Absorption,translocation, and assimilation of foliar-applied urea compared with nitrate and ammonium in tomato plants

To evaluate the use of foliar application of N fertilizer and the occurrence of leaf injury in tomato plants (Lycopersicon esculentum Mill., cv. Momotaro), the effects of the form and concentration of N and solution pH on the leaf injury were studied in the first experiment (Expt. 1). The effects of solution pH and leaf surface on the absorption, translocation, and assimilation of urea were compared with those of nitrate and ammonium in the second experiment (Expt. 2). In Expt. 1, no leaf injury was observed regardless of N sources applied at the N concentration of 1.0 g L^-1. Compared with nitrate or ammonium, the index of leaf injury was the lowest in the leaf to which urea had been applied (hereafter referred to as “urea-applied leaf”), when the N level increased from 2.0 to 10.0 g L^-1. Leaf injury was not affected by the solution pH in the case of urea, but it increased in the case of ammonium and decreased when nitrate was applied with increasing solution pH. In Expt. 2, the absorption of nitrate and ammonium by a leaf within 4 d was 34% and 74% of that of urea, respectively. N absorption at the lower leaf surface was much greater than that at the upper leaf surface for each N source. No apparent effect of solution pH on the absorption of urea was detected. With increasing solution pH, however, the absorption of nitrate decreased. The absorption of ammonium was the greatest at solution pH 7.5. Total-¹⁵N translocation from applied leaf to other plant parts within 4 d was the largest in the urea-applied plants. Effects of solution pH and leaf surface on ¹⁵N distribution were not appreciable. ¹⁵N assimilation was the quickest in the urea-applied plants. Two days after application, ¹⁵N assimilation in the whole plant was up to 76.9% in the urea-applied plants, but only 33.7% and 43.0% in the nitrate- and ammonium-applied plants, respectively. Urea was an appropriate foliar N source due to the low ability to injure foliage because of the rapid absorption and translocation, fast assimilation, and the wide and suitable range of solution pH. Foliar application of N to the lower leaf surface was recommended.     

Nitrogen concentrations and proportions of ammonium and nitrate in the nutrition and growth of yellow passion fruit seedlings

Abstract

Despite the importance of nitrogen (N) supply to plants, there are still doubts concerning the optimal relations of ammonium and nitrate in the nutrition of yellow passion fruit seedlings. This study aims to evaluate the interaction between nitrogen concentrations and ammonium and nitrate proportions in the nutrition, growth, and dry matter production of passion fruit seedlings grown in a substrate with a nutrient solution. The experiment was conducted in a greenhouse in randomized complete block design with three replications in a 4 × 5 factorial design, consisting of four N concentrations (2.5, 5.0, 10.0 and 20.0?mmol L^?1) and five ammonium proportions (0, 25, 50, 75 and 100% in relation to the total N supply). At 60?days after transplanting, green color index; accumulation of N, potassium, calcium, and magnesium in roots and shoots; stem diameter; leaf area; root length; nitrogen use efficiency (NUE); and dry matter of roots and shoots were evaluated. For the formation of seedlings of yellow passion fruit, the nutrient solution should have 13?mmol L^?1 of N, with 40% of this nutrient in the form of ammonium. The passion fruit is a plant tolerant to ammonium. However, a critical concentration above 5.7?mmol L^?1 of NH₄⁺ in the nutrient solution decreases absorption of cations, NUE, and production of dry matter.     

Mineral Nitrogen Associated Changes in Growth and Xylem-N Compounds in Amazonian Legume Tree

In nodulated young Inga edulis plants, nodule and plant growth, nitrogen (N) in xylem sap and tissues total contents of amino acid, ureide, and nitrate were determined in response to nutrition with nitrate, ammonium, or no mineral N. Additionally, the amount of soluble sugars in the different plant tissues was quantified. It was found that mineral N improved plant growth in height and diameter especially with ammonium. However, nitrate dramatically reduced nodule dry weight on a root dry weight basis and impaired N organic transport by xylem sap. Additionally, a higher amount of amino acids was observed in the roots and nodules of plants fed with mineral N but sugar levels remained constant. Although nitrate inhibited symbiosis, data support the idea that I. edulis is able to use both molecular and mineral nitrogen during the life cycle.     

