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 Relationship of Nitrate Reductase Activity to Uptake and Assimilation of Atmospheric 15NO2-Nitrogen in Needles of Norway Spruce (Picea abies [L.] Karst.)

Abstract

Using ¹⁵NO₂, relations between nitrate reductase activity and stomatal conductance, ¹⁵N-uptake and ¹⁵N-glutamate were studied in the two youngest needles flushes of potted Norway spruce (Picea abies [L.] Karst.). There were linear correlations between the stomatal conductance and the ¹⁵N-uptake and between the ¹⁵N-uptake and nitrate reductase (E.C. 1.6.6.1/1.6.6.2) activity. The ¹⁵N labelling of free glutamate shows the assimilation of NO₂ from the atmosphere in addition to the nitrogen from the soil. The portion of glutamate originating from ¹⁵NO₂ was linearly related to nitrate reductase activity in spring experiments. This indicates that this enzyme activity reflected the rate of NO₂-assimilation.     

The first in vivo observation of (13)C-(15)N coupling in mammalian brain.

[5-(13)C,(15)N]Glutamine, with (1)J((13)C-(15)N) of 16 Hz, was observed in vivo in the brain of spontaneously breathing rats by (13)C MRS at 4.7 T. The brain [5-(13)C]glutamine peak consisted of the doublet from [5-(13)C,(15)N]glutamine and the center [5-(13)C,(14)N]glutamine peak, resulting in an apparent triplet with a separation of 8 Hz. The time course of formation of brain [5-(13)C,(15)N]glutamine was monitored in vivo with a time resolution of 20-35 min. This [5-(13)C,(15)N]glutamine was formed by glial uptake of released neurotransmitter [5-(13)C]glutamate and its reaction with (15)NH(3) catalyzed by the glia-specific glutamine synthetase. The neurotransmitter glutamate C5 was selectively (13)C-enriched by intravenous [2,5-(13)C]glucose infusion to (13)C-label whole-brain glutamate C5, followed by [(12)C]glucose infusion to chase (13)C from the small and rapidly turning-over glial glutamate pool, leaving (13)C mainly in the neurotransmitter [5-(13)C]glutamate pool, which is sequestered in vesicles until release. Hence, the observed [5-(13)C,(15)N]glutamine arises from a coupling between (13)C of neuronal origin and (15)N of glial origin. Measurement of the rate of brain [5-(13)C,(15)N]glutamine formation provides a novel noninvasive method of studying the kinetics of neurotransmitter uptake into glia in vivo, a process that is crucial for protecting the brain from glutamate excitotoxicity.     

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 (15)N(2) incorporation after incubation with (15)N(2) labeled air or/and by acetylene reduction. These bacterial strains were able to fix N(2) 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 NH(4) (+) than NO(3) (-). The N(2) fixation of P. agglomerans decreased only by NH(4) (+) -addition, but was stimulated by NO(3) (-). 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.     

Rapid, Sensitive and Highly Selective (15)N Analysis of (15)N Enriched Nitrite in Water Samples and Soil Extracts by Nitric Oxide Production and CF-QMS Measurement

Abstract Nitrite is a very important intermediate in many microbiological N transformations in soils and water. The stable isotope (15)N is often used to investigate these processes. The determination of (15)N in low concentrations of nitrite in the presence of large concentrations of nitrate is very difficult. Methods used so far for the isotope analysis of nitrite are unsatisfactory, because the nitrite must be calculated as the difference between nitrate plus nitrite and nitrate alone. More useful are mehods by which the nitrite is selectively converted into a chemical form that is suitable for (15)N analysis and that is free from interference from other N species, particularly nitrate. Using this principle in the present study we developed a method where the nitrite is reduced to nitric oxide by iodide in acid medium. This reaction is fast and quantitative, and the (15)N abundance of NO can be precisely measured by continuous flow mass spectrometry. This method is used for samples from tracer experiments with artificially enriched nitrogen 15. Therefore, the use of simple quadrupole mass spectrometers directly linked to the reaction unit is possible with sufficient precision (Reaction-Continuous Flow Quadrupole Mass Spektrometry-RCFQMS). Using the technique developed sample volumes up to 10ml containing at least 1.0 μg nitrite-N (0, 1 μg/ml) with a (15)N abundance of ? 0.42 at.% gave a precision of RSD ? ± 3%.     

