

67

Neutrino Physics Neutrinos rarely interact despite their vast abundance in nature. To give a sense of  

E-print Network

Chapter 1 Neutrino Physics Neutrinos rarely interact despite their vast abundance in nature. To give a sense of scale, a person has roughly 1016 neutrinos passing through them each second, completely unnoticed. Nonetheless, neutrinos can still be used to probe the fundamental laws of na- ture

68

Plant Characteristics Associated with Natural Enemy Abundance at Michigan Native Plants  

E-print Network

BEHAVIOR Plant Characteristics Associated with Natural Enemy Abundance at Michigan Native Plants A. K. FIEDLER1 AND D. A. LANDIS Department of Entomology, 204 Center for Integrated Plant Systems populations by providing them with plant resources such as pollen and nectar. Insects are known to respond

Landis, Doug

69

New Zealand Natural Sciences (2002) 27: 1-14 Estimating the abundance of banded kokopu  

E-print Network

in streams in the North Island, New Zealand, to population estimates determined by removal electric fishingNew Zealand Natural Sciences (2002) 27: 1-14 Estimating the abundance of banded kokopu (Galaxias of Science and Technology, The University of Waikato, Private Bag 3105, Hamilton, New Zealand. e-mail: b

Waikato, University of

70

Sources and transformations of N in reclaimed coastal tidelands: evidence from soil ?15N data  

NASA Astrophysics Data System (ADS)

Electrical conductivity of saturated soil extracts (ECe) in three reclaimed tideland (RTL) soils on the west coast of Korea decreased with time since reclamation, indicating natural desalinization through leaching of salts by precipitation water. Soil N concentration increased with decreasing ECe. With the increase in soil N concentration, the ?15N decreased, likely caused by the input of 15N-depleted N sources. As N2-fixing plant species were found in the oldest RTL, atmospheric N2 fixation likely contributed to the increase in soil N concentration in the oldest RTL. Negative ?15N (-7.1 to -2.0‰) of total inorganic N (NH4 ++NO3 -) and published data on N deposition near the study area indicate that atmospheric N deposition might be another source of N in the RTLs. Meanwhile, the consistently negative ?15N of soil NO3 - excluded N input from chemical fertilizer through groundwater flow as a potential N source, since NO3 - in groundwater generally have a positive ?15N. The patterns of ?15N of NH4 + (+2.3 to +5.1‰) and NO3 - (-9.2 to -5.0‰) suggested that nitrification was an active process that caused 15N enrichment in NH4 + but denitrification was probably minimal which would otherwise have caused 15N enrichment in NO3 -. A quantitative approach on N budget would provide a better understanding of soil N dynamics in the studied RTLs.

Kwak, Jin-Hyeob; Choi, Woo-Jung; Lim, Sang-Sun; Lee, Seung-Heon; Lee, Sang-Mo; Chang, Scott X.; Jung, Jae-Woon; Yoon, Kwang-Sik; Choi, Soo-Myung

2008-01-01

71

Determination of lithium isotopes at natural abundance levels by atomic absorption spectrometry  

USGS Publications Warehouse

The relationships of the absorption of 6Li and 7Li hollow cathode lamp emissions are used to determine lithium isotopic composition in the natural abundance range of geologic materials. Absorption was found to have a nonlinear dependence upon total lithium concentration and isotopic composition. A method using nonlinear equations to describe the relationship of the absorption of 6Li and 7Li lamp radiation is proposed as a means of calculating isotopic composition that is independent of total lithium concentration.

Meier, A.L.

1982-01-01

72

A novel method for determination of the (15) N isotopic composition of Rubisco in wheat plants exposed to elevated atmospheric carbon dioxide.  

PubMed

Although ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is mostly known as a key enzyme involved in CO2 assimilation during the Calvin cycle, comparatively little is known about its role as a pool of nitrogen storage in leaves. For this purpose, we developed a protocol to purify Rubisco that enables later analysis of its (15) N isotope composition (?(15) N) at the natural abundance and (15) N-labeled plants. In order to test the utility of this protocol, durum wheat (Triticum durum var. Sula) exposed to an elevated CO2 concentration (700 vs 400 µmol mol(-1) ) was labeled with K(15) NO3 (enriched at 2 atom %) during the ear development period. The developed protocol proves to be selective, simple, cost effective and reproducible. The study reveals that (15) N labeling was different in total organic matter, total soluble protein and the Rubisco fraction. The obtained data suggest that photosynthetic acclimation in wheat is caused by Rubisco depletion. This depletion may be linked to preferential nitrogen remobilization from Rubisco toward grain filling. PMID:25272325

Aranjuelo, Iker; Molero, Gemma; Avice, Jean Christophe; Bourguignon, Jacques

2015-02-01

73

Light-mediated 15N fractionation in Caribbean gorgonian octocorals: implications for pollution monitoring  

NASA Astrophysics Data System (ADS)

The stable nitrogen isotope ratio ( ? 15N) of coral tissue is a useful recorder of anthropogenic pollution in tropical marine ecosystems. However, little is known of the natural environmentally induced fractionations that affect our interpretation of coral ? 15N values. In symbiotic scleractinians, light affects metabolic fractionation of N during photosynthesis, which may confound the identification of N pollution between sites of varied depth or turbidity. Given the superiority of octocorals for ? 15N studies, our goal was to quantify the effect of light on gorgonian ? 15N in the context of monitoring N pollution sources. Using field collections, we show that ? 15N declined by 1.4‰ over 20 m depth in two species of gorgonians, the common sea fan, Gorgonia ventalina, and the slimy sea plume, Pseudopterogorgia americana. An 8-week laboratory experiment with P. americana showed that light, not temperature causes this variation, whereby the lowest fractionation of the N source was observed in the highest light treatment. Finally, we used a yearlong reciprocal depth transplant experiment to quantify the time frame over which ? 15N changes in G. ventalina as a function of light regime . Over the year, ? 15N was unchanged and increased slightly in the deep control colonies and shallow colonies transplanted to the deep site, respectively. Within 6 months, colonies transplanted from deep to shallow became enriched by 0.8‰, mirroring the enrichment observed in the shallow controls, which was likely due to the combined effect of an increase in the source ? 15N and reduced fractionation. We conclude that light affects gorgonian ? 15N fractionation and should be considered in sampling designs for N pollution monitoring. However, these fractionations are small relative to differences observed between natural and anthropogenic N sources.

Baker, D. M.; Kim, K.; Andras, J. P.; Sparks, J. P.

2011-09-01

74

Rotation isomers of bis(diethyldithiocarbamato)zinc(II) adduct with pyridine, Zn(EDtc) 2·Py: ESR, 13C and 15N CP\\/MAS NMR and single-crystal X-ray diffraction studies  

Microsoft Academic Search

The adduct of bis(diethyldithiocarbamato)zinc(II) with pyridine, Zn(EDtc)2·Py, was prepared and studied by means of ESR (63Cu2+ and 65Cu2+ were used as spin labels), solid-state natural abundance 13C and 15N CP\\/MAS NMR spectroscopy and single-crystal X-ray diffraction data analysis. Two rotation isomers of the adduct were unambiguously determined by these three independent methods. It was found that these two isomers have

Alexander V. Ivanov; Valentina I. Mitrofanova; Mikael Kritikos; Oleg N. Antzutkin

1999-01-01

75

Rotor-driven spin diffusion in natural-abundance 13C spin systems  

NASA Astrophysics Data System (ADS)

A novel method for enhancing carbon spin diffusion in magic-angle spinning NMR experiments of solid samples is presented. The energy balance for the flip-flop process of two carbon-13 spins is provided by coupling to the mechanical rotation of the sample. Thus requires that the rotor frequency is adjusted to an integer fraction of the isotropic chemical shift difference between two particular carbon resonances. The spin-diffusion rate constant is found to be enhanced by more than two orders of magnitude in threonine with natural isotopic abundance.

Colombo, M. G.; Meier, B. H.; Ernst, R. R.

1988-05-01

76

Natural abundances of carbon isotopes in acetate from a coastal marine sediment  

NASA Technical Reports Server (NTRS)

Measurements of the natural abundances of carbon isotopes were made in acetate samples isolated from the anoxic marine sediment of Cape Lookout Bight, North Carolina. The typical value of the total acetate carbon isotope ratio (delta 13C) was -16.1 +/- 0.2 per mil. The methyl and carboxyl groups were determined to be -26.4 +/- 0.3 and -6.0 +/- 0.3 per mil, respectively, for one sample. The isotopic composition of the acetate is thought to have resulted from isotopic discriminations that occurred during the cycling of that molecule. Measurements of this type, which have not been made previously in the natural environment, may provide information about the dominant microbial pathways in anoxic sediments as well as the processes that influence the carbon isotopic composition of biogenic methane from many sources.

Blair, N. E.; Martens, C. S.; Des Marais, D. J.

1987-01-01

77

High-resolution magic-angle spinning (13)C spectroscopy of brain tissue at natural abundance.  

PubMed

High-resolution magic-angle spinning (MAS) (1)H and (13)C magnetic resonance spectroscopy (MRS) has recently been applied to study the metabolism in intact biological tissue samples. Because of the low natural abundance and the low gyromagnetic ratio of the (13)C nuclei, signal enhancement techniques such as cross-polarization (CP) and distortionless enhancement by polarization transfer (DEPT) are often employed in MAS (13)C MRS to improve the detection sensitivity. In this study, several sensitivity enhancement techniques commonly used in liquid- and solid-state NMR, including CP, DEPT and nuclear Overhauser enhancement (NOE), were combined with MAS to acquire high-resolution (13)C spectra on intact rat brain tissue at natural abundance, and were compared for their performances. The results showed that different signal enhancement techniques are sensitive to different classes of molecules/metabolites, depending on their molecular weights and mobility. DEPT was found to enhance the signals of low-molecular weight metabolites exclusively, while the signals of lipids, which often are associated with membranes and have relatively lower mobility, were highly sensitive to CP enhancement. PMID:16477685

Yang, Yongxia; Chen, Lei; Gao, Hongchang; Zeng, Danlin; Yue, Yong; Liu, Maili; Lei, Hao; Deng, Feng; Ye, Chaohui

2006-03-01

78

Modeling Soil-Plant Delta 15N in Southern African Ecosystems: Effects of Precipitation, Overgrazing and Tree-Grass Interactions.  

NASA Astrophysics Data System (ADS)

Nitrogen isotopic signatures in ecosystems have a great potential to indicate mechanisms of N cycling. However, the natural abundance of 15N is affected by fractionations during several external and internal processes, making it often difficult to asses the ecological meaning of the isotopic signatures. In addition, there is a lack of knowledge regarding many of the fractionation factors, processes and flux rates involved in the in situ N cycles in general, but especially in southern Africa. Indeed, mechanistic modeling is needed to infer dominant ecosystem processes causing the observed isotopic patterns and establish research priorities. Studies in southern Africa have indicated a 15N enrichment with aridity and overgrazing, and little effect by fires on plants and soils. Trees and grasses responded differently to precipitation, indicating different sources or N processing for these two plant types. Several hypotheses are postulated to explain these patterns: changes in the "openness" of the N cycle with aridity; temporal or chemical niche differentiation between trees and grasses; competitive interactions between trees and grasses; volatilization of ammonium caused by overgrazing; and nitrogen fixation. In this study, an adaptation of the NIFTE model is applied to southern African savannas, as a test of the suggested hypotheses. Different scenarios of precipitation, overgrazing and grass-tree interactions are simulated to predict the observed isotopic signatures and identify the processes acting in the ecosystems. These processes have implications on the effects of global change on the N cycle and maintenance of vegetation structure in savannas.

Aranibar, J. N.; Macko, S. A.; Shugart, H. H.; Ramontsho, J.

2002-05-01

79

On the nature of Lithium-rich giant stars: constraints from Beryllium abundances  

E-print Network

We have derived beryllium abundances for 7 Li-rich giant (A(Li) > 1.5) stars and 10 other Li-normal giants, with the aim of investigating the origin of the Lithium in the Li-rich giants. In particular, we test the predictions of the engulfment scenario proposed by Siess & Livio (1999), where the engulfment of a brown dwarf or one or more giant planets would lead to a simultaneous enrichment of 7Li and 9Be. We show that regardless their nature, none of the stars studied in this paper were found to have detectable beryllium. Using simple dilution arguments we show that the engulfment of an external object as the sole source of Li enrichment is ruled out by the Li and Be abundance data. The present results favor the idea that Li has been produced in the interior of the stars by a Cameron-Fowler process and brought up to the surface by an extra mixing mechanism.

C. H. F. Melo; P. de Laverny; N. C. Santos; G. Israelian; S. Randich; J. D. do Nascimento Jr.; J. R. De Medeiros

2005-04-06

80

HCNMBC - A pulse sequence for H-(C)-N Multiple Bond Correlations at natural isotopic abundance  

NASA Astrophysics Data System (ADS)

We propose a pulse sequence, HCNMBC for multiple-bond H-(C)-N correlation experiments via one-bond 1J(C,H) and one- or multiple bond nJ(N,C) coupling constants (typically n = 1-3) at the natural isotopic abundance. A new adiabatic refocussing sequence is introduced to provide accurate and robust refocussing of both chemical shift and J-evolution over wide ranges of C-13 and N-15 frequencies. It is demonstrated that the proposed pulse sequence provides high quality spectra even for sub-milligram samples. We show that when a 1.7 mm cryoprobe is available as little as 10 ?g of glycine in D2O is sufficient to obtain the HCNMBC spectrum in ca. 12 h. The preliminary results indicate that the pulse sequence has a great potential in the structure determination of nitrogen heterocycles especially in cases where synthesis produces regioisomers.

Cheatham, Steve; Gierth, Peter; Bermel, Wolfgang; Kup?e, ?riks

2014-10-01

81

Anti-Gal: an abundant human natural antibody of multiple pathogeneses and clinical benefits  

PubMed Central

Summary Anti-Gal is the most abundant natural antibody in humans, constituting ? 1% of immunoglobulins. Anti-Gal is naturally produced also in apes and Old World monkeys. The ligand of anti-Gal is a carbohydrate antigen called the ‘?-gal epitope’ with the structure Gal?1-3Gal?1-4GlcNAc-R. The ?-gal epitope is present as a major carbohydrate antigen in non-primate mammals, prosimians and New World monkeys. Anti-Gal can contributes to several immunological pathogeneses. Anti-Gal IgE produced in some individuals causes allergies to meat and to the therapeutic monoclonal antibody cetuximab, all presenting ?-gal epitopes. Aberrant expression of the ?-gal epitope or of antigens mimicking it in humans may result in autoimmune processes, as in Graves' disease. ?-Gal epitopes produced by Trypanosoma cruzi interact with anti-Gal and induce ‘autoimmune like’ inflammatory reactions in Chagas' disease. Anti-Gal IgM and IgG further mediate rejection of xenografts expressing ?-gal epitopes. Because of its abundance, anti-Gal may be exploited for various clinical uses. It increases immunogenicity of microbial vaccines (e.g. influenza vaccine) presenting ?-gal epitopes by targeting them for effective uptake by antigen-presenting cells. Tumour lesions are converted into vaccines against autologous tumour-associated antigens by intra-tumoral injection of ?-gal glycolipids, which insert into tumour cell membranes. Anti-Gal binding to ?-gal epitopes on tumour cells targets them for uptake by antigen-presenting cells. Accelerated wound healing is achieved by application of ?-gal nanoparticles, which bind anti-Gal, activate complement, and recruit and activate macrophages that induce tissue regeneration. This therapy may be of further significance in regeneration of internally injured tissues such as ischaemic myocardium and injured nerves. PMID:23578170

Galili, Uri

2013-01-01

82

The distribution of nitrate 15 N in marine sediments  

E-print Network

The distribution of nitrate 15 N/14 N in marine sediments and the impact of benthic nitrogen loss on the isotopic composition of oceanic nitrate Moritz F. Lehmann a,*, Daniel M. Sigman b , Daniel C. McCorkle c 15 N/14 N ratios of porewater nitrate in sediments from the Bering Sea basin, where microbial nitrate

Sigman, Daniel M.

83

Measurement of isotope abundance variations in nature by gravimetric spiking isotope dilution analysis (GS-IDA).  

PubMed

Subtle variations in the isotopic composition of elements carry unique information about physical and chemical processes in nature and are now exploited widely in diverse areas of research. Reliable measurement of natural isotope abundance variations is among the biggest challenges in inorganic mass spectrometry as they are highly sensitive to methodological bias. For decades, double spiking of the sample with a mix of two stable isotopes has been considered the reference technique for measuring such variations both by multicollector-inductively coupled plasma mass spectrometry (MC-ICPMS) and multicollector-thermal ionization mass spectrometry (MC-TIMS). However, this technique can only be applied to elements having at least four stable isotopes. Here we present a novel approach that requires measurement of three isotope signals only and which is more robust than the conventional double spiking technique. This became possible by gravimetric mixing of the sample with an isotopic spike in different proportions and by applying principles of isotope dilution for data analysis (GS-IDA). The potential and principle use of the technique is demonstrated for Mg in human urine using MC-TIMS for isotopic analysis. Mg is an element inaccessible to double spiking methods as it consists of three stable isotopes only and shows great potential for metabolically induced isotope effects waiting to be explored. PMID:23419016

Chew, Gina; Walczyk, Thomas

2013-04-01

84

Organic vs. Conventional Grassland Management: Do 15N and 13C Isotopic Signatures of Hay and Soil Samples Differ?  

PubMed Central

Distinguishing organic and conventional products is a major issue of food security and authenticity. Previous studies successfully used stable isotopes to separate organic and conventional products, but up to now, this approach was not tested for organic grassland hay and soil. Moreover, isotopic abundances could be a powerful tool to elucidate differences in ecosystem functioning and driving mechanisms of element cycling in organic and conventional management systems. Here, we studied the ?15N and ?13C isotopic composition of soil and hay samples of 21 organic and 34 conventional grasslands in two German regions. We also used ??15N (?15N plant - ?15N soil) to characterize nitrogen dynamics. In order to detect temporal trends, isotopic abundances in organic grasslands were related to the time since certification. Furthermore, discriminant analysis was used to test whether the respective management type can be deduced from observed isotopic abundances. Isotopic analyses revealed no significant differences in ?13C in hay and ?15N in both soil and hay between management types, but showed that ?13C abundances were significantly lower in soil of organic compared to conventional grasslands. ??15N values implied that management types did not substantially differ in nitrogen cycling. Only ?13C in soil and hay showed significant negative relationships with the time since certification. Thus, our result suggest that organic grasslands suffered less from drought stress compared to conventional grasslands most likely due to a benefit of higher plant species richness, as previously shown by manipulative biodiversity experiments. Finally, it was possible to correctly classify about two third of the samples according to their management using isotopic abundances in soil and hay. However, as more than half of the organic samples were incorrectly classified, we infer that more research is needed to improve this approach before it can be efficiently used in practice. PMID:24205126

Klaus, Valentin H.; Hölzel, Norbert; Prati, Daniel; Schmitt, Barbara; Schöning, Ingo; Schrumpf, Marion; Fischer, Markus; Kleinebecker, Till

2013-01-01

85

Organic vs. conventional grassland management: do (15)N and (13)C isotopic signatures of hay and soil samples differ?  

PubMed

Distinguishing organic and conventional products is a major issue of food security and authenticity. Previous studies successfully used stable isotopes to separate organic and conventional products, but up to now, this approach was not tested for organic grassland hay and soil. Moreover, isotopic abundances could be a powerful tool to elucidate differences in ecosystem functioning and driving mechanisms of element cycling in organic and conventional management systems. Here, we studied the ?(15)N and ?(13)C isotopic composition of soil and hay samples of 21 organic and 34 conventional grasslands in two German regions. We also used ??(15)N (?(15)N plant - ?(15)N soil) to characterize nitrogen dynamics. In order to detect temporal trends, isotopic abundances in organic grasslands were related to the time since certification. Furthermore, discriminant analysis was used to test whether the respective management type can be deduced from observed isotopic abundances. Isotopic analyses revealed no significant differences in ?(13)C in hay and ?(15)N in both soil and hay between management types, but showed that ?(13)C abundances were significantly lower in soil of organic compared to conventional grasslands. ??(15)N values implied that management types did not substantially differ in nitrogen cycling. Only ?(13)C in soil and hay showed significant negative relationships with the time since certification. Thus, our result suggest that organic grasslands suffered less from drought stress compared to conventional grasslands most likely due to a benefit of higher plant species richness, as previously shown by manipulative biodiversity experiments. Finally, it was possible to correctly classify about two third of the samples according to their management using isotopic abundances in soil and hay. However, as more than half of the organic samples were incorrectly classified, we infer that more research is needed to improve this approach before it can be efficiently used in practice. PMID:24205126

Klaus, Valentin H; Hölzel, Norbert; Prati, Daniel; Schmitt, Barbara; Schöning, Ingo; Schrumpf, Marion; Fischer, Markus; Kleinebecker, Till

2013-01-01

86

Direct measurement of the 15N(p,?)16O total cross section at novae energies  

NASA Astrophysics Data System (ADS)

The 15N(p,?)16O reaction controls the passage of nucleosynthetic material from the first to the second carbon-nitrogen-oxygen (CNO) cycle. A direct measurement of the total 15N(p,?)16O cross section at energies corresponding to hydrogen burning in novae is presented here. Data have been taken at 90-230 keV center-of-mass energy using a windowless gas target filled with nitrogen of natural isotopic composition and a bismuth germanate summing detector. The cross section is found to be a factor 2 lower than previously believed.

Bemmerer, D.; Caciolli, A.; Bonetti, R.; Broggini, C.; Confortola, F.; Corvisiero, P.; Costantini, H.; Elekes, Z.; Formicola, A.; Fülöp, Zs; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, Gy; Junker, M.; Limata, B.; Marta, M.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Alvarez, C. Rossi; Somorjai, E.; Straniero, O.; LUNA Collaboration

2009-04-01

87

Relation of desert pupfish abundance to selected environmental variables in natural and manmade habitats in the Salton Sea basin  

USGS Publications Warehouse

We assessed the relation between abundance of desert pupfish, Cyprinodon macularius, and selected biological and physicochemical variables in natural and manmade habitats within the Salton Sea Basin. Field sampling in a natural tributary, Salt Creek, and three agricultural drains captured eight species including pupfish (1.1% of the total catch), the only native species encountered. According to Bray-Curtis resemblance functions, fish species assemblages differed mostly between Salt Creek and the drains (i.e., the three drains had relatively similar species assemblages). Pupfish numbers and environmental variables varied among sites and sample periods. Canonical correlation showed that pupfish abundance was positively correlated with abundance of western mosquitofish, Gambusia affinis, and negatively correlated with abundance of porthole livebearers, Poeciliopsis gracilis, tilapias (Sarotherodon mossambica and Tilapia zillii), longjaw mudsuckers, Gillichthys mirabilis, and mollies (Poecilia latipinnaandPoecilia mexicana). In addition, pupfish abundance was positively correlated with cover, pH, and salinity, and negatively correlated with sediment factor (a measure of sediment grain size) and dissolved oxygen. Pupfish abundance was generally highest in habitats where water quality extremes (especially high pH and salinity, and low dissolved oxygen) seemingly limited the occurrence of nonnative fishes. This study also documented evidence of predation by mudsuckers on pupfish. These findings support the contention of many resource managers that pupfish populations are adversely influenced by ecological interactions with nonnative fishes. ?? Springer 2005.

Martin, B.A.; Saiki, M.K.

2005-01-01

88

?15N patterns of Douglas-fir and red alder riparian forests in the Oregon Coast Range  

USGS Publications Warehouse

We used naturally occurring stable isotopes of N to compare N dynamics in near-stream and upslope environments along riparian catenas in N-fixing red alder (Alnus rubra) and Douglas-fir (Pseudotsuga menziesii) forests in the Coast Range of western Oregon. Based on the existing literature, we expected soil ?15N to be enriched closer to streams owing to inputs of isotopically heavy, marine-derived N by spawning salmon, higher rates of denitrification near the stream, or both. However, it has been unclear what effect red alder might have on soil ?15N patterns near streams. We found a consistent ?1‰ ?15N signature in red alder foliage, and ?15N of total N in soils under red alder averaged 2.2‰ along sampling transects extending 20 m upslope from the stream. Surprisingly, ?15N of total N in soil under Douglas-fir was progressively depleted nearer to streams, opposite from the pattern expected from N losses by denitrification or N inputs from anadromous salmon. Instead, ?15N of total N in soil under Douglas-fir converged toward soil ?15N values typical of red alder sites. We consider that the historic presence of red alder may have contributed a legacy of lower soil ?15N nearer to streams on sites that are currently dominated by young Douglas-fir forest.

Scott, E.E.; Perakis, S.S.; Hibbs, D.E.

2008-01-01

89

Synthesis of 24 bacteriochlorin isotopologues, each containing a symmetrical pair of 13C or 15N atoms in the inner core of the macrocycle.  

PubMed

Synthetic bacteriochlorins containing site-specific isotopic substitution enable spectroscopic interrogation to delineate physicochemical features relevant to bacteriochlorophylls in photosynthesis but have been little explored. A de novo synthesis has been employed to prepare bacteriochlorins wherein each macrocycle contains a pair of (13)C or (15)N atoms yet lacks substituents other than a geminal dimethyl group in each pyrroline ring. Preparation of a dihydrodipyrrin–acetal with single-isotopic substitution gives rise to a bacteriochlorin that contains two isotopic substitutions symmetrically disposed by a 180° rotation about the normal to the plane of the macrocycle. Eight such isotopically substituted bacteriochlorins were prepared from commercially available reactants (bacteriochlorin sites): ((13)C)paraformaldehyde (1, 11); ((13)C)formamide (4, 14); triethyl ((13)C)orthoformate (5, 15); K(13)CN (6, 16); (13)CH3NO2 (9, 19); N,N-dimethyl((13)C)formamide (10, 20); ((15)N)pyrrole (21, 23); CH3(15)NO2 (22, 24). Some loss of (15)N upon TiCl3-mediated McMurry-type ring closure of a nitro((15)N)hexanone is attributed to a parallel sequence of three reactions (Nef, exchange with natural-abundance NH4OAc buffer, and Paal–Knorr ring closure) leading to the dihydrodipyrrin–acetal. Zinc and copper chelates of each bacteriochlorin also were prepared. Together, the 24 bacteriochlorin isotopologues should provide valuable benchmarks for understanding ground- and excited-state molecular physics of the macrocycles related to photosynthetic function of bacteriochlorophylls. PMID:24422909

Chen, Chih-Yuan; Bocian, David F; Lindsey, Jonathan S

2014-02-01

90

Variations in nitrogen-15 natural abundance of plant and soil systems in four remote tropical rainforests, southern China.  

PubMed

The foliar stable N isotope ratio (?(15)N) can provide integrated information on ecosystem N cycling. Here we present the ?(15)N of plant and soil in four remote typical tropical rainforests (one primary and three secondary) of southern China. We aimed to examine if (1) foliar ?(15)N in the study forests is negative, as observed in other tropical and subtropical sites in eastern Asia; (2) variation in ?(15)N among different species is smaller compared to that in many N-limited temperate and boreal ecosystems; and (3) the primary forest is more N rich than the younger secondary forests and therefore is more (15)N enriched. Our results show that foliar ?(15)N ranged from -5.1 to 1.3‰ for 39 collected plant species with different growth strategies and mycorrhizal types, and that for 35 species it was negative. Soil NO3 (-) had low ?(15)N (-11.4 to -3.2‰) and plant NO3 (-) uptake could not explain the negative foliar ?(15)N values (NH4 (+) was dominant in the soil inorganic-N fraction). We suggest that negative values might be caused by isotope fractionation during soil NH4 (+) uptake and mycorrhizal N transfer, and by direct uptake of atmospheric NH3/NH4 (+). The variation in foliar ?(15)N among species (by about 6‰) was smaller than in many N-limited ecosystems, which is typically about or over 10‰. The primary forest had a larger N capital in plants than the secondary forests. Foliar ?(15)N and the enrichment factor (foliar ?(15)N minus soil ?(15)N) were higher in the primary forest than in the secondary forests, albeit differences were small, while there was no consistent pattern in soil ?(15)N between primary and secondary forests. PMID:24085637

Wang, Ang; Fang, Yun-Ting; Chen, De-Xiang; Koba, Keisuke; Makabe, Akiko; Li, Yi-De; Luo, Tu-Shou; Yoh, Muneoki

2014-02-01

91

Calibration of an elastic recoil setup for D/H-ratios close to natural abundance  

NASA Astrophysics Data System (ADS)

Nominally Anhydrous Minerals (NAM) in the Earth's mantle contain trace amounts of hydrogen, as a result of the NAM's ability to incorporate hydroxyl ions. The isotopic composition of these hydrogen reservoirs is for the Earth's crust, well characterized. The knowledge of the isotopic composition of the Earth's interior on the other hand is limited. It is believed that the hydrogen composition in the interior is isotopically heterogeneous and that there may exist several reservoirs of hydrogen, characterized by different deuterium/hydrogen-ratios. Characterization of these hydrogen reservoirs can provide valuable information about the mass transport of hydrogen during the evolution of the planet. In this work we present a variant of the proton-proton scattering technique with which we are capable of performing simultaneous measurements of deuterium and hydrogen. The method has been tested with a 2.9 MeV deuteron beam on a polyethylene standard, with D/H ratio close to the natural abundance, and on a thin sample of Muscovite with a hydrogen concentration of 4800 wt-ppm. This is followed by a discussion about limitations and capabilities of the technique.

Ros, L.; Borysiuk, M.; Kristiansson, P.; Abdel, N.; Elfman, M.; Nilsson, E. J. C.; Pallon, J.

2014-08-01

92

Natural abundance high field (43)Ca solid state NMR in cement science.  

PubMed

This work is a systematic attempt to determine the possibilities and the limitations of the (43)Ca high field solid state NMR in the study of cement-based materials. The low natural abundance (0.135%) and small gyromagnetic ratio of (43)Ca present a serious challenge even in a high magnetic field. The NMR spectra of a number of cement compounds of known structure and composition are examined. The spectra of several phases important in cement science, e.g., anhydrous beta di-calcium silicate (beta-C(2)S) and tri-calcium (C(3)S) silicate were obtained for the first time and the relation of spectroscopic and structural parameters is discussed. The method was also applied to the hydrated C(3)S and synthetic calcium silicate hydrates (C-S-H) of different composition in order to understand the state of calcium and transformations in the structure during hydrolysis. The spectra of hydrated C(3)S reveals a calcium environment similar to that of the C-S-H samples and 11 A Tobermorite. These observations support the validity of using layered crystalline C-S-H systems as structural models for the C-S-H that forms in the hydration of Portland cement. PMID:20463996

Moudrakovski, Igor L; Alizadeh, Rouhollah; Beaudoin, James J

2010-07-14

93

The Determination of the Natural Abundance of the Isotopes of Chlorine: An Introductory Experiment in Mass Spectrometry.  

ERIC Educational Resources Information Center

Describes a laboratory experiment which introduces basic principles and experimental techniques of mass spectrometry for fourth year undergraduate (B.Sc.) students. Laboratory procedures, background information, and discussion of results are provided for the experiment in which the natural isotopic abundance of chlorine is determined. (Author/JN)

O'Malley, Rebecca M.

1982-01-01

94

Natural abundance-level measurement of the nitrogen isotopic composition of oceanic nitrate: an adaptation of the ammonia diffusion method  

Microsoft Academic Search

We have adapted the “ammonia diffusion” method of nitrate extraction for natural-abundance level nitrogen isotopic measurement of oceanic nitrate. The method involves: (1) sample concentration (by boiling or evaporation); (2) conversion of nitrate to ammonia using Devarda's alloy; and (3) the gas-phase diffusion of ammonia onto an acidified glass fiber disk which is sandwiched between two porous Teflon membranes. We

D. M. Sigman; M. A. Altabet; R. Michener; D. C. McCorkle; B. Fry; R. M. Holmes

1997-01-01

95

Elevated Bacterial Abundance in Laboratory-Grown and Naturally Occurring Frost Flowers Under Late Winter Conditions  

NASA Astrophysics Data System (ADS)

Sea ice has been identified as an important microbial habitat, with bacteria and other microbes concentrated in the brine inclusions between ice crystals. Frost flowers, thought to draw brine from underlying sea ice, have not been characterized from a microbial standpoint. To test whether frost flowers serve as an upward vector of bacteria contained within sea ice brines we grew frost flowers in a freezer laboratory (air temperature of -21°C) from saline water spiked with the mesophilic (and thus passive under experimental conditions) bacterium Halomonas pacifica. Salinity of melted samples was measured and bacterial abundance determined by epifluorescent microscopy. Bacterial counts scaled to ice-melt volume averaged 2.82 x 106 ml-1 for frost flowers, compared to 9.47 x 105 ml-1 for underlying ice (3 x higher). Bacterial counts also correlated significantly with salinity (maximum value of 62.5 psu) for frost flowers, brine skim, and ice (df = 17, r = 0.59, p < 0.0001). Segregation coefficients were calculated to describe the efficiency of transport of both cells and salt from the starting solution into frost flowers. From these coefficients an enrichment index was calculated to test for bacterial concentration into frost flowers at a different rate than salt. Analysis with a Student’s T-test (df = 24, t = 0.306, p = .76) indicated that cells and salt were not transported into frost flowers with a significantly different efficiency. To test these findings in the field we then collected frost flowers (and related samples) from new sea ice near Barrow, Alaska in April 2009. Bacterial counts were significantly elevated (again, a 3-fold increase) in natural frost flowers (mean = 2.73 x 105 ml-1) compared to underlying sea ice (mean = 8.46 x 104 cells ml-1). For all field samples collected (frost flowers, underlying brine skim and sea ice, as well as snow), bacterial abundance correlated significantly with salinity (maximum value 124 psu, df = 40, r = 0.60, p < 0.0001). The presence of elevated numbers of bacteria in frost flowers may have implications for the previously observed chemical reactions that take place in them, especially if microbial activity can be shown to occur in this unique low temperature, low water activity microbial habitat.

Bowman, J. S.; Deming, J. W.

2009-12-01

96

?15N Value Does Not Reflect Fasting in Mysticetes  

PubMed Central

The finding that tissue ?15N values increase with protein catabolism has led researchers to apply this value to gauge nutritive condition in vertebrates. However, its application to marine mammals has in most occasions failed. We investigated the relationship between ?15N values and the fattening/fasting cycle in a model species, the fin whale, a migratory capital breeder that experiences severe seasonal variation in body condition. We analyzed two tissues providing complementary insights: one with isotopic turnover (muscle) and one that keeps a permanent record of variations in isotopic values (baleen plates). In both tissues ?15N values increased with intensive feeding but decreased with fasting, thus contradicting the pattern previously anticipated. The apparent inconsistency during fasting is explained by the fact that a) individuals migrate between different isotopic isoscapes, b) starvation may not trigger significant negative nitrogen balance, and c) excretion drops and elimination of 15N-depleted urine is minimized. Conversely, when intensive feeding is resumed in the northern grounds, protein anabolism and excretion start again, triggering 15N enrichment. It can be concluded that in whales and other mammals that accrue massive depots of lipids as energetic reserves and which have limited access to drinking water, the ?15N value is not affected by fasting and therefore cannot be used as an indicatior of nutritive condition. PMID:24651388

Aguilar, Alex; Giménez, Joan; Gómez–Campos, Encarna; Cardona, Luís; Borrell, Asunción

2014-01-01

97

Interactions between natural-occurring landscape conditions and land use influencing the abundance of riverine smallmouth bass, micropterus dolomieu  

USGS Publications Warehouse

This study examined how interactions between natural landscape features and land use influenced the abundance of smallmouth bass, Micropterus dolomieu, in Missouri, USA, streams. Stream segments were placed into one of four groups based on natural-occurring watershed characteristics (soil texture and soil permeability) predicted to relate to smallmouth bass abundance. Within each group, stream segments were assigned forest (n = 3), pasture (n = 3), or urban (n = 3) designations based on the percentages of land use within each watershed. Analyses of variance indicated smallmouth bass densities differed between land use and natural conditions. Decision tree models indicated abundance was highest in forested stream segments and lowest in urban stream segments, regardless of group designation. Land use explained the most variation in decision tree models, but in-channel features of temperature, flow, and sediment also contributed significantly. These results are unique and indicate the importance of natural-occurring watershed conditions in defining the potential of populations and how finer-scale filters interact with land use to further alter population potential. Smallmouth bass has differing vulnerabilities to land-use attributes, and the better the natural watershed conditions are for population success, the more resilient these populations will be when land conversion occurs.

Brewer, S.K.; Rabeni, C.F.

2011-01-01

98

15N/14N variations in Cretaceous Atlantic sedimentary sequences: implication for past changes in marine nitrogen biogeochemistry  

USGS Publications Warehouse

At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds ("black shales") were found to have significantly lower ??15N values (lower 15N/14N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have ??15N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools. In contrast, black, organic-carbon-rich beds at a third site (DSDP Site 603) contain predominantly terrestrial organic matter and have C- and N-isotopic compositions similar to organic matter of modern terrestrial origin. The recurring 15N depletion in the marine-derived Cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry. Existing isotopic and other data indicate that the low 15N relative abundance is the consequence of pelagic rather than post-depositional processes. Reduced ocean circulation, increased denitrification, and, hence, reduced euphotic zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N2-fixing blue-green algae, a possible source of this sediment 15N-depletion. Lack of parallel isotopic shifts in Cretaceous terrestrially-derived nitrogen (Site 603) argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment. ?? 1987.

Rau, G.H.; Arthur, M.A.; Dean, W.E.

1987-01-01

99

Natural abundance deuterium nuclear magnetic resonance spectroscopy: Study of the biosynthesis of monoterpenes  

SciTech Connect

Deuterium NMR spectroscopy at natural abundance (D NMR-na) is a new technique for exploring the biosynthesis of small molecules such as monoterpenes. The analysis of relative site-specific deuterium integration values is an effective means of measuring isotope effects, and examining the regio- and stereochemistry of biosynthetic reactions. The deuterium integration values of linalyl acetate and limonene isolated from the same source were consistent and showed that proton abstraction from the postulated {alpha}-terpinyl cation intermediate to form limonene is regioselective from the methyl derived from the Cs methyl of the precursor, geranyl diphosphate. This regiochemistry was observed in limonene samples from different sources and the measured primary kinetic isotope effect ranged from 0.25 to in excess of 100 (no deuterium was removed within experimental error). Various {alpha}- and {beta}-pinene samples were isolated and D NMR-na analysis showed evidence of isotopically sensitive partitioning of the pinylcation in the formation of these products. This spectral analysis supported published radiolabeling studies but did not require synthesis of substrates or enzyme purification. The formation of 3-carene occurs without isomerization of the double bond which was previously postulated. The olefinic deuterium of the bicyclic compound was traced to the depleted deuterium at C{sub 2} of isopentyl diphosphate by D NMR-na data and this supported unpublished radiolabeling studies. Study of irregular monoterpenes, chrysanthemyl acetate and lyratyl acetate, showed partitioning of dimethylallyl diphosphate (DMAPP) by chrysanthemyl cyclase. The {alpha}-secondary kinetic isotope effect of 1.06-1.12, obtained from relative deuterium integration values, suggested that S{sub N}1 ionization of one molecule of DMAPP is the first step in the condensation reaction.

Leopold, M.F.

1990-01-01

100

Phenylalanine ?15N in Paleo Archives as a New Proxy for ?15N of Exported Primary Production  

NASA Astrophysics Data System (ADS)

Compound-specific isotope analysis of individual amino acids (CSI-AA) is emerging as a powerful new tool for studying the paleo nitrogen cycle. Because most detrital organic nitrogen is composed of amino acids, CSI-AA can reveal the mechanistic basis for organic nitrogen diagenesis, preserve a record of past food web structure, and potentially reconstruct the ?15N values of past nitrate and primary production. Within the commonly measured amino acids, the ?15N value of phenylalanine (Phe) appears uniquely promising as a new proxy that reflects the nitrogen isotopic value of the original source. Phe ?15N values remain almost unchanged with trophic transfer through food webs, and also during at least the initial stages of organic matter degradation. Here we synthesize results from both bio-archives and recent sediments, which together suggest that at least in Holocene archives the Phe ?15N value does in fact record the average inorganic nitrogen ?15N value at the base of planktonic food webs. However, several important unknowns also remain. These include the extent of variation in amino acid isotopic fractionation patterns in phylogenetically distinct algal groups. The stability of Phe ?15N values in older sediments where organic matter has undergone extensive diagenesis is also an important research area, which may ultimately establish the temporal limit for application of this approach to study past geological epochs. Together, however, results to date suggest that of Phe ?15N values in paleo archives represent a novel molecular-level proxy which is not tied to any specific organism or group, but rather can provide an integrated estimate of ?15N value of exported primary production.

McCarthy, M.; Batista, F. C.; Vokhshoori, N. L.; Brown, J. T.; Guilderson, T. P.; Ravelo, A. C.; Sherwood, O.

2012-12-01

101

The natural 13C abundance of plasma glucose is a useful biomarker of recent dietary caloric sweetener intake.  

PubMed

There is a need for objective biomarkers of dietary intake, because self-reporting is often subject to bias. We tested the validity of a biomarker for the fraction of dietary carbohydrate (CHO) from cane sugar and high fructose corn syrup (C(4) sugars) using natural (13)C abundance of plasma glucose. In a randomized, single-blinded, crossover design, 5 participants consumed 3 weight-maintaining diets for 7 d, with a 2-wk washout between diet periods. Diets differed in the fraction of total CHO energy from C(4) sugars (5, 16, or 32%). During each diet period, blood samples were drawn at hours 0800 and 1600 on d 1, 3, and 5 and at 0800, 1000, 1200, 1400, and 1600 on d 7. The delta(13)C abundance of plasma glucose was analyzed via GC- isotope ratio MS. Within each diet period, delta(13)C abundance of the 0800 fasting glucose did not change from baseline with increasing time during a diet period; however, there was a strong positive correlation (R(2) = 0.89) between delta(13)C abundance of the glucose concentration at 1000 on d 7 and the percent of breakfast CHO from C(4) sugars. Also, delta(13)C abundance of the combined plasma glucose samples on d 7 demonstrated a strong positive correlation (R(2) = 0.90) with the percent of total daily CHO from C(4) sugars. The natural delta(13)C abundance of postprandial plasma glucose relative to dietary C(4) CHO content was a valid biomarker for contributions of C(4) caloric sweeteners from the previous meal. PMID:20018804

Cook, Chad M; Alvig, Amy L; Liu, Yu Qiu David; Schoeller, Dale A

2010-02-01

102

Rivermouth alteration of agricultural impacts on consumer tissue ?15N  

USGS Publications Warehouse

Terrestrial agricultural activities strongly influence riverine nitrogen (N) dynamics, which is reflected in the ?15N of riverine consumer tissues. However, processes within aquatic ecosystems also influence consumer tissue ?15N. As aquatic processes become more important terrestrial inputs may become a weaker predictor of consumer tissue ?15N. In a previous study, this terrestrial-consumer tissue ?15N connection was very strong at river sites, but was disrupted by processes occurring in rivermouths (the ‘rivermouth effect’). This suggested that watershed indicators of N loading might be accurate in riverine settings, but could be inaccurate when considering N loading to the nearshore of large lakes and oceans. In this study, the rivermouth effect was examined on twenty-five sites spread across the Laurentian Great Lakes. Relationships between agriculture and consumer tissue ?15N occurred in both upstream rivers and at the outlets where rivermouths connect to the nearshore zone, but agriculture explained less variation and had a weaker effect at the outlet. These results suggest that rivermouths may sometimes be significant sources or sinks of N, which would cause N loading estimates to the nearshore zone that are typically made at discharge gages further upstream to be inaccurate. Identifying definitively the controls over the rivermouth effect on N loading (and other nutrients) will require integration of biogeochemical and hydrologic models.

Larson, James H.; Richardson, William B.; Vallazza, Jon M.; Nelson, John C.

2013-01-01

103

Optimization of (15)n detection with an atomic emission detector.  

PubMed

Gas chromatography with atomic emission detection is a useful tool for the detection of stable isotope labels in complex samples. While papers involving the analysis of D and (13)C are numerous, little work has been done in the area of (15)N detection. For (15)N isotope detection, three reagent gases are used:? H(2), O(2), and CH(4). In this work, the reagent gas flows were varied to optimize the sensitivity of (15)N detection without sacrificing isotope selectivity. The optimal gas flows determined in this work produce the following ratios of the spectral peak areas:? O 725 area/He 728 area = 0.039 with only O(2) flowing; H 486 area/He 492 area = 12 with only H(2) flowing; C 496 area/He 502 area = 0.41 with O(2), H(2), and CH(4) flowing for C and no gases flowing for He. When using these gas settings, the (15)N sensitivity is increased by nearly 2 orders of magnitude relative to the manufacturer-recommended settings. It was also demonstrated that the presence of a compound in both the labeled and unlabeled forms in the same sample does not affect the response. The ratios of (15)N to (14)N in standards, calculated from calibration plots (which are linear for both isotopes), agree well with the actual values. A tobacco smoke sample containing various (15)N-labeled compounds was used to show the utility of the GC-AED for indicating which compounds in a complex sample contain the label. This sample also demonstrates the necessity for optimal sensitivity when dealing with samples containing small amounts of compounds with low incorporation levels. PMID:21662777

Stevens, N A; Borgerding, M F

1999-03-01

104

Is the Multicolored Asian Ladybeetle, Harmonia axyridis, the Most Abundant Natural Enemy to Aphids in Agroecosystems?  

PubMed Central

The multicolored Asian ladybeetle, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), was introduced into Western Europe in the late 1990s. Since the late 2000s, this species has been commonly considered one of the most abundant aphid predators in most Western European countries. In spite of the large amount of research on H. axyridis, information concerning its relative abundance in agroecosystems is lacking. This study aims to evaluate the abundance of H. axyridis within the aphidophage community in four crops situated in southern Belgium: wheat, Triticum aestivum L. (Poales: Poaceae), corn, Zea mays, potato, Solanum tuberosum (Solanales: Solanaceae), and broad bean Vicia faba (Fabales: Fabaceae). In order to assess the species diversity, the collected data were analyzed by considering (1) the species richness and (2) the evenness according to the Shannon diversity index. Eleven aphidophages were observed in every inventoried agroecosystem, including five abundant species: three coccinellids, the seven-spotted ladybug, Coccinella septempunctata L. (Coleoptera: Coccinellidae), the 14-spotted Ladybird, Propylea quatuordecimpunctata, and H. axyridis; one hoverfly, the marmalade hoverfly, Episyrphus balteatus De Geer (Diptera: Syrphidae); and one lacewing, the common green lacewing, Chrysoperla carnea Stephens sensu lato (= s.l.) (Neuroptera: Chrysopidae). Harmonia axyridis has been observed to thrive, breed, and reproduce on the four studied crops. Harmonia axyridis is the most abundant predator of aphids in corn followed by C. septempunctata, which is the main aphid predator observed in the three other inventoried crops. In wheat and potato fields, H. axyridis occurs in low numbers compared to other aphidophage. These observations suggest that H. axyridis could be considered an invasive species of agrosystems, and that potato and wheat may intermittently act as refuges for other aphidophages vulnerable to intraguild predation by this invader. Harmonia axyridis is not the most abundant aphid predator in the main Belgian crops. PMID:24785375

Vandereycken, Axel; Durieux, Delphine; Joie, Emilie; Sloggett, John J.; Haubruge, Eric; Verheggen, François J.

2013-01-01

105

Is the multicolored Asian ladybeetle, Harmonia axyridis, the most abundant natural enemy to aphids in agroecosystems?  

PubMed

The multicolored Asian ladybeetle, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), was introduced into Western Europe in the late 1990s. Since the late 2000s, this species has been commonly considered one of the most abundant aphid predators in most Western European countries. In spite of the large amount of research on H. axyridis, information concerning its relative abundance in agroecosystems is lacking. This study aims to evaluate the abundance of H. axyridis within the aphidophage community in four crops situated in southern Belgium: wheat, Triticum aestivum L. (Poales: Poaceae), corn, Zea mays, potato, Solanum tuberosum (Solanales: Solanaceae), and broad bean Vicia faba (Fabales: Fabaceae). In order to assess the species diversity, the collected data were analyzed by considering (1) the species richness and (2) the evenness according to the Shannon diversity index. Eleven aphidophages were observed in every inventoried agroecosystem, including five abundant species: three coccinellids, the seven-spotted ladybug, Coccinella septempunctata L. (Coleoptera: Coccinellidae), the 14-spotted Ladybird, Propylea quatuordecimpunctata, and H. axyridis; one hoverfly, the marmalade hoverfly, Episyrphus balteatus De Geer (Diptera: Syrphidae); and one lacewing, the common green lacewing, Chrysoperla carnea Stephens sensu lato (= s.l.) (Neuroptera: Chrysopidae). Harmonia axyridis has been observed to thrive, breed, and reproduce on the four studied crops. Harmonia axyridis is the most abundant predator of aphids in corn followed by C. septempunctata, which is the main aphid predator observed in the three other inventoried crops. In wheat and potato fields, H. axyridis occurs in low numbers compared to other aphidophage. These observations suggest that H. axyridis could be considered an invasive species of agrosystems, and that potato and wheat may intermittently act as refuges for other aphidophages vulnerable to intraguild predation by this invader. Harmonia axyridis is not the most abundant aphid predator in the main Belgian crops. PMID:24785375

Vandereycken, Axel; Durieux, Delphine; Joie, Emilie; Sloggett, John J; Haubruge, Eric; Verheggen, François J

2013-01-01

106

The 15N NMR powder spectra of semicrystalline nylon 6  

NASA Astrophysics Data System (ADS)

The solid state 15N NMR chemical shift anisotropy (CSA) spectra of nylon 6 is reported. Nylon 6 (20 percent 15N enriched) was prepared by anionic polymerization of isotopically enriched caprolactam. The samples observed were prepared by extraction with methanol to remove unreacted caprolactam, then either annealed to promote crystallization or artificially plasticized by immersion in molten caprolactam. The anisotropic linewidth was approximately 200 ppm, intermediate between the range reported for sp2 and sp3 hybridized nitrogens and consistent with the partial double-bond character of the carbon-nitrogen bond in amides.

Powell, Douglas G.; Mathias, Lon J.

1989-05-01

107

Refining cotton-wick method for 15N plant labelling.  

