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1

15N NATURAL ABUNDANCE AND 15N LABELLING STUDIES IN FOREST ECOSYSTEMS  

EPA Science Inventory

The relative amounts of the two stable isotopes of Nitrogen (N), 15N, and N, vary predictably in soils and plant tissues of forests and other non-cultivated ecosystems. light fractionations, or discriminations against the heavier N isotope, that can occur as N cycles through vege...

2

Symbiotic nitrogen fixation in an arid ecosystem measured by sup 15 N natural abundance  

SciTech Connect

Plants dependent on nitrogen fixation have an {sup 15}N abundance similar to the atmosphere, while non-nitrogen fixing plants usually are enriched in {sup 15}N and are similar to soil nitrogen values. The natural abundance of {sup 15}N in leaf tissues and soils was determined to evaluate symbiotic nitrogen fixation by several legumes and actinorhizal species in the Sevilleta Long-term Ecological Research area in central New Mexico. Comparison of {delta}{sup 15}N values for the legume Prosopis glandulosa (mesquite) to adjacent Atriplex canascens (fourwing saltbush) indicated that P. glandulosa obtained 66% of its nitrogen by fixation. The legume Hoffmanseggia jamesii was found to be utilizing soil nitrogen. The {delta}{sup 15}N values for the actinorhizal plants, Elaeagnus angustifolia and Cercocarpus montanus, while below values for soil nitrogen, did not differ from associated non-fixing plants.

Johnson, G.V. (Univ. of New Mexico, Albuquerque (USA))

1990-05-01

3

Indirectly detected heteronuclear correlation solid-state NMR spectroscopy of naturally abundant 15N nuclei.  

PubMed

Two-dimensional indirectly detected through-space and through-bond (1)H{(15)N} solid-state NMR experiments utilizing fast magic angle spinning (MAS) and homonuclear multipulse (1)H decoupling are evaluated. Remarkable efficiency of polarization transfer can be achieved at a MAS rate of 40 kHz by both cross-polarization and INEPT, which makes these methods applicable for routine characterizations of natural abundance solids. The first measurement of 2D (1)H{(15)N} HETCOR spectrum of natural abundance surface species is also reported. PMID:24287060

Althaus, Stacey M; Mao, Kanmi; Stringer, John A; Kobayashi, Takeshi; Pruski, Marek

2014-01-01

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 (vrzea) 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

Regional patterns of 15N natural abundance in forest ecosystems along a large transect in eastern China  

NASA Astrophysics Data System (ADS)

The regional determining factors underlying inter- and intra-site variation of 15N natural abundance in foliage, O horizon and mineral soil were investigated in eastern China.15N natural abundance values for these forest ecosystems were in the middle of the range of values previously found for global forest ecosystems. In contrast to commonly reported global patterns, temperate forest ecosystems were significantly more15N-enriched than tropical forest ecosystems, and foliage ?15N was negatively correlated with increasing mean annual temperature and net soil N mineralisation in eastern China. Tight N cycling in forest ecosystems and the use of atmospheric N deposition by trees might underlie the ?15N distribution patterns in eastern China. The existence of mycorrhizal fungi and root distribution profiles in the soil may also influence the15N natural abundance patterns in forest ecosystems of eastern China.

Sheng, Wenping; Yu, Guirui; Fang, Huajun; Liu, Yingchun; Wang, Qiufeng; Chen, Zhi; Zhang, Li

2014-02-01

6

Variation in 15N natural abundance of soil, humic fractions and plant materials in a disturbed and an undisturbed grassland  

Microsoft Academic Search

The natural abundance of ?15N in disturbed and undisturbed pasture soils was examined. From the disturbed soil, the top 10?cm of the profile was examined\\u000a and the soil split into fractions based on particle size. Plant shoot and root material contained similar low enrichments\\u000a in 15N, whereas recently deposited shoot residues were highly enriched. Differences between the soil fractions in

S. J. Kerley; S. C. Jarvis

1997-01-01

7

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

Microsoft Academic Search

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

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

1997-01-01

8

Climate and ecosystem 15N natural abundance along a transect of Inner Mongolian grasslands: Contrasting regional patterns and global patterns  

Microsoft Academic Search

Nitrogen isotopes provide integrated information about nitrogen cycling in terrestrial ecosystems. This study explores the regional patterns of ecosystem 15N abundance along a 1200 km transect in Inner Mongolian grasslands and their relationships with climate. Results indicate that climatic variables control approximately 50% of the variation in ecosystem 15N abundance along the transect. Ecosystem 15N abundance decreases as both mean

Weixin Cheng; Quansheng Chen; Yuqing Xu; Xingguo Han; Linghao Li

2009-01-01

9

Symbiotic nitrogen fixation in an arid ecosystem measured by sup 15 N natural abundance  

Microsoft Academic Search

Plants dependent on nitrogen fixation have an ¹⁵N abundance similar to the atmosphere, while non-nitrogen fixing plants usually are enriched in ¹⁵N and are similar to soil nitrogen values. The natural abundance of ¹⁵N in leaf tissues and soils was determined to evaluate symbiotic nitrogen fixation by several legumes and actinorhizal species in the Sevilleta Long-term Ecological Research area in

Johnson

1990-01-01

10

13C and 15N natural abundance of the soil microbial biomass  

Microsoft Academic Search

Stable isotope analysis is a powerful tool in the study of soil organic matter formation. It is often observed that more decomposed soil organic matter is 13C, and especially 15N-enriched relative to fresh litter and recent organic matter. We investigated whether this shift in isotope composition relates to the isotope composition of the microbial biomass, an important source for soil

Paul Dijkstra; Ayaka Ishizu; Richard Doucett; Stephen C. Hart; Egbert Schwartz; Oleg V. Menyailo; Bruce A. Hungate

2006-01-01

11

Quantifying nitrate retention processes in a riparian buffer zone using the natural abundance of 15N in NO3-.  

PubMed

Quantifying the relative importance of denitrification and plant uptake to groundwater nitrate retention in riparian zones may lead to methods optimising the construction of riparian zones for water pollution control. The natural abundance of 15N in NO3- has been shown to be an interesting tool for providing insights into the NO3- retention processes occurring in riparian zones. In this study, 15N isotope fractionation (variation in delta15N of the residual NO3-) due to denitrification and due to plant uptake was measured in anaerobic soil slurries at different temperatures (5, 10 and 15 degrees C) and in hydroponic systems with different plant species (Lolium perenne L., Urtica dioica L. and Epilobium hirsutum L.). It was found that temperature had no significant effect on isotope fractionation during denitrification, which resulted in a 15N enrichment factor epsilonD of -22.5 +/- 0.6 per thousand. On the other hand, nitrate uptake by plants resulted in 15N isotope fractionation, but was independent of plant species, leading to a 15N enrichment factor epsilonP of -4.4 +/- 0.3 per thousand. By relating these two laboratory-defined enrichment factors to a field enrichment factor for groundwater nitrate retention during the growing season (epsilonR = -15.5 +/- 1.0 per thousand ), the contribution of denitrification and plant uptake to groundwater nitrate retention could be calculated. The relative importance of denitrification and plant uptake to groundwater nitrate retention in the riparian buffer zone was 49 and 51% during spring, 53 and 47% during summer, and 75 and 25% during autumn. During wintertime, high micropore dissolved organic carbon (DOC) concentrations and low redox potentials due to decomposition of the highly productive riparian vegetation probably resulted in a higher denitrification rate and favoured other nitrate retention processes such as nitrate immobilisation or dissimilatory nitrate reduction to ammonium (DNRA). This could have biased the 15N isotope fractionation and led to a low 15N enrichment factor for groundwater nitrate retention during wintertime (-6.2 +/- 0.9 per thousand ). In contradiction to what many other studies suggest, it is possible that due to plant decomposition during the winter period other nitrate transformation processes compete with denitrification. PMID:14648895

Dhondt, Karel; Boeckx, Pascal; Van Cleemput, Oswald; Hofman, Georges

2003-01-01

12

Natural-abundance 15N NMR studies of Turkey ovomucoid third domain. Assignment of peptide 15N resonances to the residues at the reactive site region via proton-detected multiple-quantum coherence  

NASA Astrophysics Data System (ADS)

Heteronuclear two-dimensional 1H{ 15N} multiple-quantum (MQ) spectroscopy has been applied to a protein sample at natural abundance: ovomucoid third domain from turkey ( Meleagris gallopavo), a serine proteinase inhibitor of 56 amino acid residues. Peptide amide 1H NMR assignments obtained by two-dimensional 1H{ 1H} NMR methods (R. Krishnamoorthi and J. L. Markley, unpublished data) led to identification of the corresponding 1H{ 15N} MQ coherence cross peaks. From these, 15N NMR chemical shifts were determined for several specific backbone amide groups of amino acid residues located around the reactive site region of the inhibitor. The results suggest that amide 15N chemical shifts, which are readily obtained in this way, may serve as sensitive probes for conformational studies of proteins.

Ortiz-Polo, Gilberto; Krishnamoorthi, R.; Markley, John L.; Live, David H.; Davis, Donald G.; Cowburn, David

13

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

Microsoft Academic Search

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

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

1995-01-01

14

Symbiotic nitrogen fixation in eight Acacia senegal provenances in dryland clays of the Blue Nile Sudan estimated by the 15 N natural abundance method  

Microsoft Academic Search

The symbiotic biological N2fixation by Acacia senegal was estimated using the 15N natural abundance (?\\u000a \\u0009\\u0009\\u0009\\u0009\\u0009\\u0009\\u0009\\u000915N) procedure on eight provenances collected from different environments and soil types grown in a clay soil in the Blue Nile\\u000a region, Sudan. Balanites aegyptiaca (a non-legume) was used as a non-N2-fixing reference plant to allow 15N-based estimates of the proportion of the Acacia N

El Amin Yousif Raddad; Ahmed Ali Salih; Mohamed Ahmed El Fadl; Vesa Kaarakka; Olavi Luukkanen

2005-01-01

15

Determination of the natural abundance delta15N of nortropane alkaloids by gas chromatography-isotope ratio mass spectrometry of their ethylcarbamate esters.  

PubMed

An important route for the detoxification of tropane alkaloids involves N-demethylation to the nor-compounds followed by further degradation. In order to study the mechanisms of the pertinent reactions, a suitable means to determine the isotope ratios of the substrates and products is required. However, the polarity and functionality of the nortropane compounds makes their analysis as free bases difficult. A method is described which allows both the quantification of nortropane alkaloids and the determination of their natural abundance delta(15)N values. The protocol exploits the derivatisation of the alkaloids by reaction with ethyl chloroformate in aqueous medium and the quantitative extraction of the ensuing ethylcarbamate esters. The improved chromatographic properties of these derivatives gives ample separation of the isomeric nortropine and norpseudotropine for measurement of their delta(15)N (per thousand) values by isotope ratio mass spectrometry interfaced to gas chromatography. Adequate separation could not be achieved with the underivatised compounds. Repeatability and precision are sufficient to allow differences in the delta(15)N values (Deltadelta(15)N) > 0.8 per thousand to be measured, with a standard deviation routinely approximately 0.3 per thousand. The methodology has been tested by determining the changes in the delta(15)N values of nortropine and norpseudotropine during degradation by cell suspension cultures of a Pseudomonas strain expressing a specific capacity for tropine catabolism. The precision and reproducibility are shown sufficient to allow the evolution of the delta(15)N values to be followed during the fermentation. PMID:20024532

Kosieradzka, Katarzyna; Tea, Illa; Gentil, Emmanuel; Robins, Richard J

2010-02-01

16

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

17

Natural 15N abundances of inorganic nitrogen in soil treated with fertilizer and compost under changing soil moisture regimes  

Microsoft Academic Search

This study was conducted to examine whether the applications of N-inputs (compost and fertilizer) having different N isotopic compositions (?15N) produce isotopically different inorganic-N and to investigate the effect of soil moisture regimes on the temporal variations in the ?15N of inorganic-N in soils. To do so, the temporal variations in the concentrations and the ?15N of NH4+ and NO3?

Woo-Jung Choi; Hee-Myong Ro; Sang-Mo Lee

2003-01-01

18

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

PubMed Central

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

Temperton, Vicky M.; Martin, Lea L. A.; Roder, Daniela; Lucke, Andreas; Kiehl, Kathrin

2012-01-01

19

Variations in the Natural (15)N Abundance of Brassica chinensis Grown in Uncultivated Soil Affected by Different Nitrogen Fertilizers.  

PubMed

To further investigate the method of using ?(15)N as a marker for organic vegetable discrimination, the effects of different fertilizers on the ?(15)N in different growing stages of Brassica chinensis (B. chinensis) grown in uncultivated soil were investigated with a pot experiment. B. chinensis was planted with uncultivated soil and different fertilizer treatments and then harvested three times in three seasons consecutively. For the spring experiments in the years of 2011 and 2012, the ?(15)N value of B. chinensis, which increased due to organic manure application and decreased due to chemical fertilizer application, was significantly different (p < 0.05) with manure treatment and chemical treatment. The ?(15)N value of vegetables varied among three growing stages and ranged from +8.6 to +11.5 for the control, from +8.6 to +12.8 for the compost chicken manure treatment, from +2.8 to +7.7 for the chemical fertilizer urea treatment, and from +7.7 to +10.9 for the compost-chemical fertilizer treatment. However, the ?(15)N values observed in the autumn experiment of 2011 without any fertilizer application increased ranging from +13.4 to +15.4, + 11.2 to +17.7, +10.7 to +17.1, and +10.6 to +19.1, respectively, for the same treatments mentioned above. This result was not significantly different between manure treatment and chemical treatment. The ?(15)N values of soil obtained in the spring of 2011 during three growing stages were slightly affected by fertilizers and varied in the range of +1.6 to +2.5 for CK, +4.7 to +6.5 for compost treatment, +2.1 to +2.4 for chemical treatment, and +2.7 to +4.6 for chemical-compost treatment, respectively. High ?(15)N values of B. chinensis were observed in these experiments, which would be useful to supplement a ?(15)N database for discriminating organic vegetables. Although there was a significant difference between manure treatment and chemical treatment, it was still difficult to discriminate whether a labeled organic vegetable was really grown without chemical fertilizer just with a fixed high ?(15)N value, especially for the vegetables planted simultaneously with chemical and compost fertilizer. PMID:25369912

Yuan, Yuwei; Hu, Guixian; Zhao, Ming; Chen, Tianjin; Zhang, Yongzhi; Zhu, Jiahong; Wang, Qiang

2014-11-26

20

Natural abundance 15N CP/MAS of nylons and aramids: A sensitive technique for examining crystalline composition and conformation in solid polyamides  

NASA Astrophysics Data System (ADS)

We have examined a variety of polyamides and aramids using natural abundance 15N CP/MAS NMR. These have included commercially available A-B and AA-BB nylons, Kevlar and poly(p-benzamide) as well as a number of block and graft copolymers synthesized in our laboratory. Excellent correlation was observed between the type of crystalline form adopted by polyamides (alpha and gamma modifications) and the chemical shift of the rigid amide nitrogens. Values for the two forms center around 84 ppm (relative to glycine at 0 ppm) and 88 ppm, respectively. For some samples, unexplained peaks between the two main crystalline peaks are tentatively assigned to rigid amide conformations that are not X-ray active but are seen by NMR. Aramids show similar complexity. Block and graft copolymers display characteristic peaks for composition (aryl vs alkyl nitrogen substituents) and for conformation and crystallinity.

Powell, Douglas G.; Sikes, Allison M.; Mathias, Lon J.

1988-09-01

21

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

Microsoft Academic Search

Nitrogen fixation by field-grown soybean (Glycine max (L.) Merrill) was assessed by the natural ¹⁵N abundance and ureide methods. The field sites (five) and genotypes (six, plus two levels of inoculation on Bragg) were chosen to provide a range of proportions of plant N derived from nitrogen fixation (P). Genotypes K466, K468, nts 1007, and nts 1116 and Davis were

D. F. Herridge; F. J. Bergersen; M. B. Peoples

1990-01-01

22

Nutrient cycling relative to ? 15 N and ? 13 C natural abundance in a coastal wetland with long-term nutrient additions  

Microsoft Academic Search

Because nitrogen and phosphorus are primary resources for plant, algal, and microbial production, increases in nutrient inputs\\u000a can markedly alter aquatic ecosystems. Coastal wetland plots at Belle W. Baruch Marine Field Laboratory (South Carolina, USA)\\u000a have been amended with nitrogen and phosphorus for ~20years to determine the effects of nutrient loading on coastal wetlands.\\u000a We conducted a survey of ?15N

Melody J. Bernot; Randall J. Bernot; James T. Morris

2009-01-01

23

Original article The response of soil nitrogen and15N natural  

E-print Network

Original article The response of soil nitrogen and15N natural abundance to different amendments. The major sources of N supply to plants are i) the mineralisation of soil nitrogen, ii) the application of nitrogen from residues of N fixing plants. The mineralisation of soil nitrogen is influ- enced by the same

Boyer, Edmond

24

Leaf 15 N abundance of subarctic plants provides field evidence that ericoid, ectomycorrhizal and non-and arbuscular mycorrhizal species access different sources of soil nitrogen  

Microsoft Academic Search

The natural abundance of the nitrogen isotope 15, d15N, was analysed in leaves of 23 subarctic vascular plant species and two lichens from a tree-line heath at 450 m altitude and a fellfield at 1150 m altitude close to Abisko in N. Sweden, as well as in soil, rain and snow. The aim was to reveal if plant species with

Anders Michelsen; Inger K. Schmidt; Sven Jonasson; Chris Quarmby; Darren Sleep

1996-01-01

25

? 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

26

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

NASA Astrophysics Data System (ADS)

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

Smith, Richard L.; BHlke, John Karl; Garabedian, Stephen P.; Revesz, Kinga M.; Yoshinari, Tadashi

2004-07-01

27

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

PubMed Central

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

Poupin, Nathalie; Bos, Cecile; Mariotti, Francois; Huneau, Jean-Francois; Tome, Daniel; Fouillet, Helene

2011-01-01

28

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. PMID:16662517

Shearer, Georgia; Feldman, Lori; Bryan, Barbara A.; Skeeters, Jerri L.; Kohl, Daniel H.; Amarger, Nelle; Mariotti, Franoise; Mariotti, Andr

1982-01-01

29

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

Microsoft Academic Search

Denitrification was measured within a nitrate-contaminated aquifer on Cape Cod, Massachusetts, using natural gradient tracer tests with 15N nitrate. The aquifer contained zones of relatively high concentrations of nitrite (up to 77 ?M) and nitrous oxide (up to 143 ?M) and has been the site of previous studies examining ground water denitrification using the acetylene block technique. Small-scale (1524 m

Richard L. Smith; John Karl Bhlke; Stephen P. Garabedian; Kinga M. Revesz; Tadashi Yoshinari

2004-01-01

30

The use of nitrogen-15 natural abundance in white clover (Trifolium repens L.) to determine nitrogen fixation under different management practices  

Microsoft Academic Search

The 15N natural abundance (?15N) of white clover (Trifolium repens L.) grown in pasture under different management practices was determined. Plants were split into leaflets, petioles and stolons\\u000a and the 15N signature of each tissue was measured. The ?15N of leaflet tissue from plants of two non-N2-fixing species (Lolium perenne L. and Ranunculus repens L.), growing in close proximity to

S. J. Kerley; S. C. Jarvis

1999-01-01

31

Influence of forage preferences and habitat use on 13C and 15N abundance in wild caribou (Rangifer tarandus caribou) and moose (Alces alces) from Canada.  

PubMed

Stable isotope composition (delta(13)C and delta(15)N) of moose (Alces alces) and caribou (Rangifer tarandus) hair from the boreal forest of Jacques-Cartier Park and Cote-Nord (Quebec) and arctic tundra of Queen Maud Gulf and Southampton Island (Nunavut) was investigated as an indicator of dietary preferences and habitat use. Values of delta(13)C(hair) and delta(15)N(hair) in moose were consistently lower compared to those of caribou. This is consistent with the depletion in (13)C and (15)N in the plants preferred by moose, essentially browse (shrub and tree leaves), compared to caribou forage, which included significant amounts of graminoids, lichen and fungi. The delta(13)C(hair) values of caribou differed between closed boreal forest and open-tundra ecosystems. This pattern followed that expected from the canopy effect observed in plant communities. Variation in delta(15)N(hair) values of caribou was probably linked to the effect of different climatic conditions on plant communities. This study underlines the potential of isotopic analysis for studies on diet and habitat selection within a pure C(3) plant environment. PMID:20229388

Drucker, Dorothee G; Hobson, Keith A; Ouellet, Jean-Pierre; Courtois, Rehaume

2010-03-01

32

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 19871988 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

33

Nicotine, acetanilide and urea multi-level2H-,13C- and15N-abundance reference materials for continuous-flow isotope ratio mass spectrometry  

USGS Publications Warehouse

Accurate determinations of stable isotope ratios require a calibration using at least two reference materials with different isotopic compositions to anchor the isotopic scale and compensate for differences in machine slope. Ideally, the S values of these reference materials should bracket the isotopic range of samples with unknown S values. While the practice of analyzing two isotopically distinct reference materials is common for water (VSMOW-SLAP) and carbonates (NBS 19 and L-SVEC), the lack of widely available organic reference materials with distinct isotopic composition has hindered the practice when analyzing organic materials by elemental analysis/isotope ratio mass spectrometry (EA-IRMS). At present only L-glutamic acids USGS40 and USGS41 satisfy these requirements for ??13C and ??13N, with the limitation that L-glutamic acid is not suitable for analysis by gas chromatography (GC). We describe the development and quality testing of (i) four nicotine laboratory reference materials for on-line (i.e. continuous flow) hydrogen reductive gas chromatography-isotope ratio mass-spectrometry (GC-IRMS), (ii) five nicotines for oxidative C, N gas chromatography-combustion-isotope ratio mass-spectrometry (GC-C-IRMS, or GC-IRMS), and (iii) also three acetanilide and three urea reference materials for on-line oxidative EA-IRMS for C and N. Isotopic off-line calibration against international stable isotope measurement standards at Indiana University adhered to the 'principle of identical treatment'. The new reference materials cover the following isotopic ranges: ??2Hnicotine -162 to -45%o, ??13Cnicotine -30.05 to +7.72%, ?? 15Nnicotine -6.03 to +33.62%; ??15N acetanilide +1-18 to +40.57%; ??13Curea -34.13 to +11.71%, ??15Nurea +0.26 to +40.61% (recommended ?? values refer to calibration with NBS 19, L-SVEC, IAEA-N-1, and IAEA-N-2). Nicotines fill a gap as the first organic nitrogen stable isotope reference materials for GC-IRMS that are available with different ??13N values. Comparative ??13C and ??15N on-line EA-IRMS data from 14 volunteering laboratories document the usefulness and reliability of acetanilides and ureas as EA-IRMS reference materials.

Schimmelmann, A.; Albertino, A.; Sauer, P.E.; Qi, H.; Molinie, R.; Mesnard, F.

2009-01-01

34

Correlation between delta13C and delta15N in C4 and C3 plants of natural and artificial sand-binding microhabitats in the Tengger Desert of China  

Microsoft Academic Search

Carbon isotope ratio (?13C) and nitrogen isotope ratio (?15N) of leaf in shrubs and overground matter in herbage were measured on plant species occurring in different aged artificial sand-binding microhabitats, as well as in natural habitat at the south-eastern margin of the Tengger Desert, China. Both ?13C and ?15N of C3 and C4 plants varied widely (?28.12??13C ()??23.77 and ?4.45??15N

Liangju Zhao; Honglang Xiao; Guodong Cheng; Xiaohong Liu; Qiu Yang; Li Yin; Caizhi Li

2010-01-01

35

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

36

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...

37

QUANTITATIVE 15N NMR SPECTROSCOPY  

EPA Science Inventory

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

38

Preliminary studies of the impact of excreted N on cycling and uptake of N in pasture systems using natural abundance stable isotopic discrimination  

Microsoft Academic Search

The possibility of using natural abundance techniques to determine N transformations and flows after deposition of cattle dung has been examined. These preliminary results showed that d15N in dung was greater than in plants growing in association with particular pats. This, and other observational information, indicated that dung pats of different ages were being examined. There were significant variations in

S. J. Kerley; S. C. Jarvis

1996-01-01

39

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

40

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

USGS Publications Warehouse

Effects of anthropogenic nitrogen (N) deposition and the ability of terrestrial ecosystems to store carbon (C) depend in part on the amount of N retained in the system and its partitioning among plant and soil pools. We conducted a meta-analysis of studies at 48 sites across four continents that used enriched 15N isotope tracers in order to synthesize information about total ecosystem N retention (i.e., total ecosystem 15N recovery in plant and soil pools) across natural systems and N partitioning among ecosystem pools. The greatest recoveries of ecosystem 15N tracer occurred in shrublands (mean, 89.5%) and wetlands (84.8%) followed by forests (74.9%) and grasslands (51.8%). In the short term (15N tracer application), total ecosystem 15N recovery was negatively correlated with fine-root and soil 15N natural abundance, and organic soil C and N concentration but was positively correlated with mean annual temperature and mineral soil C:N. In the longer term (318 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 Nha-1yr-1 above which most ecosystems showed net losses of applied 15N tracer in response to N fertilizer addition.

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

2012-01-01

41

Chemical method for nitrogen isotopic analysis of ammonium at natural abundance.  

PubMed

We report a new chemical method to determine the (15)N natural abundance (?(15)N) for ammonium (NH4(+)) in freshwater (e.g., precipitation) and soil KCl extract. This method is based on the isotopic analysis of nitrous oxide (N2O). Ammonium is initially oxidized to nitrite (NO2(-)) by hypobromite (BrO(-)) using previously established procedures. NO2(-) is then quantitatively converted into N2O by hydroxylamine (NH2OH) under strongly acid conditions. The produced N2O is analyzed by a commercially available purge and cryogenic trap system coupled to an isotope ratio mass spectrometer (PT-IRMS). On the basis of a typical analysis size of 4 mL, the standard deviation of ?(15)N measurements is less than 0.3 and often better than 0.1 (3 to 5 replicates). Compared to previous methods, the technique here has several advantages and the potential to be used as a routine method for (15)N/(14)N analysis of NH4(+): (1) substantially simplified preparation procedures and reduced preparation time particularly compared to the methods in which diffusion or distillation is involved since all reactions occur in the same vial and separation of NH4(+) from solution is not required; (2) more suitability for low volume samples including those with low N concentration, having a blank size of 0.6 to 2 nmol; (3) elimination of the use of extremely toxic reagents (e.g., HN3) and/or the use of specialized denitrifying bacterial cultures which may be impractical for many laboratories. PMID:24654992

Liu, Dongwei; Fang, Yunting; Tu, Ying; Pan, Yuepeng

2014-04-15

42

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

PubMed Central

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

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

2010-01-01

43

Positionally dependent 15N fractionation factors in the UV photolysis of N2O determined by high resolution FTIR spectroscopy  

NASA Astrophysics Data System (ADS)

Positionally dependent fractionation factors for the photolysis of isotopomers of N2O in natural abundance have been determined by high resolution FTIR spectroscopy at three photolysis wavelengths. Fractionation factors show clear 15N position and photolysis wavelength dependence and are in qualitative agreement with theoretical models but are twice as large. The fractionation factors increase with photolysis wavelength from 193 to 211 nm, with the fractionation factors at 207.6 nm for 14N15N16O, 15N14N16O and 14N14N18O equal to -66.55,-27.16 and -4910, respectively.

Turatti, F.; Griffith, D. W. T.; Wilson, S. R.; Esler, M. B.; Rahn, T.; Zhang, H.; Blake, G. A.

44

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

45

Positionally dependent 15N fractionation factors in the UV photolysis of N2O determined by high resolution FTIR spectroscopy  

Microsoft Academic Search

Positionally dependent fractionation factors for the photolysis of isotopomers of N2O in natural abundance have been determined by high resolution FTIR spectroscopy at three photolysis wavelengths. Fractionation factors show clear 15N position and photolysis wavelength dependence and are in qualitative agreement with theoretical models but are twice as large. The fractionation factors increase with photolysis wavelength from 193 to 211

F. Turatti; D. W. T. Griffith; S. R. Wilson; M. B. Esler; T. Rahn; H. Zhang; G. A. Blake

2000-01-01

46

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

47

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

PubMed

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

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

2014-01-01

48

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

Microsoft Academic Search

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

Roy Neilson; Brian Boag; Michael Smith

2000-01-01

49

Box-modeling of 15N/14N in mammals.  

PubMed

The 15N/14N signature of animal proteins is now commonly used to understand their physiology and quantify the flows of nutrient in trophic webs. These studies assume that animals are predictably 15N-enriched relative to their food, but the isotopic mechanism which accounts for this enrichment remains unknown. We developed a box model of the nitrogen isotope cycle in mammals in order to predict the 15N/14N ratios of body reservoirs as a function of time, N intake and body mass. Results of modeling show that a combination of kinetic isotope fractionation during the N transfer between amines and equilibrium fractionation related to the reversible conversion of N-amine into ammonia is required to account for the well-established approximately 4 per thousand 15N-enrichment of body proteins relative to the diet. This isotopic enrichment observed in proteins is due to the partial recycling of 15N-enriched urea and the urinary excretion of a fraction of the strongly 15N-depleted ammonia reservoir. For a given body mass and diet delta15N, the isotopic compositions are mainly controlled by the N intake. Increase of the urea turnover combined with a decrease of the N intake lead to calculate a delta15N increase of the proteins, in agreement with the observed increase of collagen delta15N of herbivorous animals with aridity. We further show that the low delta15N collagen values of cave bears cannot be attributed to the dormancy periods as it is commonly thought, but inversely to the hyperphagia behavior. This model highlights the need for experimental investigations performed with large mammals in order to improve our understanding of natural variations of delta15N collagen. PMID:16328553

Balter, Vincent; Simon, Laurent; Fouillet, Hlne; Lcuyer, Christophe

2006-03-01

50

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

51

Complete Thermodynamic Characterization of the Multiple Protonation Equilibria of the Aminoglycoside Antibiotic Paromomycin: A Calorimetric and Natural Abundance 15N NMR Study  

Microsoft Academic Search

The binding of aminoglycoside antibiotics to a broad range of macromolecular targets is coupled to protonation of one or more of the amino groups that typify this class of drugs. Determining how and to what extent this linkage influences the energetics of the aminoglycoside-macromolecule binding reaction requires a detailed understanding of the thermodynamics associated with the protonation equilibria of the

Christopher M. Barbieri; Daniel S. Pilch

2006-01-01

52

Juniperus communis L. ssp. communis at Balnaguard, Scotland: Foliar carbon discrimination (?C) and 15-N natural abundance (?N) suggest gender-linked differences in water and N use  

Microsoft Academic Search

The ecophysiology of stands of Juniperus communis L. ssp. communis at Balnaguard was examined by the relatively non-invasive methods of analysis of foliar C and N and the N and chlorophyll contents of foliar samples of genets of known sex and location in three sub-sites. The ratio of male to female plants was close to 1.0 on the two

Paul W. Hill; L. L. Handley; J. A. Raven

1996-01-01

53

Synthesis and multinuclear NMR study ( 1H, 11B, 13C, 14N, 15N, 31P, 77Se) of N-azolyl-phosphorus compounds  

NASA Astrophysics Data System (ADS)

The synthesis of N-azolyl (pyrrole, pyrazole, 1,2,4-triazole) phosphorus compounds containing P III or P V is described. The title compounds were studied by multinuclear NMR ( 1H, 11B, 13C, 14N, 15N, 31P, 77Se) with particular emphasis on [ 15N]NMR parameters. Experimental details are given for the natural abundance [ 15N]NMR spectra and the advantage of the various techniques is discussed. The comparison between values 1J( 31P 15N azole) and 1J( 31P 15N alkyl) shows that the nature of the lone electron pair of the trigonal nitrogen atoms is of minor importance as far as the changes in the magnitude of the coupling constants are concerned. Sterical interactions and inductive effects are reflected by the [ 15N]NMR parameters. Both P III and P V appear to be very weak ?-acceptors as is evident from ? 15N and ? 13C values. P?N( dp)? interactions are hardly reflected by [ 15N]NMR parameters.

Wrackmeyer, Bernd

54

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

USGS Publications Warehouse

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

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

2009-01-01

55

Differential growth of the fungus Absidia cylindrospora on 13C/15N-labelled media.  

PubMed

Many studies utilise enrichment of stable isotopes as tracers to follow the interactions occurring within soil food webs and methods have been developed to enrich bacteria, soil fauna and plant litter, Here for the first time we attempt to enrich a soil fungus to 99 atom% with (13)C and (15)N stable isotopes. In this study our objectives were to (a) assess whether the saprotrophic zygomycete fungus Absidia cylindrospora could grow on a medium enriched to 99 atom% with (13)C-glucose and (15)N-ammonium chloride, (b) to determine the level of enrichment obtained, and (c) to examine the change in growth rate of this fungus while it was growing on the dually enriched medium. To achieve this, the fungus was grown on agar enriched with (13)C and (15)N to 99 atom% and its growth rate monitored. The results showed that A. cylindrospora would grow on the highly labelled growth medium, but that its rate of growth was affected compared with the rate on either natural abundance media or media highly enriched with a single isotope ((13)C or (15)N). The implications of these results is that although the fungus is able to utilise these heavier isotopes, the biochemical processes involved in growth are affected, and consideration should be given to these differences when using stable isotope tracers in, for example, soil food web studies. PMID:21594920

Crotty, F V; Blackshaw, R P; Murray, P J

2011-06-15

56

Experimental evidence for diel ?15N-patterns in different tissues, xylem and phloem saps of castor bean (Ricinus communis L.).  

PubMed

Nitrogen isotope signatures in plants might give insights in the metabolism and allocation of nitrogen. To obtain a deeper understanding of the modifications of the nitrogen isotope signatures, we determined ?(15)N in transport saps and in different fractions of leaves, axes and roots during a diel course along the plant axis. The most significant diel variations were observed in xylem and phloem saps where ?(15)N was significantly higher during the day compared with during the night. However in xylem saps, this was observed only in the canopy, but not at the hypocotyl positions. In the canopy, ?(15)N was correlated fairly well between phloem and xylem saps. These variations in ?(15)N in transport saps can be attributed to nitrate reduction in leaves during the photoperiod as well as to (15)N-enriched glutamine acting as transport form of N. ?(15)N of the water soluble fraction of roots and leaves partially affected ?(15)N of phloem and xylems saps. ?(15)N patterns are likely the result of a complex set of interactions and N-fluxes between plant organs. Furthermore, the natural nitrogen isotope abundance in plant tissue is not constant during the diel course - a fact that needs to be taken into account when sampling for isotopic studies. PMID:23663089

Peuke, A D; Gessler, A; Tcherkez, G

2013-12-01

57

Diversity and abundance of phosphonate biosynthetic genes in nature  

PubMed Central

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

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

2013-01-01

58

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...

59

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

60

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

PubMed

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

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

2014-01-01

61

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

PubMed Central

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

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

2014-01-01

62

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

63

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

64

Natural variability in abundance of prevalent soybean proteins.  

PubMed

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

Natarajan, Savithiry S

2010-12-01

65

Influence of flooding on delta15N, delta18O, 1delta15N and 2delta15N signatures of N2O released from estuarine soils--a laboratory experiment using tidal flooding chambers.  