Determination of (15)N in (15)N-enriched nitrite and nitrate in aqueous samples by reaction continuous flow quadrupole mass spectrometry

The (15)N tracer method is the most suitable method for studying complex N transformation processes in microbiology and biochemistry. It entails the constant determination of the (15)N abundance of the inorganic nitrogen (N) compounds nitrite and nitrate. However, (15)N analytical methods are time-consuming, difficult to automate, and require at least 10 μg of N per determination. An additional obstacle in the case of nitrite is that it usually only occurs in very small amounts (ppb) dwarfed by much larger quantities of nitrate (ppm). More useful is an approach in which the N compound is selectively converted into a gaseous form suitable for direct measurement by mass spectrometry. By using this 'reaction continuous-flow mass spectrometry' (R/CFMS) we developed methods for the (15)N determination of nitrite and nitrate from tracer experiment samples, i.e. artificially enriched in (15)N. Because both methods are based on the same principle, one continuous flow setup connected directly to a quadrupole mass spectrometer for all determinations was used. Nitrite and nitrate are reduced to NO by iodide and titanium(III) chloride, respectively. The technique developed ensures a precision of relative standard deviation /=1 at.% are to be measured for nitrite and nitrate, respectively. Copyright 1999 John Wiley & Sons, Ltd.     

双波长法快速测定饮用水中的硝酸盐氮和亚硝酸盐氮

针对快速性要求较高的场合,提出基于双波长法测定硝酸盐氮和亚硝酸盐氮含量的方法,该法首先测定混合溶液在203、216、220nm处的吸光度值,其次计算216nm与203nm处的吸光度差值,通过差值的线性回归方程计算出硝酸盐氮的浓度,再通过亚硝酸盐溶液的校准曲线计算亚硝酸盐氮的含量。通过实验和分析计算,可知此法原理简单,使用方便,精密度和准确度较高,而且在没有分光光度计的情况下也能使用,大大提高了分析效率,适合用在快速估算硝酸盐氮和亚硝酸盐氮含量的场合。     

Spectrophotometry Determination of Nitrate Nitrogen and Nitrite Nitrogen in Sewage Sludges

Extraction followed by spectrophotometry was employed to determine nitrate and nitrite in sewage sludge. Recovery of added nitrate and nitrite was complete. The procedure was suitable for the determination of nitrate nitrogen and nitrite nitrogen in this matrix.     

二阶导数光谱法快速测定硝酸盐氮和亚硝酸盐氮

紫外吸收方法中，硝酸盐氮(NO-₃-N)的紫外吸收峰在202.0 nm左右，而亚硝酸盐氮(NO-₂-N)的紫外吸收峰在210.0 nm左右，两者吸收峰位置距离很近，因此，在分析过程中两者的紫外吸收曲线严重重叠，相互之间严重干扰，不经过分离很难用单波长对二者的含量进行测定而常用的国标方法过程又过于繁琐，耗时较长。为了准确、快速、环保的实现环境水体和饮用水中的硝酸盐氮和亚硝酸盐氮快速监测，避免国标方法中对二者测定的诸多不足，结合紫外吸收和二阶导数光谱法，在不经过任何预先分离处理的情况下，建立了水体中这两种物质的快速分析方法，实现水样中二者的快速准确测定。研究采用优级纯试剂配制硝酸盐氮和亚硝酸盐氮系列标准溶液。以去离子水做参比，采用紫外-可见光分光光度计扫描其在195～250 nm范围内的紫外吸收光谱，之后采用Origin软件对所获得的光谱图做二阶导数处理，并采用Origin软件中的Savitzky-Golay方法对处理后的二阶导数光谱进行平滑处理以去除其他无关的干扰和噪声。通过观察上述所得两组二阶导数光谱图，得出以下结论，不同浓度的亚硝酸盐氮样品在223.5 nm处吸光度的二阶导数均为0，不同浓度的硝酸盐氮样品在216.5 nm处的吸光度的二阶导数也均为0。通过实验可见硝酸盐氮和亚硝酸盐氮混合样品的紫外吸收光谱的二阶导数在这两个特定波长处符合朗伯比尔定律。实验通过配制硝酸盐氮和亚硝酸盐氮混合样品，并扫描混合样品的紫外吸收光谱，采用上述方法对所得光谱做二阶导数及平滑去噪处理。研究混合样品二阶导数光谱图可以看出在硝酸盐氮浓度相同而亚硝酸盐氮浓度不同时，亚硝酸盐氮的浓度变化会对硝酸盐氮的吸光度的二阶导数有影响，但是各种混合样品的二阶导数光谱在223.5 nm处几乎交叉于一点，说明此处亚硝酸盐氮的浓度不同不会对硝酸盐氮的二阶导数吸光度有影响。且在223.5 nm处硝酸盐氮二阶导数吸光度随浓度增加而线性增加。因此，223.5 nm可作为混合组分中硝酸盐氮的测定波长。参照以上方法，可得亚硝酸盐氮的测定波长为216.5 nm。在223.5 nm处对单组分的硝酸盐氮的浓度值及其相应的吸光度的二阶导数进行线性回归，其线性关系良好，得到标准曲线的回归方程为C=438.69A+0.015，R2=0.995 9。同理，得到亚硝酸盐氮在216.5 nm处回归方程为C=-657.29A+0.068 8，R2=0.998。为了验证这种方法在实际水样测量中能否成立，取秦皇岛市新河、汤河以及戴河三种河水水样进行实验验证，结果表明，回收率在96.7%～103.0%之间，相对标准偏差在1.46～3.68之间。该方法结果较准确，且操作更加简便，成本较低，可同时实现硝酸盐氮和亚硝酸盐氮快速在线监测。     