NASA Astrophysics Data System (ADS)

The symbiosis Fabaceae/Rhizobiaceae plays a critical role in the nitrogen cycle. It gives the plant the ability to fix high amounts of atmospheric N. A part of this N can be transferred to the soil via rhizodeposition. The contribution of Fabaceae to the soil N pool is difficult to measure, since it is necessary for assessing N benefits for other crops, for soil biological activity, and for reducing water pollution in sustainable agriculture (Fustec, 2009). The aim of this study was to test and improve the reliability of the 15N cotton-wick method for measuring the soil N derived from plant rhizodeposition (Mahieu et al., 2007). The effects of the concentration of the 15N-urea labelling solution and of the feeding frequency (continuous or pulses) on the assessment of nitrogen rhizodeposition were studied in two greenhouse experiments using the field pea (Pisum sativum L.) and the non-nodulating isoline P2. The plant parts and the soil were prepared for 15N:14N measurements for assessing N rhizodeposition (Mahieu et al., 2009). The fraction of plants' belowground nitrogen allocated to rhizodeposition in both Frisson pea and P2 was 20 to more than 50% higher when plants were labelled continuously than when they were labelled using fortnightly pulses. Our results suggested that when 15N root enrichment was high, nitrogen rhizodeposition was underestimated only for plants that were 15N-fed by fortnightly pulses, and not in plants 15N-fed continuously. This phenomenon was especially observed for plants relying on symbiotic N fixation for N acquisition; it may be linked to the concentration of the labelling solution. In conclusion, N rhizodeposition assessment was strongly influenced by the 15N-feeding frequency and the concentration of the labelling solution. The estimation of N rhizodeposition was more reliable when plants were labelled continuously with a dilute solution of 15N urea. Fustec et al. 2009. Agron. Sustain. Dev., DOI 10.1051/agro/2009003, in press. Mahieu et al. 2007. Plant Soil 295, 193-205. Mahieu et al. 2009. Soil Biol. Biochem. 41, 2236-2243.

Fustec, Joëlle; Mahieu, Stéphanie

2010-05-01

108

-Amino acids, although less abundant than their -analogues, are also present in peptides and other natural  

E-print Network

-Amino acids, although less abundant than their -analogues, are also present in peptides and other. A number of methods for synthesis and transformations leading to -amino acids in diastereomerically and enantiomerically enriched forms have been reported.1 The synthesis of modified peptides containing -amino acids

109

Maize planting time and arthropod abundance in southern Mindanao, Philippines. II. Population dynamics of natural enemies  

Microsoft Academic Search

Beneficial arthropods were monitored in monthly plantings over 4 years in a rainfed, triple-maize cropping system in southern Mindanao, Philippines. Generalist predators and two egg parasitoids of the Asian corn borer Ostrinia furnacalis (Guenée) (ACB) did not show significant differences in abundance with respect to calendar month of planting over 39 crops. Two species of Trichogramma (T. evanescens Westwood and

J. A. Litsinger; C. G. Dela Cruz; B. L. Canapi; A. T. Barrion

2007-01-01

110

The contamination of commercial 15N2 gas stocks with 15N-labeled nitrate and ammonium and consequences for nitrogen fixation measurements.  

PubMed

We report on the contamination of commercial 15-nitrogen (15N) N2 gas stocks with 15N-enriched ammonium, nitrate and/or nitrite, and nitrous oxide. 15N2 gas is used to estimate N2 fixation rates from incubations of environmental samples by monitoring the incorporation of isotopically labeled 15N2 into organic matter. However, the microbial assimilation of bioavailable 15N-labeled N2 gas contaminants, nitrate, nitrite, and ammonium, is liable to lead to the inflation or false detection of N2 fixation rates. 15N2 gas procured from three major suppliers was analyzed for the presence of these 15N-contaminants. Substantial concentrations of 15N-contaminants were detected in four Sigma-Aldrich 15N2 lecture bottles from two discrete batch syntheses. Per mole of 15N2 gas, 34 to 1900 µmoles of 15N-ammonium, 1.8 to 420 µmoles of 15N-nitrate/nitrite, and ?21 µmoles of 15N-nitrous oxide were detected. One 15N2 lecture bottle from Campro Scientific contained ?11 µmoles of 15N-nitrous oxide per mole of 15N2 gas, and no detected 15N-nitrate/nitrite at the given experimental 15N2 tracer dilutions. Two Cambridge Isotopes lecture bottles from discrete batch syntheses contained ?0.81 µmoles 15N-nitrous oxide per mole 15N2, and trace concentrations of 15N-ammonium and 15N-nitrate/nitrite. 15N2 gas equilibrated cultures of the green algae Dunaliella tertiolecta confirmed that the 15N-contaminants are assimilable. A finite-differencing model parameterized using oceanic field conditions typical of N2 fixation assays suggests that the degree of detected 15N-ammonium contamination could yield inferred N2 fixation rates ranging from undetectable, <0.01 nmoles N L(-1) d(-1), to 530 nmoles N L(-1) d(-1), contingent on experimental conditions. These rates are comparable to, or greater than, N2 fixation rates commonly detected in field assays. These results indicate that past reports of N2 fixation should be interpreted with caution, and demonstrate that the purity of commercial 15N2 gas must be ensured prior to use in future N2 fixation rate determinations. PMID:25329300

Dabundo, Richard; Lehmann, Moritz F; Treibergs, Lija; Tobias, Craig R; Altabet, Mark A; Moisander, Pia H; Granger, Julie

2014-01-01

111

A new method for the identification of the origin of natural products. Quantitative ²H NMR at the natural abundance level applied to the characterization of anetholes  

Microsoft Academic Search

We have shown by high-field ²H NMR spectrometry at the natural abundance level that very spectacular differences exist in the interal distribution of ²H in organic molecules. This phenomenon has been exemplified in particular by the case of ethyl and vinyl derivatives. We show in this study of various anethole samples the potential of this new method as a very

G. J. Martin; M. L. Martin; F. Mabon; J. Bricont

1982-01-01

112

14N15N detectability in Pluto’s atmosphere  

NASA Astrophysics Data System (ADS)

Based on the vapor pressure behavior of Pluto’s surface ices, Pluto’s atmosphere is expected to be predominantly composed of N2 gas. Measurement of the N2 isotopologue 15N/14N ratio within Pluto’s atmosphere would provide important clues to the evolution of Pluto’s atmosphere from the time of formation to its present state. The most straightforward way of determining the N2 isotopologue 15N/14N ratio in Pluto’s atmosphere is via spectroscopic observation of the 14N15N gas species. Recent calculations of the 80-100 nm absorption behavior of the 14N2 and 14N15N isotopologues by Heays et al. (Heays, A.N. et al. [2011]. J. Chem. Phys. 135, 244301), Lewis et al. (Lewis, B.R., Heays, A.N., Gibson, S.T., Lefebvre-Brion, H., Lefebvre, R. [2008]. J. Chem. Phys. 129, 164306); Lewis et al. (Lewis, B.R., Gibson, S.T., Zhang, W., Lefebvre-Brion, H., Robbe, J.-M. [2005]. J. Chem. Phys. 122, 144302), and Haverd et al. (Haverd, V.E., Lewis, B.R., Gibson, S.T., Stark, G. [2005]. J. Chem. Phys. 123, 214304) show that the peak magnitudes of the 14N2 and 14N15N absorption bandhead cross-sections are similar, but the locations of the bandhead peaks are offset in wavelength by ?0.05-0.1 nm. These offsets make the segregation of the 14N2 and 14N15N absorption signatures possible. We use the most recent N2 isotopologue absorption cross-section calculations and the atmospheric density profiles resulting from photochemical models developed by Krasnopolsky and Cruickshank (Krasnopolsky, V.A., Cruickshank, D.P. [1999]. J. Geophys. Res. 104, 21979-21996) to predict the level of solar light that will be transmitted through Pluto’s atmosphere as a function of altitude during a Pluto solar occultation. We characterize the detectability of the isotopic absorption signature per altitude assuming 14N15N concentrations ranging from 0.1% to 2% of the 14N2 density and instrumental spectral resolutions ranging from 0.01 to 0.3 nm. Our simulations indicate that optical depth of unity is attained in the key 14N15N absorption bands located between 85 and 90 nm at altitudes ?1100-1600 km above Pluto’s surface. Additionally, an 14N15N isotope absorption depth ?4-15% is predicted for observations obtained at these altitudes at a spectral resolution of ?0.2-0.3 nm, if the N2 isotopologue 15N/14N percent ratio is comparable to the 0.37-0.6% ratio observed at Earth, Titan and Mars. If we presume that the predicted absorption depth must be at least 25% greater than the expected observational uncertainty, then it follows that a statistically significant detection of these signatures and constraint of the N2 isotopologue 14N/15N ratio within Pluto’s atmosphere will be possible if the attainable observational signal-to noise (S/N) ratio is ?9. The New Horizons (NH) Mission will be able to obtain high S/N, 0.27-0.35 nm full-width half-max 80-100 nm spectral observations of Pluto using the Alice spectrograph. Based on the NH/Alice specifications we have simulated 0.3 nm spectral resolution solar occultation spectra for the 1100-1600 km altitude range, assuming 30 s integration times. These simulations indicate that NH/Alice will obtain spectral observations within this altitude range with a S/N ratio ?25-50, and should be able to reliably detect the 14N15N gas absorption signature between 85 and 90 nm if the 14N15N concentration is ?0.3% or greater. This, additionally, implies that the non-detection of the 14N15N species in the 1100-1600 km range by NH/Alice may be used to reliably establish an upper limit to the N2 isotopologue 15N/14N ratio within Pluto’s atmosphere. Similar results may be derived from 0.2 to 0.3 nm spectral resolution observations of any other N2-rich Solar System or exoplanet atmosphere, provided the observations are attained with similar S/N levels.

Jessup, Kandis Lea; Gladstone, G. R.; Heays, A. N.; Gibson, S. T.; Lewis, B. R.; Stark, G.

2013-11-01

113

Infection by mycorrhizal fungi increases natural enemy abundance on tobacco (Nicotiana rustica).  

PubMed

The presence of arbuscular mycorrhizal fungi (AMF) influences plant nutrient uptake, growth, and plant defensive chemistry, thereby directly influencing multi-trophic interactions. Different fungal isolates (genotypes of the same fungal species) have been shown to differ in nutrient uptake ability. Plants infected with different AMF genotypes may vary in foliar nutrient or defensive chemical levels, potentially influencing multi-trophic interactions. Using a completely randomized design, we compared the effect of two isolates of the mycorrhizal fungus Glomus etunicatum W. N. Becker & Gerdemann on silver leaf whitefly (Bemisia argentifolii Bellows & Perring) (Hemiptera: Aleyrodidae) and parasitic wasp (Eretmocerus eremicus Rose & Zolnerowich) (Hymenoptera: Aphelinidae) abundance. Whitefly populations were not influenced by AMF infection. Parasite populations were higher on plants infected with the isolate collected from Georgia, even after controlling for whitefly abundance and plant architecture. We propose that AMF indirectly influences parasite abundance and parasitism through a change in leaf surface chemicals that affect parasitic wasps. Because of the ubiquity of and genetic variation in AMF, multi-trophic interactions are likely to be strongly influenced by belowground processes. PMID:22182609

Wooley, Stuart C; Paine, Timothy D

2011-02-01

114

Nature's Starships. I. Observed Abundances and Relative Frequencies of Amino Acids in Meteorites  

NASA Astrophysics Data System (ADS)

The class of meteorites called carbonaceous chondrites are examples of material from the solar system which have been relatively unchanged from the time of their initial formation. These meteorites have been classified according to the temperatures and physical conditions of their parent planetesimals. We collate available data on amino acid abundance in these meteorites and plot the concentrations of different amino acids for each meteorite within various meteorite subclasses. We plot average concentrations for various amino acids across meteorites separated by subclass and petrologic type. We see a predominance in the abundance and variety of amino acids in CM2 and CR2 meteorites. The range in temperature corresponding to these subclasses indicates high degrees of aqueous alteration, suggesting aqueous synthesis of amino acids. Within the CM2 and CR2 subclasses, we identify trends in relative frequencies of amino acids to investigate how common amino acids are as a function of their chemical complexity. These two trends (total abundance and relative frequencies) can be used to constrain formation parameters of amino acids within planetesimals. Our organization of the data supports an onion shell model for the temperature structure of planetesimals. The least altered meteorites (type 3) and their amino acids originated near cooler surface regions. The most active amino acid synthesis likely took place at intermediate depths (type 2). The most altered materials (type 1) originated furthest toward parent body cores. This region is likely too hot to either favor amino acid synthesis or for amino acids to be retained after synthesis.

Cobb, Alyssa K.; Pudritz, Ralph E.

2014-03-01

115

[Isotopic signature (15N/14N and 13C/12C) confirms similarity of trophic niches of millipedes (Myriapoda, Diplopoda) in a temperate deciduous forest].  

PubMed

The species composition, abundance, and isotopic signature of millipedes (Myriapoda, Diplopoda) were investigated in seven biotopes of Kaluzhskie Zaseki State Nature Reserve. Nine Diplopoda species were found in total, and the local species diversity (within a sampling plot) reached seven species. The Diplopoda tissues were similar to the plant litter in the isotopic composition of nitrogen (delta15N was by 0.4% per hundred higher, on average), but were more strongly enriched in heavy carbon (delta13C was by 4% per hundred higher, on average). Removal of mineral carbon from the cuticle reduced delta13C of Diplopoda by about 1.4% per hundred on average. Differences in the delta15N and delta13C values between the species did not exceed 2.5 per hundred. Differences in the isotopic compositions of the considered species are insignificant, and thus, it is impossible to distinguish particular trophic guilds in the Diplopoda community. Analysis of the published data confirmed that isotopic differentiation of millipedes was much less pronounced than in other investigated groups of soil animals. Hence, millipedes of the deciduous forest form a uniform trophic group. PMID:21789998

Semeniuk, I I; Tiunov, A V

2011-01-01

116

Stepwise enrichment of 15N along food chains: Further evidence and the relation between ? 15N and animal age  

NASA Astrophysics Data System (ADS)

The isotopic composition of nitrogen was measured in marine and fresh-water animals from the East China Sea, The Bering Sea, Lake Ashinoko and Usujiri intertidal zone. Primary producers, showed average ?15Nversus atmospheric nitrogen of +5.0%. (+3.4 to +7.5) in the Bering Sea and Lake Ashinoko, and +6.8%. (+6.0 to +7.6) in Usujiri intertidal zone. Blue green algae from the East China Sea show an average -0.55%. (-0.8 to +1.2). All consumers, Zooplankton, fish and bird exhibited Stepwise enrichment of 15N with increasing trophic level. The 15N enrichment at a single feeding process ranged from +1.3 to +5.3 averaging +3.4 ± 1.1%.. This isotopic fractionation seems to be independent of habitat. The effect of age in animals was obtained by analyzing two marine mussels. The soft tissue nitrogen showed +2.0%. enrichment relative to that of primary producers, and the magnitude was almost constant with shell ages ranging from 0 to 8 years. A similar 15N enrichment occurs in all Molluscs, Crustaceans, Insecta, Amphibia, Fish, Ave and Mammal species regardless of the difference in the form of excreted nitrogen and in laboratory cultured fish, brine shrimp and mice (+2.9 to +4.9%.). The excreted ammonia from guppy was sufficiently light to balance the concentration of 15N to animal body.

Minagawa, Masao; Wada, Eitaro

1984-05-01

117

Deuterium isotope shifts for backbone 1H, 15N and 13C nuclei in intrinsically disordered protein -synuclein  

PubMed Central

Intrinsically disordered proteins (IDPs) are abundant in nature and characterization of their potential structural propensities remains a widely pursued but challenging task. Analysis of NMR secondary chemical shifts plays an important role in such studies, but the output of such analyses depends on the accuracy of reference random coil chemical shifts. Although uniform perdeuteration of IDPs can dramatically increase spectral resolution, a feature particularly important for the poorly dispersed IDP spectra, the impact of deuterium isotope shifts on random coil values has not yet been fully characterized. Very precise 2H isotope shift measurements for 13C?, 13C?, 13C’, 15N, and 1HN have been obtained by using a mixed sample of protonated and uniformly perdeuterated -synuclein, a protein with chemical shifts exceptionally close to random coil values. Decomposition of these isotope shifts into one-bond, two-bond and three-bond effects as well as intra- and sequential residue contributions shows that such an analysis, which ignores conformational dependence, is meaningful but does not fully describe the total isotope shift to within the precision of the measurements. Random coil 2H isotope shifts provide an important starting point for analysis of such shifts in structural terms in folded proteins, where they are known to depend strongly on local geometry. PMID:22960996

Maltsev, Alexander S.; Ying, Jinfa; Bax, Ad

2012-01-01

118

Trends in Fishing Mortality Rate along with Errors in Natural Mortality Rate can cause Spurious Time Trends in Fish Stock Abundances Estimated by Virtual Population Analysis (VPA)  

Microsoft Academic Search

Many researchers have reported biases in estimates of fish abundance reconstructed by virtual population analysis (VPAI. We document that VPA can produce changing levels of bias through time, thereby creating spurious time trends in recruitment and stock biomass estimates. We generated catch data from empirically based simulations oi nine fish populations. estimated abundances using VPA with a deliberately mis-specified natural

Michael F. Lapointe; Randall M. Peterman; Alec D. MacCall

1989-01-01

119

Resolving Isotopic Fine Structure to Detect and Quantify Natural Abundance- and Hydrogen/Deuterium Exchange-Derived Isotopomers  

PubMed Central

Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) is used for analyzing protein dynamics, protein folding/unfolding, and molecular interactions. Until this study, HDX MS experiments employed mass spectral resolving powers that afforded only one peak per nominal mass in a given peptide’s isotope distribution, and HDX MS data analysis methods were developed accordingly. A level of complexity that is inherent to HDX MS remained unaddressed, namely, various combinations of natural abundance heavy isotopes and exchanged deuterium shared the same nominal mass and overlapped at previous resolving powers. For example, an A + 2 peak is comprised of (among other isotopomers) a two-2H-exchanged/zero-13C isotopomer, a one-2H-exchanged/one-13C isotopomer, and a zero-2H-exchanged/two-13C isotopomer. Notably, such isotopomers differ slightly in mass as a result of the ~3 mDa mass defect between 2H and 13C atoms. Previous HDX MS methods did not resolve these isotopomers, requiring a natural-abundance-only (before HDX or “time zero”) spectrum and data processing to remove its contribution. It is demonstrated here that high-resolution mass spectrometry can be used to detect isotopic fine structure, such as in the A + 2 profile example above, deconvolving the isotopomer species resulting from deuterium incorporation. Resolving isotopic fine structure during HDX MS therefore permits direct monitoring of HDX, which can be calculated as the sum of the fractional peak magnitudes of the deuterium-exchanged isotopomers. This obviates both the need for a time zero spectrum as well as data processing to account for natural abundance heavy isotopes, saving instrument and analysis time. PMID:24328359

Liu, Qian; Easterling, Michael L.; Agar, Jeffrey N.

2014-01-01

120

Influences of trees on abundance of natural enemies of insect pests: a review  

Microsoft Academic Search

In this article we review the use of natural enemies in crop pest management and describe research needed to better meet information needs for practical applications. Endemic natural enemies (predators and parasites) offer a potential but understudied approach to controlling insect pests in agricultural systems. With the current high interest in environmental stewardship, such an approach has special appeal as

M. E. Dix; R. J. Johnson; M. O. Harrell; R. M. Case; R. J. Wright; L. Hodges; J. R. Brandle; M. M. Schoeneberger; N. J. Sunderman; R. L. Fitzmaurice; L. J. Young; K. G. Hubbard

1995-01-01

121

COVALENT BINDING OF REDUCED METABOLITES OF [15N3] TNT TO SOIL ORGANIC MATTER DURING A BIOREMEDIATION PROCESS ANALYZED BY 15N NMR SPECTROSCOPY. (R826646)  

EPA Science Inventory

Evidence is presented for the covalent binding of biologically reduced metabolites of 2,4,6-15N3-trinitrotoluene (TNT) to different soil fractions (humic acids, fulvic acids, and humin) using liquid 15N NMR spectroscopy. A silylation p...

122

Fate of nitrogen in riparian forest soils and trees: an 15N tracer study simulating salmon decay.  

PubMed

We introduced an 15N-NH4+ tracer to the riparian forest of a salmon-bearing stream (Kennedy Creek, Washington, USA) to quantify the cycling and fate of a late-season pulse of salmon N and, ultimately, mechanisms regulating potential links between salmon abundance and tree growth. The 15N tracer simulated deposition of 7.25 kg of salmon (fresh) to four 50-m2 plots. We added NH4+ (the initial product of salmon carcass decay) and other important nutrients provided by carcasses (P, S, K, Mg, Ca) to soils in late October 2003, coincident with local salmon spawning. We followed the 15N tracer through soil and tree pools for one year. Biological uptake of the 15N tracer occurred quickly: 64% of the 15N tracer was bound in soil microbiota within 14 days, and roots of the dominant riparian tree, western red cedar (Thuja plicata), began to take up 15N tracer within seven days. Root uptake continued through the winter. The 15N tracer content of soil organic matter reached a maximum of approximately 52%, five weeks after the application, and a relative equilibrium of approximately 40% within five months. Six months after the addition, in spring 2004, at least 37% of the 15N tracer was found in tree tissues: approximately 23% in foliage, approximately 11% in roots, and approximately 3% in stems. Within the stems, xylem and phloem sap contained approximately 96% of the tracer N, and approximately 4% was in structural xylem N. After one year, at least 28% of the 15N tracer was still found in trees, and loss from the plots was only approximately 20%. The large portion of tracer N taken up in the fall and reallocated to leaves and stems the following spring provides mechanistic evidence for a one-year-lagged tree-growth response to salmon nutrients. Salmon nutrients have been deposited in the Kennedy Creek system each fall for centuries, but the system shows no evidence of nutrient saturation. Rates of N uptake and retention are a function of site history and disturbance and also may be the result of a legacy effect, in which annual salmon nutrient addition may lead to increased efficiency of nutrient uptake and use. PMID:16761604

Drake, Deanne C; Naiman, I Robert J; Bechtold, J Scott

2006-05-01

123

15N chemical shift referencing in solid state NMR.  

PubMed

Solid-state NMR spectroscopy has much advanced during the last decade and provides a multitude of data that can be used for high-resolution structure determination of biomolecules, polymers, inorganic compounds or macromolecules. In some cases the chemical shift referencing has become a limiting factor to the precision of the structure calculations and we have therefore evaluated a number of methods used in proton-decoupled (15)N solid-state NMR spectroscopy. For (13)C solid-state NMR spectroscopy adamantane is generally accepted as an external standard, but to calibrate the (15)N chemical shift scale several standards are in use. As a consequence the published chemical shift values exhibit considerable differences (up to 22 ppm). In this paper we report the (15)N chemical shift of several commonly used references compounds in order to allow for comparison and recalibration of published data and future work. We show that (15)NH4Cl in its powdered form (at 39.3 ppm with respect to liquid NH3) is a suitable external reference as it produces narrow lines when compared to other reference compounds and at the same time allows for the set-up of cross-polarization NMR experiments. The compound is suitable to calibrate magic angle spinning and static NMR experiments. Finally the temperature variation of (15)NH4Cl chemical shift is reported. PMID:24746715

Bertani, Philippe; Raya, Jésus; Bechinger, Burkhard

2014-01-01

124

ASSESSING ABUNDANCE DISTRIBUTIONS IN NATURAL COMMUNITIES OF ECTOMYCORRHIZAS ALONG AN ENVIRONMENTAL GRADIENT  

EPA Science Inventory

Alpha diversity indices often fail to distinguish between natural populations that a more detailed investigation of the distribution of ramets among types would show are quite different. We studied the effectiveness of applying SHE analyses to morphotype classifications of ectom...

125

Intercontinental Differences in the Abundance of Solenopsis Fire Ants (Hymenoptera: Formicidae): Escape from Natural Enemies?  

Microsoft Academic Search

Environ. Entomol. 26(2): 373-384 (1997) ABSTRACT The absence of natural enemies often allows exotic pests to reach densities that are much higher than normally occur in their native habitats. When SoLnopsis fire ants were introduced into the United States, their numerous natural enemies were left behind in South America. To compare intercontinental fire ant densities, we selected 13 areas in

SANFORD D. PORTER; DAVID F. WILLIAMS; RICHARD S. PATTERSON; HAROLD G. FOWLERl

126

Nitrate dynamics in natural plants: insights based on the concentration and natural isotope abundances of tissue nitrate  

PubMed Central

The dynamics of nitrate (NO?3), a major nitrogen (N) source for natural plants, has been studied mostly through experimental N addition, enzymatic assay, isotope labeling, and genetic expression. However, artificial N supply may not reasonably reflect the N strategies in natural plants because NO?3 uptake and reduction may vary with external N availability. Due to abrupt application and short operation time, field N addition, and isotopic labeling hinder the elucidation of in situ NO?3-use mechanisms. The concentration and natural isotopes of tissue NO?3 can offer insights into the plant NO?3 sources and dynamics in a natural context. Furthermore, they facilitate the exploration of plant NO?3 utilization and its interaction with N pollution and ecosystem N cycles without disturbing the N pools. The present study was conducted to review the application of the denitrifier method for concentration and isotope analyses of NO?3 in plants. Moreover, this study highlights the utility and advantages of these parameters in interpreting NO?3 sources and dynamics in natural plants. We summarize the major sources and reduction processes of NO?3 in plants, and discuss the implications of NO?3 concentration in plant tissues based on existing data. Particular emphasis was laid on the regulation of soil NO?3 and plant ecophysiological functions in interspecific and intra-plant NO?3 variations. We introduce N and O isotope systematics of NO?3 in plants and discuss the principles and feasibilities of using isotopic enrichment and fractionation factors; the correlation between concentration and isotopes (N and O isotopes: ?18O and ?17O); and isotope mass-balance calculations to constrain sources and reduction of NO?3 in possible scenarios for natural plants are deliberated. Finally, we offer a preliminary framework of intraplant ?18O-NO?3 variation, and summarize the uncertainties in using tissue NO?3 parameters to interpret plant NO?3 utilization. PMID:25101106

Liu, Xue-Yan; Koba, Keisuke; Makabe, Akiko; Liu, Cong-Qiang

2014-01-01

127

Nitrate dynamics in natural plants: insights based on the concentration and natural isotope abundances of tissue nitrate.  

PubMed

The dynamics of nitrate (NO(-) 3), a major nitrogen (N) source for natural plants, has been studied mostly through experimental N addition, enzymatic assay, isotope labeling, and genetic expression. However, artificial N supply may not reasonably reflect the N strategies in natural plants because NO(-) 3 uptake and reduction may vary with external N availability. Due to abrupt application and short operation time, field N addition, and isotopic labeling hinder the elucidation of in situ NO(-) 3-use mechanisms. The concentration and natural isotopes of tissue NO(-) 3 can offer insights into the plant NO(-) 3 sources and dynamics in a natural context. Furthermore, they facilitate the exploration of plant NO(-) 3 utilization and its interaction with N pollution and ecosystem N cycles without disturbing the N pools. The present study was conducted to review the application of the denitrifier method for concentration and isotope analyses of NO(-) 3 in plants. Moreover, this study highlights the utility and advantages of these parameters in interpreting NO(-) 3 sources and dynamics in natural plants. We summarize the major sources and reduction processes of NO(-) 3 in plants, and discuss the implications of NO(-) 3 concentration in plant tissues based on existing data. Particular emphasis was laid on the regulation of soil NO(-) 3 and plant ecophysiological functions in interspecific and intra-plant NO(-) 3 variations. We introduce N and O isotope systematics of NO(-) 3 in plants and discuss the principles and feasibilities of using isotopic enrichment and fractionation factors; the correlation between concentration and isotopes (N and O isotopes: ?(18)O and ?(17)O); and isotope mass-balance calculations to constrain sources and reduction of NO(-) 3 in possible scenarios for natural plants are deliberated. Finally, we offer a preliminary framework of intraplant ?(18)O-NO(-) 3 variation, and summarize the uncertainties in using tissue NO(-) 3 parameters to interpret plant NO(-) 3 utilization. PMID:25101106

Liu, Xue-Yan; Koba, Keisuke; Makabe, Akiko; Liu, Cong-Qiang

2014-01-01

128

(15)N- and (2)H proteomic stable isotope probing links nitrogen flow to archaeal heterotrophic activity.  

PubMed

Understanding how individual species contribute to nutrient transformations in a microbial community is critical to prediction of overall ecosystem function. We conducted microcosm experiments in which floating acid mine drainage (AMD) microbial biofilms were submerged - recapitulating the final stage in a natural biofilm life cycle. Biofilms were amended with either (15)NH4(+) or deuterium oxide ((2)H2O) and proteomic stable isotope probing (SIP) was used to track the extent to which different members of the community used these molecules in protein synthesis across anaerobic iron-reducing, aerobic iron-reducing and aerobic iron-oxidizing environments. Sulfobacillus spp. synthesized (15)N-enriched protein almost exclusively under iron-reducing conditions whereas the Leptospirillum spp. synthesized (15)N-enriched protein in all conditions. There were relatively few (15)N-enriched archaeal proteins, and all showed low atom% enrichment, consistent with Archaea synthesizing protein using the predominantly (14)N biomass derived from recycled biomolecules. In parallel experiments using (2)H2O, extensive archaeal protein synthesis was detected in all conditions. In contrast, the bacterial species showed little protein synthesis using (2)H2O. The nearly exclusive ability of Archaea to synthesize proteins using (2)H2O may be due to archaeal heterotrophy, whereby Archaea offset deleterious effects of (2)H by accessing (1)H generated by respiration of organic compounds. PMID:24750948

Justice, Nicholas B; Li, Zhou; Wang, Yingfeng; Spaudling, Susan E; Mosier, Annika C; Hettich, Robert L; Pan, Chongle; Banfield, Jillian F

2014-10-01

129

A thalium-doped sodium iodide well counter for radioactive tracer applications with naturally-abundant 40K  

NASA Astrophysics Data System (ADS)

The use of a thallium-doped sodium-iodide well-type scintillation detector for the assay of the low-activity radioisotope 40K, in open-source potassium chloride aqueous solutions, is described. The hazards, safety concerns and radiowaste generation associated with using open-source radioactive isotopes can present significant difficulties, the use of hot cells and escalated costs in radioanalytical laboratory research. A solution to this is the use of low-hazard alternatives that mimic the migration and dispersion characteristics of notable fission products (in this case 137Cs). The use of NaI(Tl) as a detection medium for naturally-abundant levels of 40K in a range of media is widespread, but the use of 40K as a radioactive tracer has not been reported. The use of such low-activity sources is often complicated by the ability to detect them efficiently. In this paper a scintillator detector designed to detect the naturally-abundant 40K present in potassium chloride in tracer applications is described. Examples of the use of potassium chloride as a tracer are given in the context of ion exchange and electrochemical migration studies, and comparisons in performance are drawn from literature with hyper pure germanium semiconductor detectors, which are more commonly utilised detectors in high-resolution counting applications.

Parker, Andrew J.; Boxall, Colin; Joyce, Malcolm J.; Schotanus, Paul

2013-09-01

130

Direct measurement of the 15N(p,gamma)16O total cross section at novae energies  

E-print Network

The 15N(p,gamma)16O reaction controls the passage of nucleosynthetic material from the first to the second carbon-nitrogen-oxygen (CNO) cycle. A direct measurement of the total 15N(p,gamma)16O cross section at energies corresponding to hydrogen burning in novae is presented here. Data have been taken at 90-230 keV center-of-mass energy using a windowless gas target filled with nitrogen of natural isotopic composition and a bismuth germanate summing detector. The cross section is found to be a factor two lower than previously believed.

D Bemmerer; A Caciolli; R Bonetti; C Broggini; F Confortola; P Corvisiero; H Costantini; Z Elekes; A Formicola; Zs Fulop; G Gervino; A Guglielmetti; C Gustavino; Gy Gyurky; M Junker; B Limata; M Marta; R Menegazzo; P Prati; V Roca; C Rolfs; C Rossi Alvarez; E Somorjai; O Straniero

2009-02-04

131

New method for estimating bacterial cell abundances in natural samples by use of sublimation  

NASA Technical Reports Server (NTRS)

We have developed a new method based on the sublimation of adenine from Escherichia coli to estimate bacterial cell counts in natural samples. To demonstrate this technique, several types of natural samples, including beach sand, seawater, deep-sea sediment, and two soil samples from the Atacama Desert, were heated to a temperature of 500 degrees C for several seconds under reduced pressure. The sublimate was collected on a cold finger, and the amount of adenine released from the samples was then determined by high-performance liquid chromatography with UV absorbance detection. Based on the total amount of adenine recovered from DNA and RNA in these samples, we estimated bacterial cell counts ranging from approximately 10(5) to 10(9) E. coli cell equivalents per gram. For most of these samples, the sublimation-based cell counts were in agreement with total bacterial counts obtained by traditional DAPI (4,6-diamidino-2-phenylindole) staining.

Glavin, Daniel P.; Cleaves, H. James; Schubert, Michael; Aubrey, Andrew; Bada, Jeffrey L.

2004-01-01

132

Automated Protein Turnover Calculations from 15N Partial Metabolic Labeling LC/MS Shotgun Proteomics Data  

PubMed Central

Protein turnover is a well-controlled process in which polypeptides are constantly being degraded and subsequently replaced with newly synthesized copies. Extraction of composite spectral envelopes from complex LC/MS shotgun proteomics data can be a challenging task, due to the inherent complexity of biological samples. With partial metabolic labeling experiments this complexity increases as a result of the emergence of additional isotopic peaks. Automated spectral extraction and subsequent protein turnover calculations enable the analysis of gigabytes of data within minutes, a prerequisite for systems biology high throughput studies. Here we present a fully automated method for protein turnover calculations from shotgun proteomics data. The approach enables the analysis of complex shotgun LC/MS 15N partial metabolic labeling experiments. Spectral envelopes of 1419 peptides can be extracted within an hour. The method quantifies turnover by calculating the Relative Isotope Abundance (RIA), which is defined as the ratio between the intensity sum of all heavy (15N) to the intensity sum of all light (14N) and heavy peaks. To facilitate this process, we have developed a computer program based on our method, which is freely available to download at http://promex.pph.univie.ac.at/protover. PMID:24736476

Lyon, David; Castillejo, Maria Angeles; Staudinger, Christiana; Weckwerth, Wolfram; Wienkoop, Stefanie; Egelhofer, Volker

2014-01-01

133

Inferring the nature of anthropogenic threats from long-term abundance records.  

PubMed

Diagnosing the processes that threaten species persistence is critical for recovery planning and risk forecasting. Dominant threats are typically inferred by experts on the basis of a patchwork of informal methods. Transparent, quantitative diagnostic tools would contribute much-needed consistency, objectivity, and rigor to the process of diagnosing anthropogenic threats. Long-term census records, available for an increasingly large and diverse set of taxa, may exhibit characteristic signatures of specific threatening processes and thereby provide information for threat diagnosis. We developed a flexible Bayesian framework for diagnosing threats on the basis of long-term census records and diverse ancillary sources of information. We tested this framework with simulated data from artificial populations subjected to varying degrees of exploitation and habitat loss and several real-world abundance time series for which threatening processes are relatively well understood: bluefin tuna (Thunnus maccoyii) and Atlantic cod (Gadus morhua) (exploitation) and Red Grouse (Lagopus lagopus scotica) and Eurasian Skylark (Alauda arvensis) (habitat loss). Our method correctly identified the process driving population decline for over 90% of time series simulated under moderate to severe threat scenarios. Successful identification of threats approached 100% for severe exploitation and habitat loss scenarios. Our method identified threats less successfully when threatening processes were weak and when populations were simultaneously affected by multiple threats. Our method selected the presumed true threat model for all real-world case studies, although results were somewhat ambiguous in the case of the Eurasian Skylark. In the latter case, incorporation of an ancillary source of information (records of land-use change) increased the weight assigned to the presumed true model from 70% to 92%, illustrating the value of the proposed framework in bringing diverse sources of information into a common rigorous framework. Ultimately, our framework may greatly assist conservation organizations in documenting threatening processes and planning species recovery. Inferencia la Naturaleza de las Amenazas Antropogénicas para los Registros de Abundancia a Largo Plazo. PMID:25065712

Shoemaker, Kevin T; Akçakaya, H Resit

2015-02-01

134

Effects of weed cover composition on insect pest and natural enemy abundance in a field of Dracaena marginata (Asparagales: Asparagaceae) in Costa Rica.  

PubMed

Weeds and their influence on pest and natural enemy populations were studied on a commercial ornamental farm during 2009 in the Atlantic Zone of Costa Rica. A baseline survey of the entire production plot was conducted in February, along a 5 by 5 m grid to characterize and map initial weed communities of plants, cicadellids, katydids, and armored scales. In total, 50 plant species from 21 families were found. Seven weed treatments were established to determine how weed manipulations would affect communities of our targeted pests and natural enemies. These treatments were selected based on reported effects of specific weed cover on herbivorous insects and natural enemies, or by their use by growers as a cover crop. Treatments ranged from weed-free to being completely covered with endemic species of weeds. Although some weed treatments changed pest abundances, responses differed among arthropod pests, with the strongest effects observed for Caldwelliola and Empoasca leafhoppers. Removal of all weeds increased the abundance of Empoasca, whereas leaving mostly cyperacaeous weeds increased the abundance of Caldwelliola. Weed manipulations had no effect on the abundance of katydid and scale populations. No weed treatment reduced the abundance of all three of the target pests. Differential responses of the two leafhopper species to the same weed treatments support hypotheses, suggesting that noncrop plants can alter the abundance of pests through their effects on arthropod host finding and acceptance, as well as their impacts on natural enemies. PMID:24517852

Sadof, Clifford S; Linkimer, Mildred; Hidalgo, Eduardo; Casanoves, Fernando; Gibson, Kevin; Benjamin, Tamara J

2014-04-01

135

A New Method for Estimating Bacterial Abundances in Natural Samples using Sublimation  

NASA Technical Reports Server (NTRS)

We have developed a new method based on the sublimation of adenine from Escherichia coli to estimate bacterial cell counts in natural samples. To demonstrate this technique, several types of natural samples including beach sand, seawater, deep-sea sediment, and two soil samples from the Atacama Desert were heated to a temperature of 500 C for several seconds under reduced pressure. The sublimate was collected on a cold finger and the amount of adenine released from the samples then determined by high performance liquid chromatography (HPLC) with UV absorbance detection. Based on the total amount of adenine recovered from DNA and RNA in these samples, we estimated bacterial cell counts ranging from approx. l0(exp 5) to l0(exp 9) E. coli cell equivalents per gram. For most of these samples, the sublimation based cell counts were in agreement with total bacterial counts obtained by traditional DAPI staining. The simplicity and robustness of the sublimation technique compared to the DAPI staining method makes this approach particularly attractive for use by spacecraft instrumentation. NASA is currently planning to send a lander to Mars in 2009 in order to assess whether or not organic compounds, especially those that might be associated with life, are present in Martian surface samples. Based on our analyses of the Atacama Desert soil samples, several million bacterial cells per gam of Martian soil should be detectable using this sublimation technique.

Glavin, Daniel P.; Cleaves, H. James; Schubert, Michael; Aubrey, Andrew; Bada, Jeffrey L.

2004-01-01

136

The Nature of QSO Absorption Lines: Abundances, Physical Conditions, and Environment  

NASA Astrophysics Data System (ADS)

This dissertation presents spectroscopic studies of HS1946+7658, HS1700+6416, and H1821+643, three radio-quiet QSOs at redshifts of 3.05, 2.72, and 0.297 respectively. High resolution (20 km s-1) high signal-to-noise spectroscopy of HS1946+7658 and HS1700+6416 yields the following results. (1) Several of the C IV absorbers are narrow implying that T < 50000 K, and therefore these absorbers are probably photoionized. (2) The abundance patterns of two damped Lyman ? absorbers are similar to those of low metallicity Milky Way stars suggesting early stages of chemical enrichment. (3) Photoionization modeling of the HS1946+7658 associated absorber near the QSO redshift indicates that the metallicity is high, comparable to solar, but the models also indicate that the absorbing gas is at least a few hundred kpc away from the QSO. Modeling of the HS1700+6416 associated absorber indicates that the metallicity must be at least 1/5 solar, but the single zone photoionization model may be too simplistic. (4) Two C IV doublets in a dense C IV cluster show the weak line of one C IV doublet apparently aligned with the strong line of a different C IV doublet, i.e., line locked, but this may be coincidental. (5) The metallicities of the HS1700+6416 Lyman limit absorbers are constrained. Finally, we have studied the relationship between low redshift $/rm Ly? clouds and galaxies in the direction of H1821+643. We find: (1) The O VI doublet is unambiguously detected at z = 0.2250 along with H I Ly? and Ly? . Two emission line galaxies are close to the sight line at this redshift, so the O VI could arise in the intracluster medium of a group of galaxies or the large gaseous halo of the closer galaxy. (2) The number of Ly? clouds per unit redshift is significantly greater than the number observed in lower sensitivity surveys. (3) Some Ly? clouds are associated with single galaxies or groups of galaxies, and some are apparently located in voids. However, there are no strong Ly? clouds in the vicinity of the two most prominent galaxy clusters.

Tripp, Todd Maitland

1997-06-01

137

Salinity-induced Patterns of Natural Abundance Carbon-13 and Nitrogen-15 in Plant Jan-Willem van Groenigen* and Chris van Kessel  

E-print Network

Salinity-induced Patterns of Natural Abundance Carbon-13 and Nitrogen-15 in Plant and Soil Jan, and the amount of fossil fuel derived CO2 in the atmosphere (ShearerAlthough it is estimated that salinity stress from the air, modeling 13 C concentrations in the plant terize the impact of salinity stress on natural

van Kessel, Chris

138

Time-dependent extinction rate and species abundance in a tangled-nature model of biological evolution.  

PubMed

We present a model of evolutionary ecology consisting of a web of interacting individuals, a tangle-nature model. The reproduction rate of individuals characterized by their genome depends on the composition of the population in genotype space. Ecological features such as the taxonomy and the macroevolutionary mode of the dynamics are emergent properties. The macrodynamics exhibit intermittent two-mode switching with a gradually decreasing extinction rate. The generated ecologies become gradually better adapted as well as more complex in a collective sense. The form of the species abundance curve compares well with observed functional forms. The model's error threshold can be understood in terms of the characteristics of the two dynamical modes of the system. PMID:12241381

Hall, Matt; Christensen, Kim; di Collobiano, Simone A; Jensen, Henrik Jeldtoft

2002-07-01

139

HCNMBC--a pulse sequence for H-(C)-N Multiple Bond Correlations at natural isotopic abundance.  

PubMed

We propose a pulse sequence, HCNMBC for multiple-bond H-(C)-N correlation experiments via one-bond (1)J(C,H) and one- or multiple bond (n)J(N,C) coupling constants (typically n=1-3) at the natural isotopic abundance. A new adiabatic refocussing sequence is introduced to provide accurate and robust refocussing of both chemical shift and J-evolution over wide ranges of C-13 and N-15 frequencies. It is demonstrated that the proposed pulse sequence provides high quality spectra even for sub-milligram samples. We show that when a 1.7 mm cryoprobe is available as little as 10 ?g of glycine in D2O is sufficient to obtain the HCNMBC spectrum in ca. 12 h. The preliminary results indicate that the pulse sequence has a great potential in the structure determination of nitrogen heterocycles especially in cases where synthesis produces regioisomers. PMID:25233112

Cheatham, Steve; Gierth, Peter; Bermel, Wolfgang; Kup?e, ?riks

2014-10-01

140

Compound-Specific ?15N Amino Acid Measurements in Littoral Mussels in the California Upwelling Ecosystem: A New Approach to Generating Baseline ?15N Isoscapes for Coastal Ecosystems  

PubMed Central

We explored ?15N compound-specific amino acid isotope data (CSI-AA) in filter-feeding intertidal mussels (Mytilus californianus) as a new approach to construct integrated isoscapes of coastal primary production. We examined spatial ?15N gradients in the California Upwelling Ecosystem (CUE), determining bulk ?15N values of mussel tissue from 28 sites between Port Orford, Oregon and La Jolla, California, and applying CSI-AA at selected sites to decouple trophic effects from isotopic values at the base of the food web. Bulk ?15N values showed a strong linear trend with latitude, increasing from North to South (from ?7‰ to ?12‰, R2?=?0.759). In contrast, CSI-AA trophic position estimates showed no correlation with latitude. The ?15N trend is therefore most consistent with a baseline ?15N gradient, likely due to the mixing of two source waters: low ?15N nitrate from the southward flowing surface California Current, and the northward transport of the California Undercurrent (CUC), with15N-enriched nitrate. This interpretation is strongly supported by a similar linear gradient in ?15N values of phenylalanine (?15NPhe), the best AA proxy for baseline ?15N values. We hypothesize ?15NPhe values in intertidal mussels can approximate annual integrated ?15N values of coastal phytoplankton primary production. We therefore used ?15NPhe values to generate the first compound-specific nitrogen isoscape for the coastal Northeast Pacific, which indicates a remarkably linear gradient in coastal primary production ?15N values. We propose that ?15NPhe isoscapes derived from filter feeders can directly characterize baseline ?15N values across major biochemical provinces, with potential applications for understanding migratory and feeding patterns of top predators, monitoring effects of climate change, and study of paleo- archives. PMID:24887109

Vokhshoori, Natasha L.; McCarthy, Matthew D.

2014-01-01

141

Detection of 15NNH+ in L1544: non-LTE modelling of dyazenilium hyperfine line emission and accurate 14N/15N values  

NASA Astrophysics Data System (ADS)

Context. Samples of pristine solar system material found in meteorites and interplanetary dust particles are highly enriched in 15N. Conspicuous nitrogen isotopic anomalies have also been measured in comets, and the 14N/15N abundance ratio of the Earth is itself higher than the recognised presolar value by almost a factor of two. Low-temperature ion/molecule reactions in the proto-solar nebula have been repeatedly indicated as being responsible for these 15N-enhancements. Aims: We have searched for 15N variants of the N2H+ ion in L1544, a prototypical starless cloud core that is one of the best candidate sources for detection owing to its low central core temperature and high CO depletion. The goal is to evaluate accurate and reliable 14N/15N ratio values for this species in the interstellar gas. Methods: A deep integration of the 15NNH+(1-0) line at 90.4 GHz was obtained with the IRAM 30 m telescope. Non-LTE radiative transfer modelling was performed on the J = 1-0 emissions of the parent and 15N-containing dyazenilium ions, using a Bonnor-Ebert sphere as a model for the source. Results: A high-quality fit of the N2H+(1-0) hyperfine spectrum has allowed us to derive a revised value of the N2H+ column density in L1544. Analysis of the observed N15NH+ and 15NNH+ spectra yielded an abundance ratio N(N15NH+)/N(15NNH+) = 1.1 ± 0.3. The obtained 14N/15N isotopic ratio is ~1000 ± 200, suggestive of a sizeable 15N depletion in this molecular ion. Such a result is not consistent with the prediction of the current nitrogen chemical models. Conclusions: Since chemical models predict high 15N fractionation of N2H+, we suggest that 15N14N, or 15N in some other molecular form, tends to deplete onto dust grains. Based on observations carried out with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).Full Tables B.1-B.6 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A109

Bizzocchi, L.; Caselli, P.; Leonardo, E.; Dore, L.

2013-07-01

142

Study of Early Leaf Senescence in Arabidopsis thaliana by Quantitative Proteomics Using Reciprocal 14N\\/15N Labeling and Difference Gel Electrophoresis  

Microsoft Academic Search

Leaf senescence represents the final stage of leaf develop- ment and is associated with fundamental changes on the level of the proteome. For the quantitative analysis of changes in protein abundance related to early leaf senes- cence, we designed an elaborate double and reverse label- ing strategy simultaneously employing fluorescent two-di- mensional DIGE as well as metabolic 15N labeling followed

Romano Hebeler; Silke Oeljeklaus; Kai A. Reidegeld; Martin Eisenacher; Christian Stephan; Barbara Sitek; Kai Stuhler; Helmut E. Meyer; Marcel J. G. Sturre; Paul P. Dijkwel; Bettina Warscheid

2007-01-01

143

Estimation of Carbon and Nitrogen Allocation during Stalk Elongation by 13C and 15N Tracing in Zea mays L. 1  

PubMed Central

Zea mays L. (cv Dea) plants grown to the stage of stalk elongation, were allowed to assimilate 13CO2 and 15N-nitrates from 45 to 53 days after sowing. Isotopic abundances in labeled nutrients were slightly enriched compared to natural abundances. The new C in plant was acropetally distributed and the new N was preferentially accumulated in the sheath and stalk in the medium region. C input was 25-fold higher than N input. The new C in total plant C was 20%, whereas it was 10% for N. The stalk acted as a major sink because it accumulated, respectively, 27.5 and 47.5% of the C and N inputs. The new C in soluble carbohydrates was 76% in growing organs (upper stalk) and only 39% in source leaves, whereas it was 43% and 13% in starch, respectively. New N in nitrates+amino-acids spanned in the range from 20% (leaf) to 50% (stalk). New C and N in soluble proteins were, respectively, 13.4 and 3.8% in leaves, 8.8 and 9.6% in stalk, and 8.7 and 14.3% in roots. In the middle stalk and leaves, the proteins and carbohydrates represent an equivalent C and N source for remobilization. Images Figure 2 Figure 3 Figure 4 PMID:16667269

Cliquet, Jean-Bernard; Deléens, Eliane; Bousser, Agnès; Martin, Michel; Lescure, Jean-Charles; Prioul, Jean-Louis; Mariotti, André; Morot-Gaudry, Jean-François

1990-01-01

144

Factors Driving the Abundance of Ixodes ricinus Ticks and the Prevalence of Zoonotic I. ricinus-Borne Pathogens in Natural Foci  

PubMed Central

Environmental factors may drive tick ecology and therefore tick-borne pathogen (TBP) epidemiology, which determines the risk to animals and humans of becoming infected by TBPs. For this reason, the aim of this study was to analyze the influence of environmental factors on the abundance of immature-stage Ixodes ricinus ticks and on the prevalence of two zoonotic I. ricinus-borne pathogens in natural foci of endemicity. I. ricinus abundance was measured at nine sites in the northern Iberian Peninsula by dragging the vegetation with a cotton flannelette, and ungulate abundance was measured by means of dung counts. In addition to ungulate abundance, data on variables related to spatial location, climate, and soil were gathered from the study sites. I. ricinus adults, nymphs, and larvae were collected from the vegetation, and a representative subsample of I. ricinus nymphs from each study site was analyzed by PCR for the detection of Borrelia burgdorferi sensu lato and Anaplasma phagocytophilum DNA. Mean prevalences of these pathogens were 4.0% ± 1.8% and 20.5% ± 3.7%, respectively. Statistical analyses confirmed the influence of spatial factors, climate, and ungulate abundance on I. ricinus larva abundance, while nymph abundance was related only to climate. Interestingly, cattle abundance rather than deer abundance was the main driver of B. burgdorferi sensu lato and A. phagocytophilum prevalence in I. ricinus nymphs in the study sites, where both domestic and wild ungulates coexist. The increasing abundance of cattle seems to increase the risk of other hosts becoming infected by A. phagocytophilum, while reducing the risk of being infected by B. burgdorferi sensu lato. Controlling ticks in cattle in areas where they coexist with wild ungulates would be more effective for TBP control than reducing ungulate abundance. PMID:22286986

Fernández-de-Mera, Isabel G.; Acevedo, Pelayo; Gortázar, Christian; de la Fuente, José

2012-01-01

145

Cadaverine turnover in soybean seedlings using 15N-labelled lysine and cadaverine.  