PubMed

The influence of flooding on N2O fluxes, denitrification rates, dual isotope (delta18O and delta15N) and isotopomer (1delta15N and 2delta15N) ratios of emitted N2O from estuarine intertidal zones was examined in a laboratory study using tidal flooding incubation chambers. Five replicate soil cores were collected from two differently managed intertidal zones in the estuary of the River Torridge (North Devon, UK): (1) a natural salt marsh fringing the estuary, and 2 a managed retreat site, previous agricultural land to which flooding was restored in summer 2001. Gas samples from the incubated soil cores were collected from the tidal chamber headspaces over a range of flooding conditions, and analysed for the delta18O, delta15N, 1delta15N and 2delta15N values of the emitted N2O. Isotope signals did not differ between the two sites, and nitrate addition to the flooding water did not change the isotopic content of emitted N2O. Under non-flooded conditions, the isotopic composition of the emitted N2O displayed a moderate variability in delta18O and 2delta15N delta values that was expected for microbial activity associated with denitrification. However, under flooded conditions, half of the samples showed strong and simultaneous depletions in 1delta15N and delta18O values, but not in 2delta15N. Such an isotope signal has not been reported in the literature, and it could point towards an unidentified N2O production pathway. Its signature differed from denitrification, which was generally the N2O production pathway in the salt marsh and the managed retreat site. PMID:15282780

Bol, R; Rckmann, T; Blackwell, M; Yamulki, S

2004-01-01

66

Synthesis of [15N]Glutamate from [15N]H4+ and [15N]Glycine by Mitochondria Isolated from Pea and Corn Shoots 1  

PubMed Central

Metabolically competent mitochondria were isolated from pea and corn shoots on Percoll discontinuous density gradients. Rates of synthesis of [15N]glutamate were measured by gas chromatography-mass spectrometry after the incubation of mitochondria with either 2 millimolar [15N] H4+ or [15N]glycine in the presence of 1 millimolar citrate as the respiratory substrate. When [15N]H4+ was provided, mitochondria isolated from light-grown pea shoots synthesized [15N]glutamate with a rate of 2.64 nanomoles per hour per milligram mitochondrial protein. Corn mitochondria produced [15N]glutamate at a rate approximately 11 times greater than the pea mitochondria. Dark treatment during growth for the last 24 hours caused a slight reduction in the rate of synthesis in both species. When [15N]glycine was used, pea mitochondria synthesized [15N]glutamate with a rate of 6.32 nanomoles per hour per milligram protein. Rapid disappearance of [15N]glycine and synthesis of [15N]serine was observed with a molar ratio of 2 glycine to 0.78 serine. The rate of glutamate synthesis was only 0.2% that of serine, due in part to the dilution of [15N]H4+ by the [14N]H4+ pool in the mitochondria. The majority of the [15N]H4+ released from glycine appears to have been released from or remains unmetabolized in the mitochondria. Corn mitochondria showed no apparent disappearance of [15N]glycine and little synthesis of [15N]serine, indicating that our preparation originated primarily from mesophyll cells. Under our conditions of glycine/serine conversion, [15N]glutatmate was synthesized at a rate of 7% of that of [15N]serine synthesis by corn mitochondria. PMID:16664897

Yamaya, Tomoyuki; Oaks, Ann; Rhodes, David; Matsumoto, Hideaki

1986-01-01

67

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

PubMed

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

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

2011-01-01

68

A Computational Framework for High-Throughput Isotopic Natural Abundance Correction of Omics-Level Ultra-High Resolution FT-MS Datasets  

PubMed Central

New metabolomics applications of ultra-high resolution and accuracy mass spectrometry can provide thousands of detectable isotopologues, with the number of potentially detectable isotopologues increasing exponentially with the number of stable isotopes used in newer isotope tracing methods like stable isotope-resolved metabolomics (SIRM) experiments. This huge increase in usable data requires software capable of correcting the large number of isotopologue peaks resulting from SIRM experiments in a timely manner. We describe the design of a new algorithm and software system capable of handling these high volumes of data, while including quality control methods for maintaining data quality. We validate this new algorithm against a previous single isotope correction algorithm in a two-step cross-validation. Next, we demonstrate the algorithm and correct for the effects of natural abundance for both 13C and 15N isotopes on a set of raw isotopologue intensities of UDP-N-acetyl-D-glucosamine derived from a 13C/15N-tracing experiment. Finally, we demonstrate the algorithm on a full omics-level dataset. PMID:24404440

Carreer, William J.; Flight, Robert M.; Moseley, Hunter N. B.

2013-01-01

69

Plant Characteristics Associated with Natural Enemy Abundance at Michigan Native Plants  

E-print Network

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

Landis, Doug

70

Using patch and landscape variables to model bird abundance in a naturally heterogeneous landscape  

Microsoft Academic Search

Regression models were developed to predict relative bird abundance in a naturally heterogeneous landscape using patch and landscape spatial scales. Breeding birds were surveyed with point counts on 140 study sites in 1997 and 1998. Aerial photographs were digitized to obtain habitat patch information, such as area, shape, and edge con- trast. Classified remote-sensing data were gathered to provide information

Gaea E. Crozier; Gerald J. Niemi

2003-01-01

71

Manipulating the abundance of natural enemies in ornamental landscapes with floral resource plants  

Microsoft Academic Search

We manipulated densities of floral resource plants to test the hypothesis that natural enemies would be more abundant in artificial ornamental landscapes that contained high densities of floral resource plants than in landscapes without these plants. We established an experimental landscape consisting of 33m plots that contained a central bed of Euonymus fortunei (Turcz.) and either a low or high

Eric J. Rebek; Clifford S. Sadof; Lawrence M. Hanks

2005-01-01

72

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

E-print Network

New Zealand Natural Sciences (2002) 27: 1-14 Estimating the abundance of banded kokopu (Galaxias (Galaxias fasciatus Gray) in small streams has usually been determined by the labour intensive and invasive for visual counts of banded kokopu by spotlight in summer months. Keywords: banded kokopu - Galaxias

Waikato, University of

73

An Isotopic 15 N Analysis of Ectomycorrhizal Associations and the Effect  

E-print Network

appeared in the fungal abundance and nitrogen content of the hyphae in the soil warming plots hyphae/ g soil, and the nitrogen content of the hyphae ranged from 0.024 to 0.029 mg N/ g soil. The total values. Key Words and Phrases: ectomycorrhizal fungi, 15 N, soil warming plots, hydrolytic, nitrogen

Vallino, Joseph J.

74

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

75

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

76

Quantification of the contribution of biological nitrogen fixation to tropical green manure crops and the residual benefit to a subsequent maize crop using 15N-isotope techniques.  

PubMed

In this study the contribution of biological N2 fixation (BNF) to leguminous green manures was quantified in the field at different sites with different 15N methodologies. In the first experiment, conducted on a Terra Roxa soil in Cuba, the BNF contribution to three legumes (Crotalaria juncea, Mucuna aterrima and Canavalia ensiformis) was quantified by applying 15N-labelled ammonium sulphate to the soil. The second experiment was planted in a very low fertility sandy soil near Rio de Janeiro, and the 15N natural abundance technique was applied to quantify BNF in C. juncea, M. niveum and soybean. In both studies the advantages of using several non-N2-fixing reference plants was apparent and despite the much greater accumulation of the C. juncea in the experiment performed on the fertile soil of Cuba, the above ground contributions of BNF at both sites were similar (40-80 kg N x ha(-1)) and greater than for the other legumes. In a further experiment the possible contribution of root-derived N to the soil/plant system of two of the legumes was quantified using a 15N-leaf-labelling technique performed in pots. The results of this study suggested that total below-ground N could constitute as much as 39 to 49% of the total N accumulated by the legume crops. PMID:11566383

Ramos, M G; Villatoro, M A; Urquiaga, S; Alves, B J; Boddey, R M

2001-10-01

77

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

USGS Publications Warehouse

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

Meier, A.L.

1982-01-01

78

13 C natural abundance variations in carbonates and organic carbon from boreal forest wetlands  

Microsoft Academic Search

13C natural abundance variations were measured in peat soil and vegetation from two contrasting boreal forest wetlands: an upland\\u000a watershed basin and a permanently saturated lowland mire. Evidence of methane oxidation was shown in the permanently saturated\\u000a wetland with ?13C values as low as -97 in carbonate minerals found in floating peat mats. It is postulated that13C depleted CH4

H. M. Rask; J. J. Schoenau

1993-01-01

79

The relative importance of resources and natural enemies in determining herbivore abundance: thistles, tephritids and parasitoids.  

PubMed

1. The relative importance of host-plant resources and natural enemies in influencing the abundance of insect herbivores was investigated in potted plant and natural population experiments, using tephritid (Diptera: Tephritidae) flies, their host plant, creeping thistle Cirsium arvense, and their Hymenoptera parasitoids. 2. Experimental manipulation of host-plant quality (i.e. levels of host-plant nutrients) and resource availability (i.e. the number of buds) increased tephritid abundance. There was no evidence that the seed-feeding tephritid fly Xyphosia miliaria preferentially oviposited on fertilized C. arvense. 3. At low thistle densities, X. miliaria showed a constant rate of resource exploitation. At higher thistle densities, a threshold was detected, above which additional buds were not attacked. 4. Parasitism attack was variable across host (tephritid) densities but levels of parasitism were consistently higher on the fertilized thistles. 5. Experimental manipulation of host-plant quality and resource availability (quantity) not only directly affects the tephritid population but also, indirectly, leads to high rates of parasitism. Both chemical and physical characteristics of host plants affect the performance of natural enemies. 6. Both top-down and bottom-up forces act to influence tephritid abundance, with bottom-up influences appearing to be the most important. PMID:18507695

Walker, Matthew; Hartley, Susan E; Jones, T Hefin

2008-09-01

80

Nitrogen fixation in legumes and actinorhizal plants in natural ecosystems: values obtained using N natural abundance  

Microsoft Academic Search

Background: Nitrogen fixation has been quantified for a range of crop legumes and actinorhizal plants under different agricultural\\/?agroforestry conditions but much less is known of legume and actinorhizal plant N2 fixation in natural ecosystems.Aims: To assess the proportion of total plant N derived from the atmosphere via the process of N2 fixation (%Ndfa) by actinorhizal and legume plants in natural

Mitchell Andrews; Euan K. James; Janet I. Sprent; Robert M. Boddey; Eduardo Gross; Fabio Bueno dos Reis Jr

2011-01-01

81

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.; Bhlke, J.K.

2003-01-01

82

FOLIAR NITROGEN CONCENTRATIONS AND NATURAL ABUNDANCE OF 15N SUGGEST NITROGEN ALLOCATION PATTERNS OF DOUGLAS-FIR AND MYCORRHIZAL FUNGI DURING DEVELOPMENT IN ELEVATED CARBON DIOXIDE CONCENTRATION AND TEMPERATURE  

EPA Science Inventory

In an experiment using Pseudotsuga menziesii (Mirb.) Franco (Douglas-fir) seedlings and a 2x2 factorial design in enclosed mesocosms, temperatures were maintained at ambient or +3.5 degrees C above ambient, and CO2 levels were maintained at ambient or 179 ppm above ambient. Two ...

83

Fractionation of 14N15N16O and 15N14N16O during photolysis at 213 nm  

NASA Astrophysics Data System (ADS)

Motivated by Yung and Miller's [1997] suggestion that N2O is isotopically fractionated during UV photolysis in the stratosphere, we have studied the photolysis rates of the 14N15N16O and 15N14N16O structural isotopomers. In this study, we follow the concentrations of these compounds with FTIR spectroscopy during photolysis at 213 nm. When fitted to a Rayleigh fractionation model, the observations yield single-stage enrichment factors of ?(14N15N16O / 14N14N16O) = -73 5 per mil and ?(15N14N16O / 14N14N16O) = -41 10 per mil. As predicted by Yung and Miller [1997], the photolysis rate of 15N14N16O is faster than 14N15N16O at this wavelength. The magnitude of the observed fractionation, however, is significantly larger than predicted.

Zhang, Hui; Wennberg, Paul O.; Wu, Vincent H.; Blake, Geoffrey A.

84

Nitrogen isotope compositions of the Cooma metamorphic complex, Australia: Implications for 15N-enriched reservoirs  

NASA Astrophysics Data System (ADS)

The well-studied Paleozoic (435 Ma) Cooma metamorphic complex is centered on the township of Cooma 110 km south of Canberra, Australia. It is characterized by a uniform siliciclastic protolith, with a range of metamorphic grade from lowest-grade greenschist- to highest-grade granulite facies; the metamorphic zone index minerals are chlorite, biotite, andalusite, and sillimanite, and migmatite (Johnson and Vernon, 1995). Accordingly, it provides a natural window to investigate the variations of nitrogen concentrations and ? 15N values during prograde metamorphism. Nitrogen contents decrease, whereas ? 15N increase through progressive metamorphic zones from slates containing 250 ppm N, ? 15N = 2.4 permil; through chlorite zone (greenschist facies) with 210 ppm N, ? 15N = 3.2 permil; and the biotite and andalusite zones (amphibolite facies) having 130 ppm N, ? 15N = 3.8 permil, and 125 ppm N, ? 15N = 4.3 permil, respectively; to the sillimanite and migmatite zones (granulate facies) with 71 ppm N, ? 15N = 12.3 permil, and 77 ppm N, ? 15N = 12.9 permil, respectively. These results show: (1) only small ? 15N shifts of 1 to 2 permil from lower greenschist to amphibolite facies metamorphism, consistent with previous empirical studies of the Catalina Schist Complex (Bebout and Fogel, 1992) and the Erzgebirge terrane (Mingram and Brauer, 2001), and experimental studies on the fractionation of nitrogen isotopes (Ader et al., 1998); and (2) large fractionations of 8 to 10% at granulite facies. Low-grade N systematics can be explained by N2-NH4+ exchange at temperatures of 300 to 600oC for Rayleigh distillation or Batch devolatilization, whereas high-grade shifts can be interpreted as NH3-NH4+ exchanges at temperature of 600-730oC using equilibrium models. Archean cherts, at greenschist facies, show a range of ? 15N from -6 to +30 permil, where depleted values have been interpreted as primary, indicative of reducing conditions, and enriched values as metamorphic shifts Beaumont and Robert, 1999; Pinti et al., 2001). The results rule out those interpretations of metamorphic shifts, but rather a ? 15N-enriched reservoir exists (Jia and Kerrich, 2004), as well as locally oxic conditions from low Th/U ratios in 2.7 Ga shales (Jia et al., 2003).

Jia, Y.

2004-05-01

85

The distribution of nitrate 15 N in marine sediments  

E-print Network

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

Sigman, Daniel M.

86

Abundance, growth and allometry of red raspberry ( Rubus idaeus L.) along a natural light gradient in a northern hardwood forest  

Microsoft Academic Search

The effects of a natural light gradient on abundance, growth and allometry of red raspberry (Rubus idaeus L.) was investigated in 1993 in a temperate deciduous forest (near Quebec city, Canada) in which 30% of total basal area had been removed in 1989. One hundred and three 1-m2 plots were sampled to evaluate red raspberry abundance along a light gradient

Jean-Pierre Ricard; Christian Messier

1996-01-01

87

? 15 N of forest soil and understorey vegetation reflect the former agricultural land use  

Microsoft Academic Search

Since the middle of the 19th century, the area covered by forests in France has doubled. These new forests grow on previous\\u000a agricultural lands. We have studied the influence of this agricultural history on the 15N abundance of present-day forests planted on farmlands in the Vosges mountains (north-eastern France) between 1898 and 1930.\\u000a Different types of land use were identified

W. Koerner; E. Dambrine; J. L. Dupouey; M. Benot

1999-01-01

88

Evaluating the source of streamwater nitrate using ??15N and ??18O in nitrate in two watersheds in New Hampshire, USA  

USGS Publications Warehouse

The natural abundance of nitrogen and oxygen isotopes in nitrate can be a powerful tool for identifying the source of nitrate in streamwater in forested watersheds, because the two main sources of nitrate, atmospheric deposition and microbial nitrification, have distinct ??18O values. Using a simple mixing model, we estimated the relative fractions in streamwater derived from these sources for two forested watersheds with markedly different streamwater nitrate outputs. In this study, we monitored ??15N and ?? 18O of nitrate biweekly in atmospheric deposition and in streamwater for 20 months at the Hubbard Brook Experimental Forest, New Hampshire, USA (moderate nitrogen export), and monthly in streamwater at the Bowl Research Natural Area, New Hampshire, USA (high nitrogen export). For rain, ??18O values ranged from +47 to +77??? (mean: +58???) and ??15N from -5 to +1??? (mean: -3???); for snow, ??18O values ranged from +52 to +75??? (mean: +67???) and ?? 15N from -3 to +2??? (mean: -1???). Streamwater nitrate, in contrast to deposition, had ?? 18O values between +12 and +33??? (mean: +18???) and ??15N between -3 and +6??? (mean: 0???). Since nitrate produced by nitrification typically has ?? 18O values ranging from -5 to +15???, our field data suggest that most of the nitrate lost from the watersheds in streamflow was nitrified within the catchment. Our results confirm the importance of microbial nitrogen transformations in regulating nitrogen losses from forested ecosystems and suggest that hydrologic storage may be a factor in controlling catchment nitrate losses. ?? 2004 John Wiley and Sons, Ltd.

Pardo, L.H.; Kendall, C.; Pett-Ridge, J.; Chang, C.C.Y.

2004-01-01

89

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

E-print Network

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

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

2005-04-06

90

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

91

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

PubMed Central

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

Galili, Uri

2013-01-01

92

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

93

Rivermouth Alteration of Agricultural Impacts on Consumer Tissue ?15N  

PubMed Central

Terrestrial agricultural activities strongly influence riverine nitrogen (N) dynamics, which is reflected in the ?15N of riverine consumer tissues. However, processes within aquatic ecosystems also influence consumer tissue ?15N. As aquatic processes become more important terrestrial inputs may become a weaker predictor of consumer tissue ?15N. In a previous study, this terrestrial-consumer tissue ?15N connection was very strong at river sites, but was disrupted by processes occurring in rivermouths (the rivermouth effect). This suggested that watershed indicators of N loading might be accurate in riverine settings, but could be inaccurate when considering N loading to the nearshore of large lakes and oceans. In this study, the rivermouth effect was examined on twenty-five sites spread across the Laurentian Great Lakes. Relationships between agriculture and consumer tissue ?15N occurred in both upstream rivers and at the outlets where rivermouths connect to the nearshore zone, but agriculture explained less variation and had a weaker effect at the outlet. These results suggest that rivermouths may sometimes be significant sources or sinks of N, which would cause N loading estimates to the nearshore zone that are typically made at discharge gages further upstream to be inaccurate. Identifying definitively the controls over the rivermouth effect on N loading (and other nutrients) will require integration of biogeochemical and hydrologic models. PMID:23935980

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

2013-01-01

94

Rivermouth alteration of agricultural impacts on consumer tissue ?(15)N.  

PubMed

Terrestrial agricultural activities strongly influence riverine nitrogen (N) dynamics, which is reflected in the ?(15)N of riverine consumer tissues. However, processes within aquatic ecosystems also influence consumer tissue ?(15)N. As aquatic processes become more important terrestrial inputs may become a weaker predictor of consumer tissue ?(15)N. In a previous study, this terrestrial-consumer tissue ?(15)N connection was very strong at river sites, but was disrupted by processes occurring in rivermouths (the 'rivermouth effect'). This suggested that watershed indicators of N loading might be accurate in riverine settings, but could be inaccurate when considering N loading to the nearshore of large lakes and oceans. In this study, the rivermouth effect was examined on twenty-five sites spread across the Laurentian Great Lakes. Relationships between agriculture and consumer tissue ?(15)N occurred in both upstream rivers and at the outlets where rivermouths connect to the nearshore zone, but agriculture explained less variation and had a weaker effect at the outlet. These results suggest that rivermouths may sometimes be significant sources or sinks of N, which would cause N loading estimates to the nearshore zone that are typically made at discharge gages further upstream to be inaccurate. Identifying definitively the controls over the rivermouth effect on N loading (and other nutrients) will require integration of biogeochemical and hydrologic models. PMID:23935980

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

2013-01-01

95

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

96

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, Jolle; Mahieu, Stphanie

2010-05-01

97

Seasonal Abundance of the Greenbug and its Natural Enemies in Grain Sorghum in the Texas High Plains.  

E-print Network

BULLETIN LTURAL EXPERIMENT STATION1 J. E. Miller, Director1 Texas A&M University/ College Station, Texas I w B-1162 1 1 December 1975 1 SUMMA1 Rac SEASONAL ABUNDANCE OF THE GREENBUG AND ITS NATURAL ENEMIES IN GRAIN SORGHUM IN THE TEXAS HIGH...BULLETIN LTURAL EXPERIMENT STATION1 J. E. Miller, Director1 Texas A&M University/ College Station, Texas I w B-1162 1 1 December 1975 1 SUMMA1 Rac SEASONAL ABUNDANCE OF THE GREENBUG AND ITS NATURAL ENEMIES IN GRAIN SORGHUM IN THE TEXAS HIGH...

Teetes, George L.; Lopez, Ector G.; Schaefer, Curtis A.

1975-01-01

98

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

USGS Publications Warehouse

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

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

2005-01-01

99

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

PubMed

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

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

2010-07-14

100

Characterization of Stratum Corneum Molecular Dynamics by Natural-Abundance 13C Solid-State NMR  

PubMed Central

Despite the enormous potential for pharmaceutical applications, there is still a lack of understanding of the molecular details that can contribute to increased permeability of the stratum corneum (SC). To investigate the influence of hydration and heating on the SC, we record the natural-abundance 13C signal of SC using polarization transfer solid-state NMR methods. Resonance lines from all major SC components are assigned. Comparison of the signal intensities obtained with the INEPT and CP pulse sequences gives information on the molecular dynamics of SC components. The majority of the lipids are rigid at 32C, and those lipids co-exist with a small pool of mobile lipids. The ratio between mobile and rigid lipids increases with hydration. An abrupt change of keratin filament dynamics occurs at RH?=?8085%, from completely rigid to a structure with rigid backbone and mobile protruding terminals. Heating has a strong effect on the lipid mobility, but only a weak influence on the keratin filaments. The results provide novel molecular insight into how the SC constituents are affected by hydration and heating, and improve the understanding of enhanced SC permeability, which is associated with elevated temperatures and SC hydration. PMID:23626744

Bouwstra, Joke A.; Sparr, Emma; Topgaard, Daniel

2013-01-01

101

A high-sensitivity Mssbauer spectrometer facilitates the study of iron proteins at natural abundance  

NASA Astrophysics Data System (ADS)

A Wide-Angle Mssbauer Spectrometer has been constructed, tested and shown to have approximately ten times the sensitivity of a standard Mssbauer spectrometer. The most innovative feature of the spectrometer is the eighty degree, conical acceptance geometry of its gamma-ray detector, which is constructed of 77 argon gas proportional counters with their associated charge-sensitive preamplifiers and single channel analyzers. The spectrometer has demonstrated the following features: (1) it has approximately 100 times the countrate of most existing Mssbauer spectrometers; (2) velocities reproduce to an accuracy of 0.005 mm/s over periods of several weeks; (3) the temperatures of the source and the sample are regulated with an accuracy of 0.1C in the range of 4.2 to 300 K. By obtaining a high quality Mssbauer spectrum of un-enriched 0.3 mM K 3Fe(CN) 6, we have shown that the study of high molecular weight natural abundance iron proteins can be greatly facilitated by this spectrometer.

Moon, Namdoo; Coffin, C. Tristram; Steinke, David C.; Sands, Richard H.; Dunham, W. Richard

1996-12-01

102

Natural-abundance sup 13 C NMR study of glycogen repletion in human liver and muscle  

SciTech Connect

Optimizing the surface-coil design and spectral-acquisition parameters has led to the observation of the {sup 13}C NMR natural abundance glycogen signal in man at 2.1 T. Both the human muscle and hepatic glycogen signals can be detected definitively with a time resolution of {approx}13 min. A {sup 1}H/{sup 13}C concentric surface coil was used. The {sup 1}H outer coil was 11 cm in diameter; the {sup 13}C inner coil was 8 cm in diameter. The coils were tuned to 89.3 MHz and 22.4 MHz, respectively. The {sup 1}H coil was used for optimizing field homogeneity (shimming) the magnet and for single-frequency decoupling of the C{sub 1} glycogen signal. Total power deposition from both the transmitter pulse and the continuous wave decoupling did not exceed the Food and Drug Administration guideline of 8 W/kg of tissue. Experiments were done for which healthy subjects returned to the magnets at different times for {sup 13}C NMR measurement. The spectral difference between experiments was within the noise in the C{sub 1} glycogen region. Because of the spectral reproducibility and the signal sensitivity, hepatic glycogen repletion can be followed. Four hours postprandial, hepatic glycogen increases by 3.8 times from the basal fasted state. The hepatic glycogen data correspond directly to previous biopsy results and support the use of {sup 13}C NMR as a noninvasive probe of human metabolism.

Jue, T.; Rothman, D.L.; Tavitian, B.A.; Shulman, R.G. (Yale Univ., New Haven, CT (USA))

1989-03-01

103

Characterization of stratum corneum molecular dynamics by natural-abundance C solid-state NMR.  

PubMed

Despite the enormous potential for pharmaceutical applications, there is still a lack of understanding of the molecular details that can contribute to increased permeability of the stratum corneum (SC). To investigate the influence of hydration and heating on the SC, we record the natural-abundance (13)C signal of SC using polarization transfer solid-state NMR methods. Resonance lines from all major SC components are assigned. Comparison of the signal intensities obtained with the INEPT and CP pulse sequences gives information on the molecular dynamics of SC components. The majority of the lipids are rigid at 32C, and those lipids co-exist with a small pool of mobile lipids. The ratio between mobile and rigid lipids increases with hydration. An abrupt change of keratin filament dynamics occurs at RH?=?80-85%, from completely rigid to a structure with rigid backbone and mobile protruding terminals. Heating has a strong effect on the lipid mobility, but only a weak influence on the keratin filaments. The results provide novel molecular insight into how the SC constituents are affected by hydration and heating, and improve the understanding of enhanced SC permeability, which is associated with elevated temperatures and SC hydration. PMID:23626744

Bjrklund, Sebastian; Nowacka, Agnieszka; Bouwstra, Joke A; Sparr, Emma; Topgaard, Daniel

2013-01-01

104

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

PubMed

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

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

2014-02-01

105

Rotational spectrum of deuterated and 15N ethyl cyanides: CH3CHDCN and CH2DCH2CN and of CH3CH2C15N  

E-print Network

Ethyl cyanide is an abundant molecule in hot molecular clouds. Lines from 13C isotopically substituted ethyl cyanide were identified in Orion. 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 of15N substituted ethyl cyanide CH3CH2C15N. 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). 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 for the first time in Orion. The derived column density and rotational temperature are 10^13 cm-2 and 150 K for the plateau and 3 10^14 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 10^14 cm-2.

Laurent Marguls; Roman Motiyenko; Karine Demyk; Belen Tercero; Jose Cernicharo; M. Sheng; M. Weidmann; J. Gripp; H. Mder; J. Demaison

2008-11-07

106

13C- and 15N-NMR spectroscopic examination of the transformation of organic nitrogen in plant biomass during thermal treatment  

Microsoft Academic Search

Structural changes in lignocellulosic biomass heated under conditions comparable to those encountered in several types of natural or planned burnings have been studied by solid-state 13C- and 15N-CPMAS NMR spectroscopy of 15N-enriched ryegrass (Lolium rigidum) after being subjected to progressive thermal treatment. The solid-state 15N-NMR spectra of biomass subjected to severe heating revealed amide-N in forms which are resistant to

H. Knicker; G. Almendros; F. J. Gonzlez-Vila; F. Martin; H.-D. Ldemann

1996-01-01

107

14N15N detectability in Plutos atmosphere  

NASA Astrophysics Data System (ADS)

Based on the vapor pressure behavior of Plutos surface ices, Plutos atmosphere is expected to be predominantly composed of N2 gas. Measurement of the N2 isotopologue 15N/14N ratio within Plutos atmosphere would provide important clues to the evolution of Plutos atmosphere from the time of formation to its present state. The most straightforward way of determining the N2 isotopologue 15N/14N ratio in Plutos 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 Plutos 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 Plutos 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 Plutos 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 Plutos 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

108

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

109

Rotational spectrum of deuterated and 15N ethyl cyanides: CH3CHDCN and CH2DCH2CN and of CH3CH2C15N  

E-print Network

Ethyl cyanide is an abundant molecule in hot molecular clouds. Lines from 13C isotopically substituted ethyl cyanide were identified in Orion. 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 of15N substituted ethyl cyanide CH3CH2C15N. 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). 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 ...

Marguls, Laurent; Demyk, Karine; Tercero, Belen; Cernicharo, Jose; Sheng, M; Weidmann, M; Gripp, J; Mder, H; Demaison, J

2008-01-01

110

The Contamination of Commercial 15N2 Gas Stocks with 15N-Labeled Nitrate and Ammonium and Consequences for Nitrogen Fixation Measurements  

PubMed Central

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

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

2014-01-01

111

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

NASA Astrophysics Data System (ADS)

Natural variations in the ratios of nitrogen isotopes in biomass reflect variations in nutrient sources utilized for growth. In order to use ? 15N values of chloropigments of photosynthetic organisms to determine the corresponding ? 15N values of biomass - and by extension, surface waters - the isotopic offset between chlorophyll and biomass must be constrained. Here we examine this offset in various geologically-relevant taxa, grown using nutrient sources that may approximate ocean conditions at different times in Earth's history. Phytoplankton in this study include cyanobacteria (diazotrophic and non-diazotrophic), eukaryotic algae (red and green), and anoxygenic photosynthetic bacteria (Proteobacteria), as well as environmental samples from sulfidic lake water. Cultures were grown using N 2, NO 3-, and NH 4+ as nitrogen sources, and were examined under different light regimes and growth conditions. We find surprisingly high variability in the isotopic difference (? 15N biomass - ? 15N chloropigment) for prokaryotes, with average values for species ranging from -12.2 to +11.7. We define this difference as ?por, a term that encompasses diagenetic porphyrins and chlorins, as well as chlorophyll. Negative values of ?por reflect chloropigments that are 15N-enriched relative to biomass. Notably, this enrichment appears to occur only in cyanobacteria. The average value of ?por for freshwater cyanobacterial species is -9.8 1.8, while for marine cyanobacteria it is -0.9 1.3. These isotopic effects group environmentally but not phylogenetically, e.g., ?por values for freshwater Chroococcales resemble those of freshwater Nostocales but differ from those of marine Chroococcales. Our measured values of ?por for eukaryotic algae (range = 4.7-8.7) are similar to previous reports for pure cultures. For all taxa studied, values of ?por do not depend on the type of nitrogen substrate used for growth. The observed environmental control of ?por suggests that values of ?por could be useful for determining the fractional burial of eukaryotic vs. cyanobacterial organic matter in the sedimentary record.

Higgins, Meytal B.; Wolfe-Simon, Felisa; Robinson, Rebecca S.; Qin, Yelun; Saito, Mak A.; Pearson, Ann

2011-11-01

112

Soil organic matter stability in agricultural land: New insights using ?15N, ?13C and C:N ratio  

NASA Astrophysics Data System (ADS)

Soil organic matter (SOM) contains three times more carbon than in the atmosphere or terrestrial vegetation. This major pool of organic carbon is sensitive to climate change, but the mechanisms for carbon stabilization in soils are still not well understood and the ultimate potential for carbon stabilization is unknown. For predicting SOM dynamics, it is necessary to gain information on the turnover rates or stability of different soil organic carbon pools. The common method to determine stability and age of SOM is the 14C radio carbon technique, which is very expensive and therefore limited in use. Conen et al. (2008) developed a model to estimate the SOM stability based on the isotopic discrimination of 15N natural abundance by soil micro-organisms, and the decreasing C:N ratio during organic matter decomposition. This model has been developed for permanent grasslands in the Swiss Alps under steady-state conditions. The objective of our study was to validate whether this model could be used or adapted, in combination with 13C isotope signatures of SOM, to predict the relative age and stability of SOM fractions in more disturbed agricultural ecosystems. The present study was carried out on soils collected from six long-term experimental trials (from 12 to 50 years) under different agricultural management practices (e.g. no tillage vs conventional tillage, and mulch, fertilizer, green or animal manure application), located in Austria, Belgium, Kenya and China. Top and subsoil were sampled until 80-100 cm depth. Particulate organic matter (POM) fraction was obtained by wet sieving (> 63?m) after sonification and density separation (<1.8 g cm-3). Carbon and nitrogen contents and their stable isotopic ratios (i.e. 15N and 13C) were measured in POM and bulk soils. The mineral associated matter fraction (mOM), as the protected carbon, was calculated by difference to the bulk soil organic carbon. The relative age of the SOM was calculated using the Conen model and preliminary validated by 14C dating. At all sites, the POM has a higher C:N ratio and a lower ?15N signature compared to the mOM fraction. The POM in top soil layers (<30 cm) has a lower C:N ratio than in deep soil. The C:N ratio and ?15N of POM was influenced by agricultural management. The mOM fraction has 53 to 2063 times longer turnover rate than POM, the relative age of the SOM raised with increasing soil depth. The combination of the above results with ?13C data lead to a more comprehensive understanding of the processes underlying SOM dynamics. Tillage practices increased the bulk ?13C signature of the SOM in the deeper subsoil, suggesting the presence of more stable decomposed materials. The results of this research seem to indicate that the model, developed for grasslands, can be used to determine the stability of SOM in agricultural ecosystems. The C:N ratio and ?15N signature of the POM and mOM fraction follow the expected model pattern. The isotopic ?13C signature can further enhance the understanding of the processes driving SOM stability.

Mao, Yanling; Heiling, Maria; De Clercq, Tim; Resch, Christian; Aigner, Martina; Mayr, Leo; Vanlauwe, Bernard; Thuita, Moses; Steier, Peter; Leifeld, Jens; Merckx, Roel; Spiegel, Heide; Cepuder, Peter; Nguyen, Minh-Long; Zaman, Mohammad; Dercon, Gerd

2014-05-01

113

Natural-abundance 13C nuclear-magnetic-resonance study of toxin II from Anemonia sulcata.  

PubMed

Natural-abundance 13C NMR spectra (at 15.04 MHz) of the polypeptide toxin II from the sea anemone Anemonia sulcata have been analysed and compared with corresponding spectra reported recently for a closely related polypeptide anthopleurin A. The spectra contain many resolved one-carbon and two-carbon resonances from carbonyl, aromatic and methyl carbons, many of which have been assigned to individual carbons in the molecule on the basis of their chemical shifts, including their pH dependence, and by comparison with the 13C NMR spectrum of anthopleurin A. Analysis of the effects of pH on the spectrum yields estimates for the pKa values of a number of functional groups in the molecule, as follows: side-chain carboxylates of the two aspartic acid residues 2 and 3.1; COOH-terminal carboxylic acid, 3.5; imidazolium moieties of the two histidine residues, 6.7 and 7.6 NH2-terminal ammonium, 8. The similarity between the pKa values of these functional groups in toxin II and those of corresponding groups in anthopleurin A, together with the close agreement between chemical shifts of conserved carbons, indicates that many local interactions are nearly identical in the two molecules, and thus supports the thesis that their overall conformations in solution are similar. However, the local interactions involving one of the aspartic acid residues are altered in toxin II. Together with other data, this leads to a proposal for the site in these two molecules which is responsible for their cardiac stimulatory activity. PMID:6109631

Norton, R S; Zwick, J; Bress, L

1980-12-01

114

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

SciTech Connect

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

Leopold, M.F.