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.     

应用数码相机进行绿肥翻压后春玉米氮素营养诊断和产量预测

在绿肥翻压条件下,常规的玉米氮素营养诊断技术存在耗时、费力和可靠性差的缺点。基于数码相机的可见光光谱技术已被广泛应用于大田作物的氮素营养诊断,但尚未见应用于绿肥翻压后的玉米氮素营养诊断。为评价利用图像处理技术进行绿肥翻压后玉米氮素营养诊断和玉米产量预测的可行性,设置了不同施氮水平下的绿肥翻压试验,利用数码相机获取不同生育期玉米冠层数字图像,分析了玉米冠层图像色彩参数与氮素营养诊断指标和成熟期籽粒产量之间的关系。结果表明,绿肥翻压显著改善了玉米的氮素营养,不同生育期的玉米叶绿素含量(SPAD值)、地上部生物量和吸氮量均高于单施化肥处理;绿肥翻压处理下,玉米冠层光谱指数与氮素营养指标间的相关性较单施化肥处理低,且其相关性在不同的生育期有较大变异,其中,12叶期(V12)的蓝光标准化值(B/(R+G+B))与灌浆期(R4)的红光标准化值(R/(R+G+B))与植株氮营养指标相关性较好,二者均与玉米产量间呈显著直线回归关系,回归系数分别为45%和46%。因此,数字图像技术在进行绿肥翻压后玉米氮素营养的诊断和产量预测方面具有应用潜力,但应注意诊断时期和关键指标的选择。     

玉米叶片的光谱响应及其氮素含量预测研究

以不同施肥水平下两年玉米田间试验为基础,利用高光谱技术探讨大喇叭口期不同层次玉米叶片光谱响应的敏感区域,并依据叶片氮素含量与原始光谱反射率及其一阶导数的相关性,最终构建了叶片氮素含量的预测模型。结果表明：不同施肥水平下叶片光谱反射率差别明显区域集中在550 nm附近波段、761～1 300 nm波段,不同层次间叶片光谱反射率差别明显区域集中在550 nm附近波段,叶片氮素含量与470～760 nm波段光谱反射率及其一阶导数呈极显著相关。经过对比筛选,以光谱指数DSI(564,681)和DSI(681,707)构建的指数预测模型效果最好,预测精度达93.43%和93.39%,能有效估测叶片氮素含量。     

Laser-Induced Chlorophyll Fluorescence: A Technique for Detection of Dimethoate Effect on Chlorophyll Content and Photosynthetic Activity of Wheat Plant

Laser-induced chlorophyll fluorescence (LICF) spectra and fluorescence induction kinetics (FIK) curves of wheat plant leaves treated with different concentrations (50, 100 and 200 ppm) of dimethoate are recorded. LICF spectra are recorded in the region of 650-780 nm using violet diode laser (405 nm) and FIK curve at 685 and 730 nm with red diode laser (635 nm) for excitation. The fluorescence intensity ratios (FIR) are determined from LICF spectra and vitality index (R(fd)) from FIK curves. These parameters along with photosynthetic pigment contents and growth parameters are used to analyze the effect of dimethoate on wheat plants. The result indicates that lower concentration of 50 ppm shows stimulatory response while higher concentrations of dimethoate are hazardous for growth, photosynthetic pigments and activity of wheat plants.     