PubMed

The synthesis and translocation of the diamine cadaverine during soybean (Glycine max L. Meer cv. Sakai) germination were studied using 15N-labelled lysine (the cadaverine precursor) and 15N-labelled cadaverine, both under light/dark (12 h/12 h) and total dark germinating conditions. 15N-cadaverine and non-labelled polyamines were simultaneously detected using ionspray ionization-mass spectrometry. Both 15N-cadaverine and 15N-lysine were taken up by soybean. 15N-lysine was transported to the shoot and root and converted into 15N-cadaverine, whereas relatively little 15N-cadaverine was formed from 15N-lysine in the cotyledon. The acropetal translocation of 15N-cadaverine from the cotyledon to the shoot seemed to predominate over basipetal transport to the root. Although no other 15N-derivatised polyamines were found, supplying exogenous 15N-lysine seemed to indirectly affect the metabolism of 14N putrescine, spermidine and spermine, while no significant effect was detected after supplying 15N-cadaverine. PMID:20153659

Ohe, Masato; Sasaki, Hitomi; Niitsu, Masaru; Bagni, Nello; Tassoni, Annalisa; Matsuzaki, Shigeru

2010-07-01

146

Female offspring desertion and male-only care increase with natural and experimental increase in food abundance  

PubMed Central

In species with biparental care, one parent may escape the costs of parental care by deserting and leaving the partner to care for the offspring alone. A number of theoretical papers have suggested a link between uniparental offspring desertion and ecological factors, but empirical evidence is scarce. We investigated the relationship between uniparental desertion and food abundance in a natural population of Tengmalm's owl Aegolius funereus, both by means of a 5-year observational study and a 1-year experimental study. Parents and offspring were fitted with radio-transmitters in order to reveal the parental care strategy (i.e. care or desert) of individual parents, and to keep track of the broods post-fledging. We found that 70 per cent of the females from non-experimental nests deserted, while their partner continued to care for their joint offspring alone. Desertion rate was positively related to natural prey population densities and body reserves of the male partner. In response to food supplementation, a larger proportion of the females deserted, and females deserted the offspring at an earlier age. Offspring survival during the post-fledging period tended to be lower in deserted than in non-deserted broods. We argue that the most important benefit of deserting may be remating (sequential polyandry). PMID:19324835

Eldegard, Katrine; Sonerud, Geir A.

2009-01-01

147

Paleoenvironmental implications of taxonomic variation among ??15N values of chloropigments  

USGS Publications Warehouse

Natural variations in the ratios of nitrogen isotopes in biomass reflect variations in nutrient sources utilized for growth. In order to use ??15N values of chloropigments of photosynthetic organisms to determine the corresponding ??15N values of biomass - and by extension, surface waters - the isotopic offset between chlorophyll and biomass must be constrained. Here we examine this offset in various geologically-relevant taxa, grown using nutrient sources that may approximate ocean conditions at different times in Earth's history. Phytoplankton in this study include cyanobacteria (diazotrophic and non-diazotrophic), eukaryotic algae (red and green), and anoxygenic photosynthetic bacteria (Proteobacteria), as well as environmental samples from sulfidic lake water. Cultures were grown using N2, NO3-, and NH4+ as nitrogen sources, and were examined under different light regimes and growth conditions. We find surprisingly high variability in the isotopic difference (??15Nbiomass-??15Nchloropigment) for prokaryotes, with average values for species ranging from -12.2??? to +11.7???. We define this difference as ??por, a term that encompasses diagenetic porphyrins and chlorins, as well as chlorophyll. Negative values of ??por reflect chloropigments that are 15N-enriched relative to biomass. Notably, this enrichment appears to occur only in cyanobacteria. The average value of ??por for freshwater cyanobacterial species is -9.8??1.8???, while for marine cyanobacteria it is -0.9??1.3???. These isotopic effects group environmentally but not phylogenetically, e.g., ??por values for freshwater Chroococcales resemble those of freshwater Nostocales but differ from those of marine Chroococcales. Our measured values of ??por for eukaryotic algae (range=4.7-8.7???) are similar to previous reports for pure cultures. For all taxa studied, values of ??por do not depend on the type of nitrogen substrate used for growth. The observed environmental control of ??por suggests that values of ??por could be useful for determining the fractional burial of eukaryotic vs. cyanobacterial organic matter in the sedimentary record. ?? 2011 Elsevier Ltd.

Higgins, M.B.; Wolfe-Simon, F.; Robinson, R.S.; Qin, Y.; Saito, M.A.; Pearson, A.

2011-01-01

148

Quantification of nitrogen excretion rates for three lumbricid earthworms using 15 N  

Microsoft Academic Search

Nitrogen excretion rates of 15N-labeled earthworms and contributions of 15N excretion products to organic (dissolved organic N) and inorganic (NH4-N, NO3-N) soil N pools were determined at 10??°C and 18??°C under laboratory conditions. Juvenile and adult Lumbricus terrestris L., pre-clitellate and adult Aporrectodea tuberculata (Eisen), and adult Lumbricus rubellus (Hoffmeister) were labeled with 15N by providing earthworms with 15N-labeled organic

J. K. Whalen; R. W. Parmelee; S. Subler

2000-01-01

149

Paleobiological Implications of the Isotopic Signatures ( 13C, 15N) of Fossil Mammal Collagen in Scladina Cave (Sclayn, Belgium)  

NASA Astrophysics Data System (ADS)

An isotopic investigation of upper Pleistocene mammal bones and teeth from Scladina cave (Sclayn, Belgium) demonstrated the very good quality of collagen preservation. A preliminary screening of the samples used the amount of nitrogen in whole bone and dentine in order to estimate the preserved amount of collagen before starting the extraction process. The isotopic abundances of fossil specimens from still-extant species are consistent with their trophic position. Moreover, the 15N isotopic abundance is higher in dentine than in bone in bears and hyenas, a phenomenon already observed in modern specimens. These results demonstrate that the isotopic compositions of samples from Scladina cave can be interpreted in ecological terms. Mammoths exhibit a high 15N isotopic abundance relative to other herbivores, as was the case in Siberian and Alaskan samples. These results suggest distinctive dietary adaptations in herbivores living in the mammoth steppe. Cave bears are clearly isotopically different from coeval brown bears, suggesting an ecological separation between species, with a pure vegetarian diet for cave bear and an omnivorous diet for brown bear.

Bocherens, Hervé; Billiou, Daniel; Patou-Mathis, Marylène; Bonjean, Dominique; Otte, Marcel; Mariotti, André

1997-11-01

150

Nutrient regime shift in the western North Atlantic indicated by compound-specific ?15N of deep-sea gorgonian corals  

PubMed Central

Despite the importance of the nitrogen (N) cycle on marine productivity, little is known about variability in N sources and cycling in the ocean in relation to natural and anthropogenic climate change. Beyond the last few decades of scientific observation, knowledge depends largely on proxy records derived from nitrogen stable isotopes (?15N) preserved in sediments and other bioarchives. Traditional bulk ?15N measurements, however, represent the combined influence of N source and subsequent trophic transfers, often confounding environmental interpretation. Recently, compound-specific analysis of individual amino acids (?15N-AA) has been shown as a means to deconvolve trophic level versus N source effects on the ?15N variability of bulk organic matter. Here, we demonstrate the first use of ?15N-AA in a paleoceanographic study, through analysis of annually secreted growth rings preserved in the organic endoskeletons of deep-sea gorgonian corals. In the Northwest Atlantic off Nova Scotia, coral ?15N is correlated with increasing presence of subtropical versus subpolar slope waters over the twentieth century. By using the new ?15N-AA approach to control for variable trophic processing, we are able to interpret coral bulk ?15N values as a proxy for nitrate source and, hence, slope water source partitioning. We conclude that the persistence of the warm, nutrient-rich regime since the early 1970s is largely unique in the context of the last approximately 1,800 yr. This evidence suggests that nutrient variability in this region is coordinated with recent changes in global climate and underscores the broad potential of ?15N-AA for paleoceanographic studies of the marine N cycle. PMID:21199952

Sherwood, Owen A.; Lehmann, Moritz F.; Schubert, Carsten J.; Scott, David B.; McCarthy, Matthew D.

2011-01-01

151

Natural Carbon Isotope Abundance of Plasma Metabolites and Liver Tissue Differs between Diabetic and Non-Diabetic Zucker Diabetic Fatty Rats  

PubMed Central

Background ‘You are what you eat’ is an accurate summary for humans and animals when it comes to carbon isotope abundance. In biological material, natural13C/12C ratio is subject to minute variations due to diet composition (mainly from ingestion of C3 and C4 metabolism plants) and to the discrimination between ‘light’ and ‘heavy’ isotopes during biochemical reactions (isotope effects and isotopic fractionation). Methodology/Principal Findings Carbon isotopic abundance was measured in ZDF (fa/+) and ZDF (fa/fa), (lean and obese-diabetic rats respectively) fed the same diet. By analysing plasma metabolites (glucose and non-esterified fatty acids), breath and liver tissue by high-precision isotope ratio mass spectrometry, we demonstrate for the first time statistically distinguishable metabolic carbon isotope abundance between ZDF (fa/+) and ZDF (fa/fa) rats based on plasma glucose, palmitic, oleic, linoleic, arachidonic acids and bulk analysis of liver tissue (P<0.005) resulting into clear isotopic fingerprints using principal component analysis. We studied the variation of isotopic abundance between both groups for each metabolite and through the metabolic pathways using the precursor/product approach. We confirmed that lipids were depleted in 13C compared to glucose in both genotypes. We found that isotopic abundance of linoleic acid (C18: 2n-6), even though both groups had the same feed, differed significantly between both groups. The likely reason for these changes between ZDF (fa/+) and ZDF (fa/fa) are metabolic dysregulation associated with various routing and fluxes of metabolites. Conclusion/Significance This work provides evidence that measurement of natural abundance isotope ratio of both bulk tissue and individual metabolites can provide meaningful information about metabolic changes either associated to phenotype or to genetic effects; irrespective of concentration. In the future measuring the natural abundance ?13C of key metabolites could be used as endpoints for studying in vivo metabolism, especially with regards to metabolic dysregulation, and development and progression of metabolic diseases. PMID:24086387

Godin, Jean-Philippe; Ross, Alastair B.; Cléroux, Marilyn; Pouteau, Etienne; Montoliu, Ivan; Moser, Mireille; Kochhar, Sunil

2013-01-01

152

15N2 formation and fast oxygen isotope exchange during pulsed 15N18O exposure of MnOx/CeO2  

SciTech Connect

Pulsing 15N18O onto an annealed 1% Mn16Ox/Ce16O2 catalyst resulted in very fast oxygen isotope exchange and 15N2 formation at 295 K. In the 1st 15N18O pulse, due to the presence of large number of surface oxygen defects, extensive 15N218O and 15N2 formations were observed. In subsequent pulses oxygen isotope exchange dominated as a result of highly labile oxygen in the oxide. We gratefully acknowledge the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy/Vehicle Technologies Program for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.

Kwak, Ja Hun; Szanyi, Janos

2014-12-23

153

Natural Abundance 43Ca NMR Spectroscopy of Tobermorite and Jennite: Model Compounds for C–S–H  

SciTech Connect

There are few effective methods for characterizing the molecular scale structural environments of Ca2? in hydrated cements, which has limited our ability to understand the structure of, for example, Ca–silicate hydrate (C–S–H). 43Ca nuclear magnetic resonance (NMR) spectroscopy has long been considered too insensitive to provide useful data in this regard, but 43Ca magic angle spinning (MAS) NMR spectra reported here for synthetic tobermorite and jennite with naturally abundant levels of 43Ca demonstrate that this is a viable approach.We show that spectra with useful signal/noise ratios can be obtained in a reasonable acquisition period (~2 days) using an H? field strength of 21.1 T, 5 mm rotors spinning at a frequency of 5 kHz, and a double frequency sweep preparatory pulse sequence. Tobermorite and jennite produce relatively broad resonances due to their complex structures and structural disorder, however, the chemical shift differences between six-coordinate 43Ca in jennite and seven-coordinate 43Ca in 11? tobermorite are large enough that the signals are entirely resolved at this field. These data suggest that signal from ideal tobermorite-like and jennite-like sites in cement C–S–H can most likely be distinguished by 43Ca NMR and that this method will be a powerful approach for studying cement-based ceramic materials in the coming decade.

Bowers, Geoffrey M.; Kirkpatrick, Robert J.

2009-02-13

154

Natural Abundance Carbon Isotope Composition of Isoprene Reflects Incomplete Coupling between Isoprene Synthesis and Photosynthetic Carbon Flow  

PubMed Central

Isoprene emission from leaves is dynamically coupled to photosynthesis through the use of primary and recent photosynthate in the chloroplast. However, natural abundance carbon isotope composition (?13C) measurements in myrtle (Myrtus communis), buckthorn (Rhamnus alaternus), and velvet bean (Mucuna pruriens) showed that only 72% to 91% of the variations in the ?13C values of fixed carbon were reflected in the ?13C values of concurrently emitted isoprene. The results indicated that 9% to 28% carbon was contributed from alternative, slow turnover, carbon source(s). This contribution increased when photosynthesis was inhibited by CO2-free air. The observed variations in the ?13C of isoprene under ambient and CO2-free air were consistent with contributions to isoprene synthesis in the chloroplast from pyruvate associated with cytosolic Glc metabolism. Irrespective of alternative carbon source(s), isoprene was depleted in 13C relative to mean photosynthetically fixed carbon by 4‰ to 11‰. Variable 13C discrimination, its increase by partially inhibiting isoprene synthesis with fosmidomicin, and the associated accumulation of pyruvate suggested that the main isotopic discrimination step was the deoxyxylulose-5-phosphate synthase reaction. PMID:12692331

Affek, Hagit P.; Yakir, Dan

2003-01-01

155

Are vascular epiphytes nitrogen or phosphorus limited? A study of plant (15) N fractionation and foliar N : P stoichiometry with the tank bromeliad Vriesea sanguinolenta.  

PubMed

Although there is unambiguous evidence for vascular epiphytic plants to be limited by insufficient water and nutrient supply under natural conditions, it is an open debate whether they are primarily phosphorus (P) or nitrogen (N) limited. Plant (15) N fractionation and foliar N : P stoichiometry of a tank epiphyte (Vriesea sanguinolenta), and its response to combined N-P fertilization, were studied under semi-natural conditions over 334 d to clarify the type of nutrient limitation. Plants collected in the field and experimental plants with limited nutrient supply showed significant plant (15) N fractionation (mean 5‰) and plant N : P ratios of c. 13.5. Higher relative growth rates and declines in plant (15) N fractionation (0.5‰) and in foliar N : P ratios to 8.5 in the high N-P treatment indicated that these epiphytes were P limited in situ. The critical foliar N : P ratio was 10.4, as derived from the breakpoint in the relationship between plant (15) N fractionation and foliar N : P. We interpret the widespread (15) N depletion of vascular epiphytes relative to their host trees as deriving from (15) N fractionation of epiphytes as a result of P limitation. High foliar N : P ratios (> 12) corroborate widespread P limitation (or co-limitation by N and P) of epiphytic bromeliads and, possibly, other epiphyte species. PMID:21729088

Wanek, Wolfgang; Zotz, Gerhard

2011-10-01

156

HYDROGEN ISOTOPE PROFILE OF METHYL GROUPS IN MILIACIN (OLEAN-18-EN-3OL ME) BY NATURAL ABUNDANCE DEUTERIUM 2D-NMR  

E-print Network

.lesot@u-psud.fr; jeremy.jacob@univ-orleans.fr Compound-specific hydrogen isotope analyses are gaining increasing interestHYDROGEN ISOTOPE PROFILE OF METHYL GROUPS IN MILIACIN (OLEAN- 18-EN-3OL ME) BY NATURAL ABUNDANCE to which extent these modifications can be accompanied by a hydrogen isotope fractionation process

Paris-Sud XI, Université de

157

Seasonal abundance of Agrilus planipennis (Coleoptera: Buprestidae) and its natural enemies Oobius agrili (Hymenoptera: Encyrtidae) and Tetrastichus planipennisi (Hymenoptera: Eulophidae) in China  

Microsoft Academic Search

The seasonal abundance and population dynamics of Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) and its natural enemies Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) and Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae) were studied on ash (Fraxinus spp.) in northeastern China in 2004 and 2005. A. planipennis population density varied greatly between sites, trees, and heights in Manchurian ash (Fraxinus mandshurica) forests. At

Houping Liu; Leah S. Bauer; Deborah L. Miller; Tonghai Zhao; Ruitong Gao; Liwen Song; Qingshu Luan; Ruozhong Jin; Changqi Gao

2007-01-01

158

Determination of ??18O and ??15N in Nitrate  

USGS Publications Warehouse

The analyses of both O and N isotopic compositions of nitrate have many potential applications in studies of nitrate sources and reactions in hydrology, oceanography, and atmospheric chemistry, but simple and precise methods for these analyses have yet to be developed. Testing of a new method involving reaction of potassium nitrate with catalyzed graphite (C + Pd + Au) at 520 ??C resulted in quantitative recovery of N and O from nitrate as free CO2, K2CO3, and N2. The ??18O values of nitrate reference materials were obtained by analyzing both the CO2 and K2CO3 from catalyzed graphite combustion. Provisional values of ??18OVSMOW for the internationally distributed KNO3 reference materials IAEA-N3 and USGS-32 were both equal to +22.7 ???? 0.5???. Because the fraction of free CO2 and the isotopic fractionation factor between CO2 and K2CO3 were constant in the combustion products, the ??18O value of KNO3 could be calculated from measurements of the ??18O of free CO2. Thus, ??18KNO3 = a??18OfreeCO2 - b, where a and b were equal to 0.9967 and 3.3, respectively, for the specific conditions of the experiments. The catalyzed graphite combustion method can be used to determine ??18O of KNO3 from measurements of ??18O of free CO2 with reproducibility on the order of ??0.2??? or better if local reference materials are prepared and analyzed with the samples. Reproducibility of ??15N was ??0.1??? after trace amounts of CO were removed.

Revesz, K.; Böhlke, J.K.; Yoshinari, T.

1997-01-01

159

Spectroscopic factors for low-lying 16N levels and the astrophysical 15N(n,gamma)16N reaction rate  

E-print Network

Fluorine is a key element for nucleosynthetic studies since it is extremely sensitive to the physical conditions within stars. The astrophysical site to produce fluorine is suggested to be asymptotic giant branch (AGB) stars. In these stars the 15N(n, g)16N reaction could affect the abundance of fluorine by competing with 15N(a, g)19F. The 15N(n, g)16N reaction rate depends directly on the neutron spectroscopic factors of the low-lying states in 16N. The angular distributions of the 15N(7Li, 6Li)16N reaction populating the ground state and the first three excited states in 16N are measured using a Q3D magnetic spectrograph and are used to derive the spectroscopic factors of these states based on distorted wave Born approximation (DWBA) analysis. The spectroscopic factors of these four states are extracted to be 0.96+-0.09, 0.69+-0.09, 0.84+-0.08 and 0.65+-0.08, respectively. Based on the new spectroscopic factors we derive the 15N(n,g)16N reaction rate. The accuracy and precision of the spectroscopic factors are enhanced due to the first application of high-precision magnetic spectrograph for resolving the closely-spaced 16N levels which can not be achieved in most recent measurement. The present result demonstrates that two levels corresponding to neutron transfers to the 2s1/2 orbit in 16N are not so good single-particle levels although 15N is a closed neutron-shell nucleus. This finding is contrary to the shell model expectation. The present work also provides an independent examination to shed some light on the existing discrepancies in the spectroscopic factors and the 15N(n, g)16N rate.

B. Guo; Z. H. Li; Y. J. Li; J. Su; D. Y. Pang; S. Q. Yan; Z. D. Wu; E. T. Li; X. X. Bai; X. C. Du; Q. W. Fan; L. Gan; J. J. He; S. J. Jin; L. Jing; L. Li; Z. C. Li; G. Lian; J. C. Liu; Y. P. Shen; Y. B. Wang; X. Q. Yu; S. Zeng; L. Y. Zhang; W. J. Zhang; W. P. Liu

2013-12-31

160

Natural-abundance stable carbon isotopes of small-subunit ribosomal RNA (SSU rRNA) from Guaymas Basin (Mexico)  

NASA Astrophysics Data System (ADS)

Small-subunit ribosomal RNA (SSU rRNA) is a phylogenetically informative molecule found in all species. Because it is poorly preserved in most environments, it is a useful marker for active microbial populations. We are using the natural-abundance stable carbon isotopic composition of specific microbial groups to help identify the carbon substrates contributing to microbial biomass in a variety of marine environments. At Guaymas Basin, hydrothermal fluids interact with abundant sedimentary organic carbon to produce natural gas and petroleum. Where this reaches the sediment surface, it can support dense patches of seafloor life, including Beggiatoa mats. We report here on the stable carbon isotopic composition of SSU rRNA from a Beggiatoa mat transect, a cold background site, a warm site with high oil concentration, and a second Beggiatoa mat. The central part of the transect mat overlay the steepest temperature gradient, and was visually dominated by orange Beggiatoa. This was fringed by white Beggiatoa mat and bare, but still warm, sediment. Methane concentrations were saturating beneath the orange and white mats and at the oily site, lower beneath bare sediment, and below detection at the background site. Our initial hypotheses were that rRNA isotopic composition would be strongly influenced by methane supply, and that archaeal rRNA might be lighter than bacterial due to contributions from methanogens and anaerobic methane oxidizers. We used biotin-labeled oligonucleotides to capture Bacterial and Archaeal SSU rRNA for isotopic determination. Background-site rRNA was isotopically heaviest, and bacterial RNA from below 2 cm at the oily site was lightest, consistent with control by methane. Within the transect mat, however, the pattern was more complicated; at some sediment depths, rRNA from the mat periphery was isotopically lightest. Part of this may be due to the spatially and temporally variable paths followed by hydrothermal fluid, which can include horizontal flow. There was no consistent isotopic difference between rRNAs captured by the two probes, although RNA recoveries were too low for isotopic determinations at depths where methanogens and methane oxidizers are expected. Our prediction that rRNA stable carbon isotopic composition would correlate with methane supply was borne out by the comparison between background and mat sediments, but may be an oversimplification for sites within hydrothermal features. Future work will include the isotopic characterization of other potential carbon substrates, such as acetate. We are also investigating cold-seep sediments and brine pools in the Gulf of Mexico, where methane is significantly more 13C-depleted than at Guaymas Basin and may therefore leave a stronger imprint on microbial biomass.table carbon isotopes of rRNA captured with Bacterial and Archaeal probes at mat transect and background sites.

MacGregor, B. J.; Mendlovitz, H.; Albert, D.; Teske, A. P.

2012-12-01

161

Resolving the bulk ? 15N values of ancient human and animal bone collagen via compound-specific nitrogen isotope analysis of constituent amino acids  

NASA Astrophysics Data System (ADS)

Stable nitrogen isotope analysis is a fundamental tool in assessing dietary preferences and trophic positions within contemporary and ancient ecosystems. In order to assess more fully the dietary contributions to human tissue isotope values, a greater understanding of the complex biochemical and physiological factors which underpin bulk collagen ? 15N values is necessary. Determinations of ? 15N values of the individual amino acids which constitute bone collagen are necessary to unravel these relationships, since different amino acids display different ? 15N values according to their biosynthetic origins. A range of collagen isolates from archaeological faunal and human bone ( n = 12 and 11, respectively), representing a spectrum of terrestrial and marine protein origins and diets, were selected from coastal and near-coastal sites at the south-western tip of Africa. The collagens were hydrolysed and ? 15N values of their constituent amino acids determined as N-acetylmethyl esters (NACME) via gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). The analytical approach employed accounts for 56% of bone collagen nitrogen. Reconstruction of bulk bone collagen ? 15N values reveals a 2‰ offset from bulk collagen ? 15N values which is attributable to the ? 15N value of the amino acids which cannot currently be determined by GC-C-IRMS, notably arginine which comprises 53% of the nitrogen unaccounted for (23% of the total nitrogen). The ? 15N values of individual amino acids provide insights into both the contributions of various amino acids to the bulk ? 15N value of collagen and the factors influencing trophic position and the nitrogen source at the base of the food web. The similarity in the ? 15N values of alanine, glutamate, proline and hydroxyproline reflects the common origin of their amino groups from glutamate. The depletion in the ? 15N value of threonine with increasing trophic level indicates a fundamental difference between the biosynthetic pathway of threonine and the other amino acids. The ? 15N value of phenylalanine does not change significantly with trophic level, reflecting its conservative nature as an essential amino acid, and thus represents the isotopic composition of the nitrogen at the base of the food web. ? 15N Glu-Phe values in particular are shown to reflect trophic level nitrogen sources within a food web. In relation to the reconstruction of ancient human diet the contribution of marine and terrestrial protein are strongly reflected in ? 15N Glu-Phe values. Differences in nitrogen metabolism are also shown to have an influence upon individual amino acid ? 15N values with ? 15N Glu-Phe values emphasising differences between the different physiological adaptations. The latter is demonstrated in tortoises, which can excrete nitrogen in the form of uric acid and urea and display negative ? 15N Glu-Phe values whereas those for marine and terrestrial mammals are positive. The findings amplify the potential advantages of compound-specific nitrogen isotope analysis in the study of nitrogen flow within food webs and in the reconstruction of past human diets.

Styring, Amy K.; Sealy, Judith C.; Evershed, Richard P.

2010-01-01

162

Acceleration of natural-abundance solid-state MAS NMR measurements on bone by paramagnetic relaxation from gadolinium-DTPA  

NASA Astrophysics Data System (ADS)

Reducing the data collection time without affecting the signal intensity and spectral resolution is one of the major challenges for the widespread application of multidimensional nuclear magnetic resonance (NMR) spectroscopy, especially in experiments conducted on complex heterogeneous biological systems such as bone. In most of these experiments, the NMR data collection time is ultimately governed by the proton spin-lattice relaxation times (T1). For over two decades, gadolinium(III)-DTPA (Gd-DTPA, DTPA = Diethylene triamine pentaacetic acid) has been one of the most widely used contrast-enhancement agents in magnetic resonance imaging (MRI). In this study, we demonstrate that Gd-DTPA can also be effectively used to enhance the longitudinal relaxation rates of protons in solid-state NMR experiments conducted on bone without significant line-broadening and chemical-shift-perturbation side effects. Using bovine cortical bone samples incubated in different concentrations of Gd-DTPA complex, the 1H T1 values were calculated from data collected by 1H spin-inversion recovery method detected in natural-abundance 13C cross-polarization magic angle spinning (CPMAS) NMR experiments. Our results reveal that the 1H T1 values can be successfully reduced by a factor of 3.5 using as low as 10 mM Gd-DTPA without reducing the spectral resolution and thus enabling faster data acquisition of the 13C CPMAS spectra. These results obtained from 13C-detected CPMAS experiments were further confirmed using 1H-detected ultrafast MAS experiments on Gd-DTPA doped bone samples. This approach considerably improves the signal-to-noise ratio per unit time of NMR experiments applied to bone samples by reducing the experimental time required to acquire the same number of scans.

Mroue, Kamal H.; Zhang, Rongchun; Zhu, Peizhi; McNerny, Erin; Kohn, David H.; Morris, Michael D.; Ramamoorthy, Ayyalusamy

2014-07-01

163

Evaluating microbial carbon sources in Athabasca oil sands tailings ponds using natural abundance stable and radiocarbon isotopes  

NASA Astrophysics Data System (ADS)

Natural abundance stable (?13C) and radiocarbon (?14C) isotopes of phospholipid fatty acids (PLFAs) were used to evaluate the carbon sources utilized by the active microbial populations in surface sediments from Athabasca oil sands tailings ponds. The absence of algal-specific PLFAs at three of the four sites investigated, in conjunction with ?13C signatures for PLFAs that were generally within ~3‰ of that reported for oil sands bitumen (~ -30‰), indicated that the microbial communities growing on petroleum constituents were dominated by aerobic heterotrophs. The ?14C values of PLFAs ranged from -906 to -586‰ and pointed to a significant uptake of fossil carbon (up to ~90% of microbial carbon derived from petroleum), particularly in PLFAs (e.g., cy17:0 and cy19:0) often associated with petroleum hydrocarbon degrading bacteria. The comparatively higher levels of 14C in other, less specific PLFAs (e.g., 16:0) indicated the preferential uptake of younger organic matter by the general microbial population (~50-80% of microbial carbon derived from petroleum). Since the main carbon pools in tailings sediment were essentially 'radiocarbon dead' (i.e., no detectable 14C), the principal source for this modern carbon is considered to be the Athabasca River, which provides the bulk of the water used in the bitumen extraction process. The preferential uptake of the minor amount of young and presumably more biodegradable material present in systems otherwise dominated by recalcitrant petroleum constituents has important implications for remediation strategies. On the one hand, it implies that mining-related organic contaminants could persist in the environment long after tailings pond reclamation has begun. Alternatively, it may be that the young, labile organic matter provided by the Athabasca River plays an important role in stimulating or supporting the microbial utilization of petroleum carbon in oil sands tailings ponds via co-metabolism or priming processes. Further research needs to examine the role which priming processes play in controlling the fate of organic contaminants in Athabasca oil sands tailings ponds, such as understanding to what extent the addition of labile material may hinder or enhance microbial uptake of fossil carbon. This knowledge can be subsequently used to optimize conditions which favour natural attenuation processes in reclamation sites following mine closure.

Ahad, J. M.; Pakdel, H.

2013-12-01

164

15N2 Fixation and H2 Evolution by Six Species of Tropical Leguminous Trees 1  

PubMed Central

The C2H4/15N2 and H2/15N2 ratios for six species of tropical leguminous trees are reported. C2H4/15N2 ratios ranged from 2.4 to 4.7; values for the H2/15N2 ratios were between 0.6 and 1.4. Relative efficiency values, based on C2H2 reduction, 15N incorporation, and H2 evolution during 15N incorporation varied between 0.68 and 0.84 for the six species. Overall, approximately 30% of the electron flow through nitrogenase was used for H2 evolution. PMID:16663109

van Kessel, Christopher; Roskoski, Joann P.; Wood, Timothy; Montano, Jorge

1983-01-01

165

/sup 18/O isotope shift in /sup 15/N NMR spectroscopy. 3. Effects of structure and solvent  

SciTech Connect

Various /sup 15/N, /sup 18/O-labeled compounds were synthesized and the /sup 18/O-induced isotope shifts on their /sup 15/N NMR spectra were measured in order to examine the effects of structural changes on the magnitudes of the shifts. The measured shifts vary greatly, ranging from 0.027 ppm for a nitrile oxide to 0.159 ppm for an isoxazole. The large isotope shifts of isoxazoles compared to oximes and isoxazoline are attributed to the aromatic nature and shorter N-O bond lengths of the isoxazoles. The nature of substituents in the para position of some aromatic aldehyde and ketone oximes affects the magnitude of the /sup 18/O-induced shift. Intramolecular hydrogen bonding significantly decreases the magnitude of the isotope shift in oximes. A study of the effect of solvents on the isotope shifts of three oximes is made. A significant decrease in the isotope shift is observed in solvents having an electron donor atom such as oxygen or nitrogen. This decrease in the magnitude of the isotope shift is ascribed to the formation of hydrogen bonds between the oxime hydroxyl proton and the oxygen or nitrogen of the solvent. Possible applications of the /sup 18/O isotope in /sup 15/N NMR are briefly discussed.

Rajendran, G.; Santini, R.E.; Van Etten, R.L.

1987-07-08

166

Is ?15N of sedimentary organic matter a good proxy for paleodenitrification in coastal waters of the eastern Arabian Sea?  

NASA Astrophysics Data System (ADS)

We compared recently published sedimentary records of ?15N from several coastal areas affected by both natural and anthropogenically produced shallow hypoxia with the objective of testing this as a proxy for denitrification in coastal settings. We examined the eastern boundary systems of continental shelves off western India and Peru, which appear to be experiencing intensification of bottom-water oxygen depletion, most likely as a consequence of intensification of eastern boundary coastal upwelling over the last few decades. In systems that are significantly affected by an enhanced inventory of nutrients from organic matter in soils due to continental erosion following colonial land clearing (e.g., Chesapeake Bay), fertilizer and wastewater runoff (e.g., western Indian shelf and Long Island Sound), the productivity increase is largely local and induced by anthropogenic activity. The western Indian shelf thus experiences a double effect, being both an upwelling zone and prone to nutrient enrichment from land. While in other regions of both natural and anthropogenic bottom-water hypoxia, sedimentary ?15N has undergone significant increases over the Anthropocene; in the eastern Arabian Sea, an opposite trend is noticed despite historical water-column measurements revealing a contemporaneous intensification of denitrification. Plausible causes are discussed here in detail, which led us to conclude that the sedimentary ?15N may not always work as a reliable proxy of denitrification in coastal regions.

Agnihotri, Rajesh; Naqvi, S. Wajih A.; Kurian, Siby; Altabet, Mark A.; Bratton, J. F.

167

Variability of the 15N Chemical Shielding Tensors in the B3 Domain of Protein G from 15N Relaxation Measurements at Several Fields  

PubMed Central

We applied a combination of 15N relaxation and CSA/dipolar cross-correlation measurements at five magnetic fields (9.4, 11.7, 14.1, 16.4, and 18.8 Tesla) to determine the 15N chemical shielding tensors for backbone amides in protein G in solution. The data were analyzed using various model-independent approaches and those based on Lipari-Szabo approximation, all of them yielding similar results. The results indicate a range of site-specific values of the anisotropy (CSA) and orientation of the 15N chemical shielding tensor, similar to those in ubiquitin. Assuming a Gaussian distribution of the 15N CSA values, the mean anisotropy is -173.9 to -177.2 ppm (for 1.02-Å NH-bond length) and the site-so-site CSA variability is ±17.6 to ±21.4 ppm, depending on the method used. This CSA variability is significantly larger than derived previously for ribonuclease H or recently, using “meta-analysis” for ubiquitin. Standard interpretation of 15N relaxation studies of backbone dynamics in proteins involves an a priori assumption of a uniform 15N CSA. We show that this assumption leads to a significant discrepancy between the order parameters obtained at different fields. Using the site-specific CSAs obtained from our study removes this discrepancy and allows simultaneous fit of relaxation data at all five fields to Lipari-Szabo spectral densities. These findings emphasize the necessity of taking into account the variability of 15N CSA for accurate analysis of protein dynamics from 15N relaxation measurements. PMID:16771499

Hall, Jennifer B.; Fushman, David

2008-01-01

168

Sources of ?15N variability in sinking particulate nitrogen in the Cariaco Basin, Venezuela  

NASA Astrophysics Data System (ADS)

Ten years of monthly observations of the ?15N of sinking particulate nitrogen (?15N-PN (in ‰ versus atmospheric N2)=[(15N/14N)sample/(15N/14N)standard)-1]1000) in the Cariaco Basin, Venezuela, confirm that the basin's bottom sediments store information about nitrogen dynamics related to seasonal and interannual variability in regional surface ocean processes. During the upwelling period of the southern Caribbean Sea (February-April), the ?15N-PN is similar to that of the thermocline nitrate (˜3.5‰). This nitrate is imported into the Cariaco Basin with Subtropical Underwater (SUW), which wells up near the coast. Thus, particles generated by phytoplankton photosynthesis during this productive period bear a sub-tropical North Atlantic isotopic imprint of N2 fixation (low compared to the global average of nitrate ?15N?5‰). During the non-upwelling period when surface waters are stratified (September-November), the ?15N-PN is also 3.5-4.0‰, and reflects a mixture of local N2 fixation within the mixed layer, inputs of terrigenous organic matter and SUW nitrate consumption by phytoplankton below the mixed layer, which most likely exerts the strongest control on the ?15N-PN signal during this time. In the transition periods of May-July and December-January, the ?15N-PN increases to 4.5-6.5‰. This coincides with maxima of continental material fluxes (terrestrial PON ?15N is >6‰) into the Cariaco Basin. The ?15N signal in the sediments of the Cariaco Basin thus provides information about the relative strength of the local coastal upwelling, the relative input of continental material via river runoff, and local N2 fixation. The findings contribute to interpretations of the basin's paleoclimatic nitrogen cycle variations based on observations of the sedimentary ?15N record at this location.

Montes, Enrique; Thunell, Robert; Muller-Karger, Frank E.; Lorenzoni, Laura; Tappa, Eric; Troccoli, Luis; Astor, Yrene; Varela, Ramón

2013-09-01

169

Symbiotic nitrogen fixation by legumes in two Chinese grasslands estimated with the 15 N dilution technique  

Microsoft Academic Search

Symbiotic nitrogen (N) fixation by legumes was investigated using the 15N dilution technique in two Chinese grasslands: one in the north-eastern Tibetan Plateau and the other in Inner Mongolia in\\u000a China. A small amount (0.03 g N m?2) of 15N labelled (NH4)2SO4 fertilizer was evenly distributed in two soils. One month after the 15N addition, four legumes (Astragalus sp., Gueldenstaedtia diversifolia, Oxytropis ochrocephala

Baijie Yang; Na Qiao; Xingliang Xu; Hua Ouyang

170

Effects of climate on deer bone ?15N and ?13C: Lack of precipitation effects on ?15N for animals consuming low amounts of C 4 plants  

NASA Astrophysics Data System (ADS)

We have examined the relationship of bone collagen ?15N and ?13C to climatic variables, humidity, temperature, and amount of precipitation using fifty-nine specimens of North American white-tailed deer ( Odocoileus virginianus) from forty-six different locations. In previous studies of African mammals there was a significant correlation between bone collagen ?15N and local amount of precipitation. Results presented here similarly show an increase in ?15N with decreasing amount of precipitation but only for 25% of the animals, namely those consuming more than 10% C 4 plants. These animals also exhibited a significant correlation between ?13C and temperature which mirrors previous observations for grasses suggesting that these deer consume grasses during times of population and nutrient stress. In contrast, even in dry areas containing high proportions of C 4 grasses, the majority of the deer had consumed low amounts of C 4 plants and these deer did not have ?15N which correlate with amount of precipitation. Only when deer deviated from their normal feeding pattern by consuming C 4 plants or grasses did their ?15N correlate with amount of rainfall. For these animals, consumption of C 4 plants or grasses may signal conditions of water and nutrient stress. An increase in ?15N of bone collagen may result from combined effects from excretion of concentrated urine (to conserve water) and increased internal recycling of nitrogen (to conserve nitrogen).

Cormie, A. B.; Schwarcz, H. P.

1996-11-01

171

N-15 NMR spectra of naturally abundant nitrogen in soil and aquatic natural organic matter samples of the International Humic Substances Society  

SciTech Connect

The naturally abundant nitrogen in soil and aquatic NOM samples from the International Humic Substances Society has been characterized by solid state CP/MAS ¹?N NMR. Soil samples include humic and fulvic acids from the Elliot soil, Minnesota Waskish peat and Florida Pahokee peat, as well as the Summit Hill soil humic acid and the Leonardite humic acid. Aquatic samples include Suwannee River humic, fulvic and reverse osmosis isolates, Nordic humic and fulvic acids and Pony Lake fulvic acid. Additionally, Nordic and Suwannee River XAD-4 acids and Suwannee River hydrophobic neutral fractions were analyzed. Similar to literature reports, amide/aminoquinone nitrogens comprised the major peaks in the solid state spectra of the soil humic and fulvic acids, along with heterocyclic and amino sugar/terminal amino acid nitrogens. Spectra of aquatic samples, including the XAD-4 acids, contain resolved heterocyclic nitrogen peaks in addition to the amide nitrogens. The spectrum of the nitrogen enriched, microbially derived Pony Lake, Antarctica fulvic acid, appeared to contain resonances in the region of pyrazine, imine and/or pyridine nitrogens, which have not been observed previously in soil or aquatic humic substances by ¹?N NMR. Liquid state ¹?N NMR experiments were also recorded on the Elliot soil humic acid and Pony Lake fulvic acid, both to examine the feasibility of the techniques, and to determine whether improvements in resolution over the solid state could be realized. For both samples, polarization transfer (DEPT) and indirect detection (¹H–¹?N gHSQC) spectra revealed greater resolution among nitrogens directly bonded to protons. The amide/aminoquinone nitrogens could also be observed by direct detection experiments.

Thorn, Kevin A.; Cox, Larry G.

2009-02-28

172

?15N constraints on long-term nitrogen balances in temperate forests  

USGS Publications Warehouse

Biogeochemical theory emphasizes nitrogen (N) limitation and the many factors that can restrict N accumulation in temperate forests, yet lacks a working model of conditions that can promote naturally high N accumulation. We used a dynamic simulation model of ecosystem N and ?15N to evaluate which combination of N input and loss pathways could produce a range of high ecosystem N contents characteristic of forests in the Oregon Coast Range. Total ecosystem N at nine study sites ranged from 8,788 to 22,667 kg ha?1 and carbon (C) ranged from 188 to 460 Mg ha?1, with highest values near the coast. Ecosystem ?15N displayed a curvilinear relationship with ecosystem N content, and largely reflected mineral soil, which accounted for 96–98% of total ecosystem N. Model simulations of ecosystem N balances parameterized with field rates of N leaching required long-term average N inputs that exceed atmospheric deposition and asymbiotic and epiphytic N2-fixation, and that were consistent with cycles of post-fire N2-fixation by early-successional red alder. Soil water ?15NO3 ? patterns suggested a shift in relative N losses from denitrification to nitrate leaching as N accumulated, and simulations identified nitrate leaching as the primary N loss pathway that constrains maximum N accumulation. Whereas current theory emphasizes constraints on biological N2-fixation and disturbance-mediated N losses as factors that limit N accumulation in temperate forests, our results suggest that wildfire can foster substantial long-term N accumulation in ecosystems that are colonized by symbiotic N2-fixing vegetation.

Perakis, S.S.; Sinkhorn, E.R.; Compton, J.E.

2011-01-01

173

?(15)N variation in Ulva lactuca as a proxy for anthropogenic nitrogen inputs in coastal areas of Gulf of Gaeta (Mediterranean Sea).  

PubMed

We tested the capacity of Ulva lactuca to mark N sources across large marine areas by measuring variation in its ?(15)N at several sites in the Gulf of Gaeta. Comparisons were made with the macroalga Cystoseira amentacea. Variation of ?(15)N values was assessed also in the coastal waters off the Circeo Natural Park, where U. lactuca and C. amentacea were harvested, as these waters are barely influenced by human activities and were used as reference site. A small fragment from each frond was preserved before deployment in order to characterize the initial isotopic values. After 48 h of submersion, U. lactuca was more responsive than C. amentacea to environmental variation and ?(15)N enrichment in the Gulf of Gaeta was observed. The spatial distribution of ?(15)N enrichment indicated that different macro-areas in the Gulf were affected by N inputs from different origins. Comparison of the ?(15)N values of fragments taken from the same transplanted frond avoided bias arising from natural isotopic variability. PMID:24923814

Orlandi, Lucia; Bentivoglio, Flavia; Carlino, Pasquale; Calizza, Edoardo; Rossi, David; Costantini, Maria Letizia; Rossi, Loreto

2014-07-15

174

Estimating modal abundances from the spectra of natural and laboratory pyroxene mixtures using the modified Gaussian model  

NASA Astrophysics Data System (ADS)

The modified Gaussian model (MGM) is used to explore spectra of samples containing multiple pyroxene components as a function of modal abundance. The MGM allows spectra to be analyzed directly, without the use of actual or assumed end-member spectra and therefore holds great promise for remote applications. A series of mass fraction mixtures created from several different particle size fractions are analyzed with the MGM to quantify the properties of pyroxene mixtures as a function of both modal abundance and grain size. Band centers, band widths, and relative band strengths of absorptions from individual pyroxenes in mixture spectra are found to be largely independent of particle size. Spectral properties of both zoned and exsolved pyroxene components are resolved in exsolved samples using the MGM, and modal abundances are accurately estimated to within 5-10 percent without predetermined knowledge of the end-member spectra.

Sunshine, J. M.; Pieters, C. M.

1993-05-01

175

Human dietary ?(15)N intake: representative data for principle food items.  

PubMed

Dietary analysis using ?(15)N values of human remains such as bone and hair is usually based on general principles and limited data sets. Even for modern humans, the direct ascertainment of dietary ?(15)N is difficult and laborious, due to the complexity of metabolism and nitrogen fractionation, differing dietary habits and variation of ?(15)N values of food items. The objective of this study was to summarize contemporary regional experimental and global literature data to ascertain mean representative ?(15)N values for distinct food categories. A comprehensive data set of more than 12,000 analyzed food samples was summarized from the literature. Data originated from studies dealing with (1) authenticity tracing or origin control of food items, and (2) effects of fertilization or nutrition on ?(15)N values of plants or animals. Regional German food ?(15)N values revealed no major differences compared with the mean global values derived from the literature. We found that, in contrast to other food categories, historical faunal remains of pig and poultry are significantly enriched in (15)N compared to modern samples. This difference may be due to modern industrialized breeding practices. In some food categories variations in agricultural and feeding regimens cause significant differences in ?(15)N values that may lead to misinterpretations when only limited information is available. PMID:23921599

Huelsemann, F; Koehler, K; Braun, H; Schaenzer, W; Flenker, U

2013-09-01

176

Labeling earthworms uniformly with 13C and 15N: implications for monitoring nutrient fluxes  

Microsoft Academic Search

Stable isotopes hold promise for improving our ability to quantify energy and N released from earthworm populations through metabolic processes and mortality. However, the isotopic labels 13C and 15N must be incorporated uniformly into the structural and labile tissues of earthworms to trace C and N fluxes accurately. We examined the distribution of 13C and 15N in the tissue and

Joann K Whalen; H. Henry Janzen

2002-01-01

177

Sources of variation in consumer-diet ? 15 N enrichment: a meta-analysis  

Microsoft Academic Search

Measurements of 15N of consumers are usually higher than those of their diet. This general pattern is widely used to make inferences about trophic relationships in ecological studies, although the underlying mechanisms causing the pattern are poorly understood. However, there can be substantial variation in consumer-diet 15N enrichment within this general pattern. We conducted an extensive literature review, which yielded

Mathew A. Vanderklift; Sergine Ponsard

2003-01-01

178

Accessible NMR Experiments Studying the Hydrodynamics of [subscript 15]N-Enriched Ubiquitin at Low Fields  

ERIC Educational Resources Information Center

We have recently developed and implemented two experiments in biomolecular NMR for an undergraduate-level biophysical chemistry laboratory with commercially available [subscript 15]N-enriched human ubiquitin. These experiments take advantage of [subscript 15]N direct detection of the NMR signal. The first experiment develops skills in acquiring…

Thompson, Laura E.; Rovnyak, David

2007-01-01

179

Accessible NMR Experiments Studying the Hydrodynamics of [superscript 15]N-Enriched Ubiquitin at Low Fields  

ERIC Educational Resources Information Center

We have recently developed and implemented two experiments in biomolecular NMR for an undergraduate-level biophysical chemistry laboratory with commercially available [superscript 15]N-enriched human ubiquitin. These experiments take advantage of [superscript 15]N direct detection of the NMR signal. The first experiment develops skills in…

Thompson, Laura E.; Rovnyak, David

2007-01-01

180

15N and13C NMR investigation of hydroxylamine-derivatized humic substances  

USGS Publications Warehouse

Five fulvic and humic acid samples of diverse origins were derivatized with 15N-labeled hydroxylamine and analyzed by liquid-phase 15N NMR spectrometry. The 15N NMR spectra indicated that hydroxylamine reacted similarly with all samples and could discriminate among carbonyl functional groups. Oximes were the major derivatives; resonances attributable to hydroxamic acids, the reaction products of hydroxylamine with esters, and resonances attributable to the tautomeric equilibrium position between the nitrosophenol and monoxime derivatives of quinones, the first direct spectroscopic evidence for quinones, also were evident. The 15N NMR spectra also suggested the presence of nitriles, oxazoles, oxazolines, isocyanides, amides, and lactams, which may all be explained in terms of Beckmann reactions of the initial oxime derivatives. INEPT and ACOUSTIC 15N NMR spectra provided complementary information on the derivatized samples. 13C NMR spectra of derivatized samples indicated that the ketone/quinone functionality is incompletely derivatized with hydroxylamine. ?? 1991 American Chemical Society.

Thorn, K.A.; Arterburn, J.B.; Mikita, M.A.

1992-01-01

181

Syntheses of 15N-labeled pre-queuosine nucleobase derivatives  

PubMed Central

Summary Pre-queuosine or queuine (preQ1) is a guanine derivative that is involved in the biosynthetic pathway of the hypermodified tRNA nucleoside queuosine (Que). The core structure of preQ1 is represented by 7-(aminomethyl)-7-deazaguanine (preQ1 base). Here, we report the synthesis of three preQ1 base derivatives with complementary 15N-labeling patterns, utilizing [15N]-KCN, [15N]-phthalimide, and [15N3]-guanidine as cost-affordable 15N sources. Such derivatives are required to explore the binding process of the preQ1 base to RNA targets using advanced NMR spectroscopic methods. PreQ1 base specifically binds to bacterial mRNA domains and thereby regulates genes that are required for queuosine biosynthesis. PMID:25246950

Levic, Jasmin

2014-01-01

182

Syntheses of (15)N-labeled pre-queuosine nucleobase derivatives.  

PubMed

Pre-queuosine or queuine (preQ1) is a guanine derivative that is involved in the biosynthetic pathway of the hypermodified tRNA nucleoside queuosine (Que). The core structure of preQ1 is represented by 7-(aminomethyl)-7-deazaguanine (preQ1 base). Here, we report the synthesis of three preQ1 base derivatives with complementary (15)N-labeling patterns, utilizing [(15)N]-KCN, [(15)N]-phthalimide, and [(15)N3]-guanidine as cost-affordable (15)N sources. Such derivatives are required to explore the binding process of the preQ1 base to RNA targets using advanced NMR spectroscopic methods. PreQ1 base specifically binds to bacterial mRNA domains and thereby regulates genes that are required for queuosine biosynthesis. PMID:25246950

Levic, Jasmin; Micura, Ronald

2014-01-01

183

Correlation between the 6Li,15N coupling constant and the coordination number at lithium.  