1990-01-01

115

Far-infrared spectrum of 15N16O2  

Microsoft Academic Search

The far-infrared spectrum of 15N16O2 has been observed in the 30 to 180 cm-1 region with a resolution of 0.03 cm-1. In order to fit high K energy levels, it was necessary to use three higher order centrifugal distortion terms in addition to a set of parameters previously determined by microwave spectroscopy. The ground state parameters were obtained by fitting

Yoshiaki Hamada; Naoki Tanaka; Masamichi Tsuboi

1988-01-01

116

The 15N ground state studied with elastic electron scattering  

Microsoft Academic Search

The C0 elastic electron scattering form factor of 15N has been measured over a momentum transfer range q=0.4-3.2 fm-1. From these form factor data the ground state charge density and its RMS radius (2.612+\\/-0.009 fm) were determined. This charge density as well as its difference with that of 16O were compared to recent large-basis shell-model calculations. Although these calculations describe

J. W. de Vries; D. Doornhof; C. W. de Jager; R. P. Singhal; S. Salem; G. A. Peterson; R. S. Hicks

1988-01-01

117

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

Microsoft Academic Search

The isotopic composition of nitrogen was measured in marine and fresh-water animals from the East China Sea, The Bering Sea, Lake Ashinoko and Usujiri intertidal zone. Primary producers, showed average 15 N versus atmospheric nitrogen of +5.0%. (+3.4 to +7.5) in the Bering Sea and Lake Ashinoko, and +6.8%. (+6.0 to +7.6) in Usujiri intertidal zone. Blue green algae from

Masao Minagawa; Eitaro Wada

1984-01-01

118

Accurate rest frequencies for the submillimetre-wave lines of the 15{N}-containing isotopologues of N2H+ and N2D^+  

NASA Astrophysics Data System (ADS)

The submillimetre-wave spectrum of the molecular ions N15NH^+, 15NNH^+, N15ND^+, and 15NND+ have been investigated in the laboratory using a source-modulation microwave spectrometer equipped with a negative glow discharge cell. The diazenylium ion was produced in a Ar/N2/H2(D2) discharge plasma and the 15N-containing isotopologues were observed in natural abundance. Six new rotational transitions for the protonated species and seven for the deuterated ones were accurately measured in the frequency range 270-760 GHz. These new laboratory measurements of the rare isotopologues of N2H+ provide very precise rest frequencies at millimetre and submillimetre wavelengths useful for the radioastronomical identification of their rotational lines in the ISM.

Dore, L.; Bizzocchi, L.; Degli Esposti, C.; Tinti, F.

2009-03-01

119

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

PubMed

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

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

2013-01-01

120

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

PubMed Central

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

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

2013-01-01

121

Natural-abundance radiocarbon as a tracer of assimilation of petroleum carbon by bacteria in salt marsh sediments  

Microsoft Academic Search

The natural abundance of radiocarbon (14C) provides unique insight into the source and cycling of sedimentary organic matter. Radiocarbon analysis of bacterial phospholipid lipid fatty acids (PLFAs) in salt-marsh sediments of southeast Georgia (USA)---one heavily contaminated by petroleum residues---was used to assess the fate of petroleum-derived carbon in sediments and incorporation of fossil carbon into microbial biomass. PLFAs that are

Stuart G. Wakeham; Ann P. McNichol; Joel E. Kostka; Tamara K. Pease

2006-01-01

122

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

PubMed Central

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

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

2012-01-01

123

Preferences for 15N-ammonium, 15N-nitrate, and 15N-glycine differ among dominant exotic and subordinate native grasses from a California oak woodland  

Microsoft Academic Search

Following an invasion of exotic annual grasses into California oak woodlands, grass species dominance shifted from native perennials to exotic annuals. In combination with other ecosystem and species characteristics, species-specific N preferences may influence species coexistence and dominance. If species N preferences follow dominance patterns in California oak woodlands, then the more dominant exotic grasses should prefer the most abundant

Zachary T. Aanderud; Caroline S. Bledsoe

2009-01-01

124

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

PubMed

Understanding how individual species contribute to nutrient transformations in a microbial community is critical to prediction of overall ecosystem function. We conducted microcosm experiments in which floating acid mine drainage (AMD) microbial biofilms were submerged - recapitulating the final stage in a natural biofilm life cycle. Biofilms were amended with either (15) NH4 (+) or deuterium oxide ((2) H2 O) and proteomic stable isotope probing (SIP) was used to track the extent to which different members of the community used these molecules in protein synthesis across anaerobic iron-reducing, aerobic iron-reducing and aerobic iron-oxidizing environments. Sulfobacillus spp. synthesized (15) N-enriched protein almost exclusively under iron-reducing conditions whereas the Leptospirillum spp. synthesized (15) N-enriched protein in all conditions. There were relatively few (15) N-enriched archaeal proteins, and all showed low atom% enrichment, consistent with Archaea synthesizing protein using the predominantly (14) N biomass derived from recycled biomolecules. In parallel experiments using (2) H2 O, extensive archaeal protein synthesis was detected in all conditions. In contrast, the bacterial species showed little protein synthesis using (2) H2 O. The nearly exclusive ability of Archaea to synthesize proteins using (2) H2 O may be due to archaeal heterotrophy, whereby Archaea offset deleterious effects of (2) H by accessing (1) H generated by respiration of organic compounds. PMID:24750948

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

2014-10-01

125

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 -24.40.2\\permil, similar to the measured value of the gasoline used; ? 18O =30.00.4\\permil; ? 47=6.70.6\\permil; and ? 47=0.410.03\\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 (-22.30.2 and 34.40.3\\permil, respectively), ? 47 of 13.50.4\\permil, but ? 47 of 0.740.02\\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

126

Nitrogen-containing compounds in two CR2 meteorites: 15N composition, molecular distribution and precursor molecules  

NASA Astrophysics Data System (ADS)

Amino acids, amines and aldehydes were obtained from the water extracts of two CR2 carbonaceous chondrites from Antarctica and analyzed for their molecular and 15N isotopic content. These compounds were found to differ significantly from those of CM chondrites in both overall abundances and molecular distribution. The amino acids suites comprise a preponderant abundance of linear, 2-H amino acids, show rapid non-linear decrease with the compounds' increasing chain length and include protein amino acids never identified in meteorites before, such as threonine, tyrosine and phenylalanine. The presence of tertiary amines as well as a diverse, large abundance of aldehydes and ketones also distinguishes both CR2 organic suites. The ? 15N values determined for CR2 amino acids have a distribution between molecular subgroups that is opposite to the one of their ?D values, with 2-H amino acids having higher ? 15N and lower ?D values than 2-methyl amino acids, while the opposite is true for 2-methyl amino acids. Based on theoretical data, these isotopic findings would place the formation of the two amino acid groups or their direct precursors at different ISM stages of star formation.

Pizzarello, Sandra; Holmes, William

2009-04-01

127

MBE growth of GaN using 15N isotope for nuclear magnetic resonance applications  

NASA Astrophysics Data System (ADS)

Nuclear magnetic resonance (NMR) is a powerful tool for chemical and structural analysis. We have grown zinc-blende GaN using high-purity 15N isotope gas by plasma-assisted molecular beam epitaxy and have studied the material using NMR measurements. We have detected, using NMR, optically pumped enhancement of 15N nuclear polarization in zinc-blende Ga 15N. Initial NMR results of the optically pumped 15N polarization in Ga 15N are discussed.

Novikov, S. V.; Morris, R. D.; Kent, A. J.; Geen, H. L.; Foxon, C. T.

2007-04-01

128

Unveiling the Nature of the "Green Pea" Galaxies: Oxygen and Nitrogen Chemical Abundances  

NASA Astrophysics Data System (ADS)

We present recent results on the oxygen and nitrogen chemical abundances in the extremely compact, low-mass starburst galaxies at redshifts 0.1-0.3 usually referred to as "green pea" galaxies. We show that they are metal-poor galaxies (~1/5 solar) with lower oxygen abundances than star-forming galaxies of similar mass and N/O ratios unusually high for galaxies of the same metallicity. Recent, rapid, and massive inflows of cold gas, possibly coupled with enriched outflows from supernova winds, are used to explain the results. This is consistent with the known "pea" galaxy properties and suggest that these rare objects are experiencing a short and extreme phase in their evolution.

Amorn, R. O.; Prez-Montero, E.; Vlchez, J. M.

2011-07-01

129

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

E-print Network

The class of meteorites called carbonaceous chondrites are examples of material from the solar system which have been relatively unchanged from the time of their initial formation. These meteorites have been classified according to the temperatures and physical conditions of their parent planetesimals. We collate available data on amino acid abundance in these meteorites and plot the concentrations of different amino acids for each meteorite within various meteorite subclasses. We plot average concentrations for various amino acids across meteorites separated by subclass and petrologic type. We see a predominance in the abundance and variety of amino acids in CM2 and CR2 meteorites. The range in temperature corresponding to these subclasses indicates high degrees of aqueous alteration, suggesting aqueous synthesis of amino acids. Within the CM2 and CR2 subclasses, we identify trends in relative frequencies of amino acids to investigate how common amino acids are as a function of their chemical complexity. The...

Cobb, Alyssa K

2014-01-01

130

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

NASA Astrophysics Data System (ADS)

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

Cobb, Alyssa K.; Pudritz, Ralph E.

2014-03-01

131

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

Microsoft Academic Search

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

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

1982-01-01

132

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

PubMed Central

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

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

2014-01-01

133

13C and 15N stabilization dynamics in soil organic matter fractions during needle and fine root decomposition  

Microsoft Academic Search

Little is known about how the chemical composition of plant litter affects the amount and nature of C and N stabilized as soil organic matter (SOM). We examined the fate of dual labeled 13C and 15N Ponderosa pine fine roots (<2mm) and needles decomposing for 2yr in situ in a temperate conifer forest soil in the Sierra Nevada, CA, USA.

Jeffrey A. Bird; Markus Kleber; Margaret S. Torn

2008-01-01

134

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

EPA Science Inventory

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

135

Apelin, the natural ligand of the orphan receptor APJ, is abundantly secreted in the colostrum  

Microsoft Academic Search

By using a strategy that we have developed to search for the ligands of orphan seven-transmembrane-domain receptors [S. Hinuma et al., Nature 393 (1998) 272276], we have recently identified a natural ligand, apelin, for the orphan 7TMR, APJ [K. Tatemoto et al., Biochem. Biophys. Res. Commun. 251 (1998) 471476]. In this paper, we isolated rat and mouse apelin cDNAs, and

Yugo Habata; Ryo Fujii; Masaki Hosoya; Shoji Fukusumi; Yuji Kawamata; Shuji Hinuma; Chieko Kitada; Naoki Nishizawa; Shinji Murosaki; Tsutomu Kurokawa; Haruo Onda; Kazuhiko Tatemoto; Masahiko Fujino

1999-01-01

136

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

Microsoft Academic Search

The abundances of natural 14C in dissolved organic carbon (DOC) in the marine environment hold clues regarding the processes that influence the biogeochemical cycling of this large carbon reservoir. At present, UV irradiation is the widely accepted method for oxidizing seawater DOC for determination of their 14C abundances. This technique yields precise and accurate values with low blanks, but it

L. Johnson; T. Komada

2010-01-01

137

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

PubMed Central

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

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

2014-01-01

138

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

139

New flaxseed orbitides: Detection, sequencing, and (15) N incorporation.  

PubMed

Three new orbitides (cyclolinopeptides 17, 18, and 19) were identified in flaxseed (Linum usitatissimum L.) extracts without any form of purification. Their structures were elucidated by a combination of (15) N-labeling experiments and extensive tandem mass spectrometry (MS/MS) with electrospray ionization (ESI). Putative linear peptide sequences of the new orbitides were used as the query in the Basic Local Alignment Search Tool (BLAST) searches of flax genome database. These searches returned linear sequences for the putative precursors of cyclolinopeptides 17 and 19 among others. Cyclolinopeptide 18 contains MetO (O) and is not directly encoded, but is a product of post-translation modification of the Met present in 17. The identification of precursor proteins in flax mRNA transcripts and DNA sequences confirmed the occurrence and amino acid sequences of these orbitides as [1-9-N?C]-MLKPFFFWI, [1-9-N?C]-OLKPFFFWI, and [1-9-N?C]-GIPPFWLTL for cyclolinopeptides 17, 18, and 19, respectively. 2014 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 102: 168-175, 2014. PMID:24408479

Okinyo-Owiti, Denis P; Young, Lester; Burnett, Peta-Gaye G; Reaney, Martin J T

2014-03-01

140

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

Microsoft Academic Search

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

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

2000-01-01

141

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

USGS Publications Warehouse

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

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

2011-01-01

142

Interactions Among Flower-Size QTL of Mimulus guttatus Are Abundant but Highly Variable in Nature  

PubMed Central

The frequency and character of interactions among genes influencing complex traits remain unknown. Our ignorance is most acute for segregating variation within natural populations, the epistasis most relevant for quantitative trait evolution. Here, we report a comprehensive survey of interactions among a defined set of flower-size QTL: loci polymorphic within a single natural population of yellow monkeyflower (Mimulus guttatus). We find that epistasis is typical. Observed phenotypes routinely differ from those predicted on the basis of direct allelic affects in the isogenic background, although the direction of deviations is highly variable. Across QTL pairs, there are significantly positive and negative interactions for every trait. Across traits, specific locus pairs routinely exhibit both positive and negative interactions. There was a tendency for negative epistasis to accompany positive direct effects and vice versa for the trait of corolla width, which may be due, at least in part, to the fact that QTL were identified from their direct effects on this trait. PMID:21926295

Kelly, John K.; Mojica, Julius P.

2011-01-01

143

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

144

1H, 15N and 13C NMR Assignments of Mouse Methionine Sulfoxide Reductase B2  

PubMed Central

A recombinant mouse methionine-r-sulfoxide reductase 2 (MsrB2?S) isotopically labeled with 15N and 15N/13C was generated. We report here the 1H, 15N and 13C NMR assignments of the reduced form of this protein. PMID:19636904

Breivik, Ashild S.; Aachmann, Finn L.; Sal, Lena S.; Kim, Hwa-Young; Del Conte, Rebecca; Gladyshev, Vadim N.; Dikiy, Alexander

2011-01-01

145

Implications of heterogeneity on procedures for estimating plant 15N recovery in hedgerow intercrop system  

Microsoft Academic Search

Nitrogen flows in agroforestry systems can be quantified by applying excess 15N to one pool or part of the system and subsequently measuring the quantity of 15N in other pools. Accurate quantifications depend on accurate determination of the mass, percentage N, and percentage 15N enrichment of each pool and past studies have mainly used physically isolated subplots to reduce variability.

E. C. Rowe; G. Cadisch

2002-01-01

146

Implications of heterogeneity on procedures for estimating plant 15 N recovery in hedgerow intercrop systems  

Microsoft Academic Search

Nitrogen flows in agroforestry systems can be quantified by applying excess 15N to one pool or part of the system and subsequentlymeasuring the quantity of 15N in other pools. Accurate quantifications depend on accurate determination of the mass, percentage N, and percentage 15N enrichment of each pool and past studies have mainly used physically isolated subplots to reduce variability. We

E. C. Rowe; G. Cadisch

2002-01-01

147

Studies of individual carbon sites of proteins in solution by natural abundance carbon 13 nuclear magnetic resonance spectroscopy. Relaxation behavior.  

PubMed

The aromatic regions in proton-decoupled natural abundance 13C Fourier transform nuclear magnetic resonance spectra (at 14.2 kG) of small native proteins contain broad methine carbon bands and narrow nonprotonated carbon resonances. Some factors that affect the use of natural abundance 13C Fourier transform NMR spectroscopy for monitoring individual nonprotonated aromatic carbon sites of native proteins in solution are discussed. The effect of protein size is evaluated by comparing the 13C NMR spectra of horse heart ferrocytochrome c, hen egg white lysozyme, horse carbon monoxide myoglobin, and human adult carbon monoxide hemoglobin. Numerous single carbon resonances are observed in the aromatic regions of 13C NMR spectra of cytochrome c, lysozyme, and myoglobin. The much larger hemoglobin yields few resolved individual carbon resonances. Theoretical and some experimental values are presented for the natural linewidths (W), spin-lattice relaxation times (T1), and nuclear Overhauser enhancements (NOE) of nonprotonated aromatic carbons and Czeta of arginine residues. In general, the 13C-1H dipolar mechanism dominates the relaxation of these carbons. 13C-14N dipolar relaxation contributes significantly to 1/T1 of C epsilon2 of tryptophan residues and Czeta of arginine residues of proteins in D2O. The NOE of each nonprotonated aromatic carbon is within experimental error of the calculated value of about 1.2. As a result, integrated intensities can be used for making a carbon count. Theoretical results are presented for the effect of internal rotation on W, T1, and the NOE. A comparison with the experimental T1 and NOE values indicates that if there is internal rotation of aromatic amino acid side chains, it is not fast relative to the over-all rotational motion of the protein. PMID:169239

Oldfield, E; Norton, R S; Allerhand, A

1975-08-25

148

Mimicking floodplain reconnection and disconnection using 15N mesocosm incubations  

NASA Astrophysics Data System (ADS)

Floodplain restoration changes the nitrate delivery pattern and dissolved organic matter pool in backwaters, though the effects these changes have are not yet well known. We performed two mesocosm experiments on floodplain sediments to quantify the nitrate metabolism in two types of floodplains. Rates of denitrification, dissimilatory nitrate reduction to ammonium (DNRA) and anammox were measured using 15N-NO3 tracer additions in mesocosms of undisturbed floodplain sediments originating from (1) restored and (2) disconnected sites in the Alluvial Zone National Park on the Danube River downstream of Vienna, Austria. DNRA rates were an order of magnitude lower than denitrification and neither rate was affected by changes in nitrate delivery pattern or organic matter quality. Anammox was not detected at any of the sites. Denitrification was out-competed by assimilation, which was estimated to use up to 70% of the available nitrate. Overall, denitrification was higher in the restored sites, with mean rates of 5.7 2.8 mmol N m-2 h-1 compared to the disconnected site (0.6 0.5 mmol N m-2 h-1). In addition, ratios of N2O : N2 were lower in the restored site indicating a more complete denitrification. Nitrate addition had neither an effect on denitrification, nor on the N2O : N2 ratio. However, DOM (dissolved organic matter) quality significantly changed the N2O : N2 ratio in both sites. Addition of riverine-derived organic matter lowered the N2O : N2 ratio in the disconnected site, whereas addition of floodplain-derived organic matter increased the N2O : N2 ratio in the restored site. These results demonstrate that increasing floodplains hydrological connection to the main river channel increases nitrogen retention and decreases nitrous oxide emissions.

Welti, N.; Bondar-Kunze, E.; Mair, M.; Bonin, P.; Wanek, W.; Pinay, G.; Hein, T.

2012-11-01

149

Mimicking floodplain reconnection and disconnection using 15N mesocosm incubations  

NASA Astrophysics Data System (ADS)

Floodplain restoration changes the nitrate delivery pattern and dissolved organic matter pool in backwaters but other effects are not yet well known. We performed two mesocosm experiments to quantify the nitrate metabolism in two types of floodplains. Rates of denitrification, dissimilatory nitrate reduction to ammonium (DNRA) and anammox were measured using 15N tracer additions in mesocosms containing undisturbed floodplain sediments originating from (1) restored and (2) disconnected sites in the Alluvial Zone National Park on the Danube River downstream of Vienna, Austria. DNRA rates were an order of magnitude lower than denitrification and neither rate was affected by changes in nitrate delivery pattern or organic matter quality. Anammox was not detected at any of the sites. Denitrification was out-competed by assimilation which was estimated to use up to 70% of the available nitrate. Overall, denitrification was higher in the restored sites, with mean rates of 5.72.8 mmol N m-2 h-1 compared to the disconnected site (0.60.5 mmol N m-1 h-1). In addition, ratios of N2O : N2 were lower in the restored site indicating a more complete denitrification. Nitrate addition did not have any effect on denitrification, nor on the N2O : N2 ratio. However, DOM quality significantly changed the N2O : N2 ratio in both sites. Addition of riverine derived organic matter lowered the N2O : N2 ratio in the disconnected site, whereas addition of floodplain derived organic matter increased the N2O : N2 ratio in the restored site. These results demonstrate that increasing floodplains hydrological connection to the main river channel increases nitrogen retention and decreases nitrous oxide emissions.

Welti, N.; Bondar-Kunze, E.; Mair, M.; Bonin, P.; Wanek, W.; Pinay, G.; Hein, T.

2012-04-01

150

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.; Bhlke, J.K.; Yoshinari, T.

1997-01-01

151

Compound specific amino acid ?15N in marine sediments: A new approach for studies of the marine nitrogen cycle  

NASA Astrophysics Data System (ADS)

The nitrogen (N) isotopic composition (?15N) of bulk sedimentary N (?15Nbulk) is a common tool for studying past biogeochemical cycling in the paleoceanographic record. Empirical evidence suggests that natural fluctuations in the ?15N of surface nutrient N are reflected in the ?15N of exported planktonic biomass and in sedimentary ?15Nbulk. However, ?15Nbulk is an analysis of total combustible sedimentary N, and therefore also includes mixtures of N sources and/or selective removal or preservation of N-containing compounds. Compound-specific nitrogen isotope analyses of individual amino acids (?15NAA) are novel measurements with the potential to decouple ?15N changes in nutrient N from trophic effects, two main processes that can influence ?15Nbulk records. As a proof of concept study to examine how ?15NAA can be applied in marine sedimentary systems, we compare the ?15NAA signatures of surface and sinking POM sources with shallow surface sediments from the Santa Barbara Basin, a sub-oxic depositional environmental that exhibits excellent preservation of sedimentary organic matter. Our results demonstrate that ?15NAA signatures of both planktonic biomass and sinking POM are well preserved in such surface sediments. However, we also observed an unexpected inverse correlation between ?15N value of phenylalanine (?15NPhe; the best AA proxy for N isotopic value at the base of the food web) and calculated trophic position. We used a simple N isotope mass balance model to confirm that over long time scales, ?15NPhe values should in fact be directly dependent on shifts in ecosystem trophic position. While this result may appear incongruent with current applications of ?15NAA in food webs, it is consistent with expectations that paleoarchives will integrate N dynamics over much longer timescales. We therefore propose that for paleoceanographic applications, key ?15NAA parameters are ecosystem trophic position, which determines relative partitioning of 15N into source AA versus trophic AA pools, and the integrated ?15NAA of all common protein AA (?15NTHAA), which serves as a proxy for the ?15N of nutrient N. Together, we suggest that these can provide a coupled picture of regime shifts in planktonic ecosystem structure, ?15N at the base of food webs, and possibly additional information about nutrient dynamics.

Batista, Fabian C.; Ravelo, A. Christina; Crusius, John; Casso, Michael A.; McCarthy, Matthew D.

2014-10-01

152

Regional, seasonal and interspecific variation in 15N and 13C in sympatric mouse lemurs  

NASA Astrophysics Data System (ADS)

Madagascar provides some of the rare examples where two or more primate species of the same genus and with seemingly identical niche requirements occur in sympatry. If congeneric primate species co-occur in other parts of the world, they differ in size in a way that is consistent with Hutchinson's rule for coexisting species, or they occupy different ecological niches. In some areas of Madagascar, mouse lemurs do not follow these "rules" and thus seem to violate one of the principles of community ecology. In order to understand the mechanisms that allow coexistence of sympatric congeneric species without obvious niche differentiation, we studied food composition of two identical sized omnivorous mouse lemur species, Microcebus griseorufus and M. murinus with the help of stable isotope analyses ( ? 15N and ? 13C). The two species are closely related sister species. During the rich season, when food seems abundant, the two species do not differ in their nitrogen isotope composition, indicating that the two species occupy the same trophic level. But they differ in their ? 13C values, indicating that M. griseorufus feeds more on C4 and CAM (Crassulacean-acid-metabolism) plants than M. murinus. During the lean season, M. murinus has lower ? 15N values, indicating that the two species feed at different trophic levels during times of food shortage. Hybrids between the two species showed intermediate food composition. The results reflect subtle differences in foraging or metabolic adaptations that are difficult to quantify by traditional observations but that represent possibilities to allow coexistence of species.

Rakotondranary, S. Jacques; Struck, Ulrich; Knoblauch, Christian; Ganzhorn, Jrg U.

2011-11-01

153

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

154

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

PubMed

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

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

2014-04-01

155

Auto-induction medium for the production of [U-15N]- and [U-13C, U-15N]-labeled proteins for NMR screening and structure determination.  

PubMed

Protocols have been developed and applied for the high-throughput production of [U-15N]- or [U-13C-, U-15N]-labeled proteins using the conditional methionine auxotroph Escherichia coli B834. The large-scale growth and expression uses a chemically defined auto-induction medium containing salts and trace metals, vitamins including vitamin B12, and glucose, glycerol, and lactose. The results from nine expression trials in 2-L of the auto-induction medium (500 mL in each of four polyethylene terephthalate beverage bottles) gave an average final optical density at 600 nm of approximately 5, an average wet cell mass yield of approximately 9.5 g L(-1), and an average yield of approximately 20 mg of labeled protein in the six instances in which proteolysis of the fusion protein was observed. Correlations between the cell mass recovered, the level of protein expression, and the relative amounts of glucose, glycerol, and lactose in the auto-induction medium were noted. Mass spectral analysis showed that the purified proteins contained both 15N and 13C at levels greater than 95%. 1H-15N heteronuclear single quantum correlation spectroscopy as well as 13C; 15N-edited spectroscopy showed that the purified [U-15N]- and [U-13C, U-15N]-labeled proteins were suitable for structure analysis. PMID:15766868

Tyler, Robert C; Sreenath, Hassan K; Singh, Shanteri; Aceti, David J; Bingman, Craig A; Markley, John L; Fox, Brian G

2005-04-01

156

NATURAL ABUNDANCES OF CARBON ISOTOPES (14C, 13C) IN LICHENS AND CALCIUM OXALATE PRUINA: IMPLICATIONS FOR ARCHAEOLOGICAL AND PALEOENVIRONMENTAL STUDIES  

Microsoft Academic Search

Radiocarbon ages of calcium oxalate that occurs naturally on rock surfaces have been used recently in archae- ological and paleoenvironmental studies. Oxalate rock coatings are found globally, with most appearing to be residues from epilithic lichens. To explore the source(s) of carbon used by these organisms for the production of oxalate we measured the natural abundances of 14C and 13C

Melanie J Beazley; Richard D Rickman; Debra K Ingram; Thomas W Boutton; Jon Russ

157

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 1,800yr. This evidence suggests that nutrient variability in this region is coordinated with recent changes in global climate and underscores the broad potential of ?15N-AA for paleoceanographic studies of the marine N cycle. PMID:21199952

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

2011-01-01

158

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

PubMed

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 (?(15)N) preserved in sediments and other bioarchives. Traditional bulk ?(15)N 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 (?(15)N-AA) has been shown as a means to deconvolve trophic level versus N source effects on the ?(15)N variability of bulk organic matter. Here, we demonstrate the first use of ?(15)N-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 ?(15)N is correlated with increasing presence of subtropical versus subpolar slope waters over the twentieth century. By using the new ?(15)N-AA approach to control for variable trophic processing, we are able to interpret coral bulk ?(15)N 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 ?(15)N-AA for paleoceanographic studies of the marine N cycle. PMID:21199952

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

2011-01-18

159

Determination of 15N/14N and 13C/12C in Solid and Aqueous Cyanides  

USGS Publications Warehouse

The stable isotopic compositions of nitrogen and carbon in cyanide compounds can be determined by combusting aliquots in sealed tubes to form N2 gas and CO2 gas and analyzing the gases by mass spectrometry. Free cyanide (CN-aq + HCNaq) in simple solutions can also be analyzed by first precipitating the cyanide as copper(II) ferrocyanide and then combusting the precipitate. Reproducibility is ??0.5??? or better for both ??15N and ??13C. If empirical corrections are made on the basis of carbon yields, the reproducibility of ??13C can be improved to ??0.2???. The analytical methods described herein are sufficiently accurate and precise to apply stable isotope techniques to problems of cyanide degradation in natural waters and industrial process solutions.

Johnson, C.A.

1996-01-01

160

Valence structures and magnetic interactions of 1-D mixed-metal complexes, [Ni1-xPdxX(chxn)2]X2 (0.0 ? x ? 1.0, chxn = (1R,2R)-diaminocyclohexane; X = Cl, Br) studied by 15N solid-state NMR  

NASA Astrophysics Data System (ADS)

We performed natural-abundance 15N NMR spectroscopy measurements on 1-D mixed-metal complexes, [Ni1-xPdxX(chxn)2]X2 (0.0 ? x ? 1.0, chxn = (1R,2R)-diaminocyclohexane; X = Cl, Br). The spectra obtained for 15N bonded directly not only to Pd2+and Pd4+, but also to Pd3+, and Ni3+ could be separated from each other more clearly than those obtained previously through 13C NMR measurements. From the results obtained, a spin structure model in which several Pd2+ and Pd4+ sites next to Ni3+ sites in 1-D chains are converted into paramagnetic Pd3+ was shown, and the conversion ratio into Pd3+ was estimated.

Kimura, Noriyoshi; Tanaka, Masahiko; Shimizu, Tadashi; Ikeda, Ryuichi

2014-08-01

161

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

PubMed Central

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

Eldegard, Katrine; Sonerud, Geir A.

2009-01-01

162

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

PubMed

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

Eldegard, Katrine; Sonerud, Geir A

2009-05-01

163

Sources of material for 'loess' deposits at 15N in North Africa  

NASA Astrophysics Data System (ADS)

Africa is not a loess-rich continent. Lacking are the large expanses of glacial terrain and the high cold mountain regions, which would have provided the material and processes for loess deposits. African geomorphology and climatic history did not favour the formation of major loess deposits. However, within the African setting there are situations which could lead to particle formation and loess deposition. Loess deposits are made from 'large' dust (i.e. particles around 30m). Small dust (around 3m) is generated in large amounts in Africa, and distributed over large distances. Large dust is not generated in significant amounts in Africa, and this accounts for the relative lack of loess deposits. It is a relative lack; examination of the map of loess distribution in the World by Scheidig 1934 (still the best world loess map) shows some possible loess in Africa. In particular there is a band across the continent at around 15N. We propose some possible sources for this material, and fit these sources into a recently revised deterministic model of loess deposit formation. And look at some exotic but possible indicators of the loessic nature of the 15N band. Three possible material sources are: (1). The Fonta-Djalon highlands to the west of the loess band, (2). The Bodl Depression, towards the centre of the loess band, and (3). The Ethiopian highlands to the east. There is a convenient river associated with the loess band; the Niger rises in the Fonta-Djalon region and carries material through the loess zone. The catchment of the Niger is well placed to receive large dust material from the Bodl depression. Most Bodl material is small dust carried away in high suspension but small amounts of large dust could be transported to the Niger catchment. Material from the Ethiopian highlands makes up the Nile silt but again some could be transported to the west to contribute to the loess band- which is a modest loess deposit. The deposit can be examined with respect to the deterministic model of loess deposit formation which sets out four event aspects which must be accommodated. PTDC: provenance (of material), transportation, deposition and change- all need to be considered when loess deposit genesis is examined. In the case of the 15N loess the P actions are speculative, and probably not very effective. In fact the deposits they deliver, as mapped by Scheidig, still have to be established as genuine loess. There are indicators of loessic nature; one is that they are favoured by tunnel nesting birds, in particular bee-eaters. Merops apiaster (the European bee-eater) travels large distances to nest in the European loess. The bee-eater nesting zones map nicely on to European loess distribution. In the 15N zone there is a concentration of nesting activity by the Northern Carmine bee-eater (Merops nubicus) and we take this as an indicator of ground nature.

McLaren, Sue; Smalley, Ian; O'Hara-Dhand, Ken

2014-05-01

164

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

165

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, Ramn

2013-09-01

166

Dual 13C, 15N labelling of terrestrial slugs (Deroceras reticulatum).  

PubMed

A simple, rapid and cost-effective laboratory method is described for labelling terrestrial slugs simultaneously with 13C and 15N. Slugs (Deroceras reticulatum) were provided with a mixture of [U-13C6]glucose, 15N-enriched lettuce powder, and wheat bran. Assimilation efficiencies for 13C (24.2%) and 15N (27.4%) were not affected by feeding regimes offering ad libitum or restricted access to unlabelled food during the labelling period. Body tissue was significantly more highly enriched in 13C but significantly less in 15N than cutaneous mucus after 15 days. PMID:15370288

Dyckmans, Jens; Schmidt, Olaf

2004-09-01

167

Nutrient Status and ?15N Values in Leaves and Soils: A Cross-Biome Comparison  

NASA Astrophysics Data System (ADS)

Stable nitrogen (N) isotope ratios (?15N) are often assumed to provide an integrated measure of multiple nitrogen cycling processes. For instance, shifts in the bioavailability of soil N forms are thought to alter plant ?15N values. Demonstrating this relationship is important as ecosystems undergo anthropogenic disturbances. We evaluated patterns and implied mechanisms of the N cycle using ecosystem ?15N values from 16 plots in boreal black spruce (Picea mariana) forest and lowland wet tropical forest. Fertilizer N and phosphorus (P) was applied annually for five and 11 years prior to measurement of ecosystem ?15N values. Full sun canopy foliage and soil extractable nitrate, ammonium, and dissolved organic N (DON) were sampled in fertilized and control plots and analyzed for ?15N. In boreal forest, N fertilization reduced DON concentrations and caused a depletion of ?15N in foliage and fungal sporocarps. Of four species occurring in all plots in the tropical forest, one (Alseis blackiana) had increased foliar ?15N values following N fertilization, one (Tetragastris panamensis) had increased foliar ?15N values following P fertilization, and one (Oenocarpus mapora) had increased foliar ?15N following N+P fertilization. Surprisingly, soil nitrate in the boreal forest became substantially 15N-enriched under P fertilization, whereas nitrate in the tropical forest soil was enriched only under N or N+P fertilization. Collectively, nitrate enrichment is likely due to enhanced rates of soil denitrification as evidenced by elevated resin extractable soil nitrate concentrations and close correlations between ?15N and ?18O values. On average, foliar ?15N in tropical trees corresponded well with ?15N in soil nitrate in control and P fertilized plots, but was 2-3% more enriched than DON under N and N+P fertilization. In boreal forests, N and N+P fertilization increased foliar N concentration and ?15N values indicating substantial use of applied fertilizer. Taken together, these results suggest that altering soil fertility changes soil N fractionation pathways and resulting foliar ?15N values, although the direction and magnitude of the changes varies by biome and species, notwithstanding soil types. The utility of ?15N measurements for detecting changes in the N cycle will be discussed.

Mayor, J. R.; Schuur, E. A.; Turner, B. L.; Wright, S. J.

2011-12-01

168

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

E-print Network

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

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

2013-12-31

169

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

170

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.

171

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

USGS Publications Warehouse

Biogeochemical theory emphasizes nitrogen (N) limitation and the many factors that can restrict N accumulation in temperate forests, yet lacks a working model of conditions that can promote naturally high N accumulation. We used a dynamic simulation model of ecosystem N and ?15N to evaluate which combination of N input and loss pathways could produce a range of high ecosystem N contents characteristic of forests in the Oregon Coast Range. Total ecosystem N at nine study sites ranged from 8,788 to 22,667 kg ha?1 and carbon (C) ranged from 188 to 460 Mg ha?1, with highest values near the coast. Ecosystem ?15N displayed a curvilinear relationship with ecosystem N content, and largely reflected mineral soil, which accounted for 9698% of total ecosystem N. Model simulations of ecosystem N balances parameterized with field rates of N leaching required long-term average N inputs that exceed atmospheric deposition and asymbiotic and epiphytic N2-fixation, and that were consistent with cycles of post-fire N2-fixation by early-successional red alder. Soil water ?15NO3 ? patterns suggested a shift in relative N losses from denitrification to nitrate leaching as N accumulated, and simulations identified nitrate leaching as the primary N loss pathway that constrains maximum N accumulation. Whereas current theory emphasizes constraints on biological N2-fixation and disturbance-mediated N losses as factors that limit N accumulation in temperate forests, our results suggest that wildfire can foster substantial long-term N accumulation in ecosystems that are colonized by symbiotic N2-fixing vegetation.

