Source Of 15N Research Articles

Residual nitrogen from slurry and mineral fertiliser two years after application: Fractionation and plant availability

Fertilisation with animal manure has a long-standing tradition as a way to close nutrient cycles on farms. However, the fate of nitrogen (N) from manure in the soil beyond the year of application remains poorly understood. The aim of this research was to understand the residual N fertiliser value of mineral fertiliser (Min) and cattle slurry (Slu) in relation to the partitioning of N from the fertilisers in different soil physical fractions. To this end, we characterised the fate of 15N-labelled Min and Slu in soil organic matter (SOM) physical fractions two years after field application and related it to plant uptake of residual N. A secondary objective was to compare two fractionation methods with respect to accuracy and easiness, namely a combined density and particle size fractionation, separating five fractions, and a simple particle size fractionation, separating two fractions. All fractions were analysed for 15N abundance. The residual N fertiliser value was determined as the uptake of 15N by ryegrass (Lolium multiflorum) during 6 weeks. Furthermore, we deduced the source of 15N taken up by the plants from changes in the percentage of N derived from labelled fertilisers in each of the SOM physical fractions obtained by simple size fractionation before and after the pot experiment. Two years after application, most 15N was found in the fractions <20 μm, for both fractionation methods, i.e. in the mineral-associated organic matter (MAOM). The 15N recovery in these fractions in percent of the quantity of 15N originally applied as fertiliser tended to be higher for Slu (density-size fractionation: 19.8 ± 6.6%; simple size fractionation: 25.1 ± 6.6%) than for Min (density-size fractionation: 12.0 ± 2.1%; simple size fractionation: 16.8 ± 2.6%). Irrespective of the fertiliser type, about 2% of applied 15N was available to ryegrass plants two years after application. Out of these 2%, most 15N in the plants originated from MAOM, suggesting that the availability of the N stored in MAOM could be larger than previously thought. This finding is in line with the emerging view that MAOM is a dynamic fraction that plays an important role in the N cycle.

Spatial and temporal variation of the δ15N in Thalassia testudinum in the Mexican Caribbean (2009–2017)

Wastewater pollution in seagrass has been documented for decades. In areas where baseline data are lacking, such as the Mexican Caribbean, the δ15N of seagrass can provide information on status and trends. The aims of this study were to determine the spatial and temporal variation in δ15N values of T. testudinum from 2009 to 2017, to explore the nature and causes of isotopic variability, which must be fully understood, and to examine how isotopic variability is linked to wastewater on the coast. Samples of T. testudinum were collected during 2011–2017 in Cancún and from 2009 to 2017 in Mahahual, and analysed on a mass spectrometer. The δ15N values in Cancún (9.0±1.3 ‰) were significantly (P&amp;lt;0.005) higher than those in Mahahual (1.9±0.9 ‰). Our results reflect the continuous supply of wastewater as a source of 15N in Cancún and the atmospheric deposition of dissolved inorganic nitrogen from uncontaminated groundwater in Mahahual. Mahahual is an ideal site to continue environmental monitoring of the healthy seagrass in the southern Mexican Caribbean. Meanwhile, measures on the treatment and final disposal of wastewater in Cancun must be addressed with a great priority.

Recently fixed carbon allocation in strawberry plants and concurrent inorganic nitrogen uptake through arbuscular mycorrhizal fungi

Most crop species form a symbiotic association with arbuscular mycorrhizal (AM) fungi, receiving plant photosynthate and exchanging nutrients from the soil. The plant carbon (C) allocation to AM fungi and the nitrogen feedback are rarely studied together. In this study, a dual 13CO2 and 15NH415NO3 pulse labeling experiment was carried out to determine the allocation of recent photosynthates to mycorrhizal hyphae and the translocation of N absorbed by hyphae to strawberry plants. Plants were grown in pots in which a 50μm mesh net allowed the physical separation of the mycorrhizal hyphae from the roots in one portion of the pot. An inorganic source of 15N was added to the hyphal compartment at the same time of the 13CO2 pulse labeling. One and seven days after pulse labeling, the plants were destructively harvested and the amount of the recently fixed carbon (C) and of the absorbed N was determined. 13C allocated to belowground organs such as roots and mycorrhizal hyphae accounted for an average of 10%, with 4.3% allocated to mycorrhizal hyphae within the first 24h after the pulse labeling. Mycorrhizae absorbed labeled inorganic nitrogen, of which almost 23% was retained in the fungal mycelium. The N uptake was linearly correlated with the 13C fixed by the plants suggesting a positive correlation between a plant photosynthetic rate and the hyphal absorption capacity.