15N/14N Analysis of Amino Acids with GC-C-IRMS - Methodical Investigations and Ecotoxicological Applications

Abstract

In order to perform the ¹⁵N/¹⁴N analysis of amino acids using a gas chromatograph and isotope ratio mass spectrometer linked up via a combustion interface (GC-C-IRMS), the amino acids must be derivatized. Tert-butyldimethylsilylation is examined using various techniques (direct conversion to nitrogen gas, ConFlo-IRMS [1], GC-C-IRMS [2]) and subsequently applied to isotopic characterization of amino acids from wheat protein hydrolyzate obtained from plants exposed to ozone. The method provides a reliable tool for studying ecotoxicological effects on plants at a molecular level in addition to the investigation of the natural variations of different N fractions.     

Isotopic study of post-anthesis foliar incorporation of sulphur and nitrogen in wheat

Nitrogen (N) and sulphur (S) supplies have a strong influence on the quality and quantity of wheat storage proteins, which play an important role in the bread-making process. In order to relate the incorporation and distribution of foliar N and S fertilisers at the post-anthesis stage to the quality of wheat, 15N and 34S isotopes were used as tracers. The incorporation of these tracers in different plant parts (leaves, stems, ears) and in each storage protein fraction (gliadins, HMW and LMW glutenin subunits) was determined by isotopic ratio mass spectrometry coupled with an elemental analyser (EA-IRMS). By this means, the true recovery coefficient of N and S (TRCNfertiliser and TRCSfertiliser) and the N and S derived from fertilisers (Ndff and Sdff) could be determined. The TRCNfertiliser and TRCSfertiliser values of the different plant parts provide evidence of the applied N and S assimilation and translocation from wheat leaves to the seeds. The determination of Ndff and Sdff incorporated into storage proteins shows the efficiency and the influence of N and S incorporation into each storage protein fraction. Moreover, a favourable stage for fertiliser application can be determined by the TRCNfertiliser values in the grain and in the whole plant. The fertilisers enriched in stable isotope used in the culture techniques can be a means of understanding the effectiveness of fertilisers in the expression of wheat quality.     

病害胁迫下冬小麦冠层叶片色素含量高光谱遥感估测研究

通过人工田间诱发小麦条锈病,在不同生育期测定染病冬小麦冠层光谱和相应叶片的色素含量。把冠层光谱数据、一阶微分数据与相应的叶片色素含量数据分别进行相关分析,采用单变量线性和非线性回归技术,选取部分样本建立小麦的色素含量估测模型,并利用其余的样本对模型进行检验,结果表明绿边内一阶微分总和(SD_g)与红边内一阶微分总和(SD_r) 的归一化值为变量的线性模型是估测色素含量的最佳模型,其估测叶绿素a,叶绿素b和胡萝卜素含量的相对误差分别为17.0％,16.3％和12.4％。该研究表明可用高光谱信息估测冠层叶片色素含量,且估测精度较高。文章的研究结果对利用高光谱遥感监测农作物长势以及病害影响都具有实际应用价值。     

The First in Vivo Observation of C–N Coupling in Mammalian Brain

[5-¹³C,¹⁵N]Glutamine, with ¹J(¹³C–¹⁵N) of 16 Hz, was observed in vivo in the brain of spontaneously breathing rats by ¹³C MRS at 4.7 T. The brain [5-¹³C]glutamine peak consisted of the doublet from [5-¹³C,¹⁵N]glutamine and the center [5-¹³C,¹⁴N]glutamine peak, resulting in an apparent triplet with a separation of 8 Hz. The time course of formation of brain [5-¹³C,¹⁵N]glutamine was monitored in vivo with a time resolution of 20–35 min. This [5-¹³C,¹⁵N]glutamine was formed by glial uptake of released neurotransmitter [5-¹³C]glutamate and its reaction with ¹⁵NH₃ catalyzed by the glia-specific glutamine synthetase. The neurotransmitter glutamate C5 was selectively¹³C-enriched by intravenous [2,5-¹³C]glucose infusion to ¹³C-label whole-brain glutamate C5, followed by [¹²C]glucose infusion to chase ¹³C from the small and rapidly turning-over glial glutamate pool, leaving ¹³C mainly in the neurotransmitter [5-¹³C]glutamate pool, which is sequestered in vesicles until release. Hence, the observed [5-¹³C,¹⁵N]glutamine arises from a coupling between ¹³C of neuronal origin and ¹⁵N of glial origin. Measurement of the rate of brain [5-¹³C,¹⁵N]glutamine formation provides a novel noninvasive method of studying the kinetics of neurotransmitter uptake into glia in vivo, a process that is crucial for protecting the brain from glutamate excitotoxicity.     

