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1

Natural 15N abundance of plants and soils under different management practices in a montane grassland  

Microsoft Academic Search

The natural 15N abundance (?15N) of different ecosystem compartments is considered to be an integrator of nitrogen (N) cycle processes. Here we investigate the extent to which patterns of ?15N in grassland plants and soils reflect the effect of different management practices on N cycling processes and N balance. Investigations were conducted in long-term experimental plots of permanent montane meadows

Margarete Watzka; Karl Buchgraber; Wolfgang Wanek

2006-01-01

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

Variation of 15 N natural abundance in leaves and nodules of actinorhizal shrubs in Northwest Patagonia  

Microsoft Academic Search

This study was performed to assess the N2-fixing capability of the native actinorhizal species Ochetophila trinervis (sin. Discaria trinervis )a ndDiscaria chacaye (Rhamnaceae) in Northwest Patagonia. We measured the N concentration and 15 N natural abundance in leaves and nodules of O. trinervis and D. chacaye, in leaves of associated non-actinorhizal vegetation, and in the soils under each sampled plant.

Eugenia E. Chaia; David D. Myrold

2010-01-01

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

?15N natural abundance in permafrost soil indicates impact of fire on nitrogen cycle.  

PubMed

The impact of fire on the nitrogen (N) cycle of natural ecosystems is arguable. Here we report and interpret an observation from boreal ecosystems in the Lena River basin, Sakha Republic (Yakutia), Russian Federation. Different types of permafrost soil (0-30 cm depth) were sampled along transects (60-150 m length) from the forest edge towards the centre of four separate thermokarst depressions under grassland. The average values of ?(15)N were remarkably similar within three transects, but differed systematically between them. Three findings point towards fire being the cause of the observed pattern. First, the spatial extent of systematic differences in soil ?(15)N coincides with the extent of typical fire scars in the region. Second, soil enrichment in (15)N is larger in the proximity of settlements, where fire is generally more frequent than in more remote places. Third, there is a significant positive correlation between ?(15)N values and the ratio of black C to total N. These findings point towards fire having a marked impact on soil ?(15)N and, accordingly, on the N cycle of this cold and dry ecosystem. PMID:21290453

Conen, Franz; Yakutin, Mikhail V; Puchnin, Alexander N; Leifeld, Jens; Alewell, Christine

2011-03-15

6

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

7

Natural 15 N Abundance of Plants and Soil N in a Temperate Coniferous Forest  

Microsoft Academic Search

Measurement of nitrogen isotopic composition (d 15N) of plants and soil nitrogen might allow the characteristics of N transformation in an ecosystem to be detected. We tested the measurement of d 15N for its ability to provide a picture of N dynamics at the ecosystem level by doing a simple comparison of d 15N between soil N pools and plants,

Keisuke Koba; Muneto Hirobe; Lina Koyama; Ayato Kohzu; Naoko Tokuchi; Knute John Nadelhoffer; Eitaro Wada; Hiroshi Takeda

2003-01-01

8

Natural Abundance of ? 15N Confirms Insectivorous Habit of Roridula gorgonias , Despite it Having No Proteolytic Enzymes  

Microsoft Academic Search

Natural abundance values of plant ?15N give an indication as to the source of nitrogen. In particular, carnivorous plants are expected to be relatively enriched due to trophic enrichment of their prey. Values of ?15N for adultRoridula gorgonias(mean+3.02‰) are 4–9‰ greater than co-occurring non-carnivorous plant species and 5.24‰ greater than juvenileR. gorgoniasplants. They are also 3.5–4.26‰ greater than co-occurringDroseraspecies which,

J. J. MIDGLEY; W. D. STOCK

1998-01-01

9

Foliar 15 N natural abundance in Hawaiian rainforest: patterns and possible mechanisms  

Microsoft Academic Search

Foliar samples were obtained from symbiotic nitrogen-fixers and control plants (non-fixers) along elevational and primary successional gradients in volcanic sites in Hawai'i. Most control plants had negative d15N values (range-10.1 to +0.7‰), while most nitrogen-fixers were near 0‰. Foliar 15N in the native tree Metrosideros polymorpha did not vary with elevation (from sea level to tree-line), but it did increase

Peter M. Vitousek; Georgia Shearer; Daniel H. Kohl

1989-01-01

10

Food webs in Mongolian grasslands: the analysis of 13C and 15N natural abundances.  

PubMed

Overgrazing often lowers species richness and productivity of grassland communities. For Mongolian grassland ecosystems, a lack of detailed information about food-web structures makes it difficult to predict the effects of overgrazing on species diversity and community composition. We analysed the delta13C and delta15N signatures of herbaceous plants, arthropods (grouped by feeding habit), wild and domestic mammals, and humans in central Mongolia to understand the predominant food-web pathways in this grassland ecosystem. The delta13C and delta15N values of mammals showed little variation within species, but varied considerably with slope position for arthropods. The apparent isotopic discrimination between body tissue and hair of mammals was estimated as 2.0 per thousand for delta13C and 2.1 per thousand for delta15N, which was large enough to cause overestimation of the trophic level of mammals if not taken into account when using hair samples to measure isotopic enrichment. PMID:19507080

Kohzu, Ayato; Iwata, T; Kato, M; Nishikawa, J; Wada, Eitaro; Amartuvshin, N; Namkhaidorj, B; Fujita, N

2009-09-01

11

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

12

Leaf natural 15 N abundance and total N concentration as potential indicators of plant N nutrition in legumes and pioneer species in a rain forest of French Guiana  

Microsoft Academic Search

The suitability of the natural 15N abundance and of total N concentration of leaves as indicators of the type of plant N nutrition in a rain forest of French\\u000a Guiana were tested. Leaf samples from primary legume species, non-legumes (pioneer species) and from the non-N2-fixing species Dicorynia guianensis were analyzed. Both ?15N and total leaf N varied widely (?1 ??15N

J. C. Roggy; M. F. Prévost; F. Gourbiere; H. Casabianca; J. Garbaye; A. M. Domenach

1999-01-01

13

15N natural abundance of biologically fixed N 2 in soybean is controlled more by the Bradyrhizobium strain than by the variety of the host plant  

Microsoft Academic Search

The 15N natural abundance technique is one of those most easily applied ‘on farm’ to evaluate the contribution of biological N2 fixation (BNF) to legume crops. When proportional BNF inputs are high, the accuracy of this technique is highly dependent on an accurate estimate of the 15N abundance of the N derived from N2 fixation (the ‘B’ value). The objective of

Natalie Pauferro; Ana Paula Guimarães; Claudia P. Jantalia; Segundo Urquiaga; Bruno J. R. Alves; Robert M. Boddey

2010-01-01

14

Positive nitrogen balance of Acacia mangium woodlots as fallows in the Philippines based on 15 N natural abundance data of N 2 fixation  

Microsoft Academic Search

Nitrogen inputs from biological nitrogen fixation contribute to productivity and sustainability of agroforestry systems but\\u000a they need to be able to offset export of N when trees are harvested. This study assessed magnitudes of biological nitrogen\\u000a fixation (natural 15N abundance) and N balance of Acacia mangium woodlots grown in farmer’s fields, and determined if N2 fixation capacity was affected by

Augustin R. Mercado Jr; Meine Van Noordwijk; Georg Cadisch

2011-01-01

15

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

16

The 15N natural abundance of the N lost from an N-saturated subtropical forest in southern China  

NASA Astrophysics Data System (ADS)

The 15N-enrichment of plants and soils is believed to indicate characteristics of the open nitrogen (N) cycle in terrestrial ecosystems because N lost from an ecosystem is presumably 15N-depleted through isotopic fractionation. However, because of a lack of an appropriate analytical methodology to confirm that supposition, the ?15N value for total dissolved nitrogen (TDN, the sum of ammonium, nitrate, and dissolved organic N) in stream water from forests has been measured only rarely. This report describes the ?15N values for TDN, ammonium, and nitrate in precipitation and stream water, together with those for soil-emitted nitrous oxide (N2O; measured once) in an N-saturated subtropical forest in southern China. Concentration-weighted ?15N values of TDN were -0.7‰ in precipitation and +1.2‰ in stream water. The difference in ?15N between soil (+3.9‰) and TDN in the stream water was 2.7‰. In contrast, soil-emitted N2O was strongly 15N-depleted (-14.3‰): 18‰ lower than that of the soil. Our results demonstrate that the discharged N loss is 15N-depleted only slightly compared with soil N, and gaseous N losses can be a strong driver for raising the terrestrial ecosystem ?15N. Our findings suggest that the relation between ecosystem ?15N and the open N cycle can be interpreted better by considering the net discrimination against 15N determined by the balance between gaseous and discharge N losses. Steady state 15N budget calculations proposed by Houlton and Bai (2009) can provide important information about the gaseous N fluxes, which are difficult to measure directly. The steady state calculation for the relationships among gaseous N loss, apparent isotopic fractionation during gaseous N loss, and isotopic signature of N inputs suggests that precise measurements of unmeasured components (e.g., dry deposition, NO and N2 emission) are quite important for better estimation of gaseous N losses from the ecosystem.

Koba, Keisuke; Fang, Yunting; Mo, Jiangming; Zhang, Wei; Lu, Xiankai; Liu, Lei; Zhang, Tao; Takebayashi, Yu; Toyoda, Sakae; Yoshida, Naohiro; Suzuki, Keisuke; Yoh, Muneoki; Senoo, Keishi

2012-06-01

17

Natural abundance 15N in soil and litter across a nitrate-output gradient in New Hampshire  

Microsoft Academic Search

Stable isotopes of nitrogen are potentially a valuable tool for regional assessments of nitrogen saturation because they provide an integrated measure of the past nitrogen cycling history of a site. We measured ?15N of soil and litter, as well as net nitrification potential, at three sites across a nitrate-loss gradient in the White Mountains, New Hampshire to test the hypotheses:

L. H. Pardo; H. F. Hemond; J. P. Montoya; J. Pett-Ridge

2007-01-01

18

Using the natural 15N abundance to assess the main nitrogen inputs into the sand dune area of the north-western Negev Desert (Israel).  

PubMed

The variation of the natural 15N abundance is often used to evaluate the origin of nitrogen or the pathways of N input into ecosystems. We tried to use this approach to assess the main input pathways of nitrogen into the sand dune area of the north-western Negev Desert (Israel). The following two pathways are the main sources for nitrogen input into the system: i. Biological fixation of atmospheric nitrogen by cyanobacteria present in biological crusts and by N2-fixing vascular plants (e.g. the shrub Retama raetam); ii. Atmospheric input of nitrogen by wet deposition with rainfall, dry deposition of dust containing N compounds, and gaseous deposition. Samples were taken from selected environmental compartments such as biological crusts, sand underneath these crusts (down to a depth of 90 cm), N2-fixing and non-N2-fixing plants, atmospheric bulk deposition as well as soil from arable land north of the sandy area in three field campaigns in March 1998, 1999 and 2000. The delta15N values measured were in the following ranges: grass -2.5/1000 to +1.5/1000; R. reatam: +0.5/1000 to +4.5/1000; non-N2-fixing shrubs +1/1000 to +7/1000; sand beneath the biological crusts +4/1000 to +20/1000 (soil depth 2-90 cm); and arable land to the north up to 10/1000. Thus, the natural 15N abundance of the different N pools varies significantly. Accordingly, it should be feasible to assess different input pathways from the various 15N abundances of nitrogen. For example, the biological N fixation rates of the Fabaceae shrub R. reatam from the 15N abundances measured were calculated to be 46-86% of biomass N derived from the atmosphere. The biological crusts themselves generally show slight negative 15N values (-3/1000 to -0.5/1000), which can be explained by biological N fixation. However, areas with a high share of lichens, which are unable to fix atmospheric nitrogen, show very negative values down to -10/1000. The atmospheric N bulk deposition, which amounts to 1.9-3.8 kg N/hayr, has a 15N abundance between 4.4/1000 and 11.6/1000 and is likely to be caused by dust from the arable land to the north. Thus, it cannot be responsible for the very negative values of lichens measured either. There must be an additional N input from the atmosphere with negative delta15N values, e.g. gaseous N forms (NOx, NH3). To explain these conflicting findings, detailed information is still needed on the wet, particulate and gaseous atmospheric deposition of nitrogen. PMID:15085984

Russow, Rolf; Veste, Maik; Littmann, Thomas

2004-03-01

19

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

2012-11-08

20

Measurement of 15N\\/ 14N Isotopic Composition in Individual Plasma Free Amino Acids of Human Adults at Natural Abundance by Gas Chromatography–Combustion Isotope Ratio Mass Spectrometry  

Microsoft Academic Search

We describe a high-precision methodology to determine the15N\\/14N isotopic composition of 13 plasma free amino acids out of 500 ?l plasma, measured asN-pivaloyl-i-propyl amino acid esters by gas chromatography–isotope ratio mass spectrometry. It is now possible to measure15N isotopic natural abundances in plasma free amino acids, which has not been the case previously because of the minimum requirement of 60

Cornelia C. Metges; Klaus J. Petzke

1997-01-01

21

Estimates of dry and wet deposition using tissue N contents and 15N natural abundance in epilithic mosses in atmospheric NHy-dominated areas  

NASA Astrophysics Data System (ADS)

Measurement of dry N deposition by physical methods is time-consuming because it is usually difficult to measure directly. In this study, an alternative approach has successfully been proposed by coupling isotopic ratios with tissue N contents of epilithic mosses. The method is to use moss N contents to quantitatively estimate total N (TN) deposition and then to use 15N natural abundance in mosses to discriminate dry and wet deposition in atmospheric NHy-dominated areas (NHy/TN > 0.75). On the basis of the isotopic balance between atmospheric NHy and moss tissue N and the correlation between atmospheric NHy concentrations and their isotopes, both wet and dry N deposition can be estimated. By the approach, we have estimated rainwater ammonium concentrations and contribution percentage of wet deposition to total N deposition (fwet) in some areas of southern China. The results indicated that rainwater ammonium concentrations increased relative to those reported previously in most cities, owing to stronger anthropogenic activity. The fwet values estimated in most sites were found to be slightly higher than those reported, because faster transformation rates due to higher SO2 emission later in acid rain areas of southern China favored deposition in the form of wet deposition instead of dry deposition. The largest uncertainty of the approach comes from the influence of NOx in the atmosphere, and thus it cannot be used in areas where NOx deposition is high. The presented isotopic approach represents a new application of moss biomonitoring for estimating atmospheric N deposition in NHy-dominated areas.

Xiao, Hua-Yun; Liu, Cong-Qiang

2011-02-01

22

Nitrate dynamics after clear felling monitored by in vivo nitrate reductase activity (NRA) and natural 15 N abundance of Deschampsia flexuosa (L.) Trin  

Microsoft Academic Search

The N dynamics following clear felling, focusing on NO3? turnover, were studied at four forested sites in southern Sweden. Two different methods were used to study N availability: (i) an in vivo nitrate reductase activity (NRA) bioassay and (ii) measurements of natural abundance of stable N isotopes in leaves of the grass species Deschampsiaflexuosa, and in organic soil horizons. At

Lars Högbom; Urban Nilsson; Göran Örlander

2002-01-01

23

Food Resources of Stream Macronivertebrates Determined by Natural-Abundance stable C and N Isotopes and a 15N Tracer Addition  

Microsoft Academic Search

Trophic relationships were examined using natural-abundance ¹³C and ¹⁵N analyses and a ¹⁵N-tracer addition experiment in Walker Branch, a 1st-order forested stream in eastern Tennessee. In the ¹⁵N-tracer addition experiment, we added ¹⁵NHâ to stream water over a 6-wk period in early spring, and measured ¹⁵N:¹⁴N ratios in different taxa and biomass compartments over distance and time. Samples collected from

PATRICK J. MULHOLLAND; J ENNIFER; L. TANK; D IANE M. SANZONE; WILFRED M. WOLLHEIM; J. PETERSON; J ACKSON R. WEBSTER; JUDY L. MEYER

2000-01-01

24

Paleoclimate reconstruction:natural abundance of d13C and d15N of modern plant pollen to interpret fossil data  

NASA Astrophysics Data System (ADS)

?13 values of modern plant organic carbon allow the differentiation of the different physiological plant categories. The geographical distribution of these plants according to their photosynthetic pathways provides informations on the modifications of climatic parameters (pCO_2, temperature, rainfall...). ?13 variability of organic carbon of fossil plants enables us to interpret geographical plants distribution and associated climatic parameters over geological time. In order to do parametrisation of these relationships, well preserved molecules are suited. Sporopollenin which is the main constituent of the external part of pollen grain is well preserved in paleosediments. This makes of this molecule an interesting tool for paleovegetation reconstructions. The interest of ?15N associated measurements is demonstrated. These different aspects were discussed with our results and those of the litterature.

Descolas-Gros, C.

2003-04-01

25

Determination of 15N Abundance in Nanogram Pools of NO3- and NO2- by Denitrification Bioassay and Mass Spectrometry  

PubMed Central

Suspensions of two strains of Pseudomonas aeruginosa (ON12 and ON12-1) were used to reduce NO3- and NO2-, respectively, to N2O. The evolved N2O was quantified by gas chromatography with electron capture detection, and the 15N abundance was determined by mass spectrometry with a special inlet system and triple-collector detection. Sample gas containing unknown N2O pools as small as 0.5 ng of N was analyzed by use of a spike technique, in which a reference gas of N2O of natural 15N abundance was added to obtain enough total N for the mass spectrometer. In NO3- or NO2- pools, the 15N abundance could be determined in samples as small as approximately 3.5 ng of N. No cross-contamination took place between the NO3- and NO2- pools. The excellent separation of NO3- and NO2- pools, small sample size required, and low contamination risk during N2O analysis offer great advantages in isotope studies of inorganic N transformations by, e.g., nitrifying or denitrifying bacteria in the environment.

H?jberg, Ole; Johansen, Henrik Saaby; S?rensen, Jan

1994-01-01

26

Differences in animal 13C, 15N and D abundance between a polluted and an unpolluted coastal site: Likely indicators of sewage uptake by a marine food web  

Microsoft Academic Search

In comparing a control vs. a sewage-affected nearshore site off southern California, the natural relative abundances of 13C, 15N and D in Dover sole and Ridgeback prawn muscle were found to be significantly different. This between-site shift in animal isotope abundance is of the type expected if sewage organic materials were an important food source for animals in the latter

G. H. Rau; R. E. Sweeney; I. R. Kaplan; A. J. Mearns; D. R. Young

1981-01-01

27

Differences in animal 13C, 15N and D abundance between a polluted and an unpolluted coastal site: Likely indicators of sewage uptake by a marine food web  

NASA Astrophysics Data System (ADS)

In comparing a control vs. a sewage-affected nearshore site off southern California, the natural relative abundances of 13C, 15N and D in Dover sole and Ridgeback prawn muscle were found to be significantly different. This between-site shift in animal isotope abundance is of the type expected if sewage organic materials were an important food source for animals in the latter site. Use of stable isotope natural abundance to trace the incorporation and movement of sewage-derived organics in marine food webs is suggested.

Rau, G. H.; Sweeney, R. E.; Kaplan, I. R.; Mearns, A. J.; Young, D. R.

1981-12-01

28

? 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

29

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

30

Revision of the 15N(p, ?)16O reaction rate and oxygen abundance in H-burning zones  

NASA Astrophysics Data System (ADS)

Context. The NO cycle takes place in the deepest layer of a H-burning core or shell, when the temperature exceeds T ? 30 × 106 K. The O depletion observed in some globular cluster giant stars, always associated with a Na enhancement, may be due to either a deep mixing during the red giant branch (RGB) phase of the star or to the pollution of the primordial gas by an early population of massive asymptotic giant branch (AGB) stars, whose chemical composition was modified by the hot bottom burning. In both cases, the NO cycle is responsible for the O depletion. Aims: The activation of this cycle depends on the rate of the 15N(p, ?)16O reaction. A precise evaluation of this reaction rate at temperatures as low as experienced in H-burning zones in stellar interiors is mandatory to understand the observed O abundances. Methods: We present a new measurement of the 15N(p, ?)16O reaction performed at LUNA covering for the first time the center of mass energy range 70-370 keV, which corresponds to stellar temperatures between 65 × 106 K and 780 × 106 K. This range includes the 15N(p, ?)16O Gamow-peak energy of explosive H-burning taking place in the external layer of a nova and the one of the hot bottom burning (HBB) nucleosynthesis occurring in massive AGB stars. Results: With the present data, we are also able to confirm the result of the previous R-matrix extrapolation. In particular, in the temperature range of astrophysical interest, the new rate is about a factor of 2 smaller than reported in the widely adopted compilation of reaction rates (NACRE or CF88) and the uncertainty is now reduced down to the 10% level.

Caciolli, A.; Mazzocchi, C.; Capogrosso, V.; Bemmerer, D.; Broggini, C.; Corvisiero, P.; Costantini, H.; Elekes, Z.; Formicola, A.; Fülöp, Zs.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, Gy.; Imbriani, G.; Junker, M.; Lemut, A.; Marta, M.; Menegazzo, R.; Palmerini, S.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.; Vomiero, A.

2011-09-01

31

13 C and 15 N isotopic fractionation in trees, soils and fungi in a natural forest stand and a Norway spruce plantation  

Microsoft Academic Search

15N and 13C natural abundances of foliage, branches, trunks, litter, soil, fungal sporophores, mycorrhizas and mycelium were determined\\u000a in two forest stands, a natural forest and a Norway spruce plantation, to obtain some insights into the role of the functional\\u000a diversity of saprotrophic and ectomycorrhizal fungi in carbon and nitrogen cycles. Almost all saprotrophic fungi sporophores\\u000a were enriched in 13C

Bernd Zeller; Claude Brechet; Jean-Paul Maurice; François Le Tacon

2007-01-01

32

A new approach to determining the content and 15N abundance of total dissolved nitrogen in aqueous samples: TOC analyser-QMS coupling.  

PubMed

The standard method for determining the 15N abundance of total dissolved nitrogen (TDN) in aqueous samples (e.g., soil leachate, sewage, urine) is currently Kjeldahl digestion followed by steam distillation or diffusion to isolate the ammonium, and then 15N measurement using IRMS. However, this technique is both time-consuming and laborious. One way of overcoming these disadvantages could be to couple a TOC analyser to determine the TDN with a sufficient quadrupole MS to determine the 15N abundance. The high TOC analyser (Elementar Analysensysteme Hanau, Germany), which catalytically oxidises the sample's total nitrogen with a high, constant yield to nitrogen monoxide (NO), appeared particularly suitable. The quadrupole-MS ESD 100 (InProcess Instruments Bremen, Germany) proved to be a suitable mass spectrometer for the 15N determination of NO. This combination of instruments was found to provide a workable method in numerous measurements of standard and actual samples. The detection limit concerning the N amount required per analysis is 2 microg, corresponding to an N concentration of 0.7 mg/l in a maximum sample volume of 3ml. Depending on the N concentration, 15N abundances starting from 0.5 at.% can be measured with the required precision of better than 3% (simple standard deviation). For example, measuring the abundance of 0.5 at.% requires about 50 microg N, whereas for 1 at.% or more only about 5 microg N is needed per analysis. PMID:12725425

Russow, R; Kupka, H J; Götz, A; Apelt, B

2002-12-01

33

15N Abundance of Nodules as an Indicator of N Metabolism in N2-Fixing Plants 1  

PubMed Central

This paper expands upon previous reports of 15N elevation in nodules (compared to other tissues) of N2-fixing plants. N2-Fixing nodules of Glycine max (soybeans), Vigna unguiculata (cowpea), Phaseolus vulgaris (common bean), Phaseolus coccineus (scarlet runner bean), Prosopis glandulosa (mesquite), and Olneya tesota (desert ironwood) were enriched in 15N. Nodules of Vicia faba (fava beans), Arachis hypogaea (peanut), Trifolium pratense (red clover), Pisum sativum (pea), Lathyrus sativus (grass pea), Medicago sativa (alfalfa), and Lupinus mutabilis (South American lupine) were not; nor were the nodules of nine species of N2-fixing nonlegumes. The nitrogen of ineffective nodules of soybeans and cowpeas was not enriched in 15N. Thus, 15N elevation in nodules of these plants depends on active N2-fixation. Results obtained so far on the generality of 15N enrichment in N2-fixing nodules suggest that only the nodules of plants which actively fix N2 and which transport allantoin or allantoic acid exhibit 15N enrichment.

Shearer, Georgia; Feldman, Lori; Bryan, Barbara A.; Skeeters, Jerri L.; Kohl, Daniel H.; Amarger, Noelle; Mariotti, Francoise; Mariotti, Andre

1982-01-01

34

Pattern of natural 15 N abundance in lakeside forest ecosystem affected by cormorant-derived nitrogen  

Microsoft Academic Search

Waterbirds are one of the most important groups of organisms inhabiting the land-water interface, especially with regard to\\u000a mediating the transport of materials from the aquatic to the terrestrial environment. The great cormorant (Phalacrocorax carbo) is a colonial piscivorous bird that transports nutrients from fresh water to forest. We measured cormorant-derived nitrogen\\u000a at two nesting colonies on the Isaki Peninsula

Kayoko Kameda; Keisuke Koba; Satoru Hobara; Takashi Osono; Masakazu Terai

35

Pattern of natural 15 N abundance in lakeside forest ecosystem affected by cormorant-derived nitrogen  

Microsoft Academic Search

Waterbirds are one of the most important groups of organisms inhabiting the land–water interface, especially with regard to\\u000a mediating the transport of materials from the aquatic to the terrestrial environment. The great cormorant (Phalacrocorax carbo) is a colonial piscivorous bird that transports nutrients from fresh water to forest. We measured cormorant-derived nitrogen\\u000a at two nesting colonies on the Isaki Peninsula

Kayoko Kameda; Keisuke Koba; Satoru Hobara; Takashi Osono; Masakazu Terai

2006-01-01

36

Preliminary insights into ?15N and ?18O of nitrate in natural mosses: a new application of the denitrifier method.  

PubMed

Natural mosses have been employed as reactive and accumulative indicators of atmospheric pollutants. Using the denitrifier method, the concentration, ?(15)N and ?(18)O of moss nitrate (NO(3)(-)) were measured to elucidate the sources of NO(3)(-) trapped in natural mosses. Oven drying at 55-70 °C, not lyophilization, was recommended to dry mosses for NO(3)(-) analyses. An investigation from urban to mountain sites in western Tokyo suggested that moss [NO(3)(-)] can respond to NO(3)(-) availability in different habitats. NO(3)(-) in terricolous mosses showed isotopic ratios as close to those of soil NO(3)(-), reflecting the utilization of soil NO(3)(-). Isotopic signatures of NO(3)(-) in corticolous and epilithic mosses elucidated atmospheric NO(3)(-) sources and strength from the urban (vehicle NO(x) emission) to mountain area (wet-deposition NO(3)(-)). However, mechanisms and isotopic effects of moss NO(3)(-) utilization must be further verified to enable the application of moss NO(3)(-) isotopes for source identification. PMID:22243846

Liu, Xue-Yan; Koba, Keisuke; Takebayashi, Yu; Liu, Cong-Qiang; Fang, Yun-Ting; Yoh, Muneoki

2011-11-10

37

Impact of point source pollution on nitrogen isotope signatures (d 15 N) of vegetation in SE Brazil  

Microsoft Academic Search

This study presents novel evidence that 15N natural abundance can be used as a robust indicator to detect pollutant nitrogen in natural plant communities. Vegetation from the heavily polluted industrial area of Cubatão in São Paulo State, SE Brazil, was strongly 15N depleted compared to plants at remote sites. Historic herbarium samples from Cubatão were significantly less 15N depleted than

George R. Stewart; Marcos P. M. Aidar; Carlos A. Joly; Susanne Schmidt

2002-01-01

38

Analysis of sup 15 N/ sup 14 N Ratios in Natural Samples, with Emphasis on Nitrate and Ammonium in Precipitation.  

National Technical Information Service (NTIS)

The nitrogen cycle is one of the most important of the earth's elemental cycles. The report describes the procedures used for the analysis of sup 15 N/ sup 14 N ratios in ammonium and nitrate (and organic nitrogen), and summarizes without discussion the d...

T. H. E. Heaton G. M. Collett

1985-01-01

39

Regional patterns in foliar 15N across a gradient of nitrogen deposition in the northeastern US  

Microsoft Academic Search

Recent studies have demonstrated that natural abundance 15N can be a useful tool for assessing nitrogen saturation, because as nitrification and nitrate loss increase, ?15N of foliage and soil also increases. We measured foliar ?15N at 11 high-elevation spruce-fir stands along an N deposition gradient in 1987–1988 and at seven paired northern hardwood and spruce-fir stands in 1999. In 1999,

Linda H. Pardo; Steven G. McNulty; Johnny L. Boggs; Sara Duke

2007-01-01

40

Stable isotope abundances ( 13C, 15N) in collagen and soft tissues from Pleistocene mammals from Yakutia: Implications for the palaeobiology of the Mammoth Steppe  

Microsoft Academic Search

A suite of skeletons and frozen carcasses of upper Pleistocene mammals from Yakutia (Sakha Republic, Russia) has been analyzed for their stable isotopic abundances in carbon and nitrogen. Results from bone collagen and soft tissues have been compared. The samples studied belong to herbivorous (mammoths, woolly rhinoceros, horse, bison, muskox) and carnivorous (wolf, lion) species. Bone collagen of herbivorous and

Hervé Bocherens; Gilles Pacaud; Petr A. Lazarev; André Mariotti

1996-01-01

41

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...

42

Natural Resource Abundance and Economic Growth  

Microsoft Academic Search

One of the surprising features of modern economic growth is that economies with abundant natural resources have tended to grow less rapidly than natural-resource-scarce economies. In this paper we show that economies with a high ratio of natural resource exports to GDP in 1971 (the base year) tended to have low growth rates during the subsequent period 1971-89. This negative

Jeffrey D. Sachs; Andrew M. Warner

1995-01-01

43

Ortho-to-para Abundance Ratio (OPR) of Ammonia in 15 Comets: OPRs of Ammonia Versus 14N\\/15N Ratios in CN  

Microsoft Academic Search

The ortho-to-para abundance ratio (OPR) of cometary molecules is considered to be one of the primordial characteristics of cometary ices. We present OPRs of ammonia (NH3) in 15 comets based on optical high-dispersion spectroscopic observations of NH2, which is a photodissociation product of ammonia in the gaseous coma. The observations were mainly carried out with the VLT\\/UVES. The OPR of

Yoshiharu Shinnaka; Hideyo Kawakita; Hitomi Kobayashi; Emmanuël Jehin; Jean Manfroid; Damien Hutsemékers; Claude Arpigny

2011-01-01

44

Helium isotopic abundance variation in nature  

SciTech Connect

The isotopic abundance of helium in nature has been reviewed. This atomic weight value is based on the value of helium in the atmosphere, which is invariant around the world and up to a distance of 100,000 feet. Helium does vary in natural gas, volcanic rocks and gases, ocean floor sediments, waters of various types and in radioactive minerals and ores due to {alpha} particle decay of radioactive nuclides.

Holden, N.E.

1993-08-01

45

Distribution of 15N within Pea, Lupin, and Soybean Nodules 1  

PubMed Central

The 15N abundance of some, but not all, legume root nodules is significantly elevated compared to that of the whole plant. It seems probable that differences in 15N enrichment reflect differences in the assimilatory pathway of fixed N. In that context, we have determined the distribution of naturally occurring 15N in structural fractions of nodules from soybean (Glycine max L. Merr.), yellow lupin (Lupinus luteus), and pea (Pisum sativum) nodules and in chemical components from soybean nodules and to a lesser extent, pea and lupin nodules. None of the fractions of pea nodules (cortex, bacteriod, or host plant cytoplasm) was enriched in 15N. The differences among bacteriods, cortex, and plant cytoplasm were smaller in lupin than in soybean nodules, but in both, bacteriods had the highest 15N enrichment. In soybean nodules, the 15N abundance of bacteriods and cortex was higher than plant cytoplasm, but all three fractions were more enriched in 15N than the entire plant. Plant cytoplasm from soybean nodules was fractionated into protein-rich material, nonprotein alcohol precipitable material (NA), and a low molecular weight fraction. The N of the latter was further separated into N of ureides, nucleotides and free amino acids. Most of these components were either similar to or lower in 15N abundance than the plant cytoplasm as a whole, but the NA fraction showed unusual 15N enrichment. However, the percentage of nodule N in this fraction was small. NA fractions from yellow lupin and pea nodules and from soybean leaves were not enriched in 15N. Nor was the NA fraction in ruptured bacteriods and cortical tissue of soybean nodules. Variation among soybean nodule fractions in the preponderance in protein of different amino acids was not large enough to explain the differences in 15N abundances among them. A hypothesis, consistent with all known data, concerning the mechanism leading to the observed excess 15N of lupin and soybean bacteriods is offered. Images Figure 1

Kohl, Daniel H.; Reynolds, Paul H. S.; Shearer, Georgia

1989-01-01

46

15N -enrichment of plant tissue to mark phytophagous insects, associated parasitoids, and flower-visiting entomophaga  

Microsoft Academic Search

New techniques are presented on the use of 15N to mark insects. 15N, a stable isotope of nitrogen, was enriched above natural abundance in plant and insect tissues. Two laboratory studies demonstrated that enriched 15N- concentrations could be tracked from plant to insect using mass spectrometry. In the first study, adult Cotesia plutellae (Kurdjimov) (Hymenoptera: Braconidae) and Hippodamia convergensGuérin-Méneville (Coleoptera:

Shawn A. Steffan; Kent M. Daane; Daniel L. Mahr

2001-01-01

47

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...

48

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...

49

Food Resources of Stream Macronivertebrates Determined by Natural-Abundance stable C and N Isotopes and a 15N Tracer Addition  

SciTech Connect

Trophic relationships were examined using natural-abundance {sup 13}C and {sup 15}N analyses and a {sup 15}N-tracer addition experiment in Walker Branch, a 1st-order forested stream in eastern Tennessee. In the {sup 15}N-tracer addition experiment, we added {sup 15}NH{sub 4} to stream water over a 6-wk period in early spring, and measured {sup 15}N:{sup 14}N ratios in different taxa and biomass compartments over distance and time. Samples collected from a station upstream from the {sup 15}N addition provided data on natural-abundance {sup 13}C:{sup 12}C and {sup 15}N:{sup 14}N ratios. The natural-abundance {sup 15}N analysis proved to be of limited value in identifying food resources of macroinvertebrates because {sup 15}N values were not greatly different among food resources. In general, the natural-abundance stable isotope approach was most useful for determining whether epilithon or detritus were important food resources for organisms that may use both (e.g., the snail Elimia clavaeformis), and to provide corroborative evidence of food resources of taxa for which the {sup 15}N tracer results were not definitive. The {sup 15}N tracer results showed that the mayflies Stenonema spp. and Baetis spp. assimilated primarily epilithon, although Baetis appeared to assimilate a portion of the epilithon (e.g., algal cells) with more rapid N turnover than the bulk pool sampled. Although Elimia did not reach isotopic equilibrium during the tracer experiment, application of a N-turnover model to the field data suggested that it assimilated a combination of epilithon and detritus. The amphipod Gammarus minus appeared to depend mostly on fine benthic organic matter (FBOM), and the coleopteran Anchytarsus bicolor on epixylon. The caddisfly Diplectrona modesta appeared to assimilate primarily a fast N-turnover portion of the FBOM pool, and Simuliidae a fast N-turnover component of the suspended particulate organic matter pool rather than the bulk pool sampled. Together, the natural-abundance stable C and N isotope analyses and the experimental {sup 15}N tracer approach proved to be very useful tools for identifying food resources in this stream ecosystem.

Mulholland, P. J.

2000-01-01

50

Dual stable isotope analysis (? 13C and ? 15N) of soil invertebrates and their food sources  

Microsoft Academic Search

More research is required to validate and refine natural abundance stable isotope ratio techniques as a tool for the investigation of the feeding ecology of soil animals and trophic relations in soil food webs. Isotope ratios of C (?13C) and N (?15N) were measured in herbivorous and detritivorous invertebrate groups, namely lumbricid earthworms (7 species), enchytraeid worms (3 species), slugs

Olaf Schmidt; James P Curry; Jens Dyckmans; Emilia Rota; Charles M Scrimgeour

2004-01-01

51

Use of foliar 15 N and 13 C abundance to evaluate effects of microbiotic crust on nitrogen and water utilization in Pinus massoniana in deteriorated pine stands of south China  

Microsoft Academic Search

We compared the foliar ? 15N and ? 13C values of Pinus massoniana growing on soils with and without microbiotic crust to examine the influence of the microbiotic crust on N and water use in plants in deteriorated watersheds in southern China. At our study site, litterfall and undergrowth had been intensively removed for fuel and soil N concentration was

Ryunosuke Tateno; Shigeo Katagiri; Hideyuki Kawaguchi; Yasuhide Nagayama; Changhua Li; Atsuko Sugimoto; Keisuke Koba

2003-01-01

52

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

53

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

54

New Method of Denitrification Analysis of Bradyrhizobium Field Isolates by Gas Chromatographic Determination of 15N-Labeled N2  

PubMed Central

To evaluate the denitrification abilities of many Bradyrhizobium field isolates, we developed a new 15N-labeled N2 detection methodology, which is free from interference from atmospheric N2 contamination. 30N2 (15N15N) and 29N2 (15N14N) were detected as an apparent peak by a gas chromatograph equipped with a thermal conductivity detector with N2 gas having natural abundance of 15N (0.366 atom%) as a carrier gas. The detection limit was 0.04% 30N2, and the linearity extended at least to 40% 30N2. When Bradyrhizobium japonicum USDA110 was grown in cultures anaerobically with 15NO3?, denitrification product (30N2) was detected stoichiometrically. A total of 65 isolates of soybean bradyrhizobia from two field sites in Japan were assayed by this method. The denitrification abilities were partly correlated with filed sites, Bradyrhizobium species, and the hup genotype.

Sameshima-Saito, Reiko; Chiba, Kaori; Minamisawa, Kiwamu

2004-01-01

55

Combustion influences on natural abundance nitrogen isotope ratio in soil and plants following a wildfire in a sub-alpine ecosystem.  

PubMed

This before-and-after-impact study uses the natural abundance N isotope ratio (?(15)N) to investigate the effects of a wildfire on sub-alpine ecosystem properties and processes. We measured the (15)N signatures of soil, charred organic material, ash and foliage in three sub-alpine plant communities (grassland, heathland and woodland) in south-eastern Australia. Surface bulk soil was temporarily enriched in (15)N immediately after wildfire compared to charred organic material and ash in all plant communities. We associated the enrichment of bulk soil with fractionation of N during combustion and volatilization of N, a process that also explains the sequential enrichment of (15)N of unburnt leaves > ash > charred organic material in relation to duration and intensity of heating. The rapid decline in (15)N of bulk soil to pre-fire values indicates that depleted ash, containing considerable amounts of total N, was readily incorporated into the soil. Foliar ?(15)N also increased with values peaking 1 year post-fire. Foliar enrichment was foremost coupled with the release of enriched NH4 (+) into the soil owing to isotopic discrimination during volatilization of soluble N and combustion of organic material. The mode of post-fire regeneration influenced foliar (15)N enrichment in two species indicating use of different sources of N following fire. The use of natural abundance of (15)N in soil, ash and foliage as a means of tracing transformation of N during wildfire has established the importance of combustion products as an important, albeit temporary source of inorganic N for plants regenerating after wildfire. PMID:23649752

Huber, Edith; Bell, Tina L; Adams, Mark A

2013-05-07

56

A robust method for ammonium nitrogen isotopic analysis in freshwater and seawater at natural abundance levels  

NASA Astrophysics Data System (ADS)

Natural ammonium N isotopic abundance has been increasingly used in studies of marine and freshwater biogeochemistry. However, current methods are time-consuming, subject to interference from DON, and not reliable at low concentrations. Our new method for determining the ?15N of ammonium overcomes these difficulties by employing the oxidation of ammonium to nitrite followed by conversion of nitrite to nitrous oxide. In the first step, ammonium is quantitatively oxidized by hypobromite at pH~12. After the addition of sodium arsenite to consume excess hypobromite, yield is verified by colorimetric NO2-measurement using sulfanilamide and naphthyl ethylenediamine (NED). Nitrite is further reduced to N2O by a 1:1 sodium azide and acetic acid buffer solution using previously established procedures. Buffer concentration can be varied according to sample matrix to ensure that a reaction pH between 2 and 4 is reached. The product nitrous oxide is then isotopically analyzed using a continuous flow purge and cryogenic trap system coupled to an isotope ratio mass spectrometer. Reliable ?15N values (±0.31‰) are obtained over a concentration range of 0.5 ?M to 20 ?M using 20 ml volumes of either fresh or seawater samples. Reagent blanks are very low, about 0.05 ?M. There is no interference from any of the nitrogen containing compounds tested except short chain aliphatic amino acid (i.e. glycine) which typically are not present at sufficiently high environmental concentrations to pose a problem.