PubMed

The 6Li,15N coupling constants of lithium amide dimers and their mixed complexes with n-butyllithium, formed from five different chiral amines derived from (S)-[15N]phenylalanine, were determined in diethyl ether (Et2O), tetrahydrofuran (THF) and toluene. Results of NMR spectroscopy studies of these complexes show a clear difference in 6Li,15N coupling constants between di-, tri- and tetracoordinated lithium atoms. The lithium amide dimers with a chelating ether group exhibit 6Li,15N coupling constants of approximately 3.8 and approximately 5.5 Hz for the tetracoordinated and tricoordinated lithium atoms, respectively. The lithium amide dimers with a chelating thioether group show distinctly larger 6Li,15N coupling constants of approximately 4.4 Hz for the tetracoordinated lithium atoms, and the tricoordinated lithium atoms have smaller 6Li,15N coupling constants, approximately 4.9 Hz, than their ether analogues. In diethyl ether and tetrahydrofuran, mixed dimeric complexes between the lithium amides and n-butyllithium are formed. The tetracoordinated lithium atoms of these complexes have 6Li,15N coupling constants of approximately 4.0 Hz, and the 6Li,15N coupling constants of the tricoordinated lithium atoms differ somewhat, depending on whether the chelating group is an ether or a thioether; approximately 5.1 and approximately 4.6 Hz, respectively. In toluene, mixed trimeric complexes are formed from two lithium amide moieties and one n-butyllithium. In these trimers, two lithium atoms are tricoordinated with 6Li,15N coupling constants of approximately 4.6 Hz and one lithium is dicoordinated with 6Li,15N coupling constants of approximately 6.5 Hz. PMID:16526078

Granander, Johan; Sott, Richard; Hilmersson, Göran

2006-05-15

184

Importance of bacterivory and preferential selection toward diatoms in larvae of Crepidula fornicata (L.) assessed by a dual stable isotope (13C, 15N) labeling approach  

NASA Astrophysics Data System (ADS)

In Europe, the gastropod Crepidula fornicata is an invasive species characterized by a long reproductive period (from February to November). Thus, its larvae are exposed to variations in available food sources (in terms of quantity and quality). We aimed to investigate if bacteria could contribute to larval food both in presence or absence of phytoplankton, and to compare these results to seasonal variations of bacteria and phytoplankton abundances at a coastal site in the English Channel. First, ingestion of fluorescent beads of 0.5 to 2 ?m diameter, showed that larvae were able to ingest particles of typical bacterial size. Then we used a dual stable isotope labeling approach which consisted in labeling a bacterial pelagic community with 15N and a diatom (Chaetoceros gracilis) culture with 13C, and supplying larvae with 15N-labeled bacteria, 13C-labeled diatoms, and both labeled sources. This technique has, to our knowledge, never been applied to invertebrate larvae. After 24 h of experiment, larvae were significantly enriched in all treatments: + 21.5‰ (??13C) when supplied with diatoms, + 1364‰ (??15N) when supplied with bacteria, and + 24‰ (??13C) and + 135‰ (??15N) when supplied with the two mixed sources. These results indicated that bacteria can contribute to the larval nutrition in C. fornicata, even in the presence of phytoplankton. Our results however suggested that larvae of C. fornicata preferentially used diatoms and showed that the supply of free bacteria did not alter the uptake of diatoms. Considering the seasonal variations of bacteria and phytoplankton abundances at the study site, these results suggested that bacteria may constitute a complementary resource for the larvae of C. fornicata when phytoplankton is abundant and may become a substitute resource when phytoplankton is less available. This approach offers promising perspectives to trace food sources and assess nitrogen and carbon fluxes between planktotrophic larvae and their preys.

Leroy, Fanny; Riera, Pascal; Jeanthon, Christian; Edmond, Frédérique; Leroux, Cédric; Comtet, Thierry

2012-05-01

185

Bacterial abundance and aerobic microbial activity across natural and oyster aquaculture habitats during summer conditions in a northeastern Pacific estuary  

Microsoft Academic Search

We measured sediment properties and the abundance and aerobic metabolism of microbes in Willapa Bay, Washington, USA, to test\\u000a the response of sediment microbes to oyster aquaculture. Sites spanned the estuary gradient (practical salinity units ranged\\u000a from 24 to 30 under seasonally low river flows) and six different low-intertidal habitat types: eelgrass (Zostera marina), unstructured tideflat, oyster hummocks (reefs of

Nehemiah F. Richardson; Jennifer L. Ruesink; Shahid Naeem; Sally D. Hacker; Heather M. Tallis; Brett R. Dumbauld; Lorena M. Wisehart

2008-01-01

186

Pumpkinseed sunfish ( Lepomis gibbosus ) invasions facilitated by introductions and nature management strongly reduce macroinvertebrate abundance in isolated water bodies  

Microsoft Academic Search

The pumpkinseed sunfish, Lepomis gibbosus, originates from Eastern North America and was introduced to the Netherlands in 1902 as an aquarium and garden pond fish.\\u000a At present the pumpkinseed is widely spread throughout the Netherlands and occurs in a variety of aquatic habitats. It is\\u000a especially abundant in moorland pools, fishing ponds and urban waters. Strong population development of the

H. H. van Kleef; G. van der Velde; R. S. E. W. Leuven; H. Esselink

2008-01-01

187

?13C and ?15N values in scales of Micropterus salmoides largemouth bass as a freshwater environmental indicator.  

PubMed

We have investigated the effectiveness of using the Micropterus salmoides largemouth bass, which is a top predator found throughout the world, as the index of a hydrosphere environment and its food chain. To this end, we used stable carbon and nitrogen isotope analysis (SIA). Largemouth bass were collected from eight dam reservoirs and two ponds in Toyama Prefecture, Japan. Toyama is located in central Japan and features a variety of distinct geographical environments, a result of the 3000-m elevation that changes over short distances, and abundant water systems. The mean ?(13)C and ?(15)N values for the lipid-extracted muscle of largemouth bass from all sampling locations showed large variability, but there were only small standard deviations at each sampling location. The isotope ratios for largemouth bass express the characteristics of each investigated hydrosphere environment and food chain. A very high correlation (?(13)C: Y(scale) = 0.96 X(muscle) + 1.58, R(2) = 0.98, ?(15)N: Y(scale) = 0.92 X(muscle) - 1.15, R(2) = 0.95) of SIA values was found between largemouth bass scales and lipid-extracted muscles, which suggests that the more easily analyzed scales are useful as SIA samples for the monitoring and comparison of hydrosphere environments throughout the world. PMID:22215573

Inamura, O; Zhang, J; Minagawa, M

2012-01-15

188

Synthesis and utilization of 13C and 15N backbone-labeled proline: NMR study of synthesized oxytocin with backbone-labeled C-terminal tripeptide amide.  

PubMed

The 13C and 15N backbone-labeled proline was prepared using Oppolzer's method based on application of a sultam as chiral auxiliary. This isotopomer was used in the synthesis of the 13C, 15N backbone-labeled C-terminal tripeptide amide fragment of neurohypophyseal hormone oxytocin. Finally, this tripeptide amide was coupled by segment condensation with N-Boc- or N-Fmoc-tocinoic acid, followed by N-deprotection with TFA or piperidine. The labeled oxytocin exhibited biological activity identical with that of natural oxytocin. A detailed 1H, 13C and 15N NMR study confirmed the assigned oxytocin conformation containing a beta-turn in the cyclic part of the molecule, stabilized by H-bond(s) that can be perturbed by the C-terminal tripeptide amide moiety as indicated by comparison of NMR data for both the tocine ring in oxytocin and tocinoic acid. PMID:15791394

Budesínský, M; Ragnarsson, U; Lankiewicz, L; Grehn, L; Slaninová, J; Hlavácek, J

2005-08-01

189

Quantifying RDX biodegradation in groundwater using ?15N isotope analysis  

NASA Astrophysics Data System (ADS)

Isotope analysis was used to examine the extent of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) biodegradation in groundwater along a ca. 1.35-km contamination plume. Biodegradation was proposed as a natural attenuating remediation method for the contaminated aquifer. By isotope analysis of RDX, the extent of biodegradation was found to reach up to 99.5% of the initial mass at a distance of 1.15-1.35 km down gradient from the contamination sources. A range of first-order biodegradation rates was calculated based on the degradation extents, with average half-life values ranging between 4.4 and 12.8 years for RDX biodegradation in the upper 15 m of the aquifer, assuming purely aerobic biodegradation, and between 10.9 and 31.2 years, assuming purely anaerobic biodegradation. Based on the geochemical data, an aerobic biodegradation pathway was suggested as the dominant attenuation process at the site. The calculated biodegradation rate was correlated with depth, showing decreasing degradation rates in deeper groundwater layers. Exceptionally low first-order kinetic constants were found in a borehole penetrating the bottom of the aquifer, with half life ranging between 85.0 to 161.5 years, assuming purely aerobic biodegradation, and between 207.5 and 394.3 years, assuming purely anaerobic biodegradation. The study showed that stable isotope fractionation analysis is a suitable tool to detect biodegradation of RDX in the environment. Our findings clearly indicated that RDX is naturally biodegraded in the contaminated aquifer. To the best of our knowledge, this is the first reported use of RDX isotope analysis to quantify its biodegradation in contaminated aquifers.

Bernstein, Anat; Adar, Eilon; Ronen, Zeev; Lowag, Harald; Stichler, Willibald; Meckenstock, Rainer U.

2010-01-01

190

Nitrogen Stable Isotope Composition (?(15)N) of Vehicle-Emitted NOx.  

PubMed

The nitrogen stable isotope ratio of NOx (?(15)N-NOx) has been proposed as a regional indicator for NOx source partitioning; however, knowledge of ?(15)N values from various NOx emission sources is limited. This study presents a detailed analysis of ?(15)N-NOx emitted from vehicle exhaust, the largest source of anthropogenic NOx. To accomplish this, NOx was collected from 26 different vehicles, including gasoline and diesel-powered engines, using a modification of a NOx collection method used by the United States Environmental Protection Agency, and ?(15)N-NOx was analyzed. The vehicles sampled in this study emitted ?(15)N-NOx values ranging from -19.1 to 9.8‰ that negatively correlated with the emitted NOx concentrations (8.5 to 286 ppm) and vehicle run time because of kinetic isotope fractionation effects associated with the catalytic reduction of NOx. A model for determining the mass-weighted ?(15)N-NOx from vehicle exhaust was constructed on the basis of average commute times, and the model estimates an average value of -2.5 ± 1.5‰, with slight regional variations. As technology improvements in catalytic converters reduce cold-start emissions in the future, it is likely to increase current ?(15)N-NOx values emitted from vehicles. PMID:25621737

Walters, Wendell W; Goodwin, Stanford R; Michalski, Greg

2015-02-17

191

Steroselective synthesis and application of L-( sup 15 N) amino acids  

SciTech Connect

We have developed two general approaches to the stereoselective synthesis of {sup 15}N- and {sup 13}C-labeled amino acids. First, labeled serine, biosynthesized using the methylotrophic bacterium M. extorquens AM1, serves as a chiral precursor for the synthesis of other amino acids. For example, pyridoxal phosphate enzymes can be used for the conversion of L-({alpha}-{sup 15}N)serine to L-({alpha}-{sup 15}N)tyrosine, L-({alpha}-{sup 15}N)tryptophan, and L-({alpha}-{sup 15}N)cysteine. In the second approach, developed by Oppolzer and Tamura, an electrophilic amination'' reagent, 1-chloro-1-nitrosocyclohexane, was used to convert chiral enolates into L-{alpha}-amino acids. We prepared 1-chloro-1-({sup 15}N) nitrosocyclohexane and used it to aminate chiral enolates to produce L-({alpha}-{sup 15}N)amino acids. The stereoselectivity of this scheme using the Oppolzer sultam chiral auxiliary is remarkable, producing enantiomer ratios of 200 to 1. 22 refs., 4 figs.

Unkefer, C.J. (Los Alamos National Lab., NM (United States)); Lodwig, S.N. (Centralia Coll., WA (United States). Div. of Science)

1991-01-01

192

Abiotic and biotic factors associated with the presence of Anopheles arabiensis immatures and their abundance in naturally occurring and man-made aquatic habitats  

PubMed Central

Background Anopheles arabiensis (Diptera: Culicidae) is a potential malaria vector commonly present at low altitudes in remote areas in Reunion Island. Little attention has been paid to the environmental conditions driving larval development and abundance patterns in potential habitats. Two field surveys were designed to determine whether factors that discriminate between aquatic habitats with and without An. arabiensis larvae also drive larval abundance, comparatively in man-made and naturally occurring habitats. Methods In an initial preliminary survey, a representative sample of aquatic habitats that would be amenable to an intensive long-term study were selected and divided into positive and negative sites based on the presence or absence of Anopheles arabiensis larvae. Subsequently, a second survey was prompted to gain a better understanding of biotic and abiotic drivers of larval abundance, comparatively in man-made and naturally occurring habitats in the two studied locations. In both surveys, weekly sampling was performed to record mosquito species composition and larval density within individual habitats, as well as in situ biological characteristics and physico-chemical properties. Results Whilst virtually any stagnant water body could be a potential breeding ground for An. arabiensis, habitats occupied by their immatures had different structural and biological characteristics when compared to those where larvae were absent. Larval occurrence seemed to be influenced by flow velocity, macrofauna diversity and predation pressure. Interestingly, the relative abundance of larvae in man-made habitats (average: 0.55 larvae per dip, 95%CI [0.3–0.7]) was significantly lower than that recorded in naturally occurring ones (0.74, 95%CI [0.5–0.8]). Such differences may be accounted for in part by varying pressures that could be linked to a specific habitat. Conclusions If the larval ecology of An. arabiensis is in general very complex and factors affecting breeding site productivity sometimes not easy to highlight, our results, however, highlight lower populations of An. arabiensis immatures compared to those reported in comparable studies conducted in the African continent. Overall, this low larval abundance, resulting from both abiotic and biotic factors, suggests that vector control measures targeting larval habitats are likely to be successful in Reunion, but these could be better implemented by taking environmental variability into account. PMID:22608179

2012-01-01

193

Mammalian DNA ?15N exhibits 40‰ intramolecular variation and is unresponsive to dietary protein level  

PubMed Central

We report the first high precision characterization of molecular and intramolecular ?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 15N or 13C. 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. Cerebellar DNA of offspring was extracted at 2 and 120 days of life, nucleosides isolated and ?15N and ?13C characterized. Mean diet ?15N = 0.45±0.33‰, compared to cerebellar whole tissue and DNA ?15N = +4.1±0.7‰ and ?4.5±0.4‰, respectively. Cerebellar deoxythymidine (dT), deoxycytidine (dC), deoxyadenosine (dA), and deoxyguanosine (dG) ?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 ?15N due to dietary protein level. Using known metabolic relationships, we developed equations to calculate the intramolecular ?15N originating from aspartate (asp) in purines (pur) or pyrimidines (pyr), glutamine (glu), and glycine (gly) to be ?15NASP-PUR, ?15NASP-PYR, ?15NGLN, and ?15NGLY +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 ?15N of 4.3±3.2‰ and 13.8±3.1‰, respectively, and ?15N 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 ?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 than in adult life. Our data show that cerebellar nucleoside intramolecular ?15N vary over more than 40‰ and are not influenced by dietary protein level or age. PMID:22095504

Strable, Maggie S.; Tschanz, Carolyn L.; Varamini, Behzad; Chikaraishi, Yoshito; Ohkouchi, Naohiko; Brenna, J. Thomas

2014-01-01

194

Continuous field measurement of N2O isotopologues using FTIR spectroscopy following 15N addition  

NASA Astrophysics Data System (ADS)

Anthropogenic additions of fertilizer nitrogen (N) have significantly increased the mole fraction of nitrous oxide (N2O) in the troposphere. Tracking the fate of fertilizer N and its transformation to N2O is important to advance knowledge of greenhouse gas emissions from soils. Transport and transformations are frequently studied using 15N labeling experiments, but instruments capable of continuous measurements of 15N-N2O at the surface of soil have only recently come to the fore. Our primary aim was to quantify emissions of N2O and the fraction of 15N emitted as N2O from an agricultural soil following 15N addition using a mobile Fourier Transform Infrared (FTIR) spectrometer. We set up a short-term field experiment on a coastal floodplain site near Nowra, New South Wales. We deployed an automated chamber system connected to a multi-pass cell (optical pathlength 24 m) and low resolution FTIR spectrometer to measure fluxes of all N2O isotopologues collected from five 0.25 m2 chambers every three hours. We measured N2O fluxes pre and post-application of 15N-labeled substrate as potassium nitrate (KNO3) or urea [CO(NH2)2] to the soil surface. Root mean square uncertainties for all isotopologue measurements were less than 0.3 nmol mol-1 for 1 minute average concentration measurements, and minimum detectable fluxes for each isotopologue were <0.1 ng N m-2 s-1. Emissions of all N2O isotopologues were evident immediately following 15N addition. Emissions of 14N15NO, 15N14NO and 15N15NO isotopologues subsided within 10 d, but 14N14NO fluxes were evident over the entire experiment. The figure provides an overview of the emissions. Cumulative 15N-N2O fluxes (sum of the three 15N isotopologues) per chamber for the 14 days following 15N addition ranged from 1.5 to 10.3 mg 15N-N2O m-2. The chambers were destructively sampled after 2 weeks and 15N analyzed in soil and plant material using isotope ratio mass spectrometry. Approximately 1% (range 0.7 - 1.9%) of the total amount of 15N applied was emitted as N2O. Average fractions of 15N recovered in soil, root, shoot, and microbial biomass pools varied between trials but were approximately 0.4, 0.08, 0.1 and 0.03, respectively. The results indicate that the portable FTIR spectroscopic technique can effectively trace transfer of 15N to the atmosphere as N2O after 15N addition, allowing for powerful quantification of N2O emissions under field conditions.

Phillips, R. L.; Griffith, D. W.; Dijkstra, F. A.; Lugg, G.; Lawrie, R.; Macdonald, B.

2012-12-01

195

[The determination of a gross utilization of 15N-lysine in laboratory rats. 1. Experiment with normal intestinal flora (without antibiotic supplement)].  

PubMed

Wistar rats of a live weight of about 100 g were divided into 14 groups (5 animals/group). The rations given supplied the animals with 75%, 100% and 125% lysine, which brought about a moderate growth of the animals of approximately 2 g/animal and day achieved by limited feeding. The 3 lysine levels mentioned could be achieved by lysine supplements (L-lysine-HCl) for the following rations: barley (B), wheat (W), and wheat gluten (WG). For isolated soybean protein (assay protein) (S) the lysine levels 100% and 125% and for soybean meal (SM) the levels 116% and 125% could only be achieved. A control group with whole egg ration (W) (with its natural lysine content of 125% of the requirement) were also tested as comparison. During the 10-day period of the main experiment all 14 rations were supplemented with 0.5 g 15N-lysine (alpha amino group, 95% labelled with 15N). The N balance could only be significantly improved by lysine supplements in the rations B, W and SM with the lysine level of 125%. The biologic value of the protein sources was in rations B and WG also significantly improved by the highest lysine supplement. 15N excess (15N') from the deaminated 15N lysine was excreted with diet B rich in crude fibre mainly in faeces (more than 15% of the intake) and only about 10% in urine. With the diets without native crude fibre the excretion quota changed in favour of urine. The following 15N' amounts in per cent of 15N' intake from lysine were excreted in urine and faeces: B 75 = 31.3, B 100 = 30.9, B 125 = 28.0, W 75 = 24.3, W 100 = 32.2, W 125 = 32.6, GW 75 = 18.3, WG 100 = 24.2, WG 125 = 28.1, S 100 = 39.4, S 125 = 50.4, SM 116 = 34.9, SM 125 = 32.9, W 125 = 19.1. 15N excretion in urine and faeces increased in comparable relations in 6 cases of lysine increase levels only. Gross utilization of lysine can only conditionally be quantified by 15N labelled lysine supplement. PMID:1665059

Bergner, H; Schwandt, H

1991-10-01

196

Variable ?15N Diet-Tissue Discrimination Factors among Sharks: Implications for Trophic Position, Diet and Food Web Models  

PubMed Central

The application of stable isotopes to characterize the complexities of a species foraging behavior and trophic relationships is dependent on assumptions of ?15N diet-tissue discrimination factors (?15N). As ?15N values have been experimentally shown to vary amongst consumers, tissues and diet composition, resolving appropriate species-specific ?15N values can be complex. Given the logistical and ethical challenges of controlled feeding experiments for determining ?15N values for large and/or endangered species, our objective was to conduct an assessment of a range of reported ?15N values that can hypothetically serve as surrogates for describing the predator-prey relationships of four shark species that feed on prey from different trophic levels (i.e., different mean ?15N dietary values). Overall, the most suitable species-specific ?15N values decreased with increasing dietary-?15N values based on stable isotope Bayesian ellipse overlap estimates of shark and the principal prey functional groups contributing to the diet determined from stomach content analyses. Thus, a single ?15N value was not supported for this speciose group of marine predatory fishes. For example, the ?15N value of 3.7‰ provided the highest percent overlap between prey and predator isotope ellipses for the bonnethead shark (mean diet ?15N = 9‰) whereas a ?15N value < 2.3‰ provided the highest percent overlap between prey and predator isotope ellipses for the white shark (mean diet ?15N = 15‰). These data corroborate the previously reported inverse ?15N-dietary ?15N relationship when both isotope ellipses of principal prey functional groups and the broader identified diet of each species were considered supporting the adoption of different ?15N values that reflect the predators’ ?15N-dietary value. These findings are critical for refining the application of stable isotope modeling approaches as inferences regarding a species’ ecological role in their community will be influenced with consequences for conservation and management actions. PMID:24147026

Olin, Jill A.; Hussey, Nigel E.; Grgicak-Mannion, Alice; Fritts, Mark W.; Wintner, Sabine P.; Fisk, Aaron T.

2013-01-01

197

Variable ?(15)N diet-tissue discrimination factors among sharks: implications for trophic position, diet and food web models.  

PubMed

The application of stable isotopes to characterize the complexities of a species foraging behavior and trophic relationships is dependent on assumptions of ?(15)N diet-tissue discrimination factors (?(15)N). As ?(15)N values have been experimentally shown to vary amongst consumers, tissues and diet composition, resolving appropriate species-specific ?(15)N values can be complex. Given the logistical and ethical challenges of controlled feeding experiments for determining ?(15)N values for large and/or endangered species, our objective was to conduct an assessment of a range of reported ?(15)N values that can hypothetically serve as surrogates for describing the predator-prey relationships of four shark species that feed on prey from different trophic levels (i.e., different mean ?(15)N dietary values). Overall, the most suitable species-specific ?(15)N values decreased with increasing dietary-?(15)N values based on stable isotope Bayesian ellipse overlap estimates of shark and the principal prey functional groups contributing to the diet determined from stomach content analyses. Thus, a single ?(15)N value was not supported for this speciose group of marine predatory fishes. For example, the ?(15)N value of 3.7‰ provided the highest percent overlap between prey and predator isotope ellipses for the bonnethead shark (mean diet ?(15)N = 9‰) whereas a ?(15)N value < 2.3‰ provided the highest percent overlap between prey and predator isotope ellipses for the white shark (mean diet ?(15)N = 15‰). These data corroborate the previously reported inverse ?(15)N-dietary ?(15)N relationship when both isotope ellipses of principal prey functional groups and the broader identified diet of each species were considered supporting the adoption of different ?(15)N values that reflect the predators' ?(15)N-dietary value. These findings are critical for refining the application of stable isotope modeling approaches as inferences regarding a species' ecological role in their community will be influenced with consequences for conservation and management actions. PMID:24147026

Olin, Jill A; Hussey, Nigel E; Grgicak-Mannion, Alice; Fritts, Mark W; Wintner, Sabine P; Fisk, Aaron T

2013-01-01

198

Covalent binding of reduced metabolites of [{sup 15}N{sub 3}]TNT to soil organic matter during a bioremediation process analyzed by {sup 15}N NMR spectroscopy  

SciTech Connect

Evidence is presented for the covalent binding of biologically reduced metabolites of 2,4,6-{sup 15}N{sub 3}-trinitrotoluene (TNT) to different soil fractions, using liquid {sup 15}N NMR spectroscopy. A silylation procedure was used to release soil organic matter from humin and whole soil for spectroscopic measurements. TNT-contaminated soil was spiked with 2,4,6-{sup 15}N{sub 3}-trinitrotoluene and {sup 14}C-ring labeled TNT, before treatment in a soil slurry reactor. During the anaerobic/aerobic incubation the amount of radioactivity detected in the fulvic and humic acid fractions did not change significantly whereas the radioactivity bound to humin increased to 71%. The {sup 15}N NMR spectra of the fulvic acid samples were dominated by a large peak that corresponded to aliphatic amines or ammonia. In the early stages of incubation, {sup 15}N NMR analysis of the humic acids indicated bound azoxy compounds. The signals arising from nitro and azoxy groups disappeared with further anaerobic treatment. At the end of incubation, the NMR shifts showed that nitrogen was covalently bound to humic acid as substituted amines and amides. The NMR spectra of the silylated humin suggest formation of azoxy compounds and imine linkages. Bound metabolites possessing nitro groups were also detected. Primary amines formed during the anaerobic incubation disappeared during the aerobic treatment. Simultaneously, the amount of amides and tertiary amines increased. Nitro and azoxy groups of bound molecules were still present in humin at the end of the incubation period. Formation of azoxy compounds from partially reduced TNT followed by binding and further reduction appears to be an important mechanism for the immobilization of metabolites of TNT to soil.

Achtnich, C.; Fernandes, E.; Bollag, J.M.; Knackmuss, H.J.; Lenke, H.

1999-12-15

199

Abundances of a bean bug and its natural enemy in seminatural and cultivated habitats in agricultural landscapes.  

PubMed

To determine differences in distribution patterns between the soybean pest Riptortus pedestris F. (Hemiptera: Alydidae) and its egg parasitoid Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) in source and cultivated habitats, we compared their abundances in soybean fields and forest edges, which were assumed to be the overwintering sites of R. pedestris. We set synthetic attractant-baited traps for both species over 2 yr in mid-August, just before R. pedestris normally colonizes soybeans. During one of the 2 yr, we also examined the rate of parasitism using an egg trap. The numbers of both R. pedestris and O. nezarae trapped at forest edges were higher than the numbers caught in soybean fields, suggesting that forest edges are important source habitats. Compared with R. pedestris, the abundance of O. nezarae in soybean fields was considerably lower than in forest edges, presumably because of differences in their dispersal abilities and their responses to landscape structure and resource distribution. Better pest control service by O. nezarae was provided at forest edges than in soybean fields. Therefore, when using pest control by O. nezarae in soybean fields, spatial arrangement and distance from the forest edge should be considered. PMID:24534078

Tabuchi, Ken; Taki, Hisatomo; Iwai, Hideki; Mizutani, Nobuo; Nagasaka, Koukichi; Moriya, Seiichi; Sasaki, Rikiya

2014-04-01

200

Abundance and seasonal activity of questing Ixodes ricinus ticks in their natural habitats in southern Germany in 2011.  

PubMed

Questing ticks were sampled monthly over a period of 11 months from February, 2011 to December, 2011 at 13 sites in southern Germany using the flagging method. The ticks were identified to species, gender, and stadium. Although both I. ricinus and D. reticulatus were sampled, this study concentrated on I. ricinus, since it was the most abundant tick to be found. Additional weather data (air and soil temperature, relative air humidity, precipitation, sunshine duration) were recorded on each sampling site and the local vegetation described. A total of 14, 394 ticks was collected (7,862 larvae, 5,568 nymphs, 964 adults) and their activity was recorded in order to determine the seasonal activity pattern over different periods of the year. In contrast to the widely accepted pattern of a bimodal seasonal activity in moderate areas with a dominant peak in spring and a minor peak in autumn, a unimodal activity pattern was found for all development stages on six of the 12 sampling sites. Tick abundance was compared to weather variables. Tick host-seeking activity was found to be significantly dependent on the temperature at ground level, precipitation, and sunshine duration as well as relative air humidity. Adult ticks showed a positive correlation with the duration of sunshine, whereas nymphs were mostly unaffected by this phenomenon. PMID:24820556

Schulz, Michaela; Mahling, Monia; Pfister, Kurt

2014-06-01

201

Eastern oyster (Crassostrea virginica) ?15N as a bioindicator of nitrogen sources: Observations and modeling  

PubMed Central

Stable nitrogen isotopes (?15N) in bioindicators are increasingly employed to identify nitrogen sources in many ecosystems and biological characteristics of the eastern oyster (Crassostrea virginica) make it an appropriate species for this purpose. To assess nitrogen isotopic fractionation associated with assimilation and baseline variations in oyster mantle, gill, and muscle tissue ?15N, manipulative fieldwork in Chesapeake Bay and corresponding modeling exercises were conducted. This study (1) determined that five individuals represented an optimal sample size; (2) verified that ?15N in oysters from two locations converged after shared deployment to a new location reflecting a change in nitrogen sources; (3) identified required exposure time and temporal integration (four months for muscle, two to three months for gill and mantle); and (4) demonstrated seasonal ?15N increases in seston (summer) and oysters (winter). As bioindicators, oysters can be deployed for spatial interpolation of nitrogen sources, even in areas lacking extant populations. PMID:20381097

Fertig, B.; Carruthers, T.J.B.; Dennison, W.C.; Fertig, E.J.; Altabet, M.A.

2013-01-01

202

Preparation of 13C/15N-labeled oligomers using the polymerase chain reaction  

DOEpatents

Preparation of .sup.13 C/.sup.15 N-labeled DNA oligomers using the polymerase chain reaction (PCR). A PCR based method for uniform (.sup.13 C/.sup.15 N)-labeling of DNA duplexes is described. Multiple copies of a blunt-ended duplex are cloned into a plasmid, each copy containing the sequence of interest and restriction Hinc II sequences at both the 5' and 3' ends. PCR using bi-directional primers and uniformly .sup.13 C/.sup.15 N-labeled dNTP precursors generates labeled DNA duplexes containing multiple copies of the sequence of interest. Twenty-four cycles of PCR, followed by restriction and purification, gave the uniformly .sup.13 C/.sup.15 N-labeled duplex sequence with a 30% yield. Such labeled duplexes find significant applications in multinuclear magnetic resonance spectroscopy.

Chen, Xian (Los Alamos, NM); Gupta, Goutam (Santa Fe, NM); Bradbury, E. Morton (Santa Fe, NM)

2001-01-01

203

Facile measurement of 1 H– 15 N residual dipolar couplings in larger perdeuterated proteins  

Microsoft Academic Search

We present a simple method, ARTSY, for extracting 1JNH couplings and 1H–15N RDCs from an interleaved set of two-dimensional 1H–15N TROSY-HSQC spectra, based on the principle of quantitative J correlation. The primary advantage of the ARTSY method over\\u000a other methods is the ability to measure couplings without scaling peak positions or altering the narrow line widths characteristic\\u000a of TROSY spectra.

Nicholas C. Fitzkee; Ad Bax

2010-01-01

204

Metabolism of 15 N-labelled ammonium by the ectomycorrhizal fungus Pisolithus tinctorim (Pers.) Coker & Couch  

Microsoft Academic Search

Glutamine was the major product accumulated following transfer of nitrogen-limited cultures of the ectomycorrhizal fungus Pisolithus tinctorius to an ammonium medium. Experiments in which mycelium was transferred to [15N]H4+showed glutamine amide was the most heavily labelled product. Assimilation of ammonium into glutamate was markedly inhibited by azaserine. The kinetics of 15N-labelling and the effects of azaserine and methionine sulphoximine on

Joanna L. Kershaw; George R. Stewart

1992-01-01

205

Field evaluation of symbiotic nitrogen fixation by rhizobial strains using 15 N methodology  

Microsoft Academic Search

Summary Small differences in N2 fixation by nodulated soybeans (Glycine max. (L.) Merr.), inoculated with various strains ofRhizobium japonicum, were assessed in field experiments using15N methodology, and compared with yields of plant dry matter and total N. Percentage of plant-N derived from atmospheric N2 and from fertilizer, and values of %15N atom excess had lower coefficients of variation than did

G. Hardarson; F. Zapata; S. K. A. Danso

1984-01-01

206

Fate of nitrogen released from 15N-labeled litter in European beech forests.  

PubMed

The decomposition and fate of 15N-labeled beech litter was monitored in three European beech (Fagus sylvatica L.) forests (Aubure, France; Ebrach, Germany; and Collelongo, Italy) for 3 years. Circular plots around single beech trees were isolated from roots of neighboring trees by soil trenching, and annual litterfall was replaced by 15N-labeled litter. Nitrogen was continuously released from the decomposing litter. However, over a 2-year period, this release was balanced by the incorporation of exogenous N. Released N accumulated mainly at the soil surface and in the topsoil. Microbial biomass remained almost constant during the experiment at all sites except for considerably lower values at Ebrach. The 15N enrichment of the microbial biomass increased strongly during the first year and then remained stable. The 15N released from the decomposing litter was rapidly detected in roots and leaves of the beech trees, increasing regularly and linearly over the course of the experiment. The uptake of litter-released 15N by the trees was reduced under conditions that reduced tree growth. Under these conditions, leaves and fine roots were the dominant N sinks, and little N was allocated to other plant parts. By contrast, N uptake and N allocation from leaves to stem and bark tissues increased when tree growth was enhanced. Budgets for 15N showed that 2 to 4% of litter-released N was incorporated into the trees, about 35% remained in the litter and about 50% reached the topsoil. PMID:11303646

Zeller, B; Colin-Belgrand, M; Dambrine, E; Martin, F

2001-02-01

207

Constraints on abundance, composition, and nature of X-ray amorphous components of soils and rocks at Gale crater, Mars  

NASA Astrophysics Data System (ADS)

diffraction patterns of the three samples analyzed by Curiosity's Chemistry and Mineralogy (CheMin) instrument during the first year of the Mars Science Laboratory mission—the Rocknest sand, and the John Klein and Cumberland drill fines, both extracted from the Sheepbed mudstone—show evidence for a significant amorphous component of unclear origin. We developed a mass balance calculation program that determines the range of possible chemical compositions of the crystalline and amorphous components of these samples within the uncertainties of mineral abundances derived from CheMin data. In turn, the chemistry constrains the minimum abundance of amorphous component required to have realistic compositions (all oxides ? 0 wt %): 21-22 wt % for Rocknest and 15-20 wt % for Cumberland, in good agreement with estimates derived from the diffraction patterns (~27 and ~31 wt %, respectively). Despite obvious differences between the Rocknest sand and the Sheepbed mudstone, the amorphous components of the two sites are chemically very similar, having comparable concentrations of SiO2, TiO2, Al2O3, Cr2O3, FeOT, CaO, Na2O, K2O, and P2O5. MgO tends to be lower in Rocknest, although it may also be comparable between the two samples depending on the exact composition of the smectite in Sheepbed. The only unambiguous difference is the SO3 content, which is always higher in Rocknest. The observed similarity suggests that the two amorphous components share a common origin or formation process. The individual phases possibly present within the amorphous components include: volcanic (or impact) glass, hisingerite (or silica + ferrihydrite), amorphous sulfates (or adsorbed SO42-), and nanophase ferric oxides.

Dehouck, Erwin; McLennan, Scott M.; Meslin, Pierre-Yves; Cousin, Agnès.

2014-12-01

208

Isotopic fractionation of nitrogen and carbon in Paleoarchean cherts from Pilbara craton, Western Australia: Origin of 15N-depleted nitrogen  

NASA Astrophysics Data System (ADS)

Nitrogen and carbon isotopic compositions, together with mineralogy and trace element geochemistry, were studied in a few kerogen-rich Paleoarchean cherts, a barite and a dolomitic stromatolite belonging to the eastern (Dixon Island Formation) and western (Dresser and Strelley Pool Chert Formations; North Pole Dome and Marble Bar) terranes of Pilbara Craton, Western Australia. The aim of the study was to search for 15N-depleted isotopic signatures, often found in kerogens of this period, and explain the origin of these anomalies. Trace elements suggest silica precipitation by hydrothermal fluids as the main process of chert formation with a contamination from volcanoclastic detritus. This is supported by the occurrence of hydrothermal-derived minerals in the studied samples indicating precipitation temperatures up to 350 °C. Only a dolomitic stromatolite from Strelley Pool shows a superchondritic Y/Ho ratio of 72 and a positive Eu/Eu * anomaly of 1.8, characteristic of chemical precipitates from the Archean seawater. The bulk ? 13C vs. ? 15N values measured in the cherts show a roughly positive co-variation, except for one sample from the North Pole (PI-85-00). The progressive enrichment in 15N and 13C from a pristine source having ? 13C ? -36‰ and ? 15N ? -4‰ is correlated with a progressive depletion in N content and to variations in Ba/La and Co/As ratios. These trends have been interpreted as a progressive hydrothermal alteration of the cherts by metamorphic fluids. Isotopic exchange at 350 °C between NH 4+(rock) and N 2(fluid) may explain the isotopic and elemental composition of N in the studied cherts. However, we need to assume isotopic exchange at 350 °C between carbonate C and graphite to explain the large 13C enrichment recorded. Only sample PI-85-00 shows a large N loss (90%) with a positive ? 15N value (+11‰), while C (up to 120 ppm and ? 13C -38‰) seems to be unaffected. This pattern has been interpreted as the result of devolatilization and alteration (oxidation) of graphite by low-temperature fluids. The 15N- 13C-depleted pristine source has ? 15N values from -7‰ to -4‰ and 40Ar/ 36Ar ratios from 30,000 to 60,000, compatible with an inorganic mantle N source, although the elemental abundance ratios N/C and 40Ar/C are not exactly the same with the mantle source. The component alternatively could be explained by elemental fractionation from metabolic activity of chemolithoautotrophs and methanogens at the proximity to the hydrothermal vents. However, ambiguities between mantle vs organic sources of N subsist and need further experimental work to be fully elucidated.

Pinti, Daniele L.; Hashizume, Ko; Sugihara, Akiyo; Massault, Marc; Philippot, Pascal

2009-07-01

209

Metabolic labeling with stable isotope nitrogen (15N) to follow amino acid and protein turnover of three plastid proteins in Chlamydomonas reinhardtii  

PubMed Central

Background The length of time that a protein remains available to perform its function is significantly influenced by its turnover rate. Knowing the turnover rate of proteins involved in different processes is important to determining how long a function might progress even when the stimulus has been removed and no further synthesis of the particular proteins occurs. In this article, we describe the use of 15N-metabolic labeling coupled to GC-MS to follow the turnover of free amino acids and LC-MS/MS to identify and LC-MS to follow the turnover of specific proteins in Chlamydomonas reinhardtii. Results To achieve the metabolic labeling, the growth medium was formulated with standard Tris acetate phosphate medium (TAP) in which14NH4Cl was replaced with 15NH415NO3 and (14NH4)6Mo7O24.4H2O was replaced with Na2MoO4.2H2O. This medium designated 15N-TAP allowed CC-125 algal cells to grow normally. Mass isotopic distribution revealed successful 15N incorporation into 13 amino acids with approximately 98% labeling efficiency. Tryptic digestion of the 55 kDa SDS-PAGE bands from 14N- and 15N-labeled crude algal protein extracts followed by LC-MS/MS resulted in the identification of 27 proteins. Of these, five displayed peptide sequence confidence levels greater than 95% and protein sequence coverage greater than 25%. These proteins were the RuBisCo large subunit, ATP synthase CF1 alpha and beta subunits, the mitochondrial protein (F1F0 ATP synthase) and the cytosolic protein (S-adenosyl homocysteine hydroxylase). These proteins were present in both labeled and unlabeled samples. Once the newly synthesized 15N-labeled free amino acids and proteins obtained maximum incorporation of the 15N-label, turnover rates were determined after transfer of cells into 14N-TAP medium. The t½ values were determined for the three plastid proteins (RuBisCo, ATP synthase CF1 alpha and beta) by following the reduction of the 15N-fractional abundance over time. Conclusion We describe a more rapid and non-radioactive method to measure free amino acid and protein turnover. Our approach is applicable for determination of protein turnover for various proteins, which will lead to a better understanding of the relationship between protein lifetime and functionality. PMID:24580857

2014-01-01

210

Determination of Natural 14C Abundances in Dissolved Organic Carbon in Organic-Rich Marine Sediment Porewaters by Thermal Sulfate Reduction  

NASA Astrophysics Data System (ADS)

The abundances of natural 14C in dissolved organic carbon (DOC) in the marine environment hold clues regarding the processes that influence the biogeochemical cycling of this large carbon reservoir. At present, UV irradiation is the widely accepted method for oxidizing seawater DOC for determination of their 14C abundances. This technique yields precise and accurate values with low blanks, but it requires a dedicated vacuum line, and hence can be difficult to implement. As an alternative technique that can be conducted on a standard preparatory vacuum line, we modified and tested a thermal sulfate reduction method that was previously developed to determine ?13C values of marine DOC (Fry B. et al., 1996. Analysis of marine DOC using a dry combustion method. Mar. Chem., 54: 191-201.) to determine the 14C abundances of DOC in marine sediment porewaters. In this method, the sample is dried in a 100 ml round-bottom Pyrex flask in the presence of excess oxidant (K2SO4) and acid (H3PO4), and combusted at 550 deg.C. The combustion products are cryogenically processed to collect and quantify CO2 using standard procedures. Materials we have oxidized to date range from 6-24 ml in volume, and 95-1500 ?gC in size. The oxidation efficiency of this method was tested by processing known amounts of reagent-grade dextrose and sucrose (as examples of labile organic matter), tannic acid and humic acid (as examples of complex natural organic matter), and porewater DOC extracted from organic-rich nearshore sediments. The carbon yields for all of these materials averaged 99±4% (n=18). The 14C abundances of standard materials IAEA C-6 and IAEA C-5 processed by this method using >1mgC aliquots were within error of certified values. The size and the isotopic value of the blank were determined by a standard dilution technique using IAEA C-6 and IAEA C-5 that ranged in size from 150 to 1500 ?gC (n=4 and 2, respectively). This yielded a blank size of 6.7±0.7 ?gC, and a blank isotopic value of 0.54±0.05 fMC. The size of the blank agreed well with that determined directly by processing variable volumes of UV-irradiated deionized water (5.6±0.7 ?gC, n=9). The size of the blank amounts to <~5% of the size of porewater DOC samples that are typically recovered from organic-rich sediment cores (~100-500 ?gC). The fMC value of the blank suggests that there may be multiple sources of extraneous carbon that range in 14C abundance. In order to assess the fidelity of 14C abundances in natural porewater DOC oxidized by thermal sulfate reduction, we oxidized porewater DOC samples collected from the central floor of the Santa Monica Basin, California Borderland, using both this method and UV irradiation (the latter carried out at the Druffel laboratory, University of California Irvine). The fMC values obtained by the two methods agreed within error. Carbon yields from the two methods also agreed closely. These findings show that thermal sulfate reduction may be a promising method to oxidize small, concentrated marine DOC samples for 14C analysis.

Johnson, L.; Komada, T.

2010-12-01

211

NATURAL VARIATION IN ABUNDANCE OF SALMONID POPULATIONS IN STREAMS AND ITS IMPLICATIONS FOR DESIGN OF IMPACT STUDIES. A REVIEW  

EPA Science Inventory

Literature on stock size and production of salmonid populations in streams has been reviewed. The objective is to bring together data on the magnitude of natural variation in population size and to relate this variability to environmental conditions where possible. Recommendation...

212

A Climate Related Explanation for the Natural Control of Pacific Salmon Abundance in the First Marine Year  

Microsoft Academic Search

The belief that most natural losses of Pacific salmon occurred during the freshwater stage of their life cycle profoundly influenced how Pacific salmon were managed and researched in Canada for the past 50 years. It has only been recognized in the last few years that an understanding of the impacts of ocean habitat and climate are essential ingredients in the

Richard J. Beamish; Rusty M. Sweeting; Chrys E. Neville; Korey Poier

213

3D 15N/15N/1H chemical shift correlation experiment utilizing an RFDR-based 1H/1H mixing period at 100 kHz MAS  

NASA Astrophysics Data System (ADS)

Homonuclear correlation NMR experiments are commonly used in the high-resolution structural studies of proteins. While 13C/13C chemical shift correlation experiments utilizing dipolar recoupling techniques are fully utilized under MAS, correlation of the chemical shifts of 15N nuclei in proteins has been a challenge. Previous studies have shown that the negligible 15N-15N dipolar coupling in peptides or proteins necessitates the use of a very long mixing time (typically several seconds) for effective spin diffusion to occur and considerably slows down a 15N/15N correlation experiment. In this study, we show that the use of mixing proton magnetization, instead of 15N, via the recoupled 1H-1H dipolar couplings enable faster 15N/15N correlation. In addition, the use of proton-detection under ultrafast MAS overcomes the sensitivity loss due to multiple magnetization transfer (between 1H and 15N nuclei) steps. In fact, less than 300 nL (?1.1 micromole quantity) sample is sufficient to acquire the 3D spectrum within 5 h. Our results also demonstrate that a 3D 15N/15N/1H experiment can render higher resolution spectra that will be useful in the structural studies of proteins at ultrafast MAS frequencies. 3D 15N/15N/1H and 2D radio frequency-driven dipolar recoupling (RFDR)-based 1H/1H experimental results obtained from a powder sample of N-acetyla-L-15N-valyl-L-15N-leucine at 70 and 100 kHz MAS frequencies are presented.

Nishiyama, Yusuke; Malon, Michal; Ishii, Yuji; Ramamoorthy, Ayyalusamy

2014-07-01

214

Site-specific ?- and ?-torsion angle determination in a uniformly/extensively 13C- and 15N-labeled peptide.  

PubMed

A solid-state rotational-echo double resonance (REDOR) NMR method was introduced to identify the ?- and ?-torsion angle from a (1)H-(15)N or (1)H-(13)C' spin system of alanine-like residues in a selectively, uniformly, or extensively (15)N-/(13)C-labeled peptide. When a C(?)(i) or a (15)N peak is site-specifically obtainable in the NMR spectrum of a uniformly (15)N/(13)C-labeled sample system, the ?- or ?-torsion angle specified by the conformational structure of peptide geometry involving (15)N(i)-(1)H(?)i-(15)N(i+1) or (13)C'(i-1)-(1)H(N)i-(13)C'(i) spin system can be identified based on (13)C(?)- or (15)N-detected (1)H(?)-(15)N or (1)H(N)-(13)C REDOR experiment. This method will conveniently be utilized to identify major secondary motifs, such as ?-helix, ?-sheet, and ?-turn, from a uniformly (15)N-/(13)C-labled peptide sample system. When tested on a (13)C-/(15)N-labeled model system of a three amino acid peptide Gly-[U-(13)C, (15)N]Ala-[U-(13)C, (15)N]Leu, the ?-angle of alanine obtained experimentally, ? = -40 ± 30°, agreed reasonably well with the X-ray determined angle, ? = -39°. PMID:21889381

Wi, Sungsool; Spano, Justin

2011-10-01

215

Variation in environmental conditions, understorey species number, abundance and composition among natural and managed Picea abies forest stands  

Microsoft Academic Search

We studied four south-facing and three north-facing boreal spruce forest stands (ca. 0.1ha each) in SE Norway with the aim of testing the hypothesis that former logging has long-term effects on boreal forest-floor vegetation. The stand series comprised unlogged natural forests and forests that were selectively or clear cut 60–70 years prior to our study. Each stand was described with

Tonje Økland; Knut Rydgren; Rune Halvorsen Økland; Ken Olaf Storaunet; Jørund Rolstad

2003-01-01

216

Carbon13 kinetic isotope effects in the decarbonylations of lactic acid containing 13 C at the natural abundance level  

Microsoft Academic Search

The13C kinetic isotope fractionation in the decarbonylation of lactic acid of natural isotopic composition by sulfuric acid has been studied in the temperature range of 20–80°C. The13C(1) isotope separation in the decarbonylation of lactic acid by concentrated sulfuric acid depends strongly on the temperature above 40°C. Below this temperature the13C isotope effect in the decarbonylation of lactic acid by concentrated

M. Zielinski; G. Czarnota; H. Papiernik-Zielinska

1992-01-01

217

Natural and man-caused factors affecting the abundance and cycling of dissolved organic substances in precambrian shield lakes  

Microsoft Academic Search

Effects of natural factors (drought and forest fire), and experimental perturbations (fertilization and acidification) on\\u000a dissolved organic carbon (DOC) concentrations and ratios to other nutrients in lakes of the Experimental Lakes Area are examined\\u000a using data obtained over a period of 20 years. DOC concentration, and the ratio of dissolved iron to DOC in lakes of the area\\u000a were strongly

D. W. Schindler; S. E. Bayley; P. J. Curtis; B. R. Parker; M. P. Stainton; C. A. Kelly

1992-01-01

218

Sources of nitrate in the Arno River waters: Constraints from ?? 15N and ??18O  

USGS Publications Warehouse

Running waters in anthropogenically affected areas are susceptible to nitrate contamination. Source identification is a fundamental step for the development of effective remediation. Previous studies pointed to pollution by nitrogen-bearing contaminants in the Arno Basin. In this paper, eleven surface water samples have been analysed for main and trace components and 15N/14N and 18O/16O ratios, with the aim of identifying for the first time the origin of nitrate in the Arno River Basin so that further investigations can appropriately be designed. ?? 18O(NO3) and ??15N(NO3) values have allowed to hypothesise the main sources of nitrate, as follows: i) mineralized fertilizer, ii) soil-organic nitrogen, iii) manure and septic waste. The anomalously high ??15N and ??18O values in the Chiana (??15N=24.9??? and ??18O= 15.5???) and Usciana tributaries (??15N=30.1??? and ??18O=7.2???) show a low probability of belonging to the same population as that of the other samples and can be related to denitrification process of nitrate from animal waste/sewage and/or an industrial process (e.g. tanneries).

Nisi, B.; Vaselli, O.; Buccianti, A.; Silva, S.R.

2005-01-01

219

Natural abundance stable carbon isotope evidence for the routing and de novo synthesis of bone FA and cholesterol.  

PubMed

This research reported in this paper investigated the relationship between diet and bone FA and cholesterol in rats raised on a variety of isotopically controlled diets comprising 20% C3 or C4 protein (casein) and C3 and/or C4 nonprotein or energy (sucrose, starch, and oil) macronutrients. Compound-specific stable carbon isotope analysis (delta13C) was performed on the FA (16:0, 18:0, 18:1, and 18:2) and cholesterol isolated from the diet (n = 4) and bone (n = 8) of these animals. The dietary signals reflected by the bone lipids were investigated using linear regression analysis. delta13C values of bone cholesterol and stearic (18:0) acid were shown to reflect whole-diet delta13C values, whereas the delta13C values of bone palmitic (16:0), oleic (18:1), and linoleic (18:2) acids reflected dietary FA delta13C values. Dietary signal differences are a result of the balance between direct incorporation (or routing) and de novo synthesis of each of these bone lipids. Estimates of the degree of routing of these bone lipids gleaned from correlations between delta13C(dlipid-wdiet) (= delta13C(diet lipid) - delta13C(whole diet)) spacings and delta13C(blipid-wdiet) (= delta13C(bone lipid) - delta13C(whole diet)) fractionations demonstrated that the extent of routing, where 18:2 > 16:0 > 18:1 > 18:0 > cholesterol, reflected the relative abundances of these lipids in the diet. These findings provide the basis for more accurate insights into diet when the delta13C analysis of bone fatty FA or cholesterol is employed. PMID:12733751

Jim, Susan; Ambrose, Stanley H; Evershed, Richard P

2003-02-01

220

Determination of regional cerebral oxygen consumption in the human: 17O natural abundance cerebral magnetic resonance imaging and spectroscopy in a whole body system.  