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

2011-01-01

172

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

PubMed Central

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

Affek, Hagit P.; Yakir, Dan

2003-01-01

173

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 sms 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. PMID:19639385

Wilson, Brian D.; Namanja, Andrew T.

2010-01-01

174

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, Andr J; Sharp, Martin J; Fitzsimons, Sean J; Simpson, Myrna J

2012-04-01

175

The use of 15N to measure nitrogen uptake in eutrophic oceans; experimental considerations  

Microsoft Academic Search

The use of 15N to measure the flux of nitrogen compounds has become increasingly popular as the techniques and instrumentation for stable isotope analysis have become more widely available. Questions concerning equations for calculating uptake, effect of isotope dilution (in the case of ammonium), duration of incubation, and relationship between disappearance of a nitrogen com- pound and the 15N uptake

R. C. DUGDALE; F. P. WILKERSON

1986-01-01

176

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

177

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

Microsoft Academic Search

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

Joann K Whalen; H. Henry Janzen

2002-01-01

178

Tracking wind-dispersed seeds using (15) N-isotope enrichment.  

PubMed

Seed dispersal influences a wide range of ecological processes. However, measuring dispersal patterns, particularly long-distance dispersal, has been a difficult task. Marking bird-dispersed seeds with stable (15) N isotopes has been shown to be a user-friendly method to trace seed dispersal. In this study, we determined whether (15) N urea solution could be used to enrich seeds of two common wind-dispersed plants, Eupatorium glaucescens (Asteraceae) and Sericocarpus tortifolius (Asteraceae). We further tested if the water type (distilled versus tap) in (15) N urea solutions influences the level and variability of enrichment of plant seeds, and if increasing spraying frequency per se increases enrichment. Because droughts may lower seed set or kill plants, we wanted to investigate if the additional use of an externally applied anti-transpirant affects the intake of externally applied (15) N into seeds. The results demonstrate that (15) N enrichment of seeds can facilitate dispersal experiments with wind-dispersed plants. The use of distilled water in (15) N urea solutions did not increase (15) N enrichment compared to tap water. Further, enrichment was more efficient at lower spray frequencies. Both the use of tap water and low frequencies could lower time, effort and project costs. The results suggest that species can be protected from drought using an anti-transpirant without decreasing the incorporation of (15) N into seeds. PMID:25174806

Forster, C; Herrmann, J D

2014-11-01

179

Sensitivity of D15 N of nitrate, surface suspended and deep sinking  

E-print Network

Sensitivity of D15 N of nitrate, surface suspended and deep sinking particulate nitrogen to seasonal nitrate depletion in the Southern Ocean Martin J. Lourey1,2 Institute of Antarctic and Southern; accepted 27 May 2003; published 8 August 2003. [1] We report measurements of the d15 N of nitrate

Sigman, Daniel M.

180

Quantifying Ocean Productivity using 15N and Continuous-Flow Mass Spectrometry  

Microsoft Academic Search

15 N, a stable isotope of nitrogen, has an important application in the estimation of oceanic export productivity but less concentration of nitrogen in the samples posses serious problems in marine applications. In recent years, improvements in the mass spectrometry have revolutionized the application of different stable isotopes, especially 15N as tracers, to understand the oceanic processes and their role

Satya Prakash; R. Ramesh

181

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

E-print Network

might be because (Guy et al., 1986a and 1986b). Along a soil water poten- of higher NH3 volatilizationSalinity-induced Patterns of Natural Abundance Carbon-13 and Nitrogen-15 in Plant and Soil Jan-Willem van Groenigen* and Chris van Kessel ABSTRACT vs. C4 ), age of SOM, depth in the profile

van Kessel, Chris

182

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

Microsoft Academic Search

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

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

2007-01-01

183

Ticks (Acari: Ixodida: Ixodidae and Argasidae) abundance and associated risk factors for animals in the natural habitat of Sanandaj suburb, Iran  

Microsoft Academic Search

Ticks have been reported as the most abundant ectoparasites infesting domestic ruminants in Iran. This study reports tick diversity, fauna and seasonal distribution on the domestic ruminants and close surrounding of them in the natural habitat of Sanandaj suburb, Iran, from March 2009 to February 2010. A total number of 1140 ruminants (398 cattle, 508 sheep and 234 goats) in

Mohammad Yakhchali; Kia Bahramnejad; Omid Almasi

2012-01-01

184

15N and13C NMR investigation of hydroxylamine-derivatized humic substances  

USGS Publications Warehouse

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

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

1992-01-01

185

Syntheses of 15N-labeled pre-queuosine nucleobase derivatives  

PubMed Central

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

Levic, Jasmin

2014-01-01

186

The effect of manuring on cereal and pulse amino acid ?(15)N values.  

PubMed

Amino acid ?(15)N values of barley (Hordeum vulgare) and bread wheat (Triticum aestivum) grains and rachis and broad bean (Vicia faba) and pea (Pisum sativum) seeds, grown in manured and unmanured soil at the experimental farm stations of Rothamsted, UK and Bad Lauchstdt, Germany, were determined by GC-C-IRMS. Manuring was found to result in a consistent (15)N-enrichment of cereal grain amino acid ?(15)N values, indicating that manuring did not affect the metabolic routing of nitrogen (N) into cereal grain amino acids. The increase in cereal grain ?(15)N values with manuring is therefore due to a (15)N-enrichment in the ?(15)N value of assimilated inorganic-N. Greater variation was observed in the (15)N-enrichment of rachis amino acids with manuring, possibly due to enhanced sensitivity to changes in growing conditions and higher turnover of N in rachis cells compared to cereal grains. Total amino acid ?(15)N values of manured and unmanured broad beans and peas were very similar, indicating that the legumes assimilated N2 from the atmosphere rather than N from the soil, since there was no evidence for routing of (15)N-enriched manure N into any of the pulse amino acids. Crop amino acid ?(15)N values thus provide insights into the sources of N assimilated by non N2-fixing and N2-fixing crops grown on manured and unmanured soils, and reveal an effect of manure on N metabolism in different crop species and plant parts. PMID:24631496

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

2014-06-01

187

Extreme ultraviolet laser excitation of isotopic molecular nitrogen: The dipole-allowed spectrum of 15N2 and 14N15N  

NASA Astrophysics Data System (ADS)

Extreme ultraviolet+ultraviolet (XUV+UV) two-photon ionization spectra of the b 1?u(v=0-9), c3 1?u(v=0,1), o 1?u(v=0,1), c4' 1?u+(v=1) and b' 1?u+(v=1,3-6) states of 15N2 were recorded with a resolution of 0.3 cm-1 full-width at half-maximum (FWHM). In addition, the b 1?u(v=1,5-7) states of 14N15N were investigated with the same laser source. Furthermore, using an ultranarrow bandwidth XUV laser [~250 MHz (~0.01 cm-1) FWHM], XUV+UV ionization spectra of the b 1?u(v=0-1,5-7), c3 1?u(v=0), o 1?u(v=0), c4' 1?u+(v=0), and b' 1?u+(v=1) states of 15N2 were recorded in order to better resolve the band-head regions. For 14N15N, ultrahigh resolution spectra of the b 1?u(v=0-1,5-6), c3 1?u(v=0), and b' 1?u+(v=1) states were recorded. Rotational analyses were performed for each band, revealing perturbations arising from the effects of Rydberg-valence interactions in the 1?u and 1?u+ states, and rotational coupling between the 1?u and 1?u+ manifolds. Finally, a comprehensive perturbation model, based on the diabatic-potential representation used previously for 14N2, and involving diagonalization of the full interaction matrix for all Rydberg and valence states of 1?u+ and 1?u symmetry in the energy window 100 000-110 000 cm-1, was constructed. Term values for 15N2 and 14N15N computed using this model were found to be in good agreement with experiment.

Sprengers, J. P.; Ubachs, W.; Baldwin, K. G. H.; Lewis, B. R.; Tchang-Brillet, W.-. L.

2003-08-01

188

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

189

Resonance strengths in the 14N(p, ?)15O and 15N(p, ? ?)12C reactions  

E-print Network

The 14N(p, \\gamma)15O 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 15N(p, \\alpha \\gamma)12C reaction is frequently used in inverse kinematics for hydrogen depth profiling in materials. The 14N(p, \\gamma)15O and 15N(p, \\alpha \\gamma)12C reactions have been studied simultaneously, using titanium nitride targets of natural isotopic composition and a proton beam. The strengths of the resonances at Ep = 1058 keV in 14N(p, \\gamma)15O and at Ep = 897 and 430 keV in 15N(p, \\alpha \\gamma)12C have been determined with improved precision, relative to the well-known resonance at Ep = 278 keV in 14N(p, \\gamma)15O. The new recommended values are \\omega \\gamma = 0.353$\\pm$0.018, 362$\\pm$20, and 21.9$\\pm$1.0 eV for their respective strengths. In addition, the branching ratios for the decay of the Ep = 1058 keV resonance in 14N(p, \\gamma)15O have been redetermined. The data reported here should facilitate future studies of off-resonant capture in the 14N(p, \\gamma)15O reaction that are needed for an improved R-matrix extrapolation of the cross section. In addition, the data on the 430 keV resonance in 15N(p, \\alpha \\gamma)12C may be useful for hydrogen depth profiling.

Michele Marta; Erik Trompler; Daniel Bemmerer; Roland Beyer; Carlo Broggini; Antonio Caciolli; Martin Erhard; Zsolt Flp; Eckart Grosse; Gyrgy Gyrky; Roland Hannaske; Arnd R. Junghans; Roberto Menegazzo; Chithra Nair; Ronald Schwengner; Tams Szcs; Simone Vezz; Andreas Wagner; Dmitry Yakorev

2010-05-11

190

15N/ 14N and 18O/ 16O stable isotope ratios of nitrous oxide produced during denitrification in temperate forest soils  

NASA Astrophysics Data System (ADS)

Anaerobic incubations of upland and wetland temperate forest soils from the same watershed were conducted under different moisture and temperature conditions. Rates of nitrous oxide (N 2O) production by denitrification of nitrate ( NO3-) and the stable isotopic composition of the N 2O (? 15N, ? 18O) were measured. In all soils, N 2O production increased with elevated temperature and soil moisture. At each temperature and moisture level, the rate of N 2O production in the wetland soil was greater than in the upland soil. The 15N isotope effect (?) (product - substrate) ranged from -20 to -29. These results are consistent with other published estimates of 15N fractionation from both single species culture experiments and soil incubation studies from different ecosystems. A series of incubations were conducted with 18O-enriched water (H 2O) to determine if significant oxygen exchange (O-exchange) occurred between H 2O and N 2O precursors during denitrification. The exchange of H 2O-O with nitrite ( NO2-) and/or nitric oxide (NO) oxygen has been documented in single organism culture studies but has not been demonstrated in soils prior to this study. The fraction of N 2O-O derived from H 2O-O was confined to a strikingly narrow range that differed between soil types. H 2O-O incorporation into N 2O produced from upland and wetland soils was 86% to 94% and 64% to 70%, respectively. Neither the temperature, soil moisture, nor the rate of N 2O production influenced the magnitude of O-exchange. With the exception of one treatment, the net 18O isotope effect (? net) (product-substrate) ranged from +37 to +43. Most previous studies that have reported 18O isotope effects for denitrification of NO3- to N 2O have failed to account for the effect of oxygen exchange with H 2O. When high amounts of O-exchange occur after fractionation during reductive O-loss, the 18O-enrichment is effectively lost or diminished and ? 18O-N 2O values will be largely dictated by ? 18O-H 2O values and subsequent fractionation. The process and extent of O-exchange, combined with the magnitude of oxygen isotope fractionation at each reduction step, appear to be the dominant controls on the observed oxygen isotope effect. In these experiments, significant oxygen isotope fractionation was observed to occur after the majority of water O-exchange. Due to the importance of O-exchange, the net oxygen isotope effect for N 2O production in soils can only be determined using ? 18O-H 2O addition experiments with ? 18O-H 2O close to natural abundance. The results of this study support the continued use of ? 15N-N 2O analysis to fingerprint N 2O produced from the denitrification of NO3-. The utilization of 18O/ 16O ratios of N 2O to study N 2O production pathways in soil environments is complicated by oxygen exchange with water, which is not usually quantified in field studies. The oxygen isotope fractionation observed in this study was confined to a narrow range, and there was a clear difference in water O-exchange between soil types regardless of temperature, soil moisture, and N 2O production rate. This suggests that 18O/ 16O ratios of N 2O may be useful in characterizing the actively denitrifying microbial community.

Snider, David M.; Schiff, Sherry L.; Spoelstra, John

2009-02-01

191

Effect of High-energy Resonances on the 18O(p, ?)15N Reaction Rate at AGB and Post-AGB Relevant Temperatures  

NASA Astrophysics Data System (ADS)

The 18O(p, ?)15N reaction is of great importance in several astrophysical scenarios, as it influences the production of key isotopes such as 19F, 18O, and 15N. Fluorine is synthesized in the intershell region of asymptotic giant branch (AGB) stars, together with s-elements, by ? radiative capture on 15N, which in turn is produced in the 18O proton-induced destruction. Peculiar 18O abundances are observed in R-Coronae Borealis stars, having 16O/18O <~ 1, hundreds of times smaller than the galactic value. Finally, there is no definite explanation of the 14N/15N ratio in pre-solar grains formed in the outer layers of AGB stars. Again, such an isotopic ratio is influenced by the 18O(p, ?)15N reaction. In this work, a high accuracy 18O(p, ?)15N 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 19F. In particular, we have focused on the study of the broad 660 keV 1/2+ resonance corresponding to the 8.65 MeV level of 19F. Since ? ~ 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 ~ 0.5 109 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.; Mukhamedzhanov, A. M.

2010-11-01

192

On the measurement of 15N-{ 1H} nuclear Overhauser effects  

NASA Astrophysics Data System (ADS)

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 time scale. 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 as 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 time scales and experimentally verified using a perdeuterated sample of human ubiquitin.

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

2008-06-01

193

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

SciTech Connect

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

Thorn, Kevin A.; Cox, Larry G.

2009-02-28

194

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

NASA Astrophysics Data System (ADS)

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

Leroy, Fanny; Riera, Pascal; Jeanthon, Christian; Edmond, Frdrique; Leroux, Cdric; Comtet, Thierry

2012-05-01

195

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

DOEpatents

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

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

2001-01-01

196

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

197

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

NASA Astrophysics Data System (ADS)

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 1H N 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 (< S2> = 0.81) than the non-saturated ones (< S2> = 0.88), indicating such order parameters may be previously underestimated.

Chen, Kang; Tjandra, Nico

2011-12-01

198

lambda cro repressor complex with O/sub R/3 DNA: /sup 15/N NMR observations  

SciTech Connect

/sup 15/N NMR studies of the coliphage lambda cro repressor are presented. The protein has been uniformly labeled with /sup 15/N, and individual amino acids have been incorporated. Although the four C-terminal residues (63-66) were not located in the original crystallographic studies of the protein it has been proposed that the C-terminus is involved in DNA binding. These experiments give direct verification of that proposal. (/sup 15/N) Amide resonances are assigned for residues 56, 62, 63, and 66 in the C-terminus by enzymatic digestion and by /sup 13/C-/sup 15/N double-labeling experiments. /sup 15/N)/sup 1/H) nuclear Overhauser effects show that the C-terminus is mobile on a nanosecond time scale. Exchange experiments using distortionless enhancement via polarization transfer, which is sensitive to proton exchange on the 1/J/sub NH/(10 ms) time scale, indicate that the amide protons in the C-terminus are freely accessible to solvent. It is thus a flexible arm in solution. The binding of both specific operator and nonspecific DNA is shown to reduce both the mobility and the degree of solvent exposure of this arm. Two-dimensional /sup 15/N-/sup 1/H correlation experiments using /sup 15/N-labeled cro reveal inconsistencies with previously reported /sup 1/H NMR assignments for the lysine amides. This result suggests that those assignments require reexamination, illustrating the utility of /sup 15/N labeling for obtaining /sup 1/H resonance assignments of biomolecules. Furthermore, isomerization of the peptide bond of Pro-59, which has been previously suggested and which would significantly affect the properties of the C-terminal arm, is shown to not occur.

Leighton, P.; Lu, P.

1987-11-17

199

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

NASA Technical Reports Server (NTRS)

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

Sunshine, Jessica M.; Pieters, Carle M.

1993-01-01

200

Determination of organic milk authenticity using carbon and nitrogen natural isotopes.  

PubMed

Natural stable isotopes of carbon and nitrogen ((12)C, (13)C, (14)N, (15)N) have abundances unique to each living creature. Therefore, measurement of the stable isotope ratio of carbon and nitrogen (?(13)C=(13)C/(12)C, ?(15)N=(15)N/(14)N) in milk provides a reliable method to determine organic milk (OM) authenticity. In the present study, the mean ?(13)C value of OM was higher than that of conventional milk (CM), whereas the mean ?(15)N value of OM was lower than that of CM; nonetheless both ?(13)C and ?(15)N values were statistically different for the OM and CM (P<0.05). Furthermore, the values of ?(13)C and ?(15)N were found to differ statistically with the collection date and the milk brand (P<0.05). The combination of ?(13)C and ?(15)N values was more effective than either value alone in distinguishing between OM and CM. The results of the present study, which is based on preliminary data from a limited sample size and sampling period, could be highly valuable and helpful for consumers, the food industry, and/or government regulatory agencies as it can prevent fraudulent labelling of organic food. Further studies include additional analyses of other milk brands and analyses over longer time periods in order to accurately determine OM authenticity using stable isotopes of carbon and nitrogen. PMID:24799230

Chung, Ill-Min; Park, Inmyoung; Yoon, Jae-Yeon; Yang, Ye-Seul; Kim, Seung-Hyun

2014-10-01

201

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

PubMed Central

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

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

2013-01-01

202

Extreme ultraviolet laser excitation of isotopic molecular nitrogen: The dipole-allowed spectrum of 15N2 and 14N15N  

Microsoft Academic Search

Extreme ultraviolet+ultraviolet (XUV+UV) two-photon ionization spectra of the b 1Piu(v=0-9), c3 1Piu(v=0,1), o 1Piu(v=0,1), c4' 1Sigmau+(v=1) and b' 1Sigmau+(v=1,3-6) states of 15N2 were recorded with a resolution of 0.3 cm-1 full-width at half-maximum (FWHM). In addition, the b 1Piu(v=1,5-7) states of 14N15N were investigated with the same laser source. Furthermore, using an ultranarrow bandwidth XUV laser [~250 MHz (~0.01 cm-1)

J. P. Sprengers; W. M. G. Ubachs; K. G. H. Baldwin; B. R. Lewis; W.-. L. Tchang-Brillet

2003-01-01

203

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

204

GEOPHYSICALRESEARCHLETTERS,VOL. 27,NO. 9, PAGES1399-1402,MAY 1,2000 Measurementoftheisotopicfractionationof15N14N160,14N15N160  

E-print Network

%islostviareactionwithO(1D)(R2andR3). N20+hv-->N2+O(1D) (1) N20+O(1D)-->N2+02 (2) N20+ O(1D)-->2NO (3) The UV absorptionspectraof the heavyN20 isotopomers (mainly15N14NO,14NISNo,14N14N170and 14N14N180),are INowat

Peinke, Joachim

205

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

Microsoft Academic Search

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

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

2008-01-01

206

Comparison of backbone dynamics of oxidized and reduced putidaredoxin by 15N NMR relaxation measurements.  

PubMed

The backbone dynamics of uniformly 15N-labeled reduced and oxidized putidaredoxin (Pdx) have been studied by 2D 15N NMR relaxation measurements. 15N T1 and T2 values and 1H-15N NOEs have been measured for the diamagnetic region of the protein. These data were analyzed by using a model-free dynamics formalism to determine the generalized order parameters (S2), the effective correlation time for internal motions (tau e), and the 15N exchange broadening contributions (Rex) for each residue, as well as the overall correlation time (tau(m)). Order parameters for the reduced Pdx are generally higher than for the oxidized Pdx, and there is increased mobility on the microsecond to millisecond time scale for the oxidized Pdx, in comparison with the reduced Pdx. These results clearly indicate that the oxidized protein exhibits higher mobility than the reduced one, which is in agreement with the recently published redox-dependent dynamics studied by amide proton exchange. In addition, we observed very high T1/T2 ratios for residues 33 and 34, giving rise to a large Rex contribution. Residue 34 is believed to be involved in the binding of Pdx to cytochrome P450cam (CYP101). The differences in the backbone dynamics are discussed in relation to the oxidation states of Pdx, and their impact on electron transfer. The entropy change occurring on oxidation of reduced Pdx has been calculated from the order parameters of the two forms. PMID:10433692

Sari, N; Holden, M J; Mayhew, M P; Vilker, V L; Coxon, B

1999-08-01

207

Protein degradation in different feedstuffs labelled with 15N by using the nylon bag technique.  

PubMed

The nylon bag technique was used to determine the Nitrogen (N) and 15N degradation of 15N labelled feedstuffs in the rumen. The N and 15N degradation values were calculated according to Orskov and McDonald (1979) and ranged from 46.8 to 92.0 and from 61.8 to 93.6%, respectively. The differences between N and 15N degradation values of high fibre content feedstuffs are the highest, thus the measuring errors were greatest here. But differences also existed in concentrates. This study indicated that especially barley had a higher proportion of microbial N in the bag residues after the washing than the other concentrates. Therefore it is necessary to correct the N degradation values not only in cases of high fibre content but also in cases of low nitrogen content of feedstuffs. The calculation of the N degradation values could be possible on the basis of crude fibre and crude protein contents of feedstuffs. But experiments with a much larger number of 15N labelled feedstuffs have to be realized to give an accurate prediction of N degradation. PMID:8215900

Katzy, R; Gabel, M; Poppe, S; Krawielitzki, K

1993-01-01

208

Assignment of aliphatic side-chain 1HN/15N resonances in perdeuterated proteins.  

PubMed

The perdeuteration of aliphatic sites in large proteins has been shown to greatly facilitate the process of sequential backbone and side-chain 13C assignments and has also been utilized in obtaining long-range NOE distance restraints for structure calculations. To obtain the maximum information from a 4D 15N/15N-separated NOESY, as many main-chain and side-chain 1HN/15N resonances as possible must be assigned. Traditionally, only backbone amide 1HN/15N resonances are assigned by correlation experiments, whereas slowly exchanging side-chain amide, amino, and guanidino protons are assigned by NOEs to side-chain aliphatic protons. In a perdeuterated protein, however, there is a minimal number of such protons. We have therefore developed several gradient-enhanced and sensitivity-enhanced pulse sequences, containing water-flipback pulses, to provide through-bond correlations of the aliphatic side-chain 1HN/15N resonances to side-chain 13C resonances with high sensitivity: NH2-filtered 2D 1H-15N HSQC(H2N-HSQC), 3D H2N(CO)C gamma/beta and 3D H2N(COC gamma/beta)C beta/alpha for glutamine and asparagine side-chain amide groups; 2D refocused H(N epsilon/zeta)C delta/epsilon and H(N epsilon/zeta C delta/epsilon)C gamma/delta for arginine side-chain amino groups and non-refocused versions for lysine side-chain amino groups; and 2D refocused H(N epsilon)C zeta and nonrefocused H(N epsilon, eta)C zeta for arginine side-chain guanidino groups. These pulse sequences have been applied to perdeuterated 13C-/15N-labeled human carbonic anhydrase II (2H-HCA II). Because more than 95% of all side-chain 13C resonances in 2H-HCA II have already been assigned with the C(CC)(CO)NH experiment, the assignment of the side-chain 1HN/15N resonances has been straightforward using the pulse sequences mentioned above. The importance of assigning these side-chain HN protons has been demonstrated by recent studies in which the calculation of protein global folds was simulated using only 1HN-1HN NOE restraints. In these studies, the inclusion of NOE restraints to side-chain HN protons significantly improved the quality of the global fold that could be determined for a perdeuterated protein [R.A. Venters et al. (1995) J. Am. Chem. Soc., 117, 9592-9593]. PMID:8720832

Farmer, B T; Venters, R A

1996-01-01

209

Investigating solid $?-^{15}$N$_{2}$ as a new source of ultra-cold neutrons  

E-print Network

The dynamical structure factor of solid $^{15}$N$_{2}$ in the $\\alpha$ phase ($Tneutrons to ultra-cold neutron energies is determined as a function of incident energy, as well as the up-scattering mean free path. The UCN production cross-section is found to be approximately 20% of that of deuterium. However, UCN with energy 181 neV have an up-scattering mean free path of 46 cm at $T=5.9$ K, which is $\\sim20$ times larger than deuterium. Therefore, a large volume $\\alpha-^{15}$N$_{2}$ source may produce an improved UCN density if sufficient isotopic purity can be achieved.

D. J. Salvat; E. Gutsmiedl; C. -Y. Liu; P. Geltenbort; A. Orecchini; S. Paul; H. Schober

2013-06-23

210

Investigating solid $\\alpha-^{15}$N$_{2}$ as a new source of ultra-cold neutrons  

E-print Network

The dynamical structure factor of solid $^{15}$N$_{2}$ in the $\\alpha$ phase ($Tneutrons to ultra-cold neutron energies is determined as a function of incident energy, as well as the up-scattering mean free path. The UCN production cross-section is found to be approximately 20% of that of deuterium. However, UCN with energy 181 neV have an up-scattering mean free path of 46 cm at $T=5.9$ K, which is $\\sim20$ times larger than deuterium. Therefore, a large volume $\\alpha-^{15}$N$_{2}$ source may produce an improved UCN density if sufficient isotopic purity can be achieved.

Salvat, D J; Liu, C -Y; Geltenbort, P; Orecchini, A; Paul, S; Schober, H

2013-01-01

211

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

PubMed Central

Background Anopheles arabiensis (Diptera: Culicidae) is a potential malaria vector commonly present at low altitudes in remote areas in Reunion Island. Little attention has been paid to the environmental conditions driving larval development and abundance patterns in potential habitats. Two field surveys were designed to determine whether factors that discriminate between aquatic habitats with and without An. arabiensis larvae also drive larval abundance, comparatively in man-made and naturally occurring habitats. Methods In an initial preliminary survey, a representative sample of aquatic habitats that would be amenable to an intensive long-term study were selected and divided into positive and negative sites based on the presence or absence of Anopheles arabiensis larvae. Subsequently, a second survey was prompted to gain a better understanding of biotic and abiotic drivers of larval abundance, comparatively in man-made and naturally occurring habitats in the two studied locations. In both surveys, weekly sampling was performed to record mosquito species composition and larval density within individual habitats, as well as in situ biological characteristics and physico-chemical properties. Results Whilst virtually any stagnant water body could be a potential breeding ground for An. arabiensis, habitats occupied by their immatures had different structural and biological characteristics when compared to those where larvae were absent. Larval occurrence seemed to be influenced by flow velocity, macrofauna diversity and predation pressure. Interestingly, the relative abundance of larvae in man-made habitats (average: 0.55 larvae per dip, 95%CI [0.30.7]) was significantly lower than that recorded in naturally occurring ones (0.74, 95%CI [0.50.8]). Such differences may be accounted for in part by varying pressures that could be linked to a specific habitat. Conclusions If the larval ecology of An. arabiensis is in general very complex and factors affecting breeding site productivity sometimes not easy to highlight, our results, however, highlight lower populations of An. arabiensis immatures compared to those reported in comparable studies conducted in the African continent. Overall, this low larval abundance, resulting from both abiotic and biotic factors, suggests that vector control measures targeting larval habitats are likely to be successful in Reunion, but these could be better implemented by taking environmental variability into account. PMID:22608179

2012-01-01

212

Gas chromatography-mass spectrometry of N-heptafluorobutyryl isobutyl esters of amino acids in the analysis of the kinetics of (/sup 15/N)H/sub 4//sup +/ assimilation in Lemna minor L  

SciTech Connect

Rapid, sensitive, and selective methods for the determination of the /sup 15/N abundance of amino acids in isotopic tracer experiments with plant tissues are described and discussed. Methodology has been directly tested in an analysis of the kinetics of (/sup 15/N)H/sub 4//sup +/ assimilation in Lemna minor L. The techniques utilize gas chromatography-mass spectrometry selected ion monitoring of major fragments containing the N moiety of N-heptafluorobutyryl isobutyl esters of amino acids. The ratio of selected ion pairs at the characteristic retention time of each amino acid derivative can be used to calcuulate /sup 15/N abundance with an accuracy of +/- 1 atom % excess /sup 15/N using samples containing as little as 30 picomoles of individual amino acids. Up to 11 individual amino acid derivatives can be selectively monitored in a single chromatogram of 30 minutes. It is suggested that these techniques will be useful in situations where the small quantities of N available for analysis have hitherto hindered the use of /sup 15/N-labeled precursors.

Rhodes, D.; Myers, A.C.; Jamieson, G.

1981-11-01

213

Lithium isotope systematics of volcanic glasses from ridge axes and off-axis seamounts in the northern EPR (10-15N)  

NASA Astrophysics Data System (ADS)

It is now widely recognized that the upper mantle source of mid-ocean ridge basalt (MORB) is compositionally heterogeneous on various scales, from whole ocean basins [e.g., Castillo and Batiza, Nature, 342, 1989] to individual minerals [e.g., Laubier et al., Chem. Geol., 240, 2007]. Studies on the geochemical heterogeneity of MORB have primarily been based on abundances of incompatible trace elements and long-lived radiogenic isotope ratios. Light stable isotopes, such as Li, have geochemical behavior that potentially can complement these petrogenetic studies because of their anomalously heavy isotopic composition in seawater-altered oceanic crust or subduction wedge mantle and, conversely, light composition in subducted slab [e.g., Elliott et al., Nature, 443, 2006]. However, the lack of correlations between Li isotopes and other conventional geochemical indices (e.g., incompatible trace element ratios) in the global MORB data set [Tomascak et al., Geochim. Cosmochim. Acta., 72, 2008] requires detailed studies of the regions where closely spaced samples can be examined. In this study we attempt to better constrain the composition of mantle source and the nature of mantle heterogeneity beneath the East Pacific Rise (EPR) by analyzing Li isotopic ratios of a group of well-characterized volcanic glasses from the northern EPR between 10N and 15N. The analyzed samples are from both ridge axes and off-axis seamounts where small volumes of melts that undergo low degree of crystal fractionation and mixing and, thus, provide direct geochemical information of mantle heterogeneity. They span a wide range of compositions, from normal-MORB (K2O/TiO2<0.1) to enriched-MORB (K2O/TiO2>0.1). The ?7Li values of on- and off-axis glasses show systematic correlations with conventional geochemical indices of mantle heterogeneity, forming a trend toward more enriched compositions. In detail, heavier Li isotopic ratios are associated with higher highly/moderately incompatible trace element ratios (e.g., K2O/TiO2, (Ce/Yb)N, and Ba/Zr ratios), more radiogenic 87Sr/86Sr and less radiogenic 143Nd/144Nd. The data are consistent with previous conclusions that lateral compositional variability exists in the upper mantle beneath the EPR and axial and off-axis seamount volcanism share a common heterogeneous mantle source. Moreover, our data suggest that incorporation of a heavy-Li-enriched component, most likely a recycled subduction-metasomatized mantle [e.g., Elliott et al., Nature, 443, 2006], is responsible for the geochemical heterogeneity of the suboceanic mantle in the eastern Pacific.

Tian, L.; Shirey, S. B.; Castillo, P. R.

2012-12-01

214

Tracing Nitrogen through Landscapes to Coastal Wetlands using d15N of Larval Fish  

EPA Science Inventory

Our objective was to evaluate the use of the nitrogen stable isotope value (d15N) of larval fish as an indicator of incipient anthropogenic nitrogen loading to coastal wetlands in the Great Lakes. We sampled coastal wetlands in five Lake Superior south shore tributaries that had ...

215

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

E-print Network

Sources of d15 N variability in sinking particulate nitrogen in the Cariaco Basin, Venezuela, Venezuela a r t i c l e i n f o Keywords: Cariaco Basin Sinking particulate organic matter Nitrogen isotopes Nitrogen fixation Sediment traps Climate variability a b s t r a c t Ten years of monthly observations

Meyers, Steven D.

216

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

PubMed

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

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

2009-06-01

217

Plant ?15N Correlates with the Transpiration Efficiency of Nitrogen Acquisition in Tropical Trees1[OA  

PubMed Central

Based upon considerations of a theoretical model of 15N/14N fractionation during steady-state nitrate uptake from soil, we hypothesized that, for plants grown in a common soil environment, whole-plant ?15N (?P) should vary as a function of the transpiration efficiency of nitrogen acquisition (FN/v) and the difference between ?P and root ?15N (?P ? ?R). We tested these hypotheses with measurements of several tropical tree and liana species. Consistent with theoretical expectations, both FN/v and ?P ? ?R were significant sources of variation in ?P, and the relationship between ?P and FN/v differed between non-N2-fixing and N2-fixing species. We interpret the correlation between ?P and FN/v as resulting from variation in mineral nitrogen efflux-to-influx ratios across plasma membranes of root cells. These results provide a simple explanation of variation in ?15N of terrestrial plants and have implications for understanding nitrogen cycling in ecosystems. PMID:19726571

Cernusak, Lucas A.; Winter, Klaus; Turner, Benjamin L.

2009-01-01

218

Detection of Wastewater Plumes from the 15 N Isotopic Composition of  

E-print Network

Detection of Wastewater Plumes from the 15 N Isotopic Composition of Groundwater, Algae that a main source of nutrient loading is due to wastewater contamination of groundwater within the watershed via septic systems and wastewater treatment facilities. 5 Mya arenaria were collected at each

Vallino, Joseph J.

219

Measuring nitrogen fixation by Sesbania sesban planted fallows using 15 N tracer technique in Kenya  

Microsoft Academic Search

A field experiment was performed in eastern Kenya to estimate N2 fixation by Sesbania sesban over an 18-month period using the 15N dilution method. The influence of three reference species, Senna spectabilis, Eucalyptus saligna and Grevillea robusta, on the estimates of N2 fixation was also assessed. Percentage Ndfa (nitrogen derived from the atmosphere) was calculated based on foliar atom excess

Lena Sthl; Peter Hgberg; Anita Sellstedt; Roland J. Buresh

2005-01-01

220

Using a Macroalgal d15N Bioassay to Detect Cruise Ship Waste Water Effluent Inputs  

EPA Science Inventory

Nitrogen stable isotopes are a powerful tool for tracking sources of N to marine ecosystems. I used green macroalgae as a bioassay organism to evaluate if the d15N signature of cruise ship waste water effluent (CSWWE) could be detected in Skagway Harbor, AK. Opportunistic green...

