15N-Labelled Ammonium and Nitrate Uptake by the Grass Calamagrostis villosa

Abstract

Calamagrostis villosa dominates the understory vegetation in declining spruce forests at higher elevations of the Central European mountain areas which show symptoms of needle yellowing and associated magnesium (Mg) deficiency. It was hypothesized that grasses would preferentially take up nitrate-nitrogen (NO₃-N) over ammonium-nitrogen (NH₄-N) which would support the cation balance in Mg deficient soils. In order to test this hypothesis, growth experiments were carried out in the greenhouse using plants which were cultivated in sand for nine weeks with full nutrient solution containing 0.2 or 2 mmol of N with different NH₄ ⁺ to NO₃ ^? ratios (1:0, 0.5:0.5, 0:1). In a short term experiment with labelled ¹⁵NH₄ ⁺ and ¹⁵NO₃ ^?, uptake of NH₄ ⁺ and NO₃ ^? was measured. When NO₃ ^? was the only N source it was taken up at similar rate per g dry mass as in the experiment in which NH₄ ⁺ was the only N source. However, at high supply pure NO₃ ^? nutrition resulted in higher biomass. In contrast, supply of only NH₄ ⁺ caused accumulation of N in the roots but growth remained restricted. If NH₄ ⁺ and NO₃ ^? were supplied at equal amounts, NH₄ ⁺ was the preferred form for N uptake. Biomass of the plants with mixed supply did not differ from the plants with pure NO₃ ^? nutrition.

The results point to an interesting interaction of carbon and nitrogen relation, but they do not support the initial hypothesis that grasses may prefer NO₃ ^? over NH₄ ⁺.     

15N-Isotopenmessung mit dem Emissionsspektrometer NOI-6PC

Die emissionsspektroskopische ¹⁵N-Analyse ist eine leistungsfähige Methode für ¹⁵N-Tracerexperimente in Landwirtschaft, Biologie und Medizin. Vorteile des NOI-6 ¹⁵N-Analysatorsystems sind die geringe Probemenge (10 μg), die kurze MeBzeit und der hohe Bedienungskomfort. In Koppulung mit einer Verbrennung nach Dumas ist die gleichzeitige Bestimmung der Gesamt-Stickstoffkonzentration und des prozentualen ¹⁵N-Anteiles möglich.

The emission spectroscopic ¹⁵N analysis is a powerful tool for ¹⁵N tracer experiments in agriculture, biology, and medicine. Advantages of the NOI-6 ¹⁵N analyzer systems are the low sample amount, the short measuring time, and the high handling comfort.

In the future, methods for the simultaneous determination of total nitrogen and of nitrogen-IS will get increasing importance.     

Präparative Darstellung von hochangereichertem 15N-markiertem Hefeprotein

A method of biological preparation of highly-enriched yeast protein labelled ¹⁵N is described. The special relevance of such completely labelled proteins results from their importance for tracer-kinetic investigations of metabolism.     

Separation of Nitrogen Isotopes by Thermal Diffusion

The prototype of a thermal diffusion column for the use as basic unit in a N¹⁴N¹⁵ cascade is described. The hot wire separation column consists of a brass tube of effective length of 250 cm and inner diameter of 10 mm. Four columns are connected in series on a square cascade, the separation factors of which are compared with the values obtained by other investigators.     

Incorporation of 15NO2 Nitrogen into Individual Amino Acids by Sunflowers Using Gc-C-Irms

Abstract

The nitrogen isotopic composition of individual amino acids in sunflower leaves after exposures to ¹⁵NO₂ in the range of ambient NO₂ concentrations (5–37 ppb) was analysed by Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometry (GC-C-IRMS). Amino acids as well as the amides glutamine and asparagine were converted with MTBSTFA (N-methyl-N-(tert.-butyldimethylsilyl)-tri-fluoroacetamid) in pyridine to their corresponding TBDMS derivatives (N, O-tert.-butyldimethylsilyl) in a simple one-step silylation reaction. The derivatized amino acids were separated by gas chromatography, combusted on-line, and the products were sent continuously to an isotope ratio mass spectrometer. Accurate measurements were obtained, when more than 7 nmol N₂ were introduced into the ion source of the mass spectrometer per gas chromatographically separated and combusted compound. No interferences of the silicate and fluor containing derivatization agents on the performance of the system were observed.

In the range of ambient NO₂ concentrations sunflower leaves predominately incorporate the nitrogen derived from atmospheric NO₂ into soluble amino acids. The highest δ¹⁵N values were measured for alanine. The ¹⁵N enrichments of the detectable amino acids increased with increasing ¹⁵NO₂ concentration.     