PubMed

17O natural abundance imaging in a whole body imager is demonstrated using standard MRI spectrometer and 1H imaging methods. A novel design of a highly sensitive 17O/1H doubly tuned surface head coil is shown. The head probe allows simultaneous acquisition of 17O and 1H images using a single coil. The relatively low 17O signal intensity due to the low natural abundance of 17O (0.037 atom percent) is partially compensated by fast repetition of the pulse sequence, achievable due to the short spin lattice relaxation time, T1. A small number of signal averages (e.g., NEX = 50) is sufficient for obtaining images having signal to noise of about 5:1. Due to the short longitudinal relaxation time of 17O, i.e., 2-5 msec, short TR values can be used. 128 phase encoding steps with TR = 10-25 msec correspond to total acquisition time of 1 to 2.5 min. Due to the small gyromagnetic ratio of 17O and the relatively small gradients in a standard whole body system, i.e. 0.5 G/cm, the image in-plane resolution is about 3 mm and a slice thickness of 15 mm. In vivo 17O MRS and MRI natural abundance spectroscopic signals and images of human brain have been observed. The transverse relaxation time, T2 was found to be 2.00 +/- 0.17 msec at 1.5 T. MRS 17O measurements of signal intensity in the occipital cortex during inhalation of oxygen gas, 21.8% 17O enriched, showed a maximum signal enhancement of 25% within the inhalation period. The rate of the metabolism of oxygen (CMRO2) in the occipital cortex was found to be 1.5 mumole/(g tissue) in good agreement with the value of 1.435 mumole/(g tissue) given in the literature. Current measurements using higher 17O enrichments and larger quantities of 17O enriched oxygen gas will enhance resolution and provide more accurate determination of the rate of oxygen metabolism rate and blood flow. The potential of 17O imaging is thus demonstrated in physiological in vivo studies of cerebral metabolism of oxygen and blood flow. PMID:8105403

Fiat, D; Dolinsek, J; Hankiewicz, J; Dujovny, M; Ausman, J

1993-08-01

221

Multiple regression models of ?13C and ?15N for fish populations in the eastern Gulf of Mexico  

NASA Astrophysics Data System (ADS)

Multiple regression models were created to explain spatial and temporal variation in the ?13C and ?15N values of fish populations on the West Florida Shelf (eastern Gulf of Mexico, USA). Extensive trawl surveys from three time periods were used to acquire muscle samples from seven groundfish species. Isotopic variation (?13Cvar and ?15Nvar) was calculated as the deviation from the isotopic mean of each fish species. Static spatial data and dynamic water quality parameters were used to create models predicting ?13Cvar and ?15Nvar in three fish species that were caught in the summers of 2009 and 2010. Additional data sets were then used to determine the accuracy of the models for predicting isotopic variation (1) in a different time period (fall 2010) and (2) among four entirely different fish species that were collected during summer 2009. The ?15Nvar model was relatively stable and could be applied to different time periods and species with similar accuracy (mean absolute errors 0.31-0.33‰). The ?13Cvar model had a lower predictive capability and mean absolute errors ranged from 0.42 to 0.48‰. ?15N trends are likely linked to gradients in nitrogen fixation and Mississippi River influence on the West Florida Shelf, while ?13C trends may be linked to changes in algal species, photosynthetic fractionation, and abundance of benthic vs. planktonic basal resources. These models of isotopic variability may be useful for future stable isotope investigations of trophic level, basal resource use, and animal migration on the West Florida Shelf.

Radabaugh, Kara R.; Peebles, Ernst B.

2014-08-01

222

Complexity of the food web structure of the Ascophyllum nodosum zone evidenced by a ?13C and ?15N study  

NASA Astrophysics Data System (ADS)

Rocky shores dominated by canopy-forming macroalgae are characterized by complex communities making it difficult to assess whether the most abundant primary producers are at the base of the food web. This difficulty is exacerbated by the seasonal- and regional-scale variations of environmental and biotic factors that can affect the main trophic pathways. The food web structure of the Ascophyllum nodosum zone was studied during three seasons and at two sites separated by several 100s of kilometers by measuring the ?13C and ?15N of the major food sources and the dominant consumers of the zone. Despite the variability in isotopic compositions, both sites underwent similar significant seasonal variations. The main primary producers of the zone, A.nodosum, Fucus vesiculosus and Fucus serratus, were not at the base of the main trophic pathway but part of the diverse number of basal resources supporting the food web. The use of community-wide metric indices allowed further defining the food web structure of the A. nodosum zone as one characterized by trophic redundancy and numerous major trophic pathways. Indeed, grazers were dominated by generalists, filter-feeders utilized both planktonic and benthic organic matter, and predators displayed a high degree of omnivory. The range of values in ?15N showed a high spatiotemporal variability within and an important overlap between trophic groups. This prevented establishing distinctive trophic levels and further emphasized the complexity of the food web structure. The spatiotemporal stability of the relative isotopic composition of the dominant consumers within trophic groups and the low variability of the community-wide indices suggested a stability of the food web structure of the A.nodosum zone at a regional scale.

Golléty, Claire; Riera, Pascal; Davoult, Dominique

2010-10-01

223

Oak loss increases foliar nitrogen, ?(15)N and growth rates of Betula lenta in a northern temperate deciduous forest.  

PubMed

Oak forests dominate much of the eastern USA, but their future is uncertain due to a number of threats and widespread failure of oak regeneration. A sudden loss of oaks (Quercus spp.) could be accompanied by major changes in forest nitrogen (N) cycles with important implications for plant nutrient uptake and tree species composition. In this study, we measured the changes in N use and growth rates of black birch trees (Betula lenta L.) following oak girdling at the Black Rock Forest in southeastern New York, USA. Data were collected from nine experimental plots composed of three treatments: 100% oaks girdled (OG), 50% oaks girdled (O50) and control (C). Foliar N concentration and foliar (15)N abundance increased significantly in the oak-girdled plots relative to the control, indicating that the loss of oaks significantly altered N cycling dynamics. As mineralization and nitrification rates increase following oak loss, black birch trees increase N absorption as indicated by higher foliar N content and increased growth rates. Foliar N concentration increased by 15.5% in the O50 and 30.6% in the OG plots relative to the control, while O50 and OG plots were enriched in (15)N by 1.08‰ and 3.33‰, respectively (P?

Falxa-Raymond, Nancy; Patterson, Angelica E; Schuster, William S F; Griffin, Kevin L

2012-09-01

224

Membrane insertion and orientation of polyalanine peptides: a (15)N solid-state NMR spectroscopy investigation.  

PubMed Central

Polyalanine-based peptides were prepared by solid-phase peptide synthesis, labeled with (15)N at selected sites, reconstituted into oriented phosphatidylcholine bilayers, and investigated by proton-decoupled (15)N solid-state NMR spectroscopy. The anisotropic (15)N chemical shift is a direct indicator of helix alignment with respect to the membrane normal. The in-plane to transmembrane equilibrium is the focus of this study. Time- and solvent-dependent transmembrane alignments of K(3)A(18)K(3) have been obtained, and these are stabilized when a few alanine residues are replaced with leucine. The results are discussed in the context of a model where polyalanines adopt a variety of configurations, which are interconnected by multiple equilibria. The data indicate hydrophobicity values of alanine close to zero when studied in the context of helical polypeptides (> or =24 residues) and phospholipid bilayers. PMID:11566795

Bechinger, B

2001-01-01

225

Resonance Raman spectroscopy of specifically [epsilon-15N]lysine-labeled bacteriorhodopsin.  

PubMed Central

The possible interaction of a second lysine with the retinylidene Schiff base of bacteriorhodopsin (Lewis, A., Marcus, M. A., Ehrenberg, B. & Crespi, H. (1978) Proc. Natl. Acad. Sci. USA 75, 4642-4646) has been investigated by specific incorporation of 15N into the epsilon-amino groups of the lysine residues. Comparison of resonance Raman spectra of bacteriorhodopsin grown on 100%, 0%, and 50% labeled lysine demonstrates that 15N isotope effects on the Schiff base vibration can be accounted for by 15N labeling only at the Schiff base nitrogen. Our data also provide in situ confirmation of the linkage of the retinal chromophore with the epsilon-amino nitrogen of lysine. PMID:6785758

Argade, P V; Rothschild, K J; Kawamoto, A H; Herzfeld, J; Herlihy, W C

1981-01-01

226

Advances in 15N-tracing experiments: new labelling and data analysis approaches.  

PubMed

To obtain an in-depth understanding of soil nitrogen dynamics, it is necessary to quantify a variety of simultaneously occurring gross nitrogen transformation processes. In order to do so, most studies apply 15N in a disturbed soil-microbial-root system and quantify gross rates based on the principles of 15N isotope dilution. However, this approach has several shortcomings. First, studying disturbed soil provides only limited information on in situ soil nitrogen dynamics. Secondly, the analytical data analysis allows the quantification of total production and consumption rates of the labelled pool, but does not provide information on process-specific transformation rates. Combining in situ 15N isotope labelling over 1-2 weeks with numerical data analysis allows determining process-specific gross nitrogen transformations in undisturbed soils under field conditions in the presence of live roots and their associated microbial communities. This has the potential to increase our understanding of nitrogen dynamics in the soil environment. PMID:21265788

Rütting, Tobias; Huygens, Dries; Staelens, Jeroen; Müller, Christoph; Boeckx, Pascal

2011-01-01

227

Unusually negative nitrogen isotopic compositions (?15N) of mangroves and lichens in an oligotrophic, microbially-influenced ecosystem  

NASA Astrophysics Data System (ADS)

Extremes in ?15N values in mangrove tissues and lichens (range =+4 to -22‰) were measured from a mangrove forest ecosystem located on Twin Cays, offshore islands in Belize, Central America. The N isotopic compositions and concentrations of NH4+/NH3 in porewater, rainwater, and atmospheric ammonia, and the ?15N of lichens, mangrove leaves, roots, stems, and wood were examined to study the biogeochemical processes important for establishing these unusual N isotopic ratios. Dwarfed Rhizophora mangle trees had the most negative ?15N, whereas fringing Rhizophora trees, the most positive ?15N values. Porewater ammonium concentrations had little relationship to N isotopic fractionation in mangrove tissues. In dwarfed mangroves, the ?15N of fine and coarse roots were 6-9‰ more positive than leaf tissue from the same tree, indicating different sources of N for root and leaf tissues. When P was added to dwarfed mangrove trees without added N, ?15N increased within one year from -12‰ to -2‰, approaching the ?15N of porewater ammonium (?15N=+4‰). Isotopically depleted ammonia in the atmosphere (?15N=-19‰) and in rainwater (?15N=-10‰) were found on Twin Cays. We propose that foliar uptake of these atmospheric sources by P-stressed, dwarfed mangrove trees and lichens can explain their very negative ?15N values. In environments where P is limiting for growth, uptake of atmospheric N by Rhizophora mangle may be an important adaptive strategy.

Fogel, M. L.; Wooller, M. J.; Cheeseman, J.; Smallwood, B. J.; Roberts, Q.; Romero, I.; Meyers, M. J.

2008-12-01

228

Nitrate removal in two relict oxbow urban wetlands: a 15N mass-balance approach  

NASA Astrophysics Data System (ADS)

A mass-balance approach was used to directly determine the flow of 15NO3- to plants, algae, and sediments,with unaccounted for 15N assumed to be denitrified. During the summer, plant and algal uptake accounted for 42%, of the added 15NO3 - in oxbow 1, less than 1% remained in the water column and 57% was unaccounted for. In oxbow 2 during the summer, plant and algal uptake accounted for 63% of the added 15NO3 -, with 1% remaining in the water column and 38% unaccounted for. During the early spring, plant and algal uptake were much lower in both oxbows, ranging from 0.05 to 13.3% of the 15N added, with 97 and 87% was unaccounted for in oxbow 1 and 2, respectively. The amount of unaccounted for 15N was equivalent to estimated areal denitrification rates of 12 and 6 mg N m-2 d-1 in the summer and 78 and 15 mg N m-2 d-1 in the spring, in oxbow 1 and oxbow 2, respectively. However, the uncertainty of these estimates is high as it was difficult to detect accumulation of 15N in the sediments which could have accounted for a very large percentage of the added 15N. Our results suggest that the two relict oxbow wetlands are sinks for NO3 - during both summer and spring. Plane view of Ox1 (A) and Ox2 (B) wetlands with closed contour intervals (color scale) and surrounding stream and upland elevations (labeled in black) located at Minebank Run, near Glen Arms, MD. 15N enrichment (atom %) of measured N pools prior to (Day 0) and after (Day 5) the end of the experiment in July 2009 and April 2010 for Ox1 and Ox2. Values are mean atom % (n = 2 algae, macrophytes and sediment; n = 6 for water samples).

Harrison, M. D.; Groffman, P. M.; Mayer, P. M.; Kaushal, S.

2012-12-01

229

Towards interpreting nitrate-?15N records in ice cores in terms of nitrogen oxide sources  

NASA Astrophysics Data System (ADS)

The isotopic composition of nitrate preserved in ice cores offers unique potential for reconstructing past contributions of nitrogen oxides (NOx = NO and NO2) to the atmosphere. Sources of NOx imprint a nitrogen stable isotopic (?15N) signature, which can be conserved during subsequent oxidation to form nitrate. Major sources of NOx include fossil fuels combustion, biomass burning, microbial processes in soils, and lightning, and thus a quantitative tracer of emissions would help detail connections between the atmosphere, the biosphere, and climate. Unfortunately, the ?15N signatures of most NOx sources are not yet well enough constrained to allow for quantitative partitioning, though new methodology for directly collecting NOx for isotopic analysis is promising (Fibiger and Hastings, A43D-0265, AGU 2010). Still, a growing network of ice core ?15N records may offer insight into source signatures, as different sources are important to different regions of the world. For example, a 300-year ice core record of nitrate-?15N from Summit, Greenland shows a clear and significant 12% (vs. N2) decrease since the Preindustrial that reflects emissions from fossil fuel combustion and/or soils related to changing agricultural practices in North America and Europe. Over the same time period, Antarctic ice cores show no such trend in ?15N. This would be consistent with previous work suggesting that biomass burning and/or stratospheric intrusion of NOx produced from N2O oxidation are dominant sources for nitrate formation at high southern latitudes. In comparison to the polar records, nitrate in tropical ice cores should represent more significant inputs from lightning, microbial processes in soils, and biomass burning. This may be reflected in new results from a high-elevation site in the Peruvian Andes that shows strong seasonal ?15N cycles of up to 15% (vs. N2). We compare and contrast these records in an effort to evaluate the contribution of NOx sources to nitrate over time.

Hastings, M. G.; Buffen, A. M.

2011-12-01

230

Improved ^13C Natural-abundance Correction Methods in REDOR NMR Distance Measurements used for Restrained Molecular Dynamics of Shikimate-3-Phosphate and Glyphosate  

NASA Astrophysics Data System (ADS)

The 1.1translation of rotational-echo double-resonance (REDOR) NMR data into dipolar couplings when ^31P or ^19F is observed. An equation for calculating dipolar couplings to specific ^13C labels in the presence of substantial natural-abundance ^13C background dephasing was derived. The equation results were compared to a calculation of REDOR dephasing that assumed a model lattice containing a central ^31P and 64 possible carbon sites. A single lattice was used to fit all data for four differently labeled protein complexes. Thus, ^31P-^13C dipolar couplings were obtained and translated into internuclear distances for complexes of 5-enolpyruvyl-shikimate-3- phosphate synthase (EPSPS), shikimate-3-phosphate (S3P), and glyphosate (Glp). Restrained molecular dynamics simulations of S3P and Glp compared to unrestrained simulations of the EPSPS tetrahedral intermediate and its phosphonate analog show that Glp is unlikely to act as an intermediate or transition state analog.

McDowell, L. M.; Klug, C. A.; Beusen, D. D.; Schaefer, J.

1996-03-01

231

First results on the incorporation and excretion of 15N from orally administered urea in lactating pony mares.  

PubMed

Two lactating pony mares were given oral offers of 20 g 15N urea [95 atom-% 15N-excess (15N')] on 6 subsequent days. About 80% of the consumed 15N' were excreted via urine and faeces, but only about 2% via milk. The 15N' secreted via milk-lysine only amounted to 0.04% of the 15N' intake. The recovery was about 90% in each case. Tissues with active metabolism had an unexpectedly high labelling (greater than 0.3 atom-% 15N'). The low extent of the conversion of oral urea N into milk-lysine speaks against an essential participation of the enteral synthesis in meeting the amino acid requirement of lactating mares. It was already concluded from this results that the determination of the amino acid requirement will be necessary for this group of performance. PMID:1888274

Schubert, R; Zander, R; Gruhn, K; Hennig, A

1991-05-01

232

The degree of urbanization across the globe is not reflected in the ?(15)N of seagrass leaves.  

PubMed

Many studies show that seagrass ?(15)N ratios increase with the amount of urbanization in coastal watersheds. However, there is little information on the relationship between urbanization and seagrass ?(15)N ratios on a global scale. We performed a meta-analysis on seagrass samples from 79 independent locations to test if seagrass ?(15)N ratios correlate with patterns of population density and fertilizer use within a radius of 10-200 km around the sample locations. Our results show that seagrass ?(15)N ratios are more influenced by intergeneric and latitudinal differences than the degree of urbanization or the amount of fertilizer used in nearby watersheds. The positive correlation between seagrass ?(15)N ratios and latitude hints at an underlying pattern in discrimination or a latitudinal gradient in the (15)N isotopic signature of nitrogen assimilated by the plants. The actual mechanisms responsible for the correlation between ?(15)N and latitude remain unknown. PMID:23866922

Christiaen, Bart; Bernard, Rebecca J; Mortazavi, Behzad; Cebrian, Just; Ortmann, Alice C

2014-06-30

233

?15N measurement of organic and inorganic substances by EA-IRMS: a speciation-dependent procedure.  

PubMed

Little attention has been paid so far to the influence of the chemical nature of the substance when measuring ?(15)N by elemental analysis (EA)-isotope ratio mass spectrometry (IRMS). Although the bulk nitrogen isotope analysis of organic material is not to be questioned, literature from different disciplines using IRMS provides hints that the quantitative conversion of nitrate into nitrogen presents difficulties. We observed abnormal series of ?(15)N values of laboratory standards and nitrates. These unexpected results were shown to be related to the tailing of the nitrogen peak of nitrate-containing compounds. A series of experiments were set up to investigate the cause of this phenomenon, using ammonium nitrate (NH(4)NO(3)) and potassium nitrate (KNO(3)) samples, two organic laboratory standards as well as the international secondary reference materials IAEA-N1, IAEA-N2-two ammonium sulphates [(NH(4))(2)SO(4)]-and IAEA-NO-3, a potassium nitrate. In experiment 1, we used graphite and vanadium pentoxide (V(2)O(5)) as additives to observe if they could enhance the decomposition (combustion) of nitrates. In experiment 2, we tested another elemental analyser configuration including an additional section of reduced copper in order to see whether or not the tailing could originate from an incomplete reduction process. Finally, we modified several parameters of the method and observed their influence on the peak shape, ?(15)N value and nitrogen content in weight percent of nitrogen of the target substances. We found the best results using mere thermal decomposition in helium, under exclusion of any oxygen. We show that the analytical procedure used for organic samples should not be used for nitrates because of their different chemical nature. We present the best performance given one set of sample introduction parameters for the analysis of nitrates, as well as for the ammonium sulphate IAEA-N1 and IAEA-N2 reference materials. We discuss these results considering the thermochemistry of the substances and the analytical technique itself. The results emphasise the difference in chemical nature of inorganic and organic samples, which necessarily involves distinct thermochemistry when analysed by EA-IRMS. Therefore, they should not be processed using the same analytical procedure. This clearly impacts on the way international secondary reference materials should be used for the calibration of organic laboratory standards. PMID:23099528

Gentile, Natacha; Rossi, Michel J; Delémont, Olivier; Siegwolf, Rolf T W

2013-01-01

234

Simultaneous preparation of naturally abundant and rare catechins by tannase-mediated biotransformation combining high speed counter current chromatography.  

PubMed

Simultaneous preparation of naturally rare catechins, EGC and EC, has been realized by tannase-mediated biotransformation combining high speed counter current chromatography. In addition, simultaneous preparation of the four catechins, EGCG, ECG, EGC, and EC in green tea extract has also been achieved by HSCCC under the normal phase and the reversed phase modes. The identity of the catechins was determined by HPLC-DAD-ESI-MS and quantification of the catechins was performed by HPLC-DAD. In a typical HSCCC separation, 27.2 mg 98.8% EGCG, 14.1 mg 94.7% EGC, and 9.3 mg 97.5% EC were obtained. This new method is efficient, time-saving and valuable for biological studies. PMID:24423547

Xia, Guobin; Hong, Shan; Liu, Songbai

2014-05-15

235

13C Natural Abundance in Serum Retinol Acts as a Biomarker for Increases in Dietary Provitamin A  

PubMed Central

The natural isotopic composition of 13C and 12C in tissues is largely determined by the diet. Sources of provitamin A carotenoids (e.g., vegetables) typically have a lower 13C to 12C ratio (13C:12C) than preformed vitamin A sources (i.e., dairy and meat) from corn-fed animals, which are prevalent in the US. The 13C:12C of serum retinol (13C:12C-retinol) was evaluated as a biomarker for vegetable intake in a 3-mo dietary intervention designed to promote weight-loss by increased vegetable consumption or reduced calorie and fat intake. Subjects were 21–50 y of age with a BMI between 30–40 kg/m2 and were enrolled from one geographic area in the US. The high vegetable group (n = 20) was encouraged to increase daily vegetable and fruit consumption to 0.95 liter vegetables and 0.24–0.35 liter fruits. The caloric reduction group (n = 17) was encouraged to lower caloric intake by 500 kcal and consume ?25% kcal from fat daily. Provided meals supplied 75–100% vegetable and fruit goals and 50–67% kcal and fat g per day. Carotenoid supplementation was discontinued by subjects during the study. Serum retinol and provitamin A carotenoid concentrations; intake of preformed vitamin A, provitamin A, and fat; and body weight, fat mass, and lean mass were analyzed for correlations to 13C:12C-retinol. 13C:12C-Retinol decreased in the vegetable group after intervention (P = 0.050) and the correlation with provitamin A intake was approaching significance (P = 0.079). 13C:12C-Retinol did not change in the caloric reduction group (P = 0.43). 13C:12C-Retinol changes with the vitamin A source in the diet and can be used as a biomarker for increases in dietary provitamin A vegetable intake. PMID:19116317

Howe, Julie A; Valentine, Ashley R; Hull, Angela K; Tanumihardjo, Sherry A

2009-01-01

236

15N Uptake from Manure and Fertilizer Sousrces by Three Consecutive Crops Under Controlled Conditions.  

Technology Transfer Automated Retrieval System (TEKTRAN)

The North Central “La Comarca Lagunera” region (25° 31’ N, 103° 14’ W), is one of the most important dairy production areas of Mexico. We conducted the first isotopic nitrogen (15N) labeled manure study in Mexico to assess the potential to supply nitrogen (N) to three consecutive forage crops with a...

237

? 15N values in Lake Erie sediments as indicators of nitrogen biogeochemical dynamics during cultural eutrophication  

Microsoft Academic Search

We have measured the stable nitrogen isotope values (?15N) in two sediment cores sampled 15years apart (1988 and 2003) from the Eastern Basin of Lake Erie and compared them to the total phosphorus (TP) and biogenic silica (BSi) concentrations in the 2003 core. Changes in the TP, BSi and total nitrogen (TN) accumulations in the 2003 core correspond to three

Yuehan Lu; Philip A. Meyers; Thomas H. Johengen; Brian J. Eadie; John A. Robbins; Haejin Han

2010-01-01

238

Sources of d15 N variability in sinking particulate nitrogen in the Cariaco  

E-print Network

Sources of d15 N variability in sinking particulate nitrogen in the Cariaco Basin, Venezuela Oriente, Boca de Ri´o, Isla de Margarita, PO 247, Venezuela d Estacio´n de Investigaciones Marinas de, Venezuela a r t i c l e i n f o Keywords: Cariaco Basin Sinking particulate organic matter Nitrogen isotopes

Meyers, Steven D.

239

The use of delta(15)N in assessing sewage stress on coral reefs.  

PubMed

While coral reefs decline, scientists argue, and effective strategies to manage land-based pollution lag behind the extent of the problem. There is need for objective, cost-effective, assessment methods. The measurement of stable nitrogen isotope ratios, delta(15)N, in tissues of reef organisms shows promise as an indicator of sewage stress. The choice of target organism will depend upon study purpose, availability, and other considerations such as conservation. Algae are usually plentiful and have been shown faithfully to track sewage input. The organic matrix of bivalve shells can provide time series spanning, perhaps, decades. Gorgonians have been shown to track sewage, and can provide records potentially centuries-long. In areas where baseline data are lacking, which is almost everywhere, delta(15)N in gorgonians can provide information on status and trends. In coral tissue, delta(15)N combined with insoluble residue determination can provide information on both sewage and sediment stress in areas lacking baseline data. In the developed world, delta(15)N provides objective assessment in a field complicated by conflicting opinions. Sample handling and processing are simple and analysis costs are low. This is a method deserving widespread application. PMID:19286230

Risk, Michael J; Lapointe, Brian E; Sherwood, Owen A; Bedford, Bradley J

2009-06-01

240

Nitrate Removal in Two Relict Oxbow Urban Wetlands: A 15N Mass-balance Approach  

EPA Science Inventory

A 15N-tracer method was used to quantify nitrogen (N) removal processes in two relict oxbow wetlands located adjacent to the Minebank Run restored stream reach in Baltimore County (Maryland, USA) during summer 2009 and early spring 2010. A mass-balance approach was used to determ...

241

The structural reorganisation of bis(diethyldithiocarbamato)morpholine–zinc(II) and –copper(II) in the course of solid-state solvation with morpholine and benzene molecules studied by ESR, solid-state 13C and 15N CP\\/MAS NMR spectroscopy and single-crystal X-ray diffraction  

Microsoft Academic Search

Six forms of both non-solvated and solvated adducts of bis(diethyldithiocarbamato)–zinc(II) and –copper(II) with morpholine, of general formulas [M{O(CH2)4NH}{S2CN(C2H5)2}2] and [M{O(CH2)4NH}{S2CN(C2H5)2}2]·L (M=Zn(II) (1): L=O(CH2)4NH (2), C6H6 (3); M=Cu(II) (4): L=O(CH2)4NH (5), C6H6 (6)), have been prepared and studied by means of ESR, solid-state natural abundance 13C and 15N CP\\/MAS NMR spectroscopy and single crystal X-ray diffraction data. The existence of two

Alexander V. Ivanov; Mikael Kritikos; Oleg N. Antzutkin; Willis Forsling

2001-01-01

242

On the potential sedimentological origin of downcore variations of bulk sedimentary ? 15N  

NASA Astrophysics Data System (ADS)

ODP site 1144 is located less than ten kilometers from core site SONNE 17940 on the continental slope of the northern South China Sea (SCS). Despite their proximity, the sedimentary nitrogen isotope records are distinctly different at both sites, with glacial-interglacial variations of ca. 1 permil at site 17940, and up to 4 permil at site ODP1144. Here we explore the potential origin of these differences in the ? 15N records, focussing on three aspects of the variable sedimentology at both sites on glacial-interglacial timescales. 1) Based on major element contents (Si/Al and Zr/Al ratios), glacial sediments at site ODP1144 are significantly finer-grained than at site 17940. As evident from a suite of samples from the SCS, finer-grained sediments are associated with higher ? 15N values, thus contributing to the offset in the ? 15N records between both sites. 2) Sediments at site ODP1144 contain lower amounts of potassium, and, by inferrence, ammonium, which substitutes for potassium in K-bearing minerals. Given the low ? 15N of ammonium fixed in clay minerals this difference in mineralogy further contributes to lower glacial ? 15N values at site 17940 compared to ODP1144. 3) We will also be presenting radiocarbon dates of total organic carbon (TOC), in an attempt to elucidate the different origin and sedimentological history of TOC at both sites. Sediments found at both ODP1144 and 17940 originate from an area affected by eustatic sediment redistribution, gravity- and fluvially-driven sediment mobilization from the broad northern SCS continental shelf. Rare earth element analyses (Shao et al., 2001) indicate that a significant part of the detrital material at ODP1144 originates from Taiwan, transported through the Penghu channel to the coring site in the northern SCS, and is not representative of the vertical particle flux to the sea floor. Sediment redistribution therefore potentially affects downcore variations in bulk sedimentary ? 15N, and cautions the interpretation of a single downcore record with respect to local/regional ? 15N variations in the past, and indeed with respect to other sedimentary proxies.

Kienast, M.; Higginson, M. J.; Mollenhauer, G.; Eglinton, T. I.; Calvert, S. E.

2003-12-01

243

Changes in Natural Abundance Carbon Stable isotopes of Human Blood and Saliva After 24 Days of Controlled Carbohydrate Supplementation  

NASA Astrophysics Data System (ADS)

With the advent of corporate agriculture, large-scale economic decisions have given rise to unique global environmental effects. Emphasis on corn production results in dramatic changes in nitrogen and water cycling via the intensive cultivation practices necessary to support Zea mays (Tilman, 1998). In particular, consumption of corn derived food additive high-fructose corn syrup (HFCS) has increased more than 1000% since 1970 and may be associated with the epidemics of obesity and diabetes (Bray et al., 2004). Plausible mechanisms for an adverse effect of fructose load on glucose homeostasis have been proposed (Havel, 2005). The unusually heavy 13C signature of corn, as compared to other plants, offers the opportunity to develop a biomarker for sugar consumption. Among the many experiments that are needed to establish such a technique, the demonstration of change in 13C signature of human tissues with known change in carbohydrate consumption is foremost. Here we report on a controlled feeding study performed in cooperation with the United States Department of Agriculture (USDA), to test the effect of supplementation of human diet with carbohydrate of known ?13C value. During this study, 13 individuals were fed a typical American diet (32% calories from fat, 15% calories from protein, 53% carbohydrate) for ~six months. Each participant was fed a random sequence of carbohydrate supplements (50 grams of supplement per day): 1. resistant maltodextrin (?13C = -10.59‰); 2. maltodextrin (?13C = -23.95‰); 3. a 50-50 mixture of the two (?13C = -15.94‰). After 24 days of feeding, subjects showed enrichment in blood serum that was significantly correlated (p = 0.0038) with the ?13C value of the supplement. However, blood clot and saliva showed no such correlation, suggesting that the half-lives of these substrates may render them unsuitable for carbohydrate dietary reconstruction over day-to-month timescales. All subjects of the study showed a net enrichment in the ?13C value of their blood and saliva relative to baseline: blood clot was enriched by 0.27‰; blood serum by 0.50‰ and saliva by 1.12‰. We believe this overall enrichment resulted from a 13C-enriched bulk diet (?13C = - 20.42‰) relative to the subjects free-living diet. Evidence for this derives from inspection of foods within the bulk diet provided, compared to published profiles of the typical American diet. We will discuss possible complicating factors, such as differential absorption and metabolism of the supplements according to solubility and caloric value. These results are encouraging for the development of a ?13C blood serum biomarker that, in the company of other tests, could be used to indicate a change in carbohydrate intake. Bray, G.A., Nielsen, S.J. and Popkin, B.M., 2004. Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity. American Journal of Clinical Nutrition, 79: 537-543. Havel, P.J., 2005. Dietary fructose: Implications for dysregulation of energy homeostasis and lipid/carbohydrate metabolism. Nutrition Reviews, 63(5): 133-157. Tilman D., 1998. The greening of the green revolution. Nature, 396:211-212.

Kraft, R. A.; Jahren, A. H.; Baer, D. J.; Caballero, B.

2008-12-01

244

Determination of 15N chemical shift anisotropy from a membrane bound protein by NMR spectroscopy  

PubMed Central

Chemical shift anisotropy (CSA) tensors are essential in the structural and dynamic studies of proteins using NMR spectroscopy. Results from relaxation studies in biomolecular solution and solid-state NMR experiments on aligned samples are routinely interpreted using well-characterized CSA tensors determined from model compounds. Since CSA tensors, particularly the 15N CSA, highly depend on a number of parameters including secondary structure, electrostatic interaction and the amino acid sequence, there is a need for accurately determined CSA tensors from proteins. In this study we report the backbone amide-15N CSA tensors for a 16.7-kDa membrane-bound and paramagnetic-heme containing protein, rabbit cytochrome b5 (cytb5), determined using the 15N CSA/15N-1H dipolar transverse cross-correlation rates. The mean values of 15N CSA determined for residues in helical, sheet and turn regions are ?187.9, ?166.0, and ?161.1 ppm, respectively, with an overall average value of ?171.7 ppm. While the average CSA value determined from this study is in good agreement with previous solution NMR experiments on small globular proteins, the CSA value determined for residues in helical conformation is slightly larger which may be attributed to the paramagnetic effect from Fe(III) of the heme unit in cytb5. However, like in previous solution NMR studies, the CSA values reported in this study are larger than the values measured from solid-state NMR experiments. We believe that the CSA parameters reported in this study will be useful in determining the structure, dynamics and orientation of proteins, including membrane proteins, using NMR spectroscopy. PMID:22620865

Pandey, Manoj Kumar; Vivekanandan, Subramanian; Ahuja, Shivani; Pichumani, Kumar; Im, Sang-Choul; Waskell, Lucy; Ramamoorthy, Ayyalusamy

2012-01-01

245

Labile Dissolved Organic Carbon Availability Controls Hyporheic Denitrification: a 15N Tracer Study  

NASA Astrophysics Data System (ADS)

We used an in situ 15N-labeled nitrate (15NO3-) and acetate injection experiment to determine how the availability of labile dissolved organic carbon (DOC) as acetate influences microbial denitrification in the hyporheic zone (HZ) of an upland (3rd-order) agricultural stream. A 48 h steady-state injection of a conservative tracer, chloride, and 15NO3- was used to quantify ambient HZ denitrification via 15N2 production. Following ambient plateau measurements of denitrification during the first 24 h, a second conservative tracer, bromide, and labile DOC source, acetate, were co-injected for an additional 24 h to measure HZ denitrification under increased DOC supply. Conservative tracers were observed at 4 of the 6 down gradient wells. Receiving wells represented HZ median residence times of 7.0 to 13.1 h, nominal flowpath lengths of 0.7 to 3.7 m, and hypoxic conditions (7.5 to 9.3 mg-O2 L-1 deficit). All 4 receiving wells demonstrated 15N2 production during ambient conditions indicating that the HZ was an active denitrification environment. Acetate addition stimulated significant increases in 15N2 production by factors of 2.7 to 26.1 in all receiving wells, and significant decreases of NO3- and DOC aromaticity (via SUVA254) in the two wells most hydrologically connected to the injection. In all receiving wells, increases of bromide and 15N2 production occurred without concurrent increases in acetate indicating that 100% of acetate was retained in the HZ, a portion of which is due to biological consumption. These results support our hypothesis that microbial denitrification in anaerobic portions of the hyporheic zone is limited by labile DOC supply.

Zarnetske, J. P.; Haggerty, R.; Wondzell, S. M.; Baker, M. A.

2009-12-01

246

Do Low 15N Values in Paleozoic Epeiric Basins Indicate High Rates of N Fixation?  

NASA Astrophysics Data System (ADS)

As a consequence of the high energetic requirements of dinitrogen (N2) fixation, organic N produced by diazotrophic microorganisms typically exhibits ?15N values similar to atmospheric N2 (approximately 0%). Because the ?15N of organic-rich Paleozoic epeiric basin sediments often has values in the vicinity of 0%, it is frequently asserted that N2 fixation was the primary source of new reactive N for productivity. There are two broad reasons why recourse to widespread and intensive N fixation as the primary source of the organic N is problematic. First, there are substantial physiological and ecological constraints on marine N fixation that limit its extent in modern oceans primarily to open ocean basins. Second, preservation of an unaltered isotopic signature of diazotrophy in underlying sediments is not a likely outcome of oxic and anoxic diagenetic alteration and repeated cycles of mineralization and assimilation. Constraining the sources of reactive N for primary productivity is critical to understanding the N cycle in Paleozoic epeiric seas. In this study we report ?15N values from high organic matter Middle Ordovician through Late Devonian dysoxic and euxinic basinal sediments. We propose a nitrogen isotope mass balance model that incorporates the microbial ecology of a stratified water column and the biochemical stoichiometry of primary production and organic matter diagenesis. Results from the model support our contention that high rates of N fixation over extended time periods were not the cause of depleted nitrogen isotope values in organic-rich Paleozoic basinal sediments. Rather, the depleted values were a consequence of a diminished role for nitrification and subsequent N loss via denitrification and anammox, and the preferential preservation of a substantially 15N-depleted chlorophyll-influenced lipid fraction. The model may be applicable to earlier and later geological periods where high organic matter sediments feature depleted ?15N values.

Tuite, M. L.; Macko, S. A.

2011-12-01

247

Evaluating ?(15)N-body size relationships across taxonomic levels using hierarchical models.  

PubMed

Ecologists routinely set out to estimate the trophic position of individuals, populations, and species composing food webs, and nitrogen stable isotopes (?(15)N) are a widely used proxy for trophic position. Although ?(15)N values are often sampled at the level of individuals, estimates and confidence intervals are frequently sought for aggregations of individuals. If individual ?(15)N values are correlated as an artifact of sampling design (e.g., clustering of samples in space or time) or due to intrinsic groupings (e.g., life history stages, social groups, taxonomy), such estimates may be biased and exhibit overly optimistic confidence intervals. However, these issues can be accommodated using hierarchical modeling methods. Here, we demonstrate how hierarchical models offer an additional quantitative tool for investigating ?(15)N variability and we explicitly evaluate how ?(15)N varies with body size at successively higher levels of taxonomic aggregation in a diverse fish assemblage. The models take advantage of all available data, better account for uncertainty in parameters estimates, may improve inferences on coefficients corresponding to groups with small to moderate sample sizes, and partition variation across model levels, which provides convenient summaries of the 'importance' of each level in terms of unexplained heterogeneity in the data. These methods can easily be applied to diet-based studies of trophic position. Although hierarchical models are well-understood and established tools, their benefits have yet to be fully reaped by stable isotope and food web ecologists. We suggest that hierarchical models can provide a robust framework for conceptualizing and statistically modeling trophic position at multiple levels of aggregation. PMID:23812110

Reum, Jonathan C P; Marshall, Kristin N

2013-12-01

248

**1**5N-NMR INVESTIGATION OF HYDROXYLAMINE DERIVATIZED HUMIC SUBSTANCES.  

USGS Publications Warehouse

Humic substances are the most abundant naturally occurring refactory organic compounds in soils and water. They have a broad range of physical, chemical and physiological properties. In soils, humic substances contribute to the cation exchange capacity, help maintain the physical structure, and play a role in plant growth and nutrition. In aquatic systems, humic substances serve to regulate the levels of inorganic constituents, yield trihalomethanes upon chlorination, and transport or concentrate organic and inorganic pollutants. The oxygen containing functional groups of humic and fulvic acids are believed to play a key role in the chemical properties of humic substances. This study was undertaken to gain additional information on the specific types of oxygen functionalities in humic substances. Since the analysis of hydroxyl moieties had been earlier established, we focused our attention on the analysis of ketone and aldehyde functional groups in humic substances.

Thorn, Kevin A.; Arterburn, Jeffrey B.; Mikita, Michael A.

1986-01-01

249

Determining Degradation and Synthesis Rates of Arabidopsis Proteins Using the Kinetics of Progressive 15N Labeling of Two-dimensional Gel-separated Protein Spots*  

PubMed Central

The growth and development of plant tissues is associated with an ordered succession of cellular processes that are reflected in the appearance and disappearance of proteins. The control of the kinetics of protein turnover is central to how plants can rapidly and specifically alter protein abundance and thus molecular function in response to environmental or developmental cues. However, the processes of turnover are largely hidden during periods of apparent steady-state protein abundance, and even when proteins accumulate it is unclear whether enhanced synthesis or decreased degradation is responsible. We have used a 15N labeling strategy with inorganic nitrogen sources coupled to a two-dimensional fluorescence difference gel electrophoresis and mass spectrometry analysis of two-dimensional IEF/SDS-PAGE gel spots to define the rate of protein synthesis (KS) and degradation (KD) of Arabidopsis cell culture proteins. Through analysis of MALDI-TOF/TOF mass spectra from 120 protein spots, we were able to quantify KS and KD for 84 proteins across six functional groups and observe over 65-fold variation in protein degradation rates. KS and KD correlate with functional roles of the proteins in the cell and the time in the cell culture cycle. This approach is based on progressive 15N labeling that is innocuous for the plant cells and, because it can be used to target analysis of proteins through the use of specific gel spots, it has broad applicability. PMID:22215636

Li, Lei; Nelson, Clark J.; Solheim, Cory; Whelan, James; Millar, A. Harvey

2012-01-01

250

The Pure Rotational Spectra of Acetaldehyde and Glycolaldehyde Isotopologues Measured in Natural Abundance by Chirped-Pulse Fourier Transform Microwave Spectroscopy  

NASA Astrophysics Data System (ADS)

Complex organic molecules (COMs) such as glycolaldehyde (HOCH_2CHO) and acetaldehyde (CH_3CHO) have now been detected in numerous interstellar sources. Glycolaldehyde has been detected in two hot cores, Sgr B2(N) and G31.41+0.31. Acetaldehyde has been observed in various sources, including the translucent clouds CB 17 and CB 24, cold molecular clouds such as TMC-1 and L134N, and hot cores such as Sgr B2(N), NGC 6334F, and the Orion Compact Ridge. Such COMs are known to have rich and complex spectra that add to the line confusion problem faced in observations of molecule-rich sources. Laboratory studies of excited vibrational states and isotopologues for known COMs therefore provide important guidance for sorting out the interstellar line confusion problem. Detection of isotopologues and determination of their abundance relative to the main isotopic species would also provide important constraints on interstellar chemical models, as these isotopic ratios are dependent on the formation mechanism for each species. The isotopic ratios for 13C/12C, 18O/16O, and D/H are known in various interstellar environments for simple molecules, but remain relatively unexplored for more complex species such as glycolaldehyde and acetaldehyde. The rotational spectra of the main isotopologues for glycolaldehyde and acetaldehyde have been well-characterized through microwave, millimeter, and submillimeter laboratory spectroscopy. Here we present the laboratory characterization of the isotopologues of acetaldehyde and glycolaldehyde in natural abundance by chirped pulse Fourier transform microwave spectroscopy (CP-FTMW). This spectroscopic information lays the groundwork for additional higher-frequency studies that can be directly applied to the interpretation of millimeter and submillimeter observations.

Carroll, P. Brandon; McGuire, Brett A.; Weaver, Susanna L. Widicus; Zaleski, Daniel P.; Neill, Justin L.; Pate, Brooks H.

2011-06-01

251

Landlessness amidst Abundance?  

Microsoft Academic Search

Developing countries like Uganda are abundantly endowed with natural resources with large chunks of land lying under -utilized. Ironically, landlessness is one of most frequently cited cause of poverty, particularly among the chronically poor. Factors that perpetuate landlessness among the poorest are not well understood. This paper provides insights into the categories of the chronically poor that are most susceptible

Rosetti Nabbumba Nayenga

2003-01-01

252

Molecular Investigation of the Short-term Sequestration of Natural Abundance 13C -labelled Cow Dung in the Surface Horizons of a Temperate Grassland Soil  

NASA Astrophysics Data System (ADS)

An adequate understanding of the carbon (C) sequestration potential of grasslands requires that the quantity and residence times of C inputs be measured. Herbivore dung is largely comprised of plant cell wall material, a significant source of stable C in intensively grazed temperate grassland ecosystems that contributes to the soil carbon budget. Our work uses compound-specific isotope analysis to identify the pattern of input of dung-derived compounds from natural abundance 13C/-labelled cow dung into the surface horizons of a temperate grassland soil over one year. C4 dung (? 13C \\-12.6 ‰ ) from maize fed cows was applied to a temperate grassland surface (? 13C \\-29.95 ‰ ) at IGER-North Wyke (Devon, UK), and dung remains and soil cores beneath the treatments collected at ? = 7, 14, 28, 56, 112, 224 and 372 days. Bulk dung carbon present in the 0\\-1 cm and 1\\-5 cm surface horizons of a grassland soil over one year was estimated using ? 13C between C4 dung and C3 dung, after Bol {\\et al.} (2000). The major biochemical components of dung were quantified using proximate forage fibre analyses, after Goering and Van Soest (1970) and identified using `wet' chemical and GC-MS methods. Plant cell wall polysaccharides and lignin were found to account for up to 67 {%} of dung dry matter. Hydrolysed polysaccharides were prepared as alditol acetates for analyses (after Docherty {\\et al.}, 2001), and a novel application of an off-line pyrolysis method applied to measure lignin-derived phenolic compounds (after Poole & van Bergen, 2002). This paper focuses on major events in the incorporation of dung carbon, estimated using natural abundance 13C&-slash;labelling technique. This revealed a major bulk input of dung carbon after a period of significant rainfall with a consequent decline in bulk soil ? 13C values until the end of the experiment (Dungait {\\et al.}, submitted). Findings will be presented revealing contribution of plant cell wall polysaccharides and lignin to these bulk ? 13C values, and their potential for sequestration considered. References: Bol, R., Amelung, W., Friedrich, C. Ostle, N. (2000). Tracing dung-derived carbon in temperate grassland using 13C natural abundance measurements. Soil Biology and Biochemistry, 32, 1337-1343. Goering and Van Soest (1970). Forage fibre analysis (apparatus, reagents, procedures and some applications). In: USDA-ARS Agricultural Handbook, 379. U. S. Government Printing Office, Washington D.C. Docherty, G., Jones, V. and Evershed, R.P. (2001). Practical and theoretical considerations in the gas chromatography/combustion/isotope ratio mass spectrometry ? 13C analysis of small polyfunctional compounds. Rapid Communications in Mass Spectrometry, 15, 730-738. Poole, I. & van Bergen, P. F. (2002). Carbon isotope ratio analysis of organic moieties from fossil mummified wood: establishing optimum conditions for off-line pyrolysis extraction using gas chromatography/mass spectrometry. Rapid Communications in Mass Spectrometry, 16, 1976-1981. Dungait, J. A. J., Bol, R. and Evershed, R.P. (submitted). The Fate of Dung Carbon in Temperate Grassland Soil: 1. Preliminary Findings Based on Bulk Stable Carbon Isotope Determinations. Isotopes in Health and Environmental Studies

Dungait, J.; Bol, R.; Evershed, R. P.

2004-12-01

253

Thousand Year Archives of the Bulk and Compound-Specific ?15N of Export Production From the North Pacific Subtropical Gyre Indicate Increasing Nitrogen Fixation Over the Past 150 Years  

NASA Astrophysics Data System (ADS)

Stable nitrogen isotopic analysis of amino acids (?15N-AA) preserved in proteins has emerged as a powerful new tool to explore trophic levels and nutrient cycling in nature. To date, little has been done to explore ?15N-AA in paleo-studies of the marine nitrogen cycle. We analysed the bulk and AA-specific ?15N in the long-lived, deep-sea, proteinaceous coral Gerardia. By feeding on sinking particulate organic matter, proteinaceous corals integrate the biogeochemical signature of recently exported production within discrete skeletal growth layers. Sub-decadal resolution time-series records spanning the time period 1000 AD to present were generated from specimens of Gerardia collected from the main Hawaiian Islands, Cross Seamount, and French Frigate Shoals in the North Pacific Subtropical Gyre (NPSG). Records of bulk ?15N from the three different locations, geographically separated by up to 1000 km, showed remarkably similar long term trends. Bulk ?15N remained relatively stable from ~1000-1850 years AD, and then decreased by a total of 2 ‰ from ~1850 AD to the present. The ?15N-AA of the "trophic" group of amino acids indicated no significant changes in trophic level or microbial re-synthesis of export production over this time period. The ?15N of "source" amino acids was significantly correlated with corresponding values of bulk ?15N, with the ?15N of phenylalanine decreasing from 4.2 to 2.1‰. The latter value is similar to recent measurements of subsurface nitrate ?15N near Hawaii, suggesting that the ?15N of phenylalanine may be used to quantitatively track changes in the isotopic signature of nitrate at the base of the food web. Using a simple isotopic mass balance between upwelled nitrate and nitrogen fixation we calculate a 30% increase in nitrogen fixation in the NPSG since ~1850. These results provide invaluable long-term context for recent observations, and highlight profound changes in the marine biogeochemical cycling of nitrogen over the past 150 years in this climatically-sensitive area of the world ocean.

Sherwood, O.; Batista, F. C.; Brown, J. T.; Guilderson, T. P.; McCarthy, M.

2012-12-01

254

Vibrational spectra and structure of RDX and its 13C- and 15N-labeled derivatives: A theoretical and experimental study  

NASA Astrophysics Data System (ADS)

Unambiguous vibrational band assignments have been made to cyclic nitramine hexahydro-1,3,5-trinitro-s-triazine, commonly known as the ?-phase of RDX or ?-RDX, with the use of 13C and 15N (on ring) enriched isotopic RDX analogues. Vibrational spectra were collected using Raman and IR spectroscopy in solid state and ab initio normal mode calculations were performed using density functional theory (DFT) and a 6-311G++** basis set. The calculated isotopic frequency shifts, induced by 13C and 15N labeling, are in very good accordance with measures ones. The changes in vibrational modes associated with the isotopic substitutions are well modeled by the calculation and previous assignments of the vibrational spectra have been revised, especially where the exact nature of the vibrational modes had been either vague or contradictory.

Infante-Castillo, Ricardo; Pacheco-Londoño, Leonardo; Hernández-Rivera, Samuel P.

2010-07-01

255

Vibrational spectra and structure of RDX and its 13C- and 15N-labeled derivatives: a theoretical and experimental study.  

PubMed

Unambiguous vibrational band assignments have been made to cyclic nitramine hexahydro-1,3,5-trinitro-s-triazine, commonly known as the alpha-phase of RDX or alpha-RDX, with the use of (13)C and (15)N (on ring) enriched isotopic RDX analogues. Vibrational spectra were collected using Raman and IR spectroscopy in solid state and ab initio normal mode calculations were performed using density functional theory (DFT) and a 6-311G++** basis set. The calculated isotopic frequency shifts, induced by (13)C and (15)N labeling, are in very good accordance with measures ones. The changes in vibrational modes associated with the isotopic substitutions are well modeled by the calculation and previous assignments of the vibrational spectra have been revised, especially where the exact nature of the vibrational modes had been either vague or contradictory. PMID:20381411

Infante-Castillo, Ricardo; Pacheco-Londoño, Leonardo; Hernández-Rivera, Samuel P

2010-07-01

256

Field evidence of differential food utilization of phytal harpacticoids collected from Fucus serratus indicated by ? 13C and ? 15N stable isotopes  

NASA Astrophysics Data System (ADS)

The present study is the first to compare trophic relationships of several co-occurring phytal harpacticoid species, in their natural habitat, using both ? 13C and ? 15N signatures. Three phytal harpacticoid species/taxa ( Zaus spinatus, Tisbe spp., and Parathalestris cf. intermedia) all collected from the alga Fucus serratus, at different times of the year, were analyzed. The results indicated that the harpacticoids were utilizing food sources differently. Specific food sources of the three species/taxa could not be accurately pinpointed, but there were strong indications that F. serratus and fragments from it did contribute significantly to the diet of P. cf. intermedia and Tisbe spp. Both of these harpacticoid species overlapped in ? 13C and ? 15N values with some of the macrofaunal species, collected from the same site in Hvassahraun, Iceland, while no overlap was seen for Z. spinatus. The signatures for Z. spinatus indicated that its food sources changed seasonally.

Steinarsdóttir, M. B.; Ingólfsson, A.; Ólafsson, E.