Significance of Nickel Supply for Growth and Chlorophyll Content of Wheat Supplied with Urea or Ammonium Nitrate

ABSTRACT

Nickel (Ni) is an essential element for activation of urease in higher plants. The effects of Ni as an essential micronutrient on growth and chlorophyll content of wheat plants grew in nutrient solutions supplied either with ammonium nitrate or urea as two different nitrogen (N) sources were investigated. Plants were allowed to grow for six weeks, then leaf chlorophyll content, shoot and root fresh and dry weights, and Ni concentration in shoots and roots were determined. Shoot and root Ni concentration in both urea and ammonium nitrate-fed plants increased significantly with the increase in Ni concentration. Growth and chlorophyll content in leaves of the urea-fed plants increased when Ni concentration in the solution was as high as 0.05 mg L^?1 and decreased at 0.1 mg Ni L^?1. In ammonium nitrate-fed plants, these parameters increased up to 0.01 mg Ni L^?1 and started to decrease with further increase in Ni concentration. Plants that grew in nutrient solutions containing urea had more shoots and roots fresh and dry weight at third and fourth Ni levels (0.05 and 0.1 mg L^?1) than those that grew in media containing ammonium nitrate with similar Ni levels. Total chlorophyll content was also higher in plants supplied with urea plus Ni. The amount of Ni required for optimum wheat growth was dependent on the forms of N used. When supplied with ammonium nitrate or urea, the amount of Ni needed was 0.01 and 0.05 mgL^?1 of nutrient solutions, respectively.     

盐胁迫下氮素形态对油菜和水稻幼苗离子运输和分布的影响

【目的】土壤盐碱化是制约农作物产量的主要因素之一,盐胁迫影响养分运输和分布,造成植物营养失衡,导致作物发育迟缓,植株矮小,严重威胁着我国的粮食生产。在必需营养元素中,氮素是需求量最大的元素,NO-3和NH+4是植物吸收氮素的两种离子形态。植物对盐胁迫的响应受到不同形态氮素的调控,研究不同形态氮素营养下植物的耐盐机制对提高植物耐盐性及产量具有重要的意义。【方法】本文以喜硝植物油菜(Brassica napus L.)和喜铵植物水稻(Oryza sativa L.)为试验材料,采用室内营养液培养方法,研究了NO-3和NH+4对Na Cl胁迫下油菜及水稻苗期生长状况、对Na+运输和积累的影响,以对照与盐胁迫植株生物量之差与Na+积累量之差的比值,评估Na+对植株的伤害程度。【结果】1)在非盐胁迫条件下,硝态氮营养显著促进油菜和水稻根系的生长;盐胁迫条件下,油菜和水稻生物量均显著受到抑制,Na Cl对供应铵态氮营养植株的抑制更为显著。2)盐胁迫条件下,两种供氮形态下,油菜和水稻植株Na+含量均显著增加,硝态氮营养油菜叶柄Na+显著高于铵态氮营养,叶柄Na+含量/叶片Na+含量大于铵营养油菜,硝态氮营养水稻根系Na+含量显著低于铵营养,地上部则相反。3)铵营养油菜和水稻Na+伤害度显著高于硝营养植株。4)盐胁迫条件下,硝态氮营养油菜地上部和水稻根系K+含量均显著高于铵态氮营养。5)盐胁迫条件下,硝营养油菜和水稻木质部Na+浓度,韧皮部Na+和K+浓度及水稻木质部K+浓度均高于铵营养植株。【结论】与铵营养相比,硝营养油菜和水稻具有更好的耐盐性。硝态氮处理油菜叶柄Na+显著高于铵态氮处理,能够截留Na+向叶片运输。同时,供应硝态氮营养更有利于油菜和水稻吸收K+,有助于维持植物体内离子平衡。盐胁迫下,硝营养油菜和水稻木质部Na+浓度,韧皮部Na+和K+浓度及水稻木质部K+浓度均高于铵营养植株,表明硝态氮营养油菜和水稻木质部-韧皮部对离子有较好的调控能力,是其耐盐性高于铵营养的原因之一。     

15N study on the partitioning of the nitrogen taken by soybeans from atmospheric dinitrogen,medium nitrate or ammonium

Abstract

Soybean plants (Glycine max, cv. Akisengoku) were water-grown in a greenhouse with a low concentration of nitrate in the culture solution. Under these conditions root nodulation mostly on primary roots was profuse. At the vegetative and pod-filling stages, plants were fed ¹⁵N-labeled dinitrogen, nitrate, or ammonium for 7 to 8 hr in the daytime.