Zhang, L.; Altabet, M. A.; Wu, T.; Hadas, O.

2006-12-01

57

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

Microsoft Academic Search

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

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

2002-01-01

58

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

59

Measurement of N 2 fixation in 30 cowpea ( Vigna unguiculata L. Walp.) genotypes under field conditions in Ghana, using the 15 N natural abundance technique  

Microsoft Academic Search

In 2005 and 2006, 30 and 15 cowpea genotypes were respectively evaluated for plant growth and symbiotic performance at Manga\\u000a in Northern Ghana, in order to identify N2-fixing potential of these cowpea genotypes as source of N for cropping systems. The results showed differences in biomass\\u000a production by the 30 or 15 cowpea genotypes. In 2005, cultivars Fahari, Mchanganyiko, IT97K-499-39,

Alphonsus K. Belane; Felix D. Dakora

2009-01-01

60

Saprotrophic versus symbiotic strategy during truffle ascocarp development under holm oak. A response based on 13 C and 15 N natural abundance  

Microsoft Academic Search

– \\u000a \\u000a • The development of truffles in the soil is not well understood. It is not known if a direct transfer of carbohydrates takes\\u000a place between the host tree and the developing ascocarps through ectomycorrhizal structures or whether sporophores become\\u000a independent from their hosts after several weeks or months and are able to use dead host tissues or soil organic

Bernd Zeller; Claude Bréchet; Jean-Paul Maurice; François Le Tacon

2008-01-01

61

Analysis of the urinary glucose-[15N, 15N]-ureide content in the study of the lactose-[15N, 15N]-ureide metabolism in healthy humans  

Microsoft Academic Search

Background\\/Objectives:Lactose-[15N, 15N]-ureide is used to study the fate of the colonic urea-nitrogen metabolism. During the passage through the gastrointestinal tract, lactose ureide is hydrolysed to glucose ureide, which is absorbed to a limited extent from the small intestine and is excreted urinarily. In the present study, a procedure has been developed to quantify the urinary excretion of glucose-[15N, 15N]-ureide. In

V De Preter; E Houben; K Windey; A Luypaerts; K Verbeke

2011-01-01

62

Practical recommendations for the reduction of memory effects in compound-specific 15N/14N-ratio analysis of enriched amino acids by gas chromatography/combustion/isotope ratio mass spectrometry.  

PubMed

Gas chromatography/combustion/isotope ratio mass spectrometry (GC-C-IRMS) is a highly sensitive approach which allows the analysis of the (13)C/(12)C and (15)N/(14)N isotope composition of amino acids in the range of natural abundance or in slightly (13)C- and (15)N-enriched samples. However, the accuracy of measurements remains a permanent challenge. Here we show the effect of the presence of slightly (15)N-enriched compounds in physiological samples on the accuracy and reproducibility of (15)N-abundances of amino acids within or between analytical runs. We spiked several individual amino acids with the respective (15)N-labelled isotopomer and measured the (15)N/(14)N ratios of other amino acids in the same sample or in the following analytical runs. Intra- and inter-run memory effects can be observed in (15)N/(14)N ratios of amino acids. Sample throughput is reduced when cleaning runs using standard mixtures are required to restore initial conditions after runs of samples with (15)N-enriched analytes. Possible reasons for the observed phenomenon and its implications for work in the lower (15)N-enrichment range (<0.5 APE) are discussed and include different aspects of gas chromatography, derivatisation, and hot catalytic metal surface effects. Results need to be interpreted with caution if complex physiological samples contain (15)N-enriched amino acids beyond 500‰ ?(15)N (~0.18 APE). PMID:22173808

Petzke, Klaus J; Metges, Cornelia C

2012-01-30

63

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

64

Dynamic nuclear polarization enhanced natural abundance 17O spectroscopy.  

PubMed

We show that natural abundance oxygen-17 NMR of solids could be obtained in minutes at a moderate magnetic field strength by using dynamic nuclear polarization (DNP). Electron spin polarization could be transferred either directly to (17)O spins or indirectly via (1)H spins in inorganic oxides and hydroxides using an oxygen-free solution containing a biradical polarization agent (bTbK). The results open up a powerful method for rapidly acquiring high signal-to-noise ratio solid-state NMR spectra of (17)O nuclear spins and to probe sites on or near the surface, without the need for isotope labeling. PMID:23379257

Blanc, Frédéric; Sperrin, Luke; Jefferson, David A; Pawsey, Shane; Rosay, Melanie; Grey, Clare P

2013-02-13

65

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

66

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...

67

PARTITIONING THE RELATIVE INFLUENCE OF SOIL N, MYCORRHIZAE, AND FOLIAR N UPTAKE ON FOLIAR delta15N PATTERNS: CAN WE DETECT FOLIAR UPTAKE OF REACTIVE N?  

Microsoft Academic Search

Vegetation is an important sink for atmospheric reactive N in N-limited systems and may be capable of incorporating reactive N compounds directly into leaves through the foliar uptake pathway. A proxy for atmospheric reactive N entering vegetation would be useful to estimate the impact of direct foliar N uptake on plant metabolism. Natural abundance foliar N isotopic composition (delta15N) is

D. Vallano; J. P. Sparks

2009-01-01

68

Human and climate impact on ¹?N natural abundance of plants and soils in high-mountain ecosystems: a short review and two examples from the Eastern Pamirs and Mt. Kilimanjaro.  

PubMed

Population pressure increasingly endangers high-mountain ecosystems such as the pastures in the Eastern Pamirs and the mountain forests on Mt. Kilimanjaro. At the same time, these ecosystems constitute the economic basis for millions of people living there. In our study, we, therefore, aimed at characterising the land-use effects on soil degradation and N-cycling by determining the natural abundance of (15)N. A short review displays that ?(15)N of plant-soil systems may often serve as an integrated indicator of N-cycles with more positive ?(15)N values pointing towards N-losses. Results for the high-mountain pastures in the Eastern Pamirs show that intensively grazed pastures are significantly enriched in (15)N compared to the less-exploited pastures by 3.5 ‰, on average. This can be attributed to soil organic matter degradation, volatile nitrogen losses, nitrogen leaching and a general opening of the N-cycle. Similarly, the intensively degraded savanna soils, the cultivated soils and the soils under disturbed forests on the foothill of Mt. Kilimanjaro reveal very positive ?(15)N values around 6.5 ‰. In contrast, the undisturbed forest soils in the montane zone are more depleted in (15)N, indicating that here the N-cycle is relatively closed. However, significantly higher ?(15)N values characterise the upper montane forest zone at the transition to the subalpine zone. We suggest that this reflects N-losses by the recently monitored and climate change and antropogenically induced increasing fire frequency pushing the upper montane rainforest boundary rapidly downhill. Overall, we conclude that the analysis of the (15)N natural abundance in high-mountain ecosystems is a purposeful tool for detecting land-use- or climate change-induced soil degradation and N-cycle opening. PMID:21745030

Zech, Michael; Bimüller, Carolin; Hemp, Andreas; Samimi, Cyrus; Broesike, Christina; Hörold, Claudia; Zech, Wolfgang

2011-07-11

69

Increasing plant use of organic nitrogen with elevation is reflected in nitrogen uptake rates and ecosystem delta15N.  

PubMed

It is hypothesized that decreasing mean annual temperature and rates of nitrogen (N) cycling causes plants to switch from inorganic to organic forms of N as the primary mode of N nutrition. To test this hypothesis, we conducted field experiments and collected natural-abundance delta15N signatures of foliage, soils, and ectomycorrhizal sporocarps along a steep elevation-climate gradient in the White Mountains, New Hampshire, USA. Here we show that with increasing elevation organic forms of N became the dominant source of N taken up by hardwood and coniferous tree species based on dual-labeled glycine uptake analysis, an important confirmation of an emerging theory for the biogeochemistry of the N cycle. Variation in natural abundance foliar delta15N with elevation was also consistent with increasing organic N uptake, though a simple, mass balance model demonstrated that the uptake of delta15N depleted inorganic N, rather than fractionation upon transfer of N from mycorrhizal fungi, best explains variations in foliar delta15N with elevation. PMID:21661551

Averill, Colin; Finzi, Adrien

2011-04-01

70

Analytical methods in 15 N research  

Microsoft Academic Search

Although the stable isotope15N is an indispensable tool in research to trace the fate of fertilizer nitrogen in soil\\/plant systems, the analytical methods used in this research are time consuming and prone to many errors. This paper outlines the methods used in an international program of nitrogen research coordinated by the International Fertilizer Development Center (IFDC). The different steps in

RJ Buresh; ER Austin; ET Craswell

1982-01-01

71

Maize Residue Decomposition Measurement Using Soil Surface Carbon Dioxide Fluxes and Natural Abundance of Carbon13  

Microsoft Academic Search

organic matter content and nutrient cycling. We hypothesized that mation obtained is mostly relevant to aboveground crop natural abundance 13 C analyses could be used with soil CO2 flux measurements to quantify the short-term decomposition rates of residues. The natural abundance of 13 C has also been maize (Zea mays L.) residues under undisturbed field conditions. For used to study

Philippe Rochette; Denis A. Angers; Lawrence B. Flanagan

1999-01-01

72

Tree Species of the Central Amazon Affects Natural Abundance of Nitrous Oxide Isotopes  

NASA Astrophysics Data System (ADS)

The use of stable isotopes of N and O in N2O has been proposed as a way to better constrain the global budget of atmospheric N2O and to better understand relative contribution of the main microbial processes (nitrification and denitrification) responsible for N2O formation in soil. This study examined the effects of tree species used in plantation systems of the Brazilian Amazon in comparison to natural and secondary forests on the isotopic composition of N{2}O emitted from the soil. We also compared the effects of tree species with those of soil moisture, as we expected the latter to be the main factor regulating the proportion of nitrifier and denitrifier derived N2O and, consequently, isotopic signatures of N2O. To our knowledge, this is the first study to show that tree species significantly affect the 15N composition of nitrous oxide, likely due to tree-mediated changes in microbial communities. However, we found no evidence that varying contributions of nitrification and denitrification to N2O flux contributed to variation in the 15N composition of N2O. In our study, all N2O was likely produced by denitrification. We suspect that the differences in 15N observed were due to effect of nitrate immobilization on isotopes of N in nitrate, the substrate for denitrification. However, this explanation needs further verification. While tree species did affect the 15N composition of N2O, they did not affect the rate of N2O emission. We conclude that tree species contribute to a large isotopic variation in N2O observed in a range tropical forest soils. We found that soil water affects both 15N and 18O in N2O, with wetter soils producing N2O depleted in 15N and 18O. This is likely caused by increased activity of denitrification and/or decrease nitrate immobilization in case of 15N, and both by denitrification and by direct exchange of 18O-H2O and N2O with NO3-.

Menyailo, O. V.; Lehmann, J.; Gebauer, G.; Hungate, B. A.; Zech, W.

2001-05-01

73

Some natural variations in the relative abundance of copper isotopes  

USGS Publications Warehouse

The relative isotopic abundance of copper has been measured in a number of minerals and a few plant materials. Suites of samples from Michigan and the Colorado Plateau have been examined in more detail to determine if local variations due to isotopic exchange or diffusion could be found. The relative isotopic abundance of copper in specimens from several other localities was also determined. The variations noted were small but in some cases were felt to be significant because they were larger than the experimental error (0??1 per cent in the ratio). A total spread of -1 to +8 parts per mil compared to the standard was found in the specimens tested. ?? 1958.

Walker, E. C.; Cuttitta, F.; Senftle, F. E.

1958-01-01

74

Indirect Measurement of {sup 15}N(p,{alpha}){sup 12}C and {sup 18}O(p,{alpha}){sup 15}N. Applications to the AGB Star Nucleosynthesis  

SciTech Connect

The Trojan Horse Method has been recently applied to the study of reactions involved in fluorine nucleosynthesis inside AGB stars. Fluorine abundance is important since it allows to constrain mixing models from the comparison of the observed fluorine abundances with the ones predicted by models. Anyway direct measurements of the cross section do not extend down to the Gamow peak, which is the astrophysically relevant energy region. In particular the study focuses on the {sup 15}N(p,{alpha}){sup 12}C and the {sup 18}O(p,{alpha}){sup 15}N reactions which can influence fluorine yield as they are part of {sup 19}F production/destruction network.

La Cognata, M.; Spitaleri, C.; Cherubini, S.; Crucilla, V.; Gulino, M.; Lamia, L.; Pizzone, R. G.; Puglia, S. M. R.; Rapisarda, G. G.; Romano, S.; Sergi, M. L.; Tumino, A. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud and Universita degli Studi di Catania, Catania (Italy); Tribble, R.; Al-Abdullah, T.; Banu, A.; Fu, C.; Goldberg, V.; Mukhamedzhanov, A.; Tabacaru, G.; Trache, L. [Cyclotron Institute, Texas A and M University, College Station, TX 77843 (United States)] (and others)

2008-04-06

75

Abundant Shale Gas Resources: Long-Term Implications for U.S. Natural Gas Markets  

Microsoft Academic Search

According to recent assessments, the United States has considerably more recoverable natural gas in shale formations than was previously thought. Such a development raises expectations that U.S. energy consumption will shift toward natural gas. To examine how the apparent abundance of natural gas and projected growth of its use might affect natural gas prices, production, and consumption, we use NEMS-RFF

Stephen P. A. Brown; Alan Krupnick

2010-01-01

76

Natural Abundance 14C Content of Dibutyl Phthalate (DBP) from Three Marine Algae  

PubMed Central

Analysis of the natural abundance 14C content of dibutyl phthalate (DBP) from two edible brown algae, Undaria pinnatifida and Laminaria japonica, and a green alga, Ulva sp., revealed that the DBP was naturally produced. The natural abundance 14C content of di-(2-ethylhexyl) phthalate (DEHP) obtained from the same algae was about 50–80% of the standard sample and the 14C content of the petrochemical (industrial) products of DBP and DEHP were below the detection limit.

Namikoshi, Michio; Fujiwara, Takeshi; Nishikawa, Teruaki; Ukai, Kazuyo

2006-01-01

77

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

78

Does landscape composition affect pest abundance and their control by natural enemies? A review  

Microsoft Academic Search

Landscape management could contribute to sustainable pest control. Landscape composition, in particular, could either directly impact a pest abundance by affecting its dispersal, mortality or reproduction, or indirectly by affecting its natural enemies. We performed an analysis of the scientific literature to assess how the proportion of different land covers at the landscape level is related to the abundance of

Andrea Veres; Sandrine Petit; Cyrille Conord; Claire Lavigne

79

Detection of human muscle glycogen by natural abundance /sup 13/C NMR  

SciTech Connect

Natural abundance /sup 13/C nuclear magnetic resonance spectroscopy was used to detect signals from glycogen in the human gastrocnemius muscle. The reproducibility of the measurement was demonstrated, and the ability to detect dynamic changes was confirmed by measuring a decrease in muscle glycogen levels after exercise and its subsequent repletion. Single frequency gated /sup 1/H decoupling was used to obtain decoupled natural abundance /sup 13/C NMR spectra of the C-1 position of muscle glycogen.

Avison, M.J.; Rothman, D.L.; Nadel, E.; Shulman, R.G.

1988-03-01

80

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

2010-08-13

81

Investigating microbial carbon cycling using natural abundance isotope analysis of PLFA  

Microsoft Academic Search

Understanding microbial carbon sources and cycling is fundamental to our conceptualization of microbial ecosystems and their role in biogeochemical cycling in natural systems. Achieving this understanding requires application of a wide range of approaches. Natural abundance isotope analysis of individual compounds, particularly cellular components such as Phospholipids Fatty Acids (PLFA) can provide insights into the carbon sources and metabolic activities

G. G. Slater; A. Brady; B. Cowie

2008-01-01

82

Relationships among leaf damage, natural enemy release, and abundance in exotic and native prairie plants  

Microsoft Academic Search

The Enemy Release hypothesis holds that exotic plants may have an advantage over native plants because their specialized natural\\u000a enemies are absent. We tested this hypothesis by measuring leaf damage and plant abundance for naturally-occurring plants\\u000a in prairies, and by removing natural enemies in an enemy exclusion experiment. We classified plants as invasive exotic, noninvasive\\u000a exotic, or native, to determine

Eric C. Vasquez; Gretchen A. Meyer

2011-01-01

83

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.

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

2011-01-01

84

Determination of minor isotope abundances in naturally occurring uranium materials. The tracing power of isotopic signatures for uranium.  

National Technical Information Service (NTIS)

The mass spectrometric determination of minor abundant isotopes, (sup 234)U and (sup 236)U in naturally occurring uranium materials requires instruments of high abundance sensitivity and the use of highly sensitive detection systems. In this study the the...

R. Ovaskainen

1999-01-01

85

Biological Denitrification Technology of Sewage via delta15N Identification  

Microsoft Academic Search

In order to investigate the quantitative relations of nitrogenous compounds in the seal system and dynamic systems by molecule recognition technologies, the stable isotope 15N technology was adopted to identify these nitrogenous compounds. Experiment results showed that it's effective for the 15N identification technology to measure the quantitative relation of denitrification reaction. Furthermore, the denitrification could enrich 15N in its

Yongxiang Zhang; Haijuan Wei

2009-01-01

86

Measurement at the field scale of soil delta13C and delta15N under improved grassland.  

PubMed

Variations in natural abundance of carbon (C) and nitrogen (N) stable isotopes are widely used as tools for many aspects of scientific research. By examining variations in the ratios of heavy to light stable isotopes, information can be obtained as to what physical, chemical and biological processes may be occurring. The spatial heterogeneity of soil delta(15)N- and delta(13)C-values across a range of scales and under different land use have been described by a number of researchers and the natural abundances of the C and N stable isotopes in soils have been found to be correlated with many factors including hydrology, topography, land use, vegetation cover and climate. In this study the Latin square sampling +1 (LSS+1) sampling method was compared with a simple grid sampling approach for delta(13)C and delta(15)N measurement at the field scale. A set of 144 samples was collected and analysed for delta(15)N and delta(13)C from a 12 x 12 grid (in a 1 ha improved grassland field in south-west England). The dimension of each cell of the grid was approximately 11 x 6 m. The 12 x 12 grid was divided into four 6 x 6 grids and the LSS+1 sampling technique was applied to these and the main 12 x 12 grid for a comparison of sample means and variation. The LSS+1 means from the 12 x 12 grid and the four 6 x 6 grids compared well with the overall grid mean because of the low variation within the field. The LSS+1 strategy (13 samples) generated representative samples from the 12 x 12 grid, and hence would be an acceptable method for sampling similar plots for the measurement of mean isotopic composition. PMID:20112268

Dixon, E R; Blackwell, M S A; Dhanoa, M S; Berryman, Z; de la Fuente Martinez, N; Junquera, D; Martinez, A; Murray, P J; Kemp, H F; Meier-Augenstein, W; Duffy, A; Bol, R

2010-03-15

87

The magnitude of spatial and temporal variation in ?15N and ?13C differs between taxonomic groups: Implications for food web studies  

NASA Astrophysics Data System (ADS)

Understanding variability in stable isotope abundance is essential for effective hypothesis testing and evaluating food sources, trophic levels and food web structure. The magnitude and sources of variability are likely to differ among taxonomic and functional groups. We aimed to quantify variability of ?13C and ?15N for 16 species representing seven distinct taxonomic groups of benthic invertebrates and autotrophs in a marine ecosystem. We quantified the magnitude of variability among individuals or shoots separated by metres, among eight sites separated by kilometres, and between two survey occasions separated by months. ?13C varied by as much as 7‰ for primary producers, 4‰ for consumers, while ?15N varied by as much as 9‰ and 2‰ respectively. Variation in ?15N of seagrass was largely accounted for by differences among sites, while variation in ?13C was mainly attributable to shoots collected a few metres apart. Compared to seagrasses, variation in macroalgae was mainly explained by differences between the two survey occasions for ?15N and among individuals collected a few metres apart for ?13C. Variation was generally lower for consumers and typically explained by differences among individuals for ?15N but displayed inconsistent patterns for ?13C. Dual isotope Bayesian mixing models showed that the potential contributions of food sources for herbivorous consumers varied among sites and between survey occasions, and also that there was high variability or uncertainty in the contributions of sources within sites. The relative consistency in the main sources of variation among broad taxonomic groups in autotrophs suggests that aspects of physiology that are phylogenetically conserved might be important influences on variation in natural abundances of stable isotopes. In comparison, the sources of variability were less consistent within and among broad consumer groups, suggesting complex interactions between consumers and their food sources.

Hyndes, Glenn A.; Hanson, Christine E.; Vanderklift, Mathew A.

2013-03-01

88

Natural abundance high-resolution solid state 2 H NMR spectroscopy  

NASA Astrophysics Data System (ADS)

We report for the first time an approach for natural abundance solid state 2 H NMR spectroscopy involving magic angle sample spinning (MAS), high-power 1 H decoupling (HPPD) and 1 H- 2 H cross polarization (CP). Taking tetrakis(trimethylsilyl)silane (TTMSS), adamantane, 1-chloroadamantane, hexamethylbenzene (HMB), 2,2-dimethyl-1,3-propanediol (DMPD) and 2-hydroxymethyl-2-methyl-1,3-propanediol (HMPD) as examples, it has been shown that the combination of HPPD and MAS can be applied readily to study rotator phase solids, allowing isotropic peaks arising from chemically inequivalent 2 H nuclei to be resolved. For natural abundance samples of TTMSS and chloroadamantane, it has been shown that 2 H CP/HPPD/MAS NMR experiments, involving polarization transfer from 1 H to 2 H, may provide considerable sensitivity enhancement in comparison with single pulse experiments.

Aliev, Abil E.; Harris, Kenneth D. M.; Apperley, David C.

1994-08-01

89

Amino acids as a nitrogen source in temperate upland grasslands: the use of dual labelled ((13)C, (15)N) glycine to test for direct uptake by dominant grasses.  

PubMed

It is becoming increasingly apparent that soil amino acids are a principal source of nitrogen (N) for certain plants, and especially those of N-limited environments. This study of temperate upland grasslands used glycine-2-(13)C-(15)N and ((15)NH4)(2)SO(4) labelling techniques to test the hypothesis that plant species which dominate 'unimproved' semi-natural grasslands (Festuca-Agrostis-Galium) are able to utilise amino acid N for growth, whereas those plants which dominate 'improved' grasslands (Lolium-Cynosurus), that receive regular applications of inorganic fertiliser, use inorganic N forms as their main N source. Data from field experiments confirmed that 'free' amino acids were more abundant in 'unimproved' than 'improved' grassland and that glycine was the dominant amino acid type (up to 42% of total). Secondly, the injection of representative amounts of glycine-2-(13)C-(15)N (4.76 and 42.86 mM) into intact soil cores from the two grassland types provided evidence of direct uptake of glycine by plants, with both (15)N and (13)C being detected in plant material of both grasslands. Finally, a microcosm experiment demonstrated no preferential uptake of amino acid N by the grasses which dominate the grassland types, namely Holcus lanatus, Festuca rubra, Agrostis capillaris from the 'unimproved' grassland, and Lolium perenne from the 'improved' grassland. Again, both (13)C and (15)N were detected in all grass species suggesting uptake of intact glycine by these plants. PMID:10920354

Streeter, T C; Bol, R; Bardgett, R D

2000-01-01

90

High Resolution NMR ^15N and ^31P NMR Of Antiferroelectric Phase Transition in Ammonium Dihydrogen Arsenate and Ammonium Dihydrogen Phosphate  

NASA Astrophysics Data System (ADS)

Natural abundance ^15N CPMAS NMR has been used to investigate the paraelectric-antiferroelectric phase transition of NH4H2AsO4 (ADA) (TN˜216K) and of NH4H2PO4 (ADP) (148K), with a focus on the role of the NH4^+ ion. Isotropic chemical shift of ^15N for ADA exhibits an almost linear temperature dependence to within TN±1K, and then changes discontinuously, followed by another almost linear dependence. The spectra of the paraelectric and antiferroelectric phases coexist around the TN. The sharp anomaly around TN implies that the NH4^+ ions undergo a displacive transition, whereas the protons in the O-HO bonds undergo an order-disorder transition. The ^15N data thus support a mixed order-disorder-displacive mechanism for this transition. The ^15N data on ADP exhibit somewhat different behavior. ^31P CPMAS measurements will also be presented and discussed in terms of the above model.

Gunaydin-Sen, Ozge

2005-03-01

91

New insights into the structure and chemistry of Titan's tholins via13C and 15N solid state nuclear magnetic resonance spectroscopy  

NASA Astrophysics Data System (ADS)

Tholins are complex C,N-containing organic compounds produced in the laboratory. They are considered to provide materials that are analogous to those responsible for the haze observed in Titan's atmosphere. These compounds present an astrobiological interest due to their ability to release amino acids upon hydrolysis. Their chemical structure has been investigated using a large number of techniques. However, to date no detailed nuclear magnetic resonance (NMR) study has been performed on these materials despite the high potential of this technique for investigating the environment of given nuclei. Here 13C and 15N solid state NMR spectroscopy was applied to obtain new insights into the chemical structure of tholins produced through plasma discharge in gaseous N2sbnd CH4 mixtures designed to simulate the atmosphere of Titan. Due to the low natural abundance of these isotopes, a 13C and 15N-enriched tholin sample was synthesized using isotopically enriched gas precursors. Various pulse sequences including 13C and 15N single pulse, 1Hsbnd 13C and 1Hsbnd 15N cross-polarisation and 1Hsbnd 15Nsbnd 13C double cross-polarisation were used. These techniques allowed complete characterisation of the chemical and structural environments of the carbon and nitrogen atoms. The NMR assignments were supplemented and confirmed by ab initio electronic structure calculations for model structures and molecular fragments.

Derenne, S.; Coelho, C.; Anquetil, C.; Szopa, C.; Rahman, A. S.; McMillan, P. F.; Corà, F.; Pickard, C. J.; Quirico, E.; Bonhomme, C.

2012-11-01

92

Spatial relationship between ? 15 N and elevation in agricultural landscapes  

Microsoft Academic Search

Understanding of the nitrogen (N) cycle and its spatial variability is important for managing ecosystems. Soil 15 N, as an important indicator of different soil ni- trogen cycling processes, may provide critical information about the spatial variability in soil N cycling. The objec- tive of this study was to examine the dominant landscape scale variability of 15 N, the location

A. Biswas; F. L. Walley

2008-01-01

93

A selective 15N-to-(1)H polarization transfer sequence for more sensitive detection of 15N-choline.  

PubMed

The sensitivity and information content of heteronuclear nuclear magnetic resonance is frequently optimized by transferring spin order of spectroscopic interest to the isotope of highest detection sensitivity prior to observation. This strategy is extended to 15N-choline using the scalar couplings to transfer polarization from 15N to choline's nine methyl 1H spins in high field. A theoretical analysis of a sequence using nonselective pulses shows that the optimal efficiency of this transfer is decreased by 62% as the result of competing 15N-(1)H couplings involving choline's four methylene protons. We have therefore incorporated a frequency-selective pulse to support evolution of only the 15N-methyl 1H coupling during the transfer period. This sequence provides a 52% sensitivity enhancement over the nonselective version in in vitro experiments on a sample of thermally polarized 15N-choline in D2O. Further, the 15N T1 of choline in D2O was measured to be 217+/-38 s, the 15N-methyl 1H coupling constant was found to be 0.817+/-0.001 Hz, and the larger of choline's two 15N-methylene 1H coupling constants was found to be 3.64+/-0.0 1Hz. Possible improvements and applications to in vivo experiments using long-lived hyperpolarized heteronuclear spin order are discussed. PMID:20472478

Pfeilsticker, Jessica A; Ollerenshaw, Jason E; Norton, Valerie A; Weitekamp, Daniel P

2010-04-27

94

Two new organic reference materials for ??13C and ??15N measurements and a new value for the ?? 13C of NBS 22 oil  

USGS Publications Warehouse

Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a ?? 13C value of -26.24??? relative to VPDB and a ?? 15N value of +4.52??? relative to N2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13C and 15N. USGS41 has a ?? 13C value of +37.76??? and a ??15N value of +47.57???. The ??13C and ??15N values of both materials were measured against the international reference materials NBS 19 calcium carbonate (??13C = +1.95???), L-SVEC lithium carbonate (??13C = -46.48???), IAEA-N-1 ammonium sulfate (??15N=0.43???), and USGS32 potassium nitrate (?? 15N = 180???) by on-line combustion continuous-flow and off-line dual-inlet isotope-ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of ??13C is better than 0.13???, and that of ??15N is better than 0. 13??? in 100-??g amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass-dependent fractionations, and isotope-ratio-scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a ?? 13C value for NBS 22 oil of -29.91???, in contrast to the commonly accepted value of -29.78??? for which off-line blank corrections probably have not been quantified satisfactorily. Published in 2003 by John Wiley & Sons, Ltd.

Qi, H.; Coplen, T. B.; Geilmann, H.; Brand, W. A.; Bohlke, J. K.

2003-01-01

95

Radiative n 15N Capture at Low Energies  

NASA Astrophysics Data System (ADS)

The possibility of describing the experimental data for the total cross sections of radiative n 15N capture at energies from 25 to 370 keV is considered within the framework of the potential cluster model with classification of orbital states according to the Young schemes. It is shown that it is entirely possible to explain the magnitude of the cross sections in the considered energy range on the basis of only the E1 transitions from various states of n 15N scattering into four bound states of the 16N nucleus in the n 15N channel.

Dubovichenko, S. B.

2013-10-01

96

The role of 15N CSA and CSA/dipole cross-correlation in 15N relaxation in solid proteins  

NASA Astrophysics Data System (ADS)

The influence of the 15N CSA on 15N longitudinal relaxation is investigated for an amide group in solid proteins in powder form under MAS. This contribution is determined to be typically 20 33% of the overall longitudinal relaxation rate, at 11.74 and 16.45 T, respectively. The improved treatment is used to analyze the internal dynamics in the protein Crh, in the frame of a motional model of diffusion in a cone, using the explicit average sum approach. Significant variations with respect to the determined dynamics parameters are observed when properly accounting for the contribution of 15N CSA fluctuations. In general, the fit of experimental data including CSA led to the determination of diffusion times (?w) which are longer than when considering only an 15N 1H dipolar relaxation mechanism. CSA-Dipole cross-correlation is shown to play little or no role in protonated solids, in direct contrast to the liquid state case.

Sein, Julien; Giraud, Nicolas; Blackledge, Martin; Emsley, Lyndon

2007-05-01

97

Fast-pulsing NMR techniques for the detection of weak interactions: successful natural abundance probe of hydrogen bonds in peptides.  

PubMed

Structural investigations of peptides using NMR spectroscopy rarely include the detection of N-HO[double bond, length as m-dash]C and N-HN hydrogen bonds, because the relevant heteronuclei have a low natural abundance while the small trans hydrogen bond scalar couplings reduce the sensitivity. Fast repetition NMR techniques combined with state of the art spectrometer specifications allowed the enhancement of the sensitivity for detection of hydrogen bonds at natural isotopic abundance. PMID:24105064

Altmayer-Henzien, Amandine; Declerck, Valérie; Aitken, David J; Lescop, Ewen; Merlet, Denis; Farjon, Jonathan

2013-10-16

98

Whole Body Nitric Oxide Synthesis in Healthy Men Determined from [15N]arginine-to- [15N]citrulline Labeling  

Microsoft Academic Search

The rates of whole body nitric oxide (NO) synthesis, plasma arginine flux, and de novo arginine synthesis and their relationships to urea production, were examined in a total of seven healthy adults receiving an L-amino acid diet for 6 days. NO synthesis was estimated by the rate of conversion of the [15N]guanidino nitrogen of arginine to plasma [15N]ureido citrulline and

Leticia Castillo; Louis Beaumier; Alfred M. Ajami; Vernon R. Young

1996-01-01

99

Emissive spectral analysis applied in 15N excretion test of Helicobacter pylori  

NASA Astrophysics Data System (ADS)

A new method for detecting the infection of Helicobacter pylor (HP), 15N-urea tracing and emissive optical spectroscopy method, is described in this paper. A group of 26 patients was tested. After 15N-urea was administered orally, urine specimen was collected from 30 to 120 minutes and its volume was measured. Then the concentration of ammonia in the urine specimen was determined. A special emissive optical spectrometer was applied to measure the 15N -abundance of the urine specimen, which was designed and manufactured by us and was an intelligent system. It contains a monchromator, a high frequency generator, a precise amplifier and a computer. The ratio (R) of the 15N amount of excretion in the urine to that of ingestion was found out. HP positive infection was predicated if R>0.3%. Taking the bacterial culture or (and) Gram stain as a reference standard, the specificity, sensitivity and positive predictability of our test were 81%, 89% and 84% respectively. The new method is sensitive, noninvasive and useful for clinical practice. It is worth studying further.

Zhu, Yayi; Wu, Jicong; Zhang, Zhenhua

2002-09-01

100

Stable Isotope Probing with 15N2 Reveals Novel Noncultivated Diazotrophs in Soil?  

PubMed Central

Biological nitrogen fixation is a fundamental component of the nitrogen cycle and is the dominant natural process through which fixed nitrogen is made available to the biosphere. While the process of nitrogen fixation has been studied extensively with a limited set of cultivated isolates, examinations of nifH gene diversity in natural systems reveal the existence of a wide range of noncultivated diazotrophs. These noncultivated diazotrophs remain uncharacterized, as do their contributions to nitrogen fixation in natural systems. We have employed a novel 15N2-DNA stable isotope probing (5N2-DNA-SIP) method to identify free-living diazotrophs in soil that are responsible for nitrogen fixation in situ. Analyses of 16S rRNA genes from 15N-labeled DNA provide evidence for nitrogen fixation by three microbial groups, one of which belongs to the Rhizobiales while the other two represent deeply divergent lineages of noncultivated bacteria within the Betaproteobacteria and Actinobacteria, respectively. Analysis of nifH genes from 15N-labeled DNA also revealed three microbial groups, one of which was associated with Alphaproteobacteria while the others were associated with two noncultivated groups that are deeply divergent within nifH cluster I. These results reveal that noncultivated free-living diazotrophs can mediate nitrogen fixation in soils and that 15N2-DNA-SIP can be used to gain access to DNA from these organisms. In addition, this research provides the first evidence for nitrogen fixation by Actinobacteria outside of the order Actinomycetales.

Buckley, Daniel H.; Huangyutitham, Varisa; Hsu, Shi-Fang; Nelson, Tyrrell A.

2007-01-01

101

(15)N-Labeled ionic probes for bioanalytical mass spectrometry.  

PubMed

An effective La-complex-based probe ionization method is reported. Novel stable isotopically labeled probes containing the (15)N-labeled 2,6-bis(oxazolin-2-yl)pyridine (pybox) ligand, succinimide-tetramethylpybox (NHS-TMpybox), maleimide-tetramethylpybox (Mal-TMpybox), and 4-(tetramethylpybox)-butyl bromoacetate (BrAc-TMpybox), have been synthesized and their value in analyzing large complex molecules has been studied. The value of the (15)N-labeled pybox-La complex in ionizing various compounds, including bioactive peptides by cold-spray ionization mass spectrometry is emphasized. PMID:20714487

Ito, Fumihiro; Ando, Shin; Iuchi, Masato; Nakamura, Tomoko; Satoko Yorita; Yamaguchi, Kentaro

2010-08-13

102

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

103

Investigating microbial carbon cycling using natural abundance isotope analysis of PLFA  

NASA Astrophysics Data System (ADS)

Understanding microbial carbon sources and cycling is fundamental to our conceptualization of microbial ecosystems and their role in biogeochemical cycling in natural systems. Achieving this understanding requires application of a wide range of approaches. Natural abundance isotope analysis of individual compounds, particularly cellular components such as Phospholipids Fatty Acids (PLFA) can provide insights into the carbon sources and metabolic activities of the in situ microbial community from environmental samples. This is primarily because specific PLFA can be well resolved by gas chromatography even from complex matrices where confounding biological/organic compound abound. These PLFA can then be attributed to the viable microbial community, in some cases to specific components of this community and due to characteristic biosynthetic fractionations of stable isotope ratios, ?13C analysis of PLFA can: differentiate isotopically distinct primary carbon sources of heterotrophic communities; identify isotopic patterns characteristic of autotrophic versus heterotrophic processes; and elucidate microbial biosynthetic pathways. In cases where there ?13C cannot provide resolution of carbon sources, new approaches in ?14C of PLFA can be applied. The vast range in ?14C of ancient and modern carbon provides an easily traceable signal that can differentiate uptake and utilization of these carbon sources. This is particularly useful in cases such as contaminated sites where petroleum based contamination has occurred, or in natural systems where microbial communities may be utilizing geologic versus recently photosynthetically fixed carbon. This talk will present several examples demonstrating the utility of this approach.

Slater, G. G.; Brady, A.; Cowie, B.

2008-12-01

104

Natural abundance variations in stable isotopes and their potential uses in animal physiological ecology.  

PubMed

Chemical, biological, and physical processes lead to distinctive "isotopic signatures" in biological materials that allow tracing of the origins of organic substances. Isotopic variation has been extensively used by plant physiological ecologists and by paleontologists, and recently ecologists have adopted the use of stable isotopes to measure ecosystem patterns and processes. To date, animal physiological ecologists have made minimal use of naturally occurring stable isotopes as tracers. Here we provide a review of the current and potential uses of naturally occurring stable isotopes in animal physiological ecology. We outline the physical and biological processes that lead to variation in isotopic abundance in plants and animals. We summarize current uses in animal physiological ecology (diet reconstruction and animal movement patterns), and suggest areas of research where the use of stable isotopes can be fruitful (protein balance and turnover and the allocation of dietary nutrients). We argue that animal physiological ecologists can benefit from including the measurement of naturally occurring stable isotopes in their battery of techniques. We also argue that animal physiologists can make an important contribution to the emerging field of stable isotopes in biology by testing experimentally the plethora of assumptions upon which the techniques rely. PMID:9683412

Gannes, L Z; Martínez del Rio, C; Koch, P

1998-03-01

105

The pure rotational spectrum of glycolaldehyde isotopologues observed in natural abundance  

NASA Astrophysics Data System (ADS)

The pure rotational spectrum of glycolaldehyde has been recorded from 6.5-20 GHz and 25-40 GHz in two pulsed-jet chirped pulse Fourier transform microwave spectrometers. The high phase stability of the spectrometers enables deep signal integration, allowing transitions from the 13C-substituted, 18O-substituted, and deuterium-substituted isotopologues to be observed in natural abundance. Transitions from HCOCH218OH are reported for the first time. Additional transitions from the 13C-substituted, deuterium-substituted, and HC18OCH2OH isotopologues, as well as previously unobserved weak lines from the main isotopologue, have been observed. Transitions from all isotopologues are used with previously reported transitions to refine the spectroscopic parameters for each isotopologue. A Kraitchman analysis was performed using the experimental rotational constants to determine the molecular structure of glycolaldehyde.

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

2013-02-01

106

Automated determination of silicon isotope natural abundance by the acid decomposition of cesium hexafluosilicate.  

PubMed

A procedure for the automated determination of isotopic abundances of silicon from biogenic and lithogenic particulate matter and from dissolved silicon in fresh or saltwaters is reported. Samples are purified using proven procedures through the reaction of Si with acidified ammonium molybdate, followed by precipitation with triethylamine and combustion of the precipitate to yield silicon dioxide. The silicon dioxide is converted to cesium hexafluosilicate by dissolution in hydrogen fluoride and the addition of cesium chloride. Isotopic analysis is accomplished by decomposing the cesium hexafluosilicate with concentrated sulfuric acid to generate silicon tetrafluoride gas. Silicon tetrafluoride is purified cryogenically and analyzed on a gas source isotope ratio mass spectrometer. Yields of silicon tetrafluoride are >99.5%. The procedure can be automated by modifying commercial inlet systems designed for carbonate analysis. The procedure is free of memory effects and isotopic biases. Reproducibility is +/-0.03-0.10 per thousand for a variety of natural and synthetic materials. PMID:16944891

Brzezinski, Mark A; Jones, Janice L; Beucher, Charlotte P; Demarest, Mark S; Berg, Howard L

2006-09-01

107

Natural abundance carbon 13 nuclear magnetic resonance spectroscopy of antifreeze glycoproteins  

SciTech Connect

Natural abundance /sup 13/C NMR spectroscopy (at 67.9 MHz) is used to study an aqueous solution of the antifreeze glycoproteins 3 to 6 from the Antarctic cod. Assignments of resonances to specific carbons of the known Ala-Ala-(..beta..Gal-(1 ..-->.. 3)-..cap alpha..-N-acetylgalactosamine)Thr repeating unit are presented. Some of the carbons of the proline residues of glycoprotein 6 are also identified. Spin-lattice relaxation times (at 30/sup 0/C), linewidths (at 35/sup 0/C), nuclear Overhauser enhancements (at 35/sup 0/C), and the temperature dependence of chemical shifts (from 0/sup 0/ to 75/sup 0/C) all strongly suggest that these antifreeze glycoproteins are predominantly or entirely flexible random coil polymers.