2010-06-01

257

Distribution of 15 N fertilizer in field-lysimeters sown with garlic ( Allium sativum ) and foxtail millet ( Setaria italica )  

Microsoft Academic Search

We examined the distribution of residual15N and its uptake by a foxtail millet crop grown in field lysimeters following at previous garlic crops fertilized with either15N-urea or15N-ammonium sulphate. Garlic apprently removed more N from the lysimeters treated with urea-N than from those treated with (NH4)2SO4. Fertilizer-N in the lysmeters was similar (ca. 32% of original) following millet harvest. About 16

M. A. Lazzari

1982-01-01

258

Biomarkers: d13C and d15N Distribution Tightly Coupled to Nutrient Dynamics and Viral Lysing in a Microbial Mat From Death Valley, California  

NASA Astrophysics Data System (ADS)

Extrapolations into ancient biomes make many assumptions and inferences regarding life modes and environmental habitat. While definition of a stromatolite as an extinct microbial biome by petrographic analysis is promising, Life interacts with is environment, actively manipulating energy flow across chemical disequilibria gradients, harvesting energy crucial for physiological maintenance and reproduction. Such structuring of communities in turn, leaves specific chemical/isotopic imprints related to physiological processes of prokaryotic communities specific to each oxidation/redox horizon. We examine stable isotopic d13C signals (d13C and d15N) as potential biomarkers reflecting bacterial physiology and microbial community nutrient-energy dynamics. While isotopes may reveal ancient chemical structuring of microbial mats, we also turn to invoking viral lysing of bacterial hosts in nutrient cycling within modern extreme environments as well as ancient stromatic structures of early Earth. Our records of d13C indicate extreme enrichment(-12%) for Corg in our extant mat due to CO2 limitation across a hypersaline diffusive barrier at the mat's surface. d15N is lowest at the mat's surface (indicating N2- fixation) where nitrogen- fixing cyanobacteria Microcoleus sp. are present . Viruses are extremely abundant in the microbial mat, exceeding bacterial abundances by a factor of ten. The ratio of viruses to bacteria was very high (VBR = 39 ñ 10) compared with abundances in marine sediments. Distribution of viruses closely follows distribution of bacteria, suggesting bacteria as primary hosts. The ratio of viruses to bacteria is inversely correlated to the concentration of organic C suggesting virus abundance is responsive to host substrate availability. High ratios of viruses to bacteria in mid-mat horizons (2.5 - 3.7 cm) above increasing levels of d13C in deeper horizons, coupled with a lack of increase in bacteria, suggests that viral lysis contributes to significant downward organic C (polysaccaride exudates) transport within the mat. Subsequent accumulation of d13C as well as heavier d15N in deeper sediment(denitrification)horizons elucidates tight nutrient coupling between evaporite substrate, nitrogen fixing primary producers and downcore zones of active denitrification and sulphate reduction. Discrepencies between d13C of ancient stromatolites (in line with C-3 photosynthetic pathways) and modern analogues (Badwater, CA) suggest a migration of microbial mats towards more extreme environments through time. A methodology for isotopically testing environmental and physiological responses in the geological record is presented here.

Hewson, I.; Archer, R.; Mahaffey, C.; Scott, J.; Tsapin, A.

2002-12-01

259

Adiabatic pulses in 1H-15N direct and long-range heteronuclear correlations.  

PubMed

The application of adiabatic inversion pulses to the detection of (1)H-(15)N heteronuclear correlations is described. The pulse sequences studied were gHSQC, CRISIS-gHSQC, gHMBC and CRISIS-gHMBC. The poor inversion quality of rectangular 180 degrees X pulses can lead to a loss of signal at the peripheries of the spectrum. Replacing these pulses with adiabatic sweeps significantly improves sensitivity across the potentially large (15)N spectral window. Satellite spectrum profiles are shown to demonstrate the increase in sensitivity when employing adiabatic pulses on wide spectral widths. Additionally, the active pharmaceutical nizatidine was used as a model compound to demonstrate the improvements in the long-range correlation data. PMID:15625719

Hadden, Chad E

2005-04-01

260

Oyster and Macroalgae Bioindicators Detect Elevated ? 15 N in Maryland’s Coastal Bays  

Microsoft Academic Search

Nitrogen loading from anthropogenic sources, including fertilizer, manure, and sewage effluents, has been linked with declining\\u000a water quality in coastal lagoons worldwide. Freshwater inputs to mid-Atlantic coastal lagoons of the USA are from terrestrially\\u000a influenced sources: groundwater and overland flow via streams and agricultural ditches, with occasional precipitation events.\\u000a Stable nitrogen isotopes ratios (?15N) in bioindicator species combined with conventional

B. Fertig; T. J. B. Carruthers; W. C. Dennison; A. B. Jones; F. Pantus; B. Longstaff

2009-01-01

261

High productivity analysis of 15 N and 13 C in soil\\/plant research  

Microsoft Academic Search

On-line sample preparation and analysis enables faster testing of hypotheses in biological research, particularly in field experiments where many samples must be processed to integrate spatial variability. Soil scientists were first to recognise the need for a fast, easy-to-use15N analyser to replace the isotope ratio mass spectrometer (IRMS) and Kjeldahl-Rittenberg sample preparation. Development has since led to a variety of

A. Barrie; S. T. Brookes; S. J. Prosser; S. Debney

1995-01-01

262

The recovery of 15N-labelled fertilizer applied to Miscanthus × giganteus  

Microsoft Academic Search

Miscanthus is a perennial, rhizomatous grass which has potential for use in Europe as a biofuel crop. Little is known of its fertilizer nitrogen (N) requirements. To better understand the cycling of N within the crop-soil system, a field experiment is being conducted in which 60 kg ha?1 of 15N-labelled fertilizer is being added to Miscanthus plants of different ages.

D. G. Christian; P. R. Poulton; A. B. Riche; N. E. Yates

1997-01-01

263

SEARCH FOR AN 80-ms SPONTANEOUS FISSION ACTIVITY IN BOMBARDMENTS OF 249Bk WITH 15N  

SciTech Connect

A rotating drum system was used to search for an 80-ms spontaneous fission (sf) activity in the reaction of {sup 15}N with {sup 249}Bk. No such activity was found beyond a cross section limit of 0.3 {+-} 0.3 nb. A sf activity with a half-life of about 20 ms and a formation cross section of 12 nb at 82 MeV was observed. The identity of this activity has not been determined.

Nitschke, J.M.; Fowler, M.; Ghiorso, A.; Leber, R.E.; Nurmia, M.J.; Somerville, L.P.; Williams, K.E.; Hulet, E.K.; Landrum, J.H.; Lougheed, R.W.; Wild, J.F.; Bemis, Jr., C.E.; Silva, R.J.; Eskola, P.

1980-01-01

264

15N and 13C NMR study of protonated monoaminopyridines in CDCl3-DMSO.  

PubMed

The 2-, 3- and 4-amino-pyridine and their protonated forms, obtained by reaction with pyridinium chloride, were investigated by 15N NMR spectroscopy. Exhaustive evidence has been found that the protonation occurs mainly on the annular nitrogen. Protonation of 4-aminopyridine by dehydrohalogenation of 1,1,2,2-tetrachloroethane (TCE) was also studied by 13C NMR spectroscopy, which indicated that the protonation occurs via the formation of adducts. PMID:12396052

Beltrame, Paolo; Cadoni, Enzo; Floris, Costantino; Gelli, Gioanna; Lai, Adolfo

2002-10-01

265

Community 15N isoscapes to resolve plant-plant-interactions at the spatial scale  

NASA Astrophysics Data System (ADS)

Isoscapes have greatly improved our ability to understand biogeochemical processes on continental to global scales. However, the isoscapes framework may also have significant potential to resolve the spatial component of within-community interactions. For example, exotic plant invaders often exert strong impacts on ecosystem functioning, particularly regarding water-, carbon- and nutrient-cycles, but the spatial extent of such alterations is largely unknown. Here we show that massive N input by the N2-fixing exotic invasive Acacia longifolia to a Portuguese dune system can be traced using spatially resolved information on native plants' leaf ?15N. We found isotopic signatures of N to differ strongly between the native system (?15N c. -10 o) and the atmospherically derived N in A. longifolia phyllodes (?15N c. 0 o). Thus, sources of N for native plants could be readily distinguished. Leaf ?15N of a native, non-fixing species was increasingly enriched the closer the plant grew to the invader, indicating uptake of fixed N provided by A. longifolia. The enrichment was evident far beyond the stands of the invader, demonstrating that A. longifolia affected N budgets of native species up to a distance of 8 m exceeding the margin of the canopy. Furthermore, using the isoscapes approach, we were able to quantify the total area of N enrichment and could thus show that the area affected by invasion was at least 3.5 times larger than the area actually occupied by the invader. However, a native N2-fixing species had no such effects. Thus, downscaling isoscapes to the community level opens new frontiers in quantifying the spatial dimension of functional changes associated with plant invasions. Moreover, considering the feasibility and applicability of this approach, it may provide a promising tool to identify, quantify and monitor different types of functional plant-plant interactions within communities at a spatially explicit scale.

Hellmann, Christine; Rascher, Katherine G.; Máguas, Cristina; Werner, Christiane

2014-05-01

266

Deuterium isotope effects on 15N, 13C and 1H chemical shifts of proton sponges  

NASA Astrophysics Data System (ADS)

Deuterium isotope effects on 15N, 13C and 1H chemical shifts have been measured in the protonated forms of DMAN, 4-bromo, 4-picryl, 4-nitro and 2- and 2,7-chloro derivatives. Structures have been geometry optimised using BPW91/6-31(d)G density functional theory (DFT) methods and show good correspondence to experimental X-ray data. 15N, 13C and 1H chemical shifts are calculated using GIAO/DFT methods. Chemical shifts for the two tautomers are calculated. Equilibrium constants are determined from 1J(N,H) coupling constants. A comparison of 1J(N,H) and 1J(N,D) couplings for the non-symmetrical derivatives show that upon deuteriation the equilibrium is shifted towards the dominant form. The experimental deuterium isotope effect on chemical shifts of DMANH + shows only small values despite the apparently strong intramolecular hydrogen bonds as judged from primary isotope effects. The counter ion has little effect on the one-bond isotope effect. Secondary isotope effects on 15N and 13C chemical shifts for the non-symmetrical derivatives are divided into intrinsic and equilibrium contributions. The one-bond deuterium intrinsic isotope effect on 15N chemical shifts is close to 0.3 ppm and is related to charge delocalisation and the close proximity of the positive charge. The equilibrium contributions to the isotope effects at the nitrogens and at carbons are seen to increase throughout the series in parallel with the increase of the equilibrium constant. For 1H resonances only equilibrium contributions are found at the aromatic hydrogens. An important feature in the analysis of the protonated DMANs is the multi-isotope effect approach.

Grech, E.; Klimkiewicz, J.; Nowicka-Scheibe, J.; Pietrzak, M.; Schilf, W.; Pozharski, A. F.; Ozeryanskii, V. A.; Bolvig, S.; Abildgaard, J.; Hansen, P. E.

2002-09-01

267

Range profiles of 6-10 MeV 15N ions implanted in silicon  

NASA Astrophysics Data System (ADS)

Implantation profiles of 6 to 10 MeV 15N ions in crystalline silicon have been investigated. Measurements of the profiles at depths from 4 to 7 ?m were rendered possible by combining the depth profiling of the 15N atoms through the 15N(p, ??) 12C reaction and the exfoliation of the surface layer of the samples, accomplished by high dose 4He ion bombardment. In this way the range profiles, measured at the exfoliated crater bottom, could be obtained accurately without uncertainties due to straggling of the probing proton beam. The range parameters are compared to those of Monte Carlo calculations using the electronic stopping powers given by J.F. Ziegler, J.P. Biersack and U. Littmark [The Stopping Powers and Ranges of Ions in Matter, Vol. 1 (Pergamon, New York, 1985)]. Projected ranges were observed to be 5%-10% larger and range stragglings 27%-6% smaller than those predicted by Monte Carlo calculations along with the adopted stopping power parametrization.

Ahlgren, T.; Väkeväinen, K.; Räisänen, J.; Rauhala, E.; Keinonen, J.

1995-12-01

268

Seasonal ?13C and ?15N isoscapes of fish populations along a continental shelf trophic gradient  

NASA Astrophysics Data System (ADS)

The West Florida Shelf, located in the eastern Gulf of Mexico, transitions from a eutrophic ecosystem dominated by the Mississippi River plume to mesotrophic and oligotrophic ecosystems off the coast of peninsular Florida. Three extensive trawl surveys in this region were used to acquire samples of fish muscle, benthic algae from sea urchin stomach contents, and filtered particulate organic matter (POM) to create ?13C and ?15N isoscapes. Muscle ?15N from three widely distributed fish species, Synodus foetens (inshore lizardfish), Calamus proridens (littlehead porgy), and Syacium papillosum (dusky flounder), exhibited strong longitudinal correlations (Pearson?s r=-0.67 to -0.90, p<0.001) that coincided with the principal trophic gradient, whereas ?13C values of fish muscle and benthic algae were correlated with depth (Pearson?s r=-0.34 to -0.73, p<0.05). Correlations between isotopic values and surface concentrations of chlorophyll and particulate organic carbon (POC) imply linkages between the isotopic baseline and transitions from eutrophic to oligotrophic waters. The ?13C depth gradient and the ?15N longitudinal gradient were consistent between seasons and years, providing a foundation for future stable isotope studies of animal migration in the Gulf of Mexico.

Radabaugh, Kara R.; Hollander, David J.; Peebles, Ernst B.

2013-10-01

269

Individual protein balance strongly influences ?15N and ?13C values in Nile tilapia, Oreochromis niloticus  

NASA Astrophysics Data System (ADS)

Although stable isotope ratios in animals have often been used as indicators of the trophic level and for the back-calculation of diets, few experiments have been done under standardized laboratory conditions to investigate factors influencing ?15N and ?13C values. An experiment using Nile tilapia [Oreochromis niloticus (L.)] was therefore carried out to test the effect of different dietary protein contents (35.4, 42.3, and 50.9%) on ?15N and ?13C values of the whole tilapia. The fish were fed the isoenergetic and isolipidic semi-synthetic diets at a relatively low level. ?15N and ?13C values of the lipid-free body did not differ between the fish fed the diets with different protein contents, but the trophic shift for N and C isotopes decreased with increasing protein accretion in the individual fish, for N from 6.5‰ to 4‰ and for C in the lipid-free body from 4‰ to 2.5‰. This is the first study showing the strong influence of the individual protein balance to the degree to which the isotopic signature of dietary protein was modified in tissue protein of fish. The extrapolation of the trophic level or the reconstruction of the diet of an animal from stable isotope ratios without knowledge of the individual physiological condition and the feeding rate may lead to erroneous results.

Gaye-Siessegger, Julia; Focken, Ulfert; Abel, Hansjörg; Becker, Klaus

270

A Study of 15N/14N Isotopic Exchange over Cobalt Molybdenum Nitrides  

PubMed Central

The 14N/15N isotopic exchange pathways over Co3Mo3N, a material of interest as an ammonia synthesis catalyst and for the development of nitrogen transfer reactions, have been investigated. Both the homomolecular and heterolytic exchange processes have been studied, and it has been shown that lattice nitrogen species are exchangeable. The exchange behavior was found to be a strong function of pretreatment with ca. 25% of lattice N atoms being exchanged after 40 min at 600 °C after N2 pretreatment at 700 °C compared to only 6% following similar Ar pretreatment. This observation, for which the potential contribution of adsorbed N species can be discounted, is significant in terms of the application of this material. In the case of the Co6Mo6N phase, regeneration to Co3Mo3N under 15N2 at 600 °C occurs concurrently with 14N15N formation. These observations demonstrate the reactivity of nitrogen in the Co–Mo–N system to be a strong function of pretreatment and worthy of further consideration. PMID:24265977

2013-01-01

271

An Investigation of Wild Bee Diversity and Abundance in Plots Managed by The Nature Conservancy in South-Central Nebraska and of Beneficial Arthropods Associated with Native Nebraska Flora  

Microsoft Academic Search

Insect pollination is an essential ecosystem service, and bees are the principal pollinators of wild and cultivated plants. Habitat management and enhancement are a proven way to encourage wild bee populations, providing them with food and nesting resources. I examined bee diversity and abundance in plots managed by The Nature Conservancy near Wood River, NE. The plots were seeded with

Dori Ann Porter

2010-01-01

272

Denitrification in nitrate-rich streams: Application of N2:Ar and 15N-tracer methods in intact cores  

USGS Publications Warehouse

Rates of benthic denitrification were measured using two techniques, membrane inlet mass spectrometry (MIMS) and isotope ratio mass spectrometry (IRMS), applied to sediment cores from two NO3--rich streams draining agricultural land in the upper Mississippi River Basin. Denitrification was estimated simultaneously from measurements of N 2:Ar (MIMS) and 15N[N2] (IRMS) after the addition of low-level 15NO3- tracer ( 15N:N = 0.03-0.08) in stream water overlying intact sediment cores. Denitrification rates ranged from about 0 to 4400 lmol N??m -2??h-1 in Sugar Creek and from 0 to 1300 ??mol N??m-2??h-1 in Iroquois River, the latter of which possesses greater streamflow discharge and a more homogeneous streambed and water column. Within the uncertainties of the two techniques, there is good agreement between the MIMS and IRMS results, which indicates that the production of N2 by the coupled process of nitrification/denitrification was relatively unimportant and surface-water NO3- was the dominant source of NO3- for benthic denitrification in these streams. Variation in stream NO3- concentration (from about 20 ??mol/L during low discharge to 1000 ??mol/L during high discharge) was a significant control of benthic denitrification rates, judging from the more abundant MIMS data. The interpretation that NO3- concentration directly affects denitrification rate was corroborated by increased rates of denitrification in cores amended with NO 3-. Denitrification in Sugar Creek removed ???11% per day of the instream NO3- in late spring and removed roughly 15-20% in late summer. The fraction of NO3- removed in Iroquois River was less than that of Sugar Creek. Although benthic denitrification rates were relatively high during periods of high stream flow, when NO3 concentrations were also high, the increase in benthic denitrification could not compensate for the much larger increase in stream NO3- fluxes during high flow. Consequently, fractional NO3- losses were relatively low during high flow. ?? 2006 by the Ecological Society of America.

Smith, L.K.; Voytek, M.A.; Böhlke, J.K.; Harvey, J.W.

2006-01-01

273

Controls on Hyporheic Nitrate Removal: Assessing Transport and Substrate Limitations with 15N Tracer Studies (Invited)  

NASA Astrophysics Data System (ADS)

We examined transport time and substrate controls on hyporheic (HZ) nitrification and denitrification in an upland agricultural stream with a series of 15N tracer studies - whole-stream and in situ well-to-well steady-state 15NO3- and conservative tracer (Cl-) addition experiments. For the whole-stream experiment, we measured relevant solute, 15N isotope, and hydraulic transport conditions of the reach and along HZ flowpaths of an instrumented gravel bar. HZ exchange was observed across the entire gravel bar with flowpath lengths up to 4.2m and corresponding median residence times greater than 28.5h. The HZ transitioned from a net nitrification environment at its head (small residence times, <6.9h) to a net denitrification environment at its tail (large residence times, 6.9-28.5h). HZ denitrification was confirmed as 15N2 was produced across the entire gravel bar. Production of 15N2 across all observed flowpaths and residence times indicated that denitrification microsites are present even where net nitrification occurred. At large residence times, the rate of denitrification decreased despite persistent anoxic conditions, indicating substrate (NO3- and carbon) limitations. Consequently, we conducted in situ 15NO3-, conservative tracers (Cl- and Br), and acetate injection experiments to determine how the availability of labile dissolved organic carbon (DOC) as acetate influences microbial denitrification in the HZ, especially along anoxic flowpaths with large residence times. The acetate addition to the HZ stimulated significant increases in 15N2 production by factors of 2.7 to 26.1 in all receiving wells, and significant decreases of NO3- and DOC aromaticity in the wells most hydrologically connected to the injection. Further, 100% of acetate was retained in the HZ, a portion of which is due to biological consumption. These studies demonstrate that: 1. the HZ is an active nitrogen sink in this study system, 2. the distinction between net nitrification and denitrification in the HZ is a function of residence time and exhibits threshold behavior, and 3. microbial denitrification in anaerobic portions of the HZ can be limited by labile DOC supply.

Zarnetske, J. P.; Haggerty, R.; Wondzell, S. M.; Baker, M. A.

2010-12-01

274

Atmospheric CO2 and O3 alter the flow of 15N in developing forest ecosystems.  

PubMed

Anthropogenic O3 and CO2-induced declines in soil N availability could counteract greater plant growth in a CO2-enriched atmosphere, thereby reducing net primary productivity (NPP) and the potential of terrestrial ecosystems to sequester anthropogenic CO2. Presently, it is uncertain how increasing atmospheric CO2 and O3 will alter plant N demand and the acquisition of soil N by plants as well as the microbial supply of N from soil organic matter. To address this uncertainty, we initiated an ecosystem-level 15N tracer experiment at the Rhinelander (Wisconsin, USA) free air CO2-O3 enrichment (FACE) facility to understand how projected increases in atmospheric CO2 and 03 alter the distribution and flow of N in developing northern temperate forests. Tracer amounts of 15NH4+ were applied to the forest floor of developing Populus tremuloides and P. tremuloides-Betula papyrifera communities that have been exposed to factorial CO2 and O3 treatments for seven years. One year after isotope addition, both forest communities exposed to elevated CO2 obtained greater amounts of 15N (29%) and N (40%) from soil, despite no change in soil N availability or plant N-use efficiency. As such, elevated CO2 increased the ability of plants to exploit soil for N, through the development of a larger root system. Conversely, elevated O3 decreased the amount of 15N (-15%) and N (-29%) in both communities, a response resulting from lower rates of photosynthesis, decreases in growth, and smaller root systems that acquired less soil N. Neither CO2 nor 03 altered the amount of N or 15N recovery in the forest floor, microbial biomass, or soil organic matter. Moreover, we observed no interaction between CO2 and 03 on the amount of N or 15N in any ecosystem pool, suggesting that 03 could exert a negative effect regardless of CO2 concentration. In a CO2-enriched atmosphere, greater belowground growth and a more thorough exploitation of soil for growth-limiting N is an important mechanism sustaining the enhancement of NPP in developing forests (0-8 years following establishment). However, as CO2 accumulates in the Earth's atmosphere, future O3 concentrations threaten to diminish the enhancement of plant growth, decrease plant N acquisition, and lessen the storage of anthropogenic C in temperate forests. PMID:18027765

Zak, Donald R; Holmes, William E; Pregitzer, Kurt S

2007-10-01

275

Mangrove isotopic (??15N and ??13C) fractionation across a nitrogen vs. phosphorus limitation gradient  

USGS Publications Warehouse

Mangrove islands in Belize are characterized by a unique switching from nitrogen (N) to phosphorus (P) limitation to tree growth from shoreline to interior. Fertilization has previously shown that Rhizophora mangle (red mangrove) fringe trees (5-6 m tall) growing along the shoreline are N limited; dwarf trees (???1.5 m tall) in the forest interior are P limited; and transition trees (2-4 m tall) are co-limited by both N and P. Growth patterns paralleled a landward decrease in soil flushing by tides and an increase in bioavailable N, but P availability remained consistently low across the gradient. Stable isotopic composition was measured in R. mangle leaves to aid in explaining this nutrient switching pattern and growth variation. Along control transects, leaf ??15N decreased from +0.10??? (fringe) to -5.38??? (dwarf). The ??15N of N-fertilized trees also varied spatially, but the values were consistently more negative (by ???3???) compared to control trees. Spatial variation in ??15N values disappeared when the trees were fertilized with P, and values averaged +0.12???, similar to that in control fringe trees. Neither variation in source inputs nor microbial fractionation could fully account for the observed patterns in ??15N. The results instead suggest that the lower ??15N values in transition and dwarf control trees were due to plant fractionation as a consequence of slower growth and lower N demand. P fertilization increased N demand and decreased fractionation. Although leaf ??13C was unaffected by fertilization, values increased from fringe (-28.6???) to transition (-27.9???) to dwarf (-26.4???) zones, indicating spatial variation in environmental stresses affecting stomatal conductance or carboxylation. The results thus suggest an interaction of external supply, internal demand, and plant ability to acquire nutrients under different hydro-edaphic conditions that vary across this tree-height gradient. The findings not only aid in understanding mangrove discrimination of nitrogen and carbon isotopes, but also have implications for identifying nutrient loading and other stress conditions in coastal systems dominated by mangroves.

McKee, K.L.; Feller, I.C.; Popp, M.; Wanek, W.

2002-01-01

276

13C and 15N allocations of two alpine species from early and late snowmelt locations reflect their different growth strategies  

PubMed Central

Intense efforts are currently devoted to disentangling the relationships between plant carbon (C) allocation patterns and soil nitrogen (N) availability because of their consequences for growth and more generally for C sequestration. In cold ecosystems, only a few studies have addressed whole-plant C and/or N allocation along natural elevational or topographical gradients. 12C/13C and 14N/15N isotope techniques have been used to elucidate C and N partitioning in two alpine graminoids characterized by contrasted nutrient economies: a slow-growing species, Kobresia myosuroides (KM), and a fast-growing species, Carex foetida (CF), located in early and late snowmelt habitats, respectively, within the alpine tundra (French Alps). CF allocated higher labelling-related 13C content belowground and produced more root biomass. Furthermore, assimilates transferred to the roots were preferentially used for growth rather than respiration and tended to favour N reduction in this compartment. Accordingly, this species had higher 15N uptake efficiency than KM and a higher translocation of reduced 15N to aboveground organs. These results suggest that at the whole-plant level, there is a compromise between N acquisition/reduction and C allocation patterns for optimized growth. PMID:19401411

Baptist, Florence; Tcherkez, Guillaume; Aubert, Serge; Pontailler, Jean-Yves; Choler, Philippe; Nogués, Salvador

2009-01-01

277

13C and 15N allocations of two alpine species from early and late snowmelt locations reflect their different growth strategies.  

PubMed

Intense efforts are currently devoted to disentangling the relationships between plant carbon (C) allocation patterns and soil nitrogen (N) availability because of their consequences for growth and more generally for C sequestration. In cold ecosystems, only a few studies have addressed whole-plant C and/or N allocation along natural elevational or topographical gradients. (12)C/(13)C and (14)N/(15)N isotope techniques have been used to elucidate C and N partitioning in two alpine graminoids characterized by contrasted nutrient economies: a slow-growing species, Kobresia myosuroides (KM), and a fast-growing species, Carex foetida (CF), located in early and late snowmelt habitats, respectively, within the alpine tundra (French Alps). CF allocated higher labelling-related (13)C content belowground and produced more root biomass. Furthermore, assimilates transferred to the roots were preferentially used for growth rather than respiration and tended to favour N reduction in this compartment. Accordingly, this species had higher (15)N uptake efficiency than KM and a higher translocation of reduced (15)N to aboveground organs. These results suggest that at the whole-plant level, there is a compromise between N acquisition/reduction and C allocation patterns for optimized growth. PMID:19401411

Baptist, Florence; Tcherkez, Guillaume; Aubert, Serge; Pontailler, Jean-Yves; Choler, Philippe; Nogués, Salvador

2009-01-01

278

Unusually negative nitrogen isotopic compositions (?15N) of mangroves and lichens in an oligotrophic, microbially-influenced ecosystem  

NASA Astrophysics Data System (ADS)

Extremes in (?15N values in mangrove tissues and lichens (range = +4 to -22‰) were measured from a mangrove forest ecosystem located on Twin Cays, offshore islands in Belize, Central America. The N isotopic compositions and concentrations of NH4+/NH3 in porewater, rainwater, atmospheric ammonia, mangrove leaves, roots, stems, and wood, and lichens, were examined to study the biogeochemical processes important for establishing these unusual N isotopic ratios. Porewater ammonium concentrations had little to no relationship to N isotopic fractionation in mangrove tissues. The ?15N of fine and coarse roots was 9‰ more positive than leaf tissue from the same tree. When P was added to dwarfed mangrove trees without added N, ?15N increased within one year to a &delta:15N closer to the &delta:15N of porewater ammonium (?15N=+4‰). Isotopically negative ammonia in the atmosphere (?15N=-18‰) and in rainwater (?15N=-9‰) were found on Twin Cays and may be sources of available N for isotopically depleted mangrove trees and lichens. In highly stressed, severely P limited trees, uptake of atmospheric N by Rhizophora mangle may be an important adaptive strategy.

Fogel, M. L.; Wooller, M. J.; Cheeseman, J.; Smallwood, B. J.; Roberts, Q.; Romero, I.; Jacobsen Meyers, M.

2008-02-01

279

Penguin tissue as a proxy for relative krill abundance in East Antarctica during the Holocene  

PubMed Central

Antarctic krill (Euphausia superba) is a key component of the Southern Ocean food web. It supports a large number of upper trophic-level predators, and is also a major fishery resource. Understanding changes in krill abundance has long been a priority for research and conservation in the Southern Ocean. In this study, we performed stable isotope analyses on ancient Adélie penguin tissues and inferred relative krill abundance during the Holocene epoch from paleodiets of Adélie penguin (Pygoscelis adeliae), using inverse of ?15N (ratio of 15N/14N) value as a proxy. We find that variations in krill abundance during the Holocene are in accord with episodes of regional climate changes, showing greater krill abundance in cold periods. Moreover, the low ?15N values found in modern Adélie penguins indicate relatively high krill availability, which supports the hypothesis of krill surplus in modern ages due to recent hunt for krill-eating seals and whales by humans. PMID:24076768

Huang, Tao; Sun, Liguang; Long, Nanye; Wang, Yuhong; Huang, Wen

2013-01-01

280

The effect of drought and interspecific interactions on depth of water uptake in deep- and shallow-rooting grassland species as determined by ?18O natural abundance  

NASA Astrophysics Data System (ADS)

Increased incidence of drought, as predicted under climate change, has the potential to negatively affect grassland production. Compared to monocultures, vertical belowground niche complementarity between shallow- and deep-rooting species may be an important mechanism resulting in higher yields and higher resistance to drought in grassland mixtures. However, very little is known about the belowground responses in grassland systems and increased insight into these processes may yield important information both to predict the effect of future climate change and better design agricultural systems to cope with this. This study assessed the effect of a 9-week experimental summer drought on the depth of water uptake of two shallow-rooting species (Lolium perenne L. and Trifolium repens L.) and two deep-rooting species (Cichorium intybus L. and Trifolium pratense L.) in grassland monocultures and four-species mixtures by using the natural abundance ?18O isotope method. We tested the following three hypotheses: (1) drought results in a shift of water uptake to deeper soil layers, (2) deep-rooting species take up a higher proportion of water from deeper soil layers relative to shallow-rooting species, and (3) as a result of interspecific interactions in mixtures, the water uptake of shallow-rooting species becomes shallower when grown together with deep-rooting species and vice versa, resulting in reduced niche overlap. The natural abundance ?18O technique provided novel insights into the depth of water uptake of deep- and shallow- rooting grassland species and revealed large shifts in depth of water uptake in response to drought and interspecific interactions. Compared to control conditions, drought reduced the proportional water uptake from 0-10 cm soil depth (PCWU0-10) of L. perenne, T. repens and C. intybus in monocultures by on average 54%. In contrast, the PCWU0-10 of T. pratense in monoculture increased by 44%, and only when grown in mixture did the PCWU0-10 of T. pratense decrease under drought conditions. In line with hypothesis (2), in monoculture, the PCWU0-10 of shallow-rooting species L. perenne and T. repens was 0.53 averaged over the two drought treatments, compared to 0.16 for the deep-rooting C. intybus. Surprisingly, in monoculture, water uptake by T. pratense was shallower than for the shallow-rooting species (PCWU0-10 = 0.68). Interspecific interactions in mixtures resulted in a shift in the depth of water uptake by the different species. As hypothesised, the shallow-rooting species L. perenne and T. repens tended to become shallower, and the deep-rooting T. pratense made a dramatic shift to deeper soil layers (reduction in PCWU0-10 of 58% on average) in mixture compared to monoculture. However, these shifts did not result in a reduction in the proportional similarity of the proportional water uptake from different soil depth intervals (niche overlap) in mixtures compared to monocultures. There was no clear link between interspecific differences in depth of water uptake and the reduction of biomass production under drought compared to control conditions (drought resistance). Cichorium intybus, the species with water uptake from the deepest soil layers was one of the species most affected by drought. Interestingly, T. pratense, which was least affected by drought, also had the greatest plasticity in depth of water uptake. This suggests that there may be an indirect effect of rooting depth on drought resistance, as it determines the potential plasticity in the depth of water uptake.

Hoekstra, N. J.; Finn, J. A.; Hofer, D.; Lüscher, A.

2014-08-01

281

The effect of drought and interspecific interactions on the depth of water uptake in deep- and shallow-rooting grassland species as determined by ?18O natural abundance  

NASA Astrophysics Data System (ADS)

Increased incidence of weather drought, as predicted under climate change, has the potential to negatively affect grassland production. Compared to monocultures, vertical belowground niche complementarity between shallow- and deep-rooting species may be an important mechanism resulting in higher yields and higher resistance to drought in grassland mixtures. However, very little is known about the belowground responses in grassland systems and increased insight into these processes may yield important information both to predict the effect of future climate change and better design agricultural systems to cope with this. This study assessed the effect of a 10-week experimental summer drought on the depth of water uptake of two shallow-rooting species (Lolium perenne L. and Trifolium repens L.) and two deep-rooting species (Chicorium intybus L. and Trifolium pratense L.) in grassland monocultures and four-species-mixtures by using the natural abundance ?18O isotope method. We tested the following hypotheses: (1) drought results in a shift of water uptake to deeper soil layers, (2) deep-rooting species take up a higher proportion of water from deeper soil layers relative to shallow-rooting species, (3) as a result of interspecific interactions in mixtures, the water uptake of shallow-rooting species become shallower when grown together with deep-rooting species and vice versa, resulting in reduced niche overlap. The natural abundance ?18O technique provided novel insights into the depth of water uptake of deep- and shallow- rooting grassland species and revealed large shifts in response to drought and interspecific interactions. Compared to control conditions, drought reduced the proportional water uptake from 0-10 cm soil depth (PCWU0-10) of L. perenne, T. repens and C. intybus in monocultures by on average 54%. In contrast, the PCWU0-10 of T. pratense in monoculture increased by 44%, and only when grown in mixture did the PCWU0-10 of T. pratense decrease under drought conditions. In line with hypothesis 2, in monoculture, the PCWU0-10 of shallow-rooting species L. perenne and T. repens was 0.53 averaged over the two drought treatments, compared to 0.16 for the deep-rooting C. intybus. Surprisingly, in monoculture, water uptake by T. pratense was shallower than for the shallow-rooting species (PCWU0-10 = 0.68). Interspecific interactions in mixtures resulted in a shift in the depth of water uptake by the different species. As hypothesised, the shallow-rooting species L. perenne and T. repens tended to become shallower, and the deep-rooting T. pratense made a dramatic shift to deeper soil layers (reduction in PCWU0-10 of 58% on average) in mixture compared to monoculture. However, these shifts did not result in a reduction in the proportional similarity of the proportional water uptake from different soil depth intervals (niche overlap) in mixtures compared to monocultures. There was no clear link between interspecific differences in depth of water uptake and drought resistance. C. intybus, the species with water uptake from the deepest soil layers was one of the species most affected by drought. However, T. pratense, the species with the highest plasticity in depth of water uptake, was least affected by drought, suggesting an indirect effect of rooting depth on drought resistance. Our results show that niche complementarity in the depth of water uptake between shallow- and deep-rooting species may have contributed to the diversity effect in mixtures.

Hoekstra, N. J.; Finn, J. A.; Lüscher, A.

2014-03-01

282

DNA methylation determination by liquid chromatography–tandem mass spectrometry using novel biosynthetic [U-15N]deoxycytidine and [U-15N]methyldeoxycytidine internal standards  

PubMed Central

Methylation of the promoter CpG regions regulates gene transcription by inhibiting transcription factor binding. Deoxycytidine methylation may regulate cell differentiation, while aberrations in the process may be involved in cancer etiology and the development of birth defects (e.g. neural tube defects). Similarly, nutritional deficiency and certain nutragenomic interactions are associated with DNA hypomethylation. While LC-MS has been used previously to measure percentage genomic deoxycytidine methylation, a lack of a secure source of internal standards and the need for laborious and time-consuming DNA digestion protocols constitute distinct limitations. Here we report a simple and inexpensive protocol for the biosynthesis of internal standards from readily available precursors. Using these biosynthetic stable-isotopic [U-15N]-labeled internal standards, coupled with an improved DNA digestion protocol developed in our lab, we have developed a low-cost, high-throughput (>500 samples in 4 days) assay for measuring deoxycytidine methylation in genomic DNA. Inter- and intraassay variation for the assay (%RSD, n = 6) was <2.5%. PMID:18718928

Quinlivan, Eoin P.; Gregory, Jesse F.

2008-01-01

283

DNA methylation determination by liquid chromatography-tandem mass spectrometry using novel biosynthetic [U-15N]deoxycytidine and [U-15N]methyldeoxycytidine internal standards.  

PubMed

Methylation of the promoter CpG regions regulates gene transcription by inhibiting transcription factor binding. Deoxycytidine methylation may regulate cell differentiation, while aberrations in the process may be involved in cancer etiology and the development of birth defects (e.g. neural tube defects). Similarly, nutritional deficiency and certain nutragenomic interactions are associated with DNA hypomethylation. While LC-MS has been used previously to measure percentage genomic deoxycytidine methylation, a lack of a secure source of internal standards and the need for laborious and time-consuming DNA digestion protocols constitute distinct limitations. Here we report a simple and inexpensive protocol for the biosynthesis of internal standards from readily available precursors. Using these biosynthetic stable-isotopic [U-(15)N]-labeled internal standards, coupled with an improved DNA digestion protocol developed in our lab, we have developed a low-cost, high-throughput (>500 samples in 4 days) assay for measuring deoxycytidine methylation in genomic DNA. Inter- and intraassay variation for the assay (%RSD, n = 6) was <2.5%. PMID:18718928

Quinlivan, Eoin P; Gregory, Jesse F

2008-10-01

284

[Distribution characteristics of soil humus fractions stable carbon isotope natural abundance (delta 13C) in paddy field under long-term ridge culture].  

PubMed

A 16-year field experiment was conducted in a ridge culture paddy field in the hilly region of Sichuan Basin, aimed to investigate the distribution characteristics of stable carbon isotope natural abundance (delta 13C) in soil humus fractions. The soil organic carbon (SOC) content in the paddy field under different cultivation modes ranked in the order of wide ridge culture > ridge culture > paddy and upland rotation. In soil humus substances (HS), humin (HU) was the main composition, occupying 21% - 30% of the total SOC. In the extracted soil carbon, humic acid (HA) dominated, occupying 17% - 21% of SOC and 38% - 65% of HS. The delta 13C value of SOC ranged from -27.9 per thousand to -25.6 per thousand, and the difference of the delta 13C value between 0-5 cm and 20-40 cm soil layers was about 1.9 per thousand. The delta 13C value of HA under different cultivation modes was 1 per thousand - 2 per thousand lower than that of SOC, and more approached to the delta 13C value of rapeseed and rice residues. As for fulvic acid (FA), its delta 13C value was about 2 per thousand and 4 per thousand higher than that of SOC and HA, respectively. The delta 13C value of HU in plough layer (0-20 cm) and plow layer (20-40 cm) ranged from -23.7 per thousand - -24.9 per thousand and -22.6 per thousand - -24.2 per thousand, respectively, reflecting the admixture of young and old HS. The delta 13C value in various organic carbon fractions was HU>FA>SOC>rapeseed and rice residues>HA. Long-term rice planting benefited the increase of SOC content, and cultivation mode played an important role in affecting the distribution patterns of soil humus delta 13C in plough layer and plow layer. PMID:21774322

Tang, Xiao-hong; Luo, You-jin; Ren, Zhen-jiang; Lü, Jia-ke; Wei, Chao-fu

2011-04-01

285

Abundance of Ixodes ricinus and prevalence of Borrelia burgdorferi s.l. in the nature reserve Siebengebirge, Germany, in comparison to three former studies from 1978 onwards  

PubMed Central

Background During the last decades, population densities of Ixodes ricinus and prevalences of Borrelia burgdorferi s.l. have increased in different regions in Europe. In the present study, we determined tick abundance and the prevalence of different Borrelia genospecies in ticks from three sites in the Siebengebirge, Germany, which were already examined in the years 1987, 1989, 2001 and 2003. Data from all investigations were compared. Methods In 2007 and 2008, host-seeking I. ricinus were collected by monthly blanket dragging at three distinct vegetation sites in the Siebengebirge, a nature reserve and a well visited local recreation area near Bonn, Germany. In both years, 702 ticks were tested for B. burgdorferi s.l. DNA by nested PCR, and 249 tick samples positive for Borrelia were further genotyped by reverse line blotting. Results A total of 1046 and 1591 I. ricinus were collected in 2007 and 2008, respectively. In comparison to previous studies at these sites, the densities at all sites increased from 1987/89 and/or from 2003 until 2008. Tick densities and Borrelia prevalences in 2007 and 2008, respectively, were not correlated for all sites and both years. Overall, Borrelia prevalence of all ticks decreased significantly from 2007 (19.5%) to 2008 (16.5%), thus reaching the same level as in 2001 two times higher than in 1987/89 (7.6%). Since 2001, single infections with a Borrelia genospecies predominated in all collections, but the number of multiple infections increased, and in 2007, for the first time, triple Borrelia infections occurred. Prevalences of Borrelia genospecies differed considerably between the three sites, but B. garinii or B. afzelii were always the most dominant genospecies. B. lusitaniae was detected for the first time in the Siebengebirge, also in co-infections with B. garinii or B. valaisiana. Conclusions Over the last two centuries tick densities have changed in the Siebengebirge at sites that remained unchanged by human activity since they belong to a nature reserve. Abiotic and biotic conditions most likely favored the host-seeking activity of I. ricinus and the increase of multiple Borrelia infections in ticks. These changes have led to a potential higher risk of humans and animals to be infected with Lyme borreliosis. PMID:23171708

2012-01-01

286

Nitrate Reduction in a Groundwater Microcosm Determined by 15N Gas Chromatography-Mass Spectrometry  

PubMed Central

Aerobic and anaerobic groundwater continuous-flow microcosms were designed to study nitrate reduction by the indigenous bacteria in intact saturated soil cores from a sandy aquifer with a concentration of 3.8 mg of NO3?-N liter?1. Traces of 15NO3? were added to filter-sterilized groundwater by using a Darcy flux of 4 cm day?1. Both assimilatory and dissimilatory reduction rates were estimated from analyses of 15N2, 15N2O, 15NH4+, and 15N-labeled protein amino acids by capillary gas chromatography-mass spectrometry. N2 and N2O were separated on a megabore fused-silica column and quantified by electron impact-selected ion monitoring. NO3? and NH4+ were analyzed as pentafluorobenzoyl amides by multiple-ion monitoring and protein amino acids as their N-heptafluorobutyryl isobutyl ester derivatives by negative ion-chemical ionization. The numbers of bacteria and their [methyl-3H]thymidine incorporation rates were simultaneously measured. Nitrate was completely reduced in the microcosms at a rate of about 250 ng g?1 day?1. Of this nitrate, 80 to 90% was converted by aerobic denitrification to N2, whereas only 35% was denitrified in the anaerobic microcosm, where more than 50% of NO3? was reduced to NH4+. Assimilatory reduction was recorded only in the aerobic microcosm, where N appeared in alanine in the cells. The nitrate reduction rates estimated for the aquifer material were low in comparison with rates in eutrophic lakes and coastal sediments but sufficiently high to remove nitrate from an uncontaminated aquifer of the kind examined in less than 1 month. PMID:16348048

Bengtsson, Göran; Annadotter, Heléne

1989-01-01

287

Submillimeter Observations of Titan: Global Measures of Stratospheric Temperature, CO, HCN, HC3N, and the Isotopic Ratios 12C/13C and 14N/15N  

E-print Network

Interferometric observations of the atmosphere of Titan were performed with the Submillimeter Array on two nights in February 2004 to investigate the global average vertical distributions of several molecular species above the tropopause. Rotational transitions of CO, isomers of HCN, and HC3N were simultaneously recorded. The abundance of CO is determined to be 51+/-4 ppm, constant with altitude. The vertical profile of HCN is dependent upon the assumed temperature but generally increases from 30 ppb at the condensation altitude (~83 km) to 5 ppm at ~300 km. Further, the central core of the HCN emission is strong and can be reproduced only if the upper stratospheric temperature increases with altitude. The isotopic ratios are determined to be 12C/13C=132+/-25 and 14N/15N=94+/-13 assuming the Coustenis & Bezard (1995) temperature profile. If the Lellouch (1990) temperature profile is assumed the ratios decrease to 12C/13C=108+/-20 and 14N/15N=72+/-9. The vertical profile of HC3N is consistent with that derived by Marten et al. (2002).

Mark A. Gurwell

2004-07-08

288

Influenza A (H15N4) Virus Isolation in Western Siberia, Russia  

PubMed Central

The rarely identified influenza A viruses of the H15 hemagglutinin subtype have been isolated exclusively in Australia. Here we report the isolation of an H15N4 influenza A virus (A/teal/Chany/7119/2008) in Western Siberia, Russia. Phylogenetic analysis demonstrated that the internal genes of the A/teal/Chany/7119/2008 strain belong to the Eurasian clade and that the H15 and N4 genes were introduced into the gene pool of circulating endemic avian influenza viruses through reassortment events. PMID:23283950

Sivay, Mariya V.; Baranovich, Tatiana; Marchenko, Vasiliy Y.; Sharshov, Kirill A.; Govorkova, Elena A.; Shestopalov, Aleksander M.

2013-01-01

289

Negative pion photoproduction from {sup 15}N in the region of the {Delta} resonance  

SciTech Connect

The differential cross section for the reaction {sup 15}N({gamma},{pi}{sup {minus}}){sup 15}O{sub gs} has been measured at a photon energy of 220 MeV. We find a discrepancy between our data and a calculation based on the distorted wave impulse approximation which uses phenomenological 1{ital p}-shell wave functions. A second calculation, in which higher-shell configurations are included in the wave functions, fails to correct the discrepancy and is even more at odds with the data.

Shaw, J.; Choi, H.; Kobayashi, T.; Stoler, P. [Physics Department, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)] [Physics Department, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Gresko, T.; Keeter, K.; Mitchell, J.H.; Norum, B.; Welch, T.P. [Physics Department, University of Virginia, Charlottesville, Virginia 22901 (United States)] [Physics Department, University of Virginia, Charlottesville, Virginia 22901 (United States); Chung, H.T.; Kim, J.C. [Department of Physics, Seoul National University, Seoul 151-742 (Korea, Republic of)] [Department of Physics, Seoul National University, Seoul 151-742 (Korea, Republic of); van den Brink, H.B.; Hesselink, W.H.A. [Department of Physics and Astronomy, Free University, De Boelelaan 1081, 1081HV Amsterdam (Netherlands)] [Department of Physics and Astronomy, Free University, De Boelelaan 1081, 1081HV Amsterdam (Netherlands); Bergstrom, J.C.; Hallin, E.L.; Kaplan, H.S.; Skopik, D.M.; Vogt, J.M. [Saskatchewan Accelerator Laboratory, Saskatoon, Saskatchewan, S7N 0W0 (Canada)] [Saskatchewan Accelerator Laboratory, Saskatoon, Saskatchewan, S7N 0W0 (Canada)

1995-07-01

290

Isotopic analysis of bulk, LMW, and HMW DON d15N indicates recycled nitrogen release from marine DON  

NASA Astrophysics Data System (ADS)

Nitrogen (N) concentration and stable isotope ratio (d15N) measurements were made on bulk and size fractionated surface ocean dissolved organic nitrogen (DON) samples collected in the oligotrophic North Atlantic and Pacific Oceans. The bulk DON concentration in the upper 100 m is similar between the North Atlantic and North Pacific, between 4.5 and 5.0 uM, but the average d15N of bulk DON is significantly different, 3.9 per mil vs. air in the North Atlantic and 4.7 per mil in the North Pacific. The d15N of both bulk and HMW DON from the western tropical North Atlantic are similar to previous measurements, ~4.0 to 4.5 per mil. We report the first measurements of LMW DON d15N, which is consistently lower than HMW DON d15N. Neither the concentration nor d15N of bulk or size-fractionated DON varied with in situ N2 fixation rate, although significant variation in bulk and LMW DON d15N was observed between January and July of the same year in the western tropical North Atlantic. We propose a conceptual model to explain 1) the elevated d15N of bulk DON relative to other surface ocean N pools and fluxes, 2) the elevation of HMW DON d15N relative to LMW DON d15N, and 3) the inter-basin difference in the d15N of bulk DON. In this model, DON is produced from suspended particulate organic nitrogen (PON) without isotope fractionation because the conversion from PON to DON largely does not involve N-bearing bonds. In contrast, deamination and amide hydrolysis, with N isotope effects of 3 to 10 per mil, are major mechanisms by which DON is converted to ammonia and/or to other simple N compounds (e.g., amino acids). Thus these N-specific DON loss reactions result in an elevated d15N of residual DON relative to the parent DON and therefore also to the PON source. Moreover, the ammonium and simple organic N compounds released by microbial DON degradation are efficiently reassimilated back into the PON pool, as an integral part of the regenerated N cycle that further lowers the d15N of suspended PON relative to subsurface nitrate. Based on a d15N budget for the subtropical North Atlantic euphotic zone, we propose that this recycled N release via DON degradation (and not zooplankton ammonium excretion or N2 fixation) is the dominant mechanism lowering the d15N of PON relative to subsurface nitrate in the low-latitude ocean. DON degradation may also explain why the d15N of HMW DON is elevated relative to LMW DON: LMW DON may be produced by the isotope fractionating reactions responsible for degrading DON in general. Alternatively, LMW and HMW DON may have distinct sources. Finally, in this explanation, the difference in the d15N of DON between the North Atlantic and North Pacific primarily reflects the inter-basin difference in the d15N of subsurface nitrate fueling productivity in the euphotic zone.

Knapp, A. N.; Sigman, D. M.; Lipschultz, F.; Kustka, A.; Capone, D. G.

2010-12-01

291

Single Transition-to-single Transition Polarization Transfer (ST2-PT) in [15N,1H]-TROSY.  

PubMed

This paper describes the use of single transition-to-single transition polarization transfer (ST2-PT) in transverse relaxation-optimized spectroscopy (TROSY), where it affords a [Formula: see text] sensitivity enhancement for kinetically stable amide 15N-1H groups in proteins. Additional, conventional improvements of [15N,1H]-TROSY include that signal loss for kinetically labile 15N-1H groups due to saturation transfer from the solvent water is suppressed with the 'water flip back' technique and that the number of phase steps is reduced to two, which is attractive for the use of [15N,1H]-TROSY as an element in more complex NMR schemes. Finally, we show that the impact of the inclusion of the 15N steady-state magnetization (Pervushin et al., 1998) on the signal-to-noise ratio achieved with [15N,1H]-TROSY exceeds by up to two-fold the gain expected from the gyromagnetic ratios of 1H and 15N. PMID:21136330

Pervushin, K V; Wider, G; Wüthrich, K

1998-08-01

292

Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-?15N measurements  

NASA Astrophysics Data System (ADS)

Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of ?15N of N2 in air trapped in ice core, assuming that ?15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air- ?15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our ?15N profiles reveal a heterogeneous response of the firn structure to glacial-interglacial climatic changes. While firn densification simulations correctly predict TALDICE ?15N variations, they systematically fail to capture the large millennial-scale ?15N variations measured at BI and the ?15N glacial levels measured at JRI and EDML - a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas-ice depth offset during the Laschamp event (41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model- ?15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the ?15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

Capron, E.; Landais, A.; Buiron, D.; Cauquoin, A.; Chappellaz, J. A.; Debret, M.; Jouzel, J.; Leuenberger, M.; Martinerie, P.; Masson-Delmotte, V.; Mulvaney, R.; Parrenin, F.; Prié, F.