Partitioning of the ¹⁵N from the three nitrogen sources showed distinct characteristics. The nitrogen (N) from dinitrogen preferentially distributed to the developing organs, young leaves, and developing pods, in comparison with N from nitrate. N from ammonium showed distribution pattern similar to that of N from dinitrogen.

The nodule N was supplied by both directly fixed-N and transferred nitrogen, and fixedN was inferred to play a major role in this process. The pro tein N in the roots could be furnished by the recycled N of dinitrogen and nitrate through the shoots along with direct incorporation of amino acids produced in the roots from nitrate     

The effect of form and level of inorganic N on nitrogen use efficiency of sugarcane grown in pots

To-date, assessments of nitrogen use efficiency (NUE) of sugarcane have not included the contribution of its components, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE). This study determined these values, based on biomass and plant nitrogen (N) content, in two four-month-old pot-grown genotypes. The treatments included six N regimes, with nitrate (NO₃^—N) or ammonium (NH₄⁺-N) supplied alone, or as NO₃^?-N for the first 6 weeks and then NH₄⁺-N until harvest, each as 4 or 20 mM. Regardless of the N form, NUE was higher at four than at 20 mM due to significantly higher NUpE at low N supply. The results indicated that there was luxury N uptake and preference for NH₄⁺-N nutrition, which resulted in the highest determined NUE. There were significant differences between genotypes in biomass, morphological growth parameters, N uptake, total plant N and NUE, the latter matching previously established sucrose yield-based NUE field rankings.     

Does nitrogen concentration affect relative uptake rates of nitrate,ammonium, and glycine?

Plant roots are exposed to a variety of nitrogen forms (e.g., nitrate, ammonium, amino acids) and take up these forms at different rates. Many studies have investigated whether plants prefer nitrate, ammonium, or amino acids; but studies may not be comparable because they used substrate concentrations between 100 and 2000 μmol L^–1. This study tests the hypothesis that substrate concentrations from 10 to 1750 μmol L^–1 affect plant preference for N forms. Nitrogen uptake by the herb Ocimum basilicum and the evergreen tree Eucalyptus regnans was examined by placing roots of intact seedlings in equimolar mixtures of nitrate, ammonium, and glycine in which one of the N forms was ¹⁵N‐labelled (and ¹³C‐labelled in the case of glycine). In both species, preference for N forms was affected by substrate concentration. At 10 μmol L^–1 (O. basilicum) or 10 and 50 μmol L^–1 (E. regnans), rates of N uptake did not differ among N forms. At substrate concentrations of 50 μmol L^–1 and greater O. basilicum took up ammonium the fastest, glycine the slowest, and nitrate at an intermediate rate. At substrate concentrations from 100 to 1750 μmol L^–1, E. regnans took up ammonium the fastest with glycine and nitrate taken up at slower rates. The absence of significant differences at lower concentrations was a true biological effect rather than a function of larger relative errors. This study demonstrates that substrate concentration has a large effect on plant preference for N forms, and sounds a warning for studies of N nutrition that do not consider the concentration‐dependence of plant preference for N forms.     

Benefits of mycorrhizae to soybeans grown on various regimes of nitrogen nutrition 1

Nodulating and nonnodulating isolines of soybean (Glycine max Merr ‘Clay') were grown in sand culture in a greenhouse. The plants were cultured with or without mycorrhizal (Glomus mosseae) infection, and nodulating plants were inoculated with Rhizobium iaponicum. Phosphorous was supplied as hydroxyapatite or dicalcium phosphate with N nutrition from nitrate or as combinations of nitrate and ammonium or nitrate and urea. Best growth of the nodulating isoline was with urea nutrition. Best growth with the nonnodulating isoline was with ammonium nutrition. Urea‐treated nodulating plants showed increased growth due to mycorrhizae. Urea‐treated or ammonium‐treated nonnodulating plants showed growth increases due to mycorrhizae. Nitrate‐treated plants did not show increased growth due to mycorrhizae. Mycorrhizal infection was greatest with urea nutrition, and the infection increased the tissue N content of these plants relative to nonmycorrhizal plants. Enhancement of tissue P accumulation through mycorrhizae was greater with hydroxyapatite than with dicalcium phosphate. The efficiency of the symbiotic relationship of Glvcine‐Glomus‐Rhizobium depended on a supply of reduced nitrogen, a high N:P ratio in roots, and a neutral pH in the rhizosphere. Urea nutrition met these requirements best.