Berman, E. (Indiana Univ., Bloomington); Allerhand, A.; DeVries, A.L.

1980-05-25

108

?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

109

Preliminary 15 N studies on atmospheric nitrogenous trace gases  

Microsoft Academic Search

Preliminary nitrogen isotope data for ammonia from animal urine, fuel combustion, fertilizer use and fertilizer factories have been measured or estimated. It turns out that direct nitrogen isotope measurements of atmospheric ammonia at Jülich are in the expected range calculated from the d ranges of different sources. For deposition of atmospheric ammonium in Jülich-rain a depletion in15N with respect to

H. D. Freyer

1978-01-01

110

Preliminary15N studies on atmospheric nitrogenous trace gases  

Microsoft Academic Search

Preliminary nitrogen isotope data for ammonia from animal urine, fuel combustion, fertilizer use and fertilizer factories have been measured or estimated. It turns out that direct nitrogen isotope measurements of atmospheric ammonia at Jülich are in the expected range calculated from the delta ranges of different sources. For deposition of atmospheric ammonium in Jülich-rain a depletion in15N with respect to

H. D. Freyer

1978-01-01

111

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

112

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

2013-03-19

113

Assessing microbial uptake of petroleum hydrocarbons in groundwater systems using natural abundance radiocarbon.  

PubMed

Carbon sources utilized by the active microbial communities in shallow groundwater systems underlying three petroleum service stations were characterized using natural abundance radiocarbon ((14)C). Total organic carbon (TOC) Delta(14)C values ranged from -314 to -972 per thousand and petroleum-extracted residues (EXT-RES) ranged from -293 to -971 per thousand. Phospholipid fatty acids (PLFAs)-biomarkers for active microbial populations-ranged from -405 to -885 per thousand and a comparison of these values with potential carbon sources pointed to significant microbial assimilation of (14)C-free fossil carbon. The most (14)C-depleted PLFAs were found in the samples with the highest concentrations of total petroleum hydrocarbons (TPHs). A radiocarbon mass balance indicated up to 43% of the carbon in microbial PLFAs was derived from TPHs, providing direct evidence for biodegradation at two of three sites. At lower levels of TPHs Delta(14)C values of PLFAs were generally similar to or more enriched than all other carbon in the system indicating microbial utilization of a more (14)C-enriched carbon source and no resolvable evidence for microbial incorporation of petroleum-derived carbon. Results from this study suggest that it is possible to delineate petroleum biodegradation in groundwater systems using these techniques even in complex situations where there exists a wide range in the ages of natural organic matter (i.e., EXT-RES). PMID:20527914

Ahad, Jason M E; Burns, Leanne; Mancini, Silvia; Slater, Greg F

2010-07-01

114

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

115

Backbone dynamics of barstar: a (15)N NMR relaxation study.  

PubMed

Backbone dynamics of uniformly (15)N-labeled barstar have been studied at 32 degrees C, pH 6.7, by using (15)N relaxation data obtained from proton-detected 2D (1)H-(15)N NMR spectroscopy. (15)N spin-lattice relaxation rate constants (R(1)), spin-spin relaxation rate constants (R(2)), and steady-state heteronuclear (1)H-(15)N NOEs have been determined for 69 of the 86 (excluding two prolines and the N-terminal residue) backbone amide (15)N at a magnetic field strength of 14.1 Tesla. The primary relaxation data have been analyzed by using the model-free formalism of molecular dynamics, using both isotropic and axially symmetric diffusion of the molecule, to determine the overall rotational correlation time (tau(m)), the generalized order parameter (S(2)), the effective correlation time for internal motions (tau(e)), and NH exchange broadening contributions (R(ex)) for each residue. As per the axially symmetric diffusion, the ratio of diffusion rates about the unique and perpendicular axes (D( parallel)/D( perpendicular)) is 0.82 +/- 0.03. The two results have only marginal differences. The relaxation data have also been used to map reduced spectral densities for the NH vectors of these residues at three frequencies: 0, omega(H), and omega(N), where omega(H),(N) are proton and nitrogen Larmor frequencies. The value of tau(m) obtained from model-free analysis of the relaxation data is 5.2 ns. The reduced spectral density analysis, however, yields a value of 5.7 ns. The tau(m) determined here is different from that calculated previously from time-resolved fluorescence data (4.1 ns). The order parameter ranges from 0.68 to 0.98, with an average value of 0.85 +/- 0.02. A comparison of the order parameters with the X-ray B-factors for the backbone nitrogens of wild-type barstar does not show any considerable correlation. Model-free analysis of the relaxation data for seven residues required the inclusion of an exchange broadening term, the magnitude of which ranges from 2 to 9.1 s(-1), indicating the presence of conformational averaging motions only for a small subset of residues. PMID:11056034

Sahu, S C; Bhuyan, A K; Majumdar, A; Udgaonkar, J B

2000-12-01

116

Geomorphic control on the ?15N of mountain forest  

NASA Astrophysics Data System (ADS)

Mountain forests are subject to high rates of physical erosion which can export particulate nitrogen from ecosystems. However, the impact of geomorphic processes on nitrogen budgets remains poorly constrained. We have used the elemental and isotopic composition of soil and plant organic matter to investigate nitrogen cycling in the mountain forest of Taiwan, from 24 sites with distinct geomorphic (topographic slope) and climatic (precipitation, temperature) characteristics. The organic carbon to nitrogen ratio of soil organic matter decreased with soil 14C age, providing constraint on average rates of nitrogen loss using a mass balance model. Model predictions suggest that present day estimates of nitrogen deposition exceed contemporary and historic nitrogen losses. We found ~6‰ variability in the stable isotopic composition (?15N) of soil and plants which was not related to soil 14C age or climatic conditions. Instead, ?15N was significantly, negatively correlated with topographic slope. Using the mass balance model, we demonstrate that the correlation can be explained by an increase in nitrogen loss by non-fractioning pathways on steeper slopes, where physical erosion effectively removes particulate nitrogen. Published data from forest on steep slopes are consistent with the correlation, demonstrating that variable physical erosion rates can significantly influence soil ?15N, and that particulate nitrogen export is a major loss term in the nitrogen budget of mountain forest.

Hilton, R. G.; Galy, A.; West, A. J.; Hovius, N.; Roberts, G. G.

2012-09-01

117

Geomorphic control on the ?15N of mountain forests  

NASA Astrophysics Data System (ADS)

Mountain forests are subject to high rates of physical erosion which can export particulate nitrogen from ecosystems. However, the impact of geomorphic processes on nitrogen budgets remains poorly constrained. We have used the elemental and isotopic composition of soil and plant organic matter to investigate nitrogen cycling in the mountain forest of Taiwan, from 24 sites with distinct geomorphic (topographic slope) and climatic (precipitation, temperature) characteristics. The organic carbon to nitrogen ratio of soil organic matter decreased with soil 14C age, providing constraint on average rates of nitrogen loss using a mass balance model. Model predictions suggest that present day estimates of nitrogen deposition exceed contemporary and historic nitrogen losses. We found ∼6‰ variability in the stable isotopic composition (?15N) of soil and plants which was not related to soil 14C age or climatic conditions. Instead, ?15N was significantly, negatively correlated with topographic slope. Using the mass balance model, we demonstrate that the correlation can be explained by an increase in nitrogen loss by non-fractioning pathways on steeper slopes, where physical erosion most effectively removes particulate nitrogen. Published data from forests on steep slopes are consistent with the correlation. Based on our dataset and these observations, we hypothesise that variable physical erosion rates can significantly influence soil ?15N, and suggest particulate nitrogen export is a major, yet underappreciated, loss term in the nitrogen budget of mountain forests.

Hilton, R. G.; Galy, A.; West, A. J.; Hovius, N.; Roberts, G. G.

2013-03-01

118

Density functional calculations of 15 N chemical shifts in solvated dipeptides  

Microsoft Academic Search

We performed density functional calculations to examine the effects of solvation, hydrogen bonding, backbone conformation,\\u000a and the side chain on 15N chemical shielding in proteins. We used N-methylacetamide (NMA) and N-formyl-alanyl-X (with X being one of the 19 naturally occurring amino acids excluding proline) as model systems. In addition,\\u000a calculations were performed for selected fragments from protein GB3. The conducting

Ling Cai; David Fushman; Daniel S. Kosov

2008-01-01

119

Effects of climate, tree age, dominance and growth on ? 15 N in young pinewoods  

Microsoft Academic Search

Needles, annual rings from basal stem discs and bark of three dominant and three suppressed Pinus pinaster from a 12-year-old pine stand (naturally regenerated after a wildfire) were analysed to study the effects of climate, tree\\u000a age, dominance, and growth on tree ?15N. Foliar-N concentration in dominant pines (0.780–1.474% N) suggested that soil N availability was sufficient, a circumstance\\u000a that

A. Couto-Vázquez; S. J. González-Prieto

2010-01-01

120

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

Microsoft Academic Search

Biogeochemical theory emphasizes nitrogen (N) limitation and the many factors that can restrict N accumulation in temperate\\u000a forests, yet lacks a working model of conditions that can promote naturally high N accumulation. We used a dynamic simulation\\u000a model of ecosystem N and ?15N to evaluate which combination of N input and loss pathways could produce a range of high ecosystem

Steven S. PerakisEmily; Emily R. Sinkhorn; Jana E. Compton

121

[Humus composition and stable carbon isotope natural abundance in paddy soil under long-term fertilization].  

PubMed

Soil samples were collected from an experimental paddy field with long-term (26 years) fertilization in Taihu Lake region of Jiangsu Province to study the effects of different fertilization on the organic carbon distribution and stable carbon isotope natural abundance (delta 13C) in the soil profile, and on the humus composition. The results showed that long-term fertilization increased the organic carbon content in top soil significantly, and there was a significantly negative exponential correlation between soil organic carbon content and soil depth (P < 0.01). The organic carbon content in 10-30 cm soil layer under chemical fertilizations and in 20-40 cm soil layer under organic fertilizations was relatively stable. Soil delta 13C increased gradually with soil depth, its variation range being from -24% per thousand to -28 per thousand, and had a significantly negative linear correlation with soil organic carbon content (P < 0.05). In 0-20 cm soil layer, the delta 13C in treatments organic manure (M), M + NP, M + NPK, M + straw (R) + N, and R + N decreased significantly; while in 30-50 cm soil layer, the delta 13C in all organic fertilization treatments except R + N increased significantly. Tightly combined humus (humin) was the main humus composition in the soil, occupying 50% or more, and the rest were loosely and stably combined humus. Long-term fertilization increased the content of loosely combined humus and the ratio of humic acid (HA) to fulvic acid (FA). PMID:19102308

Ma, Li; Yang, Lin-Zhang; Ci, En; Wang, Yan; Yin, Shi-Xue; Shen, Ming-Xing

2008-09-01

122

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

123

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

124

Songbird abundance in clear-cut and burned stands: a comparison of natural disturbance and forest management  

Microsoft Academic Search

To evaluate the efficacy of forest management to emulate natural disturbance, we compared bird abundances among burned and clear-cut, former black spruce (Picea mariana (Mill.) BSP) sites, after 5, 14, and 27 years of suc- cession. Total bird density was lower in clear-cut sites resulting from fewer hermit thrushes, yellow warblers, Swainson's thrushes, and fox sparrows. Hermit thrushes were positively

N. P. P. Simon; F. E. Schwab; R. D. Otto

2002-01-01

125

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

126

14N/15N isotopic ratio in L1544 (Bi  

NASA Astrophysics Data System (ADS)

The observations towards L1544 were carried out with the IRAM 30m antenna, located at Pico Veleta (Spain) during observing sessions in June 2009 and July 2010. The J=1-0 transition of was observed with the EMIR receiver in the E090 configuration tuned at 90263.8360MHz and using the lower-inner sideband. The hyperfine-free rest frequencies were taken from the most recent laboratory investigation of 15N-dyazenilium species (Dore et al. 2009A&A...496..275D). (6 data files).

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

2013-06-01

127

The vibrational spectra of [15N2]-succinonitrile.  

PubMed

For the first time, the infrared and Raman spectra of [15N2]-succinonitrile are presented and discussed in detail. Assignments of the vibrational bands of its two rotational conformers gauche and trans, respectively, have been made for both infrared and Raman spectra. The assignments were based on a recent ab-initio force field calculation for succinonitrile, taking into account the vibrational frequencies of other succinonitrile isotopomers. There are differences in the frequencies of the vibrational bands due to the mass increase in the cyanide groups, which have been analysed in depth. PMID:11471715

Fengler, O I

2001-07-01

128

Partitioning Respiration Fluxes in a Forested Mountainous Ecosystem Using Natural Abundance of Stable Carbon Isotopes  

NASA Astrophysics Data System (ADS)

Isotopic mass balance techniques can help overcome challenges to studying ecosystem fluxes in complex terrain. Because scaling up measurements made at the leaf level compounds and magnifies measurement errors, it is desirable that ecosystem fluxes be measured using an integrative technique, such as eddy covariance. However, advective forcing complicates the use of eddy covariance in complex terrain, so we used an isotopic mass balance approach to partition ecosystem respiration flux in a forested site in a mountainous region of northern Idaho, USA. In 2006 and 2007, we analyzed the carbon-13 composition (?13C) of ecosystem respiration and both the ?13C and magnitude of soil, foliar, and stem component fluxes of ecosystem respiration. Soil- and stem-respired ?13C values were similar, from -27.24 (2.63)‰ (stem) to -26.9 (1.11)‰ (soil). Foliar respiration was consistently more enriched by up to 8‰. We took advantage of nighttime advection to collect samples of air from the forest, then used a Keeling plot approach to determine the isotopic composition of respired CO2. Ecosystem-respired CO2 had a seasonal range from -27.3 (0.67)‰ to -23.5 (1.0)‰. Using a mixing model, we then determined a ratio of soil respiration to ecosystem respiration for the forest. We compared this ratio to a ratio obtained independently by scaling up soil, foliar, and stem respiration rate measurements to the forest level. This work shows that, in the absence of eddy covariance techniques, whole-ecosystem gas exchange can be examined using the natural abundance of stable isotopes. This approach can be further used to test the accuracy of ecosystem carbon models or scaling techniques.

Berryman, E. M.; López, N. U.; Gag, P.; Kavanagh, K.; Marshall, J. D.

2008-12-01

129

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...

130

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

131

Evaluation of the influence of intermolecular electron-nucleus couplings and intrinsic metal binding sites on the measurement of 15N longitudinal paramagnetic relaxation enhancements in proteins by solid-state NMR.  

PubMed

Magic-angle spinning solid-state NMR measurements of (15)N longitudinal paramagnetic relaxation enhancements (PREs) in (13)C,(15)N-labeled proteins modified with Cu(2+)-chelating tags can yield multiple long-range electron-nucleus distance restraints up to ~20 Å (Nadaud et al. in J Am Chem Soc 131:8108-8120, 2009). Using the EDTA-Cu(2+) K28C mutant of B1 immunoglobulin binding domain of protein G (GB1) as a model, we investigate the effects on such measurements of intermolecular electron-nucleus couplings and intrinsic metal binding sites, both of which may potentially complicate the interpretation of PRE data in terms of the intramolecular protein fold. To quantitatively assess the influence of intermolecular (15)N-Cu(2+) interactions we have determined a nearly complete set of longitudinal (15)N PREs for a series of microcrystalline samples containing ~10, 15 and 25 mol percent of the (13)C,(15)N-labeled EDTA-Cu(2+)-tagged protein diluted in a matrix of diamagnetic natural abundance GB1. The residual intermolecular interactions were found to be minor on the whole and account for only a fraction of the relatively small but systematic deviations observed between the experimental (15)N PREs and corresponding values calculated using protein structural models for residues furthest removed from the EDTA-Cu(2+) tag. This suggests that these deviations are also caused in part by other factors not related to the protein structure, such as the presence in the protein of intrinsic secondary sites capable of binding Cu(2+) ions. To probe this issue we performed a Cu(2+) titration study for K28C-EDTA GB1 monitored by 2D (15)N-(1)H solution-state NMR, which revealed that while for Cu(2+):protein molar ratios of ? 1.0 Cu(2+) binds primarily to the high-affinity EDTA tag, as anticipated, at even slightly super-stoichiometric ratios the Cu(2+) ions can also associate with side-chains of aspartate and glutamate residues. This in turn is expected to lead to enhanced PREs for residues located in the vicinity of the secondary Cu(2+) binding sites, and indeed many of these residues were ones found to display the elevated longitudinal (15)N PREs in the solid phase. PMID:21826518

Nadaud, Philippe S; Sengupta, Ishita; Helmus, Jonathan J; Jaroniec, Christopher P

2011-08-09

132

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

2009-12-16

133

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.

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

2012-01-01

134

Species richness, composition, and abundance of fish larvae and juveniles inhabiting natural and developed shorelines of a glacial Iowa lake  

Microsoft Academic Search

Synopsis Young-of-the-year fish communities in naturally vegetated sites were compared with those inhabiting nearby sites where lakeshore development (i.e., construction of homes, boat docks, and beaches) reduced nearshore macrophyte species richness and abundance. The study was conducted in a 2266 hectare, glacially formed, eutrophic lake in northwestern Iowa during the summers of 1987 and 1988. Study sites were divided into

Michael D. Bryan; Dennis L. Scarnecchia

1992-01-01

135

Heteronuclear NMR of DNA with the heteronucleus in natural abundance: facilitated assignment and extraction of coupling constants.  

PubMed Central

Two heteronuclear proton-carbon NMR experiments are applied to the DNA-octamer d(TTGGCCAA)2 with carbon in natural abundance. They lead to a complete assignment of the carbon resonances of the sugars and bases. In addition, several heteronuclear coupling constants, proton-carbon as well as proton-phosphorous and phosphorous-carbon, were determined. The information can be obtained in a reasonable measuring time and offers valuable information for a detailed picture of DNA structure.

Schmieder, P; Ippel, J H; van den Elst, H; van der Marel, G A; van Boom, J H; Altona, C; Kessler, H

1992-01-01

136

Assessment of the natural variation of low abundant metabolic proteins in soybean seeds using proteomics  

Technology Transfer Automated Retrieval System (TEKTRAN)

Using two-dimensional polyacrylamide gel electrophoresis and mass spectrometry, we investigated the distribution of the low abundant proteins that are involved in soybean seed development in four wild and twelve cultivated soybean genotypes. We found proteomic variation of these proteins within and...

137

Food abundance and foraging patterns of natural colonies of Polyrhachis vicina Roger (Hymenoptera: Formicidae)  

Microsoft Academic Search

Summary The foraging pattern ofPolyrhachis vicina Roger, the composition of food collected, and the abundance and distribution of food sources were studied. Results showed:1.The food collected by workers was mostly honeydew secreted by Homoptera supplemented by small insects and plant secretions. The successful foraging rate was 35% in April, 74% in June, 91 % in August, and 83 % in

J.-F. Wang; J. Tang

1994-01-01

138

Flow and habitat effects on juvenile fish abundance in natural and altered flow regimes  

USGS Publications Warehouse

Conserving biological resources native to large river systems increasingly depends on how flow-regulated segments of these rivers are managed. Improving management will require a better understanding of linkages between river biota and temporal variability of flow and instream habitat. However, few studies have quantified responses of native fish populations to multiyear (>2 yr) patterns of hydrologic or habitat variability in flow-regulated systems. To provide these data, we quantified young-of-year (YOY) fish abundance during four years in relation to hydrologic and habitat variability in two segments of the Tallapoosa River in the southeastern United States. One segment had an unregulated flow regime, whereas the other was flow-regulated by a peak-load generating hydropower dam. We sampled fishes annually and explored how continuously recorded flow data and physical habitat simulation models (PHABSIM) for spring (April-June) and summer (July-August) preceding each sample explained fish abundances. Patterns of YOY abundance in relation to habitat availability (median area) and habitat persistence (longest period with habitat area continuously above the long-term median area) differed between unregulated and flow-regulated sites. At the unregulated site, YOY abundances were most frequently correlated with availability of shallow-slow habitat in summer (10 species) and persistence of shallow-slow and shallow-fast habitat in spring (nine species). Additionally, abundances were negatively correlated with 1-h maximum flow in summer (five species). At the flow-regulated site, YOY abundances were more frequently correlated with persistence of shallow-water habitats (four species in spring; six species in summer) than with habitat availability or magnitude of flow extremes. The associations of YOY with habitat persistence at the flow-regulated site corresponded to the effects of flow regulation on habitat patterns. Flow regulation reduced median flows during spring and summer, which resulted in median availability of shallow-water habitats comparable to the unregulated site. However, habitat persistence was severely reduced by flow fluctuations resulting from pulsed water releases for peak-load power generation. Habitat persistence, comparable to levels in the unregulated site, only occurred during summer when low rainfall or other factors occasionally curtailed power generation. As a consequence, summer-spawning species numerically dominated the fish assemblage at the flow-regulated site; five of six spring-spawning species occurring at both study sites were significantly less abundant at the flow-regulated site. Persistence of native fishes in flow-regulated systems depends, in part, on the seasonal occurrence of stable habitat conditions that facilitate reproduction and YOY survival.

Freeman, M.C.; Bowen, Z.H.; Bovee, K.D.; Irwin, E. R.

2001-01-01

139

Natural Abundance of Mass 47 in CO2 Emitted in Car Exhaust and Human Breath  

NASA Astrophysics Data System (ADS)

Atmospheric CO2 is widely studied using records of concentration, ? 13C and ? 18O, although the number and variability of sources and sinks prevents these alone from uniquely defining the budget. CO2 of mass 47 (mainly 13C18O16O) provides an additional potential tracer, but little is known about its ability to differentiate among various budget components. We present study of differences in 13C18O16O abundance between combustion and respiration. We define ? 47 as the difference in permil between the measured R47 (=[mass 47]/[mass 44]) and R47 expected for CO2 whose isotopes are distributed randomly among all isotopologues. Previous studies have shown that ? 47 values at thermodynamic equilibrium vary between zero at 1000\\deg C and 0.9\\permil at room temperature, raising the possibility that it could differentiate between CO2 produced by high temperature processes, such as combustion, and that produced in respiration. Values of ? 47 are non-linear in mixing. Therefore, it is useful to discuss the ? 47=(R47/R47ST-1)1000, where R47ST is the R47 expected for CO2 having ? 13C-VPDB=0, ? 18O-VSMOW=0 and ? 47=0. We used a Keeling plot approach to estimate ? 13C, ? 18O, ? 47 and ? 47 in CO2 from car exhaust and from human breath. Air sampled at 10am in the Caltech campus in Pasadena, CA, varied in CO2 concentration from 383 to 404ppm, in ? 13C and ? 18O from -9.2 to -10.2\\permil and from 40.7 to 42.0\\permil, respectively, in ? 47 of from 32.6 to 34.0\\permil, and in ? 47 from 0.73 to 0.96\\permil. We then sampled at varying distances from a car exhaust pipe. The intercepts in Keeling plots defined by these data, reflecting the car exhaust end-member, were similar to the values obtained very close to the exhaust pipe: ? 13C was found to equal -24.4±0.2\\permil, similar to the measured value of the gasoline used; ? 18O =30.0±0.4\\permil; ? 47=6.7±0.6\\permil; and ? 47=0.41±0.03\\permil. Both ? 18O and ? 47 are consistent with that expected for thermodynamic equilibrium at 200\\deg C between water and CO2 generated by combustion of gasoline-air mixtures. This temperature is lower than that of the catalytic converter, suggesting re-equilibration in the cooling exhaust as it travels through the tail pipe. This can explain why the ? 18O of CO2 from car exhaust is substantially greater than that of O2 in air. Samples of CO2 in human breath had ? 13C and ? 18O values broadly similar to those of car exhaust (-22.3±0.2 and 34.4±0.3\\permil, respectively), ? 47 of 13.5±0.4\\permil, but ? 47 of 0.74±0.02\\permil, far higher than exhaust and similar to that of background Pasadena air. ? 13C of human breath is similar to that of car exhaust, much as other respiration and fossil-fuel sources of CO2 generally overlap. Similarly, ? 18O of human breath and soil respiration are close to that of car exhaust. Therefore, conventional stable isotope constraints do not easily differentiate fossil-fuel and respiratory sources. In contrast, the ? 47 value of CO2 from car exhaust is easily differentiated from those of CO2 in human breath, largely due to enhanced thermodynamic stability of 13C18O16O at the low temperatures characteristic of respiration. Hence, ? 47 is a potentially useful tracer to distinguish anthropogenic, mostly combustion, CO2 sources from natural, low temperature, sources.

Affek, H. P.; Eiler, J. M.

2004-12-01

140

Rotational spectrum of deuterated and 15N ethyl cyanides: CH_3CHDCN and CH_2DCH_2CN and of CH_3CH_2C15N  

NASA Astrophysics Data System (ADS)

Context: Ethyl cyanide is an abundant molecule in hot molecular clouds. Its rotational spectrum is very dense and several hundreds of rotational transitions within the ground state have been identified in molecular clouds in the 40-900 GHz frequency range. Lines from 13C isotopically substituted ethyl cyanide were identified in Orion. Aims: To enable the search and the possible detection of other isotopologues of ethyl cyanide in interstellar objects, we have studied the rotational spectrum of deuterated ethyl cyanide: CH2DCH2CN (in-plane and out-of-plane) and CH3CHDCN and the spectrum of 15N substituted ethyl cyanide CH3CH2C15N. Using these experimental data, we have searched for these species in Orion. Methods: The rotational spectrum of each species in the ground state was measured in the microwave and millimeter-submillimeter wavelength range using a waveguide Fourier Transform spectrometer (8-17 GHz) and a source-modulated spectrometer employing backward-wave oscillators (BWOs) (150-260 and 580-660 GHz). More than 300 lines were identified for each species, for J values in the range 71-80 and Ka values in the range 28-31 depending on the isotopologues. The experimental spectra were analyzed using a Watson's Hamiltonian in the A-reduction. Results: From the fitting procedure, accurate spectroscopic constants were derived for each of the species. These new sets of spectroscopic constants enable us to predict reliably the rotational spectrum (lines frequencies and intensities) in the 4-1000 GHz frequency range and for J and Ka up to 80 and 31, respectively. Combined with IRAM 30 m antenna observations of Orion, this experimental study allowed us to detect 15N substituted ethyl cyanide CH3CH2C15N for the first time in Orion. The derived column density and rotational temperature are 1013 cm-2 and 150 K for the plateau and 3 × 1014 cm-2 and 300 K for the hot core. The deuterated species were searched for but were not detected. The upper limit to the column density of each deuterated isotopologues was 1014 cm-2. Full version of Tables [see full textsee full textsee full textsee full text] to [see full textsee full textsee full textsee full text] are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/493/565 Tables [see full textsee full textsee full textsee full text] to [see full textsee full textsee full textsee full text] are only available in electronic form at http://www.aanda.org

Margulès, L.; Motiyenko, R.; Demyk, K.; Tercero, B.; Cernicharo, J.; Sheng, M.; Weidmann, M.; Gripp, J.; Mäder, H.; Demaison, J.

2009-01-01

141

Binary nature and elemental abundances of 2 Lyn and HD 169981  

NASA Astrophysics Data System (ADS)

We analyse high-resolution spectrograms of the early A-type stars HD 169981 and 2 Lyn. For the spectroscopic and photometric binary HD 169981 we determine the abundances of certain chemical elements. The derived atmospheric parameters show the star to be an A giant. The abundances of the elements Mg, Si, Ti, Cr, and Fe are very close to solar, only C and O show slight underabundances. 2 Lyn has been primarily studied for the occurrence of radial velocity variations. The star is probably a spectroscopic binary with a period of about 3.6 years. Preliminary orbital elements are derived. The search for shorter radial velocity variations gives hints of periods of 69.2, 1.56 and 1.53 days. Both of the last-mentioned periods are in the order of the expected rotation period of the star. The stellar parameters are estimated and for certain elements we determined the abundances. The research is based on spectroscopic observations made with the 2-m telescope at the Thüringer Landessternwarte Tautenburg, Germany.

Lehmann, H.; Egorova, I.; Scholz, G.; Hildebrandt, G.; Andrievsky, S. M.

2003-04-01

142

Quantitative Community Fingerprinting Methods for Estimating the Abundance of Operational Taxonomic Units in Natural Microbial Communities?  

PubMed Central

Molecular fingerprinting techniques offer great promise for analyzing changes in microbial community structure, especially when dealing with large number of samples. However, a serious limitation has been the lack of quantification offered by such techniques since the relative abundances of the identified operational taxonomic units (OTUs) in the original samples are not measured. A quantitative fingerprinting approach designated “qfingerprinting” is proposed here. This method involves serial dilutions of the sample of interest and further systematic fingerprinting of all dilution series. Using the ultimate dilutions for which OTU are still PCR amplifiable and taking into account peak size inaccuracy and peak reproducibility, the relative abundance of each OTU is then simultaneously determined over a scale spanning several orders of magnitude. The approach was illustrated by using a quantitative version of automated ribosomal intergenic spacer analysis (ARISA), here called qARISA. After validating the concept with a synthetic mixture of known DNA targets, qfingerprinting was applied to well-studied marine sediment samples to examine specific changes in OTU abundance associated with sediment depth. The new strategy represents a major advance for the detailed quantitative description of specific OTUs within complex communities. Further ecological applications of the new strategy are also proposed.

Ramette, Alban

2009-01-01

143

Quantitative community fingerprinting methods for estimating the abundance of operational taxonomic units in natural microbial communities.  

PubMed

Molecular fingerprinting techniques offer great promise for analyzing changes in microbial community structure, especially when dealing with large number of samples. However, a serious limitation has been the lack of quantification offered by such techniques since the relative abundances of the identified operational taxonomic units (OTUs) in the original samples are not measured. A quantitative fingerprinting approach designated "qfingerprinting" is proposed here. This method involves serial dilutions of the sample of interest and further systematic fingerprinting of all dilution series. Using the ultimate dilutions for which OTU are still PCR amplifiable and taking into account peak size inaccuracy and peak reproducibility, the relative abundance of each OTU is then simultaneously determined over a scale spanning several orders of magnitude. The approach was illustrated by using a quantitative version of automated ribosomal intergenic spacer analysis (ARISA), here called qARISA. After validating the concept with a synthetic mixture of known DNA targets, qfingerprinting was applied to well-studied marine sediment samples to examine specific changes in OTU abundance associated with sediment depth. The new strategy represents a major advance for the detailed quantitative description of specific OTUs within complex communities. Further ecological applications of the new strategy are also proposed. PMID:19201961

Ramette, Alban

2009-02-06

144

Nirtogen-15-labeled oligodeoxynucleotides. 4. Tetraplex formation of d[G({sup 15}N{sup 7})GTTTTTGG] and d[T({sup 15}N{sup 7})GGGT] monitored by {sup 1}H detected {sup 15}N NMR  

SciTech Connect

The authors have synthesized two molecules containing [7-{sup 15}N]-labeled 2{prime}-deoxyguanosine, d[G({sup 15}N{sup 7})GTTTTTGG], and d[T({sup 15}N{sup 7})GGGT] which, under appropriate conditions, will form tetramolecular complexes. The {sup 15}N chemical shifts of these molecules and of their Watson-Crick duplexes, d[G({sup 15}N{sup 7})GTTTTTGG]-d[CCAAAAACC] and d[T({sup 15}N{sup 7})GGGT]-d[ACCCA], were monitored as a function of temperature. The {sup 15}N chemical shift of the labeled N7 atom in each tetramolecular complex shows a similar temperature dependence, and the chemical shifts are not signal-averaged. The similarity of the chemical shifts for the tetraplex and single strand structures, and the difference seen for the two duplexes, are consistent with the different degrees of hydrogen bonding to the N7 which could be expected in each case. Thus, although more examples will be required to establish the generality of these observations, a purine [7-{sup 15}N] label appears to be able to monitor groove interactions, including hydration. 28 refs., 6 figs., 5 tabs.

Gaffney, B.L.; Chuan Wang; Jones, R.A. [State Univ. of New Jersey, Piscataway, NJ (United States)

1992-05-20

145

Anthropogenic and Natural Influences on Stratospheric Halogen Abundance as Inferred From Tropospheric Measurements of Long- and Short-Lived Gases.  

NASA Astrophysics Data System (ADS)

The chemical composition of the stratosphere is changing as a result of international limits on the industrial use of ozone-depleting substances (ODSs). Natural processes also influence the abundance of halogen- and sulfur-containing gases and affect stratospheric composition through changes in emissions or loss rates. Through a global network of flask sampling and in situ sampling, both at Earth's surface and from aircraft, we regularly measure a wide range of anthropogenic and natural ODSs, substitutes for ODSs, and other chemicals. The results suggest large changes in emission rates of chlorine and bromine from anthropogenic activities as a result of Montreal Protocol restrictions and smaller changes in the natural system. They imply a significant decline in ozone-depleting halogen abundance in the stratosphere, though the magnitude of this decline is location dependent. Here we will discuss recent changes observed for anthropogenic chemicals, explore their implications, and touch upon the magnitudes of changes in the natural system influencing the chemical composition of the stratosphere.

Dutton, G.; Montzka, S.; Hall, B.; Elkins, J. W.; Miller, B.

2008-12-01

146

Sediment Underplating Beneath Central America: Insights From N-He, ?15N Systematics of Volatile Discharges in Nicaragua  

NASA Astrophysics Data System (ADS)

We investigated N-isotope systematics and geochemistry of gases emitted from fumarolic and geothermal sources along the Nicaraguan volcanic front. The goals of this study are: 1) to quantify the contributions from different reservoirs to the volatile output along the volcanic front; 2) to map along-arc variations in sediment contribution to magmas. We report relative abundances of N2, Ar, and He, as well as N isotopes, for geothermal fluid samples from Nicaraguan volcanoes. Samples from Masaya, Tipitapa, Xiloa, Momotombo geothermal wells, Cerro Negro, and San Cristobal (from SE to NW) have N2/He ratios in the range 1,600 - 25,000 - typical of arcs. The southernmost sample, Volcan Mombacho, has N2/He =144, consistent with upper mantle derivation (N2/He ~150). N isotopes identify sources for the geothermal gases. A positive ?15N value indicates N contribution from subducted hemipelagic sediment (?15N = +7‰ ). The upper mantle, in contrast, is characterized by a ?15N = -5‰ . Samples from Masaya, Xiloa, a Momotombo well, and Cerro Negro have ?15N = +1.2, +4.9, +2.1, and +4.9‰ , a strong sediment signature. The sample from Mombacho has a ?15N = +0.5‰ , indicative of mantle nitrogen. These Nicaraguan data contrast with reported N2-He-?15N systematics of central Costa Rica, where gas discharges sample primarily mantle wedge volatiles (Zimmer et al., AGU 2001, Fischer et al., Science 2002). Most Nicaraguan samples have N2/He and ?15N values that indicate subduction of hemipelagic sediments, as is typical of other arcs. In Costa Rica and southern Nicaragua (Mombacho), underplating prevents hemipelagic sediments from reaching the zone of melting and results in low N2/He and negative ?15N values. Southern Nicaragua represents the transition from sediment underplating (in the south) to sediment subduction (in the north). The N-systematics are therefore consistent with other geochemical indicators (Ba/La, 10Be, e.g.) showing significant sedimentary contribution to Nicaraguan volcanic output.

Elkins, L.; Fischer, T.; Hilton, D.; Shaw, A.; Strauch, W.; Sharp, Z.

2002-12-01

147

Ring-substituted benzohydroxamic acids: 1H, 13C and 15N NMR spectra and NH-OH proton exchange.  

PubMed

NMR spectra (1H, 13C, 15N) of para- and meta-substituted benzohydroxamic acids were studied in dry dimethyl sulfoxide solutions. The 13C chemical shifts were very close to those found by cross-polarization magic angle spinning in solids, the hydroxamic (not hydroximic) structure of which is unambiguous. The hydroxamic structure of these acids in DMSO solutions was proved independently by their 15N chemical shifts. The 15N and 1H chemical shifts of the NH-OH fragment showed excellent mutual dependences and dependences on the nature of the ring substituent. According to these dependences and ab initio energy calculations, all the acids assume the same Z conformation. Proton exchange between hydroxamic OH and NH groups in DMSO proceeded by both intra- and intermolecular exchange and the rates did not exhibit any simple relationship to the substituent constants. PMID:15861383

Schraml, Jan; Tkadlecová, Marcela; Pataridis, Statis; Soukupová, Ludmila; Blechta, Vratislav; Roithová, Jana; Exner, Otto

2005-07-01

148

An sup 15 N NMR method for the characterization of organic sulfur in coal and coal products via iminosulfurane formation  

SciTech Connect

The indirect of organic sulfur by {sup 15}N NMR spectroscopy in the solid state is feasible by facile reactions providing the iminosulfurane structures. Unfortunately, nitrogen chemical shifts appear to be insufficiently sensitive to the nature of the sulfur substituent to be useful for structural studies. Further work is underway to determine the {sup 15}N chemical shifts of iminosulfuranes formed from dibenzothiophene, 4-4{prime}-dimethoxydiphenyl sulfide, and a sulfur-containing, methylated asphaltene to determine the sensitivity of {sup 15}N shifts to a broader variation of aromatic structure. Although double cross-polarization experiments or rotational echo experiments could make use of iminosulfurane formation for detection of carbon in proximity to sulfur, the difficulties in quantitation using these methods are not encouraging for coal product mixtures. 6 refs., 1 fig., 1 tab.

Franz, J.A.; Lamb, C.N.; Linehan, J.C.

1991-09-01

149

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.; Bohlke, J. K.; Yoshinari, T.

1997-01-01

150

New Method for Estimating Bacterial Cell Abundances in Natural Samples by Use of Sublimation  

Microsoft Academic Search

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

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

2004-01-01

151

Natural Resources and Violent Conflict: Resource Abundance, Dependence and the Onset of Civil Wars  

Microsoft Academic Search

In this paper we examine the claim that natural resources invite civil conflict, and challenge the main stylized facts in this literature. We find that the nature of causation between resource dependence and civil war is opposite to conventional wisdom. In particular, (i) civil war creates dependence on primary sector exports, but the reverse is not true, and (ii) resource

Christa N. Brunnschweiler; Erwin Bulte

2008-01-01

152

Plant Characteristics Associated with Natural Enemy Abundance at Michigan Native Plants  

Microsoft Academic Search

Habitat management is a type of conservation biological control that focuses on increasing natural enemy populations by providing them with plant resources such as pollen and nectar. Insects are known to respond to a variety of plant characteristics in their search for plant- provided resources. A better understanding of the speciÞc characteristics used by natural enemy insects in selecting these

A. K. Fiedler; D. A. Landis

2007-01-01

153

Identification of Biodegradation Pathways in a Multi-Process Phytoremediation System (MPPS) Using Natural Abundance 14C Analysis of PLFA  

NASA Astrophysics Data System (ADS)

Optimizing remediation of petroleum-contaminated soils requires thorough understanding of the mechanisms and pathways involved in a proposed remediation system. In many engineered and natural attenuation systems, multiple degradation pathways may contribute to observed contaminant mass losses. In this study, biodegradation in the soil microbial community was identified as a major pathway for petroleum hydrocarbon removal in a Multi-Process Phytoremediation System (MPPS) using natural abundance 14C analysis of Phospholipid Fatty Acids (PLFA). In contaminated soils, PLFA were depleted in ?14C to less than -800‰, directly demonstrating microbial uptake and utilization of petroleum derived carbon (?14C = -992‰) during bioremediation. Mass balance indicated that more than 80% of microbial carbon was derived from petroleum hydrocarbons and a maximum of 20% was produced from metabolism of modern carbon sources. In contrast, in a nearby uncontaminated control soil, the microbial community maintained a nearly modern 14C signature, suggesting preferential degradation of more labile, recent carbon. Mass balance using ?13C and ?14C of soil CO2 demonstrated that mineralization of petroleum carbon contributed 60-65% of soil CO2 at the contaminated site. The remainder was derived from atmospheric (27-30%) and decomposition of non- petroleum natural organic carbon (5-10%). The clean control exhibited substantially lower CO2 concentrations that were derived from atmospheric (55%) and natural organic carbon (45%) sources. This study highlights the value of using multiple carbon isotopes to identify degradation pathways in petroleum- contaminated soils undergoing phytoremediation and the power of natural abundance 14C to detect petroleum metabolism in natural microbial communities.