2013-12-01

293

Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-?15N measurements  

NASA Astrophysics Data System (ADS)

Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of ?15N of N2 in air trapped in ice core, assuming that ?15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-?15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our ?15N profiles reveal a heterogeneous response of the firn structure to glacial-interglacial climatic changes. While firn densification simulations correctly predict TALDICE ?15N variations, they systematically fail to capture the large millennial-scale ?15N variations measured at BI and the ?15N glacial levels measured at JRI and EDML - a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas-ice depth offset during the Laschamp event (~41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model-?15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the ?15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

Capron, E.; Landais, A.; Buiron, D.; Cauquoin, A.; Chappellaz, J.; Debret, M.; Jouzel, J.; Leuenberger, M.; Martinerie, P.; Masson-Delmotte, V.; Mulvaney, R.; Parrenin, F.; Prié, F.

2013-05-01

294

Red blood cell ?15N: a novel biomarker of dietary eicosapentaenoic acid and docosahexaenoic acid intake1234  

PubMed Central

Background: The long-chain omega-3 (n–3) fatty acids derived from fish, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are associated with a reduced risk of cardiovascular disease and other chronic diseases. Study of the associations between EPA and DHA intake and disease requires a valid biomarker of dietary intake; however, the direct measurement of tissue fatty acid concentrations is expensive and time consuming. Objective: Because the nitrogen stable isotope ratio (15N/14N, expressed as ?15N) is elevated in fish, we investigated whether ?15N is a valid alternative biomarker of EPA and DHA intake. Design: We examined the relation between red blood cell (RBC) ?15N and RBC EPA and DHA in a community-based sample of 496 Yup'ik Eskimos with widely varying intake of n–3 fatty acids. We also assessed the correlation between ?15N and dietary EPA and DHA intake based on 24-h dietary recalls and 3-d food records completed by a subset of 221 participants. Results: RBC ?15N was strongly correlated with RBC EPA and DHA (r = 0.83 and 0.75, respectively). These correlations differed only modestly by sex and age class. RBC ?15N also correlated with dietary EPA and DHA intake (r = 0.47 and 0.46, respectively) and did not differ by sex and age. Conclusions: The results strongly support the validity of RBC ?15N as a biomarker of EPA and DHA intake. Because the analysis of RBC ?15N is rapid and inexpensive, this method could facilitate wide-scale assessment of EPA and DHA intake in clinical and epidemiologic studies. PMID:19176727

O'Brien, Diane M; Kristal, Alan R; Jeannet, M Alyssa; Wilkinson, Michael J; Bersamin, Andrea; Luick, Bret

2009-01-01

295

Discrimination against 15N among recombinant inbred lines of Phaseolus vulgaris L. contrasting in phosphorus use efficiency for nitrogen fixation.  

PubMed

Although isotopic discrimination processes during nitrogen (N) transformations influence the outcome of (15)N based quantification of N2 fixation in legumes, little attention has been given to the effects of genotypic variability and environmental constraints such as phosphorus (P) deficiency, on discrimination against (15)N during N2 fixation. In this study, six Phaseolus vulgaris recombinant inbred lines (RILs), i.e. RILs 115, 104, 34 (P deficiency tolerant) and 147, 83, 70 (P deficiency sensitive), were inoculated with Rhizobium tropici CIAT899, and hydroaeroponically grown with P-sufficient (250 ?mol P plant(-1) week(-1)) versus P-deficient (75 ?mol P plant(-1) week(-1)) supply. Two harvests were done at 15 (before nodule functioning) and 42 (flowering stage) days after transplanting. Nodulation, plant biomass, P and N contents, and the ratios of (15)N over total N content ((15)N/Nt) for shoots, roots and nodules were determined. The results showed lower (15)N/Nt in shoots than in roots, both being much lower than in nodules. P deficiency caused a larger decrease in (15)N/Nt in shoots (-0.18%) than in nodules (-0.11%) for all of the genotypes, and the decrease in shoots was greatest for RILs 34 (-0.33%) and 104 (-0.25%). Nodule (15)N/Nt was significantly related to both the quantity of N2 fixed (R(2)=0.96***) and the P content of nodules (R(2)=0.66*). We conclude that the discrimination against (15)N in the legume N2-fixing symbiosis of common bean with R. tropici CIAT899 is affected by P nutrition and plant genotype, and that the (15)N/Nt in nodules may be used to screen for genotypic variation in P use efficiency for N2 fixation. PMID:24035519

Lazali, Mohamed; Bargaz, Adnane; Carlsson, Georg; Ounane, Sidi Mohamed; Drevon, Jean Jacques

2014-02-15

296

Side Chain and Backbone Dynamics of Phospholamban in Phospholipid Bilayers Utilizing 2H and 15N Solid-State NMR Spectroscopy†  

PubMed Central

2H and 15N solid-state NMR spectroscopic techniques were used to investigate both the side chain and backbone dynamics of wild-type phospholamban (WT-PLB) and its phosphorylated form (P-PLB) incorporated into 1-palmitoyl-2-oleoyl-sn-glycerophosphocholine (POPC) phospholipid bilayers. 2H NMR spectra of site-specific CD3-labeled WT-PLB (at Leu51, Ala24, and Ala15) in POPC bilayers were similar under frozen conditions (-25 °C). However, significant differences in the line shapes of the 2H NMR spectra were observed in the liquid crystalline phase at and above 0 °C. The 2H NMR spectra indicate that Leu51, located toward the lower end of the transmembrane (TM) helix, shows restricted side chain motion, implying that it is embedded inside the POPC lipid bilayer. Additionally, the line shape of the 2H NMR spectrum of CD3-Ala24 reveals more side chain dynamics, indicating that this residue (located in the upper end of the TM helix) has additional backbone and internal side chain motions. 2H NMR spectra of both WT-PLB and P-PLB with CD3-Ala15 exhibit strong isotropic spectral line shapes. The dynamic isotropic nature of the 2H peak can be attributed to side chain and backbone motions to residues located in an aqueous environment outside the membrane. Also, the spectra of 15N-labeled amide WT-PLB at Leu51 and Leu42 residues showed only a single powder pattern component indicating that these two 15N-labeled residues located in the TM helix are motionally restricted at 25 °C. Conversely, 15N-labeled amide WT-PLB at Ala11 located in the cytoplasmic domain showed both powder and isotropic components at 25 °C. Upon phosphorylation, the mobile component contribution increases at Ala11. The 2H and 15N NMR data indicate significant backbone motion for the cytoplasmic domain of WT-PLB when compared to the transmembrane section. PMID:17910421

Abu-Baker, Shadi; Lu, Jun-Xia; Chu, Shidong; Brinn, Clarke C.; Makaroff, Christopher A.; Lorigan, Gary A.

2009-01-01

297

Pathways for nitrate release from an alpine watershed: Determination using ??15N and ??18O  

USGS Publications Warehouse

[1] Snowpack, snowmelt, precipitation, surface water, and groundwater samples from the Loch Vale watershed in Colorado were analyzed for ??15N and ??18O of nitrate to determine the processes controlling the release of atmospherically deposited nitrogen from alpine and subalpine ecosystems. Although overlap was found between the ??15N(NO3) values for all water types (-4 to +6???), the ??18O(NO3) values for surface water and groundwater (+10 to +30???) were usually distinct from snowpack, snowmelt, and rainfall values (+40 to +70???). During snowmelt, ??18O(NO3) indicated that about half of the nitrate in stream water was the product of microbial nitrification; at other times that amount was greater than half. Springs emerging from talus deposits had high nitrate concentrations and a seasonal pattern in ??18O(NO3) that was similar to the pattern in the streams, indicating that shallow groundwater in talus deposits is a likely source of stream water nitrate. Only a few samples of surface water and groundwater collected during early snowmelt and large summer rain events had isotopic compositions that indicated most of the nitrate came directly from atmospheric deposition with no biological assimilation and release. This study demonstrates the value of the nitrate double-isotope technique for determining nitrogen-cycling processes and sources of nitrate in small, undisturbed watersheds that are enriched with inorganic nitrogen.

Campbell, D.H.; Kendall, C.; Chang, C.C.Y.; Silva, S.R.; Tonnessen, K.A.

2002-01-01

298

The Origin of Nitrogen on Jupiter and Saturn from the $^{15}$N/$^{14}$N Ratio  

E-print Network

The Texas Echelon cross Echelle Spectrograph (TEXES), mounted on NASA's Infrared Telescope Facility (IRTF), was used to map mid-infrared ammonia absorption features on both Jupiter and Saturn in February 2013. Ammonia is the principle reservoir of nitrogen on the giant planets, and the ratio of isotopologues ($^{15}$N/$^{14}$N) can reveal insights into the molecular carrier (e.g., as N$_2$ or NH$_3$) of nitrogen to the forming protoplanets, and hence the source reservoirs from which these worlds accreted. We targeted two spectral intervals (900 and 960 cm$^{-1}$) that were relatively clear of terrestrial atmospheric contamination and contained close features of $^{14}$NH$_3$ and $^{15}$NH$_3$, allowing us to derive the ratio from a single spectrum without ambiguity due to radiometric calibration (the primary source of uncertainty in this study). We present the first ground-based determination of Jupiter's $^{15}$N/$^{14}$N ratio (in the range from $1.4\\times10^{-3}$ to $2.5\\times10^{-3}$), which is consistent...

Fletcher, Leigh N; Orton, Glenn S; Irwin, Patrick G J; Mousis, Olivier; Sinclair, James A; Giles, Rohini S

2014-01-01

299

Contribution of 19F resonances on 18O( p, ?)15N reaction rate  

NASA Astrophysics Data System (ADS)

The 18O( p, ?)15N reaction influences the isotopes production such as 19F, 18O, and 15N which can be used to test the models of stellar evolution. 19F is synthesized in both asymptotic giant branch (AGB) and metal-rich Wolf-Rayet (WR) stars. Using R-matrix theory we allow new values of resonances parameters in 19F. We show that the most important contribution to the differential and total cross section at low energies, comes from the levels in 19F situated at resonances energies E R =151, 680 and 840 keV with spin and parity 1/2+. The total width of the 680 keV resonance is badly known. So, we have focused on this broad resonance corresponding to the 8.65 MeV level in 19F. We delimit the temperature range in which each resonance contribution to the total reaction rate occurs by analyzing the ratio ( N A < ??> i / N A < ??>). This allowed us to show that the 680 and 840 keV broad resonances strongly dominate the reaction rate over the stellar temperature range T 9=0.02-0.06 and T 9=0.5-5. Finally, these results were compared to NACRE and Iliadis astrophysical compilations.

Benmeslem, Meriem; Chafa, Azzedine; Barhoumi, Slimane; Tribeche, Mouloud

2014-08-01

300

UV-visible and (1)H-(15)N NMR spectroscopic studies of colorimetric thiosemicarbazide anion sensors.  

PubMed

Four model thiosemicarbazide anion chemosensors containing three N-H bonds, substituted with phenyl and/or 4-nitrophenyl units, were synthesised and studied for their anion binding abilities with hydroxide, fluoride, acetate, dihydrogen phosphate and chloride. The anion binding properties were studied in DMSO and 9?:?1 DMSO-H2O by UV-visible absorption and (1)H/(13)C/(15)N NMR spectroscopic techniques and corroborated with DFT studies. Significant changes were observed in the UV-visible absorption spectra with all anions, except for chloride, accompanied by dramatic colour changes visible to the naked eye. These changes were determined to be due to the deprotonation of the central N-H proton and not due to hydrogen bonding based on (1)H/(15)N NMR titration studies with acetate in DMSO-d6-0.5% water. Direct evidence for deprotonation was confirmed by the disappearance of the central thiourea proton and the formation of acetic acid. DFT and charge distribution calculations suggest that for all four compounds the central N-H proton is the most acidic. Hence, the anion chemosensors operate by a deprotonation mechanism of the central N-H proton rather than by hydrogen bonding as is often reported. PMID:25451865

Farrugia, Kristina N; Makuc, Damjan; Podborska, Agnieszka; Szaci?owski, Konrad; Plavec, Janez; Magri, David C

2015-01-27

301

Covalent binding of aniline to humic substances. 2. 15N NMR studies of nucleophilic addition reactions  

USGS Publications Warehouse

Aromatic amines are known to undergo covalent binding with humic substances in the environment. Although previous studies have examined reaction conditions and proposed mechanisms, there has been no direct spectroscopic evidence for the covalent binding of the amines to the functional groups in humic substances. In order to further elucidate the reaction mechanisms, the Suwannee River and IHSS soil fulvic and humic acids were reacted with 15N-labeled aniline at pH 6 and analyzed using 15N NMR spectrometry. Aniline underwent nucleophilic addition reactions with the quinone and other carbonyl groups in the samples and became incorporated in the form of anilinohydroquinone, anilinoquinone, anilide, imine, and heterocyclic nitrogen, the latter comprising 50% or more of the bound amine. The anilide and anilinohydroquinone nitrogens were determined to be susceptible to chemical exchange by ammonia. In the case of Suwannee River fulvic acid, reaction under anoxic conditions and pretreatment with sodium borohydride or hydroxylamine prior to reaction under oxic conditions resulted in a decrease in the proportion of anilinohydroquinone nitrogen incorporated. The relative decrease in the incorporation of anilinohydroquinone nitrogen with respect to anilinoquinone nitrogen under anoxic conditions suggested that inter- or intramolecular redox reactions accompanied the nucleophilic addition reactions.

Thorn, K.A.; Pettigrew, P.J.; Goldenberg, W.S.; Weber, E.J.

1996-01-01

302

Experimental assessment of the bioconcentration of (15)N-tamoxifen in Pseudokirchneriella subcapitata.  

PubMed

Nowadays, pharmaceutical compounds (PC) are ubiquitous in aquatic ecosystems. In addition to direct ecotoxicity, the bioconcentration of PC in organisms is a phenomenon which could have an impact on the whole ecosystem. In order to study this phenomenon, we exposed unicellular algae (Pseudokirchneriella subcapitata) to (15)N-tamoxifen, an anticancer drug labelled with a stable nitrogen isotope used as a tracer. By measuring (15)N enrichment over time, we were able to measure the increase of tamoxifen content in algae. This enrichment was measured by an elemental analyser coupled with an isotopic ratio mass spectrometer (EA-IRMS). Algal cells were exposed for 7d to 3 concentrations of tamoxifen: 1, 10 and 100?gL(-1). Our result shows a high bioconcentration in algae from the first minutes of contact. The highest bioconcentration factor measured is around 26500. We also observe that bioconcentration is not linked to the exposure concentration. This study is the first to use stable isotopes in order to monitor PCs in aquatic organisms such as algae. The use of stable isotopes in ecotoxicology offers interesting perspectives in the field of contaminant transfer in organisms and along the trophic web. PMID:25522849

Orias, Frédéric; Simon, Laurent; Perrodin, Yves

2015-03-01

303

Precursor discrimination of designer drug benzylpiperazine using ?(13)C and ?(15)N stable isotopes.  

PubMed

Advances in analytical technology and emerging techniques have resulted in the increased exploitation of chemical and isotopic profiling for source linkage/discrimination of illicit drugs for forensic purposes. Although not routinely used for illicit drug investigations, such information has been obtained and its application demonstrated through the use of isotope ratio mass spectrometry (IRMS). There is a solid platform of research available relating to the isotopic analysis of methylenedioxymethamphetamine (MDMA) and methamphetamine (MA), however with the recently flourishing designer drug market it was of interest to examine the isotopic profiles of the popular 'party drug' benzylpiperazine hydrochloride (BZP·HCl). A preliminary analysis of ?(13)C and ?(15)N isotopic ratios in BZP·HCl products and corresponding synthetic intermediates (piperazine·HCl) synthesized in-house from three different precursor suppliers was conducted using IRMS. Analysis of the ?(13)C and ?(15)N isotopic data indicated that discrimination and correct grouping of all the intermediates and some of the product samples examined in this study were achievable. PMID:25577008

Beckett, Nicola M; Grice, Darren I; Carter, James F; Cresswell, Sarah L

2015-01-01

304

15N depleted nitrogen isotope values in Cretaceous black shales: paleoceanographic event or diagenesis.  

NASA Astrophysics Data System (ADS)

Nitrogen isotopic values of bulk sediment samples in black shales are almost exclusively near 0 ‰ and C/N ratios are high (20-35). Sequential extraction of exchangeable and non-exchangeable N fractions demonstrates that the inorganic N fraction is negligible and bulk sediment data reflect the organic N fraction. The trend in \\delta$15N and C/N has been observed in numerous localities and depositional environments in the mid-Cretaceous (Demarara Rise, DSDP Sites 367, 603B and 530, the Cretaceous Western Interior Seaway, Wunstorf, Germany, and Bahloul, Tunisia) as well as the Toarcian of England and in Quaternary Mediterranean Sapropels. Three explanations are considered: 1) That primary production during black shale deposition was dominated by a unique community composed of nitrogen-fixing cyanobacteria; or 2) utilization of a 15N depleted ammonium source by another set of biota; or 3) that the values are the result of diagenetic loss of N prevailing in Corg-rich strata with a low capacity for N adsorption. The depleted nitrogen isotopic values suggest that nitrogen fixation or utilization of a depleted nitrogen source (e.g. ammonium) may have been important which is plausible in consideration of nitrogen deficiencies that might characterize widespread deep-water anoxia. Secular variations in nitrogen isotope values across the Cenomanian-Turonian Boundary of ODP Site 1261, Demarara Rise, show a shift from -1 to -3‰ . One interpretation of the origin of the excursion could be that a fraction of the organic matter was produced utilizing a 15N depleted ammonium source, assuming that the nitrogen isotopic composition of fixed oceanic nitrogen does not change. However, it should be noted that large (greater than 1‰ ) variations in nitrogen isotope values are observed above and below the Cenomanian-Turonian Boundary Event and have no known paleoceanographic forcing. The variations in nitrogen isotope values are matched by antithetic variations in C/N indicating diagenetic N-loss that could be interpreted as the primary control on the nitrogen isotope variations. The high C/N ratios probably result from selective removal of N-enriched compounds in the water column and during burial diagenesis. Clay-poor, Corg-rich sediments have a low sorptive capacity, allowing diffusion of dissolved N out of the Corg-rich sediments resulting in higher C/N ratios. Pore water ammonium concentrations are mM, indicating low sorption and high rates of diffusion into overlying strata. Coupled C/N and N-isotope variations occur by the removal of a 15N enriched fraction. Protein degradation has been suggested to result in negative isotopic shifts but would not result in large increases in C/N and the isotopic shifts are limited by the protein richness of the primary organic matter and the internal isotopic heterogeneity of the organic matter pools. Although we favor an explanation that involves a primary signature, diagenesis cannot be excluded in low ? 15N values.

Junium, C. K.; Arthur, M. A.

2004-12-01

305

Backbone (1)H, (15)N, and (13)C resonance assignments and secondary structure of the Tollip CUE domain.  

PubMed

The Toll-interacting protein (Tollip) is a negative regulator of the Toll-like receptor (TLR)-mediated inflammation response. Tollip is a modular protein that contains an Nterminal Tom1-binding domain (TBD), a central conserved domain 2 (C2), and a C-terminal coupling of ubiquitin to endoplasmic reticulum degradation (CUE) domain. Here, we report the sequence-specific backbone (1)H, (15)N, and (13)C assignments of the human Tollip CUE domain. The CUE domain was found to be a stable dimer as determined by size-exclusion chromatography and molecular crosslinking studies. Analysis of the backbone chemical shift data indicated that the CUE domain exhibits three helical elements corresponding to 52% of the protein backbone. Circular dichroism spectrum analysis confirmed the helical nature of this domain. Comparison of the location of these helical regions with those reported for yeast CUE domains suggest differences in length for all helical elements. We expect the structural analysis presented here will be the foundation for future studies on the biological significance of the Tollip CUE domain, its molecular interactions, and the mechanisms that modulate its function during the inflammatory response. PMID:20957454

Azurmendi, Hugo F; Mitra, Sharmistha; Ayala, Iriscilla; Li, Liwu; Finkielstein, Carla V; Capelluto, Daniel G S

2010-12-01

306

Abundance coefficients, a new method for measuring microorganism relative abundance  

USGS Publications Warehouse

A new method of measuring the relative abundance of microorganisms by using a set of interrelated coefficients, termed 'abundance coefficients' or 'AC', is proposed. These coefficients provide a means of recording abundance for geometric density categories, and each density measurement represents an approximation of the Poisson parameter ??t. The AC is the natural logarithm of a 'characteristic value,' which is a particular number for each geometric density category. The 'characteristic values' are based upon a probabilistic error statement derived from the Poisson formula, and they present evidence for separation of the geometric category boundaries by e = 2.71828. The proposed AC provide a means for recording species abundance in a manner suitable for arithmetic manipulation, for population structure studies, and for the determination of practical limits for defining the presence or absence of a species. Further, these coefficients provide for both intrasample and intersample abundance comparisons. ?? 1977 Plenum Publishing Corporation.

Forester, R.M.

1977-01-01

307

Wild Rabbit Host and Some Parasites Show Trophic-Level Relationships for ?(13)C and ?(15)N: A First Report.  

PubMed

Abstract We report the first isotopic study of an animal host-parasite system. Parasitic, intestinal nematodes, Graphidium strigosum and Passalurus ambiguus, were (15)N-enriched relative to their host, the European rabbit Oryctolagus cuniculus, while parasitic cestodes, Cittataenia denticulata and Mosgovoyia pectinata, were (15)N-depleted, suggesting different trophic relationships. Host embryos were more similar in their ?(13)C and ?(15)N values to maternal muscle than were any of the parasites. Coprophagy, the direct recycling of food by the rabbit eating its own faeces, did not lead to isotopic differences between stomach contents and faeces, suggesting that the major point for isotopic discrimination in lagomorph nitrogen metabolism is in the animal rather than in the gut. We conclude that bulk ?(13)C and ?(15)N can reveal valuable new information about host-parasite relationships, and these could be explored further at the biochemical level using compound-specific isotopic analyses. PMID:22087485

Boag, B; Neilson, R; Robinson, D; Scrimgeour, C M; Handley, L L

1997-07-01

308

Temporal and spatial variation in the ? 15 N and ? 13 C values of fish and squid from Alaskan waters  

Microsoft Academic Search

To test the hypothesis that stable isotope ratios from marine organisms vary, the ?15N and ?13C values from fish and squid collected in Alaskan waters were measured across years (1997, 2000, and 2005), seasons, geographic\\u000a locations, and different size\\/age classes, and between muscle tissue and whole animals. Temporal, geographic, and ontogenetic\\u000a differences in stable isotope ratios ranged from 0.5–2.5‰ (?15N)

Carolyn M. KurleElizabeth; Elizabeth H. Sinclair; Ann E. Edwards; Carolyn J. Gudmundson

309

Diatom-bound 15N\\/14N: New support for enhanced nutrient consumption in the ice age subantarctic  

Microsoft Academic Search

Diatom-bound 15N\\/14N was used to reconstruct the glacial nutrient status of the Subantarctic Zone in the Southern Ocean. Down-core records from both the Pacific and Indian sectors show ?15N of 5 to 6‰ during the Last Glacial Maximum and a decrease, coincident with the glacial termination, to values as low as 2‰. The effect of either diatom assemblage or physiological

Rebecca S. Robinson; Daniel M. Sigman; Peter J. DiFiore; Melissa M. Rohde; Tracy A. Mashiotta; David W. Lea

2005-01-01

310

Conformation of Alamethicin in Oriented Phospholipid Bilayers Determined by 15N Solid-State Nuclear Magnetic Resonance  

Microsoft Academic Search

The conformation of the 20-residue antibiotic ionophore alamethicin in macroscopically oriented phospholipid bilayers has been studied using 15N solid-state nuclear magnetic resonance (NMR) spectroscopy in combination with molecular modeling and molecular dynamics simulations. Differently 15N-labeled variants of alamethicin and an analog with three of the ?-amino-isobutyric acid residues replaced by alanines have been investigated to establish experimental structural constraints and

Mads Bak; Robert P. Bywater; Morten Hohwy; Jens K. Thomsen; Kim Adelhorst; Hans J. Jakobsen; Ole W. Sørensen; Niels C. Nielsen

2001-01-01

311

Nitrous oxide nitrification and denitrification 15N enrichment factors from Amazon forest soils.  

PubMed

The isotopic signatures of 15N and 18O in N2O emitted from tropical soils vary both spatially and temporally, leading to large uncertainty in the overall tropical source signature and thereby limiting the utility of isotopes in constraining the global N2O budget. Determining the reasons for spatial and temporal variations in isotope signatures requires that we know the isotope enrichment factors for nitrification and denitrification, the two processes that produce N2O in soils. We have devised a method for measuring these enrichment factors using soil incubation experiments and report results from this method for three rain forest soils collected in the Brazilian Amazon: soil with differing sand and clay content from the Tapajos National Forest (TNF) near Santarém, Pará, and Nova Vida Farm, Rondônia. The 15N enrichment factors for nitrification and denitrification differ with soil texture and site: -111 per thousand +/- 12 per thousand and -31 per thousand +/- 11 per thousand for a clay-rich Oxisol (TNF), -102 per thousand +/- 5 per thousand and -45 per thousand +/- 5 per thousand for a sandier Ultisol (TNF), and -10.4 per thousand +/- 3.5 per thousand (enrichment factor for denitrification) for another Ultisol (Nova Vida) soil, respectively. We also show that the isotopomer site preference (delta15Nalpha - delta15Nbeta, where alpha indicates the central nitrogen atom and beta the terminal nitrogen atom in N2O) may allow differentiation between processes of production and consumption of N2O and can potentially be used to determine the contributions of nitrification and denitrification. The site preferences for nitrification and denitrification from the TNF-Ultisol incubated soils are: 4.2 per thousand +/- 8.4 per thousand and 31.6 per thousand +/- 8.1 per thousand, respectively. Thus, nitrifying and denitrifying bacteria populations under the conditions of our study exhibit significantly different 15N site preference fingerprints. Our data set strongly suggests that N2O isotopomers can be used in concert with traditional N2O stable isotope measurements as constraints to differentiate microbial N2O processes in soil and will contribute to interpretations of the isotopic site preference N2O values found in the free troposphere. PMID:17205894

Pérez, Tibisay; Garcia-Montiel, Diana; Trumbore, Susan; Tyler, Stanley; de Camargo, Plínio; Moreira, Marcelo; Piccolo, Marisa; Cerri, Carlos

2006-12-01

312

Lineshape-based polarimetry of dynamically-polarized 15N2O in solid-state mixtures  

PubMed Central

Dynamic nuclear polarization (DNP) of 15N2O, known for its long-lived singlet-state order at low magnetic field, is demonstrated in organic solvent/trityl mixtures at ~1.5 K and 5 T. Both 15N polarization and intermolecular dipolar broadening are strongly affected by the sample's thermal history, indicating spontaneous formation of N2O clusters. In situ 15N NMR reveals four distinct powder-pattern spectra, attributed to the chemical-shift anisotropy (CSA) tensors of the two 15N nuclei, further split by the intramolecular dipolar coupling between their magnetic moments. 15N polarization is estimated by fitting the free-induction decay (FID) signals to the analytical model of four single-quantum transitions. This analysis implies (10:2 ± 2:2)% polarization after 37 h of DNP, and provides a direct, instantaneous probe of the absolute 15N polarization, without a need for time-consuming referencing to a thermal-equilibrium NMR signal. PMID:23851025

Kuzma, N.N.; Håkansson, P.; Pourfathi, M.; Ghosh, R.K.; Kara, H.; Kadlecek, S.J.; Pileio, G.; Levitt, M.H.; Rizi, R.R.

2013-01-01

313

Investigating patterns of symbiotic nitrogen fixation during vegetation change from grassland to woodland using fine scale ?(15) N measurements.  

PubMed

Biological nitrogen fixation (BNF) in woody plants is often investigated using foliar measurements of ?(15) N and is of particular interest in ecosystems experiencing increases in BNF due to woody plant encroachment. We sampled ?(15) N along the entire N uptake pathway including soil solution, xylem sap and foliage to (1) test assumptions inherent to the use of foliar ?(15) N as a proxy for BNF; (2) determine whether seasonal divergences occur between ?(15) Nxylem sap and ?(15) Nsoil inorganic N that could be used to infer variation in BNF; and (3) assess patterns of ?(15) N with tree age as indicators of shifting BNF or N cycling. Measurements of woody N-fixing Prosopis glandulosa and paired reference non-fixing Zanthoxylum fagara at three seasonal time points showed that ?(15) Nsoil inorganic N varied temporally and spatially between species. Fractionation between xylem and foliar ?(15) N was consistently opposite in direction between species and varied on average by 2.4‰. Accounting for these sources of variation caused percent nitrogen derived from fixation values for Prosopis to vary by up to ?70%. Soil-xylem ?(15) N separation varied temporally and increased with Prosopis age, suggesting seasonal variation in N cycling and BNF and potential long-term increases in BNF not apparent through foliar sampling alone. PMID:24890575

Soper, Fiona M; Boutton, Thomas W; Sparks, Jed P

2015-01-01

314

Using dual-bacterial denitrification to improve ??15N determinations of nitrates containing mass-independent 17O  

USGS Publications Warehouse

The bacterial denitrification method for isotopic analysis of nitrate using N2O generated from Pseudomonas aureofaciens may overestimate ??15N values by as much as 1-2??? for samples containing atmospheric nitrate because of mass-independent 17O variations in such samples. By analyzing such samples for ??15N and ??18O using the denitrifier Pseudomonas chlororaphis, one obtains nearly correct ??15N values because oxygen in N 2O generated by P. chlororaphis is primarily derived from H 2O. The difference between the apparent ??15N value determined with P. aureofaciens and that determined with P. chlororaphis, assuming mass-dependent oxygen isotopic fractionation, reflects the amount of mass-independent 17O in a nitrate sample. By interspersing nitrate isotopic reference materials having substantially different ?? 18O values with samples, one can normalize oxygen isotope ratios and determine the fractions of oxygen in N2O derived from the nitrate and from water with each denitrifier. This information can be used to improve ??15N values of nitrates having excess 17O. The same analyses also yield estimates of the magnitude of 17O excess in the nitrate (expressed as ??17O) that may be useful in some environmental studies. The 1-?? uncertainties of ??15N, ??18O and ??17O measurements are ??0.2, ??0.3 and ??5???, respectively. Copyright ?? 2004 John Wiley & Sons, Ltd.

Coplen, T.B.; Böhlke, J.K.; Casciotti, K.L.

2004-01-01

315

Single Particle Strengths and Mirror States in $^{15}$N$-^{15}$O below 12.0 MeV  

E-print Network

New $^{14}$N(d,p) angular distribution data were taken at a deuteron bombarding energy of 16 MeV to locate all narrow single particle neutron states up to 15 MeV in excitation. A new shell model calculation is able to reproduce all levels in $^{15}$N up to 11.5 MeV and is used to characterize a narrow single particle level at 11.236 MeV and to provide a map of the single particle strengths. The known levels in $^{15}$N are then used to determine their mirrors in the lesser known nucleus $^{15}$O. The 2s$_{1/2}$ and 1d$_{5/2}$ single particle centroid energies are determined for the $^{15}$N$-^{15}$O mirror pair as: $^{15}$N $(\\text{2s}_{1/2}) = 8.08$ MeV, $^{15}$O $(\\text{2s}_{1/2}) = 7.43$ MeV, $^{15}$N $(\\text{1d}_{5/2}) = 7.97$ MeV, and $^{15}$O $(\\text{1d}_{5/2}) = 7.47$ MeV. These results confirm the degeneracy of these orbits and that the $^{15}$N$-^{15}$O nuclei are where the transition between the $\\text{2s}_{1/2}$ lying below the $\\text{1d}_{5/2}$ to lying above it, takes place. The $\\text{1d}_{3/2}$ single particle strength is estimated to be centered around 13 MeV in these nuclei.

C. E. Mertin; D. D. Caussyn; A. M. Crisp; N. Keeley; K. W. Kemper; O. Momtyuk; B. T. Roeder; A. Volya

2014-07-15

316

Isotopic profiling of seized benzylpiperazine and trifluoromethylphenylpiperazine tablets using ?(13)C and ?(15)N stable isotopes.  

PubMed

This paper demonstrates the use of isotopic analysis of 23 benzylpiperazine (BZP) and trifluoromethylphenylpiperazine (TFMPP) containing tablets seized on two independent occasions by the Northern Territory (NT) Police, Australia. Isolation (High Performance Liquid Chromatography (HPLC)) of BZP and TFMPP followed by Isotope Ratio Mass Spectrometry (IRMS) (carbon and nitrogen stable isotopes) analysis was performed. Results are presented for ?(13)C and ?(15)N values of the respective piperazine analogues. The isotopic data and statistical analysis suggest a common source of manufacture for the BZP samples but suggest different sources for the TFMPP isolated from the corresponding BZP containing tablets investigated. The use of IRMS in this case study demonstrated the ability to obtain information regarding the BZP/TFMPP sources unattainable via conventional chemical analysis. PMID:25577007

Beckett, Nicola M; Cresswell, Sarah L; Grice, Darren I; Carter, James F

2015-01-01

317

/sup 15/N and /sup 13/C NMR determination of methionine metabolism in developing soybean cotyledons  

SciTech Connect

The metabolism of D- and L-methionine by immature cotyledons of soybean (Glycine max, L. cv Elf) grown in culture has been investigated using solid-state /sup 13/C and /sup 15/N nuclear magnetic resonance. D-Methionine is taken up by the cotyledons and converted to an amide, most likely by N-malonylation. About 16% of the L-methionine taken up is incorporated intact into protein, and 25% remains as soluble methionine. Almost two-thirds of the L-methionine that enters the cotyledons is degraded. The largest percentage of this is used in transmethylation of the carboxyl groups of pectin. Methionine is not extensively converted to polyamines. The authors attribute the stimulation of growth of the cotyledons by exogenous methionine to the bypassing of a rate-limiting methyl-transfer step in the synthesis of methionine itself, and subsequently of pectins and proteins.

Coker, G.T. III; Garbow, J.R.; Schaefer, J.

1987-03-01

318

Experimental and calculated 1H, 13C, 15N NMR spectra of famotidine  

NASA Astrophysics Data System (ADS)

Famotidine, 3-[[[2-[(aminoiminomethyl)amino]-4-thiazolyl]methyl]thio]- N-(aminosulfonyl), is a histamine H 2-receptor blocker that has been used mainly for the treatment of peptic ulcers and the Zollinger-Ellison syndrome. Its NMR spectra in different solvents were reported earlier; however, detailed interpretation has not been done thus far. In this work, experimental 1H, 13C and 15N NMR spectra of famotidine dissolved in DMSO-d 6 are shown. The assignment of observed chemical shifts is based on quantum chemical calculation at the Hartree-Fock/6-31G ? level. The geometry optimization of the famotidine molecule with two internal hydrogen bonds, i.e. [N(3)-H(23)⋯N(9) and N(3)⋯H(34)-N(20)], is done by using the B3LYP method with the 6-31G ? basis set.

Bara?ska, M.; Czarniecki, K.; Proniewicz, L. M.

2001-05-01

319

Changes in biomass and ? 15N of nitrate and PON during a mesoscale iron fertilization experiment in the Southern Ocean  

NASA Astrophysics Data System (ADS)

Deep-sea sedimentary ? 15N has been used to estimate past changes in relative nutrient drawdown in Fe-limited, high-nitrate, low-chlorophyll regions. In many settings, corroboration between surface-water ? 15N systematics and modern sedimentary ? 15N exists. In the Southern Ocean, in particular, sedimentary ? 15N has been used to infer greater nutrient drawdown and hence less CO2 degassing to the atmosphere during glacial periods. While the relationship between nutrient drawdown and ? 15N of sinking particles is robust with a fairly consistent fractionation factor for nitrate uptake, release from Fe-stress may produce modifications either through changes in species composition and/or phytoplankton physiological state. The Southern Ocean Fe Experiment (SOFeX), provided an opportunity to study the influence of Fe-enhanced phytoplankton growth on nitrogen isotope biogeochemistry and its relationship with nutrient drawdown. Changes in ? 15N of nitrate, ? 15N of PON and POM concentration were tracked during a mesoscale Fe fertilization (66 oS 172 oW) south of the Antarctic Polar Front, where nitrate (>20 ?M) and silicic acid (>60 ?M) concentrations were high, but initial chlorophyll concentrations low (<0.2 ?g L-1). In and out of the fertilized patch, nitrate concentrations decreased by 2 ?M or more over an 18 day period. Accompanying this NO3- drawdown was an increase in POM of about 2 ?M N and 10 ?M C in the fertilized region, but negligible POM changes out of the patch. Consistent with fractionation kinetics, ? 15N of both NO3- and PON increased by approximately 1%0, while out of the patch little or no changes in ? 15N of NO3- and PON were observed. The difference in biomass response during nutrient drawdown in and out of the patch was likely caused by the growth of large diatoms within the patch. The isotope data support interpretations that downcore changes in ? 15N in the Southern Ocean result from variations in nitrate drawdown. The observed influence of iron addition to fractionation kinetics will be discussed.

Timothy, D. A.; Altabet, M. A.; McIlvin, M.; Feng, P.

2002-12-01

320

Line Lists for the A 2?-X 2?+ (Red) and B 2?+-X 2?+ (Violet) Systems of CN, 13C14N, and 12C15N, and Application to Astronomical Spectra  

NASA Astrophysics Data System (ADS)

New red and violet system line lists for the CN isotopologues 13C14N and 12C15N have been generated. These new transition data are combined with those previously derived for 12C14N, and applied to the determination of CNO abundances in the solar photosphere and in four red giant stars: Arcturus, the bright, very low-metallicity star HD 122563, and the carbon-enhanced metal-poor stars HD 196944 and HD 201626. When both red and violet system lines are detectable in a star, their derived N abundances are in good agreement. The mean N abundances determined in this work are also generally in accord with published values.

Sneden, Christopher; Lucatello, Sara; Ram, Ram S.; Brooke, James S. A.; Bernath, Peter

2014-10-01

321

Studying ancient crop provenance: implications from ?(13)C and ?(15)N values of charred barley in a Middle Bronze Age silo at Ebla(NW Syria).  

PubMed

The discovery of a storeroom full of barley and other cereals (L.9512) in the proto-historic site of Ebla has provided a unique opportunity to study the centralized storage system of the early city-state from a different perspective. Epigraphic evidence available within the site reveals a complex system of taxation which included gathering grain tributes from satellite sites and redistributing semi-finished products such as flour. In this paper, we intend to explore the possibilities of a combined approach to studying the storage system, based on estimated barley grain volumes and ?(13)C-?(15)N analyses. This approach is used to distinguish between grain from different harvesting sites and to identify any grain cultivated using special agricultural practices (e.g. manuring or irrigation). The basic assumption for this kind of analysis is that the growth-site conditions, natural or anthropogenic, of harvested cereals are reflected in their grain size and ?(13)C-?(15)N values. Since the remains found in the storeroom were charred, the first task was to evaluate the effect of carbonization on the ?(13)C-?(15)N and the size of the grains. Thus, the effect of charring was tested on modern samples of Syrian barley landraces. Once it had been ascertained that fresh grains reduced to charred remains retain their original biometric and isotopic traits, the ancient material was examined. Thirteen groups were identified, each characterized by a specific average volume and specific carbon and nitrogen values. The analysis revealed that what had first appeared to be a homogeneous concentration of grain was in fact an assemblage of barley harvested from different sites. PMID:22223320

Fiorentino, Girolamo; Caracuta, Valentina; Casiello, Grazia; Longobardi, Francesco; Sacco, Antonio

2012-02-15

322

An isotopic (?14C, ?13C, and ?15N) investigation of particulate organic matter and zooplankton biomass in Lake Superior and across a size-gradient of aquatic systems  

NASA Astrophysics Data System (ADS)

Food webs in aquatic systems can be supported both by carbon from recent local primary productivity and by carbon subsidies, such as material from terrestrial ecosystems or past in situ primary productivity. The importance of these subsidies to respiration and biomass production remains a topic of debate, but they may play major roles in determining the fate of organic carbon and in sustaining upper trophic levels, including those contributing to economically important fisheries. While some studies have reported that terrigenous organic carbon supports disproportionately high zooplankton production, others have suggested that phytoplankton preferentially supports zooplankton production in aquatic ecosystems. Here we apply natural abundance radiocarbon (?14C) and stable isotope (?13C, ?15N) analyses to show that zooplankton in Lake Superior selectively incorporate recently-fixed, locally-produced (autochthonous) organic carbon even though other carbon sources are readily available. Estimates from Bayesian isotopic modeling based on ?14C values show that the average lakewide median contributions of recent in situ algal, terrestrial, sedimentary, and bacterial organic carbon to the bulk POM in Lake Superior were 23%, 28%, 15%, and 25%, respectively. However, the isotopic modeling estimates show that recent in situ production (algae) contributed a disproportionately large amount (median, 40-89%) of the carbon in zooplankton biomass in Lake Superior. Although terrigenous organic carbon and old organic carbon from resuspended sediments were significant portions of the available basal food resources, these contributed only a small amount to zooplankton biomass (average lakewide median, 2% from sedimentary organic carbon and 9% from terrigenous organic carbon). Comparison of zooplankton food sources based on their radiocarbon composition showed that terrigenous organic carbon was relatively more important in rivers and small lakes, and the proportion of terrestrially-derived material used by zooplankton correlated with the hydrologic residence time and the ratio of basin area to water surface area.

Zigah, P. K.; Minor, E. C.; Werne, J. P.; McCallister, S. Leigh

2012-04-01

323

An isotopic (?14C, ?13C, and ?15N) investigation of the composition of particulate organic matter and zooplankton food sources in Lake Superior and across a size-gradient of aquatic systems  

NASA Astrophysics Data System (ADS)

Food webs in aquatic systems can be supported both by carbon from recent local primary productivity and by carbon subsidies, such as material from terrestrial ecosystems, or past in situ primary productivity. The importance of these subsidies to respiration and biomass production remains a topic of debate. While some studies have reported that terrigenous organic carbon supports disproportionately high zooplankton production, others have suggested that phytoplankton preferentially support zooplankton production in aquatic ecosystems. Here we apply natural abundance radiocarbon (?14C) and stable isotope (?13C, ?15N) analyses to show that zooplankton in Lake Superior selectively incorporate recently fixed, locally produced (autochthonous) organic carbon even though other carbon sources are readily available. Estimates from Bayesian isotopic modeling based on ?14C and ?13C values show that the average lake-wide median contributions of recent in-lake primary production and terrestrial, sedimentary, and bacterial organic carbon to the bulk POM in Lake Superior were 58%, 5%, 33%, and 3%, respectively. However, isotopic modeling estimates also show that recent in situ production contributed a disproportionately large amount (median, 91%) of the carbon in mesozooplankton biomass in Lake Superior. Although terrigenous organic carbon and old organic carbon from resuspended sediments were significant portions (median, 38%) of the available basal food resources, these contributed only a small amount to mesozooplankton biomass. Comparison of zooplankton food sources based on their radiocarbon composition showed that terrigenous organic carbon was relatively more important in rivers and small lakes, and the proportion of terrestrially derived material used by zooplankton correlated with the hydrologic residence time and the ratio of basin area to water surface area.

Zigah, P. K.; Minor, E. C.; Werne, J. P.; McCallister, S. Leigh

2012-09-01

324

sup 15 N NMR study on cyanide (C sup 15 N sup minus ) complex of cytochrome P-450 sub cam. Effects of d-camphor and putidaredoxin on the iron-ligand structure  

SciTech Connect

The cyanide (C{sup 15}N{sup {minus}}) complex of Pseudomonas putida cytochrome P-450 (P-450{sub cam}) exhibited well-resolved and hyperfine-shifted {sup 15}N NMR resonances arising from the iron-bound C{sup 15}N{sup {minus}} at 423 and 500 ppm in the absence and presence of the substrate, d-camphor, respectively. The values were smaller than those for cyanide complexes of myoglobin and hemoglobin ({approx} 1000 ppm) but fell into the same range as those for the cyanide complexes of peroxidases ({approx} 500 ppm). The {sup 15}N shift values of P-450{sub cam} were not incompatible with the existence of anionic ligand, such as cysteinyl thiolate anion, at the fifth coordination site of heme iron. The difference in the {sup 15}N chemical shift values between camphor-free and bound enzymes was inferred by the increase in the steric constraint to the Fe-C-N bond upon substrate binding.

Shiro, Yoshitsugu; Iizuka, Tetsutaro (Institute of Physical and Chemical Research, Saitama (Japan)); Makino, Ryu; Ishimura, Yuzuru (Keio Univ., Tokyo (Japan)); Morishima, Isao (Kyoto Univ. (Japan))

1989-11-27

325

Stable Carbon and Nitrogen isoscapes of the California Coast: integrated ?15N and ?13C of suspended particulate organic matter inferred from tissues of the California Mussel (mytilus californianus)  

NASA Astrophysics Data System (ADS)

Spatial maps of isotopic variability in a single species, or isoscapes, can characterize the natural variability in carbon (C) and nitrogen (N) isotope ratios across ecosystems on broad spatial scales, trace the signature of a source across a given area, as well as constrain animal migration patterns (Graham et al. 2002). In this study, isoscapes of stable carbon (13C) and nitrogen (15N) isotopes were constructed using intertidal mussels for northeast Pacific coastal waters of California. In this region biogeochemical cycling is primarily controlled by upwelling intensity and large-scale transport of the California Current System (CCS). We hypothesize that sampling specific tissues of filter-feeding organisms can provide an integrated measure of variation in 15N and 13C of the suspended particulate organic matter (POM) pool vs. latitude within the CCS, as well indicate main sources of both organic C and N to littoral food webs. California mussels (mytilus californianus) were collected from 28 sites between Coos Bay, OR and La Jolla, CA in the winter of 2009-2010 and summer of 2011, and adductor tissue was analyzed for ?13C and ?15N. Mussel size classes were chosen to provide ~ 1 yr integrated signal. Spatial trends in ?15N from the winter sampling show a strong linear trend in increasing ?15N values with latitude north to south (?15N values range from 7 % to 12%) consistent with slowly attenuating northward transport of 15N-depleted nitrate via California Undercurrent (Altabet et al. 1999). The ?13C values have no strong north to south correlation, but exhibit strong location-specific variability. The ?13C values range between -13 % and -18%. We propose the site-specific signature of ?13C indicates relative source of primary productin to POM at a given region (i.e. kelp, phytoplankton, zooplankton). Overall, these results suggest that isoscapes for filter-feeding organisms may offer a more accurate integrated picture of 15N and 13C values of POM than is possible from sediment traps or discrete time sampling of POM. The average latitudinal trends we observe may also be useful in interpreting stable isotopic values of higher trophic animals in the CA current system. Keywords: isoscape, California Current, stable isotope, geographic variation

Vokhshoori, N. L.; McCarthy, M. D.

2011-12-01

326

A 15N-n.m.r. study of cerebral, hepatic and renal nitrogen metabolism in hyperammonaemic rats.  

PubMed Central

1. Rats were infused with 15NH4+ or L-[15N]alanine to induce hyperammonaemia, a potential cause of hepatic encephalopathy. HClO4 extracts of freeze-clamped brain, liver and kidney were analysed by 15N-n.m.r. spectroscopy in combination with biochemical assays to investigate the effects of hyperammonaemia on tissue concentrations of ammonia, glutamine, glutamate and urea. 2. 15NH4+ infusion resulted in a 36-fold increase in the concentration of blood ammonia. Cerebral glutamine concentration increased, with 15NH4+ incorporated predominantly into the gamma-nitrogen atom of glutamine. Incorporation into glutamate was very low. Cerebral ammonia concentration increased 5-10-fold. The results suggest that the capacity of glutamine synthetase for ammonia detoxification was saturated. 3. Pretreatment with the glutamine synthetase inhibitor L-methionine DL-sulphoximine resulted in 84% inhibition of [gamma-15N]glutamine synthesis, but incorporation of 15N into other metabolites was not observed. The result suggests that no major alternative pathway for ammonia detoxification, other than glutamine synthetase, exists in rat brain. 4. In the liver 15NH4+ was incorporated into urea, glutamine, glutamate and alanine. The specific activity of 15N was higher in the gamma-nitrogen atom of glutamine than in urea. A similar pattern was observed when [15N]alanine was infused. The results are discussed in terms of the near-equilibrium states of the reactions involved in glutamate and alanine formation, heterogeneous distribution in the liver lobules of the enzymes involved in ammonia removal and their different affinities for ammonia. 5. Synthesis of glutamine, glutamate and hippurate de novo was observed in kidney. Hippurate, as well as 15NH4+, was contributed by co-extracted urine. 6. The potential utility and limitations of 15N n.m.r. for studies of mammalian metabolism in vivo are discussed. PMID:1976007

Farrow, N A; Kanamori, K; Ross, B D; Parivar, F

1990-01-01

327

Spatial and Temporal Variations in Stable Carbon (?13C) and Nitrogen (?15N) Isotopic Composition of Symbiotic Scleractinian Corals  

PubMed Central

Tropical scleractinian corals are considered autotrophic as they rely mainly on photosynthesis-derived nutrients transferred from their photosymbionts. Corals are also able to capture and ingest suspended particulate organic matter, so heterotrophy can be an important supplementary trophic pathway to optimize coral fitness. The aim of this in situ study was to elucidate the trophic status of 10 coral species under contrasted environmental conditions in a French Polynesian lagoon. Carbon (?13C) and nitrogen (?15N) isotopic compositions of coral host tissues and photosymbionts were determined at 3 different fringing reefs during wet and dry seasons. Our results highlighted spatial variability in stable isotopic compositions of both coral host tissues and photosymbionts. Samples from the site with higher level of suspended particulate matter were 13C-depleted and 15N-enriched relative to corals and photosymbionts from less turbid sites. However, differences in both ?13C and ?15N between coral host tissues and their photosymbionts (?host-photosymbionts 13C and ?host-photosymbionts 15N) were small (0.27 ± 0.76‰ and 1.40 ± 0.90‰, respectively) and similar at all sites, thus indicating no general increases in the heterotrophic pathway. Depleted ?13C and enriched ?15N values of coral host tissues measured at the most turbid site were explained by changes in isotopic composition of the inorganic nutrients taken up by photosymbionts and also by changes in rate of isotopic fractionation with environmental conditions. Our results also highlighted a lack of significant temporal variations in ?13C and ?15N values of coral host and photosymbiont tissues and in ?host-photosymbionts 13C and ?host-photosymbionts 15N values. This temporal stability indicated that corals remained principally autotrophic even during the wet season when photosymbiont densities were lower and the concentrations of phytoplankton were higher. Increased coral heterotrophy with higher food availability thus appears to be species-specific. PMID:24312542

Nahon, Sarah; Richoux, Nicole B.; Kolasinski, Joanna; Desmalades, Martin; Ferrier Pages, Christine; Lecellier, Gael; Planes, Serge; Berteaux Lecellier, Véronique

2013-01-01

328

Plio-Pleistocene foraminifera-bound ?15N records of the Western Pacific and its global and regional implications  

NASA Astrophysics Data System (ADS)

The long term cooling trend, from the warm Pliocene period to the Pleistocene ice ages, was accompanied by decreasing atmospheric CO2. Temporal changes in the global inventory of fixed nitrogen (N), a critical nutrient for marine primary productivity, could have generated changes in the strength of the biological pump driving variations in atmospheric CO2. Two microbial processes, N2 fixation and denitrification, are the primary source and sink terms, respectively, that govern the inventory of marine fixed nitrogen. In the modern ocean, these flux terms have unique stable nitrogen isotopic (?15N)) signatures: the addition of nitrogen through N2 fixation produces fixed N of ca. ?15N = -1‰, removal of N through water-column denitrification fractionates the fixed N pool up to ca. ~15 - 25‰, and removal of N through sedimentary denitrification has small or zero isotope effect. Establishing widely distributed paleoceanographic records of sedimentary ?15N is a promising approach to quantify changes in the fixed N inventory through time. Existing sedimentary ?15N records of bulk organic matter (bulk ?15N) for the past 4 Ma are primarily from regions of high productivity, and are thus strongly influenced by denitrification, or incomplete nutrient utilization at the surface. To test the stability of the marine fixed N inventory during the Pliocene to Pleistocene transition, and determine the evolution of N2 fixation relative to existing records of denitrification, we produced two foraminifera-bound ?15N (FB-?15N) records for the last ~5 Ma in the western Pacific: one at site ODP 806 from the western equatorial Pacific, which is currently under the influence of water column denitrification through lateral transport of water from the Eastern tropical/subtropical Pacific, and the other one at site DSDP 451 from the oligotrophic North Pacific subtropical gyre, which has been observed to host high N2 fixation in the modern ocean. The FB-?15N record from site ODP 806 increases from ~5‰ to ~8‰ over the last 5 Ma, which may be due to an increase in the water column denitrification of the regional source waters to the site. The FB-?15N at DSDP 451 is stable at ~3‰, consistently lower than the present mean ocean nitrate ?15N, suggesting that 1) the region is a constant source of fixed N via N2 fixation for the last 5 Ma, and 2) the mean ocean nitrate ?15N is likely to have been relatively constant over this period of time. Our new FB-?15N records, together with the existing bulk ?15N record of the water column denitrification from the Eastern Pacific, demonstrate that a net loss of fixed N in regions of high-productivity, possibly through increases in water-column denitrification, was internally stabilized by net gains of fixed N in regions of N2 fixation.