Vesicular‐arbuscular mycorrhizal (VM) associations may improve the capacity of higher plants to acquire nutrients. These benefits have been studied extensively in relation to P nutrition since plant requirements for P are high relative to its availability in soils². Significant benefits may occur also in the nutrition of plants with micronutrients³. Reviews of literature suggest that the function of mycorrhizae in the acquisition of N by plants is variable⁴‘⁵‘⁶. The sources of N under various cultural or ecological conditions may account for the conflicting findings among researchers.

Hyphal transport of N is of little importance with NO3^‐nutrition because of the high mobility of this ion⁶ but may be important for the relatively immobile NH₄ ⁺ ion. Roots of NH₄ ^‐nourished plants often are restricted, and mycorrhizae may extend their absorbing surfaces⁷. Mycorrhizae may prefer NH₄‐N over NO₃‐N for their growth and development⁴. In some cases, NH₄ ⁺ ions restrict mycorrhizal infection compared to the effect of NO₃ ^‐ions⁷. The drop in ambient pH associated with NH₄ ⁺ nutrition may be a cause of this inhibition⁷‘⁸‘⁹. Plants grown on urea may not encounter the problems of acidity in the root zone and yet may have access to NH₄ ⁺ nutrition.

The N contents of mycorrhizally infected plants relative to those of uninfected plants are variable¹⁰‘^11,12,13. These diverse results could arise from differences in the levels and forms of N applied to the plants. Crops well‐infected with mycorrhizal fungi may not benefit from the association if N is limiting¹⁴‘¹⁵ although benefits may appear in soils supplemented with N¹⁵‘¹⁷ even if the level of P in the soil is high¹⁸.

An association of fungi, roots, and bacteria exists in nodulating’ legumes. Maximum benefits from this association may be achieved if N and P supplies are balanced properly. In the present study, the preference of the soybean‐Glomus mosseae‐rhizobial system for form of N was investigated to determine if the mycorrhizal benefits to the soybean could be optimized.     

分根区交替灌溉和氮形态影响土壤硝态氮的迁移利用

采用模拟土柱利用15N标记于土层10~20 cm、40~50 cm的方法,并设置不同形态氮肥供应(铵态氮、硝态氮)、灌溉方式(常规灌溉CI、分根区交替灌溉APRI),研究APRI下土壤中不同层次硝态氮的去向以及不同形态氮肥的影响。结果发现,APRI节水34.31%而不显著影响产量(P0.05)。随着15N标记层次下降,番茄植株对15N吸收利用率以及番茄收获后15N在1 m土层内的残留量显著下降,损失率显著增加。CI对10~20 cm土层的15N淋洗作用强于40~50 cm土层,APRI对10~20 cm的15N淋洗作用相对CI减弱,而促进了40~50 cm土层中61.3%的15N向上层土壤迁移。APRI下15N的损失率显著降低,利用率没有大幅度下降。相对于铵态氮肥料,硝态氮供应由于促进了植株生长及对15N的吸收,造成番茄收获后1m土层内15N累积量减少,而损失率与相应铵态氮供应的处理没有显著差异。因此分根区交替灌溉能够减少土壤中硝态氮的淋洗,并能够促进下层土壤硝态氮向上迁移,减少损失,增加植物吸收利用的机会;不同形态氮肥通过影响植物生长而影响土壤中硝态氮的去向。     