Cowie, B. R.; Greenberg, B. M.; Slater, G. F.

2008-12-01

154

3D H2BC: a novel experiment for small-molecule and biomolecular NMR at natural isotopic abundance.  

PubMed

3D H2BC is introduced for heteronuclear assignment on natural abundance samples even for biomolecules up to at least 10 kDa in low millimolar concentrations as an overnight experiment using the latest generation of cryogenically cooled probes. The short pulse sequence duration of H2BC is maintained in the 3D version due to multiple use of the constant-time delay. Applications ranging from a small lipid to a non-recombinant protein demonstrate the merits of 3D H2BC and the ease of obtaining assignments in chains of protonated carbons. PMID:19604710

Meier, Sebastian; Benie, Andrew J; Duus, Jens Ø; Sørensen, Ole W

2009-06-25

155

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

156

15 N–{ 1 H} NOE experiment at high magnetic field strengths  

Microsoft Academic Search

The heteronuclear 15N–{1H} NOE values are typically determined by taking the ratio of 15N signal intensities recorded in the presence and absence of 1H saturation prior to evolution of 15N magnetization. Since the intensity ratio of two independent experiments is taken, complete recovery of 15N magnetization during the scan repetition delay is critical to obtain reliable NOE values. Because it

Qingguo Gong; Rieko Ishima

2007-01-01

157

[Utilization of 15N marked urea by the laying hen. 2. Incorporation and metabolism of 15N for the synthesis of egg protein].  

PubMed

In an N-metabolism experiment 3 colostomized laying hybrids received 2870 mg 15N-excess (15N') per animal in 6 days in the form of urea with their conventional feed rations. During the 8-day experiment the 21 eggs laid were separated into eggshell, white of egg and yolk. Weight, N-content and 15N' were determined of the individual fractions of the eggs. On an average of the 21 eggs 4.6% of the heavy nitrogen was in the egg-shells, 50% in the white of egg and 45.5% in the yolk. 2.8%, 4.5% and 5.5% (hens 1...3) of the 15N' consumed were detected in the eggs. The maximum 15N'-output in the white of egg was reached on the 6th day, whereas 15N'-output in the yolk showed a nearly linear increase in the time of the experiment. The results show that labelled nitrogen from urea is incorporated into the egg to a lower degree than after the feeding of 15N-labelled proteins and that the development of its incorporation into the white of egg and the yolk differ from that after the feeding of 15N-labelled native proteins. PMID:4091643

Gruhn, K; Zander, R

1985-11-01

158

Natural resources and violent conflict: resource abundance, dependence, and the onset of civil wars  

Microsoft Academic Search

In this paper we examine the claim that natural resources invite civil conflict, and challenge the main stylized facts in this literature. We find that the conventional measure of resource dependence is endogenous with respect to conflict, and that instrumenting for dependence implies that it is no longer significant in conflict regressions. Instead, it appears that conflict increases dependence on

Christa N. Brunnschweiler; Erwin H. Bultey

2009-01-01

159

Natural Abundance Isotopic Fractionation in the Fermentation Reaction: Influence of the Fermentation Medium  

Microsoft Academic Search

The isotopic parameters of fermentation products provide reliable criteria for characterizing their carbohydrate precursors on the condition that the isotopic coefficients which relate individual sites in the products and in the reactants have strictly reproducible or predictible values. Since fermentation may be performed either in natural media (such as fruit juices) which exhibit variable compositions or in “synthetic” media prepared

Ben-Li Zhang; Yunianta; Claude Vallet; Maryvonne L. Martin

1997-01-01

160

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

161

Effect of the Squid Host on the Abundance and Distribution of Symbiotic Vibrio fischeri in Nature †  

PubMed Central

Euprymna scolopes, a Hawaiian species of bioluminescent squid, harbors Vibrio fischeri as its specific light organ symbiont. The population of symbionts grew inside the adult light organ with an average doubling time of about 5 h, which produced an excess of cells that were expelled into the surrounding seawater on a diurnal basis at the beginning of each period of daylight. These symbionts, when expelled into the ambient seawater, maintain or slightly increase their numbers for at least 24 h. Hence, locations inhabited by their hosts periodically receive a daily input of symbiotic V. fischeri cells and, as a result, become significantly enriched with these bacteria. As estimated by hybridization with a species-specific luxA gene probe, the typical number of V. fischeri CFU, both in the water column and in the sediments of E. scolopes habitats, was as much as 24 to 30 times that in similar locations where squids were not observed. In addition, the number of symbiotic V. fischeri CFU in seawater samples that were collected along a transect through Kaneohe Bay, Hawaii, decreased as a function of the distance from a location inhabited by E. scolopes. These findings constitute evidence for the first recognized instance of the abundance and distribution of a marine bacterium being driven primarily by its symbiotic association with an animal host.

Lee, Kyu-Ho; Ruby, Edward G.

1994-01-01

162

New Method for Estimating Bacterial Cell Abundances in Natural Samples by Use of Sublimation  

PubMed Central

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 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 ?105 to 109 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

163

Tracing dung-derived carbon in temperate grassland using 13C natural abundance measurements  

Microsoft Academic Search

To understand the role of dung-derived carbon in the carbon cycle of grazed temperate grasslands, we need a procedure to trace dung-derived C. The natural 13C tracer technique of applying C4 dung to a C3 grass pasture allowed us to succesfully quantify the fate of cattle dung in the soil environment. Dung was collected from beef steers fed on either

R. Bol; W. Amelung; C. Friedrich; N. Ostle

2000-01-01

164

[Ruminal 15N-straw degradation in sacco and the in vivo digestibility of 15N from straw in the sheep and pony].  

PubMed

The nylon-bag method was applied for determination of the rumen degradation of dry matter and nitrogen of 15N-labelled wheat straw. For the experiment 4 wethers fitted with a rumen cannula were used. The bags containing 15N straw were introduced into the rumen and withdrawn 3, 6 or 12 h after incubation. In a second experiment the apparent 15N-digestibility of the same straw was determined in wether and pony. The dry matter disappearance varied between 6 and 23%. For 15N-labelled straw the disappearance of 15N was higher than that of total N. 12 h after incubation 71% of 15N and only 25% of total N were disappeared. It was calculated that after incubation rumen microbial-N in the nylon bag increased from 31% (3 h) to 45% (6 h) and 61% (12 h) resp. The apparent 15N digestibility amounted 53 +/- 2% for wethers and 51 +/- 2% for ponies. PMID:2751427

Zander, R; Flachowsky, G; Schubert, R; Gruhn, K

1989-03-01

165

Use of 15N Label in Organic Synthesis and Spectroscopy. Part I: Preparation of 15N-Labeled tert-Butylamine  

NASA Astrophysics Data System (ADS)

The preparation of 15N-labeled tert-butylamine involves the conversion of the correspondingly labeled potassium cyanide into the 15N-labeled tert-butylformamide via the Ritter reaction in 85% yield, followed by hydrolysis with either aqueous sodium hydroxide or hydrochloric acid. The NMR spectra of the compounds provide a valuable opportunity for discussing several important topics in NMR spectroscopy, such as cis-trans isomerism due to restricted rotation and 15N coupling. Comparison of the IR spectra of the labeled and unlabeled compounds permits a forum for discussing the theory of vibrational frequencies.

Talaty, Erach R.; Boese, Christopher A.; Adewale, Sanni M.; Ismail, Mohammed S.; Provenzano, Frank A.; Utz, Melissa J.

2002-02-01

166

(1)H, (15)N, (13)C assignment and secondary structure determination of two domains of La protein from D. discoideum.  

PubMed

Biosynthesis of RNA polymerase III transcripts requires binding of the La protein at their 3' end. La is an abundant nuclear RNA-binding protein which protects the nascent transcripts from 3' exonuclease degradation. Here, we report the high yield expression and preliminary structural analysis through NMR spectroscopy of two recombinant RNA binding domains (La motif and NRRM) from the La protein of Dictyostelium discoideum. Both recombinant protein constructs were well-folded and allowed for an almost complete sequence-specific assignment of the (15)N and (13)C labeled domains and their secondary structure prediction using PECAN online tool. PMID:23239108

Apostolidi, Maria; Vourtsis, Dionysios J; Chasapis, Christos T; Stathopoulos, Constantinos; Bentrop, Detlef; Spyroulias, Georgios A

2012-12-14

167

(1)H, (13)C and (15)N assignments of the holo-acyl carrier protein of Pseudomonas aeruginosa.  

PubMed

Acyl carrier proteins (ACPs) are a group of highly conserved and abundant proteins in bacteria. ACPs play a central role as the acyl group carriers in bacterial fatty acid biosynthesis, providing building blocks for membrane biogenesis and the production of secondary metabolites. In the versatile human pathogen Pseudomonas aeruginosa, three ACP homologs have been identified. One homolog, AcpP, exhibits the strongest sequence homology to the canonical Escherichia coli ACP. Here we report the (1)H, (13)C and (15)N assignments of the holo-AcpP of P. aeruginosa. PMID:22843382

Duggan, Brendan M; Roca, Amancio; Zhang, Yong-Mei

2012-07-29

168

Natural landscape and stream segment attributes influencing the distribution and relative abundance of riverine smallmouth bass in Missouri  

USGS Publications Warehouse

Protecting and restoring fish populations on a regional basis are most effective if the multiscale factors responsible for the relative quality of a fishery are known. We spatially linked Missouri's statewide historical fish collections to environmental features in a geographic information system, which was used as a basis for modeling the importance of landscape and stream segment features in supporting a population of smallmouth bass Micropterus dolomieu. Decision tree analyses were used to develop probability-based models to predict statewide occurrence and within-range relative abundances. We were able to identify the range of smallmouth bass throughout Missouri and the probability of occurrence within that range by using a few broad landscape variables: the percentage of coarse-textured soils in the watershed, watershed relief, and the percentage of soils with low permeability in the watershed. The within-range relative abundance model included both landscape and stream segment variables. As with the statewide probability of occurrence model, soil permeability was particularly significant. The predicted relative abundance of smallmouth bass in stream segments containing low percentages of permeable soils was further influenced by channel gradient, stream size, spring-flow volume, and local slope. Assessment of model accuracy with an independent data set showed good concordance. A conceptual framework involving naturally occurring factors that affect smallmouth bass potential is presented as a comparative model for assessing transferability to other geographic areas and for studying potential land use and biotic effects. We also identify the benefits, caveats, and data requirements necessary to improve predictions and promote ecological understanding. ?? Copyright by the American Fisheries Society 2007.

Brewer, S. K.; Rabeni, C. F.; Sowa, S. P.; Annis, G.

2007-01-01

169

Preservation of proteinaceous material during the degradation of the green alga Botryococcus braunii: A solid-state 2D 15N 13C NMR spectroscopy study  

Microsoft Academic Search

Using solid-state cross-polarization-magic-angle-spinning (CPMAS) 13C and 15N nuclear magnetic resonance (NMR) and 2-D double cross polarization (DCP) MAS 15N 13C NMR techniques, microbially degraded Botryococcus braunii was analyzed to study the chemical nature of organic nitrogen in the algal residue. The amide linkage, as found in protein, was observed as the major nitrogen component in 201-day-old degraded algae. No significant

Xu Zang; Reno T. Nguyen; H. Rodger Harvey; Heike Knicker; Patrick G. Hatcher

2001-01-01

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

[15N-flow after in sacco incubation and feeding of sheep and goats with untreated wheat straw or straw treated with 15N horse urine].  

PubMed

Chopped wheat straw was homogeneously mixed with urine of horses (5.75 gN per 1, 16.88 atom-% 15N-excess) and airtightly stored in plastic containers for 6 months. Three rumen fistulated sheep and goats each were fed with untreated or urine treated straw. Concentrate was added to straw. Untreated and urine treated straw were given in nylon bags and incubated in the rumen of sheep and goats for 1, 3, 6, 12, 24, 48 and 72 hours. A three compartment exponential function was used to fit the measurements of 15N-excess and 15N-amount of bag content. The curves and the calculated partial Y-values of the three compartments show the inflow and outflow of 15N into or from the bags and allow conclusions about the binding of urine N. Most N of urine was not compactly bound by straw during storage. Primarily microbial N was attached to the straw in the rumen. About 6% of urine N were bound more compact to the straw. Similar curves were calculated for 15N-excess and 15N-amount of nylon bags. The curves allow conclusions about tracer flows without quantitative knowledge. There were no significant differences between animal species. PMID:7778985

Schubert, R; Flachowsky, G; Bochröder, B

1994-01-01

172

Influence of niche differentiation on the abundance of methanogenic archaea and methane production potential in natural wetland ecosystems across China  

NASA Astrophysics Data System (ADS)

Methane (CH4) emissions from natural wetland ecosystems exhibit large spatial variability. To understand the underlying factors that induce differences in CH4 emissions from natural wetlands around China, we measured the CH4 production potential and the abundance of methanogenic archaea in vertical profile soils sampled from the Poyang wetland in the subtropical zone, the Hongze wetland in the warm temperate zone, the Sanjiang marsh in the cold temperate zone, and the Ruoergai peatland in the Qinghai-Tibetan Plateau. The top soil layer had the highest population of methanogens (1.07-8.29×109 cells g-1 soil) in all wetlands except the Ruoergai peatland and exhibited the maximum CH4 production potential measured at the mean in situ summer temperature. There is a significant logarithmic correlation between the abundance of methanogenic archaea and the soil organic carbon (R2=0.718, P<0.001, n=13) and between the abundance of methanogenic archaea and the total nitrogen concentrations (R2=0.758, P<0.001, n=13) in wetland soils. This indicates that the amount of soil organic carbon may affect the population of methanogens in wetland ecosystems. While the CH4 production potential is not significantly related to methanogen population (R2=0.011, P>0.05, n=13), it is related to the dissolved organic carbon concentration (R2=0.305, P=0.05, n=13). This suggests that the methanogen population is not an effective index for predicting the CH4 production in wetland ecosystems. The CH4 production rate of the top soil layer increases with increasing latitude, from 274 ?g CH4 kg-1 soil d-1 in the Poyang wetland to 665 ?g CH4 kg-1 soil d-1 in the Carex lasiocarpa marsh of the Sanjiang Plain. The CH4 production potential in the freshwater wetlands of Eastern China is affected by the supply of methanogenic substrates rather than by temperature, whereas the supply of substrates was mainly affected by the position and stability of the wetland water table. In contrast, low summer temperatures at high elevations in the Ruoergai peatland of the Qinghai-Tibetan Plateau result in the presence of dominant species of methanogens with low CH4 production potential rather than the reduction of the supply of methanogenic substrates, which in turn suppresses CH4 production.

Liu, D.; Ding, W.; Jia, Z.; Cai, Z.

2010-10-01

173

Low-energy 15N implantation in carbon for the synthesis of carbon nitride layers  

Microsoft Academic Search

15N2+ molecular ions with an energy of 12 keV were implanted in glassy carbon and 40 keV 15N+ ions were implanted into different carbon forms (glassy carbon, graphite and polycrystalline diamond) at room temperature in order to form thin carbon nitride layers. The nitrogen depth profiles were measured using the resonant nuclear reaction 15N(p, ??)12C (Eres = 429 keV, ?

F. Link; H. Baumann; A. Markwitz; E. F. Krimmel; K. Bethge

1996-01-01

174

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

175

15 N 2 Incorporation and metabolism in the lichen Peltigera aphthosa Willd  

Microsoft Academic Search

The Nostoc in the cephalodia of the lichen Peltigera aphthosa Willd. fixed 15N2 and the bulk of the nitrogen fixed was continuously transferred from it to its eukaryotic partners (a fungus and a green alga, Coccomyxa sp.). Kinetic studies carried out over the first 30 min, after exposure of isolated cephalodia to 15N2, showed that highest initial 15N2-labelling was into

A. N. Rai; P. Rowell; W. D. P. Stewart

1981-01-01

176

Midterm tracing of 15 N derived from urine and dung in soil microbial biomass  

Microsoft Academic Search

Large amounts of C and N are returned to pasture soils by grazing animals in the form of urine and dung. Therefore, a field\\u000a trial was carried out to investigate the mid-term effects of 15N-labeled excrements, produced by feeding a cow with 15N-labeled grass silage, on the soil microbial biomass. Simulating the deposition of excrements, 15N-labeled urine and dung were

Christine Wachendorf; Rainer Georg Joergensen

2011-01-01

177

Transformation of 15 N-labelled leguminous plant material in three contrasting soils  

Microsoft Academic Search

Two soils from Pakistan (Hafizabad silt loam and Khurrarianwala silt loam) and one from Illinois, USA (Drummer silty clay loam) were incubated with 15N-labelled soybean tops for up to 20 weeks at 30°C. Mineralization of soybean 15N was slightly more rapid in the Pakistani soils, and after 20 weeks of incubation, 50%, 53%, and 56% of the applied 15N was

F. Azam; R. L. Mulvaney; F. J. Stevenson

1989-01-01

178

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

179

Nitrogen Cycling in a Forest Stream Determined a 15N Tracer Addition  

Microsoft Academic Search

Nitrogen uptake and cycling was examined using a six-week tracer addition of 15N-labeled ammonium in early spring in Walker Branch, a first-order deciduous forest stream in eastern Tennessee. Prior to the 15N addition, standing stocks of N were determined for the major biomass compartments. During and after the addition, 15N was measured in water and in dominant biomass compartments upstream

Patrick J. Mulholland; Jennifer L. Tank; Diane M. Sanzone; Wilfred M. Wollheim; Bruce J. Peterson; Jackson R. Webster; Judy L. Meyer

2000-01-01

180

Binding of thiocyanate to lactoperoxidase: 1H and 15N nuclear magnetic resonance studies  

SciTech Connect

The binding of thiocyanate to lactoperoxidase (LPO) has been investigated by 1H and 15N NMR spectroscopy. 1H NMR of LPO shows that the major broad heme methyl proton resonance at about 61 ppm is shifted upfield by addition of the thiocyanate, indicating binding of the thiocyanate to the enzyme. The pH dependence of line width of 15N resonance of SC15N- in the presence of the enzyme has revealed that the binding of the thiocyanate to the enzyme is facilitated by protonation of an ionizable group (with pKa of 6.4), which is presumably distal histidine. Dissociation constants (KD) of SC15N-/LPO, SC15N-/LPO/I-, and SC15N-/LPO/CN- equilibria have been determined by 15N T1 measurements and found to be 90 +/- 5, 173 +/- 20, and 83 +/- 6 mM, respectively. On the basis of these values of KD, it is suggested that the iodide ion inhibits the binding of the thiocyanate but cyanide ion does not. The thiocyanate is shown to bind at the same site of LPO as iodide does, but the binding is considerably weaker and is away from the ferric ion. The distance of 15N of the bound thiocyanate ion from the iron is determined to be 7.2 +/- 0.2 A from the 15N T1 measurements.

Modi, S.; Behere, D.V.; Mitra, S. (Tata Institute of Fundamental Research, Bombay (India))

1989-05-30

181

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.

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

2011-01-01

182

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).

Eldegard, Katrine; Sonerud, Geir A.

2009-01-01

183

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

2011-07-06

184

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.

Fernandez-de-Mera, Isabel G.; Acevedo, Pelayo; Gortazar, Christian; de la Fuente, Jose

2012-01-01

185

``Clumped-isotope'' geochemistry---The study of naturally-occurring, multiply-substituted isotopologues  

Microsoft Academic Search

Clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials. That is, it examines the extent to which rare isotopes (D, 13C, 15N, 18O, etc.) bond with or near each other rather than with the sea of light isotopes in which they swim. Abundances of isotopic `clumps' in natural materials are influenced by a

John M. Eiler

2007-01-01

186

“Clumped-isotope” geochemistry—The study of naturally-occurring, multiply-substituted isotopologues  

Microsoft Academic Search

Clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials. That is, it examines the extent to which rare isotopes (D, 13C, 15N, 18O, etc.) bond with or near each other rather than with the sea of light isotopes in which they swim. Abundances of isotopic ‘clumps’ in natural materials are influenced by a

John M. Eiler

2007-01-01

187

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.

188

Effects of water availability, nitrogen supply and atmospheric CO2 concentrations on plant nitrogen natural abundance values  

Microsoft Academic Search

The relative effects of soil N, water supply and elevated atmospheric CO2 on foliar delta-15N values were examined. Phalaris arundinacea L. (Holdfast) and Physalis peruviana L. (Cape Gooseberry) were grown for 80 d with three water availability treatments, two atmospheric CO2 concentrations and four N supply rates. Elevated CO2 increased total plant biomass and N for each treatment and decreased

William D. Stock; John R. Evans

2006-01-01

189

Spin and parity determinations of excited 15N based on polarized and unpolarized 12C(7Li, ?)15N reaction data at Elab = 34 MeV  

NASA Astrophysics Data System (ADS)

From an experiment conducted at the Florida State University Accelerator Laboratory with a 34 MeV polarized 7Li beam bombarding a 12C target, we have obtained angular distributions and analyzing powers for states of 15N up to 20 MeV in excitation energy. This study not only offers the possibility to assign spin and parity to several states in 15N, but also serves to obtain nuclear potential parameters used in Distorted Wave Born (DWBA) and Coupled Channel Born (CCBA) Approximations to generate theoretical angular distributions and vector analyzing powers that give the best description of the experimental data. Under the assumption that the reaction mechanism is a three nucleon transfer, the determination of shell model nucleonic configurations and spectroscopic factors is possible for the 15N states studied.

Rodriguez, F. J.; Liendo, J. A.; Roeder, B. T.; Weintraub, W.; Kemper, K. W.; Keeley, N.; Marechal, F.

2007-08-01

190

Distinguishing trophic variation from seasonal and size-based isotopic (? 15 N) variation of zooplankton  

Microsoft Academic Search

We measured the ?15N of particulate organic matter (POM), Daphnia pulex (D), Holopedium gibberum (H), Leptodiaptomus tyrelli (LT), Epischura nevadensis (E), and Chaoborus trivittatus (C) over an annual cycle in Council Lake, a pristine, oligotrophic, fishless lake. Annual averages of the ?15N of plankton (C, LT ,E>D , H> POM) matched expected differences in trophic position, but seasonal patterns differed

Blake Matthews; Asit Mazumder

2007-01-01

191

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

Microsoft Academic Search

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

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

2010-01-01

192

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. Am J Phys Anthropol 152:58-66, 2013. © 2013 Wiley Periodicals, Inc. PMID:23921599

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

2013-08-06

193

Spatial relationship between delta15N and elevation in agricultural landscapes  

Microsoft Academic Search

Understanding of the nitrogen (N) cycle and its spatial variability is important for managing ecosystems. Soil delta15N, as an important indicator of different soil nitrogen cycling processes, may provide critical information about the spatial variability in soil N cycling. The objective of this study was to examine the dominant landscape scale variability of delta15N, the location of the variability and

A. Biswas; B. C. Si; F. L. Walley

2008-01-01

194

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

195

Nitrogen Distribution a 15 N Fertilizer in Different Soil Fractions of a Barley Cultivation.  

National Technical Information Service (NTIS)

A culture of barley in the open fields has been fertilized on 9 m exp 2 with Ca(NO sub 3 ) sub 2 containing 20,8% 15N excess. At the crop, 15 N distribution shows that half of the fertilized nitrogen which is exported by the crop has become organic in the...

D. Pierre L. Jocteur Monrosier F. Andreux G. Guiraud

1981-01-01

196

Efeito da materia organica e de um inibidor da nitrificacao na absorcao de (sup 15)N H(sub 4) e (sup 15)N O(sub 3) pelo milho. (The effect of organic matter and nitrification inhibitor on (sup 15) N H(sub 4) and (sup 15) N O(sub 3) absorption by the maize).  

National Technical Information Service (NTIS)

The effect of the forms (sup 15) N H(sub 4) and (sup 15) N O(sub 3) in presence or absence of organic matter and of the nitrification inhibitor AM (2-amino-4-chloro-6-methyl-pyrimidine) in dry matter weight and nitrogen content of the plant derived from s...

S. M. T. Saito

1974-01-01

197

Preparation and characterization of 15N-enriched, size-defined heparan sulfate precursor oligosaccharides  

PubMed Central

We report the preparation of size-defined [15N]N-acetylheparosan oligosaccharides from Escherichia coli-derived 15N-enriched N-acetylheparosan. Optimized growth conditions of E. coli in minimal media containing 15NH4Cl yielded [15N]N-acetylheparosan on a preparative scale. Depolymerization of [15N]N-acetylheparosan by heparitinase I yielded resolvable, even-numbered oligosaccharides ranging from disaccharide to icosaccharide. Anion-exchange chromatography-assisted fractionation afforded size-defined [15N]N-acetylheparosan oligosaccharides identifiable by ESI-TOFMS. These isotopically labeled oligosaccharides will prove to be valuable research tools for the chemoenzymatic synthesis of heparin and heparan sulfate oligosaccharides and for the study of their structural biology.

Sigulinsky, Crystal; Babu, Ponnusamy; Victor, Xylophone V.; Kuberan, Balagurunathan

2009-01-01

198

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

199

Mapping the dynamics of ligand reorganization via 13CH3 and 13CH2 relaxation dispersion at natural abundance  

PubMed Central

Flexible ligands pose challenges to standard structure-activity studies since they frequently reorganize their conformations upon protein binding and catalysis. Here, we demonstrate the utility of side chain 13C relaxation dispersion measurements to identify and quantify the conformational dynamics that drive this reorganization. The dispersion measurements probe methylene 13CH2 and methyl 13CH3 groups; the latter are highly prevalent side chain moieties in known drugs. Combining these side chain studies with existing backbone dispersion studies enables a comprehensive investigation of µs–ms conformational dynamics related to binding and catalysis. We perform these measurements at natural 13C abundance, in congruence with common pharmaceutical research settings. We illustrate these methods through a study of the interaction of a phosphopeptide ligand with the peptidyl-prolyl isomerase, Pin1. The results illuminate the side-chain moieties that undergo conformational readjustments upon complex formation. In particular, we find evidence that multiple exchange processes influence the side chain dispersion profiles. Collectively, our studies illustrate how side-chain relaxation dispersion can shed light on ligand conformational transitions required for activity, and thereby suggest strategies for its optimization.

Wilson, Brian D.; Namanja, Andrew T.

2010-01-01

200

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.

Affek, Hagit P.; Yakir, Dan

2003-01-01

201

Molecular characterization of dissolved organic matter in glacial ice: coupling natural abundance 1H NMR and fluorescence spectroscopy.  

PubMed

Glaciers and ice sheets are the second largest freshwater reservoir in the global hydrologic cycle, and the onset of global climate warming has necessitated an assessment of their contributions to sea-level rise and the potential release of nutrients to nearby aquatic environments. In particular, the release of dissolved organic matter (DOM) from glacier melt could stimulate microbial activity in both glacial ecosystems and adjacent watersheds, but this would largely depend on the composition of the material released. Using fluorescence and (1)H NMR spectroscopy, we characterize DOM at its natural abundance in unaltered samples from a number of glaciers that differ in geographic location, thermal regime, and sample depth. Parallel factor analysis (PARAFAC) modeling of DOM fluorophores identifies components in the ice that are predominantly proteinaceous in character, while (1)H NMR spectroscopy reveals a mixture of small molecules that likely originate from native microbes. Spectrofluorescence also reveals a terrestrial contribution that was below the detection limits of NMR; however, (1)H nuclei from levoglucosan was identified in Arctic glacier ice samples. This study suggests that the bulk of the DOM from these glaciers is a mixture of biologically labile molecules derived from microbes. PMID:22385100

Pautler, Brent G; Woods, Gwen C; Dubnick, Ashley; Simpson, André J; Sharp, Martin J; Fitzsimons, Sean J; Simpson, Myrna J

2012-03-15

202

Stable Isotope Probing with 15N Achieved by Disentangling the Effects of Genome G+C Content and Isotope Enrichment on DNA Density? †  

PubMed Central

Stable isotope probing (SIP) of nucleic acids is a powerful tool that can identify the functional capabilities of noncultivated microorganisms as they occur in microbial communities. While it has been suggested previously that nucleic acid SIP can be performed with 15N, nearly all applications of this technique to date have used 13C. Successful application of SIP using 15N-DNA (15N-DNA-SIP) has been limited, because the maximum shift in buoyant density that can be achieved in CsCl gradients is approximately 0.016 g ml?1 for 15N-labeled DNA, relative to 0.036 g ml?1 for 13C-labeled DNA. In contrast, variation in genome G+C content between microorganisms can result in DNA samples that vary in buoyant density by as much as 0.05 g ml?1. Thus, natural variation in genome G+C content in complex communities prevents the effective separation of 15N-labeled DNA from unlabeled DNA. We describe a method which disentangles the effects of isotope incorporation and genome G+C content on DNA buoyant density and makes it possible to isolate 15N-labeled DNA from heterogeneous mixtures of DNA. This method relies on recovery of “heavy” DNA from primary CsCl density gradients followed by purification of 15N-labeled DNA from unlabeled high-G+C-content DNA in secondary CsCl density gradients containing bis-benzimide. This technique, by providing a means to enhance separation of isotopically labeled DNA from unlabeled DNA, makes it possible to use 15N-labeled compounds effectively in DNA-SIP experiments and also will be effective for removing unlabeled DNA from isotopically labeled DNA in 13C-DNA-SIP applications.

Buckley, Daniel H.; Huangyutitham, Varisa; Hsu, Shi-Fang; Nelson, Tyrrell A.

2007-01-01

203

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.

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

2013-01-01

204

Sequence-specific assignment of histidine and tryptophan ring 1 H, 13 C and 15 N resonances in 13 C\\/ 15 N- and 2 H\\/ 13 C\\/ 15 N-labelled proteins  

Microsoft Academic Search

Methods are described to correlate aromatic 1Hd 2\\/13Cd 2 or 1He 1\\/15Ne 1 with aliphatic 13Cß chemical shifts of histidine and tryptophan residues, respectively. The pulse sequences exclusively rely on magnetization transfers via one-bond scalar couplings and employ [15N, 1H]- and\\/or [13C, 1H]-TROSY schemes to enhance sensitivity. In the case of histidine imidazole rings exhibiting slow HN-exchange with the solvent,

Frank Löhr; Vicky Katsemi; Marco Betz; Judith Hartleib; Heinz Rüterjans

2002-01-01

205

Photochemistry of phenyl-substituted 1,2,4-thiadiazoles. 15N-labeling studies.  

PubMed

Irradiation of 5-phenyl-1,2,4-thiadiazole (6) resulted in the formation of benzonitrile (5), 3-phenyl-1,2,4-thiadiazole (4), phenyl- and diphenyl-1,3,5-triazines (7 and 8), and a trace quantity of diphenyl-1,2,4-thiadiazole (9). The formation of 4,5, 7, and 8 can be explained in terms of photoinduced electrocyclic ring closure resulting in the formation of an intermediate 4-phenyl-1,3-diaza-5-thiabicyclo[2.1.0]pentene. 15N-labeling experiments revealed that sulfur can undergo sigmatropic shifts around all four sides of the diazetine ring. Thus, irradiation of 6-4-15N led to the formation of 6-2-15N and an equimolar mixture of 4-2-15N and 4-4-15N. The thiabicyclo[2.1.0]pentene intermediate is also suggested to undergo sulfur elimination resulting in the formation of phenyldiazacyclobutadiene, which can undergo complete fragmentation to benzonitrile or [4+2] cycloaddition leading to unstable tricyclic adducts, the suggested precursors of the 1,3,5-triazine products 7 and 8. The observed 15N distribution in 7 and 8 is consistent with this mechanism. Irradiation of 4 led only to the formation of 5. 15N-labeling experiments show that 4 does not undergo electrocyclic ring closure but reacts exclusively by photofragmentation of the thiadiazole ring. PMID:12790591

Pavlik, James W; Changtong, Chuchawin; Tsefrikas, Vikki M

2003-06-13

206

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

207

Biomonitoring of traffic-related nitrogen oxides in the Maurienne valley (Savoie, France), using purple moor grass growth parameters and leaf 15N\\/ 14N ratio  

Microsoft Academic Search

Effects of traffic-related nitrogenous emissions on purple moor grass (Molinia caerulea (L.) Moench) transplants, used here as a new biomonitoring species, were assessed along 500 m long transects orthogonal to roads located in two open areas in the Maurienne valley (French Alps). Leaves were sampled during summer 2004 and 2005 for total N-content and 15N-abundance determination while nitrogen oxides (NO and

Xavier Laffray; Christophe Rose; Jean-Pierre Garrec

2010-01-01

208

Particle emission from sup 71 As sup * produced via sup 20 Ne+ sup 51 V and sup 15 N+ sup 56 Fe reactions at 530 MeV  

SciTech Connect

Charged particles from protons up to projectile particles were measured from the systems {sup 20}Ne+{sup 51}V and {sup 15}N+{sup 56}Fe at 530 MeV bombarding energy forming the same composite {sup 71}As{sup *}. The data show entrance channel effects with respect to spectral distributions and fragment abundances. The data analysis in terms of different models indicates a common reaction mechanism for all particles produced.

Buhr, G.; Machner, H.; Nolte, M.; Palarczyk, M.; Rama Rao, J. (Institut fuer Kernphysik, Forschungszentrum Juelich, Juelich (Germany))

1992-02-01

209

15N-permethylated amino acids as efficient probes for MRI-DNP applications.  

PubMed

The synthesis, NMR properties and preliminary polarization tests on protonated and perdeuterated forms of ?-trimethylglutamine (NMe3Gln), ?-trimethylglutamate (NMe3Glu) and ?-trimethyllysine (NMe3Lys) are reported. The (15)N-permethylated, perdeuterated amino acids display very long (15)N-T1 values, ranging between 190 and 330 s, are well polarized by the dynamic nuclear polarization (DNP) procedure, yielding good polarization levels (10%), and appear to be well tolerated by cells and mice. The obtained results make perdeuterated amino acids excellent candidates for innovative DNP (15)N-MRI applications such as perfusion or targeting studies. PMID:23740812

Chiavazza, Enrico; Viale, Alessandra; Karlsson, Magnus; Aime, Silvio

210

On the Measurement of 15N-{1H} Nuclear Overhauser Effects  

PubMed Central

Accurate quantification of the 15N-{1H} steady-state NOE is central to current methods for the elucidation of protein backbone dynamics on the fast, sub-nanosecond timescale. This experiment is highly susceptible to systematic errors arising from multiple sources. The nature of these errors and their effects on the determined NOE ratio is evaluated by a detailed analysis of the spin dynamics during the pair of experiments used to measure this ratio and possible improvements suggested. The experiment that includes 1H irradiation, is analyzed in the framework of Average Liouvillian Theory and a modified saturation scheme that generates a stable steady state and eliminates the need to completely saturate 1H nuclei, is presented. The largest source of error, however, in 1H-dilute systems at ultra-high fields is found to be an overestimation of the steady-state NOE value as a consequence of the incomplete equilibration of the magnetization in the so-called “reference experiment”. The use of very long relaxation delays is usually an effective, but time consuming, solution. Here, we introduce an alternative reference experiment, designed for larger, deuterated systems, that uses the fastest relaxing component of the longitudinal magnetization a closer approximation to the equilibrium state for shorter relaxation delays. The utility of the modified approach is illustrated through simulations on realistic spin-systems over a wide range of timescales and experimentally verified using a perdeuterated sample of human ubiquitin.

Ferrage, Fabien; Piserchio, Andrea; Cowburn, David; Ghose, Ranajeet

2009-01-01

211

Constraining the S factor of {sup 15}N(p,{gamma}){sup 16}O at astrophysical energies  

SciTech Connect

The {sup 15}N(p,{gamma}){sup 16}O reaction represents a breakout reaction linking the first and second cycles of the CNO cycles redistributing the carbon and nitrogen abundances into the oxygen range. The reaction is dominated by two broad resonances, at E{sub p}=338 and 1028 keV, and a direct capture contribution to the ground state of {sup 16}O. Interference effects between these contributions both in the low-energy region (E{sub p}<338 keV) and between the two resonances (33815}N(p,{gamma}){sup 16}O reaction has been remeasured covering the energy range from E{sub p}=1800 keV down to 130 keV. The results have been analyzed in the framework of a multilevel R-matrix theory and an S(0) value of 39.6 keV b has been found.

LeBlanc, P. J.; Goerres, J.; Beard, M.; Best, A.; Couder, M.; Boer, R. de; Kontos, A.; Li, Q.; O'Brien, S.; Palumbo, A.; Stech, E.; Tan, W.; Uberseder, E.; Wiescher, M. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Imbriani, G. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Universita degli Studi di Napoli 'Frederico II' and INFN, Napoli (Italy); Laboratori Nazionali del Gran Sasso (LNGS), INFN, Assergi (Italy); Junker, M.; Formicola, A.; Gustavino, C. [Laboratori Nazionali del Gran Sasso (LNGS), INFN, Assergi (Italy); Azuma, R. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Department of Physics, University of Toronto, Toronto, Ontario M55 1A7 (Canada); Bemmerer, D. [Forschungszentrum Dresden, Rossendorf, Dresden (Germany)

2010-11-15

212

Secondary sup 15 N isotope effects on the reactions catalyzed by alcohol and formate dehydrogenases  

SciTech Connect

Secondary {sup 15}N isotope effects at the N-1 position of 3-acetylpyridine adenine dinucleotide have been determined, by using the internal competition technique, for horse liver alcohol dehydrogenase (LADH) with cyclohexanol as a substrate and yeast formate dehydrogenase (FDH) with formate as a substrate. On the basis of less precise previous measurements of these {sup 15}N isotope effects, the nicotinamide ring of NAD has been suggested to adopt a boat conformation with carbonium ion character at C-4 during hydride transfer. If this mechanism were valid, as N-1 becomes pyramidal an {sup 15}N isotope effect for the reaction catalyzed by LADH was measured. These values suggest that a significant {sup 15}N kinetic isotope effect is not associated with hydride transfer for LADH and FDH. Thus, in contrast with the deformation mechanism previously postulated, the pyridine ring of the nucleotide apparently remains planar during these dehydrogenase reactions.

Rotberg, N.S.; Cleland, W.W. (Univ. of Wisconsin, Madison (USA))

1991-04-23

213

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.

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

2013-01-01

214

Lattice Vibrations of Crystalline Imidazole and exp 15 N and D Substituted Analogs.  

National Technical Information Service (NTIS)

Raman spectra of polycrystalline imidazole and seven exp 15 N and D substituted analogs have been measured. At 100 K, twelve bands are observed and related to the expected active lattice vibrations. The isotopic shifts permit unambiguous assignments for s...

M. Majoube G. Vergoten

1980-01-01

215

Regional Assessment of N saturation using foliar and root ?15N  

Microsoft Academic Search

N saturation induced by atmospheric N deposition can have serious consequences for forest health in many regions. In order to evaluate whether foliar d15N may be a robust, regional-scale measure of the onset of N saturation in forest ecosystems, we assembled a large dataset on atmospheric N deposition, foliar and root d15N and N concentration, soil C:N, mineralization and nitrification.

L. H. Pardo; P. Templer; C. L. Goodale; S. Duke; P. Groffman; M. B. Adams; P. Boeckx; J. Boggs; J. Campbell; J. Compton; B. Emmett; P. Gundersen; G. Lovett; M. Mack; A. Magill; M. J. Mitchell; M. Mbila; G. McGee; S. McNulty; K. Nadelhoffer; B. Colman; S. Ollinger; D. Ross; H. Rueth; L. Rustad; P. Schaberg; S. Schiff; P. Schleppi; J. Spoelstra; W. Wessel

216

(1)H, (13)C, and (15)N NMR assignments of a Drosophila Hedgehog autoprocessing domain.  