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.     

Astrocytic energy metabolism and glutamate formation--relevance for 13C-NMR spectroscopy and importance of cytosolic/mitochondrial trafficking

Glutamate plays a double role in ¹³C-nuclear magnetic resonance (NMR) spectroscopic determination of glucose metabolism in the brain. Bidirectional exchange between initially unlabeled glutamate and labeled α-ketoglutarate, formed from pyruvate via pyruvate dehydrogenase (PDH), indicates the rate of energy metabolism in the tricarboxylic acid (V_TCA) cycle in neurons (V_{PDH, n}) and, with additional computation, also in astrocytes (V_{PDH, g}), as confirmed using the astrocyte-specific substrate [¹³C]acetate. Formation of new molecules of glutamate during increased glutamatergic activity occurs only in astrocytes by combined pyruvate carboxylase (V_PC) and astrocytic PDH activity. V_{PDH, g} accounts for ∼15% of total pyruvate metabolism in the brain cortex, and V_PC accounts for another ∼10%. Since both PDH-generated and PC-generated pyruvates are needed for glutamate synthesis, ∼20/25 (80%) of astrocytic pyruvate metabolism proceed via glutamate formation. Net transmitter glutamate [γ-aminobutyric acid (GABA)] formation requires transfer of newly synthesized α-ketoglutarate to the astrocytic cytosol, α-ketoglutarate transamination to glutamate, amidation to glutamine, glutamine transfer to neurons, its hydrolysis to glutamate and glutamate release (or GABA formation). Glutamate-glutamine cycling, measured as glutamine synthesis rate (V_cycle), also transfers previously released glutamate/GABA to neurons after an initial astrocytic accumulation and measures predominantly glutamate signaling. An empirically established ∼1/1 ratio between glucose metabolism and V_cycle may reflect glucose utilization associated with oxidation/reduction processes during glutamate production, which together with associated transamination processes are balanced by subsequent glutamate oxidation after cessation of increased signaling activity. Astrocytic glutamate formation and subsequent oxidative metabolism provide large amounts of adenosine triphosphate used for accumulation from extracellular clefts of neuronally released K⁺ and glutamate and for cytosolic Ca²⁺ homeostasis.     

基于光谱指数波段优化算法的小麦玉米冠层含氮量估测

作物关键生育时期冠层氮素含量的实时监测对于优化氮肥用量和减少环境风险具有重要的意义。为了寻求预测不同作物氮素含量的最佳光谱参数,实现作物氮素无损营养诊断。本研究通过2008年—2011年在德国慕尼黑弗莱辛和河北曲周的不同氮量的小麦玉米田间试验,采用高光谱仪获取小麦玉米冠层的反射光谱,利用光谱理论模型进行光谱指数波段的优化,从而抽取不同冠层结构条件下的小麦玉米氮素营养敏感波段。结果表明与传统的基于红光的光谱指数相比,优化光谱指数显著提高了小麦玉米冠层氮素含量的预测能力,克服了传统的基于红光光谱指数的饱和问题。优化光谱指数的波段结合随着作物品种及其冠层结构的变化而变化,其优化波段范围主要集中在红边(730～760 nm)和红边向近红外的过渡区域(760～880 nm)。优化结果显示玉米最佳光谱指数为R_λ766/R_λ738-1,小麦最佳光谱指数为R_λ796/R_λ760-1,玉米小麦相结合优化后的最佳光谱指数为Rλ₈₇₆/Rλ₇₃₀-1。结果进一步验证了优化光谱指数估测的不同作物含氮量的预测值与实测值相关性最高,且验证偏差最小,证实了优化后的光谱特征参数可对不同作物氮素丰缺状况进行快速、准确、无损估测。试验结果也为设计作物冠层氮素传感器和更好的利用现有基于卫星的传感器实施区域上的作物氮素营养监测提供了理论基础。