Benthic nitrogen fluxes and fractionation of nitrate in the Mauritanian oxygen minimum zone (Eastern Tropical North Atlantic)

We present sedimentary geochemical data and in situ benthic flux measurements of dissolved inorganic nitrogen (DIN: NO3−, NO2−, NH4+) and oxygen (O2) from 7 sites with variable sand content along 18°N offshore Mauritania (NW Africa). Bottom water O2 concentrations at the shallowest station were hypoxic (42μM) and increased to 125μM at the deepest site (1113m). Total oxygen uptake rates were highest on the shelf (−10.3mmolO2m−2d−1) and decreased quasi-exponentially with water depth to −3.2mmolO2m−2d−1. Average denitrification rates estimated from a flux balance decreased with water depth from 2.2 to 0.2mmolNm−2d−1. Overall, the sediments acted as net sink for DIN. Observed increases in δ15NNO3 and δ18ONO3 in the benthic chamber deployed on the shelf, characterized by muddy sand, were used to calculate apparent benthic nitrate fractionation factors of 8.0‰ (15εapp) and 14.1‰ (18εapp). Measurements of δ15NNO2 further demonstrated that the sediments acted as a source of 15N depleted NO2−. These observations were analyzed using an isotope box model that considered denitrification and nitrification of NH4+ and NO2−. The principal findings were that (i) net benthic 14N/15N fractionation (εDEN) was 12.9±1.7‰, (ii) inverse fractionation during nitrite oxidation leads to an efflux of isotopically light NO2− (−22±1.9‰), and (iii) direct coupling between nitrification and denitrification in the sediment is negligible. Previously reported εDEN for fine-grained sediments are much lower (4–8‰). We speculate that high benthic nitrate fractionation is driven by a combination of enhanced porewater–seawater exchange in permeable sediments and the hypoxic, high productivity environment. Although not without uncertainties, the results presented could have important implications for understanding the current state of the marine N cycle.

Isotopic and elemental indicators of nutrient sources and status of coastal habitats in the Caribbean Sea, Yucatan Peninsula, Mexico

Nutrient inputs associated with coastal population growth threaten the integrity of coastal ecosystems around the globe. In order to assess the threat posed by rapid growth in tourism, we analyzed the nutrient concentrations as well as the δ 15N of NO 3 − and macrophytes to detect wastewater nitrogen (N) at 6 locations along a groundwater-dominated coastal seagrass bed on the Caribbean coast of Mexico. We predicted that locations with greater coastal development would have higher concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (P), as well as δ 15N of NO 3 −, reflecting wastewater sources of N. However, concentrations of NO 3 − were not significantly different between developed (3.3 ± 5.3 μM NO 3 −) and undeveloped (1.1 ± 0.7 μM) marine embayments. The most important control on DIN concentration appeared to be mixing of fresh and salt water, with DIN concentrations negatively correlated with salinity. The δ 15N of NO 3 − was elevated at an inland pond (7.0 ± 0.42‰) and a hydrologically-connected tide pool (7.6 ± 0.57‰) approximately 1 km downstream of the pond. The elevated δ 15N of NO 3 − at the pond was paralleled by high δ 15N values of Cladophora sp., a ubiquitous green alga (10 ± 1‰). We hypothesize that inputs of nitrogen rich (NO 3 − > 30 μM) groundwater, characterized by 15N enriched signatures, flow through localized submarine groundwater discharges (SGD) and contribute to the elevated δ 15N signatures observed in many benthic macrophytes. However, changes in nitrogen concentrations and isotope values over the salinity gradient suggest that other processes (e.g. denitrification) could also be contributing to the 15N enrichments observed in primary producers. More measurements are needed to determine the relative importance of nitrogen transformation processes as a source of 15N to groundwaters; however, it is clear that continued inputs of anthropogenic N via SGD have the potential to severely impact ecologically and economically valuable seagrass meadows and coral reefs along the Caribbean coast of Mexico.