PubMed

The Hedgehog (Hh) signaling pathway plays important roles in embryonic growth and patterning in different organisms. Abnormal activity of the Hh signaling pathway has been associated to cancers, holoprosencephaly and autism spectrum disorders. The backbone and side chain resonance assignments of a Drosophila Hh autoprocessing domain have been determined based on triple-resonance experiments with the [(13)C, (15)N]-labeled and [(2)H, (13)C, (15)N])-labeled proteins. PMID:23765287

Xie, Jian; Du, Zhenming; Callahan, Brian; Belfort, Marlene; Wang, Chunyu

2013-06-14

217

Decomposition of European beech ( Fagus sylvatica) litter: Combining quality theory and 15N labelling experiments  

Microsoft Academic Search

A multi-site and multi-age set of in situ 15N-labelled litter decomposition experiments was carried out in various European beech forests. The sites presented contrasted situations of climate and humus type that were representative of northern Europe temperate forests. 15N-labelled leaf litter was produced by urea spraying in an experimental beech plot, and was used in litter decomposition experiments over a

Remi d’Annunzio; Bernd Zeller; Manuel Nicolas; Jean-François Dhôte; Laurent Saint-André

2008-01-01

218

The use of 15N labelling to study the turnover and utilization of ruminant manure N  

Microsoft Academic Search

An improved understanding of the cycling of animal manure N is a prerequisite for making better use of this N source. A sheep\\u000a was fed 15N-labelled grass in order to study the fate of 15N-labelled ruminant manure N in the plant-soil system. The uniformity of labelling was found to be satisfactory when an appropriate\\u000a feeding strategy was used. The mineralization

P. Sørensen; E. S. Jensen

1998-01-01

219

Emissive spectral analysis applied in 15N excretion test of Helicobacter pylori  

Microsoft Academic Search

A new method for detecting the infection of Helicobacter pylor (HP), 15N-urea tracing and emissive optical spectroscopy method, is described in this paper. A group of 26 patients was tested. After 15N-urea was administered orally, urine specimen was collected from 30 to 120 minutes and its volume was measured. Then the concentration of ammonia in the urine specimen was determined.

Yayi Zhu; Jicong Wu; Zhenhua Zhang

2002-01-01

220

Determination of 13 C ? relaxation times in uniformly 13 C\\/ 15 N-enriched proteins  

Microsoft Academic Search

Relaxation times of 13Ca carbons of uniformly 13C\\/15N-enriched probes have been investigated. The relaxation behaviour was analyzed in terms of a multispin system. Pulse sequences for the determination of T1, T2 and the heteronuclear NOE of 13Ca in uniformly 13C\\/15N-enriched ribonuclease T1 are presented. The experiments performed in order to obtain T1 and the heteronuclear NOE were similar to those

Jan Engelke; Heinz Rüterjans

1995-01-01

221

Ecosystem N distribution and ?15N during a century of forest regrowth after agricultural abandonment  

USGS Publications Warehouse

Stable isotope ratios of terrestrial ecosystem nitrogen (N) pools reflect internal processes and input–output balances. Disturbance generally increases N cycling and loss, yet few studies have examined ecosystem ?15N over a disturbance-recovery sequence. We used a chronosequence approach to examine N distribution and ?15N during forest regrowth after agricultural abandonment. Site ages ranged from 10 to 115 years, with similar soils, climate, land-use history, and overstory vegetation (white pine Pinus strobus). Foliar N and ?15N decreased as stands aged, consistent with a progressive tightening of the N cycle during forest regrowth on agricultural lands. Over time, foliar ?15N became more negative, indicating increased fractionation along the mineralization–mycorrhizal–plant uptake pathway. Total ecosystem N was constant across the chronosequence, but substantial internal N redistribution occurred from the mineral soil to plants and litter over 115 years (>25% of ecosystem N or 1,610 kg ha?1). Temporal trends in soil ?15N generally reflected a redistribution of depleted N from the mineral soil to the developing O horizon. Although plants and soil ?15N are coupled over millennial time scales of ecosystem development, our observed divergence between plants and soil suggests that they can be uncoupled during the disturbance-regrowth sequence. The approximate 2‰ decrease in ecosystem ?15N over the century scale suggests significant incorporation of atmospheric N, which was not detected by traditional ecosystem N accounting. Consideration of temporal trends and disturbance legacies can improve our understanding of the influence of broader factors such as climate or N deposition on ecosystem N balances and ?15N.

Compton, J. E.; Hooker, T. D.; Perakis, S. S.

2007-01-01

222

Combined solid state and solution NMR studies of ?,?- 15 N labeled bovine rhodopsin  

Microsoft Academic Search

Rhodopsin is the visual pigment of the vertebrate rod photoreceptor cell and is the only member of the G protein coupled receptor\\u000a family for which a crystal structure is available. Towards the study of dynamics in rhodopsin, we report NMR-spectroscopic\\u000a investigations of ?,?-15N-tryptophan labeled rhodopsin in detergent micelles and reconstituted in phospholipids. Using a combination of solid state\\u000a 13C,15N-REDOR and

Karla Werner; Ines Lehner; Harpreet Kaur Dhiman; Christian Richter; Clemens Glaubitz; Harald Schwalbe; Judith Klein-Seetharaman; H. Gobind Khorana

2007-01-01

223

Water proton spin saturation affects measured protein backbone 15N spin relaxation rates.  

PubMed

Protein backbone 15N NMR spin relaxation rates are useful in characterizing the protein dynamics and structures. To observe the protein nuclear-spin resonances a pulse sequence has to include a water suppression scheme. There are two commonly employed methods, saturating or dephasing the water spins with pulse field gradients and keeping them unperturbed with flip-back pulses. Here different water suppression methods were incorporated into pulse sequences to measure 15N longitudinal T1 and transversal rotating-frame T1? spin relaxation. Unexpectedly the 15N T1 relaxation time constants varied significantly with the choice of water suppression method. For a 25-kDa Escherichiacoli. glutamine binding protein (GlnBP) the T1 values acquired with the pulse sequence containing a water dephasing gradient are on average 20% longer than the ones obtained using a pulse sequence containing the water flip-back pulse. In contrast the two T1? data sets are correlated without an apparent offset. The average T1 difference was reduced to 12% when the experimental recycle delay was doubled, while the average T1 values from the flip-back measurements were nearly unchanged. Analysis of spectral signal to noise ratios (s/n) showed the apparent slower 15N relaxation obtained with the water dephasing experiment originated from the differences in 1HN recovery for each relaxation time point. This in turn offset signal reduction from 15N relaxation decay. The artifact becomes noticeable when the measured 15N relaxation time constant is comparable to recycle delay, e.g., the 15N T1 of medium to large proteins. The 15N relaxation rates measured with either water suppression schemes yield reasonable fits to the structure. However, data from the saturated scheme results in significantly lower Model-Free order parameters (=0.81) than the non-saturated ones (=0.88), indicating such order parameters may be previously underestimated. PMID:22015249

Chen, Kang; Tjandra, Nico

2011-10-01

224

Does Solid-state 15 N NMR Spectroscopy Detect all Soil Organic Nitrogen?  

Microsoft Academic Search

Virtually all of the N detected by 15N cross polarization (CP) NMR spectra of four HF-treated soil clay fractions is amide N. However, the intensity of this 15N CP NMR signal (per unit N) is 27–57% lower than detected for a wheat protein, gliadin. There are two possible explanations – either the amide N in the soil clay fractions produces

Ronald J. Smernik; Jeffrey A. Baldock

2005-01-01

225

EFFECT OF HIGH-ENERGY RESONANCES ON THE {sup 18}O(p, {alpha}){sup 15}N REACTION RATE AT AGB AND POST-AGB RELEVANT TEMPERATURES  

SciTech Connect

The {sup 18}O(p, {alpha}){sup 15}N reaction is of great importance in several astrophysical scenarios, as it influences the production of key isotopes such as {sup 19}F, {sup 18}O, and {sup 15}N. Fluorine is synthesized in the intershell region of asymptotic giant branch (AGB) stars, together with s-elements, by {alpha} radiative capture on {sup 15}N, which in turn is produced in the {sup 18}O proton-induced destruction. Peculiar {sup 18}O abundances are observed in R-Coronae Borealis stars, having {sup 16}O/{sup 18}O {approx}< 1, hundreds of times smaller than the galactic value. Finally, there is no definite explanation of the {sup 14}N/{sup 15}N ratio in pre-solar grains formed in the outer layers of AGB stars. Again, such an isotopic ratio is influenced by the {sup 18}O(p, {alpha}){sup 15}N reaction. In this work, a high accuracy {sup 18}O(p, {alpha}){sup 15}N reaction rate is proposed, based on the simultaneous fit of direct measurements and of the results of a new Trojan Horse experiment. Indeed, current determinations are uncertain because of the poor knowledge of the resonance parameters of key levels of {sup 19}F. In particular, we have focused on the study of the broad 660 keV 1/2{sup +} resonance corresponding to the 8.65 MeV level of {sup 19}F. Since {Gamma} {approx} 100-300 keV, it determines the low-energy tail of the resonant contribution to the cross section and dominates the cross section at higher energies. Here, we provide a reaction rate that is a factor of two larger above T {approx} 0.5 10{sup 9} K based on our new improved determination of its resonance parameters, which could strongly influence present-day astrophysical model predictions.

La Cognata, M.; Spitaleri, C. [INFN-Laboratori Nazionali del Sud and University of Catania, I-95123 Catania (Italy); Mukhamedzhanov, A. M., E-mail: lacognata@lns.infn.i [Cyclotron Institute-Texas A and M University, College Station, TX (United States)

2010-11-10

226

/sup 18/O isotope shift in /sup 15/N NMR spectroscopy. 2. Synthesis of /sup 15/N, /sup 18/O-labeled hydroxylamine hydrochloride  

SciTech Connect

Since hydroxylamine can serve as a key intermediate in the synthesis of a variety of compounds, the synthesis of (/sup 15/N, /sup 18/O)-labelled hydroxylamine hydrochloride was undertaken. Published procedures for the synthesis of hydroxylamine resulted in poor yields in some cases and in lower percentage of /sup 18/O in the product than expected in other cases. The compound was synthesized in dry tetrahydrofuran (THF) by treating NaNO/sub 2/ with borane-methyl sulfide. The course of the reaction was examined using /sup 11/B NMR spectroscopy, and the product yield was 74%. The /sup 18/O enrichment was demonstrated by both mass spectrometry and /sup 15/N NMR of the isolated acetoxime. 23 references, 1 figure.

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

1986-03-12

227

Acetylene inhibition of N2O reduction in laboratory soil and groundwater denitrification assays: evaluation by 15N tracer and 15N site preference of N2O  

NASA Astrophysics Data System (ADS)

The measurement of denitrification in soils and aquifers is still challenging and often enough associated with considerable experimental effort and high costs. Against this background, the acetylene inhibition technique (AIT) applied in laboratory soil and groundwater denitrification assays is by far the most effective approach. However, this method has been largely criticized, as it is susceptible to underestimate denitrification rates and adds an additional carbon source to the substrates to be investigated. Here we provide evidence that the AIT is not necessarily an inappropriate approach to measure denitrification, that its reliability depends on the drivers governing the process, and that the 15N site preference of N2O (SP) may serve as a tool to assess this reliability. Two laboratory batch experiments were conducted, where sandy aquifer material and a peat soil were incubated as slurries. We established (i) a standard anaerobic treatment by adding KNO3 (10 mg N L-1), (ii) an oxygen treatment by adding KNO3 and O2 (5 mg L-1), and (iii) a glucose treatment by adding KNO3 supplemented with glucose (200 mg C L-1). Both experiments were run under 10 % (v/v) acetylene atmosphere and as 15N tracer treatments using labeled K15NO3 (60 atom % 15N). In the case of the standard anaerobic treatments, we found a very good agreement of denitrification potential obtained by the AIT and 15N tracer methods. SP of N2O of the AIT samples from this treatment ranged between -4.8 and 2.6 ‰ which is indicative for N2O production during bacterial denitrification but not for N2O reduction to N2. In contrast, we observed substantial underestimation of denitrification by AIT for the glucose treatments compared to the 15N method, i.e. denitrification was underestimated by 36 % (sandy aquifer material) and 47 % (peat soil). SP of N2O of the AIT samples from this treatment ranged between 4.5 and 9.6 ‰, which suggests occurrence of bacterial N2O reduction. In the case of the oxygen treatments, we observed a very good agreement of denitrification potential obtained by the AIT and 15N tracer methods for the aquifer material, but a significant underestimation of 20 % in the AIT samples of the peat soil. The 15N site preference of N2O again mirrored this and ranged between -1.2 and -3.5 ‰ (aquifer material) and 5.5 and 11.0 (peat soil), respectively. We conclude that the AIT can act as a reliable method in laboratory soil and groundwater bacterial denitrification assays, but our results suggest that this relies on substrate types and incubation conditions. Additional measurements of SP have potential to assess AIT efficacy and can help to reduce parallel time-consuming and expensive 15N tracer experiments.

Weymann, Daniel; Well, Reinhard; Lewicka-Szczebak, Dominika; Lena, Rohe

2013-04-01

228

Separation of Anisotropy and Exchange Broadening Using 15N CSA-15N-1H Dipole-Dipole Relaxation Cross-Correlation Experiments  

NASA Astrophysics Data System (ADS)

Based on the measurement of cross-correlation rates between 15N CSA and 15N-1H dipole-dipole relaxation we propose a procedure for separating exchange contributions to transverse relaxation rates (R2 = 1/T2) from effects caused by anisotropic rotational diffusion of the protein molecule. This approach determines the influence of anisotropy and chemical exchange processes independently and therefore circumvents difficulties associated with the currently standard use of T1/T2 ratios to determine the rotational diffusion tensor. We find from computer simulations that, in the presence of even small amounts of internal flexibility, fitting T1/T2 ratios tends to underestimate the anisotropy of overall tumbling. An additional problem exists when the N-H bond vector directions are not distributed homogeneously over the surface of a unit sphere, such as in helix bundles or ?-sheets. Such a case was found in segment 4 of the gelation factor (ABP 120), an F-actin cross-linking protein, in which the diffusion tensor cannot be calculated from T1/T2 ratios. The 15N CSA tensor of the residues for this ?-sheet protein was found to vary even within secondary structure elements. The use of a common value for the whole protein molecule therefore might be an oversimplification. Using our approach it is immediately apparent that no exchange broadening exists for segment 4 although strongly reduced T2 relaxation times for several residues could be mistaken as indications for exchange processes.

Renner, Christian; Holak, Tad A.

2000-08-01

229

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

2013-10-17

230

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.

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

2013-01-01

231

Using PLFA Biomarkers and Natural Abundance Stable and Radiocarbon Isotopes to Characterize the Microbial Ecology and Metabolism of Methane Cycling  

NASA Astrophysics Data System (ADS)

Methane generated in the subsurface is a major source of atmospheric CH4, but its release is mitigated by CH4-oxidizing bacteria (methanotrophs). Therefore, it is important to understand the ecology of methanotroph communities in various environments. Phospholipid fatty acid (PLFA) analyses are a particularly useful method for characterizing these communities for two reasons: (1) Many type I and II methanotrophs produce specific PLFA biomarkers that can be used to estimate their populations, and (2) because CH4 is often very depleted in 13C and sometimes 14C, natural abundance ?13CPLFA and ?14CPLFA values can be used to trace the flow of CH4- derived carbon through microbial ecosystems. We used these tools to evaluate the role of methanotrophs in carbon flow in three different environments: (1) a soil column overlying a coal bed methane (CBM) seep in southwest CO, and pristine, oligotrophic groundwaters within (2) sedimentary and (3) granitic host rocks in Japan. In the soil column impacted by CBM seepage, concentrations of the biomarker PLFAs for type I (16:1?8cis) and type II (18:1?8cis) methanotrophs were as high as 13 and 18 nmoles (g dry soil)-1, respectively. Depth profiles of methanotroph PLFA concentrations varied over different sampling dates indicating dynamic populations. ?13CPLFA values of the CBM soils (-25.1 to - 66.9‰) were substantially more negative than those for the control soil (-14.5 to -32.5‰) indicating that CBM is an important carbon source for the CBM-impacted soil microbial community. ?14CPLFA values (-351 to -936‰) indicate the importance of 14C-dead CBM as a carbon source to the microbial communities, contributing 32 to 66% of total carbon in PLFA structures isolated from shallow soils and 67 to 97% for those isolated from deeper soils. The biomarker for type II methanotrophs, comprised 3 and 18% of total PLFAs in sedimentary and granitic groundwaters, respectively. The ?14C values determined for type II methanotroph PLFAs in the sedimentary (- 861‰) and granite (-867‰) waters were very similar to the ?14C values of dissolved inorganic carbon (DIC) in each water (ca -850‰) suggesting that type II methanotrophs ultimately derive all of their carbon from DIC. In contrast, ?13C values of type II PLFAs in the sedimentary (- 93‰) and granite (-60‰) waters indicate that these organisms use different carbon assimilation schemes in each environment. These studies show the utility of PLFA biomarkers and ?13CPLFA and ?14CPLFA values to characterize the in situ metabolisms of methanotrophic bacteria and overall CH4 recycling in diverse environments.

Mills, C. T.; Mandernack, K. W.; Slater, G. F.; Dias, R. F.

2008-12-01

232

A new method to track seed dispersal and recruitment using 15N isotope enrichment.  

PubMed

Seed dispersal has a powerful influence on population dynamics, genetic structuring, evolutionary rates, and community ecology. Yet, patterns of seed dispersal are difficult to measure due to methodological shortcomings in tracking dispersed seeds from sources of interest. Here we introduce a new method to track seed dispersal: stable isotope enrichment. It consists of leaf-feeding plants with sprays of 15N-urea during the flowering stage such that seeds developed after applications are isotopically enriched. We conducted a greenhouse experiment with Solanum americanum and two field experiments with wild Capsicum annuum in southern Arizona, USA, to field-validate the method. First, we show that plants sprayed with 15N-urea reliably produce isotopically enriched progeny, and that delta 15N (i.e., the isotopic ratio) of seeds and seedlings is a linear function of the 15N-urea concentration sprayed on mothers. We demonstrate that three urea dosages can be used to distinctly enrich plants and unambiguously differentiate their offspring after seeds are dispersed by birds. We found that, with high urea dosages, the resulting delta 15N values in seedlings are 10(3) - 10(4) times higher than the delta 15N values of normal plants. This feature allows tracking not only where seeds arrive, but in locations where seeds germinate and recruit, because delta 15N enrichment is detectable in seedlings that have increased in mass by at least two orders of magnitude before fading to normal delta 15N values. Last, we tested a mixing model to analyze seed samples in bulk. We used the delta 15N values of batches (i.e., combined seedlings or seeds captured in seed traps) to estimate the number of enriched seeds coming from isotopically enriched plants in the field. We confirm that isotope enrichment, combined with batch-sampling, is a cheap, reliable, and user-friendly method for bulk-processing seeds and is thus excellent for the detection of rare dispersal events. This method could further the study of dispersal biology, including the elusive, but critically important, estimation of long-distance seed dispersal. PMID:20120818

Carlo, Tomás A; Tewksbury, Joshua J; Martínez Del Río, Carlos

2009-12-01

233

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

234

Studies on amino acid metabolism in the brain using 15N-labeled precursors.  

PubMed

The transfer of label from 15N-alanine and 15N-glutamate into amino acids in incubated brain slices has been followed using gas chromatography/mass spectrometry (GC/MS). 15N from alanine appeared in both amino and amide groups of glutamine more rapidly than into aspartate, glutamate and GABA, which were all labeled at similar rates. Maximum labelling of approx. 50% enrichment of these three metabolites was achieved in 3 hr. The 15N present in doubly-labeled glutamine exceeded that in the singly-labelled after 30 min. 15N from glutamate was rapidly transferred to aspartate and to alanine, with slower incorporation into glutamine and GABA. As was seen with labeling from alanine, doubly-labeled glutamine was higher than the singly-labeled species, also reaching some 50% enrichment in 3 hr. Depolarisation with 40 mM extracellular K+ caused a considerable reversal of the ratio of doubly- to singly-labeled glutamine species from both alanine and glutamate. The results are discussed in terms of the effects of depolarization on the glutamate/glutamine cycle. PMID:10555771

Jones, P; Bachelard, H S

1999-11-01

235

Low energy 15N and 14N implantation in chromium analysed by NRA and RBS  

NASA Astrophysics Data System (ADS)

The physical results of implantation processes are dependent on several interconnected parameters. For the nitrogen implantation into chromium the interdependence of fluence, dose and nitrogen profiles was investigated. Thin PVD chromium films, evaporated on polished glassy carbon and crystalline silicon substrates, were implanted with 30 keV ions (15N and 14N) in a fluence range from 1017 to 1018 at./cm2. The nitrogen depth distributions were measured by using the nuclear resonance reaction 15N(p, ??)12C at Eres = 429 keV (NRA). Information about ion beam induced effusion and diffusion of 15N was gained from the implantation of 14N in addition to preimplanted nitrogen (15N). It was observed that 15N was displaced and recoiled into greater depths of the sample. RBS measurements with 4He+ ions were used to analyse the sample composition and the release of chromium (sputtering yield). Furthermore, the results of the NRA measurements were compared with RBS measurements.

Rose, M.; Baumann, H.; Markwitz, A.; Bethge, K.

1993-06-01

236

Effect of 15 N Labeled Riparian Fertilization And Salmon Carcass Analog Addition On Food Web Dynamics And Productivity In Four Idaho Streams  

NASA Astrophysics Data System (ADS)

Nutrient budgets of stream/riparian ecosystems in the Intermountain West have been depleted through declining salmon populations and certain anthropogenic disturbances (e.g. forestry practices). We measured stream food web responses to a riparian fertilization and an in-stream carcass analog addition in 4 Idaho streams with a 15 N tracer. Aerial application of fertilizer pellets to light (224 kg/ha) and heavy (448 kg/ha) treatment sections of 2 streams and carcass analog additions to 2 others were completed in autumn. Periphyton response was measured through chlorophyll a, nutrient diffusing substrata, and stable isotope analyses. Macroinvertebrates were analyzed for abundance, biomass, community structure, and stable isotope composition. Also, willow (Salix) breakdown rates were determined. Pre-treatment chlorophyll a values showed no significant difference between treatment and reference reaches. Post-treatment results showed significantly higher chlorophyll a and ? 15 N values in treatment reaches compared to reference reaches. Macroinvertebrate abundance, richness, biomass, and ? 15 N values also increased in treated reaches. No significant differences were detected in leaf breakdown rates between reaches. Riparian fertilization effects were longer lasting than the in-stream treatment. These results suggest that nutrient addition to streams and riparian areas can be used as a management tool to increase stream productivity where nutrients are limiting.

Rugenski, A. T.; Kohler, A.; Minshall, G. W.; Danehy, R. J.; Taki, D.

2005-05-01

237

Study of the 15N(p,?)16O Reaction at LUNA with a Solid Target  

NASA Astrophysics Data System (ADS)

The case of the most recent measurement performed at LUNA, the 15N(p,?)16O reaction, is presented. This reaction, together with the 15N(p,?)12C, forms the branching point from the first to the second CNO cycle and the ratio of their respective reaction rates influences the nucleosynthesis yields of 16O, 17O e 17F. In particular, one of the three different campaigns performed by the LUNA collaboration to measure the cross section of this reaction will be discussed. This experiment was performed by impinging a proton beam from the LUNA accelerator with energies ranging from 77 to 350 keV in the centre-of-mass reference frame on a TiN solid target, enriched in 15N to 98%. The ?-rays following the (p, ?) reaction were detected by means of an high-efficiency BGO detector.

Capogrosso, Valentina

2010-03-01

238

?-ray spectroscopy of ?16O and ?15N hypernuclei via the O16(K-,?-?) reaction  

NASA Astrophysics Data System (ADS)

The bound-state level structures of the ?16O and ?15N hypernuclei were studied by ?-ray spectroscopy using a germanium detector array (Hyperball) via the O16 (K-,?-?) reaction. A level scheme for ?16O was determined from the observation of three ?-ray transitions from the doublet of states (2-,1-) at ~6.7 MeV to the ground-state doublet (1-,0-). The ?15N hypernuclei were produced via proton emission from unbound states in ?16O. Three ? rays were observed, and the lifetime of the 1/2+;1 state in ?15N was measured by the Doppler shift attenuation method. By comparing the experimental results with shell-model calculations, the spin dependence of the ?N interaction is discussed. In particular, the measured ?16O ground-state doublet spacing of 26.4±1.6±0.5 keV determines a small but nonzero strength of the ?N tensor interaction.

Ukai, M.; Ajimura, S.; Akikawa, H.; Alburger, D. E.; Banu, A.; Chrien, R. E.; Franklin, G. B.; Franz, J.; Hashimoto, O.; Hayakawa, T.; Hotchi, H.; Imai, K.; Kishimoto, T.; May, M.; Millener, D. J.; Minami, S.; Miura, Y.; Miyoshi, T.; Mizunuma, K.; Nagae, T.; Nakamura, S. N.; Nakazawa, K.; Okayasu, Y.; Pile, P.; Quinn, B. P.; Rusek, A.; Sato, Y.; Sutter, R.; Takahashi, H.; Tang, L.; Tamura, H.; Tanida, K.; Zhou, S. H.

2008-05-01

239

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

240

Belowground fate of (15)N injected into sweetgum trees (Liquidambar styraciflua) at the ORNL FACE Experiment.  

PubMed

Nitrogen (N) cycling can be an important constraint on forest ecosystem response to elevated atmospheric CO(2). Our objective was to trace the movement of (15)N, injected into tree sap, to labile and stable forms of soil organic matter derived partly from the turnover of tree roots under elevated (545 ppm) and ambient (394 ppm) atmospheric CO(2) concentrations at the Oak Ridge National Laboratory (ORNL) FACE (Free-Air Carbon Dioxide Enrichment) Experiment. Twenty-four sweetgum trees, divided equally between CO(2) treatments, were injected with 3.2 g (15)N-ammonium sulfate (99 atom %), and soil samples were collected beneath the trees over a period of 89 weeks. For 16 cm deep soil samples collected beneath the study trees, there was 28% more fine root (less than or equal to 2 mm diameter) biomass under elevated CO(2) (P = 0.001), but no significant treatment effect on the amounts of necromass, coarse root biomass, or on the N concentrations in tree roots and necromass. Nitrogen-15 moved quickly into roots from the stem injection site and the (15)N content of roots, necromass, and labile organic matter (i.e. particulate organic matter, POM) increased over time. At 89 weeks post-injection, approximately 76% of the necromass (15)N originated from fine root turnover. Nitrogen-15 in POM had a relatively long turnover time (47 weeks) compared with (15)N in roots (16 to 22 weeks). Over the 1.7 year period of the study, (15)N moved from roots into slower cycling POM and the disparity in turnover times between root N and N in POM could impose progressive limitations on soil N availability with stand maturation irrespective of atmospheric CO(2), especially if the release of N through the decomposition of POM is essential to sustain forest net primary production. PMID:19705377

Garten, Charles T; Brice, Deanne J

2009-10-01

241

Accurate proteome-wide protein quantification from high-resolution 15N mass spectra  

PubMed Central

In quantitative mass spectrometry-based proteomics, the metabolic incorporation of a single source of 15N-labeled nitrogen has many advantages over using stable isotope-labeled amino acids. However, the lack of a robust computational framework for analyzing the resulting spectra has impeded wide use of this approach. We have addressed this challenge by introducing a new computational methodology for analyzing 15N spectra in which quantification is integrated with identification. Application of this method to an Escherichia coli growth transition reveals significant improvement in quantification accuracy over previous methods.

2011-01-01

242

Comparison of pollinators and natural enemies: a meta-analysis of landscape and local effects on abundance and richness in crops.  

PubMed

To manage agroecosystems for multiple ecosystem services, we need to know whether the management of one service has positive, negative, or no effects on other services. We do not yet have data on the interactions between pollination and pest-control services. However, we do have data on the distributions of pollinators and natural enemies in agroecosystems. Therefore, we compared these two groups of ecosystem service providers, to see if the management of farms and agricultural landscapes might have similar effects on the abundance and richness of both. In a meta-analysis, we compared 46 studies that sampled bees, predatory beetles, parasitic wasps, and spiders in fields, orchards, or vineyards of food crops. These studies used the proximity or proportion of non-crop or natural habitats in the landscapes surrounding these crops (a measure of landscape complexity), or the proximity or diversity of non-crop plants in the margins of these crops (a measure of local complexity), to explain the abundance or richness of these beneficial arthropods. Compositional complexity at both landscape and local scales had positive effects on both pollinators and natural enemies, but different effects on different taxa. Effects on bees and spiders were significantly positive, but effects on parasitoids and predatory beetles (mostly Carabidae and Staphylinidae) were inconclusive. Landscape complexity had significantly stronger effects on bees than it did on predatory beetles and significantly stronger effects in non-woody rather than in woody crops. Effects on richness were significantly stronger than effects on abundance, but possibly only for spiders. This abundance-richness difference might be caused by differences between generalists and specialists, or between arthropods that depend on non-crop habitats (ecotone species and dispersers) and those that do not (cultural species). We call this the 'specialist-generalist' or 'cultural difference' mechanism. If complexity has stronger effects on richness than abundance, it might have stronger effects on the stability than the magnitude of these arthropod-mediated ecosystem services. We conclude that some pollinators and natural enemies seem to have compatible responses to complexity, and it might be possible to manage agroecosystems for the benefit of both. However, too few studies have compared the two, and so we cannot yet conclude that there are no negative interactions between pollinators and natural enemies, and no trade-offs between pollination and pest-control services. Therefore, we suggest a framework for future research to bridge these gaps in our knowledge. PMID:23578337

Shackelford, Gorm; Steward, Peter R; Benton, Tim G; Kunin, William E; Potts, Simon G; Biesmeijer, Jacobus C; Sait, Steven M

2013-04-12

243

Food web structure in two counter-rotating eddies based on ?15N and ?13C isotopic analyses  

NASA Astrophysics Data System (ADS)

We measured the natural inventories of nitrogen and carbon stable isotopes within various ecosystem fractions of two counter-rotating eddies associated with the poleward Leeuwin Current (LC), off Western Australia. Isotopic signatures ( ?15N and ?13C) were used as proxies for trophic transformation of inorganic and organic matter and are the basis for our discussion on food web functions in the two eddies. We present the first measurements of dissolved inorganic nitrogen (DIN) isotopic composition for the eastern Indian Ocean. We show that the large autotrophs (sampled within the >5-?m and >20-?m fractions of particulate organic matter (POM)), including a distinctive diatom population in the warm-core (WC) eddy, are likely to have taken up sources of DIN which were primarily nitrate, while the picoplankton are likely to have assimilated a large fraction of recycled ammonium. We show that phytoplankton in the cold-core (CC) eddy had distinctly more enriched ?15N signatures than in the WC eddy, probably due to the higher vertical fluxes of nitrate into the CC eddy. A clear negative correlation between mixed-layer depth and ?15N in POM across both eddies also supports the role of vertical nitrate fluxes in determining the primary ?15N signature of the autotrophs. Within the WC eddy, there was a significant ?13C-enrichment in comparison to the CC eddy across all size fractions of the mesozooplankton community, which, in combination with a low C:N molar ratio the >200- and >500-?m mesozooplankton size fractions, suggests a healthier mesozooplankton community, with greater lipid storage, in the WC eddy. This is consistent with the greater productivity and biomass of large diatoms in the WC eddy. Larval fish from the WC eddy also had an enriched ?13C signature compared to those from the CC eddy. The WC eddy had higher production rates than the CC eddy, and harboured a physiologically healthier population of zooplankton. Paradoxically, this seemed to occur despite higher overall nitrate fluxes into the CC eddy, and may have to do with the particularly active diatom population within the WC eddy operating within the unusually deep mixed layer.

Waite, A. M.; Muhling, B. A.; Holl, C. M.; Beckley, L. E.; Montoya, J. P.; Strzelecki, J.; Thompson, P. A.; Pesant, S.

2007-04-01

244

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

2012-07-31

245

The effect of dietary nitrogen content on trophic level 15N enrichment  

Microsoft Academic Search

Given the great potential value of stable isotopes in a variety of scientific investigations, surprisingly little attention has been paid to the underlying physiological and biochemical mechanisms that account for trophic in- creases in d 15 N values. This has lead to a general call for controlled studies investigating the relationship between organismal diet and corresponding isotopic composition. We conducted

Thomas S. Adams; Robert W. Sterner

2000-01-01

246

Proton NMR of (15)N-choline metabolites enhanced by dynamic nuclear polarization.  

PubMed

Chemical shifts of protons can report on metabolic transformations such as the conversion of choline to phosphocholine. To follow such processes in vivo, magnetization can be enhanced by dynamic nuclear polarization (DNP). We have hyperpolarized in this manner nitrogen-15 spins in (15)N-labeled choline up to 3.3% by irradiating the 94 GHz electron spin resonance of admixed TEMPO nitroxide radicals in a magnetic field of 3.35 T during ca. 3 h at 1.2 K. The sample was subsequently transferred to a high-resolution magnet, and the enhanced polarization was converted from (15)N to methyl- and methylene protons, using the small (2,3)J((1)H,(15)N) couplings in choline. The room-temperature lifetime of nitrogen polarization in choline, T(1)((15)N) approximately 200 s, could be considerably increased by partial deuteration of the molecule. This procedure enables studies of choline metabolites in vitro and in vivo using DNP-enhanced proton NMR. PMID:19848401

Sarkar, Riddhiman; Comment, Arnaud; Vasos, Paul R; Jannin, Sami; Gruetter, Rolf; Bodenhausen, Geoffrey; Hall, Hélène; Kirik, Deniz; Denisov, Vladimir P

2009-11-11

247

{sup 15}N(p,{alpha}{sub 0}){sup 12}C S factor  

SciTech Connect

Experimental values of the astrophysical S factor for the {sup 15}N(p,{alpha}{sub 0}){sup 12}C reaction are available both from direct measurements and from the Trojan horse method. We here use R-matrix formulas to fit these values and to extrapolate to zero energy to obtain values of S(0)

Barker, F. C. [Department of Theoretical Physics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, Australian Capital Territory 0200 (Australia)

2008-10-15

248

Exploration of the nitrogen transport system of a nodulated legume using 15 N  

Microsoft Academic Search

Feeding experiments using 15N2 or 15NO3 are described investigating the transport of nitrogen in the field pea (Pisum arvense L.). Nitrogen assimilated by root or nodules moves preferentially upwards to the shoot through the xylem. Parts of the root below or distal to a region of assimilation can benefit from this nitrogen but do so to a much greater extent

C. G. O. Oghoghorie; J. S. Pate

1972-01-01

249

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

2009-03-14

250

Measurement of 15N relaxation rates in perdeuterated proteins by TROSY-based methods  

PubMed Central

While extracting dynamics parameters from backbone 15N relaxation measurements in proteins has become routine over the past two decades, it is increasingly recognized that accurate quantitative analysis can remain limited by the potential presence of systematic errors associated with the measurement of 15N R1 and R2 or R1? relaxation rates as well as heteronuclear 15N-{1H} NOE values. We show that systematic errors in such measurements can be far larger than the statistical error derived from either the observed signal-to-noise ratio, or from the reproducibility of the measurement. Unless special precautions are taken, the problem of systematic errors is shown to be particularly acute in perdeuterated systems, and even more so when TROSY instead of HSQC elements are used to read out the 15N magnetization through the NMR-sensitive 1H nucleus. A discussion of the most common sources of systematic errors is presented, as well as TROSY-based pulse schemes that appear free of systematic errors to the level of < 1%. Application to the small perdeuterated protein GB3, which yields exceptionally high S/N and therefore is an ideal test molecule for detection of systematic errors, yields relaxation rates that show considerably less residue by residue variation than previous measurements. Measured R2?/R1? ratios fit an axially symmetric diffusion tensor with a Pearson’s correlation coefficient of 0.97, comparable to fits obtained for backbone amide RDCs to the Saupe matrix.

Lakomek, Nils-Alexander; Ying, Jinfa; Bax, Ad

2012-01-01

251

Speeding up direct 15N detection: hCaN 2D NMR experiment  

PubMed Central

Experiments detecting low gyromagnetic nuclei have recently been proposed to utilize the relatively slow relaxation properties of these nuclei in comparison to 1H. Here we present a new type of 15N direct—detection experiment. Like the previously proposed CaN experiment (Takeuchi et al. 2010), the hCaN experiment described here sequentially connects amide 15N resonances, but utilizes the initial high polarization and the faster recovery of the 1H nucleus to shorten the recycling delay. This allows recording 2D 15N- detected NMR experiments on proteins within a few hours, while still obtaining superior resolution for 13C and 15N, establishing sequential assignments through prolines, and at conditions where amide protons exchange rapidly. The experiments are demonstrated on various biomolecules, including the small globular protein GB1, the 22kDa HEAT2 domain of eIF4G, and an unstructured polypeptide fragment of NFAT1, which contains many SerPro sequence repeats.

Gal, Maayan; Edmonds, Katherine A.; Milbradt, Alexander G.; Takeuchi, Koh; Wagner, Gerhard

2012-01-01

252

Mechanical properties of steel Kh15N5D2T after heat treatment  

Microsoft Academic Search

1.Annealing of hot-rolled steel Kh15N5D2T at 580–700°C leads to the a?? transformation, accompanied by higher plasticity.2.After normalization and low-temperature aging the steel is strengthened as the result of the martensitic transformation and the precipitation of excess intermetallic phase.

F. D. Miroshnichenko; V. G. Kanibolotskii; V. L. Snezhnoi; M. I. Kanibolotskaya

1969-01-01

253

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...

254

Backbone dynamics of free barnase and its complex with barstar determined by 15N NMR relaxation study  

Microsoft Academic Search

Backbone dynamics of uniformly 15N-labeled free barnase and its complex with unlabelled barstar have been studied at 40?°C, pH 6.6, using 15N relaxation data obtained from proton-detected 2D {1H}-15N NMR spectroscopy. 15N spin-lattice relaxation rate constants (R1), spin-spin relaxation rate constants (R2), and steady-state heteronuclear {1H}-15N NOEs have been measured at a magnetic field strength of 14.1 Tesla for 91 residues

Sarata C. Sahua; Abani K. Bhuyan; Jayant B. Udgaonkar; R. V. Hosur

2000-01-01

255

In vivo uniform (15)N-isotope labelling of plants: using the greenhouse for structural proteomics.  

PubMed

Isotope labelling of proteins is important for progress in the field of structural proteomics. It enables the utilisation of the power of nuclear magnetic resonance spectroscopy (NMR) for the characterisation of the three-dimensional structures and corresponding dynamical features of proteins. The usual approach to obtain isotopically labelled protein molecules is by expressing the corresponding gene in bacterial or yeast host organisms, which grow on isotope-enriched media. This method has several drawbacks. Here, we demonstrate that it is possible to fully label a plant with (15)N-isotopes. The advantage of in vivo labelling of higher organisms is that all constituting proteins are labelled and become available as functional, post-translationally modified, correctly folded proteins. A hydroponics set-up was used to create the first example of a uniformly (15)N-labelled (> 98%) plant species, the potato plant (Solanum tuberosum L., cv. Elkana). Two plants were grown at low costs using potassium-[(15)N]-nitrate as the sole nitrogen source. At harvest time, a total of 3.6 kg of potato tubers and 1.6 kg of foliage, stolons and roots were collected, all of which were fully (15)N-labelled. Gram quantities of soluble (15)N-labelled proteins (composed mainly of the glycoprotein patatin and Kunitz-type protease inhibitors) were isolated from the tubers. NMR results on the complete proteome of potato sap and on an isolated protease inhibitor illustrate the success of the labelling procedure. The presented method of isotope labelling is easily modified to label other plants. Its envisioned impact in the field of structural proteomics of plants is discussed. PMID:14730684

Ippel, Johannes H; Pouvreau, Laurice; Kroef, Toos; Gruppen, Harry; Versteeg, Geurt; van den Putten, Peter; Struik, Paul C; van Mierlo, Carlo P M

2004-01-01

256

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

257

?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

2012-10-26

258

Abiotic and biotic factors associated with the presence of Anopheles arabiensis immatures and their abundance in naturally occurring and manmade aquatic habitats.  

PubMed

ABSTRACT: 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

Gouagna, Louis Clément; Rakotondranary, Manpionona; Boyer, Sebastien; Lempérière, Guy; Dehecq, Jean-Sébastien; Fontenille, Didier

2012-05-19

259

1H, 13C and 15N resonance assignments of URNdesign, a computationally redesigned RRM protein  

SciTech Connect

Protein design represents one of the great challenges of computational structural biology. The ability to successfully design new proteins would allow us to generate new reagents and enzymes, while at the same time providing us with an understanding of the principles of protein stability. Here we report 1H, 15N and 13C resonance assignments of a redesigned U1A protein, URNdesign. U1A has been studied extensively by our group and hence was chosen as a design target. For the assignments we sued 2D and 3D heteronuclearNMR experiments with uniformly 13C, 15N-labeled URNdesign. The assignments for the backbone NH, CO,Ca and Cb nuclei are 94%complete. Sidechain 1Hand13C, aromatic andQ/NNH2 resonances are essentially complete with guanidinium and K NH3 residues unassigned. BMRB deposit with accession number 6493

Dobson, Neil; Dantas, Gautam; Varani, Gabriele

2005-10-01

260

Study of the 15N(p,?)16O at LUNA  

NASA Astrophysics Data System (ADS)

The 15N(p,?)16O reaction links the first CNO cycle with the second one allowing the production of the oxygen and fluorine isotopes during the hydrogen burning in novae and AGB and RGB stars. In recent years, this reaction has been studied deeply by LUNA (Laboratory for Underground Nuclear Astrophysics). As a matter of fact three different experiments have been run to measure the 15N(p,?)16O S factor down to the energy of the novae and ABG hydrogen burning reaching for the first time the 72.8 keV in the center of mass. In this contribution the results of the first two experiments are summarized and the results of the recently performed experiment, which is dedicated to the study at very low energies, are presented.

