Course of Uptake of Weed-Borne Nitrogen by Maize,Tested with 15N

Abstract

The course of uptake of weed-borne nitrogen by maize was tested with ¹⁵N in a pot experiment with silty loam after common growth of maize and Chenopodium album L., and mulching the weed in the 5-leaf stage of maize. Harvests 4,8 and 12 weeks after mulching show that the maize took up 35, 63 and 70% of the weed-borne nitrogen, resp., in consequence of a rapid and almost complete mineralization. The portion of weed-borne nitrogen in total N of the maize was 16% at all harvest dates. The differences in yield between weeded and unweeded maize were not significant neither at 5-leaf stage nor at corn maturity.     

Abstracts

Abstract

Uptake of weed-borne nitrogen by maize was tested with ¹⁵N in field experiments on silty loam (haplic phaeozem) after common growth of maize and Chenopodium album L. and incorporating the weeds at the 4- to 6-leaf stage of maize. Maize took up 22–23% of the weed-borne N in the year of incorporating and residual 7–32% in the following year. Uptake of weed-borne N was higher in comparable pot experiments. Different soil humidity after different water supply was mainly reasonable for these differences. Weed-borne nitrogen contributed 7–16% to total N of maize in the year of incorporating and 4–11% in the following year. Yield and N uptake between weeded and unweeded maize differed partly significant.     

Temporary Biological N Cońservation by Winter Oilseed Turnip (Brassica Rapa L.) and its Influence on Following Crops and N-Percolation

Abstract

As shown in field plot trials with application of ¹⁵N on loamy sand (albic luvisol), winter oilseed turnip (Brassica rapa L.; ssp. oleifera (Dc.) METZG.) incorporated considerable N amounts during the winter period. By this a reduction of N percolation into deeper soil layers was achieved. After mulching, about 30% of the catch crop N was taken up by the following crop, maize (Zea mays L., cv. ‘BEKENOVA’). Maize covered 11% of its total N demand deriving from the catch crop.     

The Impact of Ozone on the 15N Incorporation and Nitrogen Assimilation of Wheat and Maize

Abstract

Young wheat (C3) and maize (C4) plants were exposed to near-ambient concentrations of ozone in open-top chambers in order to investigate the possible effects of ozone on nitrogen metabolism. Nitrogen was supplied to the plants by adding ¹⁵N-labelled tracer substances via the soil substrate. Enzyme activities (NADH nitrate reductase, nitrite reductase, glutamine synthetase and NADH glutamate dehydrogenase) and the incorporation of ¹⁵N were determined.

The findings show that nitrogen metabolism was affected by O₃, however, there were distinct differences between the two species. In plants treated with O₃, NADH nitrate reductase activity in maize leaves was reduced, while NR activity in wheat leaves only slightly declined. Only minor changes were observed with respect to the activities of nitrite reductase, glutamine synthetase and NADH glutamate dehydrogenase.

Feeding experiments using ¹⁵NO₃ ^? showed that the incorporation of nitrate nitrogen in wheat plants exposed to ozone remains virtually unchanged, whereas in maize plants reduced incorporation rates were observed for nitrate nitrogen. The incorporation of ammonium nitrogen was distinctly increased in wheat and maize by the impact of ozone.

When investigating pigment contents, reduced levels of chlorophyll a and b and carotenoids were observed, whereas the pigment content of wheat leaves remained unchanged. These results indicate that young maize plants are more susceptible than wheat plants to short-term ozone exposure.     

The Effect of Catch Crops on the 15N Nitrogen Percolation and Leaching During the Early Winter Period

Abstract

Lysimeter experiments with application of ¹⁵N in growth chambers were used to investigate to what extent the growth of oil radish can prevent by temporary biological N conservation the nitrogen percolation and leaching during late autumn and early winter periods. It could be shown that the oil radish plants incorporated 47% of the applied ¹⁵N and thus reduced substantially the ¹⁵N percolation to the deeper soil layers (60–100 cm) and the ¹⁵N leaching losses. Before giving final recommendations, the fate of the ¹⁵N contained in the oil radish must be examined in the late winter and early spring periods, after freezing of the plants.     

15N-Dynamics of Cucumber (Cucumis sativus L.) in Field Trials on Sandy Loam in Brandenburg (Germany)

Abstract

Field experiments were conducted to study the ¹⁵N-utilization of cucumbers (Cucumis sativus L.) grown on sandy loam under black mulch film. With the progress of the ontogenetic development the plants took up rising ¹⁵N-amounts, which were increasingly transferred to the fruits after the beginning of flowering. At the end of the vegetation period more than 55% of the applied ¹⁵N-labelled fertilizer was found in the plants, and from this portion more than 70% in the fruits. Up to 13% of the total plant nitrogen were derived from the fertilizer. In the top soil layer (0–30 cm) the ¹⁵N-content was strongly reduced during plant growth. Though most of the ¹⁵N was taken up by the plants, a ¹⁵N transfer to deeper soil layers (30–60 cm, 60–90 cm) was observed. Balancing the amount of applied ¹⁵N-fertilizer indicates a loss of 11% during the experimental period.     