叶施15N-尿素增加棉花苗期氮素吸收利用的生理生化机制研究

【目的】苗期棉花根系发育缓慢,吸收能力弱,根系吸收的氮素不能满足棉株生长发育的需要,很容易出现僵苗、 弱苗。叶面施氮可以及时补充氮素营养,解决棉花苗期阶段性营养不足的问题。本研究利用15N同位素示踪技术研究喷施尿素对棉花苗期氮素吸收利用及生理生化特性的影响,以明确棉花苗期叶面喷施尿素的适宜浓度,了解其促进棉花生长发育的机理。【方法】本试验选用黄河流域常规栽培品种中棉所79为试验材料,采用随机区组设计,在棉花苗期叶面喷施0.5%、 1%和2%的15N-尿素溶液,以喷清水为对照,调查了尿素不同喷施浓度棉花氮素的吸收利用及生理生化特性。【结果】1)叶面喷施15N-尿素能显著提高棉株15N含量,各施氮处理棉株内15N含量随时间的变化趋势一致,即叶面喷施后2～96 h之间,逐渐升高,96 h达到最高,此后出现下降。2)棉株可以快速吸收叶面喷施的15N-尿素,各处理棉株叶面氮素平均吸收速率的变化趋势一致,因中午气孔关闭,2～4 h出现降低;4～6 h达到最大,期间急剧上升;6～8 h急剧下降,8～12 h下降也较快,12 h后缓慢下降。0～12 h平均吸收速率非常高,为0.23～0.29 mg/(gh)。棉株对于叶施氮素的吸收主要出现在喷施后12 h之内。3)15N-尿素浓度为0.5%、 1%时,叶面吸收显著促进了根系氮素吸收,且根系吸收的氮很快被转运到地上部分。4)1%尿素喷施浓度内,硝酸还原酶、 谷氨酰胺合成酶活性,叶绿素含量的变化趋势一致,均随尿素喷施浓度的增加而提高,在喷施浓度为1%时达到峰值,超过1%后开始下降。【结论】叶面尿素喷施浓度在0.5%～2%之间均能显著提高棉株15N含量,促进棉株的氮素代谢,以1%效果最佳。棉株对于喷施氮素的吸收主要发生在喷施后0～12 h,平均吸收速率为0.23～0.29 mg/(gh),96 h棉株中15N含量达到最高。棉花叶面施氮促进了根系对氮素的吸收。叶面施氮主要通过增强硝酸还原酶、 谷氨酰胺合成酶活性,提高叶绿素含量,增加叶面积,促进叶片的光合作用,以此提高氮素利用效率,增加棉花株高和总生物量。     

Ethylene evolution and ammonium accumulation by tomato plants with various nitrogen forms and regimes of acidity. Part I

Ammonium nutrition of plants in soil or solution culture leads to development of a strongly acidic regime in the medium. Foliar evolution of ethylene and accumulation of ammonium are stimulated by ammonium nutrition. This stimulation may be due in part to the acidification of media by ammonium nutrition. To determine the effects of medium pH on ethylene evolution and ammonium accumulation by plants, tomato (Lycopersicon esculentum Mill. ‘Heinz 1350’ and neglecta‐1) were grown with nitrate, ammonium, or urea nutrition and with various pH regimes in solution culture. Ammonium nutrition decreased medium pH to 3.5 and increased ethylene evolution and ammonium accumulation by plants. Urea nutrition at pH 3.5 also increased ammonium accumulation and ethylene evolution by plants. Nitrate nutrition at pH 3.5 slightly increased ammonium accumulation but had no effect on ethylene evolution. Media supplied with different ratios of nitrate to ammonium relieved toxic effect of ammonium relative to 100% ammonium nutrition. The symptoms of ammonium toxicity were observed on the plants with high ethylene evolution. High ethylene evolution occurred on the plants with relative high ammonium accumulation regardless of nitrogen forms and pH regimes. The results indicate that toxic symptoms and increased ethylene evolution are directly related to high ammonium accumulation and that low pH may cause ammonium accumulation in plants.     

Lettuce (Lactuca sativa L.) growth,yield and quality response to nitrogen fertilization in a non-circulating hydroponic system

The objective of this study was to determine the effect of nitrogen fertilization rate on growth and quality of leafy lettuce grown during the winter season in non-circulating hydroponic system. Plants were subjected to seven nitrogen (N) concentrations, i.e. 0, 30, 60, 90, 120, 150 and 180 mg L^?1 N using ammonium nitrate. Nitrogen treatments did not have a significant effect on leaf fresh and dry mass, root fresh and dry mass, number leaves and leaf area. Leaf ascorbic acid and total phenolic content, and antioxidant capacity peaked at 100 and 120 mg L^?1 N, whereas leaf chlorophyll concentration linearly increased with increasing N application. The results indicate that a solution N concentration of 100 and 120 mg L^?1 may be sufficient to improve growth, yield and quality parameters of leafy lettuce grown in non-circulating hydroponic system.     