Caciolli, Antonio; LUNA Collaboration

2012-02-01

261

Interference effects in proton scattering on {sup 15}N nuclei at intermediate energies  

SciTech Connect

The differential cross section for proton scattering on {sup 15}N nuclei is calculated within Glauber diffraction theory at energies of 0.2, 0.6, and 1.0 GeV. Use is made of the shell-model wave function for the {sup 15}N nucleus. The contribution of single and double collisions to the Glauber operator {Omega} is taken into account. The sensitivity of the differential cross sections to the contributions of scattering on nucleons from different shells, to the parameters of the elementary pN amplitude, and to the energy of projectile protons is investigated. It is shown that the interference between amplitudes corresponding to different collision multiplicities, as well as between the amplitudes for scattering on nucleons from different shells, determines special features of the cross section.

Ibraeva, E. T., E-mail: ibr@inp.k [National Nuclear Center of the Republic of Kazakhstan, Institute of Nuclear Physics (Kazakhstan); Zhusupov, M.A.; Imambekov, O. [Al-Farabi Kazakh National University (Kazakhstan); Krassovitskiy, P. M. [National Nuclear Center of the Republic of Kazakhstan, Institute of Nuclear Physics (Kazakhstan)

2010-08-15

262

Studies of lake environments using stable isotope ratios of nitrogen (?15N) and carbon (?13C)  

NASA Astrophysics Data System (ADS)

Increasing numbers of studies have recently used stable isotopes of nitrogen (?15N) and carbon (?13C) to clarify the source of nutrients in lake water and sediments, the structure and energy flow of food webs, the bioaccumulation and biomagnification of hazardous chemicals in aquatic animals, and temporal trends in lake environments. In lake research in particular, the analysis of ?15N and ?13C is a powerful tool in analyzing the structure of the food web and energy flows, as well as the bioaccumulation and biomagnification of toxic chemicals in aquatic animals. Furthermore, the integration of data on food webs, stable isotope ratios, and environmental geochemistry can be useful in evaluating the risks of exposure to environmental contaminants. It is hoped that further research on lake environments using stable isotopic methods can be performed with the aim of conserving water quality and aquatic ecosystems.

Iizumi, Yoshiko

263

Eine einfache apparative Anordnung zur emissionsspektroskopischen 15 N-Bestimmung im Mikromaßstab  

Microsoft Academic Search

A simple device for emission-spectroscopic 15N determination with photoelectric recording is described. The nitrogen is stimulated for light emission in glass tubes between capacitor plates of an oscillator circuit. The frequency is regulated to 13.9 MHz by means of a high frequency generator (DX-60, Heathkit) with an effective power of 15–20 W. The dispersion and detection of the emitted light

Nikolaus Seiler; Gottfried Werner

1968-01-01

264

Competition between siratro and kleingrass for 15 N labelled mineralized nitrogen  

Microsoft Academic Search

Summary  Isotope dilution provides a method for measuring plant competition for mineral N and transfer of biologically fixed N from\\u000a a legume to a grass. A plant growth medium was enriched with15N, and used to grow Siratro (Macropitilium atropurpureum D.C. Urb.) and Kleingrass 75 (Panicum coloratum L.) in 20 liter pots for 98 days in a glasshouse. The plants were grown

Mohammed Ismaili; R. W. Weaver

1986-01-01

265

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

266

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

267

Determination of the ?15N of total nitrogen in solids; RSIL lab code 2893  

USGS Publications Warehouse

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2893 is to determine the ?(15N/14N), abbreviated as ?15N , of total nitrogen in solid samples. A Carlo Erba NC 2500 elemental analyzer (EA) is used to convert total nitrogen in a solid sample into N2 gas. The EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines relative difference in the isotope-amount ratios of stable nitrogen isotopes (15N/14N)of the product N2 gas. The combustion is quantitative; no isotopic fractionation is involved. Samples are placed in a tin capsule and loaded into the Costech Zero Blank Autosampler of the EA. Under computer control, samples are dropped into a heated reaction tube that contains an oxidant, where the combustion takes place in a helium atmosphere containing an excess of oxygen gas. Combustion products are transported by a helium carrier through a reduction tube to remove excess oxygen and convert all nitrous oxides into N2 and through a drying tube to remove water. The gas-phase products, mainly CO2 and N2, are separated by a gas chromatograph. The gas is then introduced into the isotope-ratio mass spectrometer (IRMS) through a Finnigan MAT (now Thermo Scientific) ConFlo II interface, which also is used to inject N2 reference gas and helium for sample dilution. The IRMS is a Thermo Scientific Delta V Plus CF-IRMS. It has a universal triple collector, two wide cups with a narrow cup in the middle, capable of measuring mass/charge (m/z) 28, 29, 30, simultaneously. The ion beams from N2 are as follows: m/z 28 = N2 = 14N14N; m/z 29 = N2 = 14N15N primarily; m/z 30 = NO = 14N16O primarily, which is a sign of contamination or incomplete reduction.

Revesz, Kinga; Qi, Haiping; Coplen, Tyler B.

2006-01-01

268

Grain refining in stainless steel 08Kh15N5D2T  

Microsoft Academic Search

1.Steel 08Kh15N5D2T is sensitive to overheating at the highest strength (aged at 450°), which is manifest in a substantial reduction of the impact strength at +20 and -70° when the quenching temperature is raised from 950 to 1200°. The strength and ductile characteristics remain unchanged.2.Complete structural recrystallization of austenite occurs during repeated heating of the over-heated steel to 950°, i.e.,

S. I. Birman; Yu. F. Orzhekhovskii

1973-01-01

269

Fate of 15N-nitrate in unplanted, planted and harvested riparian wetland soil microcosms  

Microsoft Academic Search

Riparian wetlands are important for the protection of river water quality in agricultural landscapes by intercepting and removing nutrients, such as nitrate (NO3?), in runoff. However, limited information is available on the relative importance of biological NO3? removal processes in these ecosystems. In this study the fate of 15N-NO3? was investigated for 32 days in three types of wetland soil

F. E Matheson; M. L Nguyen; A. B Cooper; T. P Burt; D. C Bull

2002-01-01

270

Body nitrosation potential measured by a novel 15N breath test.  

PubMed

Oxygenated nitrogen species, for example, the protonated form of nitrous acid (H2ONO+), dinitrogentrioxide (N2O3), dinitrogentetroxide (N2O4), or peroxynitrite (ONOO-), can react with amines to form molecular nitrogen. These reactions can occur spontaneously with primary aliphatic amines or via cytochrome P450 catalysed reactions with secondary amines. In principle measurements of the excretion of the molecular nitrogen generated by these reactions could be used as an index of the levels of oxygenated nitrogen compounds acting as nitrosating agents. To test this idea, [15N2]urea (3 mmol) was administered orally to five patients infected with Helicobacter pylori (as diagnosed by the [13C]urea breath test) and to four healthy volunteers. All participants ingested 3-mmol sodium nitrate as a precursor for NA 5 min before the ingestion of the nitrogen tracer. During the test the participants breathed 100% oxygen to increase the sensitivity of detection of endogenous molecular nitrogen. After the administration of [15N2]urea, the patients with H. pylori showed significantly increased 15N enrichments of exhaled N2, expressed as delta value (per 1000), compared with healthy volunteers (patients: 3.5 +/- 0.9 vs. volunteers: 1.3 +/- 0.4; p < .05). We speculate that the endogenous production of molecular nitrogen is a protective process controlling the body NO and nitrite levels. The 15N breath technique allows the noninvasive estimation of the body nitrosation and could indicate the health risk, possibly the oxidative stress status, caused by highly reactive oxygenated nitrogen species and carbenium ion intermediates. PMID:10641724

Junghans, P; Fischer, U; Kuklinski, B

1999-12-01

271

Use of simulations of 15N profiling in studying hydrogen segregation at interfaces  

Microsoft Academic Search

We describe the use of simulations of experimental data in studying the behavior of hydrogen in thin layers using inverse (rho, lambda) reactions with 15N ions. Hydrogen is trapped in both disordered and epitaxial interfaces with crystalline silicon, in metal\\/SiO2 interfaces, and at other sites within thin deposited layers. A simulation program has been developed which calculates the expected gamma

A. D. Marwick; Joyce C. Liu; T. H. Zabel; J. P. Doyle

1992-01-01

272

Foliar retention of 15N-nitrate and 15N-ammonium by red maple (Acer rubrum) and white oak (Quercus alba) leaves from simulated rain  

SciTech Connect

Studies of nitrogen cycling in forests indicate that trees assimilate atmospheric nitrate and ammonium and that differences between atmospheric deposition to the forest canopy and deposition measured in forest throughfall can be attributed to the removal of these ions from rain by tree leaves. Red maple and white oak leaves were exposed to artificial rain solutions (pH 4.1) containing {sup 15}N-labeled nitrate (3.5 {micro}g N/ml) or ammonium (2.2 {micro}g N/ml). At two time intervals after exposure (2 hr and 2 days) an exposed leaf and a control (non-exposed) leaf were removed from replicate seedlings. Based on results from {sup 15}N analysis, most of the nitrate applied to tree leaves was removed by washing with water; the mean per cent removal ({+-} standard error, N = 4) was 87 {+-} 1 and 73 {+-} 4% of the {sup 15}NO-N Applied to red maple and white oak leaves, respectively. Relative retention of {sup 15}NH{sub 4}-N by the leaves was greater than that observed for {sup 15}NO{sub 3}-N. In red maple and white oak leaves, 58 {+-} 9 and 84 {+-} 7% (mean {+-} standard error, N = 4), respectively, of the applied ammonium was not removed by washing treatments. Our results show that the foliar uptake of {sup 15}NH{sub 4}{sup +} from simulated rain by deciduous tree leaves is greater than that for {sup 15}NO{sub 3}{sup -}. Greater retention of NH{sub 4}{sup +} than NO{sub 3}{sup -} ions by red maple and white oak leaves from simulated rainfall is consistent with field observations showing a preferential retention of ammonium from rainfall by forest canopies. As nitrogen chemistry and the relative importance of nitrogen compounds in the atmosphere change in response to proposed emission reductions (and possibly climate change), an improved understanding of the fate of airborne nitrogen compounds in forest biogeochemical cycles will be necessary.

Garten Jr, Charles T [ORNL; Hanson, Paul J [ORNL

1990-07-01

273

A Survey of \\delta18O and \\delta15N Ratios in Ground Water from an Agricultural Community in the San Joaquin Valley, California  

NASA Astrophysics Data System (ADS)

We studied ground water samples from domestic and monitoring wells in an agricultural community in the eastern side of the San Joaquin Valley, California. The study area is rich in alluvial soils creating an extremely fertile farmland. Livestock farms and agricultural fields are abundant in the area. Fifty-four ground water samples were analyzed for \\delta18O and \\delta15N in dissolved nitrate, in addition to nutrients and major minerals. Nitrate concentration levels in groundwater are elevated and affected by agricultural and other activities. Possible sources of nutrients include: a municipal waste-water treatment facility, a raisin processing plant, a meat processing plant, a turkey farm, diary operations, and agricultural fields. However, except for the turkey farm and a diary, we found no statistical significant contribution of nitrate from the other facilities as compared to the rest of the area. The \\delta18O versus \\delta15N ratios plot of dissolved ground water nitrate shows most samples clustered around an area consistent with soil organic nitrogen. In addition, the rest of the samples show a trend that is indicative of denitrification process. Generally, high \\delta15N values are associated with low nitrate concentrations. The isotopic signal of denitrification is particularly pronounced in samples in the vicinity of the waste water treatment facility, where the highest values of \\delta15N and the lowest nitrate concentrations are observed. However, these samples also have elevated chloride concentrations indicating a waste-water source. These data suggest that the denitrification in the subsurface may have been enhanced by bacteria species introduced by the effluence of the plant. [This study was performed with the collaboration of Steven R Silva of USGS, Menlo Park, and Iris Yamagata and Holly Jo Ferrin of California Department of Water Resources.

Glowacki, S. D.; Suen, C. J.

2004-12-01

274

Backbone dynamics of the 269-residue protease Savinase determined from 15N-NMR relaxation measurements.  

PubMed

Backbone dynamics of Savinase, a subtilisin of 269 residues secreted by Bacillus lentus, have been studied using 15N relaxation measurements derived from proton-detected dimensional 1H-15N-NMR spectroscopy. 15N spin-lattice rate constants (R1), spin-spin relaxation-rate constants(R2), and 1H-15N nuclear Overhauser effects (NOE) were determined for 84% of the backbone amide 15N nuclei. The model-free formalism [Lipari, G. & Szabo, A. (1982) J. Am. Chem. Soc. 104, 4546-4559] was used to derive values for a generalized order parameter, S2, interpretable as a measure of the amplitude of motion on the picosecond-nanosecond timescale, for each N-H bond vector. Additional terms used to fit the data include an effective correlation time for internal motions (taue) and an exchange term (Rex) to account for exchange contributions to R2. The overall rotational correlation time (taum) is 9.59 +/- 0.02 ns; the average order parameter (S2) is 0.90 +/- 0.07, indicative of a rigid structure consistent with Savinase's high degree of secondary structure and compact tertiary fold. Residues S125-S128, located in the substrate-binding region, represent the longest stretch of protein which exhibits disorder on the picosecond-nanosecond timescale. These residues also exhibit significant exchange terms, possibly indicative of motion on the microsecond-millisecond timescale, which could also be influenced by the proximity of the phenyl ring of the substituted aryl boronic acid inhibitor used in this study. S103 and G219 in the substrate-binding region, represent the longest stretch of protein which exhibits disorder on the picosecond-nanosecond timescale. These residues also exhibit significant exchange terms, possibly indicative of motion on the microsecond-millisecond timescale, which could also be influenced by the proximity of the phenyl ring of the substituted aryl boronic acid inhibitor used in this study. S103 and G219 in the substrate-binding region also show flexibility on the picosecond-nanosecond timescale. There is also significant motion in the turn, G258-T260, of a small solvent-exposed loop region which may make the protein vulnerable autolysis at that point. Some residues in both calcium-binding sites and nearby also show mobility. PMID:8654411

Remerowski, M L; Pepermans, H A; Hilbers, C W; Van De Ven, F J

1996-02-01

275

Determination of 15N isotopic enrichment and concentrations of allantoin and uric acid in urine by gas chromatography/mass spectrometry.  

PubMed

A method for the determination of 15N enrichment and concentration of allantoin and uric acid simultaneously in urine using gas chromatography/mass spectrometry (GC/MS) is described. The urine samples contained [1,3-15N2] uric acid and its oxidation product allantoin. The uric acid and allantoin were isolated using an AG1-X8 (Cl-form) anion-exchange column and heated with a mixture containing 1:1 dimethylformamide and N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA). The tert-butyldimethylsilyl (TBDMS) derivatives of allantoin and uric acid formed were injected into a gas chromatograph interfaced with a mass spectrometer operated under electron impact ionization conditions. Isotope ratio measurements were made from the abundance of the M-57 ions at m/z 398, 399 and 400 for allantoin and at m/z 567 and 569 for uric acid. 15N2 allantoin (99 at.%) was produced from [1,3-15N2] uric acid by treatment with uricase and used as a standard. Quantitation of allantoin and uric acid was based on isotopic dilution by spiking the urine sample with known quantities of 99 at.% [15N] uric acid and allantoin internal standards. The observed isotope ratio measurements from the prepared standards matched the theoretical values. Coefficients of variation in measurements of isotope ratio and concentration were 0.2 and 0.5%, respectively. The method was applied in a study to measure the urinary recovery of [1,3-15N2] uric acid continuously infused for 8-10 h into the blood of four sheep each on two occasions. Within 24 h, 65.9 +/- 9.1% of the tracer was excreted in the urine unchanged. Little was converted into allantoin (approximately 7% of the dose). The total recovery (5 days) of the infused tracer averaged 69.5 +/- 7.6% as uric acid and 76.8 +/- 9.3% as the sum of uric acid and allantoin. Uricase activities in plasma, liver and kidney of sheep were also measured using [1,3-15N2] uric acid as a substrate. Uricase activity was estimated to be 0.6 mU g-1 wet tissue in the liver and there appeared to be none in plasma and kidney. The low uricase activities in sheep tissues appeared to explain the limited conversion of the intravenously administered [15N] uric acid to allantoin but did not explain the large quantities of allantoin excreted in urine (8.96 +/- 0.86 and 1.36 +/- 0.25 mmol d-1 for allantoin and uric acid, respectively). The GC/MS method for the determination of 15N enrichment and concentration of allantoin and uric acid in urine is accurate and precise and provides a useful tool for studies on uric acid and allantoin metabolism. PMID:9487687

Chen, X B; Calder, A G; Prasitkusol, P; Kyle, D J; Jayasuriya, M C

1998-02-01

276

Indirect Nuclear (15)N-(15)N Scalar Coupling through a Hydrogen Bond: Dependence on Structural Parameters Studied by Quantum Chemistry Tools.  

PubMed

NMR spin-spin couplings through a hydrogen bond in the free-base and protonated forms of the complete series of [(15)N2]-N-methylated 1,8-diaminonaphthalenes have been analyzed using quantum chemistry tools. The dominating role of the overlap of the coupling pathway orbitals has been demonstrated. The correlation of the sum of the (13)C NMR shifts of the naphthalene ring C(1,8) carbons directly attached to the interacting nitrogens with the J(N-N) values and the degree of methylation found earlier by G. C. Lloyd-Jones et al. [ Chem.-Eur. J. 2003 , 9 , 4523 ] have been reexamined. It has been found that the correlations of J(N-N) and [??C1,8] with the degree of methylation have different reasons. While the former is mostly connected with the structural changes due to the solvent effect, the latter is attributed to the changes in the paramagnetic contributions from the C-N and C-C bonds caused by the replacement of a hydrogen by a methyl group. PMID:23987730

K?ístková, Anežka; Asher, James R; Malkin, Vladimir G; Malkina, Olga L

2013-09-16

277

Comparing trophic position of freshwater fish calculated using stable nitrogen isotope ratios (? 15 N) and literature dietary data  

Microsoft Academic Search

Stable nitrogen isotope ratios (?15N) are commonly used to represent the trophic structure of aquatic systems, yet the ability of ?15N to indicate the trophic position of aquatic consumers remains untested using traditional dietary methods. Interpreting the ?15N of aquatic consumers relative to large, long-lived primary consumers such as unionid mussels provides a continuous measure of an organismís trophic position

M. J. Vander Zanden; G. Cabana; J. B. Rasmussen

1997-01-01

278

Field application of the 15 N isotope dilution technique for the reliable quantification of plant-associated biological nitrogen fixation  

Microsoft Academic Search

To apply the isotope dilution (ID) technique, it is necessary to grow the “N2-fixing” crop in a soil where the mineral N is labelled with15N. Normally the “N2-fixing” crop and a suitable non-N2-fixing control crop are grown in the same labelled soil and the15N enrichment of the control crop is assumed to be equal to the15N enrichment of the nitrogen

Robert M. Boddey; Octávio C. Oliveira; Bruno J. R. Alves; Segundo Urquiaga

1995-01-01

279

Identification of Biodegradation Pathways in a Multi-Process Phytoremediation System (MPPS) Using Natural Abundance 14C Analysis of PLFA  

Microsoft Academic Search

Optimizing remediation of petroleum-contaminated soils requires thorough understanding of the mechanisms and pathways involved in a proposed remediation system. In many engineered and natural attenuation systems, multiple degradation pathways may contribute to observed contaminant mass losses. In this study, biodegradation in the soil microbial community was identified as a major pathway for petroleum hydrocarbon removal in a Multi-Process Phytoremediation System

B. R. Cowie; B. M. Greenberg; G. F. Slater

2008-01-01

280

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

281

Natural hybrids in Atlantic eels ( Anguilla anguilla , A. rostrata ): evidence for successful reproduction and fluctuating abundance in space and time  

Microsoft Academic Search

The outcome of natural hybridization is highly variable and depends on the nonexclu- sive effects of both pre- and post-mating reproductive barriers. The objective of this study was to address three specific questions regarding the dynamics of hybridization between the American and European eels ( Anguilla rostrata and Anguilla anguilla ). Using 373 AFLP loci, 1127 eels were genotyped, representing

VICKY ALBERT; BJARNI JÓNSSON; LOUIS BERNATCHEZ

282

Solution 1H, 15N NMR spectroscopic characterization of substrate-bound, cyanide-inhibited human heme oxygenase: water occupation of the distal cavity.  

PubMed

A solution NMR spectroscopic study of the cyanide-inhibited, substrate-bound complex of uniformly (15)N-labeled human heme oxygenase, hHO, has led to characterization of the active site with respect to the nature and identity of strong hydrogen bonds and the occupation of ordered water molecules within both the hydrogen bonding network and an aromatic cluster on the distal side. [(1)H-(15)N]-HSQC spectra confirm the functionalities of several key donors in particularly robust H-bonds, and [(1)H-(15)N]HSQC-NOESY spectra lead to the identification of three additional robust H-bonds, as well as the detection of two more relatively strong H-bonds whose identities could not be established. The 3D NMR experiments provided only a modest, but important, extension of assignments because of the loss of key TOCSY cross-peaks due to the line broadening from a dynamic heterogeneity in the active site. Steady-state NOEs upon saturating the water signal locate nine ordered water molecules in the immediate vicinity of the H-bond donors, six of which are readily identified in the crystal structure. The additional three are positioned in available spaces to account for the observed NOEs. (15)N-filtered steady-state NOEs upon saturating the water resonances and (15)N-filtered NOESY spectra demonstrate significant negative NOEs between water molecules and the protons of five aromatic rings. Many of the NOEs can be rationalized by water molecules located in the crystal structure, but strong water NOEs, particularly to the rings of Phe47 and Trp96, demand the presence of at least an additional two immobilized water molecules near these rings. The H-bond network appears to function to order water molecules to provide stabilization for the hydroperoxy intermediate and to serve as a conduit to the active site for the nine protons required per HO turnover. PMID:14583035

Li, Yiming; Syvitski, Ray T; Auclair, Karine; Ortiz de Montellano, Paul; La Mar, Gerd N

2003-11-01

283

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

284

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.

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

2012-01-01

285

A holistic approach to understanding the N isotopic composition (d15N) of deep-sea sediments: diatom-bound, foraminifera-bound, whole sediment and modern nitrate d15N from the equatorial Pacific  

NASA Astrophysics Data System (ADS)

The nitrogen (N) isotopic composition (d15N) of sediment is well established as a proxy of nitrate consumption and the d15N of nitrate in the surface ocean, but it is commonly assumed that post-depositional fractionation during organic matter degradation provides an additional unconstrained variable in sediments from the deep-sea. This mistrust of deep-sea sediments essentially renders most of the global ocean off-limits to the application of this powerful proxy of nutrient dynamics. Here we address this issue with new measurements of diatom-bound, foraminifera-bound, and whole sediment d15N from deep-sea sediments of the equatorial Pacific—a region where we have also investigated the processes influencing modern nitrate characteristics. With the results of these new records and previously published measurements relevant to the composition of sedimentary nitrogen, we are confident that whole sediment d15N from the deep-sea is not altered after deposition on the sea floor and that it accurately records surface ocean conditions. With these new constraints on whole sediment d15N, we discuss the exciting implications for alternative sediment d15N measurements (such as diatom- and foraminifera-bound d15N) and present evidence for a long-term increase in equatorial Pacific d15N of nitrate.

Rafter, P. A.; Charles, C. D.; Sigman, D. M.; Haug, G. H.

2010-12-01

286

Supportive breeding boosts natural population abundance with minimal negative impacts on fitness of a wild population of Chinook salmon  

PubMed Central

While supportive breeding programmes strive to minimize negative genetic impacts to populations, case studies have found evidence for reduced fitness of artificially produced individuals when they reproduce in the wild. Pedigrees of two complete generations were tracked with molecular markers to investigate differences in reproductive success (RS) of wild and hatchery-reared Chinook salmon spawning in the natural environment to address questions regarding the demographic and genetic impacts of supplementation to a natural population. Results show a demographic boost to the population from supplementation. On average, fish taken into the hatchery produced 4.7 times more adult offspring, and 1.3 times more adult grand-offspring than naturally reproducing fish. Of the wild and hatchery fish that successfully reproduced, we found no significant differences in RS between any comparisons, but hatchery-reared males typically had lower RS values than wild males. Mean relative reproductive success (RRS) for hatchery F1 females and males was 1.11 (P = 0.84) and 0.89 (P = 0.56), respectively. RRS of hatchery-reared fish (H) that mated in the wild with either hatchery or wild-origin (W) fish was generally equivalent to W × W matings. Mean RRS of H × W and H × H matings was 1.07 (P = 0.92) and 0.94 (P = 0.95), respectively. We conclude that fish chosen for hatchery rearing did not have a detectable negative impact on the fitness of wild fish by mating with them for a single generation. Results suggest that supplementation following similar management practices (e.g. 100% local, wild-origin brood stock) can successfully boost population size with minimal impacts on the fitness of salmon in the wild.

Hess, Maureen A; Rabe, Craig D; Vogel, Jason L; Stephenson, Jeff J; Nelson, Doug D; Narum, Shawn R

2012-01-01

287

Supportive breeding boosts natural population abundance with minimal negative impacts on fitness of a wild population of Chinook salmon.  

PubMed

While supportive breeding programmes strive to minimize negative genetic impacts to populations, case studies have found evidence for reduced fitness of artificially produced individuals when they reproduce in the wild. Pedigrees of two complete generations were tracked with molecular markers to investigate differences in reproductive success (RS) of wild and hatchery-reared Chinook salmon spawning in the natural environment to address questions regarding the demographic and genetic impacts of supplementation to a natural population. Results show a demographic boost to the population from supplementation. On average, fish taken into the hatchery produced 4.7 times more adult offspring, and 1.3 times more adult grand-offspring than naturally reproducing fish. Of the wild and hatchery fish that successfully reproduced, we found no significant differences in RS between any comparisons, but hatchery-reared males typically had lower RS values than wild males. Mean relative reproductive success (RRS) for hatchery F(1) females and males was 1.11 (P = 0.84) and 0.89 (P = 0.56), respectively. RRS of hatchery-reared fish (H) that mated in the wild with either hatchery or wild-origin (W) fish was generally equivalent to W × W matings. Mean RRS of H × W and H × H matings was 1.07 (P = 0.92) and 0.94 (P = 0.95), respectively. We conclude that fish chosen for hatchery rearing did not have a detectable negative impact on the fitness of wild fish by mating with them for a single generation. Results suggest that supplementation following similar management practices (e.g. 100% local, wild-origin brood stock) can successfully boost population size with minimal impacts on the fitness of salmon in the wild. PMID:23025818

Hess, Maureen A; Rabe, Craig D; Vogel, Jason L; Stephenson, Jeff J; Nelson, Doug D; Narum, Shawn R

2012-10-01

288

Natural abundance of Sb and Sc in pristine groundwaters, Springwater Township, Ontario, Canada, and implications for tracing contamination from landfill leachates.  

PubMed

Using ICP-SMS and the clean lab methods and procedures developed for determining trace element concentrations in polar snow and ice, a lower limit of detection (LOD) of 30 pg l(-1) for Sb and 5 pg l(-1) for Sc was achieved, allowing the natural abundances of Sb and Sc to be measured in pristine groundwaters. Water samples were collected from natural flows and wells between Elmvale and Wyevale in Springwater Township, Ontario, Canada. The water in this region is derived from chemical reactions between meteoric fluids and the Quaternary sediments which cover the bedrock (dolomitic limestone) to depths of more than 100 m. The chemical composition of these waters (pH 8) is primarily a reflection of reactions between the percolating fluids with calcite and dolomite. The maximum concentration of Sb was 5.0 ng l(-1), and the average of all samples collected was 2.2 +/- 1.2 ng l(-1) (n = 34). The average concentration of Sc was 8.6 +/- 4.7 ng l(-1) (n = 28). The paucity of published Sb concentration data available for comparison is probably because most of the analytical methods commonly used to date, including GFAAS, HG-AAS, HG-AFS, INAA, and ICP-QMS, have lower limits of detection which are inadequate for reliably determining the natural abundance of Sb in many uncontaminated groundwaters. Also, the measurement of extremely low concentrations of Sb requires extra care to avoid possible contamination. Given the extensive use of Sb in plastics, we show that some of the containers used to collect and store samples, and for handling and preparing samples for chemical analyses, may be important sources of contamination in the laboratory. The Sb and Sc concentrations reported here should serve as reference values for this region, against which contamination by various human impacts in future could be compared. PMID:16307077

Shotyk, William; Krachler, Michael; Chen, Bin; Zheng, James

2005-11-09

289

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.

Bengtsson, Goran; Annadotter, Helene

1989-01-01

290

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.

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

2013-01-01

291

Determination of the ?15N of nitrate in water; RSIL lab code 2899  

USGS Publications Warehouse

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2899 is to determine the ?15N of nitrate (NO3-) in water. The ?15N of the dissolved NO3- is analyzed by conversion of the NO3- to nitrous oxide (N2O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of the NO3- to N2O, which follows the pathway shown in equation 1: NO3- ? NO2- ? NO ? 1/2 N2O (1) Because the bacteria Pseudomonas aureofaciens lack N2O reductive activity, the reaction stops at N2O, unlike the typical denitrification reaction that goes to N2. After several hours, the conversion is complete, and the N2O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO4)2), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N2O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge (m/z) of the N2O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N2O = 14N14N16O; m/z = 45 = N2O = 14N15N16O or 14N14N17O; m/z = 46 = N2O = 14N14N18O. The 17O contributions to the m/z 44 and m/z 45 ion beams are accounted for before ?15N values are reported.

Coplen, Tyler B.; Qi, Haiping; Revesz, Kinga; Casciotti, Karen; Hannon, Janet E.

2007-01-01

292

Determination of the ?15N and ?18O of nitrate in solids; RSIL lab code 2897  

USGS Publications Warehouse

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2897 is to determine the ?15N and ?18O of nitrate (NO3-) in solids. The NO3- fraction of the nitrogen species is dissolved by water (called leaching) and can be analyzed by the bacterial method covered in RSIL lab code 2900. After leaching, the ?15N and ?18O of the dissolved NO3- is analyzed by conversion of the NO3- to nitrous oxide (N2O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of NO3- to N2O, which follows the pathway shown in equation 1: NO3- ? NO2- ? NO ? 1/2 N2O (1) Because the bacteria Pseudomonas aureofaciens lack N2O reductive activity, the reaction stops at N2O, unlike the typical denitrification reaction that goes to N2. After several hours, the conversion is complete, and the N2O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO4)2), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N2O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge (m/z) of the N2O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N2O = 14N14N16O; m/z = 45 = N2O = 14N15N16O or 14N14N17O; m/z = 46 = N2O = 14N14N18O. The 17O contributions to the m/z 44 and m/z 45 ion beams are accounted for before ?15N values are reported.

Coplen, Tyler B.; Qi, Haiping; Revesz, Kinga; Casciotti, Karen; Hannon, Janet E.

2007-01-01

293

Determination of the ?15N of nitrate in solids; RSIL lab code 2894  

USGS Publications Warehouse

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2894 is to determine the ?15N of nitrate (NO3-) in solids. The nitrate fraction of the nitrogen species is dissolved by water (called leaching) and can be analyzed by the bacterial method covered in RSIL lab code 2899. After leaching, the ?15N of the dissolved NO3- is analyzed by conversion of the NO3- to nitrous oxide (N2O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of NO3- to N2O, which follows the pathway shown in equation 1: NO3- ? NO2- ? NO ? 1/2 N2O (1) Because the bacteria Pseudomonas aureofaciens lack N2O reductive activity, the reaction stops at N2O, unlike the typical denitrification reaction that goes to N2. After several hours, the conversion is complete, and the N2O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO4)2), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N2O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge (m/z) of the N2O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N2O = 14N14N16O; m/z = 45 = N2O = 14N15N16O or 14N14N17O; m/z = 46 = N2O = 14N14N18O. The 17O contributions to the m/z 44 and m/z 45 ion beams are accounted for before ?15N values are reported.

Coplen, Tyler B.; Qi, Haiping; Revesz, Kinga; Casciotti, Karen; Hannon, Janet E.

2007-01-01

294

Determination of the ?15N and ?18O of nitrate in water; RSIL lab code 2900  

USGS Publications Warehouse

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2900 is to determine the ?15N and ?18O of nitrate (NO3-) in water. The ?15N and ?18O of the dissolved NO3- are analyzed by converting the NO3- to nitrous oxide (N2O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of the NO3- to N2O, which follows the pathway shown in equation 1: NO3- ? NO2- ? NO ? 1/2 N2O (1) Because the bacteria Pseudomonas aureofaciens lack N2O reductive activity, the reaction stops at N2O, unlike the typical denitrification reaction that goes to N2. After several hours, the conversion is complete, and the N2O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO4)2), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N2O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge (m/z) of the N2O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N2O = 14N14N16O; m/z = 45 = N2O = 14N15N16O or 14N14N17O; m/z = 46 = N2O = 14N14N18O. The 17O contributions to the m/z 44 and m/z 45 ion beams are accounted for before ?15N values are reported.

Coplen, Tyler B.; Qi, Haiping; Revesz, Kinga; Casciotti, Karen; Hannon, Janet E.

2007-01-01

295

2H(18F,palpha)15N reaction applied to nova gamma-ray emission  

Microsoft Academic Search

The 18F(p,alpha)15O reaction is recognized to be one of the most important reactions for nova gamma-ray astronomy, as it governs the early E<~511keV gamma emission. However, in the nova temperature regime, its rate remains largely uncertain due to unknown low-energy resonance strengths. We report here the measurement of the 2H(18F,p)19F(alpha)15N one-nucleon transfer reaction, induced by a 14-MeV 18F radioactive beam

N. De Séréville; A. Coc; C. Angulo; M. Assunção; D. Beaumel; B. Bouzid; S. Cherubini; M. Couder; P. Demaret; F. de Oliveira Santos; P. Figuera; S. Fortier; M. Gaelens; F. Hammache; J. Kiener; A. Lefebvre; D. Labar; P. Leleux; M. Loiselet; A. Ninane; S. Ouichaoui; G. Ryckewaert; N. Smirnova; V. Tatischeff; J.-P. Thibaud

2003-01-01

296

Influenza A (H15N4) virus isolation in Western Siberia, Russia.  

PubMed

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; Webby, Richard J

2013-01-02

297

Growth and foliar d15N of a Mojave desert shrub in relation to soil hydrological dynamics  

Technology Transfer Automated Retrieval System (TEKTRAN)

Foliar 15N ratios (del15N), % N, and canopy volumes were measured in the two Mojave Desert dominant shrubs, the evergreen Larrea tridentata and drought deciduous Ambrosia dumosa growing across a geomorphically determined soil mosaic. Across three soils with increasingly strong age-dependent surface...

298

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

299

Using diatom-bound ?15N to examine nitrogen cycling in the Gulf of California during the Holocene  

NASA Astrophysics Data System (ADS)

Measurements of diatom bound ?15N values from different sediment size fractions from the western Guaymas Basin, Gulf of California suggest that multiple nutrient cycling processes can be examined from a single sample. Six sections of sediment cores, dating between ~10 to 8 kya were sampled on cm and mm scale resolution representing ~30-40 years. Biogenic opal and organic carbon contents and bulk sedimentary and diatom bound ?15N values from the greater and less than 63?m size fractions were analyzed. Diatom bound ?15N values of the <63 µm size fraction may serve as a nutrient utilization proxy, whereas diatom bound ?15N values from the >63 µm size fraction provides new insights into nitrogen dynamics in the summertime. Diatoms in the >63 ?m fraction are exported once stratification breaks down at the end of summer and have been called the “fall dump” species. Modern water column diatom bound and particulate organic matter ?15N values within the Gulf of California and in adjacent waters were determined for direct comparison to the sediments. Bulk sedimentary ?15N values ranged between 10-11.5‰ and <63µm the diatom bound size fraction ranged between 7-12‰. In all but one sediment section, the ?15N value of the >63µm size fraction was significantly lower than the other two components, ranging between 1-7‰. The >63?m diatoms containing the “fall dump” species are depleted in 15N relative to water column particulate nitrogen suggesting that these diatom species export significantly lower ?15N values. The low ?15N values could have multiple processes contributing to their signal. The water column samples were collected from the nutricline, which corresponded to depths ranging between 30-70 m, at a time when N-fixation was not present. Thus, the most probable mechanism for the low diatom ?15N values is excess nutrient availability from living at the nutricline under low light conditions. Moreover, the ?15N values of the diatoms in the>63 µm fraction in the sediments correlate significantly to bulk sedimentary ?15N values indicating that these deep dwelling diatoms affect the bulk sedimentary isotopic signal. Negative correlations between %Opal and <63?m diatom bound ?15N values indicated that the smaller diatoms recorded signals that are associated with nitrate availability and assimilation of the upwelled water.

Fliegler, J.; Robinson, R. S.; Popp, B. N.

2009-12-01

300

Macroalgae ?15N values in well-mixed estuaries: Indicator of anthropogenic nitrogen input or macroalgae metabolism?  

NASA Astrophysics Data System (ADS)

Although nitrogen stable isotope ratio (?15N) in macroalgae is widely used as a bioindicator of anthropogenic nitrogen inputs to the coastal zone, recent studies suggest the possible role of macroalgae metabolism in ?15N variability. Simultaneous determinations of ?15N of dissolved inorganic nitrogen (DIN) along the land-sea continuum, inter-species variability of ?15N and its sensitivity to environmental factors are necessary to confirm the efficiency of macroalgae ?15N in monitoring nitrogen origin in mixed-use watersheds. In this study, ?15N of annual and perennial macroalgae (Ulva sp., Enteromorpha sp., Fucus vesiculosus and Fucus serratus) are compared to ?15N-DIN along the Charente Estuary, after characterizing ?15N of the three main DIN sources (i.e. cultivated area, pasture, sewage treatment plant outlet). During late winter and spring, when human activities produce high DIN inputs, DIN sources exhibit distinct ?15N signals in nitrate (NO) and ammonium (NH): cultivated area (+6.5 ± 0.6‰ and +9.0 ± 11.0‰), pasture (+9.2 ± 1.8‰ and +12.4‰) and sewage treatment plant discharge (+16.9 ± 8.7‰ and +25.4 ± 5.9‰). While sources show distinct ?N- in this multiple source catchment, the overall mixture of NO sources - generally >95% DIN - leads to low variations of ?N-NO at the mouth of the estuary (+7.7 to +8.4‰). Even if estuarine ?N-NO values are not significantly different from pristine continental and oceanic site (+7.3‰ and +7.4‰), macroalgae ?15N values are generally higher at the mouth of the estuary. This highlights high anthropogenic DIN inputs in the estuary, and enhanced contribution of 15N-depleted NH in oceanic waters. Although seasonal variations in ?N-NO are low, the same temporal trends in macroalgae ?15N values at estuarine and oceanic sites, and inter-species differences in ?15N values, suggest that macroalgae ?15N values might be modified by the metabolic response of macroalgae to environmental parameters (e.g., temperature, light, DIN concentrations). Differences between annual and perennial macroalgae indicate both a higher integration time of perennial compared to annual macroalgae and the possible role of passive versus active uptake mechanisms. Further studies are required to characterize the sensitivity of macroalgae fractionation to variable environmental conditions and uptake mechanisms.

Raimonet, Mélanie; Guillou, Gaël; Mornet, Françoise; Richard, Pierre

2013-03-01

301

A 15N-poor isotopic composition for the solar system as shown by Genesis solar wind samples.  