221

Patchy nitrate promotes inter-sector flow and 15 N allocation  

E-print Network

conductance increases under high nitrate conditions. This plasticity might increase water and nutrient, water uptake and inter-sector water transport, then empirically tested whether a high nitrate patchPatchy nitrate promotes inter-sector flow and 15 N allocation in Ocimum basilicum: a model

Orians, Colin

222

A New Spin Probe of Protein Dynamics: Nitrogen Relaxation in 15N-2H Amide Groups  

E-print Network

to set up, and, in general, straight- forward to interpret. 15N spin relaxation studies in the past have tumbling. Combining several data sets permits evaluation of the spectral density J(D + N) for each amide site. This spectral density samples a uniquely low frequency (26 MHz at a 500 MHz field) and, therefore

Skrynnikov, Nikolai

223

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

Microsoft Academic Search

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

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

2010-01-01

224

First Experimental Measurement of the 18O(p,?)15N Reaction at Astrophysical Energies  

NASA Astrophysics Data System (ADS)

The 18O(p,?)15N and 17O(p,?)14N reactions are of primary importance in several as-trophysical scenarios, including nucleosynthesis inside Asymptotic Giant Branch stars and oxygen and nitrogen isotopic ratios in meteorite grains. They are also key reactions to understand exotic systems such as R-Coronae Borealis stars and novae. Thus, the measurement of their cross sections in the low energy region can be crucial to reduce the nuclear uncertainty on theoretical predictions, because the resonance parameters are poorly determined. The Trojan Horse Method, in its newly developed form particularly suited to investigate low-energy resonances, has been applied to the 2H(18O,?15N)n and 2H(17O,?14N)n reactions to deduce the 18O(p,?)15N and 17O(p,?)14N cross sections at low energies. Resonances in the 18O(p,?)15N and 17O(p,?)14N excitation functions have been studied and the resonance parameters deduced.

La Cognata, M.; Sergi, M. L.; Spitaleri, C.; Mukhamedzhanov, A.; Coc, A.; Cherubini, S.; Goldberg, V.; Gulino, M.; Hammache, F.; Irgaziev, B.; Kiss, G.; Lamia, L.; Pizzone, R. G.; Romano, S.; de Sereville, N.; Tribble, R.; Tumino, A.

2010-11-01

225

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

E-print Network

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

Lawson, Catherine L.

226

[Characteristics of urea 15N absorption, allocation, and utilization by sweet-cherry (Prunus avium L.)].  

PubMed

With five-year old 'Zaodaguo' sweet-cherry (Prunus avium L.) as test material, this paper studied the characteristics of its urea 15N absorption, allocation, and utilization when applied before bud-break. The results showed that the Ndff of different organs increased gradually with time, and was higher in fine roots and storage organs at full-blooming stage. At fruit core-hardening stage, the Ndff of long shoots and leaves increased quickly, reaching to 0.72% and 0.59% , respectively. From fruit core-hardening to harvesting stage, the Ndff of fruit had a rapid increase, with the peak (1.78%) at harvesting stage. After harvest, the Ndff of neonatal organs increased slowly while that of storage organs increased quickly. At full-blooming stage, the absorbed 15N in roots was firstly allocated to storage organs, with the highest allocation rate (54.91%) in large roots. At fruit core-hardening stage, the allocation rate in fine roots and storage organs decreased from 85.43% to 55.11%, while that in neonatal branches and leaves increased to 44.89%. At harvesting stage, the allocation rate in different organs had no significant change, but after harvest, the absorbed 15N had a rapid translocation to storage organs, and the allocation rate in fine roots and storage organs reached the highest (72.26%) at flower bud differentiation stage. The 15N allocation rate in neonatal branches and leaves at flower bud differentiation stage was decreased by 19.31%, compared with that at harvesting stage. From full-blooming to flower bud differentiation stage, the utilization rate of urea 15N was increasing, and reached the peak (16.86%) at flower bud differentiation stage. PMID:18533545

Zhao, Feng-Xia; Jiang, Yuan-Mao; Peng, Fu-Tian; Gao, Xiang-Bin; Liu, Bing-Hua; Wang, Hai-Yun; Zhao, Lin

2008-03-01

227

Rapid and automated processing of MALDI-FTICR/MS data for 15N-metabolic labeling in a shotgun proteomics analysis  

NASA Astrophysics Data System (ADS)

Offline high performance liquid chromatography combined with matrix assisted laser desorption and Fourier transform ion cyclotron resonance mass spectrometry (HPLC-MALDI-FTICR/MS) provides the means to rapidly analyze complex mixtures of peptides, such as those produced by proteolytic digestion of a proteome. This method is particularly useful for making quantitative measurements of changes in protein expression by using 15N-metabolic labeling. Proteolytic digestion of combined labeled and unlabeled proteomes produces complex mixtures with many mass overlaps when analyzed by HPLC-MALDI-FTICR/MS. A significant challenge to data analysis is the matching of pairs of peaks which represent an unlabeled peptide and its labeled counterpart. We have developed an algorithm and incorporated it into a computer program which significantly accelerates the interpretation of 15N-metabolic labeling data by automating the process of identifying unlabeled/labeled peak pairs. The algorithm takes advantage of the high resolution and mass accuracy of FTICR mass spectrometry. The algorithm is shown to be able to successfully identify the 15N/14N peptide pairs and calculate peptide relative abundance ratios in highly complex mixtures from the proteolytic digest of a whole organism protein extract.

Jing, Li; Amster, I. Jonathan

2009-10-01

228

Sensitivity enhancement in natural-abundance solid-state 33S MAS NMR spectroscopy employing adiabatic inversion pulses to the satellite transitions.  

PubMed

The WURST (wideband uniform rate smooth truncation) and hyperbolic secant (HS) pulse elements have each been employed as pairs of inversion pulses to induce population transfer (PT) between the four energy levels in natural abundance solid-state (33)S (spin I=3/2) MAS NMR, thereby leading to a significant gain in intensity for the central transition (CT). The pair of inversion pulses are applied to the satellite transitions for a series of inorganic sulfates, the sulfate ions in the two cementitious materials ettringite and thaumasite, and the two tetrathiometallates (NH(4))(2)WS(4) and (NH(4))(2)MoS(4). These materials all exhibit (33)S quadrupole coupling constants (C(Q)) in the range 0.1-1.0 MHz, with precise C(Q) values being determined from analysis of the PT enhanced (33)S MAS NMR spectra. The enhancement factors for the WURST and HS elements are quite similar and are all in the range 1.74-2.25 for the studied samples, in excellent agreement with earlier reports on HS enhancement factors (1.6-2.4) observed for other spin I=3/2 nuclei with similar C(Q) values (0.3-1.2 MHz). Thus, a time saving in instrument time by a factor up to five has been achieved in natural abundance (33)S MAS NMR, a time saving which is extremely welcome for this important low-gamma nucleus. PMID:18082436

Hansen, Michael Ryan; Brorson, Michael; Bildse, Henrik; Skibsted, Jrgen; Jakobsen, Hans J

2008-02-01

229

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

USGS Publications Warehouse

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

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

1986-01-01

230

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

Microsoft Academic Search

The13C kinetic isotope fractionation in the decarbonylation of lactic acid of natural isotopic composition by sulfuric acid has been studied in the temperature range of 2080C. The13C(1) isotope separation in the decarbonylation of lactic acid by concentrated sulfuric acid depends strongly on the temperature above 40C. Below this temperature the13C isotope effect in the decarbonylation of lactic acid by concentrated

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

1992-01-01

231

Effects of forest decline on uptake and leaching of deposited nitrate determined from 15N and 18O measurements  

Microsoft Academic Search

ATTEMPTS to understand how atmospheric nitrogen deposition affects forest ecosystems1'2 have been hampered by the lack of a direct method to trace the fate of the deposited nitrogen. Nitrate originating in the atmosphere has natural abundances of nitrogen and oxygen isotopes that differ measurably from those of soil nitrate3. Here we present an analysis of the isotope ratios of nitrate

Walter Durka; Ernst-Detlef Schulze; Gerhard Gebauer; Susanne Voerkeliust

1994-01-01

232

Heathland vegetation as a bio-monitor for nitrogen deposition and source attribution using ?15N values  

NASA Astrophysics Data System (ADS)

The %N and ?15N signals in foliar nitrogen (N) from four heathland species have been monitored in a blanket bog plant community subjected to different experimental inputs of wet and dry N deposition. Interactions with combined additional treatments of phosphorus (P) and potassium (K) were also investigated. Calluna vulgaris, Cladonia portentosa, Sphagnum capillifolium and Hypnum cupressiforme were harvested for 15N analysis prior to wet and dry treatment applications and again after 16 months field exposure. A significant increase was observed in both %N and ?15N values for all plant species in response to both wet and dry treatments whilst PK additions also produced significant decreases in foliar %N and associated ?15N values for several of the species sampled. These enrichments in the ?15N signals for post-treatment shoot tissue were attributable to the ?15N signal in the source application, a finding of potential value in using bio-monitors for assessment of N deposition.

Skinner, R. A.; Ineson, P.; Jones, H.; Sleep, D.; Leith, I. D.; Sheppard, L. J.

233

What's on the menu? Assessing microbial carbon sources and cycling in soils using natural abundance radiocarbon analysis  

NASA Astrophysics Data System (ADS)

Organic matter in soils is composed of diverse materials in various stages of decomposition. Soil organic matter is not in a single pool but rather in multiple carbon pools with different intrinsic turnover times that can be on annual to decadal and even millennial timescales. Microorganisms can influence the total amount of carbon stored in soils and the turnover rates of these different pools. However, the links between microbes and their ability to utilize these various carbon pools are not well understood. Moreover, microbes have been shown to co-utilize a number of available carbon sources rather than a single carbon source under soil conditions which creates difficulties in identifying microbial carbon sources in the natural environment. Compound-specific radiocarbon analysis of microbial phospholipid fatty acids (PLFA) has become a useful tool in elucidating microbial carbon sources in complex environments with multiple carbon sources. We investigated microbial carbon cycling at an industrial site in Ontario which included a variety of carbon sources including vegetation, PAHs and natural organic matter (NOM). Using this approach, the 14C content of microbial membrane lipids (which reflects their carbon source) can be compared to surrounding carbon sources in order to assess which carbon source they are metabolizing and incorporating into their lipids. In addition, we assessed microbial community structure and diversity by analyzing amplified bacterial, eukaryotic and archaeal rDNA fragments with denaturing gel gradient electrophoresis (DGGE). The ?14C value for PLFAs ranged from +54 to -697% which indicates that microbial carbon sources across soils differ. The ?14CPLFA for some soils is consistent with modern carbon sources while ?14CPLFA for other soils is consistent with natural organic matter including older pools of carbon. The microbial communities at this site are not metabolizing PAHs but rather they are utilizing various pools of natural organic matter as a carbon source. Moreover, our radiocarbon analysis of total organic carbon (TOC) and non-solvent extracted residue (representative of NOM) support the notion that soil organic matter is not homogenous and is comprised of multiple carbon fractions with different intrinsic turnover times. DNA fingerprinting revealed consistent levels of diversity across soils with the greatest diversity observed in the bacteria, followed by eukarya and finally archaea which had the lowest observed diversity. It was previously thought that there is a pool of refractory organic compounds that are biologically inert in soil however our findings indicate that microbes are able to utilize almost all available carbon sources in soil. These finding brings forth questions regarding the influence of microbes on soil organic matter stabilization and the bioavailability of different carbon pools.

Mahmoudi, N.; Burns, L.; Mancini, S.; Fulthorpe, R.; Slater, G. F.

2011-12-01

234

Investigating solid ?-15N2 as a new source of ultra-cold neutrons  

NASA Astrophysics Data System (ADS)

The dynamical structure factor of solid 15N2 in the ? phase (T<35\\ \\text{K} ) is measured at the IN4 time-of-flight spectrometer at the Institut Laue Langevin, and the potential performance of this substance as a UCN converter is assessed. The cross-section to down-scatter neutrons to ultra-cold-neutron energies is determined as a function of the incident energy, as well as the up-scattering mean free path. The UCN production cross-section is found to be approximately 20% of that of deuterium. However, UCN with energy 181 neV have an up-scattering mean free path of 46 cm at T=5.9\\ \\text{K} , which is {\\sim}20 times larger than deuterium. Therefore, a large volume ?-15N2 source may produce an improved UCN density if sufficient isotopic purity can be achieved.

Salvat, D. J.; Gutsmiedl, E.; Liu, C.-Y.; Geltenbort, P.; Orecchini, A.; Paul, S.; Schober, H.

2013-07-01

235

TT2 analyzing powers from 12C (7Li,? )15N  

NASA Astrophysics Data System (ADS)

The transverse analyzing powers TT2 were obtained from a polarized beam study of the reaction 12C(7Li,? )15N at Elab(7Li) =34 MeV for several well known, strongly populated and isolated states in 15N to determine if they contained a sufficiently distinctive signature to be used to provide a test against which selectively populated and strong, but not well understood states, such as the one at 13.17 MeV could be used to determine their spins and parities. Unfortunately, current finite range distorted wave Born approximation and coupled channels Born approximation calculations were not able to describe the data to the well-known states. The current work presents these experimental analyzing powers with the expectation that they can be used as a test of future detailed reaction model calculations.

Rodrguez, F. J.; Liendo, J. A.; Keeley, N.; Kemper, K. W.; Mielgo, J. A.; Roeder, B. T.; Weintraub, W. D.

2014-10-01

236

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

237

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

NASA Astrophysics Data System (ADS)

The 18F(p,?)15O reaction is recognized to be one of the most important reactions for nova ?-ray astronomy, as it governs the early E<~511keV ? 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(?)15N one-nucleon transfer reaction, induced by a 14-MeV 18F radioactive beam impinging on a CD2 target; outgoing protons and 15N (or ? particles) were detected in coincidence in two silicon strip detectors. A distorted-wave Born approximation analysis of the data resulted in new limits to the contribution of low-energy resonances to the rate of the 18F(p,?)15O reaction.

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

2003-05-01

238

Food webs of two intermittently open estuaries receiving 15N-enriched sewage effluent  

NASA Astrophysics Data System (ADS)

Carbon and nitrogen stable isotope signatures were used to assess the response of food webs to sewage effluent discharged into two small intermittently open estuaries in northern New South Wales, Australia. One of these systems, Tallows Creek, has a history of direct sewage inputs, whilst the other, Belongil Creek, receives wastewater via an extensive wetland treatment system. The food webs of both systems were driven by algal sources of carbon, reflecting high autotrophic productivity in response to the nutrients entering the system from sewage effluent. All aquatic biota collected from Tallows Creek had significantly enriched ?15N signatures relative to their conspecifics from Belongil Creek, indicating that sewage nitrogen had been assimilated and transferred throughout the Tallows Creek food web. These ?15N values were higher than those reported from studies in permanently open estuaries receiving sewage effluent. We suggest that these enriched signatures and the transfer of nitrogen throughout the entire food web reflect differences in hydrology and associated nitrogen cycling processes between permanently open and intermittently open estuaries. Although all organisms in Tallows Creek were generally 15N-enriched, isotopically light (less 15N-enriched) individuals of estuary perchlet ( Ambassis marianus) and sea mullet ( Mugil cephalus) were also collected. These individuals were most likely recent immigrants into Tallows Creek, as this system had only recently been opened to the ocean. This isotopic discrimination between resident (enriched) and immigrant (significantly less enriched) individuals can provide information on fish movement patterns and the role of heavily polluted intermittently open estuaries in supporting commercially and recreationally valuable estuarine species.

Hadwen, Wade L.; Arthington, Angela H.

2007-01-01

239

Quantification and potential availability of non-symbiotically fixed 15 N in soil  

Microsoft Academic Search

Non-symbiotic N2 fixation was studied under laboratory conditions in two soils from Pakistan (Hafizabad silt loam and Khurrarianwala silt loam) and one from Illinois, USA (Drummer silty clay loam) incubated in a 15N-enriched atmosphere. N2 fixation was greatest with the Drummer soil (18122 g g-1 soil, depending upon the soil treatment) and lowest with the Khurrarianwala soil (481 g g-1

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

1988-01-01

240

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

241

Some characteristics of the 18O(p, alpha0)15N reaction  

Microsoft Academic Search

We present some results for the cross section in the 18O(p, alpha0)15N reaction, at a proton energy of 846 keV. For maximum alpha particle yields the proton energy is slightly above this resonance, and for these off-resonance energies the reaction is anisotropic, yields being considerably larger for small reaction angles. Samples have been prepared from as little as 150 mul

D. D. Cohen; A. Katsaros; D. Carton

1986-01-01

242

Potential of ? 13 C and ? 15 N of cladoceran subfossil exoskeletons for paleo-ecological studies  

Microsoft Academic Search

Stable isotope analyses on cladoceran subfossil exoskeletons retrieved from sediment cores could allow the reconstruction\\u000a of past changes in lake food webs provided the ?13C and ?15N values of the exoskeletons reflect those of the organisms whole body. The relationships between the C and N stable isotope\\u000a compositions of the exoskeletons and those of the whole body were investigated for

Marie-Elodie Perga

2010-01-01

243

Decomposition of 15N-labelled maize leaves in soil affected by endogeic geophagous Aporrectodea caliginosa  

Microsoft Academic Search

A microcosm experiment was carried out for 56 days at 12C to evaluate the feeding effects of the endogeic geophagous earthworm species Aporrectodea caliginosa on the microbial use of 15N-labelled maize leaves (Zea mays) added as 5mm particles equivalent to 1mgC and 57?gNg?1 soil. The dry weight of A. caliginosa biomass decreased in the no-maize treatment by 10% during the

Parva Zareitalabad; Stefanie Heinze; Nils Rottmann; Martin Potthoff; Jens Dyckmans; Rainer Georg Joergensen

2010-01-01

244

Organic Matter Stable Isotope (? 13 C, ? 15 N) Response to Historical Eutrophication of Lake Taihu, China  

Microsoft Academic Search

We explored the use of carbon and nitrogen isotope ratios (?13C, ?15N) in sediment organic matter as proxy indicators of historical changes in the trophic state of Lake Taihu, the third largest\\u000a freshwater lake in China. Stable isotope signatures in four sediment cores spanning the 20th century were compared with instrumental\\u000a records of lake-water trophic state. The comparative study shows

Jinglu Wu; Lin Lin; Michael K. Gagan; Gerhard H. Schleser; Sumin Wang

2006-01-01

245

Nitrogen stress causes unpredictable enrichments of 15N in two nectar-feeding bat species.  

PubMed

We estimated the effect of nitrogen stress on the nitrogen isotope enrichments in wing membrane and blood of two nectar-feeding bats (Glossophaga soricina and Leptonycteris curasoae) by offering a nitrogen-poor diet with a high delta(15)N and delta(13)C. Before the experiment, bats were sustained on a normal diet with a low delta(15)N and delta(13)C. Under this first food regime, the fractionation of nitrogen isotopes averaged 3.1 per thousand delta(15)N for blood and 4.4 per thousand delta(15)N for wing membrane, which was almost twice as high as the corresponding fractionation of carbon isotopes. After switching to the nitrogen-poor diet, the enrichment of heavy isotopes increased for both elements in all tissues under study. The recently published estimates of half-life of carbon isotopes indicated a low turnover rate of carbon in wing membrane and blood and an almost constant half-life over varying losses of body mass. The estimates of half-life of nitrogen were two to six times higher than those of carbon. We argue that this discrepancy was caused by the mixing of nitrogen isotopes from internal and external sources. The mixing effect was probably negligible for carbon as the amount of ingested carbon outweighed the amount of mobilized carbon from internal sources. A correlation between the estimated turnover rates of nitrogen and losses of body masses was probably obscured by the additional fractionation of nitrogen isotopes in catabolic animals. We conclude that the interpretation of nitrogen isotope data of free-ranging animals is difficult when the animal's diet is changing to a critical nitrogen content. PMID:15073206

Voigt, Christian C; Matt, Felix

2004-04-01

246

The 15N(p, n)15O reaction below 9.3 MeV  

Microsoft Academic Search

In connection with studies of differences between the polarization and analyzing power observables for the 15N(p, n)15O reaction, differential cross sections at ten proton energies between 5.5 and 9.3 MeV were measured using time-of-flight techniques. These new measurements allowed all previous data to be evaluated through use of the extensive total cross sections measured by Barnett in a study of

K. Murphy; R. C. Byrd; P. P. Guss; C. E. Floyd; R. L. Walter

1981-01-01

247

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

NASA Astrophysics Data System (ADS)

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

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

248

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

249

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

PubMed Central

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

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

2012-01-01

250

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

PubMed

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

Xia, Guobin; Hong, Shan; Liu, Songbai

2014-05-15

251

Simultaneous measurement of 13C- and 15N-isotopic enrichments of threonine by mass spectrometry.  

PubMed

Under conditions of high isotopic dilution, e.g. in a tracer study, the ability to determine accurately and quantitatively small variations in isotopic enrichments of differently labelled chemical compounds (e.g. (13)C and (15)N in threonine) in a single run by gas chromatography/mass spectrometry (GC/MS) is desirable but remains a technological challenge. Here, we report a new, rapid and simple GC/MS method for simultaneously measuring the isotopic enrichments of doubly labelled threonine ([U(13)C] and (15)N) with isotopic enrichment lower than 1.5 Molar Percent Excess (MPE). The long-term reproducibility measured was around 0.09 MPE for both tracers (throughout a 6 week period). The intra-day repeatability was lower than 0.05 and 0.06 MPE for [U(13)C]-Thr and (15)N-Thr, respectively. To calculate both isotopic enrichments, two modes of calculations were used: one based on work by Rosenblatt et al. in 1992 and the other one using a matrix approach. Both methods gave similar results (ANOVA, P >0.05) with close precision for each mode of calculation. The GC/MS method was then used to investigate the differential utilization of threonine in different organs according to its route of administration in minipigs after administration of both tracers. In plasma samples, the lowest isotopic enrichment measured between two successive time points was at 0.01 and 0.02 MPE for [U(13)C]-Thr and (15)N-Thr, respectively. Moreover, the accuracy of GC/MS (13)C-isotopic enrichment measured was validated by analyzing the same plasma samples by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Statistical analysis showed that both techniques gave the same results (ANOVA, P >0.05). This new GC/MS method offers the possibility to measure (13)C- and (15)N-isotopic enrichments with higher throughput, and using a lower amount of sample, than using GC/C/IRMS. PMID:19288537

Godin, Jean-Philippe; Mermoud, Anne-France; Rmond, Didier; Faure, Magali; Breuille, Denis; Williamson, Gary; Per-Trepat, Emma; Ramadan, Ziad; Fay, Laurent-Bernard; Kochhar, Sunil

2009-04-01

252

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

253

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

PubMed

Rates of benthic denitrification were measured using two techniques, membrane inlet mass spectrometry (MIMS) and isotope ratio mass spectrometry (IRMS), applied to sediment cores from two NO3(-)-rich streams draining agricultural land in the upper Mississippi River Basin. Denitrification was estimated simultaneously from measurements of N2:Ar (MIMS) and 15N[N2] (IRMS) after the addition of low-level 15NO3- tracer (15N:N = 0.03-0.08) in stream water overlying intact sediment cores. Denitrification rates ranged from about 0 to 4400 micromol N x m(-2) x h(-1) in Sugar Creek and from 0 to 1300 micromol N x m(-2) x h(-1) in Iroquois River, the latter of which possesses greater streamflow discharge and a more homogeneous streambed and water column. Within the uncertainties of the two techniques, there is good agreement between the MIMS and IRMS results, which indicates that the production of N2 by the coupled process of nitrification/denitrification was relatively unimportant and surface-water NO3- was the dominant source of NO3- for benthic denitrification in these streams. Variation in stream NO3- concentration (from about 20 micromol/L during low discharge to 1000 micromol/L during high discharge) was a significant control of benthic denitrification rates, judging from the more abundant MIMS data. The interpretation that NO3- concentration directly affects denitrification rate was corroborated by increased rates of denitrification in cores amended with NO3-. Denitrification in Sugar Creek removed < or = 11% per day of the instream NO3- in late spring and removed roughly 15-20% in late summer. The fraction of NO3- removed in Iroquois River was less than that of Sugar Creek. Although benthic denitrification rates were relatively high during periods of high stream flow, when NO3 concentrations were also high, the increase in benthic denitrification could not compensate for the much larger increase in stream NO3- fluxes during high flow. Consequently, fractional NO3- losses were relatively low during high flow. PMID:17205897

Smith, Lesley K; Voytek, Mary A; Bhlke, John Karl; Harvey, Judson W

2006-12-01

254

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

255

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 [ 15N indole]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 15NH 4+-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

256

Heathland vegetation as a bio-monitor for nitrogen deposition and source attribution using ? 15N values  

Microsoft Academic Search

The %N and ?15N signals in foliar nitrogen (N) from four heathland species have been monitored in a blanket bog plant community subjected to different experimental inputs of wet and dry N deposition. Interactions with combined additional treatments of phosphorus (P) and potassium (K) were also investigated. Calluna vulgaris, Cladonia portentosa, Sphagnum capillifolium and Hypnum cupressiforme were harvested for 15N

R. A. Skinner; P. Ineson; H. Jones; D. Sleep; I. D. Leith; L. J. Sheppard

2006-01-01

257

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

258

N2O and ?15N-N2O and ?18O-N2O from polar ice cores: interpretable data for interglacials  

NASA Astrophysics Data System (ADS)

Ice cores provide a wealth of information on climate change. For instance, the history of the atmospheric greenhouse gas N2O can be reconstructed using air entrapped in polar ice cores. N2O has several sources in both terrestrial and marine ecosystems, predominantly wetland soils and oxygen minimum zones in the ocean. N2O records generally follow the climatic changes during the glacial-interglacial cycles with higher N2O mixing ratios during warmer climate stages. However, the underlying processes driving these changes are difficult to identify from N2O mixing ratios alone. Additional information on the individual sources and sinks are provided by stable isotope measurements. The emission fluxes of the dominant N2O sources are ascribed to several pathways (nitrification, denitrification), with characteristic fractionation factors for the nitrogen and oxygen isotope signatures of the generated N2O (?15N-N2O and ?18O-N2O). In the end, the individual proportions of pathways are responsible for distinct ?15N-N2O and ?18O-N2O for the average terrestrial and marine sources. Here, we present new ice core measurements of ?15N-N2O and ?18O-N2O covering the Holocene, MIS 5 and MIS 11. For the past 15 kyrs the ?15N-N2O record shows a continuous decrease starting at 15 kyrs to about 6 kyrs; during the past 6 kyrs ?15N-N2O remains rather constant. The resemblance with a recently published global reconstruction of bulk ?15N is remarkable (McLauchlan et al. 2013, Nature). Taken at face value this could mean that mainly the terrestrial source signature changed rather than a shift in the relative proportions of the terrestrial and marine source. The integrity of N2O ice core records relies on the assumption that the measurements truly represent the past atmosphere. However, comparative analyses of different ice cores from the same age intervals show offsets in the N2O mixing ratios among the records. One likely assumption is that higher mixing ratios are due to in-situ production since N2O should not be lost in the ice. In situ production appears to be evident at least for glacial sections of some ice cores.

Bock, Michael; Schmitt, Jochen; Seth, Barbara; Beck, Jonas; Fischer, Hubertus

2014-05-01

259

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, Mlanie; Guillou, Gal; Mornet, Franoise; Richard, Pierre

2013-03-01

260

Tracking the flow of bacterially derived 13C and 15N through soil faunal feeding channels.  

PubMed

The soil food web has been referred to as a 'black box', a 'poor man's tropical rainforest' and an 'enigma', due to its opacity, diversity and the limited insight into feeding specificity. Here we investigate the flow of C and N through the soil food web as a way to gain understanding of the feeding interactions occurring. A bacterium, Pseudomonas lurida, was introduced to soil cores from two different habitats, a grassland and a woodland with the same soil type, enriched to 99 atom% in (13)C and (15)N, to trace the flow of bacterial C and N through the soil food web. Throughout the experiment the soil remained enriched in (13)C and (15)N. Almost all the invertebrates tested gained C and N enrichment indicative of the labelled bacteria, implying that bacterial feeding is a common mechanism within the soil. Only three groups were significantly enriched in both (13)C and (15)N in both habitats. These were Collembola (Entomobryomorpha), Acari (Oribatida), and Nematoda, indicating that these organisms are consuming the most bacteria within both systems. When the invertebrates were grouped into hypothesised trophic levels, those considered secondary decomposers were gaining the most enrichment across all invertebrates tested. This enrichment was also high in the micro-predators within the soil, implying that their main food source was the secondary decomposers, particularly the Collembola. Using an enriched bacterium to track the trophic transfer between organisms within the soil food web is a novel way of empirically showing that interactions are occurring, which normally cannot be seen. PMID:21594923

Crotty, F V; Blackshaw, R P; Murray, P J

2011-06-15

261

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

PubMed Central

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

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

2013-01-01

262

On the resonant behavior of the 16 O+ 15 N reaction  

Microsoft Academic Search

The16O+15N reaction products have been studied by the ?-ray detection method in the CM energy range 15.5 to 36.1 MeV and by the kinematical coincidence method at energies ranging from ECM=20.6 to 33.5MeV. The ?-ray yield excitation function of the16O 3-inelastic channel shows the existence of resonant structures. Two structures with ~ 1.6 MeV width are observed in the large

N. Aissaoui; F. Haas; R. M. Freeman; C. Beck; A. Morsad; B. Djerroud; R. ?aplar; G. A. Monnehan; A. Hachem; M. Youlal

1994-01-01

263

GIAO DFT 13C/15N chemical shifts in regioisomeric structure determination of fused pyrazoles.  

PubMed

The combined use of two-dimensional NMR correlation experiments and gauge including atomic orbital density functional theory in (13)C NMR chemical shift (CS) calculations allowed reliable and simple structural determination of regioisomeric heterocyclic systems that originate from the reactions of acylquinolinones with substituted hydrazines. Moreover, the results of differential analysis between the calculated (15)N NMR CSs for hypothetical structures and the experimental data of the title azaheterocyclic systems were even more advantageous with respect to (13)C because there was no need for correlational analysis: structures of the regioisomeric compounds could be determined just by direct comparison. PMID:20589725

Chimichi, Stefano; Boccalini, Marco; Matteucci, Alessandra; Kharlamov, Sergey V; Latypov, Shamil K; Sinyashin, Oleg G

2010-08-01

264

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

265

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

266

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

267

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

268

Uptake of stormwater nitrogen in bioretention systems demonstrated from 15N tracer techniques  

NASA Astrophysics Data System (ADS)

Bioretention stormwater management systems are engineered ecosystems that capture urban stormwater in order to reduce the harmful effects of stormwater pollution on receiving waters. Bioretention systems have been shown to be effective at reducing the volume of runoff, and thereby reduce the nutrient loading to receiving waters from urban areas. However, little work has been done to evaluate the treatment processes that are responsible for reductions in effluent nitrogen (N). We hypothesize that the pulses of inorganic nitrogen associated with urban runoff events are captured in the plat tissues within these systems and not adsorbed to the soil media, thus creating a long-term, sustainable treatment approach to reducing the total nutrient loading to receiving waters. Nitrogen treatment performance was tested on two bioretention systems in Salt Lake City, UT: 1) an upland native community that does not require irrigation in semi-arid climates, and 2) a wetland community that requires 250 l of daily irrigation to offset the relatively high evaporative demand in the region. Each cell is sized to treat a 2.5 cm storm from a 140 m2 impervious surface: the area of the bioretention system is 10 m2. To test the N removal performance of each system, runoff events were simulated to represent an average precipitation regime using a synthetic stormwater blend starting in January, 2012. Effluent was collected from an underdrain and analyzed for total nitrogen (TN); mass removal was calculated for each month by subtracting the TN mass added to the garden minus the TN mass that flowed out of the garden. To test the hypothesis that plants assimilate stormwater N, 4 g of 100 atom% 15N NH4NO3 tracer was used as the N source in the synthetic stormwater during the first 2,000 l synthetic storm event in May. This isotopic label was calculated to enrich the total N pool of each garden to 100 15N/14Nair. New growth was harvested from each plant in both cells and analyzed for 15N before the isotopic label was introduced and weekly thereafter. In May 2012, the upland garden captured 6.2 grams of TN from the added stormwater (55% of TN added), and the wetland garden captured 7.1 grams of TN from the added stormwater (67% of TN added). Within two weeks of adding the label, the 15N ratio increased 500 to 3,000 in all plant tissues tested in both systems. The results of the isotopic labeling experiment support the hypothesis that the plants used in both vegetated bioretention systems directly contribute to stormwater N treatment through N assimilation.

Houdeshel, D.; Hultine, K. R.; Pomeroy, C. A.

2012-12-01

269

Synthesis of (13) C2 (15) N2 -labeled anti-inflammatory and cytoprotective tricyclic bis(cyanoenone) ([(13) C2 (15) N2 ]-TBE-31) as an internal standard for quantification by stable isotope dilution LC-MS method.  

PubMed

Tricyclic bis(cyanoenone), TBE-31, one of the most potent activators of the Keap1/Nrf2/antioxidant response element pathway, has been developed as a new anti-inflammatory and cytoprotective agent. (13) C2 (15) N2 -labeled TBE-31 ([(13) C2 (15) N2 ]-TBE-31), which has two (13) C and two (15) N atoms in two cyano groups, was designed to develop a method for quantification of cell, tissue, and plasma levels of TBE-31 that involves chromatography/mass spectrometry coupled with the use of a stable isotope-labeled internal standard. [(13) C2 (15) N2 ]-TBE-31 was successfully synthesized in four steps from a previously reported intermediate, which is prepared in 11 steps from cyclohexanone, by introduction of two (13) C atoms with ethyl [(13) C]formate and two (15) N atoms with hydroxyl[(15) N]amine. The stable isotope dilution liquid chromatography-mass spectrometry method for quantification of TBE-31 was successfully developed using [(13) C2 (15) N2 ]-TBE-31 to compensate for any variables encountered during sample processing and analysis. PMID:25196444

Zheng, Suqing; Huang, Jeffrey T-J; Knatko, Elena V; Sharp, Sheila; Higgins, Maureen; Ojima, Iwao; Dinkova-Kostova, Albena T; Honda, Tadashi

2014-08-01

270

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

PubMed

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

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

2009-01-01

271

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

PubMed Central

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

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

2009-01-01

272

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

273

The effect of FISH and CARD-FISH on the isotopic composition of (13)C- and (15)N-labeled Pseudomonas putida cells measured by nanoSIMS.  