N,O-diacylhydroxylamines—structures in crystals and solutions

The structures of four N,O-diacylhydroxylamines (RCOHNOCOR', R, R'= Me, Ph) were determined in the solid state by X-ray diffraction and studied by NMR and IR spectroscopies in solution. The interpretation of the results was supported by ab-initio calculations of various tautomers and conformers, rotational barriers and chemical shifts. The results indicate the absence of OH tautomers (R-C(OH)=N-O-C(O)-R', N-acyloxyimidic acid); the NH tautomers (R-C(O)-NH-O-C(O)-R', O-acylhydroxamic acid) are present in DMSO solutions as equilibrium mixtures of a few conformers, their exchange being the likely source of 15N and 13C NMR line broadening.

Tracing 15N through landscapes: potential uses and precautions

Stable N isotopes are used to examine the source, flow and fate of N at scales ranging from greenhouse pots to landscapes. There are two main approaches: the 15N-enriched method applies an artificially enriched source of 15N and the 15N natural abundance ( δ 15N) method uses natural 15N differences between N sources and sinks. The δ 15N method is good for semi-quantitative estimates of N flow in undisturbed ecosystems, for analyzing patterns, and for developing new hypotheses, particularly when spatial variability across a landscape or watershed can be explained. The spatial variability of δ 15N across a landscape is often non-random, following predictable spatial patterns. Topographic features control the rate of various hydrological and biological processes, resulting in significantly different δ 15N between lower and upper slope positions. However, if the difference between source- δ 15N and sink- δ 15N is small due to inherent background variability and/or if fractionating processes have a large effect on the isotopic signature of the N to be traced, δ 15N will not work as a tracer. With the 15N-enriched method, the isotopic signature of the enriched tracer can be pre-determined to ensure a significant difference in atom% 15N between source and background levels, even when fractionation occurs. In most situations, the 15N-enriched method can be successfully used as a tracer to test hypotheses and to quantify N cycling through the landscape, regardless of background variability in δ 15N. Limitations of the 15N-enriched method include the cost associated with applying an enriched tracer, especially at the landscape scale, and the potentially confounding effects of applying N to a previously undisturbed landscape.

A stable isotope evaluation of the structure and spatial heterogeneity of a Lake Superior food web

We used stable isotope analysis to derive trophic relationships and movement patterns for components of the western Lake Superior food web. Trophic linkages implied by previous gut content studies were only marginally supported by stable isotope data. Siscowet lake trout (Salvelinus namaycush siscowet) were the top predators, and trophic overlap between siscowet and lean lake trout (Salvelinus namaycush) was low. Exotic Pacific salmon (Oncorhynchus spp.) occupied a lower trophic position than native piscivores because the latter relied more on coregonids. To evaluate spatial heterogeneity of the food web, we assumed that the adjacent cities of Duluth and Superior (DS) were a point source of 15N, and we measured isotopes of organisms close to and far from DS. Slimy sculpin (Cottus cognatus) were enriched in the DS area relative to other sites, implying that they are relatively sedentary. Rainbow smelt (Osmerus mordax) showed no differences at any sites, implying high vagility. Other organisms showed differences that could not be attributed to DS, implying that other mechanisms, such as trophic ontogeny, were influencing their isotopic signatures.

A stable isotope evaluation of the structure and spatial heterogeneity of a Lake Superior food web

We used stable isotope analysis to derive trophic relationships and movement patterns for components of the western Lake Superior food web. Trophic linkages implied by previous gut content studies were only marginally supported by stable isotope data. Siscowet lake trout (Salvelinus namaycush siscowet) were the top predators, and trophic overlap between siscowet and lean lake trout (Salvelinus namaycush) was low. Exotic Pacific salmon (Oncorhynchus spp.) occupied a lower trophic position than native piscivores because the latter relied more on coregonids. To evaluate spatial heterogeneity of the food web, we assumed that the adjacent cities of Duluth and Superior (DS) were a point source of 15N, and we measured isotopes of organisms close to and far from DS. Slimy sculpin (Cottus cognatus) were enriched in the DS area relative to other sites, implying that they are relatively sedentary. Rainbow smelt (Osmerus mordax) showed no differences at any sites, implying high vagility. Other organisms showed differences that could not be attributed to DS, implying that other mechanisms, such as trophic ontogeny, were influencing their isotopic signatures.