Batista, F. C.; Ren, H. A.; Ravelo, A. C.

2012-12-01

329

Probing site-specific 13C/15N-isotope enrichment of spider silk with liquid-state NMR spectroscopy.  

PubMed

Solid-state nuclear magnetic resonance (NMR) has been extensively used to elucidate spider silk protein structure and dynamics. In many of these studies, site-specific isotope enrichment is critical for designing particular NMR methods for silk structure determination. The commonly used isotope analysis techniques, isotope-ratio mass spectroscopy and liquid/gas chromatography-mass spectroscopy, are typically not capable of providing the site-specific isotope information for many systems because an appropriate sample derivatization method is not available. In contrast, NMR does not require any sample derivatization or separation prior to analysis. In this article, conventional liquid-state (1)H NMR was implemented to evaluate incorporation of (13)C/(15)N-labeled amino acids in hydrolyzed spider dragline silk. To determine site-specific (13)C and (15)N isotope enrichments, an analysis method was developed to fit the (1)H-(13)C and (1)H-(15)N J-splitting (J CH and J NH) (1)H NMR peak patterns of hydrolyzed silk fiber. This is demonstrated for Nephila clavipes spiders, where [U-(13)C3,(15)N]-Ala and [1-(13)C,(15)N]-Gly were dissolved in their water supplies. Overall, contents for Ala and Gly isotopomers are extracted for these silk samples. The current methodology can be applied to many fields where site-specific tracking of isotopes is of interest. PMID:23435452

Shi, Xiangyan; Yarger, Jeffery L; Holland, Gregory P

2013-05-01

330

High Resolution 13C MRI With Hyperpolarized Urea: In Vivo T2 Mapping and 15N Labeling Effects  

PubMed Central

13C steady state free precession (SSFP) magnetic resonance imaging and effective spin-spin relaxation time (T2) mapping were performed using hyperpolarized [13C] urea and [13C, 15N2] urea injected intravenously in rats. 15N labeling gave large T2 increases both in solution and in vivo due to the elimination of a strong scalar relaxation pathway. The T2 increase was pronounced in the kidney, with [13C, 15N2] urea giving T2 values of 6.3±1.3 s in the cortex and medulla, and 11±2 s in the renal pelvis. The measured T2 in the aorta was 1.3±0.3 s. [13C] urea showed shortened T2 values in the kidney of 0.23±0.03 s compared to 0.28±0.03 s measured in the aorta. The enhanced T2 of [13C, 15N2] urea was utilized to generate large signal enhancement by SSFP acquisitions with flip angles approaching the fully refocused regime. Projection images at 0.94 mm in-plane resolution were acquired with both urea isotopes, with [13C, 15N2] urea giving a greater than four-fold increase in signal-to-noise ratio [13C] over urea. PMID:24235273

Reed, Galen D.; von Morze, Cornelius; Bok, Robert; Koelsch, Bertram L.; Van Criekinge, Mark; Smith, Kenneth J.; Shang, Hong; Larson, Peder E. Z.; Kurhanewicz, John; Vigneron, Daniel B.

2014-01-01

331

Exploring the Nitrogen Ingestion of Aphids — A New Method Using Electrical Penetration Graph and 15N Labelling  

PubMed Central

Studying plant-aphid interactions is challenging as aphid feeding is a complex process hidden in the plant tissue. Here we propose a combination of two well established methods to study nutrient acquisition by aphids focusing on the uptake of isotopically labelled nitrogen (15N). We combined the Electrical Penetration Graph (EPG) technique that allows detailed recording of aphid feeding behaviour and stable isotope ratio mass spectrometry (IRMS) to precisely measure the uptake of nitrogen. Bird cherry-oat aphids Rhopalosiphum padi L. (Hemiptera, Aphididae) fed for 24 h on barley plants (Hordeum vulgare L., cultivar Lina, Poaceae) that were cultivated with a 15N enriched nutrient solution. The time aphids fed in the phloem was strongly positive correlated with their 15N uptake. All other single behavioural phases were not correlated with 15N enrichment in the aphids, which corroborates their classification as non-feeding EPG phases. In addition, phloem-feeding and 15N enrichment of aphids was divided into two groups. One group spent only short time in the phloem phase and was unsuccessful in nitrogen acquisition, while the other group displayed longer phloem-feeding phases and was successful in nitrogen acquisition. This suggests that several factors such as the right feeding site, time span of feeding and individual conditions play a role for the aphids to acquire nutrients successfully. The power of this combination of methods for studying plant-aphid interactions is discussed. PMID:24376642

Kuhlmann, Franziska; Opitz, Sebastian E. W.; Inselsbacher, Erich; Ganeteg, Ulrika; Näsholm, Torgny; Ninkovic, Velemir

2013-01-01

332

Oceanic ?15N biogeography: a novel top-down approach to examine nutrient dynamics in the equatorial Pacific Ocean  

NASA Astrophysics Data System (ADS)

By mapping the ?15N and ?13C values of three top-level pelagic predators, yellowfin (Thunnus albacares), bigeye (T. obesus), and skipjack (Katsuwonus pelamis) tuna throughout the equatorial Pacific Ocean, we demonstrated systematic geographic isotopic variation (up to ~12‰ for the ?15N values) that reflect nutrient dynamics that occur at the base of the food web. Remarkably the variation observed in the ?15N values of the tunas is geographically similar to ?15N values previously reported in surface particulate organic matter and deep-sea sediments in the tropical Pacific. We discuss the mechanisms occurring at the base of the food web that could produce the spatial variability observed in tropical tuna ?15N values. We present a simple Rayleigh fractionation model that can explain much of the spatial structure. We also discuss the temporal stability in the isotopic compositions at the base and top of the food web. Overall, this nitrogen isotope cartography or “isoscapes” suggests nitrogen is tightly retained in the marine food web, up to the top predators, and that the uptake of nitrate from the equatorial upwelling zone, denitrification in the oxygen minimum zones, and nitrogen fixation at the base of the food web play major roles in the observed geographical variation. In addition to providing insight into the nutrient dynamics of the open ocean, these predator isoscapes can begin to be used to characterize regional residency in tropical tunas, which is important for the successful management of tuna fisheries.

Graham, B. S.; Fry, B.; Popp, B. N.; Allain, V.; Olson, R.; Galvan, F.

2010-12-01

333

A closer look at the nitrogen next door: 1H-15N NMR methods for glycosaminoglycan structural characterization  

NASA Astrophysics Data System (ADS)

Recently, experimental conditions were presented for the detection of the N-sulfoglucosamine (GlcNS) NHSO3- or sulfamate 1H and 15N NMR resonances of the pharmaceutically and biologically important glycosaminoglycan (GAG) heparin in aqueous solution. In the present work, we explore further the applicability of nitrogen-bound proton detection to provide structural information for GAGs. Compared to the detection of 15N chemical shifts of aminosugars through long-range couplings using the IMPACT-HNMBC pulse sequence, the more sensitive two-dimensional 1H-15N HSQC-TOCSY experiments provided additional structural data. The IMPACT-HNMBC experiment remains a powerful tool as demonstrated by the spectrum measured for the unsubstituted amine of 3-O-sulfoglucosamine (GlcN(3S)), which cannot be observed with the 1H-15N HSQC-TOCSY experiment due to the fast exchange of the amino group protons with solvent. The 1H-15N HSQC-TOCSY NMR spectrum reported for the mixture of model compounds GlcNS and N-acetylglucosamine (GlcNAc) demonstrate the broad utility of this approach. Measurements for the synthetic pentasaccharide drug Arixtra® (Fondaparinux sodium) in aqueous solution illustrate the power of this NMR pulse sequence for structural characterization of highly similar N-sulfoglucosamine residues in GAG-derived oligosaccharides.

Langeslay, Derek J.; Beni, Szabolcs; Larive, Cynthia K.

2012-03-01

334

Range expansion of the jumbo squid in the NE Pacific: ?15N decrypts multiple origins, migration and habitat use.  

PubMed

Coincident with climate shifts and anthropogenic perturbations, the highly voracious jumbo squid Dosidicus gigas reached unprecedented northern latitudes along the NE Pacific margin post 1997-98. The physical or biological drivers of this expansion, as well as its ecological consequences remain unknown. Here, novel analysis from both bulk tissues and individual amino acids (Phenylalanine; Phe and Glutamic acid; Glu) in both gladii and muscle of D. gigas captured in the Northern California Current System (NCCS) documents for the first time multiple geographic origins and migration. Phe ?(15)N values, a proxy for habitat baseline ?(15)N values, confirm at least three different geographic origins that were initially detected by highly variable bulk ?(15)N values in gladii for squid at small sizes (<30 cm gladii length). In contrast, bulk ?(15)N values from gladii of large squid (>60 cm) converged, indicating feeding in a common ecosystem. The strong latitudinal gradient in Phe ?(15)N values from composite muscle samples further confirmed residency at a point in time for large squid in the NCCS. These results contrast with previous ideas, and indicate that small squid are highly migratory, move into the NCCS from two or more distinct geographic origins, and use this ecosystem mainly for feeding. These results represent the first direct information on the origins, immigration and habitat use of this key "invasive" predator in the NCCS, with wide implications for understanding both the mechanisms of periodic D. gigas population range expansions, and effects on ecosystem trophic structure. PMID:23527242

Ruiz-Cooley, Rocio I; Ballance, Lisa T; McCarthy, Matthew D

2013-01-01

335

Range Expansion of the Jumbo Squid in the NE Pacific: ?15N Decrypts Multiple Origins, Migration and Habitat Use  

PubMed Central

Coincident with climate shifts and anthropogenic perturbations, the highly voracious jumbo squid Dosidicus gigas reached unprecedented northern latitudes along the NE Pacific margin post 1997–98. The physical or biological drivers of this expansion, as well as its ecological consequences remain unknown. Here, novel analysis from both bulk tissues and individual amino acids (Phenylalanine; Phe and Glutamic acid; Glu) in both gladii and muscle of D. gigas captured in the Northern California Current System (NCCS) documents for the first time multiple geographic origins and migration. Phe ?15N values, a proxy for habitat baseline ?15N values, confirm at least three different geographic origins that were initially detected by highly variable bulk ?15N values in gladii for squid at small sizes (<30 cm gladii length). In contrast, bulk ?15N values from gladii of large squid (>60 cm) converged, indicating feeding in a common ecosystem. The strong latitudinal gradient in Phe ?15N values from composite muscle samples further confirmed residency at a point in time for large squid in the NCCS. These results contrast with previous ideas, and indicate that small squid are highly migratory, move into the NCCS from two or more distinct geographic origins, and use this ecosystem mainly for feeding. These results represent the first direct information on the origins, immigration and habitat use of this key “invasive” predator in the NCCS, with wide implications for understanding both the mechanisms of periodic D. gigas population range expansions, and effects on ecosystem trophic structure. PMID:23527242

Ruiz-Cooley, Rocio I.; Ballance, Lisa T.; McCarthy, Matthew D.

2013-01-01

336

Combined use of 15N and 18O of nitrate and 11B to evaluate nitrate contamination in groundwater  

USGS Publications Warehouse

Isotopic composition of NO3 (??15NNO3 and ??18ONO3) and B (??11B) were used to evaluate NO3 contamination and identify geochemical processes occurring in a hydrologically complex Basin and Range valley in northern Nevada with multiple potential sources of NO3. Combined use of these isotopes may be a useful tool in identifying NO3 sources because NO3 and B co-migrate in many environmental settings, their isotopes are fractionated by different environmental processes, and because wastewater and fertilizers may have distinct isotopic signatures for N and B. The principal cause of elevated NO3 concentrations in residential parts of the study area is wastewater and not natural NO3 or fertilizers. This is indicated by some samples with elevated NO3 concentrations plotting along ??15NNO3 and NO3 mixing lines between natural NO3 from the study area and theoretical septic-system effluent. This conclusion is supported by the presence of caffeine in one sample and the absence of samples with elevated NO3 concentrations that fall along mixing lines between natural NO3 and theoretical percolate below fertilized lawns. Nitrogen isotopes alone could not be used to determine NO3 sources in several wells because denitrification blurred the original isotopic signatures. The range of ??11B values in native ground water in the study area (-8.2??? to +21.2???) is large. The samples with the low ??11B values have a geochemical signature characteristic of hydrothermal systems. Physical and chemical data suggest B is not being strongly fractionated by adsorption onto clays. ??11B values from local STP effluent (-2.7???) and wash water from a domestic washing machine (-5.7???) were used to plot mixing lines between wastewater and native ground water. In general, wells with elevated NO3 concentrations fell along mixing lines between wastewater and background water on plots of ??11B against 1/B and Cl/B. Combined use of ??15N and ??11B in the study area was generally successful in identifying contaminant sources and processes that are occurring, however, it is likely to be more successful in simpler settings with a well-characterized ??11B value for background wells.

Seiler, R.L.

2005-01-01

337

Ammonia 15N/14N Isotope Ratio in the Jovian Atmosphere  

NASA Technical Reports Server (NTRS)

Data from the Galileo Probe Mass Spectrometer has been used to derive the N-15/N-14 isotope ratio in ammonia at Jupiter. Although the mass spectral interference from the water contribution to 18 amu makes an accurate derivation of the (N-15)H3/(N-14)H3 ratio difficult from measurements of the singly ionized signals at 18 and 17 amu, this interference is not present in the doubly charged 8.5 and 9.0 amu signals from (N-14)H3++ and (N-15)H3++ respectively. Although the count rate from the 9 amu signal is low during the direct sampling of the atmosphere, the ammonia signal was considerably enhanced during the first enrichment cell (EC1) experiment that measured gas sampled between 0.8 and 2.8 bar. Count rates at 9 amu in the EC1 experiment reach 60/second and measure ammonia sampled from 0.88 to 2.8 bar. In the EC1 measurements the 8.5 amu signal is not measured directly, but can be calculated from the ammonia contribution to 17 amu and the ratio of NH3 ions of a double to single charged observed during a high resolution mass scan taken near the end of the descent. The high resolution scan gives this ratio from ammonia sampled much deeper in the atmosphere. These results are described and compared with Infrared Space Observatory-Short Wavelength Spectrometer (ISO-SWS) observations that give this ratio at 400 mbar.

Mahaffy, P.R.; Niemann, H. B.; Atreya, S. K.; Wong, M. H.; Owen, T. C; Einaudi, Franco (Technical Monitor)

2000-01-01

338

Tracking the incorporation of 15N from labeled beech litter into mineral-organic associations  

NASA Astrophysics Data System (ADS)

Nitrogen containing organic compounds are thought to have a role in the complex web of processes that control the turnover time of soil organic matter. The sequential density fractionation technique is increasingly used for the purpose of investigating the association of organic materials with the mineral matrix. Organic materials in the denser fractions (>2.0 kg L-1) typically show 13C NMR signals indicative of carbohydrate and aliphatic structures, an absence of lignin and tannin structures and a narrow C:N ratio, suggesting a microbial origin of organic matter in these fractions. Here we take advantage of a labeling experiment conducted at two different sites in Germany and in France to investigate the incorporation of organic nitrogen into physical fractions of increasing density, representing a proximity gradient to mineral surfaces. 15N labeled beech litter was applied to two acidic forest topsoils 8 and 12 years ago. Although there are differences in the distribution patterns between the two soils, and the majority of the organic nitrogen was recovered in fractions representing organic matter of plant origin and not bound to the mineral matrix, our data clearly show that after a decade, significant amounts of the nitrogen had been incorporated in mineral-organic fractions of supposedly slow turnover. It remains to be shown to which extent the N in the densest fractions was incorporated by soil microbiota and associated with mineral surfaces in organic form or adsorbed to mineral surfaces in inorganic form (NH4+).

Kleber, M.; Hatton, P.; Derrien, D.; Lajtha, K.; Zeller, B.

2008-12-01

339

Amino acid composition and ?15N of suspended matter in the Arabian Sea  

NASA Astrophysics Data System (ADS)

Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that sink rapidly through the water column. These particles sampled by sediment traps have often been proposed to interact by disaggregation and scavenging with a pool of fine suspended matter with very slow sinking velocities and thus a long residence time. We investigated the amino acid composition and stable nitrogen isotopic ratios of suspended matter sampled during the late SW monsoon season in the Arabian Sea and compared them to those of sinking particles to investigate organic matter degradation/modification during passage through the water column. We found that amino acid (AA) composition of mixed layer suspended matter corresponds more to fresh plankton and their aggregates, whereas AA composition of suspended matter in the sub-thermocline water column deviated progressively from mixed layer composition. We conclude that suspended matter in deep waters and in the mixed layers of oligotrophic stations is dominated by fine material that has a long residence time and organic matter that is resistant to degradation. Whereas SPM in areas of high primary productivity is essentially derived from fresh plankton and thus has a strong imprint of the subsurface nitrate source, SPM at oligotrophic stations and at subthermocline depths appears to exchange amino acids with the DOC pool influencing also the ?15N values.

Gaye, B.; Nagel, B.; Dähnke, K.; Rixen, T.; Lahajnar, N.; Emeis, K.-C.

2013-08-01

340

Robust Abundance Estimation in Animal Abundance Surveys with Imperfect Detection  

EPA Science Inventory

Surveys of animal abundance are central to the conservation and management of living natural resources. However, detection uncertainty complicates the sampling process of many species. One sampling method employed to deal with this problem is depletion (or removal) surveys in whi...

341

Cytochrome-P450-Cytochrome-b5 Interaction in a Membrane Environment Changes 15N Chemical Shift Anisotropy Tensors  

PubMed Central

It has been well realized that the dependence of chemical shift anisotropy (CSA) tensors on the amino acid sequence, secondary structure, dynamics and electrostatic interactions can be utilized in the structural and dynamic studies of proteins by NMR spectroscopy. In addition, CSA tensors could also be utilized to measure the structural interactions between proteins in a protein-protein complex. To this end, here we report the experimentally measured backbone amide-15N CSA tensors for a membrane-bound 16.7-kDa full-length rabbit cytochrome-b5 (cytb5), in complexation with a 55.8-kDa microsomal rabbit cytochrome P450 2B4 (cytP4502B4). The 15N-CSAs, determined using the 15N CSA/15N-1H dipolar coupling transverse cross-correlated rates, for free cytb5 are compared with that for the cytb5 bound to cytP4502B4. An overall increase in backbone amide-15N transverse cross-correlated rates for the cytb5 residues in the cytb5-cytP450 complex was observed as compared to the free cytb5 residues. Due to fast spin-spin relaxation (T2) and subsequent broadening of the signals in the complex, we were able to measure amide-15N CSAs only for 48 residues of cytb5 as compared to 84 residues of free cytb5. We observed a change in 15N CSA for most residues of cytb5 in the complex, when compared to free cytb5, suggesting a dynamic interaction between the oppositely charged surfaces of anionic cytb5 and cationic cytP450. The mean values of 15N CSA determined for residues in helical, sheet and turn regions of cytb5 in the complex are ?184.5, ?146.8, and ?146.2 ppm, respectively, with an overall average value of ?165.5 ppm (excluding the values from residues in more flexible termini). The measured CSA value for residues in helical conformation is slightly larger as compared to previously reported values. This may be attributed to the paramagnetic effect from Fe(III) of the heme in cytb5, which is similar to our previously reported values for the free cytb5. PMID:24107224

Pandey, Manoj Kumar; Vivekanandan, Subramanian; Ahuja, Shivani; Huang, Rui; Im, Sang-Choul; Waskell, Lucy; Ramamoorthy, Ayyalusamy

2013-01-01

342

Acetylene reduction, H 2 evolution and 15 N 2 fixation in the Alnus incana-Frankia symbiosis  

Microsoft Academic Search

Acetylene reduction, 15N2 reduction and H2 evolution were measured in root systems of intact plants of grey alder (Alnus incana (L.) Moench) in symbiosis with Frankia. The ratios of C2H2: 15N2 were compared with C2H2:N2 ratios calculated from C2H2 reduction and H2 evolution, and with C2H2:N2 ratios calculated from accumulated C2H4 production and nitrogen content. It was possible to calculate

A. Sellstedt

1986-01-01

343

Source and transport of terrigenous organic matter in the upper Yukon River: Evidence from isotope (?13C, ?14C, and ?15N) composition of dissolved, colloidal, and particulate phases  

Microsoft Academic Search

Natural organic matter was collected from the upper Yukon River and size fractionated into the 0.45 ?m) phases for characterization of elemental (C and N) and isotopic (13C, 14C and 15N) composition to examine their sources and transport. Concentrations of total organic carbon (TOC) decreased from 3010 ?M in mid-May to 608 ?M in September, accompanying an increase in river

Laodong Guo; Robie W. Macdonald

2006-01-01

344

Mean lifetimes and equilibrium abundances in the fast CN cycle.  

NASA Technical Reports Server (NTRS)

It is shown that the production of small nitrogen to carbon ratios is possible, in contrast to the equilibrium production in the ordinary CN cycle. Associated with such a production are high ratios of C-13/C-12 and of N-15/N-14. The final ratios depend on the conditions under which cessation of hydrogen burning occurs under astrophysical circumstances. A table showing proton capture mean lifetimes of CN nuclei is provided together with tables of the equilibrium abundances in a fast CN cycle. The ratios of final abundances of nitrogen to carbon as functions of temperature are also presented.

Caughlan, G. R.; Fowler, W. A.

1972-01-01

345

Nitrate removal in stream ecosystems measured by 15N addition experiments: 2. Denitrification  

SciTech Connect

We measured denitrification rates using a field {sup 15}N-NO{sub 3}{sup -} tracer-addition approach in a large, cross-site study of nitrate uptake in reference, agricultural, and suburban-urban streams. We measured denitrification rates in 49 of 72 streams studied. Uptake length due to denitrification (S{sub Wden}) ranged from 89 m to 184 km (median of 9050 m) and there were no significant differences among regions or land-use categories, likely because of the wide range of conditions within each region and land use. N{sub 2} production rates far exceeded N{sub 2}O production rates in all streams. The fraction of total NO{sub 3}{sup -} removal from water due to denitrification ranged from 0.5% to 100% among streams (median of 16%), and was related to NH{sub 4}{sup +} concentration and ecosystem respiration rate (ER). Multivariate approaches showed that the most important factors controlling S{sub Wden} were specific discharge (discharge/width) and NO{sub 3}{sup -} concentration (positive effects), and ER and transient storage zones (negative effects). The relationship between areal denitrification rate (U{sub den}) and NO{sub 3}{sup -} concentration indicated a partial saturation effect. A power function with an exponent of 0.5 described this relationship better than a Michaelis-Menten equation. Although U{sub den} increased with increasing NO{sub 3}{sup -} concentration, the efficiency of NO{sub 3}{sup -} removal from water via denitrification declined, resulting in a smaller proportion of streamwater NO{sub 3}{sup -} load removed over a given length of stream. Regional differences in stream denitrification rates were small relative to the proximate factors of NO{sub 3}{sup -} concentration and ecosystem respiration rate, and land use was an important but indirect control on denitrification in streams, primarily via its effect on NO{sub 3}{sup -} concentration.

Mulholland, Patrick J [ORNL; Hall, Robert [University of Wyoming, Laramie; Sobota, Daniel [Oregon State University; Dodds, Walter [Kansas State University; Findlay, Stuart [Institute of Ecosystem Studies; Grimm, Nancy [Arizona State University; Hamilton, Stephen [Michigan State University, East Lansing; McDowell, William [University of Hew Hampshire; O'Brien, Jon [Michigan State University, East Lansing; Tank, Jennifer [University of Notre Dame, IN; Ashkenas, Linda [Oregon State University, Corvallis; Cooper, Lee W [ORNL; Dahm, Cliff [University of New Mexico, Albuquerque; Gregory, Stanley [Oregon State University, Corvallis; Johnson, Sherri [Oregon State University; Meyer, Judy [University of Georgia, Athens, GA; Peterson, Bruce [Marine Biological Laboratory; Poole, Geoff [Eco-metrics; Valett, H. Maurice [Virginia Polytechnic Institute and State University (Virginia Tech); Webster, Jackson [Virginia Polytechnic Institute and State University (Virginia Tech); Arango, Clay [University of Notre Dame, IN; Beaulieu, Jake [University of Notre Dame, IN; Bernot, Melody [Murray State University; Burgin, Amy [Michigan State University, East Lansing; Crenshaw, Chelsea [University of New Mexico, Albuquerque; Helton, Ashley [University of Georgia, Athens, GA; Johnson, Laura [University of Notre Dame, IN; Niederlehner, Bobbie [Virginia Polytechnic Institute and State University (Virginia Tech); Potter, Jody [University of New Hampshire; Sheibley, Rich [Arizona State University; Thomas, Suzanne [Marine Biological Laboratory

2009-01-01

346

Nitrate removal in stream ecosystems measured by 15N addition experiments: Denitrification  

USGS Publications Warehouse

We measured denitrification rates using a field 15N-NO- 3 tracer-addition approach in a large, cross-site study of nitrate uptake in reference, agricultural, and suburban-urban streams. We measured denitrification rates in 49 of 72 streams studied. Uptake length due to denitrification (SWden) ranged from 89 m to 184 km (median of 9050 m) and there were no significant differences among regions or land-use categories, likely because of the wide range of conditions within each region and land use. N2 production rates far exceeded N2O production rates in all streams. The fraction of total NO-3 removal from water due to denitrification ranged from 0.5% to 100% among streams (median of 16%), and was related to NHz 4 concentration and ecosystem respiration rate (ER). Multivariate approaches showed that the most important factors controlling SWden were specific discharge (discharge / width) and NO-3 concentration (positive effects), and ER and transient storage zones (negative effects). The relationship between areal denitrification rate (Uden) and NO- 3 concentration indicated a partial saturation effect. A power function with an exponent of 0.5 described this relationship better than a Michaelis-Menten equation. Although Uden increased with increasing NO- 3 concentration, the efficiency of NO-3 removal from water via denitrification declined, resulting in a smaller proportion of streamwater NO-3 load removed over a given length of stream. Regional differences in stream denitrification rates were small relative to the proximate factors of NO-3 concentration and ecosystem respiration rate, and land use was an important but indirect control on denitrification in streams, primarily via its effect on NO-3 concentration. ?? 2009.

Mulholland, P.J.; Hall, R.O., Jr.; Sobota, D.J.; Dodds, W.K.; Findlay, S.E.G.; Grimm, N. B.; Hamilton, S.K.; McDowell, W.H.; O'Brien, J. M.; Tank, J.L.; Ashkenas, L.R.; Cooper, L.W.; Dahm, C. N.; Gregory, S.V.; Johnson, S.L.; Meyer, J.L.; Peterson, B.J.; Poole, G.C.; Valett, H.M.; Webster, J.R.; Arango, C.P.; Beaulieu, J.J.; Bernot, M.J.; Burgin, A.J.; Crenshaw, C.L.; Helton, A.M.; Johnson, L.T.; Niederlehner, B.R.; Potter, J.D.; Sheibley, R.W.; Thomasn, S.M.

2009-01-01

347

The studies of tautomerism in 6-mercaptopurine derivatives by 1H- 13C, 1H- 15N NMR and 13C, 15N CPMAS-experimental and quantum chemical approach  

NASA Astrophysics Data System (ADS)

Tautomerism in 6-mercaptopurine (6mpH), 2,6-dimercaptopurine (2,6dmp) and 6-mercaptopurine-9-riboside (6mp-9rb) was studied in the solution with 2D NMR methods- 1H- 13C HMBC and 1H- 15N HMQC. The 15N NMR signals were assigned and the distribution of mobile protons proposed on the basis of ?13C, ?15N chemical shifts and JHC, JHN coupling constants, determined with HECADE. These heterocycles appear in DMSO- d6 as the thionic species with predominance of the following tautomers: N(1)H, N(7)H for 6mpH; N(1)H, N(3)H, N(7)H for 2,6dmp; N(1)H for 6mp-9rb. Quantum-chemical NMR calculations by GIAO method(RHF/6-31G**//B3LYP/6-31G**) allowed to evaluate the ratios of N(7)H, N(9): N(7), N(9)H tautomeric forms as ca. 3:1 for 6mpH and nearly 10:0 for 2,6dmp. The 13C and 15N CPMAS spectra were measured for solid 6mpH·H 2O, anhydrous 6mpH, 2,6dmp and 6-mercaptopurinium chloride (6mpH 2Cl), confirming the thionic character of all compounds. The 15N chemical shifts in the solid phase were calculated (B3LYP/6-31G**) for 6mpH·H 2O and 6mpH 2Cl, basing on the re-determined single crystal X-ray data (optimised with RHF/3-21G**).

Pazderski, Leszek; ?akomska, Iwona; Wojtczak, Andrzej; Sz?yk, Edward; Sitkowski, Jerzy; Kozerski, Lech; Kamie?ski, Bohdan; Ko?mi?ski, Wiktor; Tousek, Jaromír; Marek, Radek

2006-03-01

348

Abundance, Natural Infection with Trypanosomes, and Food Source of an Endemic Species of Triatomine, Panstrongylus howardi (Neiva 1911), on the Ecuadorian Central Coast.  

PubMed

The elimination of domestic triatomines is the foundation of Chagas disease control. Regional initiatives are eliminating introduced triatomine species. In this scenario, endemic triatomines can occupy the ecological niches left open and become a threat to long-term Chagas disease control efforts. This study determined the abundance, colonization, and Trypanosoma cruzi infection rate of the endemic Panstrongylus howardi in 10 rural communities located in Ecuador's Manabí Province. In total, 518 individuals of P. howardi were collected. Infestation indices of 1.4% and 6.6% were found in the domestic and peridomestic environments, respectively. We determined a T. cruzi infection rate of 53.2% (N = 47) in this species. P. howardi has a high capacity to adapt to different habitats, especially in the peridomicile. This implies a considerable risk of transmission because of the frequency of intradomicile invasion. Therefore, this species needs to be taken into account in Chagas control and surveillance efforts in the region. PMID:25385867

Villacís, Anita G; Ocaña-Mayorga, Sofía; Lascano, Mauricio S; Yumiseva, César A; Baus, Esteban G; Grijalva, Mario J

2015-01-01

349

Insight on RDX degradation mechanism by Rhodococcus strains using 13C and 15N kinetic isotope effects.  

PubMed

The explosive Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is known to be degraded aerobically by various isolates of the Rhodococcus species, with denitration being the key step, mediated by Cytochrome P450. Our study aimed at gaining insight into the RDX degradation mechanism by Rhodococcus species and comparing isotope effects associated with RDX degradation by distinct Rhodococcus strains. For these purposes, enrichment in (13)C and (15)N isotopes throughout RDX denitration was studied for three distinct Rhodococcus strains, isolated from soil and groundwater in an RDX-contaminated site. The observable (15)N enrichment throughout the reaction, together with minor (13)C enrichment, suggests that N-N bond cleavage is likely to be the key rate-limiting step in the reaction. The similarity in the kinetic (15)N isotope effect between the three tested strains suggests that either isotope-masking effects are negligible, or are of a similar extent for all tested strains. The lack of variability in the kinetic (15)N isotope effect allows the interpretation of environmental studies with greater confidence. PMID:23215036

Bernstein, Anat; Ronen, Zeev; Gelman, Faina

2013-01-01

350

Biosynthesis and characterization of (15)N6-labeled phomopsin A, a lupin associated mycotoxin produced by Diaporthe toxica.  

PubMed

The hepatotoxin phomopsin A (PHO-A), a secondary metabolite mainly produced by the fungus Diaporthe toxica, occurs predominantly on sweet lupins. Along with the growing interest in sweet lupins for food and feed commodities, concerns have been raised about fungal infestations, and consequently, about the determination of PHO-A. High performance liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) represents the most suitable analytical technique for sensitive and selective detection of mycotoxins including PHO-A. However, isotopic labeled substances are needed as internal standards for a reliable and convenient quantification. As no isotope standard for PHO-A is currently available, a biosynthesis of fully (15)N6-labeled PHO-A was established by cultivation of D. toxica on defined media containing Na(15)NO3 and (15)N-labeled yeast extract as the only nitrogen sources. The identity of (15)N6-PHO-A was confirmed by high resolution mass spectrometry. The new (15)N6-labeled standard will facilitate the method development for PHO-A including a more accurate quantification by LC-MS/MS. PMID:25660858

Schloß, Svenja; Wedell, Ines; Koch, Matthias; Rohn, Sascha; Maul, Ronald

2015-06-15

351

Assessing waterbird habitat use in coastal evaporative systems using stable isotopes (? 13C, ? 15N and ?D) as environmental tracers  

NASA Astrophysics Data System (ADS)

Isotopic patterns of biota across salinity gradients in man-made evaporative systems could assist in determining the use of these habitats by animals. Here we report ? 13C, ? 15N and ?D measurements of a euryhaline fish, the Mediterranean toothcarp ( Aphanius fasciatus), inhabiting a range of salinities in the Thyna saltworks near Sfax (Tunisia). The contribution of these salinity niches to egg formation of two typically piscivorous bird species breeding in the area and feeding within saltworks, Little Tern ( Sternula albifrons) and Little Egret ( Egretta garzetta), was inferred trough a triple-isotope (? 13C, ? 15N and ?D) Bayesian mixing model. Isotopic trends for fish ? 15N and ?D across the salinity gradient followed the equations: ? 15N = e (1.1 + 47.68/Salinity) and ?D = -175.74 + Salinity + Salinity 2; whereas fish ? 13C increased as salinity rose (? 13C = -10.83 + 0.02·Salinity), after a sudden drop in fish isotopic values for salinities >60 (Practical Salinity Scale) (average fish ? 13C for salinities <60 = -5.92‰). Both bird species fed largely on low hypersalinity ponds (salinity = 43; average contribution = 37% and 22% for Little Egrets and Little Terns, respectively), although the use of intermediate hypersalinities (salinities 63 and 70) by Little Terns also occurred (16% and 21%, respectively). Isotopic patterns across salinity gradients allow the use of isotopic measurements to inform studies of habitat occupancy within evaporative systems and provide further insights into how wildlife communities interact with them.

Ramírez, Francisco; Abdennadher, Aida; Sanpera, Carola; Jover, Lluís; Wassenaar, Leonard I.; Hobson, Keith A.

2011-04-01

352

COMPARISON OF STABLE-NITROGEN (15N/14N) ISOTOPE RATIOS IN LARGE MOUTH BASS SCALES AND MUSCLE TISSUE  

EPA Science Inventory

Stable-nitrogen (15N/14N) isotope ratios of fish tissue are currently used to determine trophic structure, contaminant bioaccumulation, and the level of anthropogenic nitrogen enrichment in aquatic systems. The most common tissue used for these measurements is fileted dorsal musc...

353

Effect of successive cuttings on uptake and partitioning of 15 N among plant parts of Leucaena leucocephala  

Microsoft Academic Search

We studied the effect of three successive cuttings on N uptake and fixation and N distribution in Leucaena leucocephala. Two isolines, uninoculated or inoculated with three different Rhizobium strains, were grown for 36 weeks and cut every 12 weeks. The soil was labelled with 50 ppm KNO3 enriched with 10 atom % 15N excess soon after the first cutting. Except

N. Sanginga; F. Zapata; S. K. A. Danso; G. D. Bowen

1990-01-01

354

Heteronuclear transverse and longitudinal relaxation in AX4 spin systems: application to (15)N relaxations in (15)NH4(+).  

PubMed

The equations that describe the time-evolution of transverse and longitudinal (15)N magnetisations in tetrahedral ammonium ions, (15)NH4(+), are derived from the Bloch-Wangsness-Redfield density operator relaxation theory. It is assumed that the relaxation of the spin-states is dominated by (1) the intra-molecular (15)N-(1)H and (1)H-(1)H dipole-dipole interactions and (2) interactions of the ammonium protons with remote spins, which also include the contribution to the relaxations that arise from the exchange of the ammonium protons with the bulk solvent. The dipole-dipole cross-correlated relaxation mechanisms between each of the (15)N-(1)H and (1)H-(1)H interactions are explicitly taken into account in the derivations. An application to (15)N-ammonium bound to a 41kDa domain of the protein DnaK is presented, where a comparison between experiments and simulations show that the ammonium ion rotates rapidly within its binding site with a local correlation time shorter than approximately 1ns. The theoretical framework provided here forms the basis for further investigations of dynamics of AX4 spin systems, with ammonium ions in solution and bound to proteins of particular interest. PMID:25128779

Werbeck, Nicolas D; Hansen, D Flemming

2014-09-01

355

Studies on electron spin resonance spectroscopy of biradical molecules containing 14N-O and 15N-O moieties  

NASA Astrophysics Data System (ADS)

The biradicals with 14N-Oxide and 15N-Oxide at the both ends of a molecule are synthesized for the molecular ruler of protein structure, and a potential device for quantum computing. We also establish a general synthetic method for reliable biradical formation. ESR spectra are recorded for the biradicals containing 15N-Oxide and 14N-Oxide with various interdistance separations. We find that two types of biradicals yielded different ESR spectra depending upon the distance between the 15N-O and 14N-O moieties in a molecule. This is due to electron spin dipole-dipole interaction occurring between the radicals. We also find that there is an indication of isotopic nuclear effects in the dipole-dipole interactions. The present study implies feasibility of the distance measurement between two different N-Oxides containing 14N and 15N isotopes. We conclude that quantum entanglement effects are observed through the dipolar interactions, which enable application of quantum computing devices operating in the liquid state.

Kameya, Hiromi; Nakamura, Hideo; Ukai, Mitsuko; Shimoyama, Yuhei

2008-05-01

356

Variation in hair ?13C and ?15N values in long-tailed macaques (Macaca fascicularis) from Singapore  

USGS Publications Warehouse

Much of the primatology literature on stable isotope ratios of carbon (?13C) and nitrogen (?15N) has focused on African and New World species, with comparatively little research published on Asian primates. Here we present hair ?13C and ?15N isotope values for a sample of 33 long-tailed macaques from Singapore. We evaluate the suggestion by a previous researcher that forest degradation and biodiversity loss in Singapore have led to a decline in macaque trophic level. The results of our analysis indicated significant spatial variability in ?13C but not ?15N. The range of variation in ?13C was consistent with a diet based on C3 resources, with one group exhibiting low values consistent with a closed canopy environment. Relative to other macaque species from Europe and Asia, the macaques from Singapore exhibited a low mean ?13C value but mid-range mean ?15N value. Previous research suggesting a decline in macaque trophic level is not supported by the results of our study.

Schillaci, Michael A.; Castellini, J. Margaret; Stricker, Craig A.; Jones-Engel, Lisa; Lee, Benjamin P.Y.-H.

2014-01-01

357

STATISTICAL ESTIMATES OF VARIANCE FOR 15N ISOTOPE DILUTION MEASUREMENTS OF GROSS RATES OF NITROGEN CYCLE PROCESSES  

EPA Science Inventory

It has been fifty years since Kirkham and Bartholmew (1954) presented the conceptual framework and derived the mathematical equations that formed the basis of the now commonly employed method of 15N isotope dilution. Although many advances in methodology and analysis have been ma...

358

Analysis of whole body ammonia metabolism in Aedes aegypti using [15N]-labeled compounds and mass spectrometry.  

PubMed

We have established a protocol to study the kinetics of incorporation of 15N into glutamine (Gln), glutamic acid (Glu), alanine (Ala) and proline (Pro) in Aedes aegypti females. Mosquitoes were fed 3% sucrose solutions containing either 80 mM 15NH4Cl or 80 mM glutamine labeled with 15N in either the amide nitrogen or in both amide and amine nitrogens. In some experiments, specific inhibitors of glutamine synthetase or glutamate synthase were added to the feeding solutions. At different times post feeding, which varied between 0 and 96 h, the mosquitoes were immersed in liquid nitrogen and then processed. These samples plus deuterium labeled internal standards were derivatized as dimethylformamidine isobutyl esters or isobutyl esters. The quantification of 15N-labeled and unlabeled amino acids was performed by using mass spectrometry techniques. The results indicated that the rate of incorporation of 15N into amino acids was rapid and that the label first appeared in the amide side chain of Gln and then in the amino group of Gln, Glu, Ala and Pro. The addition of inhibitors of key enzymes related to the ammonia metabolism confirmed that mosquitoes efficiently metabolize ammonia through a metabolic route that mainly involves glutamine synthetase (GS) and glutamate synthase (GltS). Moreover, a complete deduced amino acid sequence for GltS of Ae. aegypti was determined. The sequence analysis revealed that mosquito glutamate synthase belongs to the category of NADH-dependent GltS. PMID:16876704

Scaraffia, Patricia Y; Zhang, Qingfen; Wysocki, Vicki H; Isoe, Jun; Wells, Michael A

2006-08-01

359

Heteronuclear transverse and longitudinal relaxation in AX4 spin systems: Application to 15N relaxations in 15NH4+  

PubMed Central

The equations that describe the time-evolution of transverse and longitudinal 15N magnetisations in tetrahedral ammonium ions, 15NH4+, are derived from the Bloch-Wangsness-Redfield density operator relaxation theory. It is assumed that the relaxation of the spin-states is dominated by (1) the intra-molecular 15N–1H and 1H–1H dipole–dipole interactions and (2) interactions of the ammonium protons with remote spins, which also include the contribution to the relaxations that arise from the exchange of the ammonium protons with the bulk solvent. The dipole–dipole cross-correlated relaxation mechanisms between each of the 15N–1H and 1H–1H interactions are explicitly taken into account in the derivations. An application to 15N-ammonium bound to a 41 kDa domain of the protein DnaK is presented, where a comparison between experiments and simulations show that the ammonium ion rotates rapidly within its binding site with a local correlation time shorter than approximately 1 ns. The theoretical framework provided here forms the basis for further investigations of dynamics of AX4 spin systems, with ammonium ions in solution and bound to proteins of particular interest. PMID:25128779

Werbeck, Nicolas D.; Hansen, D. Flemming

2014-01-01

360

1 H, 13 C and 15 N NMR assignments of Duck HBV apical stem loop of the epsilon encapsidation signal  

Microsoft Academic Search

The replication of Hepatitis B virus is initiated by binding of its reverse transcriptase to the apical stem loop and primer\\u000a loop of epsilon. Here, we present the 1H\\/13C\\/15N NMR assignments of the bases and sugars of the 29 residues apical stem loop of Duck HBV epsilon.

K. A. M. Ampt; O. M. Ottink; F. C. Girard; F. Nelissen; M. Tessari; S. S. Wijmenga

2008-01-01

361

Heteronuclear transverse and longitudinal relaxation in AX4 spin systems: Application to 15N relaxations in 15NH4+  

NASA Astrophysics Data System (ADS)

The equations that describe the time-evolution of transverse and longitudinal 15N magnetisations in tetrahedral ammonium ions, 15NH4+, are derived from the Bloch-Wangsness-Redfield density operator relaxation theory. It is assumed that the relaxation of the spin-states is dominated by (1) the intra-molecular 15N-1H and 1H-1H dipole-dipole interactions and (2) interactions of the ammonium protons with remote spins, which also include the contribution to the relaxations that arise from the exchange of the ammonium protons with the bulk solvent. The dipole-dipole cross-correlated relaxation mechanisms between each of the 15N-1H and 1H-1H interactions are explicitly taken into account in the derivations. An application to 15N-ammonium bound to a 41 kDa domain of the protein DnaK is presented, where a comparison between experiments and simulations show that the ammonium ion rotates rapidly within its binding site with a local correlation time shorter than approximately 1 ns. The theoretical framework provided here forms the basis for further investigations of dynamics of AX4 spin systems, with ammonium ions in solution and bound to proteins of particular interest.

Werbeck, Nicolas D.; Hansen, D. Flemming

2014-09-01

362

Changes in soil nitrogen storage and ?15N with woody plant encroachment in a subtropical savanna parkland landscape  

Microsoft Academic Search

Subtropical woodlands dominated by N-fixing tree legumes have largely replaced grasslands in the Rio Grande Plains, southwestern United States, during the past century. To evaluate the impact of this vegetation change on the N cycle, we measured the mass and isotopic composition (?15N) of N in the soil system of remnant grasslands and woody plant stands ranging in age from

T. W. Boutton; J. D. Liao

2010-01-01

363

Internal protein dynamics on ps to ?s timescales as studied by multi-frequency (15)N solid-state NMR relaxation.  

PubMed

A comprehensive analysis of the dynamics of the SH3 domain of chicken alpha-spectrin is presented, based upon (15)N T1 and on- and off-resonance T1? relaxation times obtained on deuterated samples with a partial back-exchange of labile protons under a variety of the experimental conditions, taking explicitly into account the dipolar order parameters calculated from (15)N-(1)H dipole-dipole couplings. It is demonstrated that such a multi-frequency approach enables access to motional correlation times spanning about 6 orders of magnitude. We asses the validity of different motional models based upon orientation autocorrelation functions with a different number of motional components. We find that for many residues a "two components" model is not sufficient for a good description of the data and more complicated fitting models must be considered. We show that slow motions with correlation times on the order of 1-10 ?s can be determined reliably in spite of rather low apparent amplitudes (below 1 %), and demonstrate that the distribution of the protein backbone mobility along the time scale axis is pronouncedly non-uniform and non-monotonic: two domains of fast (? < 10(-10) s) and intermediate (10(-9) s < ? < 10(-7) s) motions are separated by a gap of one order of magnitude in time with almost no motions. For slower motions (? > 10(-6) s) we observe a sharp ~1 order of magnitude decrease of the apparent motional amplitudes. Such a distribution obviously reflects different nature of backbone motions on different time scales, where the slow end may be attributed to weakly populated "excited states." Surprisingly, our data reveal no clearly evident correlations between secondary structure of the protein and motional parameters. We also could not notice any unambiguous correlations between motions in different time scales along the protein backbone emphasizing the importance of the inter-residue interactions and the cooperative nature of protein dynamics. PMID:24048638

Zinkevich, Tatiana; Chevelkov, Veniamin; Reif, Bernd; Saalwächter, Kay; Krushelnitsky, Alexey

2013-11-01

364

Measurement of (1)H-(15)N and (1)H-(13)C residual dipolar couplings in nucleic acids from TROSY intensities.  

PubMed

Analogous to the recently introduced ARTSY method for measurement of one-bond (1)H-(15)N residual dipolar couplings (RDCs) in large perdeuterated proteins, we introduce methods for measurement of base (13)C-(1)H and (15)N-(1)H RDCs in protonated nucleic acids. Measurements are based on quantitative analysis of intensities in (1)H-(15)N and (13)C-(1)H TROSY-HSQC spectra, and are illustrated for a 71-nucleotide adenine riboswitch. Results compare favorably with those of conventional frequency-based measurements in terms of completeness and convenience of use. The ARTSY method derives the size of the coupling from the ratio of intensities observed in two TROSY-HSQC spectra recorded with different dephasing delays, thereby minimizing potential resonance overlap problems. Precision of the RDC measurements is limited by the signal-to-noise ratio, S/N, achievable in the 2D TROSY-HSQC reference spectrum, and is approximately given by 30/(S/N) Hz for (15)N-(1)H and 65/(S/N) Hz for (13)C-(1)H. The signal-to-noise ratio of both (1)H-(15)N and (1)H-(13)C spectra greatly benefits when water magnetization during the experiments is not perturbed, such that rapid magnetization transfer from bulk water to the nucleic acid, mediated by rapid amino and hydroxyl hydrogen exchange coupled with (1)H-(1)H NOE transfer, allows for fast repetition of the experiment. RDCs in the mutated helix 1 of the riboswitch are compatible with nucleotide-specifically modeled, idealized A-form geometry and a static orientation relative to the helix 2/3 pair, which differs by ca 6° relative to the X-ray structure of the native riboswitch. PMID:21947918

Ying, Jinfa; Wang, Jinbu; Grishaev, Alex; Yu, Ping; Wang, Yun-Xing; Bax, Ad

2011-09-01

365

Stable Isotope Tracking of Endangered Sea Turtles: Validation with Satellite Telemetry and ?15N Analysis of Amino Acids  

PubMed Central

Effective conservation strategies for highly migratory species must incorporate information about long-distance movements and locations of high-use foraging areas. However, the inherent challenges of directly monitoring these factors call for creative research approaches and innovative application of existing tools. Highly migratory marine species, such as marine turtles, regularly travel hundreds or thousands of kilometers between breeding and feeding areas, but identification of migratory routes and habitat use patterns remains elusive. Here we use satellite telemetry in combination with compound-specific isotope analysis of amino acids to confirm that insights from bulk tissue stable isotope analysis can reveal divergent migratory strategies and within-population segregation of foraging groups of critically endangered leatherback sea turtles (Dermochelys coriacea) across the Pacific Ocean. Among the 78 turtles studied, we found a distinct dichotomy in ?15N values of bulk skin, with distinct “low ?15N” and “high ?15N” groups. ?15N analysis of amino acids confirmed that this disparity resulted from isotopic differences at the base of the food chain and not from differences in trophic position between the two groups. Satellite tracking of 13 individuals indicated that their bulk skin ?15N value was linked to the particular foraging region of each turtle. These findings confirm that prevailing marine isoscapes of foraging areas can be reflected in the isotopic compositions of marine turtle body tissues sampled at nesting b