PubMed

The use of nanoSIMS for the exploration of microbial activities in natural habitats often implies that stable isotope tracer experiments are combined with in situ hybridization techniques (i.e. fluorescence in situ hybridization (FISH) or catalyzed reporter deposition (CARD)-FISH). In this study, Pseudomonas putida grown on (13)C- and (15)N-labeled carbon and nitrogen, collected in exponential growth and stationary phases, was hybridized and analyzed by nanoSIMS. It was shown that (13)C and (15)N fractions decreased after FISH and CARD-FISH in comparison to chemically untreated cells. However, the fractions were influenced differently by various treatments. After paraformaldehyde fixation of exponentially growing cells, a reduction of the (13)C and (15)N fractions was measured from 941.2% and 89.53.8% to 90.20.8% and 644.6%, respectively, indicating that nitrogen isotopic composition was most influenced. A further decrease of the (13)C and (15)N fractions to 80.76.5 and 59.54.1%, respectively, was measured after FISH, while CARD-FISH decreased the fractions to 57.43.0% and 47.14.1%, respectively. The analysis of cells collected in different growth phases revealed that the effect of various treatments seemed to be dependent on the cell's physiological state. In addition, a mathematical model that can be used in further studies was developed in order to calculate the amount of carbon introduced into the cells by chemical treatments. These results can be valuable for environmental FISH-nanoSIMS studies where the isotopic composition of single cells will be used to quantitatively assess the importance of specific populations to certain biochemical processes and determine budget estimations. PMID:24702905

Musat, Niculina; Stryhanyuk, Hryhoriy; Bombach, Petra; Adrian, Lorenz; Audinot, Jean-Nicolas; Richnow, Hans H

2014-06-01

274

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

275

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

PubMed Central

Background: The long-chain omega-3 (n3) fatty acids derived from fish, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are associated with a reduced risk of cardiovascular disease and other chronic diseases. Study of the associations between EPA and DHA intake and disease requires a valid biomarker of dietary intake; however, the direct measurement of tissue fatty acid concentrations is expensive and time consuming. Objective: Because the nitrogen stable isotope ratio (15N/14N, expressed as ?15N) is elevated in fish, we investigated whether ?15N is a valid alternative biomarker of EPA and DHA intake. Design: We examined the relation between red blood cell (RBC) ?15N and RBC EPA and DHA in a community-based sample of 496 Yup'ik Eskimos with widely varying intake of n3 fatty acids. We also assessed the correlation between ?15N and dietary EPA and DHA intake based on 24-h dietary recalls and 3-d food records completed by a subset of 221 participants. Results: RBC ?15N was strongly correlated with RBC EPA and DHA (r = 0.83 and 0.75, respectively). These correlations differed only modestly by sex and age class. RBC ?15N also correlated with dietary EPA and DHA intake (r = 0.47 and 0.46, respectively) and did not differ by sex and age. Conclusions: The results strongly support the validity of RBC ?15N as a biomarker of EPA and DHA intake. Because the analysis of RBC ?15N is rapid and inexpensive, this method could facilitate wide-scale assessment of EPA and DHA intake in clinical and epidemiologic studies. PMID:19176727

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

2009-01-01

276

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

E-print Network

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

Mark A. Gurwell

2004-07-08

277

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 34 for ?15N and 107 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. Mller, E. Brggemann, 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

278

Spatial variations in ?13C and ?15N values of primary consumers in a coastal lagoon  

NASA Astrophysics Data System (ADS)

The analysis of the contribution of a food source to a consumer's diet or the trophic position of a consumer is highly sensitive to the variability of the isotopic values used as input data. However, little is known in coastal lagoons about the spatial variations in the isotopic values of primary consumers considered 'end members' in the isotope mixing models for quantifying the diet of secondary consumers or as a baseline for estimating the trophic position of consumers higher up in the food web. We studied the spatial variations in the ?13C and ?15N values of primary consumers and sedimentary organic matter (SOM) within a selected area of the Cabras lagoon (Sardinia, Italy). Our aim was to assess how much of the spatial variation in isotopic values of primary consumers was due to the spatial variability between sites and how much was due to differences in short distances from the shore. Samples were collected at four stations (50-100 m apart) selected randomly at two sites (1.5-2 km apart) chosen randomly at two distances from the shore (i.e. in proximity of the shore -Nearshore - and about 200 m away from the shore -Offshore). The sampling was repeated in March, May and August 2006 using new sites at the two chosen distances from the shore on each date. The isotopic values of size-fractionated seston and macrophytes were also analyzed as a complementary characterization of the study area. While ?15N did not show any spatial variations, the ?13C values of deposit feeders, Alitta (=Neanthes) succinea, Lekanesphaera hookeri, Hydrobia acuta and Gammarus aequicauda, were more depleted Offshore than Nearshore. For these species, there were significant effects of distance or distance dates in the mean ?13C values, irrespective of the intrinsic variation between sites. SOM showed similar spatial variations in ?13C values, with Nearshore-Offshore differences up to 6. This indicates that the spatial isotopic changes are transferred from the food sources to the deposit feeders studied. In contrast, ?13C and ?15N values of suspension feeders, Ficopomatus enigmaticus and Amphibalanus amphitrite, did not show major variations, either between sites, or between Nearshore and Offshore. These different patterns between deposit feeders and suspension feeders are probably due to a weaker trophic link of the latter with SOM. We suggest that the Nearshore-Offshore gradient might be an important source of isotopic variation that needs to be considered in future web studies in coastal lagoons.

Como, S.; Magni, P.; Van Der Velde, G.; Blok, F. S.; Van De Steeg, M. F. M.

2012-12-01

279

Nitrous oxide nitrification and denitrification 15N enrichment factors from Amazon forest soils.  

PubMed

The isotopic signatures of 15N and 18O in N2O emitted from tropical soils vary both spatially and temporally, leading to large uncertainty in the overall tropical source signature and thereby limiting the utility of isotopes in constraining the global N2O budget. Determining the reasons for spatial and temporal variations in isotope signatures requires that we know the isotope enrichment factors for nitrification and denitrification, the two processes that produce N2O in soils. We have devised a method for measuring these enrichment factors using soil incubation experiments and report results from this method for three rain forest soils collected in the Brazilian Amazon: soil with differing sand and clay content from the Tapajos National Forest (TNF) near Santarm, Par, and Nova Vida Farm, Rondnia. The 15N enrichment factors for nitrification and denitrification differ with soil texture and site: -111 per thousand +/- 12 per thousand and -31 per thousand +/- 11 per thousand for a clay-rich Oxisol (TNF), -102 per thousand +/- 5 per thousand and -45 per thousand +/- 5 per thousand for a sandier Ultisol (TNF), and -10.4 per thousand +/- 3.5 per thousand (enrichment factor for denitrification) for another Ultisol (Nova Vida) soil, respectively. We also show that the isotopomer site preference (delta15Nalpha - delta15Nbeta, where alpha indicates the central nitrogen atom and beta the terminal nitrogen atom in N2O) may allow differentiation between processes of production and consumption of N2O and can potentially be used to determine the contributions of nitrification and denitrification. The site preferences for nitrification and denitrification from the TNF-Ultisol incubated soils are: 4.2 per thousand +/- 8.4 per thousand and 31.6 per thousand +/- 8.1 per thousand, respectively. Thus, nitrifying and denitrifying bacteria populations under the conditions of our study exhibit significantly different 15N site preference fingerprints. Our data set strongly suggests that N2O isotopomers can be used in concert with traditional N2O stable isotope measurements as constraints to differentiate microbial N2O processes in soil and will contribute to interpretations of the isotopic site preference N2O values found in the free troposphere. PMID:17205894

Prez, Tibisay; Garcia-Montiel, Diana; Trumbore, Susan; Tyler, Stanley; de Camargo, Plnio; Moreira, Marcelo; Piccolo, Marisa; Cerri, Carlos

2006-12-01

280

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

281

Experimental and calculated 1H, 13C, 15N NMR spectra of famotidine  

NASA Astrophysics Data System (ADS)

Famotidine, 3-[[[2-[(aminoiminomethyl)amino]-4-thiazolyl]methyl]thio]- N-(aminosulfonyl), is a histamine H 2-receptor blocker that has been used mainly for the treatment of peptic ulcers and the Zollinger-Ellison syndrome. Its NMR spectra in different solvents were reported earlier; however, detailed interpretation has not been done thus far. In this work, experimental 1H, 13C and 15N NMR spectra of famotidine dissolved in DMSO-d 6 are shown. The assignment of observed chemical shifts is based on quantum chemical calculation at the Hartree-Fock/6-31G ? level. The geometry optimization of the famotidine molecule with two internal hydrogen bonds, i.e. [N(3)-H(23)⋯N(9) and N(3)⋯H(34)-N(20)], is done by using the B3LYP method with the 6-31G ? basis set.

Bara?ska, M.; Czarniecki, K.; Proniewicz, L. M.

2001-05-01

282

High-resolution Fourier-transform extreme ultraviolet photoabsorption spectroscopy of 14N15N  

NASA Astrophysics Data System (ADS)

The first comprehensive high-resolution photoabsorption spectrum of 14N15N has been recorded using the Fourier-transform spectrometer attached to the Desirs beamline at the Soleil synchrotron. Observations are made in the extreme ultraviolet and span 100 000-109 000 cm-1 (100-91.7 nm). The observed absorption lines have been assigned to 25 bands and reduced to a set of transition energies, f values, and linewidths. This analysis has verified the predictions of a theoretical model of N2 that simulates its photoabsorption and photodissociation cross section by solution of an isotopomer independent formulation of the coupled-channel Schrdinger equation. The mass dependence of predissociation linewidths and oscillator strengths is clearly evident and many local perturbations of transition energies, strengths, and widths within individual rotational series have been observed.

Heays, A. N.; Dickenson, G. D.; Salumbides, E. J.; de Oliveira, N.; Joyeux, D.; Nahon, L.; Lewis, B. R.; Ubachs, W.

2011-12-01

283

(1)H, (13)C and (15)N resonance assignments of the Onconase FL-G zymogen.  

PubMed

Onconase() FL-G zymogen is a 120 residue protein produced by circular permutation of the native Onconase() sequence. In this construction, the wild type N- and C-termini are linked by a 16 residue segment and new N- and C-termini are generated at wild type positions R73 and S72. This novel segment linking the native N- and C-termini is designed to obstruct Onconase's() active site and encloses a cleavage site for the HIV-1 protease. As a first step towards the resolution of its 3D structure and the study of its structure-function relationships, we report here the nearly complete NMR (1)H, (13)C and (15)N resonance chemical shift assignments at pH 5.2 and 35C (BMRB deposit no 17973). The results presented here clearly show that the structure of the wild type Onconase() is conserved in the FL-G zymogen. PMID:22392335

Serrano, Soraya; Calls, Mariona; Vilanova, Maria; Benito, Antoni; Laurents, Douglas V; Rib, Marc; Bruix, Marta

2013-04-01

284

High-resolution Fourier-transform XUV photoabsorption spectroscopy of 14N15N  

E-print Network

The first comprehensive high-resolution photoabsorption spectrum of 14N15N has been recorded using the Fourier-transform spectrometer attached to the Desirs beamline at the Soleil synchrotron. Observations are made in the extreme ultraviolet (XUV) and span 100,000-109,000 cm-1 (100-91.7 nm). The observed absorption lines have been assigned to 25 bands and reduced to a set of transition energies, f values, and linewidths. This analysis has verified the predictions of a theoretical model of N2 that simulates its photoabsorption and photodissociation cross section by solution of an isotopomer independent formulation of the coupled-channel Schroedinger equation. The mass dependence of predissociation linewidths and oscillator strengths is clearly evident and many local perturbations of transition energies, strengths, and widths within individual rotational series have been observed.

Heays, A N; Salumbides, E J; de Oliveira, N; Joyeux, D; Nahon, L; Lewis, B R; Ubachs, W; 10.1063/1.3672165

2012-01-01

285

Studies on in vitro antipyrine metabolism by /sup 13/C, /sup 15/N double labeled method  

SciTech Connect

The capacities of forms of cytochrome P-450 to oxidize antipyrine were compared. An isotope dilution gas chromatography/mass spectrometry/selected ion monitoring assay was developed to quantify the three main metabolites, norantipyrine, 3-hydroxymethyl-antipyrine and 4-hydroxyantipyrine. /sup 13/C, /sup 15/N-Double labeled antipyrine was used as a substrate and the metabolites were analyzed as their trimethylsilyl derivatives. Among forms of cytochrome P-450 examined, a male-specific form of P-450, namely P-450-male, showed higher activity to form all the three metabolites. The other forms were responsible only for the formation of norantipyrine and 4-hydroxy-antipyrine. The activities of liver microsomes from untreated male and female rats and rats treated with phenobarbital, 3-methylcholanthrene or polychlorinated biphenyl were expressed dependent on the activities of forms of cytochrome P-450 examined. 31 references, 4 figures, 3 tables.

Nakagawa, A.; Nakamura, K.; Maeda, K.; Kamataki, T.; Kato, R.

1987-07-13

286

Creating 13C- and 15N-enriched tree leaf litter for decomposition experiments  

NASA Astrophysics Data System (ADS)

Labeling plant material with heavy isotopes of carbon and nitrogen can produce a traceable nutrient signal that can be followed into the different trophic levels and decomposer food web. We treated 60 tree saplings with 13C-enriched CO2 gas and 15N-enriched ammonium nitrate over a three-month period to create dually-labeled plant material for future decomposition experiments. The trees included both early (Red maple, Sweetgum, Tulip poplar) and late (American beech, White oak) successional deciduous tree species, and a conifer, White pine. We constructed a 2.4 m 2.4 m 2.4 m environmental chamber that was climate-controlled using an air conditioning system. An Arduino microcontroller interfaced with a Vaisala GMP343 CO2 probe maintained a CO2 concentration between 500-520 ppm by controlling a solenoid valve on the CO2 tank regulator. The trees were placed into the chamber in August 2012 and remained until senescence unless they were lost to death or disease. Ammonium nitrate was added twice, in September and October. Leaf samples were collected prior to the start of the experiment and after senescence, whereas root samples were collected only in December. Samples were dried, ground and analyzed using an isotope ratio mass spectrometer. American beech and White oak had 40% mortality, and 34% of tulip poplar trees were removed because of powdery mildew overgrowth or death. Most tulip poplar trees exhibited a second leaf out following senescence in late September. Nearly 1 kg of litter was produced with tulip poplar representing over half of the total mass. Levels of enrichment varied greatly by species. Beech (-14.2) and White oak (-4.8) had low levels of enrichment in comparison to early successional species such as Sweetgum (41.7) and Tulip poplar (30.7 [first leaf fall] and 238.0 [second leaf fall]). Leaf enrichment with 15N followed a similar pattern, though it was achieved at a higher level with ?15N values varying from 271.6 to 1354.2 at the end of the experiment. Enrichment of roots was significantly higher than leaves (?13C range: 111.5-219.2; ?15N range: 1516.9-3939.3) indicating that nutrients were translocated away from leaves prior to senescence, which is supported by the increase in C:N ratio between the initial (19.0) and final (60.1) leaf sampling. Despite the variable levels of enrichment, leaves from all species were sufficiently labeled for use in future studies aimed at tracking the transformation of carbon and nitrogen during decomposition. The greatest challenges were treating diseases and pests and creating ideal growing conditions for many species within the same chamber. Reducing the number of individuals and better pest management will lead to even higher level enrichment in the future.

Szlavecz, K. A.; Pitz, S.; Chang, C.; Bernard, M.

2013-12-01

287

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

PubMed Central

Amyloid fibrils of Alzheimers ?-amyloid peptide (A?) are a primary component of amyloid plaques, a hallmark of Alzheimers 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?(140), the most abundant A? in brains, for structural studies by NMR spectroscopy. Over-expression of A?(140) 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?(140) and uniformly 15N- and/or 13C-protein A?(140) 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?(140). It was also confirmed by electron micrography and solid-state NMR analysis that the purified A?(140) 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?(140) 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. PMID:21640828

Long, Fei; Cho, Wonhwa; Ishii, Yoshitaka

2011-01-01

288

Assignment of the backbone sup 1 H and sup 15 N NMR resonances of bacteriophage T4 lysozyme  

SciTech Connect

The proton and nitrogen ({sup 15}NH-H{sup {alpha}}-H{sup {beta}}) resonances of bacteriophage T4 lysozyme were assigned by {sup 15}N-aided {sup 1}H NMR. The assignments were directed from the backbone amide {sup 1}H-{sup 15}N nuclei, with the heteronuclear single-multiple-quantum coherence (HSMQC) spectrum of uniformly {sup 15}N enriched protein serving as the master template for this work. The main-chain amide {sup 1}H-{sup 15}N resonances and H{sup {alpha}} resonances were resolved and classified into 18 amino acid types by using HMQC and {sup 15}N-edited COSY measurements, respectively, of T4 lysozymes selectively enriched with one or more of {alpha}-{sup 15}N-labeled Ala, Arg, Asn, Asp, Gly, Gln, Glu, Ile, Leu, Lys, Met, Phe, Ser, Thr, Trp, Tyr, or Val. The heteronuclear spectra were complemented by proton DQF-COSY and TOCSY spectra of unlabeled protein in H{sub 2}O and D{sub 2}O buffers, from which the H{sup {beta}} resonances of many residues were identified. The NOE cross peaks to almost every amide proton were resolved in {sup 15}N-edited NOESY spectra of the selectively {sup 15}N enriched protein samples. Residue specific assignments were determined by using NOE connectivities between protons in the {sup 15}NH-H{sup {alpha}}-H{sup {beta}} spin systems of known amino acid type. Additional assignments of the aromatic proton resonances were obtained from {sup 1}H NMR spectra of unlabeled and selectively deuterated protein samples. The secondary structure of T4 lysozyme indicated from a qualitative analysis of the NOESY data is consistent with the crystallographic model of the protein.

McIntosh, L.P.; Dahlquist, F.W. (Univ. of Oregon, Eugene (USA)); Wand, A.J. (Fox Chase Cancer Center, Philadelphia, PA (USA)); Lowry, D.F.; Redfield, A.G. (Brandeis Univ., Waltham, MA (USA))

1990-07-10

289

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. PMID:20081008

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

2010-01-01

290

15N2 Fixation by Bacteria Associated with Maize Roots at a Low Partial O2 Pressure  

PubMed Central

Nitrogen fixation by bacteria associated with roots of intact maize plants was measured by exposing the roots to 15N2 at a partial O2 pressure (pO2) of 2 or 10 kPa. The plants were grown in a mixture of Weswood soil and sand and then transferred to plastic cylinders containing an N-free plant nutrient solution. The solution was sparged continuously with a mixture of air and N2 at a pO2 of 2 or 10 kPa. Acetylene reduction was measured after the roots were exposed to the low pO2 overnight. The air-N2 atmosphere in the cylinders was then replaced with an O2-He atmosphere at the same pO2, and the roots were exposed to 20 kPa of 15N2 for 20 to 22 h. Incorporation of 15N into the roots was 200 times greater at 2 kPa of O2 than at 10 kPa of O2. Adding l-malate (1 g of C liter?1) to the nutrient solution increased root-associated nitrogenase activity, producing a strong 15N label which could be traced into the shoots. Fixed 15N was detected in the shoots within 5 days after the plants were returned to unfertilized soil. In a similar experiment with undisturbed plants grown in fritted clay, movement of fixed 15N into the shoots was evident within 4 days after the roots were exposed to 15N2 at 2 kPa of O2. Inoculation with Azospirillum lipoferum yielded no significant differences in shoot dry weight, total nitrogen content, percent nitrogen, or 15N enrichment of plant tissues. Inoculated plants did exhibit greater root dry weight than uninoculated plants, however. PMID:16347968

Alexander, David B.; Zuberer, David A.

1989-01-01

291

Longitudinal distribution of nitrate ? 15 N and ? 18 O in two contrasting tropical rivers: implications for instream nitrogen cycling  

Microsoft Academic Search

The longitudinal variations in the nitrogen (?15N) and oxygen (?18O) isotopic compositions of nitrate (NO3\\u000a ?), the carbon isotopic composition (?13C) of dissolved inorganic carbon (DIC) and the ?13C and ?15N of particulate organic matter were determined in two Southeast Asian rivers contrasting in the watershed geology and land\\u000a use to understand internal nitrogen cycling processes. The $$ \\\\delta^{15} {\\\\text{N}}_{{{\\\\text{NO}}_{3}

Toshihiro Miyajima; Chikage Yoshimizu; Yoshie Tsuboi; Yoshiyuki Tanaka; Ichiro Tayasu; Toshi Nagata; Isao Koike

2009-01-01

292

The fate of 15 N enriched throughfall in two coniferous forest stands at different nitrogen deposition levels  

Microsoft Academic Search

The stable isotope15N was added as (15NH4)2SO4 to throughfall water for one year, to study the fate of the deposited nitrogen at different levels of N deposition in two N saturated coniferous forests ecosystems in the Netherlands. The fate of the15N was followed at high-N (4455 kg N ha?1 yr?1) 1) and low-N (46 kg N ha?1 yr?1) deposition in

C. J. Koopmans; A. Tietema; A. W. Boxman

1996-01-01

293

Dynamics of soil microbial biomass N under zero and shallow tillage for spring wheat, using 15 N urea  

Microsoft Academic Search

Summary Field studies to determine the effect of zero and shallow (10 cm) cultivation on microbial biomass were conducted on several Chernozemic soils in western Canada. Using the CHCl3 fumigation method, the distribution of microbial biomass N and the immobilization and subsequent release of added15N (15N-urea) from the microbial biomass were determined in the A horizon, at the 0 to

M. R. Carter; D. A. Rennie

1984-01-01

294

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

295

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.; Bhlke, J.K.; Casciotti, K.L.

2004-01-01

296

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

Microsoft Academic Search

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

Dori Ann Porter

2010-01-01

297

MILLIMETER-WAVE OBSERVATIONS OF CN AND HNC AND THEIR {sup 15}N ISOTOPOLOGUES: A NEW EVALUATION OF THE {sup 14}N/{sup 15}N RATIO ACROSS THE GALAXY  

SciTech Connect

The N = 1 {yields} 0 transitions of CN and C{sup 15}N (X{sup 2}{Sigma}{sup +}), as well as the J = 1 {yields} 0 lines of HN{sup 13}C and H{sup 15}NC, have been observed toward 11 molecular clouds using the new 3 mm ALMA-type receiver of the 12 m telescope of the Arizona Radio Observatory. These sources span a wide range of distances from the Galactic center and are all regions of star formation. From these observations, {sup 14}N/{sup 15}N ratios have been determined using two independent methods. First, the measurements of C{sup 14}N and C{sup 15}N were directly compared to establish this ratio, correcting for high opacities when needed, as indicated by the nitrogen hyperfine intensities. Second, the ratio was calculated from the quantity [HN{sup 13}C]/[H{sup 15}NC], determined from the HNC data, and then scaled by {sup 12}C/{sup 13}C ratios previously established, i.e., the so-called double isotope method. Values from both methods are in reasonable agreement, and fall in the range {approx}120-400, somewhat lower than previous {sup 14}N/{sup 15}N ratios derived from HCN. The ratios exhibit a distinct positive gradient with distance from the Galactic center, following the relationship{sup 14}N/{sup 15}N = 21.1 (5.2) kpc{sup -1} D{sub GC} + 123.8 (37.1). This gradient is consistent with predictions of Galactic chemical evolution models in which {sup 15}N has a secondary origin in novae, while primary and secondary sources exist for {sup 14}N. The local interstellar medium value was found to be {sup 4}N/{sup 15}N = 290 {+-} 40, in agreement with the ratio found in nearby diffuse clouds and close to the value of 272 found in Earth's atmosphere.

Adande, G. R.; Ziurys, L. M. [Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

2012-01-10

298

Effect of body size and body mass on ? 13 C and ? 15 N in coastal fishes and cephalopods  

NASA Astrophysics Data System (ADS)

Carbon and nitrogen isotopes have been widely used in the investigation of trophic relations, energy pathways, trophic levels and migrations, under the assumption that ? 13C is independent of body size and that variation in ? 15N occurs exclusively due to ontogenetic changes in diet and not body size increase per se. However, several studies have shown that these assumptions are uncertain. Data from food-webs containing an important number of species lack theoretical support on these assumptions because very few species have been tested for ? 13C and ? 15N variation in captivity. However, if sampling comprises a wide range of body sizes from various species, the variation of ? 13C and ? 15N with body size can be investigated. While correlation between body size and ? 13C and ? 15N can be due to ontogenetic diet shifts, stability in such values throughout the size spectrum can be considered an indication that ? 13C and ? 15N in muscle tissues of such species is independent of body size within that size range, and thus the basic assumptions can be applied in the interpretation of such food webs. The present study investigated the variation in muscle ? 13C and ? 15N with body size and body mass of coastal fishes and cephalopods. It was concluded that muscle ? 13C and ? 15N did not vary with body size or mass for all bony fishes with only one exception, the dragonet Callionymus lyra. Muscle ? 13C and ? 15N also did not vary with body size or mass in cartilaginous fishes and cephalopods, meaning that body size/mass per se have no effect on ? 13C or ? 15N, for most species analysed and within the size ranges sampled. The assumption that ? 13C is independent of body size and that variation in ? 15N is not affected by body size increase per se was upheld for most organisms and can be applied to the coastal food web studied taking into account that C. lyra is an exception.

Vinagre, C.; Mguas, C.; Cabral, H. N.; Costa, M. J.

2011-11-01

299

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

300

Core-shell molecularly imprinted polymer nanoparticles with assistant recognition polymer chains for effective recognition and enrichment of natural low-abundance protein.  

PubMed

Core-shell molecular imprinting of nanomaterials overcomes difficulties with template transfer and achieves higher binding capacities for macromolecular imprinting, which are more important to the imprinting of natural low-abundance proteins from cell extracts. In the present study, a novel strategy of preparing core-shell nanostructured molecularly imprinted polymers (MIPs) was developed that combined the core-shell approach with assistant recognition polymer chains (ARPCs). Vinyl-modified silica nanoparticles were used as support and ARPCs were used as additional functional monomers. Immunoglobulin heavy chain binding protein (BiP) from the endoplasmic reticulum (ER) was chosen as the model protein. The cloned template protein BiP was selectively assembled with ARPCs from their library, which contained numerous limited-length polymer chains with randomly distributed recognition and immobilization sites. The resulting complex was copolymerized onto the surface of vinyl-modified silica nanoparticles under low concentrations of the monomers. After template removal, core-shell-structured nanoparticles with a thin imprinted polymer layer were produced. The particles demonstrated considerably high adsorption capacity, fast adsorption kinetics and selective binding affinities toward the template BiP. Furthermore, the synthesized MIP nanoparticles successfully isolated cloned protein BiP from protein mixtures and highly enriched BiP from an ER extract containing thousands of kinds of proteins. The enrichment reached 115-fold and the binding capacity was 5.4 ?g g(-1), which were higher than those achieved by using traditional MIP microspheres. The advantageous properties of MIP nanoparticles hold promise for further practical applications in biology, such as protein analysis and purification. PMID:24140608

Liu, Dejing; Yang, Qian; Jin, Susu; Song, Yingying; Gao, Junfei; Wang, Ying; Mi, Huaifeng

2014-02-01

301

A critical size and period hypothesis to explain natural regulation of salmon abundance and the linkage to climate and climate change  

NASA Astrophysics Data System (ADS)

We hypothesise that salmon year class strength is determined in two stages during the first year in the ocean. There is an early natural mortality that is mostly related to predation, which is followed by a physiologically-based mortality. Juvenile salmon that fail to reach a critical size by the end of their first marine summer do not survive the following winter. In this study we describe our initial tests of this critical size and critical period hypothesis using data from ocean surveys of juvenile salmon and from experimental feeding studies on coho. Conservative swept volume abundance estimates for juvenile coho, and possibly chinook, indicate that there is high mortality in fall and winter during their first year in the sea. Studies of otolith weight show that the length and otolith-weight relationship for young coho changes in the early fall of their first ocean year. Studies of growth and associated hormone levels in feeding studies show that slow growing juvenile coho are stunted and deficient in an insulin-like growth factor-I (IGF-I). Juvenile coho sampled in September had low IGF-I values, indicative of poor growth. The results of these studies provide evidence for the general hypothesis that growth-related mortality occurs late in the first marine year and may be important in determining the strength of the year class (brood year). The link between total mortality and climate could be operating via the availability of nutrients regulating the food supply and hence competition for food (i.e. bottom-up regulation).

Beamish, R. J.; Mahnken, Conrad

302

sup 15 N NMR study on cyanide (C sup 15 N sup minus ) complex of cytochrome P-450 sub cam. Effects of d-camphor and putidaredoxin on the iron-ligand structure  

SciTech Connect

The cyanide (C{sup 15}N{sup {minus}}) complex of Pseudomonas putida cytochrome P-450 (P-450{sub cam}) exhibited well-resolved and hyperfine-shifted {sup 15}N NMR resonances arising from the iron-bound C{sup 15}N{sup {minus}} at 423 and 500 ppm in the absence and presence of the substrate, d-camphor, respectively. The values were smaller than those for cyanide complexes of myoglobin and hemoglobin ({approx} 1000 ppm) but fell into the same range as those for the cyanide complexes of peroxidases ({approx} 500 ppm). The {sup 15}N shift values of P-450{sub cam} were not incompatible with the existence of anionic ligand, such as cysteinyl thiolate anion, at the fifth coordination site of heme iron. The difference in the {sup 15}N chemical shift values between camphor-free and bound enzymes was inferred by the increase in the steric constraint to the Fe-C-N bond upon substrate binding.

Shiro, Yoshitsugu; Iizuka, Tetsutaro (Institute of Physical and Chemical Research, Saitama (Japan)); Makino, Ryu; Ishimura, Yuzuru (Keio Univ., Tokyo (Japan)); Morishima, Isao (Kyoto Univ. (Japan))

1989-11-27

303

A 15N-n.m.r. study of cerebral, hepatic and renal nitrogen metabolism in hyperammonaemic rats.  

PubMed Central

1. Rats were infused with 15NH4+ or L-[15N]alanine to induce hyperammonaemia, a potential cause of hepatic encephalopathy. HClO4 extracts of freeze-clamped brain, liver and kidney were analysed by 15N-n.m.r. spectroscopy in combination with biochemical assays to investigate the effects of hyperammonaemia on tissue concentrations of ammonia, glutamine, glutamate and urea. 2. 15NH4+ infusion resulted in a 36-fold increase in the concentration of blood ammonia. Cerebral glutamine concentration increased, with 15NH4+ incorporated predominantly into the gamma-nitrogen atom of glutamine. Incorporation into glutamate was very low. Cerebral ammonia concentration increased 5-10-fold. The results suggest that the capacity of glutamine synthetase for ammonia detoxification was saturated. 3. Pretreatment with the glutamine synthetase inhibitor L-methionine DL-sulphoximine resulted in 84% inhibition of [gamma-15N]glutamine synthesis, but incorporation of 15N into other metabolites was not observed. The result suggests that no major alternative pathway for ammonia detoxification, other than glutamine synthetase, exists in rat brain. 4. In the liver 15NH4+ was incorporated into urea, glutamine, glutamate and alanine. The specific activity of 15N was higher in the gamma-nitrogen atom of glutamine than in urea. A similar pattern was observed when [15N]alanine was infused. The results are discussed in terms of the near-equilibrium states of the reactions involved in glutamate and alanine formation, heterogeneous distribution in the liver lobules of the enzymes involved in ammonia removal and their different affinities for ammonia. 5. Synthesis of glutamine, glutamate and hippurate de novo was observed in kidney. Hippurate, as well as 15NH4+, was contributed by co-extracted urine. 6. The potential utility and limitations of 15N n.m.r. for studies of mammalian metabolism in vivo are discussed. PMID:1976007

Farrow, N A; Kanamori, K; Ross, B D; Parivar, F

1990-01-01

304

Spatial and Temporal Variations in Stable Carbon (?13C) and Nitrogen (?15N) Isotopic Composition of Symbiotic Scleractinian Corals  

PubMed Central

Tropical scleractinian corals are considered autotrophic as they rely mainly on photosynthesis-derived nutrients transferred from their photosymbionts. Corals are also able to capture and ingest suspended particulate organic matter, so heterotrophy can be an important supplementary trophic pathway to optimize coral fitness. The aim of this in situ study was to elucidate the trophic status of 10 coral species under contrasted environmental conditions in a French Polynesian lagoon. Carbon (?13C) and nitrogen (?15N) isotopic compositions of coral host tissues and photosymbionts were determined at 3 different fringing reefs during wet and dry seasons. Our results highlighted spatial variability in stable isotopic compositions of both coral host tissues and photosymbionts. Samples from the site with higher level of suspended particulate matter were 13C-depleted and 15N-enriched relative to corals and photosymbionts from less turbid sites. However, differences in both ?13C and ?15N between coral host tissues and their photosymbionts (?host-photosymbionts 13C and ?host-photosymbionts 15N) were small (0.27 0.76 and 1.40 0.90, respectively) and similar at all sites, thus indicating no general increases in the heterotrophic pathway. Depleted ?13C and enriched ?15N values of coral host tissues measured at the most turbid site were explained by changes in isotopic composition of the inorganic nutrients taken up by photosymbionts and also by changes in rate of isotopic fractionation with environmental conditions. Our results also highlighted a lack of significant temporal variations in ?13C and ?15N values of coral host and photosymbiont tissues and in ?host-photosymbionts 13C and ?host-photosymbionts 15N values. This temporal stability indicated that corals remained principally autotrophic even during the wet season when photosymbiont densities were lower and the concentrations of phytoplankton were higher. Increased coral heterotrophy with higher food availability thus appears to be species-specific. PMID:24312542

Nahon, Sarah; Richoux, Nicole B.; Kolasinski, Joanna; Desmalades, Martin; Ferrier Pages, Christine; Lecellier, Gael; Planes, Serge; Berteaux Lecellier, Veronique

2013-01-01

305

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

PubMed Central

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

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

2013-01-01

306

Tracking the incorporation of 15N from labeled beech litter into mineral-organic associations  

NASA Astrophysics Data System (ADS)

Nitrogen containing organic compounds are thought to have a role in the complex web of processes that control the turnover time of soil organic matter. The sequential density fractionation technique is increasingly used for the purpose of investigating the association of organic materials with the mineral matrix. Organic materials in the denser fractions (>2.0 kg L-1) typically show 13C NMR signals indicative of carbohydrate and aliphatic structures, an absence of lignin and tannin structures and a narrow C:N ratio, suggesting a microbial origin of organic matter in these fractions. Here we take advantage of a labeling experiment conducted at two different sites in Germany and in France to investigate the incorporation of organic nitrogen into physical fractions of increasing density, representing a proximity gradient to mineral surfaces. 15N labeled beech litter was applied to two acidic forest topsoils 8 and 12 years ago. Although there are differences in the distribution patterns between the two soils, and the majority of the organic nitrogen was recovered in fractions representing organic matter of plant origin and not bound to the mineral matrix, our data clearly show that after a decade, significant amounts of the nitrogen had been incorporated in mineral-organic fractions of supposedly slow turnover. It remains to be shown to which extent the N in the densest fractions was incorporated by soil microbiota and associated with mineral surfaces in organic form or adsorbed to mineral surfaces in inorganic form (NH4+).

Kleber, M.; Hatton, P.; Derrien, D.; Lajtha, K.; Zeller, B.

2008-12-01

307

15N Solid-State NMR as a Probe of Flavin H-bonding  

PubMed Central

Flavins mediate a wide variety of different chemical reactions in biology. To learn how one cofactor can be made to execute different reactions in different enzymes, we are developing solid-state NMR (SSNMR) to probe the flavin electronic structure, via the 15N chemical shift tensor principal values (?ii). We find that SSNMR has superior responsiveness to H-bonds, compared to solution NMR. H-bonding to a model of the flavodoxin active site produced an increase of 10 ppm in the ?11 of N5 although none of the H-bonds directly engage N5, and solution NMR detected only a 4 ppm increase in the isotropic chemical shift (?iso). Moreover SSNMR responded differently to different H-bonding environments as H-bonding with water caused ?11 to decrease by 6 ppm whereas ?iso increased by less than 1 ppm. Our density functional theoretical (DFT) calculations reproduce the observations, validating the use of computed electronic structures to understand how H-bonds modulate the flavins reactivity. PMID:21619002

Cui, Dongtao; Koder, Ronald L.; Dutton, P. Leslie; Miller, Anne-Frances

2011-01-01

308

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

309

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 199798. The physical or biological drivers of this expansion, as well as its ecological consequences remain unknown. Here, novel analysis from both bulk tissues and individual amino acids (Phenylalanine; Phe and Glutamic acid; Glu) in both gladii and muscle of D. gigas captured in the Northern California Current System (NCCS) documents for the first time multiple geographic origins and migration. Phe ?15N values, a proxy for habitat baseline ?15N values, confirm at least three different geographic origins that were initially detected by highly variable bulk ?15N values in gladii for squid at small sizes (<30 cm gladii length). In contrast, bulk ?15N values from gladii of large squid (>60 cm) converged, indicating feeding in a common ecosystem. The strong latitudinal gradient in Phe ?15N values from composite muscle samples further confirmed residency at a point in time for large squid in the NCCS. These results contrast with previous ideas, and indicate that small squid are highly migratory, move into the NCCS from two or more distinct geographic origins, and use this ecosystem mainly for feeding. These results represent the first direct information on the origins, immigration and habitat use of this key invasive predator in the NCCS, with wide implications for understanding both the mechanisms of periodic D. gigas population range expansions, and effects on ecosystem trophic structure. PMID:23527242

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

2013-01-01

310

Exploring the nitrogen ingestion of aphids--a new method using electrical penetration graph and (15)N labelling.  