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.     

Course of uptake of weed-borne nitrogen by maize, tested with (15)n

Abstract The course of uptake of weed-borne nitrogen by maize was tested with (15)N in a pot experiment with silty loam after common growth of maize and Chenopodium album L., and mulching the weed in the 5-leaf stage of maize. Harvests 4,8 and 12 weeks after mulching show that the maize took up 35, 63 and 70% of the weed-borne nitrogen, resp., in consequence of a rapid and almost complete mineralization. The portion of weed-borne nitrogen in total N of the maize was 16% at all harvest dates. The differences in yield between weeded and unweeded maize were not significant neither at 5-leaf stage nor at corn maturity.     

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.     

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.     

Lysimeter Investigations on the Effect of Winter Catch Crops and Weeded Fallow on the N-Dynamics in a Sandy Treposol Soil of Northeast Germany

Abstract

Lysimeter experiments (soil: sandy treposol, from the region “Havelländisches Luch”, Brandenburg, Germany) with application of ¹⁵N labelled fertilizer (80 kg N per ha as ¹⁵NH₄ ¹⁵NO₃, 10 at.-%¹⁵N exc.; for simulating mineralization in the early autumn period) were carried out to determine to what extent the amount of mineral- N was temporary conserved by winter catch crops, taken up subsequently in the vegetation periods by following crops, taken by subsequently in the vegetation periods by following crops, or percolated in the leaching water, respectively. The results were as follows:

1) Until winter or spring respectively, the catch crop uptake rates of applied mineral-N were 32% for phacelia (Phacelia tanacetifolia BENTH.), 25% for winter rape (Brassica napus L. cv. ‘AKELA’), and 16% for white mustard (Sinapis alba L.).

2) In the year after, following maize incorporated from 2.1 to 4.5% of the fertilizerborne N. The following plant community of fallow took up from 0.2 to 0.5% N originating from the fertilizer-N.

3) In comparison with the catch crops, N-leaching losses under fallow conditions were highest and equivalent to 17% of the applied fertilizer-N amount. In contrast to 3% of white mustard, phacelia and winter rape reduced N-leaching losses to 0.2 and 0.3% of the applied fertilizer-N amount.

4) In spring of the first year after the beginning of investigations, N-leaching losses were highest under fallow conditions and white mustard cultivation. Thus, the amounts of nitrate losses would exceed the EU limit for drinking water.

5) Three years after the investigations had been started, 10% (white mustard) and 20% (fallow) of the applied fertilizer-N was still found in th lysimeter soil.     

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?     

Influence of Nitrogen,Water and Competition on Carbon Isotope Ratios (δ13C) in a CAM Plant (Crassula argentea)

Abstract

Leaf carbon isotope ratios (δ¹³C), an indicator of long-term intercellular carbon dioxide concentration, and also stem and root carbon isotope ratios were measured on the obligate CAM species Crassula argentea cultivated in pure and mixed cultures with the succulent C₃ Peperomia obtusifolia in open-air conditions under two different levels of nitrogen and water supply.

As expected, a diminished water supply and a relatively dry and hot summer climate cause a shift of δ¹³C values to a less strong ¹³C discrimination (less negative δ¹³C values). A diminished nitrogen supply causes a shift of the δ¹³C values in direction of a higher ¹³C discrimination (more negative δ¹³C values), particularly in the leaves. Competition causes also an increased ¹³C discrimination, especially valid for shoot axes.

The shift of ¹³C/¹²C isotope ratios in case of nitrogen deficiency is discussed to be a result of a decreased PEPCase activity in the night.     

The Effect of Diet Quality on δ13C and δ15N in the Tissues of Locusts,Locusta migratoria L

Abstract

Locust nymphs were raised from hatching to adult locusts on either seedling wheat (C₃) or maize (C₄), to determine whether relative enrichments/depletions of ¹⁵N and ¹³C within body tissues are influenced by diet. The maize contained less hexose sugars and protein per gram than wheat.

The isotopic spacing between the food and the whole insect was found to differ between the two diets. The lower quality maize diet showed an overall +5.1‰ enrichment in δ¹⁵N compared to + 2.8‰ for wheat, possibly due to increased fractionation due to protein recycling.

The maize diet resulted in increased depletion in lipid and trehalose and depletion in chitin relative to diet. The results for both δ¹⁵N and δ¹³C suggest that substrate recycling was occurring on the low quality maize diet. Therefore diet quality determines the enrichment/depletion in δ¹⁵N and δ¹³C within organisms.     