PubMed

The Genesis mission sampled solar wind ions to document the elemental and isotopic compositions of the Sun and, by inference, of the protosolar nebula. Nitrogen was a key target element because the extent and origin of its isotopic variations in solar system materials remain unknown. Isotopic analysis of a Genesis Solar Wind Concentrator target material shows that implanted solar wind nitrogen has a (15)N/(14)N ratio of 2.18 ± 0.02 × 10(-3) (that is, ?40% poorer in (15)N relative to terrestrial atmosphere). The (15)N/(14)N ratio of the protosolar nebula was 2.27 ± 0.03 × 10(-3), which is the lowest (15)N/(14)N ratio known for solar system objects. This result demonstrates the extreme nitrogen isotopic heterogeneity of the nascent solar system and accounts for the (15)N-depleted components observed in solar system reservoirs. PMID:21700869

Marty, B; Chaussidon, M; Wiens, R C; Jurewicz, A J G; Burnett, D S

2011-06-24

302

Measurement and interpretation of 15N-1H residual dipolar couplings in larger proteins  

PubMed Central

Summary A decade ago, Dr. L.E. Kay and co-workers described an ingenious HNCO-based triple resonance experiment from which several protein backbone RDCs can be measured simultaneously [1]. They implemented a J-scaling technique in the 15N dimension of the 3D experiment to obtain the NH RDCs. We have used this idea to carry out J-scaling in a 2D 15N-1H TROSY experiment and have found it to be an excellent method to obtain NH RDCs for larger proteins upto 70 kDa, far superior to commonly used HSQC in-phase/anti-phase and HSQC/TROSY comparisons. Here, this method, dubbed “RDC-TROSY” is discussed in detail and the limits of its utility are assessed by simulations. Prominent in the latter analysis is the evaluation of the effect of amide proton flips on the “RDC-TROSY” linewidths. The details of the technical and computational implementations of these methods for the determination of domain-orientations in 45–60 KDa Hsp70 chaperone protein constructs are described.

Bhattacharya, Akash; Revington, Matthew

2009-01-01

303

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

NASA Astrophysics Data System (ADS)

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, Donald H.; Kendall, Carol; Chang, Cecily C. Y.; Silva, Steven R.; Tonnessen, Kathy A.

2002-05-01

304

Structural insights from 15N relaxation data for an anisotropic collagen peptide  

PubMed Central

The degree of H-bonding is thought to play an important role in defining collagen recognition sites or regions that contain disease causing collagen mutations. For collagen model peptides, structure determination by standard NMR approaches is limited due to their rod-like anisotropic shape and repeating sequence. We demonstrate that NMR 15N relaxation experiments and their dependence on rotational diffusion anisotropy can be used to obtain novel structural information about the orientation of the NH bonds relative to the protein backbone in these rod-like systems. 15N relaxation measurements on a triple helical peptide that models a collagen sequence just C-terminal to the unique collagenase cleavage site indicate that the angle between the NH bond vector and the diffusion tensor of the Gly residues needs to be readjusted. After placing the Gly amide protons out of the C?-N-C? plane, the hydrogen bond angles and distances are re-calculated and are shown to be both closer to 180° and shorter. The data suggest that deviations of the Gly amide protons from its standard position arise from H-bonding effects and that these may impact on the hydrogen bond strengths in this collagen recognition region.

Xiao, Jianxi; Baum, Jean

2010-01-01

305

Effects of (/sup 15/N)leucine infused at low rates on leucine metabolism in humans  

SciTech Connect

The present studies were carried out to determine whether infusions of (/sup 15/N)leucine at low rates affect estimates of leucine oxidation and of proteolysis and protein synthesis in humans. Three groups of normal subjects were infused for 3 h with either (/sup 15/N)leucine at a rate of 0.16 or 0.26 mumol X kg-1 X min-1 or saline using (/sup 3/H)leucine and alpha-(/sup 14/C)ketoisocaproate as isotopic tracers of leucine metabolism. Data were analyzed at steady state using both single- and dual-isotope models. Preliminary studies were carried out to characterize the dual-isotope model in humans using infusions of (/sup 3/H)leucine and alpha-(/sup 14/C)ketoisocaproate. In the postabsorptive state estimates of leucine appearance, disappearance, and oxidation derived from the two isotope models were in good agreement. Infusion of stable isotope up to approximately 10% of the leucine carbon flux do not have a significant effect on leucine metabolism, but the data derived from such studies must be properly controlled and interpreted with care because these tracers are not massless.

Tessari, P.; Tsalikian, E.; Schwenk, W.F.; Nissen, S.L.; Haymond, M.W.

1985-07-01

306

Temperature dependence of protein backbone motion from carbonyl 13C and amide 15N NMR relaxation  

NASA Astrophysics Data System (ADS)

The NMR spin lattice relaxation rate (R1) and the rotating-frame spin lattice relaxation rate (R1?) of amide 15N and carbonyl 13C (13C?) of the uniformly 13C- and 15N-labeled ubiquitin were measured at different temperatures and field strengths to investigate the temperature dependence of overall rotational diffusion and local backbone motion. Correlation between the order parameter of the N H vector, SNH2, and that of the carbonyl carbon, SC2, was investigated. The effective SC2 was estimated from the direct fit of the experimental relaxation rates and from the slope of 2R2 - R1 vs. B2 using Lipari Szabo formalism. The average SNH2 decreased by 5.9%, while the average SC2 decreased by 4.6% from 15 to 47 °C. At the extreme low and high temperatures the difference in the temperature dependence of the order parameters vanishes. At the intermediate temperatures they do not change by the same amount but they follow the same trend. On the same peptide plane along the protein sequence, SC2 and SNH2 are highly correlated. The results suggest that fast local motion experienced at the site of the N H vector and carbonyl nucleus is more complicated than previously thought and it cannot be easily described by one single type of motion in a broad range of temperature.

Chang, Shou-Lin; Tjandra, Nico

2005-05-01

307

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

308

Backbone dynamics of the olfactory marker protein as studied by 15N NMR relaxation measurements.  

PubMed

Nuclear magnetic resonance (NMR) (15)N relaxation measurements of the olfactory marker protein (OMP) including longitudinal relaxation (T(1)), transverse relaxation (T(2)), and (15)N-{(1)H} NOE data were collected at low protein concentrations (

Gitti, Rossitza K; Wright, Nathan T; Margolis, Joyce W; Varney, Kristen M; Weber, David J; Margolis, Frank L

2005-07-19

309

Quantifying foliar uptake of gaseous nitrogen dioxide using enriched foliar delta15N values.  

PubMed

The magnitude and impact of gaseous nitrogen dioxide (NO(2)) directly entering the leaves were investigated using foliar nitrogen isotopic composition (delta(15)N) values in tomato (Lycopersicon esculentum) and tobacco (Nicotiana tabacum). Using a hydroponics-fumigation system, (15)NO(2) (20 and 40 ppb) was supplied to shoot systems and (50 and 500 microM) was supplied to root systems. Morphological, stable isotope and nitrate reductase activity (NRA) analyses were used to quantify foliar NO(2) uptake and to examine whether realistic concentrations of NO(2) influenced plant metabolism. Nicotiana tabacum and L. esculentum incorporated 15 and 11%, respectively, of (15)NO(2)-N into total biomass via foliar uptake under low supply. On a mass basis, N. tabacum and L. esculentum incorporated 3.3 +/- 0.9 and 3.1 +/- 0.8 mg of (15)NO(2)-N into biomass, respectively, regardless of availability. There were no strong effects on biomass accumulation or allocation, leaf delta(13)C values, or leaf or root NRA in response to NO(2) exposure. Foliar NO(2 )uptake may contribute a significant proportion of N to plant metabolism under N-limited conditions, does not strongly influence growth at 40 ppb, and may be traced using foliar delta(15)N values. PMID:18069953

Vallano, Dena M; Sparks, Jed P

2007-12-07

310

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

311

Visualization of enantiomers using natural abundant (13)C-filtered single and double quantum selective refocusing experiments: Application to small chiral molecules.  

PubMed

The routine use of proton NMR for the visualization of enantiomers, aligned in the chiral liquid crystal solvent poly-gamma-benzyl-l-glutamate (PBLG), is restricted due to severe loss of resolution arising from large number of pair wise interaction of nuclear spins. In the present study, we have designed two experimental techniques for their visualization utilizing the natural abundance (13)C edited selective refocusing of single quantum (CH-SERF) and double quantum (CH-DQSERF) coherences. The methods achieve chiral discrimination and aid in the simultaneous determination of homonuclear couplings between active and passive spins and heteronuclear couplings between the excited protons and the participating (13)C spin. The CH-SERF also overcomes the problem of overlap of central transitions of the methyl selective refocusing (SERF) experiment resulting in better chiral discrimination. Theoretical description of the evolution of magnetization in both the sequences has been discussed using polarization operator formalism. PMID:19581115

Nath, Nilamoni; Baishya, Bikash; Suryaprakash, N

2009-06-17

312

Restraints on backbone conformations in solid state NMR studies of uniformly labeled proteins from quantitative amide 15N-15N and carbonyl 13C-13C dipolar recoupling data  

PubMed Central

Recent structural studies of uniformly 15N, 13C-labeled proteins by solid state nuclear magnetic resonance (NMR) rely principally on two sources of structural restraints: (i) restraints on backbone conformation from isotropic 15N and 13C chemical shifts, based on empirical correlations between chemical shifts and backbone torsion angles; (ii) restraints on inter-residue proximities from qualitative measurements of internuclear dipole–dipole couplings, detected as the presence or absence of inter-residue crosspeaks in multidimensional spectra. We show that site-specific dipole–dipole couplings among 15N-labeled backbone amide sites and among 13C-labeled backbone carbonyl sites can be measured quantitatively in uniformly-labeled proteins, using dipolar recoupling techniques that we call 15N-BARE and 13C-BARE (BAckbone REcoupling), and that the resulting data represent a new source of restraints on backbone conformation. 15N-BARE and 13C-BARE data can be incorporated into structural modeling calculations as potential energy surfaces, which are derived from comparisons between experimental 15N and 13C signal decay curves, extracted from crosspeak intensities in series of two-dimensional spectra, with numerical simulations of the 15N-BARE and 13C-BARE measurements. We demonstrate this approach through experiments on microcrystalline, uniformly 15N, 13C-labeled protein GB1. Results for GB1 show that 15N-BARE and 13C-BARE restraints are complementary to restraints from chemical shifts and inter-residue crosspeaks, improving both the precision and the accuracy of calculated structures.

Hu, Kan-Nian; Qiang, Wei; Bermejo, Guillermo A.; Schwieters, Charles D.; Tycko, Robert

2013-01-01

313

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.

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

2009-01-01

314

Sample Artefacts in ?15N and ?18O of Nitrate in the atmosphere  

NASA Astrophysics Data System (ADS)

Nitrate is one of the major inorganic anions in aerosols. Recently nitrogen and oxygen isotopes in nitrates have been used to trace sources and chemical processes in the atmosphere. High volume samplers are used in order to gain enough material for isotope analysis, but artefacts can occur when measuring with this technique. Besides retaining NO3 from aerosol, gaseous HNO3 can be absorbed on the filter increasing the reported values of nitrate reported. Alternatively; when elevated temperatures are present in the atmosphere, nitrate is volatized in the form of NH3NO3 which would lead to an underestimation of nitrogen on the filter [Schaap et al., 2004]. The artefacts from high volume sampling may cause inaccuracies in the reported isotope values due to isotope fractionation or different initial isotope values between gaseous HNO3 and particulate nitrate. High volume samplers were deployed on board a ship in the summer of 2003 jointly with the Canadian Surface Ocean - Lower Atmosphere Study (SOLAS). A quartz filter was positioned on a high volume sampler. A cellulose acetate filter treated with potassium carbonate and glycerol was placed underneath the quartz filter. The cellulose acetate filter is designed to catch sticky gaseous (such as SO2) but was also found to catch a nitrogen gas species (most probable HNO3 and/or NH3NO3). Analysis of isotopic composition of nitrate for both nitrogen and oxygen was carried out on selected samples by the denitrifier method. Values ranged between -4 and +1‰ for ?15N and between +49 and +66‰ for ?18O for quartz filter. The nitrogen gas species had ranges between -11 and -0‰ for ?15N and between +44 and +62‰ for ?18O. Average differences between the aerosol (caught on the quartz filter) and the nitrogen gas species (on the cellulose acetate filter) were 3±4 ‰ for ?15N and 10±7 ‰ for ?18O. These values are examined to find insights in possible fractionation in the nitrate collection method currently used in other studies. Schaap, M., G. Spindler, M. Schulz, K. Acker, W. Maenhaut, A. Berner, W. Wieprecht, N. Streit, K. Müller, E. Brüggemann, X. Chi, J.-P. Putaud, R. Hitzenberger, H. Puxbaum, U. Baltensperger and H. ten Brink (2004), Artefacts in the sampling of nitrate studied in the “INTERCOMP” campaigns of EUROTRAC-AEROSOL, Atmospheric Environment, 38, 6487-6496.

Seguin, A.; Norman, A. L.

2009-12-01

315

Cerebral glutamine metabolism under hyperammonemia determined in vivo by localized 1H and 15N NMR spectroscopy  

PubMed Central

Brain glutamine synthetase (GS) is an integral part of the glutamate–glutamine cycle and occurs in the glial compartment. In vivo Magnetic Resonance Spectroscopy (MRS) allows noninvasive measurements of the concentrations and synthesis rates of metabolites. 15N MRS is an alternative approach to 13C MRS. Incorporation of labeled 15N from ammonia in cerebral glutamine allows to measure several metabolic reactions related to nitrogen metabolism, including the glutamate–glutamine cycle. To measure 15N incorporation into the position 5N of glutamine and position 2N of glutamate and glutamine, we developed a novel 15N pulse sequence to simultaneously detect, for the first time, [5-15N]Gln and [2-15N]Gln+Glu in vivo in the rat brain. In addition, we also measured for the first time in the same experiment localized 1H spectra for a direct measurement of the net glutamine accumulation. Mathematical modeling of 1H and 15N MRS data allowed to reduce the number of assumptions and provided reliable determination of GS (0.30±0.050??mol/g per minute), apparent neurotransmission (0.26±0.030??mol/g per minute), glutamate dehydrogenase (0.029±0.002??mol/g per minute), and net glutamine accumulation (0.033±0.001??mol/g per minute). These results showed an increase of GS and net glutamine accumulation under hyperammonemia, supporting the concept of their implication in cerebral ammonia detoxification.

Cudalbu, Cristina; Lanz, Bernard; Duarte, Joao MN; Morgenthaler, Florence D; Pilloud, Yves; Mlynarik, Vladimir; Gruetter, Rolf

2012-01-01

316

In Vivo Detection of 15N-Coupled Protons in Rat Brain by ISIS Localization and Multiple-Quantum Editing  

NASA Astrophysics Data System (ADS)

Three-dimensional image-selected in vivo spectroscopy (ISIS) was combined with phase-cycled 1H-15N heteronuclear multiple-quantum coherence (HMQC) transfer NMR for localized selective observation of protons J-coupled to 15N in phantoms and in vivo. The ISIS-HMQC sequence, supplemented by jump-return water suppression, permitted localized selective observation of 2-5 ?mol of [15Nindole]tryptophan, a precursor of the neurotransmitter serotonin, through the 15N-coupled proton in 20-40 min of acquisition in vitro at 4.7 T. In vivo, the amide proton of [5-15N]glutamine was selectively observed in the brain of spontaneously breathing 15NH4+-infused rats, using a volume probe with homogeneous 1H and 15N fields. Signal recovery after three-dimensional localization was 72-82% in phantoms and 59 +/- 4% in vivo. The result demonstrates that localized selective observation of 15N-coupled protons, with complete cancellation of all other protons except water, can be achieved in spontaneously breathing animals by the ISIS-HMQC sequence. This sequence performs both volume selection and heteronuclear editing through an addition/subtraction scheme and predicts the highest intrinsic sensitivity for detection of 15N-coupled protons in the selected volume. The advantages and limitations of this method for in vivo application are compared to those of other localized editing techniques currently in use for non-exchanging protons.

Kanamori, Keiko; Ross, Brian D.

1999-08-01

317

Seawater-peridotite interactions: First insights from ODP Leg 209, MAR 15°N  

NASA Astrophysics Data System (ADS)

We present first results of a petrographic study of hydrothermally altered peridotites drilled during Ocean Drilling Program (ODP) Leg 209 in the 15°20'N fracture Zone area on the Mid-Atlantic Ridge (MAR). We find that serpentinization is extensive at all drill sites. Where serpentinization is incomplete, phase relations indicate two major reaction pathways. One is reaction of pyroxene to talc and tremolite, and the other is reaction of olivine to serpentine, magnetite, and brucite. We interpret these reactions in the light of recent peridotite-seawater reaction experiments and compositions of fluids venting from peridotite massifs at a range of temperatures. We suggest that the replacement of pyroxene by talc and tremolite takes place at temperatures >350°-400°C, where olivine is stable. The breakdown of olivine to serpentine, magnetite, and brucite is favored at temperatures below 250°C, where olivine reacts faster then pyroxene. High-temperature hydrothermal fluids venting at the Logatchev and Rainbow sites are consistent with rapid reaction of pyroxene and little or no reaction of olivine. Moderate-temperature fluids venting at the Lost City site are consistent with ongoing reaction of olivine to serpentine and brucite. Many completely serpentinized peridotites lack brucite and talc because once the more rapidly reacting phase is exhausted, interaction with the residual phase will change fluid pH and silica activity such that brucite or talc react to serpentine. At two sites we see strong evidence for continued fluid flow and fluid-rock interaction after serpentinization was complete. At Site 1268, serpentinites underwent massive replacement by talc under static conditions. This reaction requires either removal of Mg from or addition of Si to the system. We propose that the talc-altered rocks are Si-metasomatized and that the source of Si is likely gabbro-seawater reaction or breakdown of pyroxene deeper in the basement. The basement at Site 1268 is heavily veined, with talc and talc-oxide-sulfide veins being the most common vein types. It appears that the systems evolved from reducing (oxygen fugacity buffered by magnetite-pyrrhotite-pyrite and lower) to oxidizing (dominantly hematite). We propose that this transition is indicative of high fluid flux under retrograde conditions and that the abundance of hematite may relate to the Ca-depleted nature of the basement that prevents near-quantitative removal of seawater sulfate by anhydrite precipitation. At site 1272 we find abundant iowaite partly replacing brucite. While this is the first report of iowaite from a mid-ocean ridge setting, its presence indicates, again, fairly oxidizing conditions. Our preliminary results indicate that peridotite-seawater and serpentinite-seawater interactions can take place under a wider range of temperature and redox conditions than previously appreciated.

Bach, Wolfgang; Garrido, Carlos J.; Paulick, Holger; Harvey, Jason; Rosner, Martin

2004-09-01

318

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.

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

2009-01-01

319

Diffusion technique for 15N and inorganic N analysis of low-N aqueous solutions and Kjeldahl digests.  

PubMed

Diffusion of ammonia is a common sample preparation method for the stable isotope analysis of inorganic nitrogen in aqueous solution. Classical diffusion methods usually require 6-12 days of diffusion and often focus on (15)N/(14)N analysis only. More recent studies have discussed whether complete N recovery was necessary for the precise analysis of stable N isotope ratios. In this paper we present a newly revised diffusion technique that allows correct and simultaneous determination of total N and (15)N at% from aqueous solutions and Kjeldahl digests, with N concentrations down to sub-0.5-mg N L(-1) levels, and it is tested under different conditions of (15)N isotope labelling. With the modification described, the diffusion time was reduced to 72 h, while the ratios of measured and expected (15)N at% were greater than 99% and the simultaneous recovery of total N was >95%. Analysis of soil microbial biomass N and its (15)N/(14)N ratio is one of the most important applications of this diffusion technique. An experiment with soil extracts spiked with (15)N-labelled yeast showed that predigestion was necessary to prevent serious N loss during Kjeldahl digestion of aqueous samples (i.e. soil extracts). The whole method of soil microbial biomass N preparation for (15)N/(14)N analysis included chloroform fumigation, predigestion, Kjeldahl digestion and diffusion. An experiment with soil spiked with (15)N-labelled yeast was carried out to evaluate the method. Results showed a highly significant correlation of recovered and added N, with the same recovery rate (0.21) of both total N and (15)N. A k(N) value of 0.25 was obtained based on the data. In conclusion, the diffusion method works for soil extracts and microbial biomass N determination and hence could be useful in many types of soil/water studies. PMID:18438764

Chen, Rui Rui; Dittert, Klaus

2008-06-01

320

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

321

Biosynthesis of agmatine in isolated mitochondria and perfused rat liver: studies with 15N-labelled arginine  

PubMed Central

An important but unresolved question is whether mammalian mitochondria metabolize arginine to agmatine by the ADC (arginine decarboxylase) reaction. 15N-labelled arginine was used as a precursor to address this question and to determine the flux through the ADC reaction in isolated mitochondria obtained from rat liver. In addition, liver perfusion system was used to examine a possible action of insulin, glucagon or cAMP on a flux through the ADC reaction. In mitochondria and liver perfusion, 15N-labelled agmatine was generated from external 15N-labelled arginine. The production of 15N-labelled agmatine was time- and dose-dependent. The time-course of [U-15N4]agmatine formation from 2 mM [U-15N4]arginine was best fitted to a one-phase exponential curve with a production rate of approx. 29 pmol·min?1·(mg of protein)?1. Experiments with an increasing concentration (0– 40 mM) of [guanidino-15N2]arginine showed a Michaelis constant Km for arginine of 46 mM and a Vmax of 3.7 nmol·min?1·(mg of protein)?1 for flux through the ADC reaction. Experiments with broken mitochondria showed little changes in Vmax or Km values, suggesting that mitochondrial arginine uptake had little effect on the observed Vmax or Km values. Experiments with liver perfusion demonstrated that over 95% of the effluent agmatine was derived from perfusate [guanidino-15N2]arginine regardless of the experimental condition. However, the output of 15N-labelled agmatine (nmol·min?1·g?1) increased by approx. 2-fold (P<0.05) in perfusions with cAMP. The findings of the present study provide compelling evidence that mitochondrial ADC is present in the rat liver, and suggest that cAMP may stimulate flux through this pathway.

2005-01-01

322

Isotope dilution models and the mystery of the vanishing /sup 15/N  

SciTech Connect

An examination of recently published /sup 15/NH/sub 4//sup +/ uptake data shows that the amount of /sup 15/N which disappeared from the NH/sub 4//sup +/ phase was consistently greater than that which appeared in the particulate phase. The discrepancy, which ranged from 1.5 to 5.6 times at nine stations, did not seem to be caused by analytical errors in NH/sub 4//sup +/ or isotope ratio measurements. A new method for calculating the average atom % excess of the NH/sub 4//sup +/ improves estimates of NH/sub 4//sup +/ assimilation in cases where experimental data indicate that uptake and regeneration are not in balance. Correction of a mathematical misconception regarding the Blackburr-Caperon model allows more accurate estimates of NH/sub 4//sup +/ uptake and regeneration rates.

Laws, E.

1984-03-01

323

15N and 13C NMR Determination of Methionine Metabolism in Developing Soybean Cotyledons 1  

PubMed Central

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 13C and 15N 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. We 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, George T.; Garbow, Joel R.; Schaefer, Jacob

1987-01-01

324

1H, 13C, and 15N resonance assignments of murine amelogenin, an enamel biomineralization protein.  

SciTech Connect

Amelogenin is the predominant matrix protein in developing dental enamel. Making extensive use of residue-specific 15N-labeled amino acids samples, the majority of the main and side chain resonances for murine amelogenin were assigned in 2% aqueous acetic acid at pH 3.0. This research was performed at Pacific Northwest National Laboratory, operated by Battelle for the US-DOE. A large part of this research was performed at the W.R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by U.S. Department of Energy’s Office of Biological and Environmental Research (BER) program located at Pacific Northwest National Laboratory (PNNL).

Buchko, Garry W.; Bekhazi, Jacky G.; Cort, John R.; Valentine, Nancy B.; Snead, Malcolm L.; Shaw, Wendy J.

2008-06-01

325

Simultaneous determinations of nitrification and nitrate reduction in coastal sediments by a 15N dilution technique.  

PubMed Central

Nitrification, the oxidation of ammonia to nitrite and nitrate, and nitrate reduction by bacteria in coastal sediments of Mangoku-Ura and Odawa Bay were simultaneously determined by a 15N dilution technique. In muddy sediments of Mangoku-Ura, nitrate reduction proceeded at a rate of 10(-2) to 10 X 10(-2) microgram-atoms of N/g per h. Nitrification was far less intensive. Denitrification, or N2 production from nitrate, accounted for about 30% of the nitrate reduction. A simultaneous occurrence of nitrification and nitrate reduction with a similar rate of 10(-2) microgram-atoms of N/g per h was demonstrated in sandy sediment collected from a Zostera bed of Odawa Bay.

Koike, I; Hattori, A

1978-01-01

326

The 15N(?,?)19F reaction and nucleosynthesis of 19F  

NASA Astrophysics Data System (ADS)

Several resonances in the 15N(?,?)19F reaction have been investigated in the energy range between 0.6 MeV and 2.7 MeV. Resonance strengths and branching ratios have been determined. High sensitivity could be obtained by the combination of the Dynamitron high current accelerator, the windowless gas target system Rhinoceros, and actively shielded germanium detectors. Two levels of 19F could be observed for the first time in the (?,?) channel, and several weak branchings below the detection limits of previous experiments were measured. Two observed resonances correspond to ?-cluster states in 19F, which have been assigned unambiguously. The astrophysical reaction rate is derived from this set of resonance strengths.

Wilmes, S.; Wilmes, V.; Staudt, G.; Mohr, P.; Hammer, J. W.

2002-12-01

327

Resonance strengths in the {sup 14}N(p,gamma){sup 15}O and {sup 15}N(p,alphagamma){sup 12}C reactions  

SciTech Connect

The {sup 14}N(p,gamma){sup 15}O reaction is the slowest reaction of the carbon-nitrogen-oxygen cycle of hydrogen burning in stars. As a consequence, it determines the rate of the cycle. The {sup 15}N(p,alphagamma){sup 12}C reaction is frequently used in inverse kinematics for hydrogen depth profiling in materials. The {sup 14}N(p,gamma){sup 15}O and {sup 15}N(p,alphagamma){sup 12}C reactions have been studied simultaneously, using titanium nitride targets of natural isotopic composition and a proton beam. The strengths of the resonances at E{sub p} = 1058 keV in {sup 14}N(p,gamma){sup 15}O and at E{sub p} = 897 and 430 keV in {sup 15}N(p,alphagamma){sup 12}C have been determined with improved precision, relative to the well-known resonance at E{sub p} = 278 keV in {sup 14}N(p,gamma){sup 15}O. The new recommended values are omegagamma=0.353+-0.018, 362+-20, and 21.9+-1.0 eV for their respective strengths. In addition, the branching ratios for the decay of the E{sub p} = 1058 keV resonance in {sup 14}N(p,gamma){sup 15}O have been redetermined. The data reported here should facilitate future studies of off-resonant capture in the {sup 14}N(p,gamma){sup 15}O reaction that are needed for an improved R-matrix extrapolation of the cross section. In addition, the data on the 430 keV resonance in {sup 15}N(p,alphagamma){sup 12}C may be useful for hydrogen depth profiling.

Marta, Michele; Trompler, Erik; Bemmerer, Daniel; Beyer, Roland; Grosse, Eckart; Hannaske, Roland; Junghans, Arnd R.; Nair, Chithra; Schwengner, Ronald; Wagner, Andreas; Yakorev, Dmitry [Forschungszentrum Dresden-Rossendorf (FZD), Dresden (Germany); Broggini, Carlo; Caciolli, Antonio; Erhard, Martin; Menegazzo, Roberto [Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Padova, Padova (Italy); Fueloep, Zsolt; Gyuerky, Gyoergy [Institute of Nuclear Research (ATOMKI), Debrecen (Hungary); Szuecs, Tamas [Forschungszentrum Dresden-Rossendorf (FZD), Dresden (Germany); Institute of Nuclear Research (ATOMKI), Debrecen (Hungary); Vezzu, Simone [Coordinamento Interuniversitario Veneto per le Nanotechnologie (CIVEN), Venice (Italy)

2010-05-15

328

Backbone dynamics of the oligomerization domain of p53 determined from 15N NMR relaxation measurements.  

PubMed Central

The backbone dynamics of the tetrameric p53 oligomerization domain (residues 319-360) have been investigated by two-dimensional inverse detected heteronuclear 1H-15N NMR spectroscopy at 500 and 600 MHz. 15N T1, T2, and heteronuclear NOEs were measured for 39 of 40 non-proline backbone NH vectors at both field strengths. The overall correlation time for the tetramer, calculated from the T1/T2 ratios, was found to be 14.8 ns at 35 degrees C. The correlation times and amplitudes of the internal motions were extracted from the relaxation data using the model-free formalism (Lipari G, Szabo A, 1982, J Am Chem Soc 104:4546-4559). The internal dynamics of the structural core of the p53 oligomerization domain are uniform and fairly rigid, with residues 327-354 exhibiting an average generalized order parameter (S2) of 0.88 +/- 0.08. The N- and C-termini exhibit substantial mobility and are unstructured in the solution structure of p53. Residues located at the N- and C-termini, in the beta-sheet, in the turn between the alpha-helix and beta-sheet, and at the C-terminal end of the alpha-helix display two distinct internal motions that are faster than the overall correlation time. Fast internal motions (< or = 20 ps) are within the extreme narrowing limit and are of uniform amplitude. The slower motions (0.6-2.2 ns) are outside the extreme narrowing limit and vary in amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)

Clubb, R. T.; Omichinski, J. G.; Sakaguchi, K.; Appella, E.; Gronenborn, A. M.; Clore, G. M.

1995-01-01

329

A Pipeline for (15)N Metabolic Labeling and Phosphoproteome Analysis in Arabidopsis thaliana.  

PubMed

Within the past two decades, the biological application of mass spectrometric technology has seen great advances in terms of innovations in hardware, software, and reagents. Concurrently, the burgeoning field of proteomics has followed closely (Yates et al., Annu Rev Biomed Eng 11:49-79, 2009)-and with it, importantly, the ability to globally assay altered levels of posttranslational modifications in response to a variety of stimuli. Though many posttranslational modifications have been described, a major focus of these efforts has been protein-level phosphorylation of serine, threonine, and tyrosine residues (Schreiber et al., Proteomics 8:4416-4432, 2008). The desire to examine changes across signal transduction cascades and networks in their entirety using a single mass spectrometric analysis accounts for this push-namely, preservation and enrichment of the transient yet informative phosphoryl side group. Analyzing global changes in phosphorylation allows inferences surrounding cascades/networks as a whole to be made. Towards this same end, much work has explored ways to permit quantitation and combine experimental samples such that more than one replicate or experimental condition can be identically processed and analyzed, cutting down on experimental and instrument variability, in addition to instrument run time. One such technique that has emerged is metabolic labeling (Gouw et al., Mol Cell Proteomics 9:11-24, 2010), wherein biological samples are labeled in living cells with nonradioactive heavy isotopes such as (15)N or (13)C. Since metabolic labeling in living organisms allows one to combine the material to be processed at the earliest possible step, before the tissue is homogenized, it provides a unique and excellent method for comparing experimental samples in a high-throughput, reproducible fashion with minimal technical variability. This chapter describes a pipeline used for labeling living Arabidopsis thaliana plants with nitrogen-15 ((15)N) and how this can be used, in conjunction with a technique for enrichment of phosphorylated peptides (phosphopeptides), to determine changes in A. thaliana's phosphoproteome on an untargeted, global scale. PMID:24057376

Minkoff, Benjamin B; Burch, Heather L; Sussman, Michael R

2014-01-01

330

15N CP\\/MAS solid-state NMR spectroscopy of a 15N-enriched hindered amine light stabilizer photolyzed in acrylic\\/melamine and acrylic\\/urethane coatings  

Microsoft Academic Search

Solid-state cross-polarization magic angle spinning 15N nuclear magnetic resonance spectroscopy has been used to follow the chemistry of a 15N-enriched hindered amine light stabilizer and its corresponding nitroxide in an acrylic\\/melamine and an acrylic\\/urethane coating system, as a function of ultraviolet light exposure. The two coating systems are based on the same acrylate copolymer. Samples were photolyzed in a QUV

M. J Rokosz; J. L Gerlock; A. V Kucherov; K. D Belfield; N. L Fryer; G Moad

2000-01-01

331

Electron spin resonance spectroscopy studies on 15N-labeled and their deuterated nitroxyl spin probes used in molecular imaging  

NASA Astrophysics Data System (ADS)

Electron Spin Resonance (ESR) studies were carried out for 2 mM concentration of 15N labeled carbamoyl-PROXYL, carboxy-PROXYL, MC-PROXYL and their deuterated derivatives using X-band ESR spectrometer. The ESR parameters such as linewidth, hyperfine coupling constant, g-factor, spin-spin relaxation time were determined. The lineshape analysis was also carried out. The observed linewidth values are ~50% higher for undeuterated nitroxyl radicals compared with their deuterated derivatives. The lineshape analysis reveals that the observed ESR lineshape is a voigt lineshape, which is the convolution of a lorentzian and guassian profile. ESR lineshape analysis results that the lorentzian contribution is ~20% higher for deuterated nitroxyl radicals compared with undeuterated nitroxyl radicals. The observed spin-spin relaxartion time for deuterated nitroxyl radicals is ~50% longer compared with undeuterated nitroxyl radicals. The g value indicates the isotropic nature of nitroxyl radicals in pure water. From these results, the deuterated nitroxyl radicals are suitable spin probes for ESR/Overhauser-enhanced magnetic resonance (OMR) studies.

Jebaraj, D. David; Benial, A. Milton Franklin; Ichikawa, Kazuhiro; Yamada, Kenichi; Utsumi, Hideo

2013-06-01

332

Synthesis of 7-(15)N-Oroidin and evaluation of utility for biosynthetic studies of pyrrole-imidazole alkaloids by microscale (1)H-(15)N HSQC and FTMS.  

PubMed

Numerous marine-derived pyrrole-imidazole alkaloids (PIAs), ostensibly derived from the simple precursor oroidin, 1a, have been reported and have garnered intense synthetic interest due to their complex structures and in some cases biological activity; however very little is known regarding their biosynthesis. We describe a concise synthesis of 7-(15)N-oroidin (1d) from urocanic acid and a direct method for measurement of (15)N incorporation by pulse labeling and analysis by 1D (1)H-(15)N HSQC NMR and FTMS. Using a mock pulse labeling experiment, we estimate the limit of detection (LOD) for incorporation of newly biosynthesized PIA by 1D (1)H-(15)N HSQC to be 0.96 microg equivalent of (15)N-oroidin (2.4 nmole) in a background of 1500 microg of unlabeled oroidin (about 1 part per 1600). 7-(15)N-Oroidin will find utility in biosynthetic feeding experiments with live sponges to provide direct information to clarify the pathways leading to more complex pyrrole-imidazole alkaloids. PMID:20095632

Wang, Yong-Gang; Morinaka, Brandon I; Reyes, Jeremy Chris P; Wolff, Jeremy J; Romo, Daniel; Molinski, Tadeusz F

2010-03-26

333

Synthesis of 7-15N-Oroidin and Evaluation of Utility for Biosynthetic Studies of Pyrrole-Imidazole Alkaloids by Microscale1H-15N HSQC and FTMS†  

PubMed Central

Numerous marine-derived pyrrole-imidazole alkaloids (PIAs), ostensibly derived from the simple precursor oroidin, 1a, have been reported and have garnered intense synthetic interest due to their complex structures and in some cases biological activity; however very little is known regarding their biosynthesis. We describe a concise synthesis of 7-15N-oroidin (1d) from urocanic acid and a direct method for measurement of 15N incorporation by pulse labeling and analysis by 1D 1H-15N HSQC NMR and FTMS. Using a mock pulse labeling experiment, we estimate the limit of detection (LOD) for incorporation of newly biosynthesized PIA by 1D 1H-15N HSQC to be 0.96 ?g equivalent of 15N oroidin (2.4 nmole) in a background of 1500 ?g unlabeled oroidin (about 1 part per 1600). 7-15N-Oroidin will find utility in biosynthetic feeding experiments with live sponges to provide direct information to clarify the pathways leading to more complex pyrrole-imidazole alkaloids.

Wang, Yong-Gang; Morinaka, Brandon I.; Reyes, Jeremy Chris P.; Wolff, Jeremy H.; Romo, Daniel; Molinski, Tadeusz F.

2010-01-01

334

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

335

Anomalous 14N/15N ratio in comets 122P/1995 S1 (de Vico) and 153P/2002 C1 (Ikeya-Zhang)  

NASA Astrophysics Data System (ADS)

High-resolution (R 60,000) spectra of the Halley-type comet 122P/1995 S1 de Vico (Period 74 years) and the ``intermediate-period" comet 153P/2002 C1 Ikeya-Zhang (P 370 yr) were obtained with the 2DCoude spectrograph at the 2.7-m Harlan J. Smith telescope of the McDonald Observatory. These comets were within 1 AU from the Sun (0.66 and 0.92 AU, respectively). The spectra display CN (0,0) bands indicating an anomalous 14N/15N isotope ratio, in the sense that it is close to half the value in Earth's atmosphere (the so-called ``Solar system value") and about half that obtained in comet Hale-Bopp from sub-millimeter measurements on HCN, generally believed to be the main parent of CN. Similar conclusions had been reached for C/1995 O1 (Hale-Bopp), an ``old long-period", and for C/2000 WM1 (LINEAR), a ``young long-period" comet. As suggested by Arpigny et al. (2003), this apparent abundance anomaly points towards the existence of other unknown parent(s) of CN, with an even higher 15N excess. Organic compounds like those found in interplanetary dust particles (IDPs) are good candidates. The similarity between comets of different dynamical ages is pointed out. 1 Research Director FNRS (Belgium) 2 Research Associate FNRS (Belgium)

Arpigny, C.; Cochran, A. L.; Jehin, E.; Manfroid, J.; Hutsemékers, D.; Zucconi, J.-M.; Endl, M.; Cochran, W. D.; Schulz, R.

2003-05-01

336

Nitrogen acquisition, transport and metabolism in intact ectomycorrhizal associations studied by (sup 15)N stable isotope techniques.  

National Technical Information Service (NTIS)

The focus of this thesis is on the external mycelium and its role in nitrogen uptake, assimilation and translocation. Tree seedlings in association with ectomycorrhizal fungi were grown in observation chambers. The fungal mycelium were fed with 15-N ammon...

H. Ek

1993-01-01

337

Improved measurement of (15)N-[(1)H] NOEs in the presence of H(N)-water proton chemical exchange.  

PubMed

A simple method is presented to accurately determine (15)N-[(1)H] NOEs in biomolecules in the presence of H(N)-water proton chemical exchange. Three measurements are required: one with nonselective proton saturation and two with different water saturation conditions to determine the equilibrium value of the (15)N signal. This approach is exemplified with data on two peptides, one helix-forming 17-mer and one compactly folded 56-mer. Results indicate that (15)N-[(1)H] NOEs determined using the standard approach with short recycle times (3 to 4 s) can be significantly in error when H(N)-water proton chemical exchange is relatively rapid, water proton relaxation is relatively slow, and (15)N-[(1)H] NOEs are away from the value of -1. This new method avoids such inaccuracies resulting from the use of short recycle times. PMID:11700091

Idiyatullin, D; Daragan, V A; Mayo, K H

2001-11-01

338

Measurements of carbon to amide-proton distances by C-H dipolar recoupling with 15N NMR detection.  

PubMed

A new magic-angle spinning NMR method for measuring internuclear distances between a 13C-labeled site and amide protons is described. The magnetization of the protons evolves under homonuclear decoupling and the recoupled 13C-1H dipolar interaction, which provides simple spin-pair REDOR curves if only one 13C-labeled site is present. The modulation of the amide proton HN is detected via short 1H-15N cross polarization followed by 15N detection. The method is demonstrated on two specifically 13C- and 15N-labeled peptides, with 13C-HN distances from 2.2 to ca. 6 A. This technique promises to be particularly useful for measuring distances between 13C=O and H-15N groups, to identify hydrogen bonds in peptides and proteins. PMID:12733900

Schmidt-Rohr, Klaus; Hong, Mei

2003-05-14

339

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

340

Dynamic effects of soil bulk density on denitrification and mineralisation by (sup 15)N labelled lettuce residue and paper wastes.  

National Technical Information Service (NTIS)

Two laboratory incubation experiments aimed to study the denitrification and mineralisation influenced by different additives ((sup 15)N labelled lettuce residue, paper wastes and mixture of both) and soil bulk densities were carried out by means of acety...