PubMed

Studying plant-aphid interactions is challenging as aphid feeding is a complex process hidden in the plant tissue. Here we propose a combination of two well established methods to study nutrient acquisition by aphids focusing on the uptake of isotopically labelled nitrogen ((15)N). We combined the Electrical Penetration Graph (EPG) technique that allows detailed recording of aphid feeding behaviour and stable isotope ratio mass spectrometry (IRMS) to precisely measure the uptake of nitrogen. Bird cherry-oat aphids Rhopalosiphum padi L. (Hemiptera, Aphididae) fed for 24 h on barley plants (Hordeum vulgare L., cultivar Lina, Poaceae) that were cultivated with a (15)N enriched nutrient solution. The time aphids fed in the phloem was strongly positive correlated with their (15)N uptake. All other single behavioural phases were not correlated with (15)N enrichment in the aphids, which corroborates their classification as non-feeding EPG phases. In addition, phloem-feeding and (15)N enrichment of aphids was divided into two groups. One group spent only short time in the phloem phase and was unsuccessful in nitrogen acquisition, while the other group displayed longer phloem-feeding phases and was successful in nitrogen acquisition. This suggests that several factors such as the right feeding site, time span of feeding and individual conditions play a role for the aphids to acquire nutrients successfully. The power of this combination of methods for studying plant-aphid interactions is discussed. PMID:24376642

Kuhlmann, Franziska; Opitz, Sebastian E W; Inselsbacher, Erich; Ganeteg, Ulrika; Nsholm, Torgny; Ninkovic, Velemir

2013-01-01

311

Range expansion of the jumbo squid in the NE Pacific: ?15N decrypts multiple origins, migration and habitat use.  

PubMed

Coincident with climate shifts and anthropogenic perturbations, the highly voracious jumbo squid Dosidicus gigas reached unprecedented northern latitudes along the NE Pacific margin post 1997-98. The physical or biological drivers of this expansion, as well as its ecological consequences remain unknown. Here, novel analysis from both bulk tissues and individual amino acids (Phenylalanine; Phe and Glutamic acid; Glu) in both gladii and muscle of D. gigas captured in the Northern California Current System (NCCS) documents for the first time multiple geographic origins and migration. Phe ?(15)N values, a proxy for habitat baseline ?(15)N values, confirm at least three different geographic origins that were initially detected by highly variable bulk ?(15)N values in gladii for squid at small sizes (<30 cm gladii length). In contrast, bulk ?(15)N values from gladii of large squid (>60 cm) converged, indicating feeding in a common ecosystem. The strong latitudinal gradient in Phe ?(15)N values from composite muscle samples further confirmed residency at a point in time for large squid in the NCCS. These results contrast with previous ideas, and indicate that small squid are highly migratory, move into the NCCS from two or more distinct geographic origins, and use this ecosystem mainly for feeding. These results represent the first direct information on the origins, immigration and habitat use of this key "invasive" predator in the NCCS, with wide implications for understanding both the mechanisms of periodic D. gigas population range expansions, and effects on ecosystem trophic structure. PMID:23527242

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

2013-01-01

312

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

313

Exploring the Nitrogen Ingestion of Aphids -- A New Method Using Electrical Penetration Graph and 15N Labelling  

PubMed Central

Studying plant-aphid interactions is challenging as aphid feeding is a complex process hidden in the plant tissue. Here we propose a combination of two well established methods to study nutrient acquisition by aphids focusing on the uptake of isotopically labelled nitrogen (15N). We combined the Electrical Penetration Graph (EPG) technique that allows detailed recording of aphid feeding behaviour and stable isotope ratio mass spectrometry (IRMS) to precisely measure the uptake of nitrogen. Bird cherry-oat aphids Rhopalosiphum padi L. (Hemiptera, Aphididae) fed for 24 h on barley plants (Hordeum vulgare L., cultivar Lina, Poaceae) that were cultivated with a 15N enriched nutrient solution. The time aphids fed in the phloem was strongly positive correlated with their 15N uptake. All other single behavioural phases were not correlated with 15N enrichment in the aphids, which corroborates their classification as non-feeding EPG phases. In addition, phloem-feeding and 15N enrichment of aphids was divided into two groups. One group spent only short time in the phloem phase and was unsuccessful in nitrogen acquisition, while the other group displayed longer phloem-feeding phases and was successful in nitrogen acquisition. This suggests that several factors such as the right feeding site, time span of feeding and individual conditions play a role for the aphids to acquire nutrients successfully. The power of this combination of methods for studying plant-aphid interactions is discussed. PMID:24376642

Kuhlmann, Franziska; Opitz, Sebastian E. W.; Inselsbacher, Erich; Ganeteg, Ulrika; Nasholm, Torgny; Ninkovic, Velemir

2013-01-01

314

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

315

Slow motions in microcrystalline proteins as observed by MAS-dependent 15N rotating-frame NMR relaxation  

NASA Astrophysics Data System (ADS)

15N NMR relaxation rate R1? measurements reveal that a substantial fraction of residues in the microcrystalline chicken alpha-spectrin SH3 domain protein undergoes dynamics in the ?s-ms timescale range. On the basis of a comparison of 2D site-resolved with 1D integrated 15N spectral intensities, we demonstrate that the significant fraction of broad signals in the 2D spectrum exhibits the most pronounced slow mobility. We show that 15N R1?'s in proton-diluted protein samples are practically free from the coherent spin-spin contribution even at low MAS rates, and thus can be analysed quantitatively. Moderate MAS rates (10-30 kHz) can be more advantageous in comparison with the rates >50-60 kHz when slow dynamics are to be identified and quantified by means of R1? experiments.

Krushelnitsky, Alexey; Zinkevich, Tatiana; Reif, Bernd; Saalwchter, Kay

2014-11-01

316

Abundance coefficients, a new method for measuring microorganism relative abundance  

USGS Publications Warehouse

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

Forester, R.M.

1977-01-01

317

Dynamics in the isotropic phase of nematogens using 2D IR vibrational echo measurements on natural-abundance 13CN and extended lifetime probes.  

PubMed

The long time scale orientational relaxation of nematogens in the isotropic phase is associated with the randomization of pseudonematic domains, which have a correlation length that grows as the isotropic-to-nematic phase transition temperature is approached from above. Here we begin to address the fast dynamics of the nematogen molecules within the domains using two-dimensional infrared (2D IR) vibrational echo experiments. The problems of performing ultrafast IR experiments in pure liquids are discussed, and solutions are presented. In addition, the issue of short vibrational lifetimes, which limit the ability of 2D IR experiments to examine dynamics over a wide range of times, is addressed. The experiments were performed on the nematogen 4-cyano-4'-pentylbiphenyl (5CB), with the CN stretch initially used as the vibrational probe. Although the CN stretch has a small transition dipole, because the sample is a pure liquid it is necessary to use an exceedingly thin sample to perform the experiments. The small sample volume leads to massive heating effects that distort the results. In addition, the high concentration in the pure liquid can result in vibrational excitation transfer that interferes with the measurements of structural dynamics, and the CN vibrational lifetime is very short (3.6 ps). These problems were overcome by performing the experiments on the natural-abundance (13)CN stretch (5(13)CB), which greatly reduced the absorbance, eliminating the heating problems; also, this stretch has a longer lifetime (7.9 ps). Experiments were also performed on benzonitrile, which showed that the heating problems associated with pure liquids are not unique to 5CB. Again, the problems were eliminated by conducting measurements on the (13)CN stretch, which has an even longer lifetime (20.2 ps) compared with the (12)CN stretch (5.6 ps). Finally, to extend the range of the dynamical measurements, 4-pentyl-4'-thiocyanobiphenyl (5SCB) was synthesized and studied as a dilute solute in 5CB. The CN stretch of 5SCB has a vibrational lifetime of 103 ps, which permits dynamical measurements to 200 ps, revealing the full range of fast structural dynamics in the isotropic phase of 5CB. It is shown that the 5SCB probe reports essentially the same dynamics as 5(13)CB on the short time scale that is observable with the 5(13)CB vibrational probe. PMID:24156524

Sokolowsky, Kathleen P; Fayer, Michael D

2013-12-01

318

Conformational study of C8 diazocine turn mimics using {sup 3}J{sub CH} coupling constants with {sup 13}C in natural abundance  

SciTech Connect

The conformations of two diazocine turn mimics, which were later incorporated into GPIIb/IIIa peptide antagonists, were investigated using nuclear magnetic resonance techniques. The two compounds, methyl (2,5-dioxo-3-(S)-(3-{omega}-tosylguanidino-propyl)-4-methyl-octahydro-1,4-dazocin-1-yl)acetate (1) and methyl (2,5-dioxo-3-(S)-(3-{omega}-tosyl-guanidino-propyl)-octahydro-1,5-diazocin-1-yl)acetate (2), differ only in their substituent at the diazocine position 4 nitrogen, yet this substitution results in a marked difference in the affinity of the resulting analogs for the GPIIb/IIIa receptor. It was of interest to determine if the difference observed in the antagonistic potency between these analogs was related to constitutional or, perhaps, conformational differences. The backbone conformations of these two molecules can be determined by measuring vicinal coupling constants along the trimethylene portion of the C8 ring backbone and by measuring interproton NOE intensities between the diazocine methine proton and the protons of the trimethylene group. For compound 1, {sup 3}J{sub HH} values measured from a P.E.COSY spectrum and interproton distances calculated from ROESY buildup curves indicated the presence of a single C8 ring backbone conformation where the trimethylene bridge adopted a staggered conformation and the H{alpha}1 and H{gamma}1 protons of the trimethylene group were 2.2 A from the methine proton. For compound 2, however, partial overlap of the central H{beta}1 and H{beta}2 protons made it impossible to measure {sup 3}J{sub HH} values from the P.E.COSY spectrum. We therefore used a {sup 13}C-filtered TOCSY experiment to measure the {sup 3}J{sub CH} values in both compounds 1 and 2. These heteronuclear vicinal coupling constants measured with {sup 13}C in natural abundance in conjunction with measured interproton NOE intensities indicate that these compounds share a common C8 ring backbone conformation.

Bean, J.W.; Briand, J.; Burgess, J.L.; Callahan, J.F. [SmithKline Beecham Pharmaceuticals, King of Prussia, PA (United States)

1994-12-01

319

Line Lists for the A 2?-X 2?+ (Red) and B 2?+-X 2?+ (Violet) Systems of CN, 13C14N, and 12C15N, and Application to Astronomical Spectra  

NASA Astrophysics Data System (ADS)

New red and violet system line lists for the CN isotopologues 13C14N and 12C15N have been generated. These new transition data are combined with those previously derived for 12C14N, and applied to the determination of CNO abundances in the solar photosphere and in four red giant stars: Arcturus, the bright, very low-metallicity star HD 122563, and the carbon-enhanced metal-poor stars HD 196944 and HD 201626. When both red and violet system lines are detectable in a star, their derived N abundances are in good agreement. The mean N abundances determined in this work are also generally in accord with published values.

Sneden, Christopher; Lucatello, Sara; Ram, Ram S.; Brooke, James S. A.; Bernath, Peter

2014-10-01

320

Separating the contributions to 15N transverse relaxation in a fibronectin type III domain.  

PubMed

In proteins, dynamic mobility is an important feature of structure, stability, and biomolecular recognition. Uniquely sensitive to motion throughout the milli- to picosecond range, rates of transverse relaxation, R2, are commonly obtained for the characterization of chemical exchange, and the construction of motional models that attempt to separate overall and internal mobility. We have performed an in-depth study of transverse relaxation rates of backbone 15N nuclei in TNfn3(1-90), the third fibronectin type III domain from human tenascin. By combining the results of spin-echo (CPMG) and off-resonance T1 rho experiments, we present R2 rates at effective field strengths of 2 to 40 krad/s, obtaining a full spectrum of 16 independent R2 data points for most residues. Collecting such a large number of replicate measurements provides insight into intrinsic uncertainties. The median standard deviation in R2 for non-exchanging residues is 0.31, indicating that isolated measurements may not be sufficiently accurate for a precise interpretation of motional models. Chemical exchange events on a timescale of 570 microseconds were observed in a cluster of residues at the C terminus. Rates of exchange for five other residues were faster than the sampled range of frequencies and could not be determined. Averaged 'exchange free' transverse relaxation rates, R2(0), were used to calculate the diffusion tensor for rotational motion. Despite a highly asymmetric moment of inertia, the narrow angular dispersion of N-H vectors within the beta sandwich proves insufficient to define deviations from isotropic rotation. Loop residues provide exclusive evidence for axially symmetric diffusion (Dpar/Dper = 1.55). PMID:10382303

Meekhof, A E; Freund, S M

1999-05-01

321

Acetylene reduction, H 2 evolution and 15 N 2 fixation in the Alnus incana-Frankia symbiosis  

Microsoft Academic Search

Acetylene reduction, 15N2 reduction and H2 evolution were measured in root systems of intact plants of grey alder (Alnus incana (L.) Moench) in symbiosis with Frankia. The ratios of C2H2: 15N2 were compared with C2H2:N2 ratios calculated from C2H2 reduction and H2 evolution, and with C2H2:N2 ratios calculated from accumulated C2H4 production and nitrogen content. It was possible to calculate

A. Sellstedt

1986-01-01

322

Nitrogen mineralization from selected /sup 15/N-labelled crop residues and humus as affected by inorganic nitrogen  

SciTech Connect

The use of cover crops or crop residues as a source of N to succeeding crops has become a matter of increasing importance for economic and environmental reason. Greenhouse and field studies were conducted to determine the N contribution of four /sup 15/N labelled crop residues, rye (Secale cereale L.), wheat (Triticum aestivum L.), crimson clover (Trifolium encarnatum L.), and hairy vetch (Vicia sativa L.), to successive crops and to evaluate the effect of different organic (ON) and inorganic N (IN) combinations on mineralization of the above residues. Total /sup 15/N recovery from the residues ranged from 51% to 85% and 4% to 74% for the greenhouse and field studies, respectively.

Santos, J.A.

1987-01-01

323

Paramagnetic 13C and 15N NMR analyses of cyanide- (13C15N-) ligated ferric peroxidases: the push effect, not pull effect, modulates the compound I formation rate.  

PubMed

Paramagnetic (13)C and (15)N NMR spectroscopy of heme-bound cyanide ((13)C(15)N) was utilized to quantitatively distinguish the electron donor effect (the push effect) from the proximal histidine and hydrogen-bonding effect (the pull effect) from the distal amino acid residues in cytochrome c peroxidase (CcP), ascorbate peroxidase (APX), lignin peroxidase (LiP), and manganese peroxidase (MnP). Paramagnetic (13)C NMR signals of heme-bound (13)C(15)N of these peroxidases were observed in a wide range, -3501 ppm (CcP), -3563 ppm (APX), -3823 ppm (MnP), and -3826 ppm (LiP), while paramagnetic (15)N NMR signals of those were detected in a narrow range, 574 ppm (ARP), 605 ppm (CcP), 626 ppm (LiP), and 654 ppm (MnP). Detailed analysis, combined with the previous results for horseradish peroxidase and Arthromyces ramosus peroxidase, indicated that the push effect is quite different among these peroxidases while the pull effect is similar. More importantly, a strong correlation between the (13)C NMR shift (the push effect) and the compound I formation rate was observed, indicating that the push effect causes a variation in the compound I formation rate. Comparison of the (13)C and (15)N NMR results of these peroxidases with their crystal structures suggests that the orientation of the proximal imidazole plane to the heme N-Fe-N axis controls the push effect and the compound I formation rate of peroxidase. PMID:19187033

Nonaka, Daisuke; Wariishi, Hiroyuki; Fujii, Hiroshi

2009-02-10

324

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 (163153 ?g kg-1 d-1) than in OP (3.92.0 ?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 (0.180.02) than in JC (0.080.02). Mean (SE) DNRA rates in JC (3.52.3 ?g N kg-1 d-1) were significantly higher (p<0.05) than in OP (2.42.1 ?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

325

Pressure effect on the dynamics of an isolated alpha-helix studied by 15N-1H NMR relaxation.  

PubMed

Dynamics and structure of (1-36)bacteriorhodopsin solubilized in chloroform/methanol mixture (1:1) were investigated by 1H-15N NMR spectroscopy under a hydrostatic pressure of 2000 bar. It was shown that the peptide retains its spatial structure at high pressure. 15N transverse and longitudinal relaxation times, 15N[1H] nuclear Overhauser effects, chemical shifts and the translation diffusion rate of the peptide at 2000 bar were compared with the respective data at ambient pressure [Orekhov et al. (1999) J. Biomol. NMR, 14, 345-356]. The model free analysis of the relaxation data for the helical 9-31 fragment revealed that the high pressure decreases the overall rotation and translation diffusion, as well as apparent order parameters of fast picosecond internal motions (S2) but has no effect on internal nanosecond motions (S2 and taus) of the peptide. The decrease of translation and overall rotation diffusion was attributed to the increase in solvent viscosity and the decrease of apparent order parameters S2f to a compression of hydrogen bonds. It is suggested that this compression causes an elongation of H-N bonds and a decrease of absolute values of chemical shift anisotropy (CSA). In particular, the observed decrease of S2f at 2000 bar can be explained by 0.001 nm increase of N-H bond lengths and 10 ppm decrease of 15N CSA values. PMID:10959632

Orekhov, V Y; Dubovskii, P V; Yamada, H; Akasaka, K; Arseniev, A S

2000-07-01

326

Contrasting food web linkages for the grazing pathway in 3 temperate forested streams using {sup 15}N as a tracer  

SciTech Connect

Nitrogen is a critical element controlling the productivity and dynamics of stream ecosystems and many streams are limited by the supply of biologically available nitrogen. The authors are learning more about the fate of inorganic nitrogen entering streams through {sup 15}N tracer additions. The Lotic Intersite Nitrogen Experiment (LINX) is studying the uptake, cycling, and fate of {sup 15}N-NH{sub 4} in the stream food web of 10 streams draining different biomes. Using the {sup 15}N tracer method and data from 3 sites in the study, the authors can differentiate patterns in the cycling of nitrogen through the grazing pathway (N from the epilithon to grazing macroinvertebrates) for 3 temperate forested streams. Here, they quantify the relationship between the dominant grazer and its proposed food resource, the epilithon, by comparing {sup 15}N levels of grazers with those of the epilithon, as well as the biomass, nitrogen content, and chlorophyll a standing stocks of the epilithon in 3 streams.

Tank, J.L.; Mulholland, P.J.; Meyer, J.L.; Bowden, W.B.; Webster, J.R.; Peterson, B.J.

1998-11-01

327

STATISTICAL ESTIMATES OF VARIANCE FOR 15N ISOTOPE DILUTION MEASUREMENTS OF GROSS RATES OF NITROGEN CYCLE PROCESSES  

EPA Science Inventory

It has been fifty years since Kirkham and Bartholmew (1954) presented the conceptual framework and derived the mathematical equations that formed the basis of the now commonly employed method of 15N isotope dilution. Although many advances in methodology and analysis have been ma...

328

COMPARISON OF STABLE-NITROGEN (15N/14N) ISOTOPE RATIOS IN LARGE MOUTH BASS SCALES AND MUSCLE TISSUE  

EPA Science Inventory

Stable-nitrogen (15N/14N) isotope ratios of fish tissue are currently used to determine trophic structure, contaminant bioaccumulation, and the level of anthropogenic nitrogen enrichment in aquatic systems. The most common tissue used for these measurements is fileted dorsal musc...

329

Heteronuclear transverse and longitudinal relaxation in AX4 spin systems: Application to (15)N relaxations in (15)NH4(+).  

PubMed

The equations that describe the time-evolution of transverse and longitudinal (15)N magnetisations in tetrahedral ammonium ions, (15)NH4(+), are derived from the Bloch-Wangsness-Redfield density operator relaxation theory. It is assumed that the relaxation of the spin-states is dominated by (1) the intra-molecular (15)N-(1)H and (1)H-(1)H dipole-dipole interactions and (2) interactions of the ammonium protons with remote spins, which also include the contribution to the relaxations that arise from the exchange of the ammonium protons with the bulk solvent. The dipole-dipole cross-correlated relaxation mechanisms between each of the (15)N-(1)H and (1)H-(1)H interactions are explicitly taken into account in the derivations. An application to (15)N-ammonium bound to a 41kDa domain of the protein DnaK is presented, where a comparison between experiments and simulations show that the ammonium ion rotates rapidly within its binding site with a local correlation time shorter than approximately 1ns. The theoretical framework provided here forms the basis for further investigations of dynamics of AX4 spin systems, with ammonium ions in solution and bound to proteins of particular interest. PMID:25128779

Werbeck, Nicolas D; Hansen, D Flemming

2014-09-01

330

Heteronuclear transverse and longitudinal relaxation in AX4 spin systems: Application to 15N relaxations in 15NH4+  

NASA Astrophysics Data System (ADS)

The equations that describe the time-evolution of transverse and longitudinal 15N magnetisations in tetrahedral ammonium ions, 15NH4+, are derived from the Bloch-Wangsness-Redfield density operator relaxation theory. It is assumed that the relaxation of the spin-states is dominated by (1) the intra-molecular 15N-1H and 1H-1H dipole-dipole interactions and (2) interactions of the ammonium protons with remote spins, which also include the contribution to the relaxations that arise from the exchange of the ammonium protons with the bulk solvent. The dipole-dipole cross-correlated relaxation mechanisms between each of the 15N-1H and 1H-1H interactions are explicitly taken into account in the derivations. An application to 15N-ammonium bound to a 41 kDa domain of the protein DnaK is presented, where a comparison between experiments and simulations show that the ammonium ion rotates rapidly within its binding site with a local correlation time shorter than approximately 1 ns. The theoretical framework provided here forms the basis for further investigations of dynamics of AX4 spin systems, with ammonium ions in solution and bound to proteins of particular interest.

Werbeck, Nicolas D.; Hansen, D. Flemming

2014-09-01

331

Using macroalgal d15N bioassay to detect cruise ship waste water effluent inputs in Skagway, AK  

EPA Science Inventory

Nitrogen stable isotopes are a powerful tool for tracking sources of N to marine ecosystems. I used green macroalgae as a bioassay organism to evaluate if the d15N signature of cruise ship waste water effluent (CSWWE) could be detected in Skagway Harbor, AK. Opportunistic green...

332

Effects of region, genotype, harvest year and their interactions on ?(13)C, ?(15)N and ?D in wheat kernels.  

PubMed

The objective of this study was to investigate the influences of region, genotype, harvest year and their interactions on stable carbon, nitrogen and hydrogen isotopic ratio (?(13)C, ?(15)N and ?D) fingerprints in wheat kernels. A total of 270 wheat kernel samples including ten genotypes were collected from three different regions of China during 2011-2013 harvest. Analysis of variance was employed to investigate the effects of region, genotype, harvest year and their interactions on the ?(13)C, ?(15)N and ?D. The results showed that the ?(13)C and ?(15)N values in wheat kernels were significantly influenced by the region, genotype, harvest year and their interactions (regiongenotype, genotypeyear, regionyear and regiongenotypeyear), ?D was significantly affected by region, genotype, harvest year and regionyear. Region accounted for the largest proportion of the total variation and explained 47.57%, 58.02% and 27.96% for ?(13)C, ?(15)N and ?D, respectively. PMID:25308642

Liu, Hongyan; Guo, Boli; Wei, Yimin; Wei, Shuai; Ma, Yiyan; Zhang, Wan

2015-03-15

333

1H and 15N nuclear magnetic resonance assignment and secondary structure of the cytotoxic ribonuclease alpha-Sarcin.  

PubMed Central

The ribosome-inactivating protein alpha-Sarcin (alpha S) is a 150-residue fungal ribonuclease that, after entering sensitive cells, selectively cleaves a single phosphodiester bond in an universally conserved sequence of the major rRNA to inactivate the ribosome and thus exert its cytotoxic action. As a first step toward establishing the structure-dynamics-function relationships in this system, we have carried out the assignment of the 1H and 15N NMR spectrum of alpha S on the basis of homonuclear (1H-1H) and heteronuclear (1H-15N) two-dimensional correlation spectra of a uniformly 15N-labeled sample, and two selectively 15N-labeled (Tyr and Phe) samples, as well as a single three-dimensional experiment. The secondary structure of alpha S, as derived from the characteristic patterns of dipolar connectivities between backbone protons, conformational chemical shifts, and the protection of backbone amide protons against exchange, consists of a long N-terminal beta-hairpin, a short alpha-helical segment, and a C-terminal beta-sheet of five short strands arranged in a + 1, + 1, + 1, + 1 topology, connected by long loops in which the 13 Pro residues are located. PMID:8732769

Campos-Olivas, R.; Bruix, M.; Santoro, J.; Martnez del Pozo, A.; Lacadena, J.; Gavilanes, J. G.; Rico, M.

1996-01-01

334

1H and 15N nuclear magnetic resonance assignment and secondary structure of the cytotoxic ribonuclease alpha-Sarcin.  

PubMed

The ribosome-inactivating protein alpha-Sarcin (alpha S) is a 150-residue fungal ribonuclease that, after entering sensitive cells, selectively cleaves a single phosphodiester bond in an universally conserved sequence of the major rRNA to inactivate the ribosome and thus exert its cytotoxic action. As a first step toward establishing the structure-dynamics-function relationships in this system, we have carried out the assignment of the 1H and 15N NMR spectrum of alpha S on the basis of homonuclear (1H-1H) and heteronuclear (1H-15N) two-dimensional correlation spectra of a uniformly 15N-labeled sample, and two selectively 15N-labeled (Tyr and Phe) samples, as well as a single three-dimensional experiment. The secondary structure of alpha S, as derived from the characteristic patterns of dipolar connectivities between backbone protons, conformational chemical shifts, and the protection of backbone amide protons against exchange, consists of a long N-terminal beta-hairpin, a short alpha-helical segment, and a C-terminal beta-sheet of five short strands arranged in a + 1, + 1, + 1, + 1 topology, connected by long loops in which the 13 Pro residues are located. PMID:8732769

Campos-Olivas, R; Bruix, M; Santoro, J; Martnez del Pozo, A; Lacadena, J; Gavilanes, J G; Rico, M

1996-05-01

335

Improved determination of the astrophysical S(0) factor of the (15)N(p,alpha)(12)C reaction  

E-print Network

We present new improved R matrix fits of direct data and indirect Trojan Horse data for the (15)N(p,alpha)(12)C reaction and provide a more accurate recommended value of S(0)=73.0 +/- 5.0 MeV b from direct Redder data [A. Redder , Z. Phys. A 305...

La Cognata, M.; Goldberg, V. Z.; Mukhamedzhanov, A. M.; Spitaleri, C.; Tribble, Robert E.

2009-01-01

336

Mtabolisme de l'azote chez le ray-grass (Lolium perenne L.). Etude par marquage15N  

E-print Network

Agronomie Métabolisme de l'azote chez le ray-grass (Lolium perenne L.). Etude par marquage15N des la teneur en sucres solubles totaux. Lolium perenne L. - repousse - effet d'une coupe - remobilisations d'azote - protéines - nitrate Summary Nitrogen metabolism in Ryegrass (Lolium perenne L

Boyer, Edmond

337

Macrophytes as indicators of land-derived wastewater: Application of a ?15N method in aquatic systems  

Microsoft Academic Search

We measured ?15N signatures of macrophytes and particulate organic matter (POM) in six estuaries and three freshwater ponds of Massachusetts to assess whether the signatures could be used as indicators of the magnitude of land-derived nitrogen loads, concentration of dissolved inorganic nitrogen in the water column, and percentage of N loads contributed by wastewater disposal. The study focused specifically on

Marci L. Cole; Kevin D. Kroeger; James W. McClelland; Ivan Valiela

2005-01-01

338

Assessing waterbird habitat use in coastal evaporative systems using stable isotopes (? 13C, ? 15N and ?D) as environmental tracers  

NASA Astrophysics Data System (ADS)

Isotopic patterns of biota across salinity gradients in man-made evaporative systems could assist in determining the use of these habitats by animals. Here we report ? 13C, ? 15N and ?D measurements of a euryhaline fish, the Mediterranean toothcarp ( Aphanius fasciatus), inhabiting a range of salinities in the Thyna saltworks near Sfax (Tunisia). The contribution of these salinity niches to egg formation of two typically piscivorous bird species breeding in the area and feeding within saltworks, Little Tern ( Sternula albifrons) and Little Egret ( Egretta garzetta), was inferred trough a triple-isotope (? 13C, ? 15N and ?D) Bayesian mixing model. Isotopic trends for fish ? 15N and ?D across the salinity gradient followed the equations: ? 15N = e (1.1 + 47.68/Salinity) and ?D = -175.74 + Salinity + Salinity 2; whereas fish ? 13C increased as salinity rose (? 13C = -10.83 + 0.02Salinity), after a sudden drop in fish isotopic values for salinities >60 (Practical Salinity Scale) (average fish ? 13C for salinities <60 = -5.92). Both bird species fed largely on low hypersalinity ponds (salinity = 43; average contribution = 37% and 22% for Little Egrets and Little Terns, respectively), although the use of intermediate hypersalinities (salinities 63 and 70) by Little Terns also occurred (16% and 21%, respectively). Isotopic patterns across salinity gradients allow the use of isotopic measurements to inform studies of habitat occupancy within evaporative systems and provide further insights into how wildlife communities interact with them.

Ramrez, Francisco; Abdennadher, Aida; Sanpera, Carola; Jover, Llus; Wassenaar, Leonard I.; Hobson, Keith A.

2011-04-01

339

Microcrystalline U-15N-Labeled Protein by 3D Dipolar-Shift Solid-State NMR Spectroscopy  

SciTech Connect

Structural studies of uniformly labeled proteins by magic-angle spinning NMR spectroscopy have rapidly matured in recent years. Site-specific chemical shifts of several proteins have been assigned and structures determined from 2D or 3D data sets containing internuclear distance information. Here we demonstrate the application of a complementary technique for constraining protein backbone geometry using a site-resolved 3D dipolar-shift pulse sequence. The dipolar line shapes report on the relative orientations of {sup 1}H-{sup 15}N[i] to {sup 1}H-{sup 15}N[i+1] dipole vectors, constraining the torsion angles {phi}[i] and {psi}[i]. In addition, from the same 3D data set, several {sup 1}H-{sup 15}N[i] to{sup 1}H-{sup 15}N[i+2] line shapes are extracted to constrain the torsion angles {phi}[i], {psi}[i], {phi}[i+1], and {psi}[i+1]. We report results for the majority of sites in the 56-residue {beta}1 immunoglobulin binding domain of protein G (GB1), using 3D experiments at 600 MHz {sup 1}H frequency. Excellent agreement between the SSNMR results and a new 1.14 {angstrom} crystal structure illustrate the general potential of this technique for high-resolution structural refinement of solid proteins.

Franks,W.; Wylie, B.; Stellfox, S.; Rienstra, C.

2006-01-01

340

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

Rom Ogaya; Josep Peuelas

2008-01-01

341

Standing Out From the Crowd: New Fish Recruits Have Unique ?15N Signatures in a Heavily Polluted Intermittently Open Estuary.  

NASA Astrophysics Data System (ADS)

Intermittently open estuaries (IOEs) are the dominant coastal ecosystems of the Australian coastline. Conditions in IOEs range from freshwater when closed, to marine when open to the ocean, during which time marine fish often migrate into these systems. Many IOEs are facing increasing pressure from coastal development and ongoing nutrient inputs from industrial and urban sources have been shown to increase the ?15N isotope signatures of biota in receiving waters. In this study, we examined the food web structure of Tallows Creek, a relatively small IOE in northern NSW, Australia, which receives ongoing sewage treatment plant inputs. We first sampled Tallows Creek when it was closed to the ocean and found that all components of the food web had enriched ?15N signatures relative to biota sampled from a relatively undisturbed neighbouring system. However, samples collected immediately following an entrance opening event revealed some individuals of highly mobile taxa with ?15N signatures more typical of unpolluted estuaries. We suggest that these isotopically light individuals were recent migrants into Tallows Creek and that ?15N signatures can act as a guide to the importance of heavily polluted systems as nursery grounds for mobile taxa, owing to the distinction between resident and migrant signatures.

Hadwen, W. L.; Arthington, A. H.

2005-05-01

342

Recovery of 15 N-labelled urea: Influence of zero tillage, and time and method of application  

Microsoft Academic Search

The availability of N fertilizer to the crops under zero tillage versus conventional tillage may be affected by position of applied N, N immobilization and N loss from soil. The objectives of this study was to determine the influence of tillage, time of application and method of placement on the recovery of15N-labelled urea in barley (Hordeum vulgare L.) plants and

S. S. Malhi; M. Nyborg

1991-01-01

343

Stable isotope tracking of endangered sea turtles: validation with satellite telemetry and ?15N analysis of amino acids.  

PubMed

Effective conservation strategies for highly migratory species must incorporate information about long-distance movements and locations of high-use foraging areas. However, the inherent challenges of directly monitoring these factors call for creative research approaches and innovative application of existing tools. Highly migratory marine species, such as marine turtles, regularly travel hundreds or thousands of kilometers between breeding and feeding areas, but identification of migratory routes and habitat use patterns remains elusive. Here we use satellite telemetry in combination with compound-specific isotope analysis of amino acids to confirm that insights from bulk tissue stable isotope analysis can reveal divergent migratory strategies and within-population segregation of foraging groups of critically endangered leatherback sea turtles (Dermochelys coriacea) across the Pacific Ocean. Among the 78 turtles studied, we found a distinct dichotomy in ?(15)N values of bulk skin, with distinct "low ?(15)N" and "high ?(15)N" groups. ?(15)N analysis of amino acids confirmed that this disparity resulted from isotopic differences at the base of the food chain and not from differences in trophic position between the two groups. Satellite tracking of 13 individuals indicated that their bulk skin ?(15)N value was linked to the particular foraging region of each turtle. These findings confirm that prevailing marine isoscapes of foraging areas can be reflected in the isotopic compositions of marine turtle body tissues sampled at nesting beaches. We use a Bayesian mixture model to show that between 82 and 100% of the 78 skin-sampled turtles could be assigned with confidence to either the eastern Pacific or western Pacific, with 33 to 66% of all turtles foraging in the eastern Pacific. Our forensic approach validates the use of stable isotopes to depict leatherback turtle movements over broad spatial ranges and is timely for establishing wise conservation efforts in light of this species' imminent risk of extinction in the Pacific. PMID:22666354

Seminoff, Jeffrey A; Benson, Scott R; Arthur, Karen E; Eguchi, Tomoharu; Dutton, Peter H; Tapilatu, Ricardo F; Popp, Brian N

2012-01-01

344

Sedimentary records of ?(13)C, ?(15)N and organic matter accumulation in lakes receiving nutrient-rich mine waters.  