Molecular magnetism in closo-azadodecaborane supericosahedrons

ABSTRACT

The connection of 12 s = ½ closo-azadodecaborane radical units (NB₁₁H₁₁?), where a hydrogen atom is removed from the nitrogen atom, produces a supericosahedron [(NB₁₁H₆?)₁₂]^(S), S being the total spin of the system. This work describes the study of the low-lying energy spin-projected states of this supericosahedron with two different geometrical arrangements, each nitrogen atom pointing (1) inwards or (2) outwards with respect to radial axes. These spin-projected states are mapped into a Heisenberg spin Hamiltonian, thus allowing the determination of coupling constants between magnetic sites. The eigenvalues of this model Hamiltonian then predict the ground spin state and the corresponding combinations of spin orientations of the magnetic centres. We show that the energy minimum in the [(N_in/outB₁₁H₆?)₁₂]^(S) systems corresponds to a high-spin S = 6 state.     

Dinitrogen Fixation of Microbe-Plant Associations as Affected by Nitrate and Ammonium Supply

Abstract

The dinitrogen fixation activity of Azospirillum sp., and Pantoea agglomerans strains was determined by ¹⁵N₂ incorporation after incubation with ¹⁵N₂ labeled air or/and by acetylene reduction. These bacterial strains were able to fix N₂ both in pure culture and in association with wheat plants in hydroponics. Nitrogenase activity of Azospirillum sp., in pure culture was more rapidly inhibited by the addition of NH₄ ⁺ than NO₃ ^?. The N₂ fixation of P. agglomerans decreased only by NH₄ ⁺ -addition, but was stimulated by NO₃ ^?. Nitrogen fixation in association with wheat plants remained unaffected by both N compounds. However, nitrogen derived from the atmosphere (N_dfa) contributed only very little to the overall nitrogen nutrition of the plants.     

Nitrogen Isotope Ratios in Different Compartments of a Mixed Stand of Spruce,Larch and Beech Trees and of Understorey Vegetation Including Fungi

Abstract

Natural nitrogen isotope ratios were measured in different compartments (needles or leaves and twigs of different age classes and crown positions, roots and soil of different horizons) of spruce (Picea abies), larch (Larix decidua) and beech (Fagus sylvatica) trees in an 11-year-old mixed stand in the Fichtelgebirge, NE Bavaria, Germany. In addition, samples of understorey vegetation (mainly ericaceous shrubs and grass) and of ectomycorrhizal and saprophytic fungi were analyzed. The δ¹⁵N values found for all samples ranged between ?7.5 and + 4.5‰. No significant differences were found for the nitrogen isotope ratios of the three tree species despite of their evergreen versus deciduous foliage and despite of their different rooting depth. Ericaceous shrubs had the most negative and fungi and soil from the mineral horizon the most positive δ¹⁵N values. Positive δ¹⁵N values of the fungi indicate their ability to utilize organic soil nitrogen, but the data do not unequivocally show that plants forming mycorrhizas profit from this organic nitrogen source.     

BaxOy小团簇修饰Ru(0001)表面的结构稳定性和氮分子吸附性质

为了说明钡助剂的存在形式, 本文采用第一性原理方法研究了Ba_xO_y小团簇修饰Ru(0001)表面的结构稳定性和氮分子吸附性质. 基于总能的热力学分析发现, 在实验条件下(500 K, P_H2O/P_H2<10^-3), Ba₂O团簇比BaO₂, BaO, Ba和O等团簇(原子)更加稳定. 这证实含有金属性钡原子的团簇也是氧化钡助剂可能的工作状态. 表面电荷差分密度说明Ba₂O团簇的氧和钡原子与衬底的作用不同. 不过Ba₂O团簇氧和钡原子附近的氮分子吸附行为相似, Ba₂O团簇增强了氮分子和衬底的相互作用. Ba₂O团簇氧和钡原子附近的氮分子吸附能分别为0.78 和0.88 eV, 均大于清洁表面的0.67 eV. 氮分子间距和氮分子的拉伸振动频率都表明Ba₂O团簇在一定程度上活化了吸附氮分子. Ba₂O团簇氧和钡原子附近的N–N键长分别为0.117和0.116 nm, 大于清洁表面的0.114 nm. 氧和钡原子附近氮分子的拉伸振动频率分别为 1888 和1985 cm^-1, 小于清洁表面的2193 cm^-1. 电荷差分密度的计算结果说明, 削弱作用主要来自于Ba₂O团簇中钡离子和氮分子间的静电作用. 两者间的静电作用增加了氮分子π 反键轨道的占据数, 促进了氮分子极化, 从而削弱氮分子键.     

Untersuchungen mit 15N im Dauerdüngungsfeldversuch

Abstract

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

A New Approach to Determining the Content and 15N Abundance of Total Dissolved Nitrogen in Aqueous Samples: TOC Analyser-QMS Coupling

Abstract

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