Seasonal variation in the suitability of different methods for estimating biological nitrogen fixation by grain legumes under rainfed conditions

Biological nitrogen fixation (BNF) by legume crops was estimated in a Mediterranean environment at ICARDA in northern Syria for 3 consecutive seasons beginning in 1991-92. Using the classical isotope dilution technique (NID), estimates ranged from 32 to 82 kg N/ha for chickpea and from 18 to 82 kg N/ha for lentil. In comparison the simple N-difference method gave lower, sometimes negative, estimates for BNF by both crops in the latter 2 seasons but a higher estimate for chickpea in the first year. Discrepancies in the estimates from N-difference were correlated with differences in the amount of soil N taken up by the legume and the non-fixing wheat reference crop. Since soil N uptake by lentil in the first year was similar to wheat, the estimates of BNF from the 2 methods for that season were similar. The indirect effects of an interaction of added N fertiliser on N derived from the soil and thus on N uptake and estimated BNF are discussed in relation to the use of the isotope dilution method with A-value modification (NAV). Despite some significant differences in A-value for soils receiving different amounts of fertiliser it is demonstrated that the A-value method used in this study, with fertiliser rates of 10 kg N/ha to the legume and 30 kg N/ha to the non-legume, resulted in BNF estimates for lentil similar to those obtained using classical isotope dilution. However, this was not the case for chickpea where a direct inhibitory effect of fertiliser N at 30 kg N/ha resulted in lower estimates of BNF from NID than NAV. Since the reference crops derived as much as 90% of their N from the soil, it is recommended that future BNF studies using isotope dilution techniques for lentil and chickpea crops at ICARDA use a fertiliser rate lower than that used in this study. An isotope dilution method utilising a slow-release source of 15N or the natural abundance technique for estimating BNF are suggested as potentially useful alternatives. The need for a basic understanding of the soil N dynamics pertinent to each site as a prerequisite for choosing an appropriate method for estimating BNF is highlighted.

Synthesis of [15N]guanosines and deoxy[15N]guanosines from 5-amino-1-(β-D-ribofuranosyl)imidazole-4-carboxamide (‘AICA-riboside’)

Methods are described for the syntheses of 15N-labelled guanosines and deoxyguanosines, suitable for incorporation into oligonucleotides. The 15N is located either at N-1 (e.g.[15N1]guanosine 1a and deoxy[15N1]guanosine 1b) or at the NH2(e.g.[15NH2]guanosine 1c and deoxy[15NH2]guanosine 1d). One of the synthetic methods starts from 5-amino-1-(β-D-ribofuranosyl)imidazole-4-carboxamide (AICA-riboside, 2a) and leads via a cyclonucleoside to mixtures of compounds 1a and 1c, in which either compound predominates depending on the source of 15N (ammonia or benzoyl isothiocyanate). The other method utilises the same starting material, but a different mode of formation of the pyrimidine ring and yields either guanosine 1a or 1c(as its 2-N-benzoyl derivative 8b), exclusively.

Assimilation of nitrogen by soil microbial population: NH 4 versus organic N

Nitrogen assimilation by microbial, biomass during the decay of organic material in soil may follow two patterns: (1) direct assimilation of low molecular weight organic N compounds (Direct hypothesis) or (2) immobilization of mineral N, while organic N is completely mineralized (MIT hypothesis). To test these hypotheses equal concentrations of NH 4-N and alanine-N were added to soils, either one or the other labeled with 15N, and incubated for 1.2 days. The K 2SO 4-extractable organic and mineral N and 15N and CO 2 release were measured periodically. Experimental results were compared with data computed by two versions of the model NCSOIL, that simulates the C-N turnover and 15N distribution among soil pools, and is structured to represent either the Direct or the MIT hypothesis. The fitted first order rate constant of mineralization of alanine was 3.2 d −1, following a delay of 0.25 d. Evolution of CO 2 proceeded at a considerable rate after alanine was decomposed and net N mineralization had ceased, indicating a rapid decomposition of the microbial population that consumed alanine. The isotopic dilution of mineral N proceeded very rapidly and fitted the simulation by MIT better than by the Direct model. The rate of 15N withdrawal from total extractable N was greater when alanine was labeled and fitted the prediction by the Direct model, but when NH 4 was the source of 15N, the Direct model failed to predict 15N consumption. It seemed that both pathways operated concurrently, with the Direct dominating N assimilation by the substrate specific population and the MIT operating at the level of the native soil population.

A convenient preparation of 2‐[15N]‐amino‐4,6‐dimethoxypyrimidine

AbstractA convenient preparation of 2‐[15N]‐amino‐4,6‐dimethoxypyrimidine using 15N‐ammonium chloride as the source of 15N is described.