PubMed

Organic C and total N concentrations, C/N ratios, ?(15)N and ?(13)C values in (210)Pb-dated sediment cores were used to reconstruct historical changes in organic matter (OM) accumulation in three Swedish lakes receiving nutrient-rich mine waters. Ammonium-nitrate-based explosives and sodium cyanide (NaCN) used in gold extraction were the major N sources, while lesser amounts of P originated from apatite and flotation chemicals. The software IsoSource was used to model the relative contribution of soil, terrestrial and littoral vegetation, and phytoplankton detritus in the lake sediments. In one lake the IsoSource modelling failed, suggesting the presence of additional, unknown OM sources. In two of the lakes sedimentary detritus of littoral vegetation and phytoplankton had increased by 15-20% and 20-35%, respectively, since ~1950, when N- and P-rich mine waters began to reach the lakes. Today, phytoplankton is the dominating OM component in these lake sediments, which appears to be a eutrophication effect related to mining operations. Changes in the N isotopic composition of biota, lake water, and sediments related to the use of ammonium-nitrate-based explosives and NaCN were evident in the two studied systems. However, N isotope signals in the receiving waters (?(15)N~+9 to +19) were clearly shifted from the primary signal in explosives (?(15)N-NO3=+3.40.3; ?(15)N-NH4=-8.00.3) and NaCN (?(15)N=+1.10.5), and direct tracing of the primary N isotope signals in mining chemicals was not possible in the receiving waters. Systems where mine waters with a well known discharge history are a major point source of N with well-defined isotopic composition should, however, be suitable for further studies of processes controlling N isotope signatures and their transformation in aquatic systems receiving mine waters. PMID:24727038

Widerlund, Anders; Chlot, Sara; hlander, Bjrn

2014-07-01

345

Measurement of 1H-15N and 1H-13C residual dipolar couplings in nucleic acids from TROSY intensities  

PubMed Central

Analogous to the recently introduced ARTSY method for measurement of one-bond 1H-15N residual dipolar couplings (RDCs) in large perdeuterated proteins, we introduce methods for measurement of base 13C-1H and 15N-1H RDCs in protonated nucleic acids. Measurements are based on quantitative analysis of intensities in 1H-15N and 13C-1H TROSY-HSQC spectra, and are illustrated for a 71-nucleotide adenine riboswitch. Results compare favorably with those of conventional frequency-based measurements in terms of completeness and convenience of use. The ARTSY method derives the size of the coupling from the ratio of intensities observed in two TROSY-HSQC spectra recorded with different dephasing delays, thereby minimizing potential resonance overlap problems. Precision of the RDC measurements is limited by the signal-to-noise ratio, S/N, achievable in the 2D TROSY-HSQC reference spectrum, and is approximately given by 30/(S/N) Hz for 15N-1H and 65/(S/N) Hz for 13C-1H. The signal-to-noise ratio of both 1H-15N and 1H-13C spectra greatly benefits when water magnetization during the experiments is not perturbed, such that rapid magnetization transfer from bulk water to the nucleic acid, mediated by rapid amino and hydroxyl hydrogen exchange coupled with 1H-1H NOE transfer, allows for fast repetition of the experiment. RDCs in the mutated helix 1 of the riboswitch are compatible with nucleotide-specifically modeled, idealized A-form geometry and a static orientation relative to the helix 2/3 pair, which differs by ca 6 relative to the X-ray structure of the native riboswitch. PMID:21947918

Ying, Jinfa; Wang, Jinbu; Grishaev, Alex; Yu, Ping; Wang, Yun-Xing; Bax, Ad

2011-01-01

346

Retrospective characterization of ontogenetic shifts in killer whale diets via ??13C and ??15N analysis of teeth  

USGS Publications Warehouse

Metabolically inert, accretionary structures such as the dentin growth layers in teeth provide a life history record of individual diet with near-annual resolution. We constructed ontogenetic ??13C and ??15N profiles by analyzing tooth dentin growth layers from 13 individual killer whales Orcinus orca collected in the eastern northeast Pacific Ocean between 1961 and 2003. The individuals sampled were 6 to 52 yr old, representing 2 ecotypes-resident and transient - collected across ???25?? of latitude. The average isotopic values of transient individuals (n = 10) are consistent with a reliance on mammalian prey, while the average isotopic values of residents (n = 3) are consistent with piscivory. Regardless of ecotype, most individuals show a decrease in ??15N values of ???2.5% through the first 3 yr of life, roughly equivalent to a decrease of one trophic level. We interpret this as evidence of gradual weaning, after which, ontogenetic shifts in isotopic values are highly variable. A few individuals (n = 2) maintained relatively stable ??15N and ??13C values throughout the remainder of their lives, whereas ??15N values of most (n = 11) increased by ???1.5%, suggestive of an ontogenetic increase in trophic level. Significant differences in mean ??13C and ??15N values among transients collected off California suggest that individuality in prey preferences may be prevalent within this ecotype. Our approach provides retrospective individual life history and dietary information that cannot be obtained through traditional field observations of free-ranging and elusive species such as killer whales, including unique historic ecological information that pre-dates modern studies. By providing insights into individual diet composition, stable isotope analysis of teeth and/or bones may be the only means of evaluating a number of hypothesized historical dietary shifts in killer whales of the northeast Pacific Ocean. ?? Inter-Research 2009.

Newsome, S. D.; Etnier, M. A.; Monson, D. H.; Fogel, M. L.

2009-01-01

347

Analysis of the structure of synthetic and natural melanins by solid-phase  

SciTech Connect

The structures of one synthetic and two natural melanins are examined by solid-state NMR using cross polarization, magic angle sample spinning, and high-power proton decoupling. The structural features of synthetic dopa malanin are compared to those of melanin from malignant melanoma cells grown in culture and sepia melanin from squid ink. Natural abundance /sup 13/C and /sup 15/N spectra show resonances consistent with known pyrrolic and indolic structures within the heterogeneous biopolymer; /sup 13/C spectra indicate the presence of aliphatic residues in all three materials. These solid-phase experiments illustrate the promise of solid-phase NMR for elucidating structural from insoluble biomaterials.

Duff, G.A.; Roberts, J.E.; Foster, N.

1988-09-06

348

Synthesis, three-dimensional structure, and specific 15N-labelling of the streptococcal protein G B1-domain.  

PubMed

The 55-amino-acid B1-domain of the streptococcal protein G shows a high binding affinity to IgG isolated from a wide range of mammalian species. Since the B1-domain forms an extremely stable globular folding unit containing the major secondary structure elements and is devoid of proline residues and disulfide bridges, it is also a useful tool for protein folding and stability studies. Its small size makes this protein an ideal candidate for production by chemical synthesis, allowing incorporation of non-natural amino acids with the possibility of assessing the influence of such residues on both the functional and structural characteristics of proteins. In this study, we employed three successive chemical syntheses of the B1-domain in order to define the optimal conditions of coupling and protection. The stepwise solid-phase methodology using the tertbutyloxycarbonyl/benzyl strategy was used for this purpose. First, the sequence assembly difficulties were evaluated. After analyzing of the problems found during assembly, a second optimized synthesis was performed leading to formation of a synthetic B1-domain with a higher yield; the synthetic B1-domain was completely functional in its binding properties to IgG. Three orthogonal purification steps (gel-permeation, reverse-phase and ion-exchange HPLC) were required to obtain a sample suitable for structural analysis by high-resolution NMR. This study led to the conclusion that the synthetic B1-domain adopts a three-dimensional structure identical to that of the molecule obtained by recombinant techniques [Gronenborn, A.M., Filpula, D. R., Essig, N. Z., Achari, A., Whitlow, M., Wingfield, P. T. & Clore, G. M. (1991) Science 253, 657-661]. To demonstrate the usefulness of the chemical approach for the specific introduction of labelled amino acids in the primary structure, fourteen alpha-15N-labelled amino acids were incorporated at selected critical positions during the third synthesis. This analog is the first in a series of molecules planned to study in detail the folding dynamics of the B1-domain. PMID:7628467

Boutillon, C; Wintjens, R; Lippens, G; Drobecq, H; Tartar, A

1995-07-01

349

Immunofluorescence assay for effects on field abundance of a naturally occurring pseudomonad during passage through the gut of a marine deposit feeder, Abarenicola pacifica.  

PubMed

In a seasonal study we used immunofluorescence to follow a specific bacterial population, as well as total numbers, through the fore-, mid-, and hindgut of a deposit feeder, Abarenicola pacifica. We chose a pseudomonad because of its high ambient abundance. On five dates, we collected A. pacifica gut contents, with concurrent measurements of sedimentary food quality (chlorophyll a, protein, bacterial abundance), animal egestion rates (inversely proportional to gut residence time), and temperature. Increasing bacterial numbers from ingested sediment to foregut contents, and decreases from foregut to midgut indicate significant selection and digestion, respectively, of both the pseudomonad and the total bacterial community. Inverse correlations between egestion rate and digestive removal of bacteria offer some support for the prediction that digestion of bacteria is proportional to time spent exposed to digestive enzymes, although the significance of the associated statistical tests is marginal. No hindgut growth of the pseudomonad was observed, likely due to the short gut residence time of A. pacifica. The pseudomonad showed variation of less than a factor of 3 in its ambient sedimentary abundance over the year. PMID:24190094

Plante, C; Jumars, P

1993-11-01

350

15N Nuclear magnetic resonance of some pyrazines, 1,2,4-triazines and their N-oxides. Correlation and interrelationship of 15N with 13C chemical shifts of ?-deficient heterocyclic systems  

NASA Astrophysics Data System (ADS)

The 15N chemical shifts of a number of pyrazines, 1,2,4-triazines, and their N-oxides are reported. The shielding effects of a substituent ortho to a ring nitrogen on that nitrogen atom depend on the ?-deficiency of the heterocyclic ring. These ?-deficiency values are related to ortho13C chemical shifts in substituted benzenes. A new relationship between 13C and 15N chemical shifts of several ?-deficient heteroaromatic compounds is described. The N-oxides of pyrazine and 1,2,4-triazine show significant "backdonation" to the groundstate of these ring systems. This contribution becomes more important as the number of nitrogens in the ring increases. The "backdonation" is also reflected by a significant shielding of nitrogen atoms ? and/or ? to the N-oxide group.

Jovanovic, Misa V.

351

Comparison of three 15N methods to correct for microbial contamination when assessing in situ protein degradability of fresh forages.  

PubMed

The use of stable (15)N as a marker to determine microbial contamination in nylon bag incubation residues to estimate protein degradability was investigated. Three methods using (15)N were compared: (15)N-labeled forage (dilution method, LF), (15)N enrichment of rumen solids-associated bacteria (SAB), and (15)N enrichment of rumen liquid-associated bacteria (LAB). Herbage from forages differing in protein and fiber contents (early-cut Italian ryegrass, late-cut Italian ryegrass, and red clover) were freeze-dried and ground and then incubated in situ in the rumen of 3 steers for 3, 6, 12, 24, and 48 h using the nylon bag technique. The (15)N-labeled forages were obtained by fertilizing the plots where herbage was grown with (15)NH4 (15)NO3. Unlabeled forages (obtained from plots fertilized with NH4NO3) were incubated at the same time that ((15)NH4)2SO4 was continuously infused into the rumen of the steers, and then pellets of labeled SAB and LAB were isolated by differential centrifugation of samples of ruminal contents. The proportion of bacterial N in the incubation residues increased from 0.09 and 0.45 g bacterial N/g total N at 3 h of incubation to 0.37 and 0.85 g bacterial N/g total N at 48 h of incubation for early-cut and late-cut ryegrass, respectively. There were differences (P < 0.001) between uncorrected N degradability values and those corrected for microbial contamination with all of the methods. Apparent N degradability of the low-N, high-fiber forage (late-cut ryegrass) was 0.51, whereas the corrected values were 0.85, 0.84, and 0.77 for the LF, SAB, and LAB methods, respectively. With early-cut ryegrass and red clover, the differences between uncorrected and corrected values ranged between 6% and 13%, with small differences among the labeling methods. Generally, methods using labeled forage or labeled SAB and LAB provided similar corrected degradability values. The accuracy in estimating the extent of degradation of protein in the rumen from in situ disappearance curves is improved when values are corrected for microbial contamination of the bag residue. PMID:25349353

Kamoun, M; Ammar, H; Thwis, A; Beckers, Y; France, J; Lpez, S

2014-11-01

352

Identification of active bacteria involved in decomposition of complex maize and soybean residues in a tropical Vertisol using 15N-DNA stable isotope probing  

Microsoft Academic Search

As limited information is available about the relationship between microbial processes and community structure in tropical soils, we used 15N-DNA stable isotope probing (15N-DNA-SIP) to identify bacteria actively involved in decomposition of plant residues of different biochemical quality. 15N-labeled (90atom%) and unlabeled (control) maize (C-to-N ratio: 32; cellulose content: 24.9%) and soybean (15; 15.5%) leaf residues were incubated in a

Mingrelia Espaa; Frank Rasche; Ellen Kandeler; Thomas Brune; Belkis Rodriguez; Gary D. Bending; Georg Cadisch

2011-01-01

353

Sources of aerosol nitrate to the Gulf of Aqaba: Evidence from ? 15N and ? 18O of nitrate and trace metal chemistry  

Microsoft Academic Search

The nitrogen (N) and oxygen (O) isotopic composition (?15N and ?18O) of water soluble aerosol nitrate was measured in aerosol samples collected in Eilat, Israel, from August 2003 to November 2004. During this period ?15N values ranged from ?6.9 to +1.9 and ?18O from +65.1 to +84.9 and exhibited strong seasonal variability with higher average ?15N values observed in the

Scott D. Wankel; Ying Chen; Carol Kendall; Anton F. Post; Adina Paytan

2010-01-01

354

Influence of canopy drip on the indicative N, S and ?(15)N content in moss Hypnum cupressiforme.  

PubMed

Samples of Hypnum cupressiforme were collected at two types of site in forest areas: within the forest stand and within forest openings, and analyzed for N and S concentrations and ?(15)N. Mosses sampled within forest openings reflect the atmospheric N deposition; however, no influence of throughfall N deposition on the N in the moss that was sampled within the forest stand was found, nor was any influence of S deposition on the S in the moss found. For the N and S concentrations in the mosses sampled within forest openings, the within-site variability was comparable to the between-site variability, and for the ?(15)N, the within-site variability was lower than the between-site. The results showed that a short distance (<1m) between the sampling location and the nearest tree canopy increases the N in the moss, and significantly higher values are found in mosses sampled in areas within the forest stand. PMID:24704808

Skudnik, Mitja; Jeran, Zvonka; Bati?, Franc; Simon?i?, Primo; Lojen, Sonja; Kastelec, Damijana

2014-07-01

355

Temporal effects of dredging and dredged material disposal on nekton in the offshore waters of Galveston, Texas, with notes on the natural histories of the most abundant taxa  

E-print Network

TEHPORAL 11FFEC S Ol DREDGING Ki'P3 DREDGED HATERIAL D. SPCSAL ON NEKTON IN THE OFF SHOPCE WATERS OI' GALVESTON, TEXAS, WITH NOTES ON THE NATLTAL HISTORIES OF THE HOST ABUNDANT 1'AXA A Thesis by BRMlDT FLYNN HENNINGSEN Submitted... to the Graduate College of Texas A&M University in partial fulfillment or the requirement for the degree of MASTER OF SCIENCE August 1977 Hajor Subject: Biology TEMPORAL EFFECTS OF DREDGING AND DREDGED MATERIAL DISPOSAL ON NEKTON IN THE OFFSHORE WATERS...

Henningsen, Brandt Flynn

2012-06-07

356

Robust Abundance Estimation in Animal Abundance Surveys with Imperfect Detection  

EPA Science Inventory

Surveys of animal abundance are central to the conservation and management of living natural resources. However, detection uncertainty complicates the sampling process of many species. One sampling method employed to deal with this problem is depletion (or removal) surveys in whi...

357

Abundance, growth, and production of the sea scallop Argopecten purpuratus (Lamarck 1819): bases for sustainable exploitation of natural scallop beds in north-central Chile  

Microsoft Academic Search

The Chilean scallop (Argopecten purpuratus) fishery has been closed for many years, but natural scallop beds are still in jeopardy because illegal harvesting continues. Overexploitation has resulted in decreased productivity, which in many areas of Chile has caused the decline or complete elimination of natural scallop populations. Moreover, illegal harvesting is of particular concern as it threatens efforts to establish

Wolfgang B. Stotz; Sergio A. Gonzlez

1997-01-01

358

Intrapopulation variation in gray wolf isotope (? 15 N and ? 13 C) profiles: implications for the ecology of individuals  

Microsoft Academic Search

Trophic relationships among organisms in terrestrial boreal ecosystems define ecological communities and are important in\\u000a determining dynamics of energy flow and ecosystem function. We examined trophic relationships between the gray wolf (Canis lupus) and 18 mammalian species from the boreal forest of central Saskatchewan, Canada, using ?13C and ?15N stable isotope values measured in guard hair samples. Variance in isotope

Erin J. M. Urton; Keith A. Hobson

2005-01-01

359

Imprint of oaks on nitrogen availability and ?15N in California grassland-savanna: A case of enhanced N inputs?  

USGS Publications Warehouse

Woody vegetation is distributed patchily in many arid and semi-arid ecosystems, where it is often associated with elevated nitrogen (N) pools and availability in islands of fertility. We measured N availability and ?15N in paired blue-oak versus annual grass dominated patches to characterize the causes and consequences of spatial variation in N dynamics of grassland-savanna in Sequoia-Kings Canyon National Park. We found significantly greater surface soil N pools (020 cm) in oak patches compared to adjacent grass areas across a 700 m elevation gradient from foothills to the savanna-forest boundary. N accumulation under oaks was associated with a 0.6 depletion in soil ?15N relative to grass patches. Results from a simple ?15N mass balance simulation model, constrained by surface soil N and ?15N measured in the field, suggest that the development of islands of N fertility under oaks can be traced primarily to enhanced N inputs. Net N mineralization and percent nitrification in laboratory incubations were consistently higher under oaks across a range of experimental soil moisture regimes, suggesting a scenario whereby greater N inputs to oak patches result in net N accumulation and enhanced N cycling, with a potential for greater nitrate loss as well. N concentrations of three common herbaceous annual plants were nearly 50% greater under oak than in adjacent grass patches, with community composition shifted towards more N-demanding species under oaks. We find that oaks imprint distinct N-rich islands of fertility that foster local feedback between soil N cycling, plant N uptake, and herbaceous community composition. Such patch-scale differences in N inputs and plantsoil interactions increase biogeochemical heterogeneity in grassland-savanna ecosystems and may shape watershed-level responses to chronic N deposition.

Perakis, S. S.; Kellogg, C. H.

2007-01-01

360

Suitability and use of the 15N-isotope dilution method to estimate nitrogen fixation by actinorhizal shrubs  

Microsoft Academic Search

Nitrogen fixation rates were estimated by the 15N-isotope dilution method for Ceanothusvelutinus and Purshia tridentata in the understory of central Oregon ponderosa pine forests. Field rates were measured in small pole-, large pole-, and sawtimber-sized pine stands using two shrubs (Arctostaphylos patula, Ribes cereum) and one graminoid (Carex rossii) as non-fixing reference species. Shrub cover ranged from 23 to 59%

Matt D. Busse

2000-01-01

361

Zonal patterns of ?13C, ?15N and 210Po in the tropical and subtropical North Pacific  

Microsoft Academic Search

Nitrogen fixation process may supply a significant fraction of bioavailable nitrogen to surface waters, increase the oceanic sequestration of atmospheric CO2, and alter the distribution of geochemical parameters. We report a zonal pattern of ?15N and ?13C in particulate organic matter (POM), and ratios of particulate 210Po to dissolved 210Po along a transect through the subtropical and tropical North Pacific.

Min Chen; Laodong Guo; Qiang Ma; Yusheng Qiu; Run Zhang; E Lv; Yipu Huang

2006-01-01

362

In Vivo Fluxes in the Ammonium-Assimilatory Pathways in Corynebacterium glutamicum Studied by 15N Nuclear Magnetic Resonance  

PubMed Central

Glutamate dehydrogenase (GDH) and glutamine synthetase (GS)glutamine 2-oxoglutarate-aminotransferase (GOGAT) represent the two main pathways of ammonium assimilation in Corynebacterium glutamicum. In this study, the ammonium assimilating fluxes in vivo in the wild-type ATCC 13032 strain and its GDH mutant were quantitated in continuous cultures. To do this, the incorporation of 15N label from [15N]ammonium in glutamate and glutamine was monitored with a time resolution of about 10 min with in vivo 15N nuclear magnetic resonance (NMR) used in combination with a recently developed high-cell-density membrane-cyclone NMR bioreactor system. The data were used to tune a standard differential equation model of ammonium assimilation that comprised ammonia transmembrane diffusion, GDH, GS, GOGAT, and glutamine amidotransferases, as well as the anabolic incorporation of glutamate and glutamine into biomass. The results provided a detailed picture of the fluxes involved in ammonium assimilation in the two different C. glutamicum strains in vivo. In both strains, transmembrane equilibration of 100 mM [15N]ammonium took less than 2 min. In the wild type, an unexpectedly high fraction of 28% of the NH4+ was assimilated via the GS reaction in glutamine, while 72% were assimilated by the reversible GDH reaction via glutamate. GOGAT was inactive. The analysis identified glutamine as an important nitrogen donor in amidotransferase reactions. The experimentally determined amount of 28% of nitrogen assimilated via glutamine is close to a theoretical 21% calculated from the high peptidoglycan content of C. glutamicum. In the GDH mutant, glutamate was exclusively synthesized over the GS/GOGAT pathway. Its level was threefold reduced compared to the wild type. PMID:10049869

Tesch, M.; de Graaf, A. A.; Sahm, H.

1999-01-01

363

Application of nitrogen and carbon stable isotopes (?(15)N and ?(13)C) to quantify food chain length and trophic structure.  

PubMed

Increasingly, stable isotope ratios of nitrogen (?(15)N) and carbon (?(13)C) are used to quantify trophic structure, though relatively few studies have tested accuracy of isotopic structural measures. For laboratory-raised and wild-collected plant-invertebrate food chains spanning four trophic levels we estimated nitrogen range (NR) using ?(15)N, and carbon range (CR) using ?(13)C, which are used to quantify food chain length and breadth of trophic resources respectively. Across a range of known food chain lengths we examined how NR and CR changed within and between food chains. Our isotopic estimates of structure are robust because they were calculated using resampling procedures that propagate variance in sample means through to quantified uncertainty in final estimates. To identify origins of uncertainty in estimates of NR and CR, we additionally examined variation in discrimination (which is change in ?(15)N or ?(13)C from source to consumer) between trophic levels and among food chains. ?(15)N discrimination showed significant enrichment, while variation in enrichment was species and system specific, ranged broadly (1.4 to 3.3), and importantly, propagated variation to subsequent estimates of NR. However, NR proved robust to such variation and distinguished food chain length well, though some overlap between longer food chains infers a need for awareness of such limitations. ?(13)C discrimination was inconsistent; generally no change or small significant enrichment was observed. Consequently, estimates of CR changed little with increasing food chain length, showing the potential utility of ?(13)C as a tracer of energy pathways. This study serves as a robust test of isotopic quantification of food chain structure, and given global estimates of aquatic food chains approximate four trophic levels while many food chains include invertebrates, our use of four trophic level plant-invertebrate food chains makes our findings relevant for a majority of ecological systems. PMID:24676331

Perkins, Matthew J; McDonald, Robbie A; van Veen, F J Frank; Kelly, Simon D; Rees, Gareth; Bearhop, Stuart

2014-01-01

364

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

NASA Astrophysics Data System (ADS)

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 plots: four of them were control plots and the other four plots received the rain exclusion treatment. Although there was a negative relationship between ?13C and soil moisture, for each species and year, the rain exclusion treatment did not have any significant effect on ?13C, and therefore on the intrinsic water use efficiency (iWUE) of the three dominant species: Phillyrea latifolia, Arbutus unedo, and Quercus ilex. On the other hand, rain exclusion clearly increased the ?15N values in the three species studied, probably indicating higher N losses at the soil level leading to a 15N enrichment of the available N. It suggested that rain exclusion exerted a greater effect on the nitrogen biogeochemical cycle than on the carbon assimilation process. ?15N values were inversely correlated with summer soil moisture in Q. ilex and A. unedo, but no relationship was observed in P. latifolia. This latter species showed the lowest iWUE values, but it was the only species with no decrease in annual basal increment in response to the rain exclusion treatment, and it also had the highest resistance to the hot and dry conditions projected for the Mediterranean basin in the coming decades. The different strategies to resist rain exclusion conditions of these species could induce changes in their competitive ability and future distribution. The losses of N from the ecosystem may further limit plant growth and ecosystem functioning.

Ogaya, Rom; Peuelas, Josep

2008-11-01

365

Solvent effects in the GIAO-DFT calculations of the (15) N NMR chemical shifts of azoles and azines.  

PubMed

The calculation of (15) N NMR chemical shifts of 27 azoles and azines in 10 different solvents each has been carried out at the gauge including atomic orbitals density functional theory level in gas phase and applying the integral equation formalism polarizable continuum model (IEF-PCM) and supermolecule solvation models to account for solvent effects. In the calculation of (15) N NMR, chemical shifts of the nitrogen-containing heterocycles dissolved in nonpolar and polar aprotic solvents, taking into account solvent effect is sufficient within the IEF-PCM scheme, whereas for polar protic solvents with large dielectric constants, the use of supermolecule solvation model is recommended. A good agreement between calculated 460 values of (15) N NMR chemical shifts and experiment is found with the IEF-PCM scheme characterized by MAE of 7.1?ppm in the range of more than 300?ppm (about 2%). The best result is achieved with the supermolecule solvation model performing slightly better (MAE 6.5?ppm). Copyright 2014 John Wiley & Sons, Ltd. PMID:25102971

Semenov, Valentin A; Samultsev, Dmitry O; Krivdin, Leonid B

2014-11-01

366

delta(15)N and delta(13)C in the Mondego estuary food web: seasonal variation in producers and consumers.  

PubMed

Assessments of temporal variation in stable carbon and nitrogen ratios were used to examine seasonal trends of the water column and benthic food webs in the Mondego estuary (Portugal). There was a marked seasonality in weather and water column conditions, including nutrient supply and chlorophyll concentrations. In spite of the pronounced environmental changes, we found little evidence of seasonal variation in delta(13)C and delta(15)N of producers and consumers in the Mondego estuary, with a few notable exceptions. Nitrogen isotope ratios in macrophytes (Zostera noltii, Ulva sp., Enteromorpha sp., and Gracilaria sp.), and in two grazers (Idotea chelipes and Lekanesphaera levii) increased during late summer, with the highest delta(15)N values being measured in July, during a period of elevated temperatures and drought, which may have favored high rates of denitrification and heavier delta(15)N values. The results suggest that stable-isotope values from macrophytes and selected grazers are useful as tracers of seasonal changes in nitrogen inputs into estuaries, and that those of consumers reflect other factors beyond seasonal variations in N and C sources. PMID:19111337

Baeta, Alexandra; Pinto, Rute; Valiela, Ivan; Richard, Pierre; Niquil, Nathalie; Marques, Joo C

2009-04-01

367

In vivo 15N-enrichment of metabolites in suspension cultured cells and its application to metabolomics.  

PubMed

The incorporation of stable isotopes in suspension cultured cells is very simple and useful as a preliminary experimental method in the experimental scene of plant metabolomics to elucidate the metabolic profiles of mutants and transformants. Stable isotope methods would afford a dynamic explanation of turnover speed that would concern the metabolic flux. Utilization of suspension cultured cells allows genes to be easily induced or suppressed, culture conditions to be controlled, and samples to be easily prepared. Stable isotope tracing allows an index of metabolic flux to be obtained. Here we present an experiment feeding (15)N-labeled inorganic salts to Arabidopsis (cell line T87) and Coptis cultured cells. Results of a comparison of (15)N labeling ratios of amino acids derived from T87 cells cultured under light with those cultured in the dark corresponded to transcriptional expressions revealed by microarray experiments published previously, demonstrating the validity of this procedure. Furthermore, (15)N labeling ratios of Coptis cultured cells revealed arginine and lysine metabolism inhibition, which should result in inhibition of polyamine biosynthesis and cell division. This very simple experiment allowed us to uncover metabolic dynamic features of the plant cell. Therefore this method is very useful for forming working hypotheses and experimental design. PMID:16889377

Harada, Kazuo; Fukusaki, Eiichiro; Bamba, Takeshi; Sato, Fumihiko; Kobayashi, Akio

2006-01-01

368

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

PubMed

A pair of 3D HNCO-based experiments have been developed with the aim of optimizing the precision of measurement of (1)J(NH) couplings. Both pulse sequences record (1)J(NH) coupling evolution during the entire constant time interval that (15)N magnetization is dephasing or rephasing with respect to the directly bonded (13)C' nucleus, with (15)N(13)C' multiple quantum coherence maintained during the (13)C' evolution period. The first experiment, designed for smaller proteins, produces an apparent doubling of the (1)J(NH) coupling without any accompanying increases in line width. The second experiment is a J-scaled TROSY-HNCO experiment in which the (1)J(NH) coupling is measured by frequency difference between resonances offset symmetrically about the position of the downfield component of the (15)N doublet (i.e. the TROSY resonance). This experiment delivers significant gains in precision of (1)J(NH) coupling measurement compared to existing J-scaled TROSY-HNCO experiments. With the proper choice of acquisition parameters and sufficient sensitivity to acquire a 3D TROSY-HNCO experiment, it is shown that (1)J(NH) couplings can be measured with a precision which approaches or exceeds the precision of measurement with which the frequency of the TROSY resonance itself can be determined. PMID:20012159

Arbogast, Luke; Majumdar, Ananya; Tolman, Joel R

2010-02-01

369

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

PubMed Central

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. The first experiment, designed for smaller proteins, produces an apparent doubling of the 1JNH coupling without any accompanying increases in line width. The second experiment is a J-scaled TROSY-HNCO experiment in which the 1JNH coupling is measured by frequency difference between resonances offset symmetrically about the position of the downfield component of the 15N doublet (i.e. the TROSY resonance). This experiment delivers significant gains in precision of 1JNH coupling measurement compared to existing J-scaled TROSY-HNCO experiments. With the proper choice of acquisition parameters and sufficient sensitivity to acquire a 3D TROSY-HNCO experiment, it is shown that 1JNH couplings can be measured with a precision which approaches or exceeds the precision of measurement with which the frequency of the TROSY resonance itself can be determined. PMID:20012159

Arbogast, Luke; Majumdar, Ananya; Tolman, Joel R.

2010-01-01

370

Acetylene reduction, H2 evolution and (15)N 2 fixation in the Alnus incana-Frankia symbiosis.  

PubMed

Acetylene reduction, (15)N2 reduction and H2 evolution were measured in root systems of intact plants of grey alder (Alnus incana (L.) Moench) in symbiosis with Frankia. The ratios of C2H2: (15)N2 were compared with C2H2:N2 ratios calculated from C2H2 reduction and H2 evolution, and with C2H2:N2 ratios calculated from accumulated C2H4 production and nitrogen content. It was possible to calculate C2H2:N2 ratios from C2H2 reduction and H2 evolution because this source of Frankia did not show any hydrogenase activity. The ratios obtained using the different methods ranged from 2.72 to 4.42, but these values were not significantly different. It was also shown that enriched (15)N could be detected in the shoot after a 1-h incubation of the root-system. It is concluded that the measurement of H2 evolution in combination with C2H2 reduction represents a nondestructive assay for nitrogen fixation in a Frankia symbiosis which shows no detectable hydrogenase activity. PMID:24240308

Sellstedt, A

1986-03-01

371

15N NMR investigation of the reduction and binding of TNT in an aerobic bench scale reactor simulating windrow composting  

USGS Publications Warehouse

T15NT was added to a soil of low organic carbon content and composted for 20 days in an aerobic bench scale reactor. The finished whole compost and fulvic acid, humic acid, humin, and lignocellulose fractions extracted from the compost were analyzed by solid-state CP/MAS and DP/MAS 15N NMR. 15N NMR spectra provided direct spectroscopic evidence for reduction of TNT followed by covalent binding of the reduced metabolites to organic matter of the composted soil, with the majority of metabolite found in the lignocellulose fraction, by mass also the major fraction of the compost. In general, the types of bonds formed between soil organic matter and reduced TNT amines in controlled laboratory reactions were observed in the spectra of the whole compost and fractions, confirming that during composting TNT is reduced to amines that form covalent bonds with organic matter through aminohydroquinone, aminoquinone, heterocyclic, and imine linkages, among others. Concentrations of imine nitrogens in the compost spectra suggestthat covalent binding bythe diamines 2,4DANT and 2,6DANT is a significant process in the transformation of TNT into bound residues. Liquid-phase 15N NMR spectra of the fulvic acid and humin fractions provided possible evidence for involvement of phenoloxidase enzymes in covalent bond formation.

Thorn, K.A.; Pennington, J.C.; Hayes, C.A.

2002-01-01

372

15N NMR investigation of the covalent binding of reduced TNT amines to soil humic acid, model compounds, and lignocellulose  

USGS Publications Warehouse

The five major reductive degradation products of TNT-4ADNT (4-amino-2,6-dinitrotoluene), 2ADNT (2-amino-4,6-dinitrotoluene), 2,4DANT (2,4-diamino-6-nitrotoluene), 2,6DANT (2,6-diamino-4-nitrotoluene), and TAT (2,4,6-triaminotoluene)-labeled with 15N in the amine positions, were reacted with the IHSS soil humic acid and analyzed by 15N NMR spectrometry. In the absence of catalysts, all five amines underwent nucleophilic addition reactions with quinone and other carbonyl groups in the soil humic acid to form both heterocyclic and nonheterocyclic condensation products. Imine formation via 1,2-addition of the amines to quinone groups in the soil humic acid was significant with the diamines and TAT but not the monoamines. Horseradish peroxidase (HRP) catalyzed an increase in the incorporation of all five amines into the humic acid. In the case of the diamines and TAT, HRP also shifted the binding away from heterocyclic condensation product toward imine formation. A comparison of quantitative liquid phase with solid-state CP/MAS 15N NMR indicated that the CP experiment underestimated imine and heterocyclic nitrogens in humic acid, even with contact times optimal for observation of these nitrogens. Covalent binding of the mono- and diamines to 4-methylcatechol, the HRP catalyzed condensation of 4ADNT and 2,4DANT to coniferyl alcohol, and the binding of 2,4DANT to lignocellulose with and without birnessite were also examined.

Thorn, K.A.; Kennedy, K.R.

2002-01-01

373

Reconstruction of the oceanic nitrate inventory in the Pliocene Caribbean Sea: Foraminifera-bound ?15N - A new approach  

NASA Astrophysics Data System (ADS)

The nitrate budget in the low-latitude surface ocean is mainly controlled by the opposing effects of denitrification and nitrate fixation. The state of the global ocean nitrate inventory highly affects primary production, which allows sequestering CO2 into the deep ocean. This may influence climate variability and control warm and cold periods in Earth history. Studies have shown that nitrogen isotopes reflect the nutrient status of the upper water column and therefore can be used as proxy for the state of the oceans biological pump. The nitrate inventory has mostly been reconstructed based on bulk sedimentary N-isotope measurements, which can be affected by syn- and post-sedimentary processes. Promising approaches to circumvent these potential biases are based on measurements of foraminif