Measuring of the Integral Airborne Nitrogen-Input into a Soil-Plant System by the 15N-Isotope Dilution Method

Abstract

Airborne nitrogen-inputs so far have only been measured in single fractions (deposition on plant surfaces or on soil and direct absorption of nitrogen containing gases by plants) by intensive exposition experiments in gas chambers, measurement of wet and dry N-deposition in the field and very expensive micrometereological field measurements. It is very difficult to estimate any overall N-input with practical relevance from these single N-component measurements. In this introduced field experiment an isolated measuring system is labelled with a ¹⁵N-tracer since it is not possible to label the nitrogen compounds of the atmosphere (e.g. NH₃, NO_x) which are to be absorbed. Through the dilution of this ¹⁵N-tracer by nitrogen derived from the atmosphere the total input of airborne nitrogen is determined. As soil resembling substrate sand was used and summer wheat was planted. With the regular and automated irrigation of nitrogen-free nutrient solution and the collection of precipitation surpluses this system measured the total input of airborne nitrogen for one vegetation period.

The first application of the described system gave an airborne nitrogen input into the soil-plant system during a vegetation period of 10 weeks (April-June) of about 32 kg ha^?1.     

基于小波阀值消噪的硝铵NQR信号处理

针对硝铵（AN）核电四极矩共振（NQR）信号通过傅立叶变换频域分析缺乏信号时域信息的特点,对硝铵NQR信号进行时频分析,达到从强背景噪声下检测出NQR信号的目的. 引入小波分析阀值去噪的方法对硝铵NQR信号进行处理. 对处理后数据与标准信号之间的相关系数进行分析. 实验结果表明小波阀值去噪方法可以成功检测到硝铵的NQR信号.     

A Sensitive Method for the Fast and Simultaneous Determination of δ15N- and δ18O-Values in Nitrate

A new method for on-line measurements of the isotopic abundances of N and O in nitrate using a Pyrolysis-GC-IRMS system is presented. The salt is heated to 1200°C together with graphite powder, the reaction products are separated by a GC column and allowed into an IRMS. The sample size could be reduced to 200 nmoles element for one measurement, which can be performed within 10 minutes with an accuracy of better than 1‰.     

The Influence of Ammonium on Nitrate Uptake and Assimilation in 2-Year-Old Ash and Oak Trees - A Tracer-Study with 15N

Abstract

Interactions between ammonium and nitrate as competitive N sources depend on various biotic and abiotic factors. The preference for one of these N sources and the influence of ammonium on nitrate uptake and nitrate reductase activity was investigated in a ¹⁵N labelling experiment using 2-year-old potted plants of ash (Fraxinus excelsior L.) and oak (Quercus robur L.) under greenhouse conditions.

Seedlings of both tree species use ammonium and nitrate in equal amounts when both N forms are supplied in a 1:1 ratio (1.5 mM NH₄ ⁺ + 1.5 mM NO₃ ^?), although there is a slight tendency that ammonium is preferred. In both species total N uptake is higher if ammonium and nitrate are supplied simultaneously when compared with uptake of nitrate alone (3 mM nitrate). If nitrate is the sole N source N uptake is only half as high as if ammonium and nitrate are supplied in a ratio of 1:1.

The distribution of nitrate reductase between shoot and roots is not influenced by the N-form: nitrate reductase activity is always highest in the roots of both species under the conditions of this experiment.

Xylem sap analyses showed that both species transport higher concentrations of amino acids than of nitrate from the roots to the shoot. The amino acid composition is independent of the type of N source. Furthermore, ash trees contain more nitrate in the xylem sap than oak trees, reflecting the higher N uptake and the higher nitrate reductase activity in the leaves of this species.     

Nitrogen isotopic signature of vegetables from the Slovenian market and its suitability as an indicator of organic production

The aim of this study was to obtain preliminary data on δ¹⁵N values in organically and conventionally grown vegetables available on the Slovenian market to determine whether there are any characteristic differences in δ¹⁵N values, which could be used as a marker to differentiate between organically and conventionally grown vegetables, namely vegetables grown with synthetic or organic nitrogen fertilisers. Therefore, 14 different varieties of organically and conventionally grown vegetables were analysed. The results obtained show clear differences in mean δ¹⁵N values between organically and conventionally grown vegetables (up to 6.3\permil). However, due to overlapping results, it was not possible to differentiate between organically and conventionally grown counterparts in eight vegetable varieties, despite the differences in mean δ¹⁵N values. The results obtained indicate that the method has several limitations. Hence, δ¹⁵N could be a reliable indicator for organic production, but nevertheless, the conclusion has to be validated by background information.     