Hua Luo Cheng Qing A. J. A. Vinten

1997-01-01

341

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

342

Energy: Natural limits and abundances  

Microsoft Academic Search

With the decline of ancient civilization---the successive incinerations of the great Library of Alexandria in the fourth century and the Moslem conquest of Egypt in the seventh---it remained for Persian and Arabian scholars to assemble, record, and continue to enlarge knowledge. The western world became aware of this heritage during the Crusades of the twelfth century when translations of Arabic

William S. von Arx

1974-01-01

343

Availability of residual 15N in a coniferous forest soil: a greenhouse bioassay and comparison with chemical extractions  

Microsoft Academic Search

The assessment of soil N availability by chemical extraction methods often needs to be checked by methods which directly measure plant N uptake such as a greenhouse bioassay. In this paper, the recovery of residual 15N, from humus material samples with 15N labelled for 24-h, seven-month, and 31-month, in western redcedar (Thuja plicata Donn ex D. Don) and western hemlock

Scott X. Chang; Caroline M. Preston; Gordon F. Weetman

1999-01-01

344

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

NASA Astrophysics Data System (ADS)

Correct estimate of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice cores studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: output of a firn densification model and measurements of ?15N of N2 in air trapped in ice core. 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 ?15N measurements performed from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rate and temperature conditions. While firn densification simulations are able to correctly represent most of the ?15N trends over the last deglaciation measured in the EDC, BI, TALDICE and EDML ice cores, they systematically fail to capture BI and EDML ?15N glacial levels, a mismatch previously seen for Central East Antarctic ice cores. Using empirical constraints of the EDML gas-ice depth offset during the Laschamp event (~ 41 ka), we can rule out the existence of a large convective zone as the explanation of the glacial firn model-?15N data mismatch for this site. The good match between modelled and measured ?15N at TALDICE as well as the lack of any clear correlation between insoluble dust concentration in snow and ?15N records in the different ice cores suggest that past changes in loads of impurities are not the only main driver of glacial-interglacial changes in firn lock-in depth. We conclude that firn densification dynamics may instead be driven mostly by accumulation rate changes. The mismatch between modelled and measured ?15N may be due to inaccurate reconstruction of past accumulation rate or underestimated influence of accumulation rate in 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.

2012-12-01

345

Detection of 2,4,6-trinitrotoluene-utilizing anaerobic bacteria by 15N and 13C incorporation.  

PubMed

2,4,6-Trinitrotoluene ((15)N or (13)C labeled) was added to Norfolk Harbor sediments to test whether anaerobic bacteria use TNT for growth. Stable-isotope probing (SIP)-terminal restriction fragment length polymorphism (TRFLP) detected peaks in the [(15)N]TNT cultures (60, 163, and 168 bp). The 60-bp peak was also present in the [(13)C]TNT cultures and was related to Lysobacter taiwanensis. PMID:20081008

Gallagher, Erin M; Young, Lily Y; McGuinness, Lora M; Kerkhof, Lee J

2010-01-15

346

Dynamics of 15 N-labeled ammonium sulfate in various inorganic and organic soil fractions of wetland rice soils  

Microsoft Academic Search

The dynamics of basally applied 15N-labeled ammonium sulfate in inorganic and organic soil fractions of five wetland rice soils of the Philippines was studied in a greenhouse experiment. Soil and plant samples were collected and analyzed for 15N at various growth stages. Exchangeable NH4+ depletion continued after 40 days after transplanting (DAT) and corresponded with increased nitrogen uptake by rice

H. F. Schnier; S. K. De Datta; K. Mengel

1987-01-01

347

Detection of 2,4,6-Trinitrotoluene-Utilizing Anaerobic Bacteria by 15N and 13C Incorporation ?  

PubMed Central

2,4,6-Trinitrotoluene (15N or 13C labeled) was added to Norfolk Harbor sediments to test whether anaerobic bacteria use TNT for growth. Stable-isotope probing (SIP)-terminal restriction fragment length polymorphism (TRFLP) detected peaks in the [15N]TNT cultures (60, 163, and 168 bp). The 60-bp peak was also present in the [13C]TNT cultures and was related to Lysobacter taiwanensis.

Gallagher, Erin M.; Young, Lily Y.; McGuinness, Lora M.; Kerkhof, Lee J.

2010-01-01

348

Leaf ?15N as a temporal integrator of nitrogen-cycling processes at the Mojave Desert FACE experiment  

NASA Astrophysics Data System (ADS)

Ecosystem response to elevated carbon dioxide (CO2) in arid environments is regulated primarily by water, which may interact with nitrogen availability. Leaf nitrogen isotope composition (?15N) can serve as an important indicator of changes in nitrogen dynamics by integrating changes in plant physiology and ecosystem biogeochemical processes. Because of this temporal integration, careful modeling of the antecedent conditions is necessary for understanding the processes driving variation in leaf ?15N. We measured leaf ?15N of Larrea tridentata (creosotebush) over the 10-year lifetime of the Nevada Desert Free-Air CO2 Enrichment (FACE) experiment. Leaf ?15N exhibited two patterns. First, elevated atmospheric CO2 significantly increased Larrea leaf ?15N by approximately 2 to 3 % compared to plants exposed to ambient CO2 concentrations Second, plants in both CO2 treatments exhibited significant seasonal cycles in leaf ?15N, with higher values during the fall and winter seasons. We modeled leaf ?15N using a hierarchical Bayesian framework that incorporated soil moisture, temperature, and the Palmer Drought Severity Index (PDSI) covariates in addition to a CO2 treatment effect and plot random effects. Antecedent moisture effects were modeled by using a combination of the previous season's aggregated conditions and a smoothly varying weighted average of the months or weeks directly preceding the observation. The time lag between the driving antecedent condition and the observed change in leaf ?15N indicates a significant and unobserved process mechanism. Preliminary results suggest a CO2 treatment interaction with the lag effect, indicating a treatment effect on the latent process.

Sonderegger, D.; Koyama, A.; Jin, V.; Billings, S. A.; Ogle, K.; Evans, R. D.

2011-12-01

349

Net and gross incorporation of nitrogen by marine copepods fed on 15N-labelled diatoms: Methodology and trophic studies  

Microsoft Academic Search

The stable isotope of nitrogen (15N) and an appropriate three-compartment model were used in two 24-h lasting feeding experiments to trace the flow of N through the copepod Acartia discaudata and Calanus helgolandicus fed on 15N-labelled Skeletonema costatum and Thalassiosira weissflogii, respectively. Details of the labelling technique and principles of the computation of N transport rates are given. At the

Dorothée Vincent; Gerd Slawyk; Stéphane L'Helguen; Géraldine Sarthou; Morgane Gallinari; Laurent Seuront; Benoît Sautour; Olivier Ragueneau

2007-01-01

350

HNCO-based measurement of one-bond amide 15 N- 1 H couplings with optimized precision  

Microsoft Academic Search

A pair of 3D HNCO-based experiments have been developed with the aim of optimizing the precision of measurement of 1JNH couplings. Both pulse sequences record 1JNH coupling evolution during the entire constant time interval that 15N magnetization is dephasing or rephasing with respect to the directly bonded 13C? nucleus, with 15N13C? multiple quantum coherence maintained during the 13C? evolution period.

Luke Arbogast; Ananya Majumdar; Joel R. Tolman

2010-01-01

351

Comparison of five soil organic matter decomposition models using data from a 14C and 15N labeling field experiment  

NASA Astrophysics Data System (ADS)

Five alternatives of the previously published MOMOS model (MOMOS-2 to -6) are tested to predict the dynamics of carbon (C) and nitrogen (N) in soil during the decomposition of plant necromass. 14C and 15N labeled wheat straw was incubated over 2 years in fallow soils of the high Andean Paramo of Venezuela. The following data were collected: soil moisture, total 14C and 15N and microbial biomass (MB)-14C and -15N, daily rainfall, air temperature and total radiation. Daily soil moisture was predicted using the SAHEL model. MOMOS-2 to -4 (type 1 models) use kinetic constants and flow partitioning parameters. MOMOS-2 can be simplified to MOMOS-3 and further to MOMOS-4, with no significant changes in the prediction accuracy and robustness for total-14C and -15N as well as for MB-14C and -15N. MOMOS-5 (type 2 models) uses only kinetic constants: three MB-inputs (from labile and stable plant material and from humified compounds) and two MB-outputs (mortality and respiration constants). MOMOS-5 did not significantly change the total-14C and -15N predictions but markedly improved the predictive quality and robustness of MB-14C and -15N predictions (with a dynamic different from the predictions by other models). Thus MOMOS-5 is proposed as an accurate and ecologically consistent description of decomposition processes. MOMOS-6 extends MOMOS-5 by including a stable humus compartment for long-term simulations of soil native C and N. The improvement of the predictions is not significant for this 2-year experiment, but MOMOS-6 enables prediction of a sequestration in the stable humus compartment of 2% of the initially added 14C and 5.4% of the added 15N.

Pansu, Marc; Bottner, Pierre; Sarmiento, Lina; Metselaar, Klaas

2004-12-01

352

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.; Bohlke, J. K.; Casciotti, K. L.

2004-01-01

353

Labeling with 15N as compared with homoarginine suggests a lower prececal digestibility of casein in pigs.  

PubMed

Calculations of prececal protein digestibility based on the stable isotope 15N and the chemical label homoarginine were compared, using casein doubly-labeled with both markers. After food was withheld overnight 24 miniature pigs were given a meal containing 15 g/100 g casein, including 4 g/100 g doubly-labeled protein, and chromic oxide as an indigestible marker. The intestine of eight animals each was removed 3, 6 or 12 h later, divided into 3 sections of equal length, and chyme was collected. Kjeldahl-N, 15N and homoarginine were determined in diet and chyme. Digestibility of casein in the distal third of the small intestine was 93.5 +/- 0.5% and 97.6 +/- 0.3% (P < 0.05) according to 15N and homoarginine label, respectively. Potential causes for this systematic difference were assessed. The data suggest that incorporation of 15N into endogenous proteins and re-entry into the intestinal lumen via secreta and desquamations is the major cause for the 4.2 +/- 0.4% lower digestibility based on the 15N as compared with the homoarginine labeling technique. A preferential occurrence of homoarginine in more easily digestible sections of the protein, faster release during the digestive process and absorption of homoarginine, or incorporation of 15N into proteins of intestinal bacteria are less likely to cause this difference. PMID:16856321

Roos, N; Pfeuffer, M; Hagemeister, H

1994-12-01

354

Mycorrhizal fungi supply nitrogen to host plants in Arctic tundra and boreal forests: 15N is the key signal.  

PubMed

Symbiotic fungi's role in providing nitrogen to host plants is well-studied in tundra at Toolik Lake, Alaska, but little-studied in the adjoining boreal forest ecosystem. Along a 570 km north-south transect from the Yukon River to the North Slope of Alaska, the 15N content was strongly reduced in ectomycorrhizal and ericoid mycorrhizal plants including Betula, Salix, Picea mariana (P. Mill.) B.S.P., Picea glauca Moench (Voss), and ericaceous plants. Compared with the 15N content of soil, the foliage of nonmycorrhizal plants (Carex and Eriophorum) was unchanged, whereas content of the ectomycorrhizal fungi was very much higher (e.g., Boletaceae, Leccinum and Cortinarius). It is hypothesized that similar processes operate in tundra and boreal forest, both nitrogen-limited ecosystems: (i) mycorrhizal fungi break down soil polymers and take up amino acids or other nitrogen compounds; (ii) mycorrhizal fungi fractionate against 15N during production of transfer compounds; (iii) host plants are accordingly depleted in 15N; and (iv) mycorrhizal fungi are enriched in 15N. Increased N availability for plant roots or decreased light availability to understory plants may have decreased N allocation to mycorrhizal partners and increased delta15N by 3-4 parts per million for southern populations of Vaccinium vitis-idaea L. and Salix. Fungal biomass, measured as ergosterol, correlated strongly with soil organic matter and attained amounts similar to those in temperate forest soils. PMID:19190704

Hobbie, John E; Hobbie, Erik A; Drossman, Howard; Conte, Maureen; Weber, J C; Shamhart, Julee; Weinrobe, Melissa

2009-01-01

355

A 7-year increasing trend of 15N in sinking particles at the mouth of the Tokyo Bay  

NASA Astrophysics Data System (ADS)

A sediment trap experiment was conducted for 7 years with sampling at 7 days interval at the Tokyo Bay mouth. The ?15N of the trapped particles showed an increasing trend (0.17 ‰ y-1) from 1995 to 2001. The trend is larger in summer than in winter particles. During summer, the ?15N shows large variation where maxima increase while the minima stay nearly constant. The summertime elevation in ?15N is due to increased contribution of freshly derived 15N rich particles produced in the inner-bay surface water. The high ?15N in trapped particles lagged one or two weeks behind the >50 mm d-1 rainfall events. Freshwater supplied by heavy rainfall appears to accelerate estuarine circulation and results in increased contribution of inner-bay surface water particles. The increased frequency of the short-term heavy rainfall events in metropolis Tokyo during our observation could be a cause for the 7 year increasing trend of ?15N in the sinking particles.

Sukigara, Chiho; Saino, Toshiro

2006-05-01

356

Expression and purification of 15N- and 13C-isotope labeled 40-residue human Alzheimer's ?-amyloid peptide for NMR-based structural analysis  

PubMed Central

Amyloid fibrils of Alzheimer’s ?-amyloid peptide (A?) are a primary component of amyloid plaques, a hallmark of Alzheimer’s disease (AD). Enormous attention has been given to the structural features and functions of A? in amyloid fibrils and other type of aggregates in associated with development of AD. This report describes an efficient protocol to express and purify high-quality 40-residue A?(1–40), the most abundant A? in brains, for structural studies by NMR spectroscopy. Over-expression of A?(1–40) with glutathione S-transferase (GST) tag connected by a Factor Xa recognition site (IEGR?) in E. Coli resulted in the formation of insoluble inclusion bodies even with the soluble GST tag. This problem was resolved by efficient recovery of the GST-A? fusion protein from the inclusion bodies using 0.5% (w/v) sodium lauroyl sarcosinate as solubilizing agent and subsequent purification by affinity chromatography using a glutathione agarose column. The removal of the GST tag by Factor Xa enzymatic cleavage and purification by HPLC yielded as much as ~7 mg and ~1.5 mg of unlabeled A?(1–40) and uniformly 15N- and/or 13C-protein A?(1–40) from 1 L of the cell culture, respectively. Mass spectroscopy of unlabeled and labeled A? and 1H/15N HSQC solution NMR spectrum of the obtained 15N-labeled A? in the monomeric form confirmed the expression of native A?(1–40). It was also confirmed by electron micrography and solid-state NMR analysis that the purified A?(1–40) self-assembles into ?-sheet rich amyloid fibrils. To the best of our knowledge, our protocol offers the highest yields among published protocols for production of recombinant A?(1–40) samples that are amendable for an NMR-based structural analysis. The protocol may be applied to efficient preparation of other amyloid-forming proteins and peptides that are 13C- and 15N-labeled for NMR experiments.

Long, Fei; Cho, Wonhwa; Ishii, Yoshitaka

2011-01-01

357

The 14N/15N Isotope Ratio in Dense Molecular Clouds  

NASA Astrophysics Data System (ADS)

Observations of the 3-2 and 1-0 transitions of HNC at 271.981 and 90.663 GHz, H15NC at 266.567 and 88.865 GHz were conducted using the Arizona Radio Observatory (ARO) 12m at 2 and 3mm in wavelength and Submillimeter Telescopes (SMT) at 1mm. The 13C isotopomer was also observed to evaluate the high optical depth in the main isotope, hence the 3-2, 2-1, 1-0 transitions of HN13C at 261.263, 174.179 and 87.090 GHz were recorded as well. Observations were made toward the molecular clouds SgrB2, W31, G34.3, W51M, M17-SW, DR-21, L134, Orion A, W3 (OH), NGC7538 and S156, located at various distances from the Galactic Center. The preliminary results indicate a ratio 14N/15N of 120-200, similarly to the values found in comets.

Adande, G.; Ziurys, L. M.

2010-06-01

358

Tracing sewage water by 15N in a mangrove ecosystem to test its bioremediation ability.  

PubMed

Mangrove forests could be a simple and effective alternative to conventional sewage treatment, particularly for island communities given its low cost and low maintenance. Due to their high adaptation capacity, these plants are able to tolerate and bioremediate the high levels of nutrients and pollutants found in sewage water. This solution could be applied to small tropical islands with high population density such as Mayotte in the Indian Ocean. This paper reports on a trial by stable isotopic (15)N tracing of such a bioremediation process on pre-treated wastewater near the village of Malamani, in the middle of the large coastal mangrove in the bay near Chirongui. The first results show a boost in the mangrove growth, but a longer period of observation is needed to confirm the beneficial effects, and also to clarify the role of the local crab population, whose engineering activities play an important part in the ecosystem. The exact denitrification process is not yet understood, and the mass balance equation also reveals loss of nitrogen-containing compounds, which needs to be analyzed more closely. PMID:21913255

Lambs, Luc; Léopold, Audrey; Zeller, Bernd; Herteman, Mélanie; Fromard, Francois

2011-10-15

359

Feeding on Different Host Plants Alters the Natural Abundances of delta (1)(3)C and delta (1)N in Longidoridae (Nemata).  

PubMed

Natural abundances of the stable isotope pairs (1)(3)C/(1)(2)C (delta (1)(3)C) and (1)N/(1)N (delta (1)N) have been used previously to study food sources and trophic relationships in soil invertebrates. In this study, delta (1)(3)C and delta (1)N were measured in five species of Longidoridae to investigate the effect of transferring nematodes from one plant host to another. Longidorus elongatus, Paralongidorus maximus, Xiphinema diversicaudatum, X. index, and X. vuittenezi were cultured initially on Lolium perenne, Petunia hybrida, Rubus ideaus, Ficus carica, and Rubus ideaus, respectively, and subsequently transferred to 4-week-old P. hybrida seedlings. After feeding on P. hybrida for 28 days, whole body delta (1)(3)C and delta (1)N values of the three Xiphinema species were depleted (P = 0.001) and enriched (P = 0.001), respectively, compared to nematode populations that had fed solely on the original plant hosts. Similar changes in L. elongatus and P. maximus whole body delta (1)(3)C and delta (1)N were not detected. Changes in whole body delta (1)(3)C are considered to be indicative of the new plant host (P. hybrida), whereas differences in whole body delta (1)N are probably related to the different feeding strategies used by the longidorid nematodes in this study. PMID:19270871

Neilson, R; Brown, D J

1999-03-01

360

Satellite transitions in natural abundance solid-state 33S MAS NMR of alums—Sign change with zero-crossing of CQ in a variable temperature study  

NASA Astrophysics Data System (ADS)

Experiences obtained from recent improvements in the performance of solid-state 14N MAS NMR spectroscopy have been used in a natural abundance 33S MAS NMR investigation of the satellite transitions for this interesting spin I = 3/2 isotope. This study reports the first observation of manifolds of spinning sidebands for these transitions in 33S MAS NMR as observed for the two alums XAl(SO4)2·12H2O with X = NH4 and K. For the NH4-alum a variable temperature 33S MAS NMR study, employing the satellite transitions, shows that the 33S quadrupole coupling constant (CQ) exhibits a linear temperature dependence (in the range -35 °C to 70 °C) with a temperature gradient of 3.1 kHz/°C and undergoes a sign change with zero-crossing for CQ at 4 °C (277 K). For the isostructural K-alum a quite similar increase in the magnitude of CQ with increasing temperature is observed, and with a temperature gradient of 2.3 kHz/°C. Finally, for optimization purposes, a study on the effect of the applied pulse widths at constant rf field strength on the intensity and variation in second-order quadrupolar lineshape for the central (1/2 ? -1/2) transition of the K-alum has been performed.

Jakobsen, Hans J.; Hove, Anders R.; Bildsøe, Henrik; Skibsted, Jørgen

2006-06-01

361

Purification, recovery, and laser-driven fluorination of silicon from dissolved and particulate silica for the measurement of natural stable isotope abundances.  

PubMed

A procedure for the purification, recovery, and determination of isotopic abundances of silicon from biogenic and lithogenic particulate matter and dissolved silicic acid is reported. Purification involves the reaction of acid molybdate with dissolved silicon in natural waters or that produced by the dissolution of particulate silica by hydrofluoric acid. The resulting silicomolybdic acid is then quantitatively precipitated by reaction with triethylamine hydrochloride. The silicon is recovered as silicon dioxide through stepwise combustion of the dried precipitate. Fluorination of the product for isotopic analysis is accomplished by laser heating under pure fluorine generated by the decomposition of a fluorine-based salt. The resulting silicon tetrafluoride is separated from hydrogen fluoride and other fluorination byproducts cryogenically using a variable-temperature cold trap. Yields for silicon recovery are 99.9% for precipitation and greater than 95% for the purification/fluorination procedure. Reproducibility of the isotopic composition for pure quartz granules processed through the procedure is ±0.1‰ for ?(30)Si. PMID:21619245

De La Rocha, C L; Brzezinski, M A; Deniro, M J

1996-11-01

362

A novel method for measuring long range proton-proton J coupling constants in multi-methylene fragments with 13C in natural abundance  

NASA Astrophysics Data System (ADS)

A new heteronuclear two-dimensional NMR experiment, X.E.COSY, is described which makes possible the measurement of 3JHH coupling constants between adjacent methylene groups in multi-methylene fragments. This new experiment exploits E.COSY multiplet structures based on large heteronuclear one-bond 1JXH coupling constants for resolving basic patterns. It necessitates only one NMR-active heteronuclear spin per molecule, and therefore is feasible with isotopes in natural abundance. X.E.COSY complements the XLOC pulse sequence, which works well for CH and CH3 groups but for methylene moieties only allows measurement of the sum of JHH coupling constants between a proton and the two protons attached to the heteronuclear spin. The new sequence has been tested on CH2CH and CH2CH2 moieties of a Gramicidin S sample, a C2 symmetric cyclic pentapeptide dimer. X.E.COSY will be useful for studying sidechain conformations in peptides and conformationally constrained peptides and peptide analogues containing methylene linkers or bridgers.

Briand, Jacques

1998-12-01

363

Overwinter transformations of nitrate derived from soil and sup 15 N-labeled potassium nitrate  

Microsoft Academic Search

Transformation of NOâ-N from fall through spring were examined in a Typic Cryoboralf and a Typic Arigalboll in northcentral Alberta. Nitrogen-15 labeled KNOâ (96% atom abundance) was applied at the rate of 2.4 kg N ha⁻¹ to fallow and stubble plots in October and incorporated to a depth of 0.13 m. Isotopic analyses of NHâ-N, NOâ-N, and total-N were performed

D. J. Heaney; M. Nyborg

2008-01-01

364

Effect of Straw Incorporation on 15N?Labeled Ammonium Nitrogen Uptake and Rice Growth  

Microsoft Academic Search

A greenhouse experiment was conducted to determine the effect of rice straw residue on growth and uptake of added N?labeled ammonium nitrogen (NH4?N) (3% N abundance at the rate of 150 kg N ha) by rice in Crowley silt loam soil (Typic Albaqualfs). Higher rates of rice straw addition had an adverse affect on plant growth from the first to sixth

Manoch Kongchum; R. D. DeLaune; Wayne H. Hudnall; Patrick K. Bollich

2007-01-01

365

Spatial Patterns of Plant ?13C and ?15N Along a Topoedaphic Gradient in a Subtropical Savanna Landscape  

NASA Astrophysics Data System (ADS)

?13C and ?15N values of plants are powerful tools in physiological ecology, ecosystem science, and global biogeochemistry, yet we know relatively little about their variation and controls at the landscape scale. In this study, we investigated landscape-scale spatial variations in the foliar isotopic composition of 3 woody plant species across a 308 m topoedaphic gradient, along which soil texture and plant resources (water and nitrogen availability) varied from upland (86 m) to lowland (84 m) portions of the landscape. The study was conducted in a subtropical savanna at the La Copita Research Area, approximately 60 km west of Corpus Christi, TX. Foliar ?13C, ?15N, leaf nitrogen concentration ([N]), and specific leaf area (SLA) were measured on all individuals of Prosopis glandulosa, Condalia hookeri, and Zanthoxylum fagara present within a belt transect 308 m long x 12 m wide. Soil texture, available soil moisture, and total N were measured at 1 m intervals along the center-line of the belt transect. Clay content, available soil moisture, and soil total N were all negatively correlated with elevation along the transect. Leaf ?13C and ?15N values for all 3 species increased by 1-4 o/oo with decreasing elevation along the transect. Contrary to theory and previous studies, ?13C values were highest where soil water was most available, suggesting that some other variable could be overriding or interacting with water availability. Foliar [N] appeared to exert the strongest control over landscape-level variation, and was positively correlated with ?13C of all species (R 2 = 0.58, p<0.0001). Since leaf [N] is positively related to photosynthetic capacity, plants with high [N] are likely to have low Ci/Ca ratios and therefore higher ?13C values. ?15N values of Zanthoxylum and Condalia were positively correlated with leaf [N] and soil water availability; however, these relationships were absent for Prosopis, an N-fixing tree legume. We speculate that the relationship between ?15N and leaf [N] and soil water may reflect the fact that plants with high ?15N values occurred on lower-lying portions of the landscape with relatively high N-transformation rates where soil mineral N was both relatively available and 15N-enriched. The lack of variation in ?15N values of Prosopis suggests that it may be somewhat uncoupled from these processes because it is an N-fixer. Results of this study indicate that N-availability plays an important role in landscale scale variation in plant ?13C and ?15N.

Bai, E.; Boutton, T. W.; Liu, F.; Wu, B.; Archer, S. R.

2005-12-01

366

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, Jr. , R. O.; 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

367

Is there an excuse for the non-conformist? Notes on the calculated energies, atom–atom contacts and natural abundance of the different conformers of alanine in proteins  

Microsoft Academic Search

The calculated energies of alanine model conformers correlate with the natural abundance of alanine conformers in proteins. However, the observed conformational distribution of alaine in proteins cannot be described solely on the basis of quantum chemical calculations of the corresponding diamide. We suggest that amino acid residue conformation in a folded protein is the result of multiple factors, among which

Zoltán Gáspári; Ilona Hudáky; András Czajlik; András Perczel

2004-01-01

368

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.

Ruiz-Cooley, Rocio I.; Ballance, Lisa T.; McCarthy, Matthew D.

2013-01-01

369

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

370

Elucidating the trophodynamics of four coral reef fishes of the Solomon Islands using ?15N and ?13C  

NASA Astrophysics Data System (ADS)

Size-related diet shifts are important characteristics of fish trophodynamics. Here, body size-related changes in muscle ?15N and ?13C of four coral reef fishes, Acanthurus nigrofuscus (herbivore), Chaetodon lunulatus (corallivore) , Chromis xanthura (planktivore) and Plectropomus leopardus (piscivore) were investigated at two locations in the Solomon Islands. All four species occupied distinct isotopic niches and the concurrent ?13C' values of C. xanthura and P. leopardus suggested a common planktonic production source. Size-related shifts in ?15N, and thus trophic level, were observed in C. xanthura, C. lunulatus and P. leopardus, and these trends varied between location, indicating spatial differences in trophic ecology. A literature review of tropical fishes revealed that positive ?15N-size trends are common while negative ?15N-size trends are rare. Size-?15N trends fall into approximately equal groups representing size-based feeding within a food chain, and that associated with a basal resource shift and occurs in conjunction with changes in production source, indicated by ?13C. The review also revealed large scale differences in isotope-size trends and this, combined with small scale location differences noted earlier, highlights a high degree of plasticity in the reef fishes studied. This suggests that trophic size analysis of reef fishes would provide a productive avenue to identify species potentially vulnerable to reef impacts as a result of constrained trophic behaviour.

Greenwood, N. D. W.; Sweeting, C. J.; Polunin, N. V. C.

2010-09-01

371

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

372

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

373

Potential probe for examining opiate-receptor interactions: model compound study of dynamic effects on /sup 15/N INEPT enhancements  

SciTech Connect

Model systems were chosen in an attempt to mimic the proton exchange environment of an agonist nitrogen in an opiate-receptor interaction. The two model systems studied were an ammonium: 18-crown-6 ether complex and a quinuclidine-trifluoroacetic acid ion pair. Each system was examined for their effects on /sup 15/N NMR INEPT enhancements. Both models were found to retard proton exchange dynamics, as observed by increased enhancements relative to free ions in neutral aqueous solutions. These results suggest that the confinement of a protonated nitrogen, such as that expected in receptor binding, may alter exchange dynamics to favor INEPT enhancements, while unbound agonists would remain unenhanced. As a result, /sup 15/N NMR INEPT enhancements from a solution of receptor subtypes with an appropriate /sup 15/N-labeled agonist may present a means of exploring the dynamics of direct opiate-receptor interactions.

Schilling, K.H.; Mikita, M.A.

1987-10-01

374

Intramolecular 1H-13C Distance Measurement in Uniformly 13C, 15N Labeled Peptides by Solid-State NMR  

PubMed Central

A 1H-13C frequency-selective REDOR (FS-REDOR) experiment is developed for measuring intramolecular 1H-13C distances in uniformly 13C, 15N-labeled molecules. Theory and simulations show that the experiment removes the interfering homonuclear 1H-1H, 13C-13C and heteronuclear 1H-15N, 13C-15N dipolar interactions while retaining the desired heteronuclear 1H-13C dipolar interaction. Our results indicate that this technique, combined with the numerical fitting, can be used to measure a 1H-13C distance up to 5 Å. We also demonstrate that the measured intramolecular 1H-13C distances are useful to determine dihedral angles in proteins.

Li, Shenhui; Su, Yongchao; Hong, Mei

2012-01-01

375

[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

376

Interactions of /sup 14/N:/sup 15/N stearic acid spin-label pairs: effects of host lipid alkyl chain length and unsaturation  

SciTech Connect

Electron-electron double resonance (ELDOR) and saturation recovery electron paramagnetic resonance (EPR) spectroscopy have been employed to examine the interactions of /sup 14/N:/sup 15/N stearic acid spin-label pairs in fluid-phase model membrane bilayers composed of a variety of phospholipids. The (/sup 14/N)-16-doxylstearate:(/sup 15/N)-16-doxylstearate (16:16) pair was utilized to measure lateral diffusion of the spin-labels, while the (/sup 14/N)-16-doxylstearate:(/sup 15/N)-5-doxylstearate (16:5) pair provided information on vertical fluctuations of the 16-doxylstearate nitroxide moiety toward the membrane surface. Three saturated host lipids of varying alkyl chain length (dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), and distearoylphosphatidylcholine (DSPC)), an ..cap alpha..-saturated, ..beta..-unsaturated lipid (1-palmitoyl-2-oleoylphosphatidylcholine (POPC)), and phosphatidylcholine from a natural source (egg yolk phosphatidylcholine (egg PC)) were utilized as host lipids. Lateral diffusion of the stearic acid spin-labels was only slightly affected by alkyl chain length at a given reduced temperature (T/sub r/) in the saturated host lipids but was significantly decreased in POPC at the same T/sub r/. Lateral diffusion in DMPC, POPC, and egg PC was quite similar at 37/sup 0/C. A strong correlation was noted between lateral diffusion constants and rotational mobility of (/sup 14/N)-16-doxylstearate. Vertical fluctuations were likewise only slightly influenced by alklyl chain length but were strongly diminished in POPC and egg PC relative to the saturated systems. This diminution of the 16:5 interaction was observed even under conditions where no differences were discernible by conventional EPR.

Feix, J.B.; Yin, J.J.; Hyde, J.S.

1987-06-30

377

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

378

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.

2012-01-01

379

New insight in tholin chemical structure through 13C and 15N solid state nuclear magnetic resonance  

NASA Astrophysics Data System (ADS)

Tholins are complex materials synthesized in laboratory as models of the molecules occurring in the atmosphere of Titan. Using labeled gases, pure 13C and 15N-enriched tholins were synthesized and analyzed using 13C and 15N nuclear magnetic resonance. This study allowed confirming the presence of some functional groups (cyano, amino, imino) previously inferred from other techniques and to assess their relative contribution. It also indicated that some other functions (such as carbodiimide, protonated aromatic carbons) if present, only show a very low contribution and ruled out the occurrence of hydrazones.

Derenne, S.; Coelho, C.; Anquetil, C.; Szopa, C.; Quirico, E.; Bonhomme, C.

2011-10-01

380

The fate of nitrogen in grain cropping systems: a meta-analysis of 15N field experiments.  

PubMed

Intensively managed grain farms are saturated with large inputs of nitrogen (N) fertilizer, leading to N losses and environmental degradation. Despite decades of research directed toward reducing N losses from agroecosystems, progress has been minimal, and the currently promoted best management practices are not necessarily the most effective. We investigated the fate of N additions to temperate grain agroecosystems using a meta-analysis of 217 field-scale studies that followed the stable isotope 15N in crops and soil. We compared management practices that alter inorganic fertilizer additions, such as application timing or reduced N fertilizer rates, to practices that re-couple the biogeochemical cycles of carbon (C) and N, such as organic N sources and diversified crop rotations, and analyzed the following response variables: 15N recovery in crops, total recovery of 15N in crops and soil, and crop yield. More of the literature (94%) emphasized crop recovery of 15N than total 15N recovery in crops and soil (58%), though total recovery is a more ecologically appropriate indicator for assessing N losses. Findings show wide differences in the ability of management practices to improve N use efficiency. Practices that aimed to increase crop uptake of commercial fertilizer had a lower impact on total 15N recovery (3-21% increase) than practices that re-coupled C and N cycling (30-42% increase). A majority of studies (66%) were only one growing season long, which poses a particular problem when organic N sources are used because crops recover N from these sources over several years. These short-term studies neglect significant ecological processes that occur over longer time scales. Field-scale mass balance calculations using the 15N data set show that, on average, 43 kg N x ha(-1) x yr(-1) was unaccounted for at the end of one growing season out of 114 kg N x ha(-1) x yr(-1), representing approximately 38% of the total 15N applied. This comprehensive assessment of stable-isotope research on agroecosystem N management can inform the development of policies to mitigate nonpoint source pollution. Nitrogen management practices that most effectively increase N retention are not currently being promoted and are rare on the landscape in the United States. PMID:20014586

Gardner, Jennifer B; Drinkwater, Laurie E

2009-12-01

381

Simultaneous Occurrences of Denitrification and DNRA in Groundwaters: An In Situ 15N Tracer Study  

NASA Astrophysics Data System (ADS)

Understanding nitrogen (N) transformations in groundwater ecosystems is important for the management of N in agricultural systems and to mitigate the effects of reactive N on the environment. In situ groundwater denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were determined at three depths: subsoil (grassland only), bedrock-interface and bedrock (5, 12 and 20 m below ground level, bgl) in intensively managed grassland and arable farming systems. The grassland site had poorly drained soil overlying Ordovician sediments of sandstones and shales. The arable (spring barley) had well drained soil overlying limestone. Denitrification rates were quantified directly using the 15N-enriched nitrate "push-pull" method. Mean (±SE) denitrification rates were significantly higher (p<0.05) in JC (163±153 ?g kg-1 d-1) than in OP (3.9±2.0 ?g kg-1 d-1). In situ denitrification rates were consistently higher at bedrock-interface than in subsoil and bedrock (p>0.05) where the later two were similar. This indicates that denitrification processes are not limited to shallow groundwater rather it is an important process in shallow to deeper groundwaters along groundwater flow paths. In situ N2O/N2O+N2 ratios were significantly higher in OP (0.18±0.02) than in JC (0.08±0.02). Mean (±SE) DNRA rates in JC (3.5±2.3 ?g N kg-1 d-1) were significantly higher (p<0.05) than in OP (2.4±2.1 ?g N kg-1 d-1) and rates were higher at bedrock-interface than in subsoil and bedrock. Total nitrate losses via denitrification plus DNRA were 25 and 0.5% of the injected nitrate, respectively in JC and OP, where contribution of DNRA was low. Poorly drained top and subsoils can create favourable conditions (low dissolved oxygen/redox potential and longer residence time) in groundwater to convert nitrate to benign N2 and NH4+. Conversely, high N input on free draining sites with high dissolved oxygen and redox potential, groundwater can be vulnerable to nitrate contamination and indirect N2O emissions. The contrasting rates of denitrification and DNRA between sites suggest that it can be an important sink for nitrate in some sites, but not in others, depending on hydrogeologic conditions. The strong variation with hydrogeologic conditions suggests that we should be able to spatially predict sites with significant subsurface denitrification capacity.

Jahangir, M. M.; Johnston, P.; Khalil, M. I.; Groffman, P. M.; Richards, K. G.

2011-12-01

382

Amplitudes and directions of internal protein motions from a JAM analysis of 15N relaxation data.  

PubMed

A method has been developed for characterizing dynamic structures of proteins in solution by using nuclear magnetic resonance (NMR) restraints and 15N relaxation data. This method is based on the concept of the jumping-among-minima (JAM) model. In this model we assume that protein dynamics can be described on the basis of conformational substates, and involves intra- and inter-substate motion. A set of substates is created by picking energy-minimized conformations from the conformational space consistent with the geometric NMR restraints. Intra-substate motions, which occur on the timescale of approximately 10 ps, are simulated with molecular dynamics (MD) calculations with force-field energy terms. Statistical weights of the conformational substates are determined to reproduce the NMR relaxation parameters. The refinement procedure consists of four stages: (i) determination of the ensemble of structures that satisfy NMR restraints, (ii) determination of intra-substate fluctuation, (iii) determination of statistical weights of conformational substates to reproduce model-free relaxation parameters, and (iv) analysis of the resulting dynamic structure to determine amplitudes and directions of internal protein motions. This method was employed to investigate structure and dynamics of the adhesion domain of human CD2 (hCD2) in solution. Two major collective modes, whose contributions to atomic mean-square fluctuations are 77.1% in total, are identified by the refinement. The first mode is interpreted as a rigid-body motion of a protein segment consisting of a part of the B--C loop, a part of the F strand, and the F--G loop. Another type of smaller-amplitude mode is indicated for the C'--C'' loop. The motions affect primarily the curvature of the slightly concave counterreceptor-binding site and represent transitions between a concave (closed) and flat (open) binding face. By comparing the ensemble of structures in solution to the complex structure with counterreceptor CD58, we found that these two types of motions resemble the change upon counterreceptor binding. PMID:16823895

Kitao, Akio; Wagner, Gerhard

2006-07-01

383

Trophic subsidies of Crassostrea gigas, Mytilus edulis and Crepidula fornicata in the Bay of Mont Saint Michel (France): A ?13C and ?15N investigation  

NASA Astrophysics Data System (ADS)

This study focussed on the determination of the main trophic subsidies for three dominant filter feeding molluscs of the benthic community, namely, Crassostrea gigas (Thunberg), Mytilus edulis (L.) and Crepidula fornicata (L.), cultivated or naturally occurring in the Bay of Mont Michel (France). ?13C and ?15N values revealed that the diet of these filter feeders was primarily based on marine plankton together with a lower contribution of the organic matter derived from salt marsh phanerogames, as estimated through the isotopic mixing equations (Isosource). The microphytobenthos inhabiting the intertidal flat and the salt marshes do not contribute significantly to the diet of cultivated and naturally occurring C. gigas and M. edulis. Hence, in this bay, the major trophic pathways differ from previous results obtained in several coastal systems devoted to shellfish culture. This could result from ecological particularities and/or strong hydrodynamic conditions in the Bay of Mont Michel.

Riera, Pascal

2007-03-01

384

The first synthesis of [9,Amino-{sup 15}N{sub 2}]adenine and {beta}- 2{prime}-Deoxy-[9,Amino-{sup 15}N{sub 2}]adenosine  

SciTech Connect

{beta}-2{prime}-Deoxy-[9, Amino-{sup 15}N{sub 2}] Adenosine has been constructed in 4 steps from commercially available 5-amino-4,6-dichloropyrimidine and {sup 15}NH{sub 3}. The reactions have been scaled provide grams quantities of labeled nucleoside.

Orji, C.C.; Silks, L.A. III

1995-12-31

385

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·H2O, anhydrous 6mpH, 2,6dmp and 6-mercaptopurinium chloride (6mpH2Cl), confirming the thionic character of all compounds. The 15N chemical shifts in the solid phase were calculated (B3LYP/6 31G**) for 6mpH·H2O and 6mpH2Cl, 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

386

Changes in leaf ? 13C and ? 15N for three Mediterranean tree species in relation to soil water availability  

Microsoft Academic Search

A rain exclusion experiment simulating drought conditions expected in Mediterranean areas for the following decades (15% decrease in soil moisture) was conducted in a Mediterranean holm oak forest to study the response of leaf ?13C, ?15N, and N concentrations to the predicted climatic changes for the coming decades. Plant material was sampled in 2000, 2003, 2004, and 2005 in eight

Romà Ogaya; Josep Peñuelas

2008-01-01

387

13C, 15N CPMAS NMR and GIAO DFT calculations of stereoisomeric oxindole alkaloids from Cat's Claw ( Uncaria tomentosa)  

Microsoft Academic Search

Oxindole alkaloids, isolated from the bark of Uncaria tomentosa [Willd. ex Schult.] Rubiaceae, are considered to be responsible for the biological activity of this herb. Five