ウンシュウミカン樹によるアルギニン-&amp;epsilon;-&lt;sup&gt;15&lt;/sup&gt;N&lt;sub&gt;2&lt;/sub&gt;, 尿素-&lt;sup&gt;15&lt;/sup&gt;N&lt;sub&gt;2&lt;/sub&gt;及びアンモニウム-&lt;sup&gt;15&lt;/sup&gt;Nの代謝

Arginine-e-15N2 was supplied to intact 1-year-old shoots of a 21-year-old satsuma mandarin tree, and arginine-e-15N2, urea-15N2 and ammonium-15N were each fed to excised 2-year-old stem sections. The 15N was traced in the bark, wood, new shoots, and new leaves. Arginine-e-15N2 was steadily metabolized via γ-guanidinobutyric acid in the bark and wood. The 15N of arginine was most markedly incorporated into the glutamine-amide N, but also into glutamine-amino N, alanine and γ-aminobutyric acid. Some 15N was also used for proline formation. The labelling patterns of amino compounds when urea-15N2 or ammonium-15N was fed were both similar to when arginine-e-15N2 was fed. This finding strongly suggests that the 15N of arginine-e-15N2 is used for amino compound synthesis via urea and/or ammonium. Arginine-e-15N2 was translocated, and appeared in an unmetabolized form in new shoots where it was incorporated into protein. The 15N of arginine was also transferred to other amino compounds, and then incorporated into protein in new shoots. Several differences in N metabolism were found between the bark and wood: whatever the source of 15N, asparagine-amino N had a higher 15N enrichment than aspartic acid in the bark, but a lower enrichment in the wood. Glutamine, asparagine and proline were more actively synthesized and accumulated in the bark, while in the wood, arginine was.

HYPHAL UPTAKE AND TRANSPORT OF NITROGEN FROM TWO 15N‐LABELLED SOURCES BY GLOMUS MOSSEAE, A VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGUS *

SUMMARYCelery (Apium graveolens L.) plants were grown in pots in which the root system was separated from the soil in a side chamber by a fine mesh screen. The side chamber was treated with either an organic (ground plant tissue) or inorganic [(NH4)2SO4] source of 15N. Mycorrhizal (Glomus mosseae) and control (non‐mycorrhizal) plants were exposed to 15N over a period of 30 days (inorganic‐15N) or 88 days (organic‐16N). Mycorrhizal and control plants did not differ in shoot dry weight or shoot P content. Dry weight of root was reduced in the mycorrhiza treatments. Mycorrhizal plants derived significantly (P= 0.01) more 16N, from both N sources, than did control plants. In the inorganic‐N treatment, 15N in mycorrhizal plants was significantly (P= 0.001) and positively correlated with percent mycorrhizal fungal colonization (r= 0.58), number of hyphal crossings (±10 μ diameter) through the mesh into the area of 15N placement (r= 0.76), total length of hyphae per gram of soil (r= 0.74), and length of hyphae of 5 μ diameter in the soil (r= 0.77). No correlations were found between the 16N content of mycorrhizal plants and any parameter in the organic‐N treatment. The 16N content of control plants was not correlated with hyphal length in the outer chamber and there were no hyphal crossings of the size ( 10 μ diameter) which was counted for the mycorrhiza treatments. The presence of the organic matter (ground plant tissue) increased the total length of saprophytic hyphae per gram of soil but decreased the number of vesicular‐arbuscular mycorrhizal fungal hyphae crossing into the area of 16N placement. The mean flux of N through the hyphae of G. mosseae was 7.42 × 10−8 mol N cm−2 s−1 for the inorganic‐N treatment over a 30‐day period, and 1.74 × 10−8 mol N cm−2 s−1 for the organic‐N treatment over an 88‐day period.

Biosynthesis of asparagne from β- L-[ 14C 15N]cyanoalanine in Lathyrus sylvestris W. seedlings origin of the amide nitrogen

β- L-[ 14 15N]Cyanoalanine administered to Lathyrus sylvestris W. seedlings formed asparagine with complete retention of cyano nitrogen. The β-cyanoalanine pathway for the young plant may be a means of conserving nitrogen as well as of detoxifying cyanide. The required β- L-[C 15N]cyanoalanine was synthesized by hydrogenolysis of carbobenzoxy- L-β-[C 15N]cyanoalanine benzyl ester, prepared by dehydration of known carbobenzoxy- L-[ amide- 15N]asparagine benzyl ester. ( 15NH 4) 2SO 4 was the source of 15N.