Isotopic Analysis by Optical Spectroscopy

The paper describes different methods of isotopic analysis for hydrogen, nitrogen, and oxygen. In the cases of the hydrogen and the oxygen, a light source with high frequency excitation and a Fabry-Perot spectrometer with photoelectric recording were employed. For the nitrogen we used a Zeiss Q-24-spectrograph, or a Zeiss SPM-2 monochromator, converted by us to photoelectric automatic recording instruments. In the last case the method teas extended for determining the nitrogen isotopic concentration in nitric oxide gas.     

Probenchemische Methode zur Bestimmung von 15N an in Gesteinen fixiertem Stickstoff

Zur Klärung geologischer Prozesse werden in zunchmendem Maße die Isotopenvariationen des Stickstoffs herangezogen. Da der größte Teil des Stickstoffs der Gesteine in gebundener Form als Ammoniumstickstoff [1–6] vorliegt, kommt der Untersuchung der Isotopenvariationen desselben eine große Bedeutung zu.     

Investigations on the Nitrogen Metabolism of Forest Trees by Mathematical Modelling of Natural Isotope Ratios

Abstract

Based on an experimental investigation of nitrogen concentrations and δ¹⁵N-values in different parts of Picea abies (L.) trees and soil samples and of their dependence on the age of plant parts and on damaging stress, mathematical models which represent main features of nitrogen turnover in the forest tree - soil system and associated isotope variations are developed. These models consider parts of 3 cycles of nitrogen: (1) transport of soluble nitrogen within trees, (2) turnover of protein nitrogen in different plant parts, and (3) the exchange of N between tree and soil via litter and the uptake of mineralized soil N by plant roots. Isotope effects of protein synthesis and mineralization of organic soil N are included. The models give a qualitative explanation of the data and lead to a better understanding of isotopic variations as indicators of forest damage.     

Isotopic Analysis of Oxygen by Optical Spectroscopy

The isotopic analysis of oxygen (range of concentration: 1 to 31 at. %O¹⁸) by emission spectroscopy (O 1 8446 Å line) by using a Fabry-Pérpt spectrometer with photoelectric recording of the spectral lines is described. The measuring error is within ± 8% (for 1 at. %O¹⁸). The results are compared with those obtained by mass spectrometry.     

Part 1: The Principles of the Method

Although the principle of the concentration measurement of the elements having great neutron cross sections, e.g. Li, B, Cd, by the method of thermal neutron flux attenuation is well known, some difficulties are encountered in its practical application. These arise mainly because of the influence of the geometry conditions on the measurement.     

“Stable Isotope Mixing”, a Proposal to Analyze Stable Isotopes Using a Technique Similar to the Isotope Dilution Analysis

A proposal (shortly expressed as stable isotope mixing) similar to the stable isotope dilution analysis is described. It deals with the determination of the stable isotope relative abundances. Several related formulae are derived and briefly discussed. Other characters e.g. formula weight may be obtained in the same way.     

A High Precision Thermostat for the Isotopic Analysis of Water by the Falling Drop Method

An a.c. bridge thermostat, using two thermistors mounted in two opposite arms as temperature sensing elements, is described. The unbalanced bridge voltage is rectified, after a previous amplification, by a phase sensitive detector, and it is applied to the input of the final stage which controls the heater. The thermostat can be used to maintain the temperature of a liquid bath with a 0.0005°C precision and can be easily reset to different temperatures in the operational range of the thermistors.     

Aufnahme von 15NO2 und Einbau des 15NO2-Stickstoffs in verschiedene Stickstofffraktionen bei Sonnenblumen (Uptake of 15NO2 and Metabolic Transfer of the 15NO2 Nitrogen to Various Nitrogen Fractions of Sunflowers)

Abstract

Sunflowers were exposed to ¹⁵NO₂ at a range between 4,9 and 42,0 ppb. The ¹⁵NO₂ uptake was quantified and the fate of the ¹⁵N in different parts and pools of nitrogen was investigated. The very high δ¹⁵N-values of the free amino acid pool can't give an answer to the question whether the NO₂-nitrogen is incorporated by a different pathway, compared to the nitrogen which derives from root uptake. Or does a compartmentation of the nitrate pool in the plant cell cause a dilution of the ¹⁵N enrichment in the mineral nitrogen pool during sample preparation?