Mitigation of ammonium toxicity by silicon in tomato depends on the ammonium concentration

Ammonium toxicity in hydroponically grown crops can affect tomato development. However, it has been shown that the silicon (Si) attenuates ammonium toxicity in plants depending on the plant species, the stage of development and the ammonium concentration in the nutrient solution. Thus, in order to investigate how Si attenuates stress caused by ammonium in tomato, a study was carried out involving plants cultivated up to 40 days after seed germination using nutrient solutions containing ammonium concentrations (1, 2, 4, 6 and 8?mmol?L^?1), in the absence or presence of Si (1?mmol?L^?1). The accumulation and efficiency of nitrogen and Si use, as well as the concentrations of chlorophyll, carotenoids, malondialdehyde, hydrogen peroxide and growth parameters was assessed. At a concentration of 1?mmol?L^?1 ammonium, Si increases the accumulation of nitrogen and Si, the nitrogen use efficiency, the root area and dry biomass of the shoot. At concentrations of 1 and 2?mmol?L^?1 ammonium, Si increases the leaf area and root dry biomass, and in higher concentrations, there was no effect of Si after the supply of ammonium. It was observed that the addition of Si mitigates ammonium toxicity by 1?mmol?L^?1 ammonium, and we can recommend its use in the nutrient solution (Si?=?1?mmol?L^?1) to grow tomato cropsthat employs ammonium concentration of 1?mmol?L^?1.     

EFFECT OF PETUNIA STOCK PLANT NUTRITIONAL STATUS ON FERTILIZER RESPONSE DURING PROPAGATION

Fertilization strategies during stock plant and cutting production are linked in terms of cutting nutrient levels and quality. Objectives were to evaluate (1) the effect of stock plant nutrition on tissue nutrient concentration and growth during vegetative propagation and (2) response to fertilizer during propagation for cuttings with 4 different initial tissue nutrient concentrations. ‘Supertunia Royal Velvet’ petunia stock plants were grown under constant fertigation of 0, 50, 100 or 200 mg nitrogen (N)^.L^?1 for 21 days. The 200 mg N^.L^?1 solution contained 150 nitrate (NO₃-N), 50 ammonium (NH₄-N), 24 phosphorus (P), 166 potassium (K), 40 calcium (Ca), 20 magnesium (Mg), 0.7 sulfur (S), 1.0 iron (Fe), 0.5 manganese (Mn), 0.5 zinc (Zn), 0.24 copper (Cu), 0.24 boron (B), and 0.1 molybdenum (Mo). Providing a complete fertilizer during propagation of petunia, beginning immediately after sticking of cuttings, reduces the risk of nutrient deficiency. Particularly in situations where fertilizer is not applied early during propagation, stock plants should be managed to ensure unrooted cuttings have adequate nutrient reserves.     

氮素形态, 光合作用, 光呼吸

Under high light conditions, ammonium nutrition has a negative effect on plant growth. This suggests that the adverse effects of ammonium nutrition on plant growth may be related to carbon gain, photosynthesis, and photorespiration. However, there is no consistent evidence of a specific mechanism that could explain the plant growth reduction under ammonium supply. It is generally accepted that during the light reaction, a surplus of nicotinamide adenine dinucleotide hydrogen phosphate （NADPH） is produced, which is not completely used during the assimilation of CO2, Nitrate reduc- tion in the leaf represents an additional sink for NADPH that is not available to ammonium-grown plants. Nitrate and ammonium nutrition may use different pathways for NADPH consumption, which leads to differences in photosynthesis and photorespiration. The morphological （i.e., cell size, mesophyll thickness, and chloroplast volume） and enzymic （i.e., ribulose-1,5-bisphosphate carboxylase/oxygenase （Rubisco）, phosphoenolpyruvate carboxylase （PEPCase）, and glutamine synthetase/glutamate synthetase （GS/GOGAT）） differences that develop when plants are treated with either nitrate or ammonium nitrogen forms are related to photosynthesis and photorespiration. The differences in photorespiration rate for plants treated with nitrate or ammonium are related to the conversion of citrate to 2-oxoglutarate （2-OG） and photorespiratory CO2 refixation.     

不同氮形态对镉胁迫下小白菜生长及镉含量的影响

【目的】研究施用速效氮肥（全铵、全硝、硝铵复合和尿素）对镉（Cd）污染土壤小白菜生长和Cd含量的影响,为合理选择氮肥,缓解Cd对植物生长的胁迫并减少Cd在作物体内的积累提供依据。【方法】以小白菜为试材,采用菜园土进行了盆栽试验。以CdCl2溶液模拟土壤Cd胁迫,设土壤Cd含量0、1、3和5 mg/kg 4个水平,每个胁迫水平分别供应小白菜铵态氮、硝态氮、硝铵（1:1）和尿素4种氮形态,总氮添加量均为N 400 mg/kg土。收获后分析各处理间小白菜的生长、光合、氧化胁迫及Cd含量的差异。【结果】 1）与无Cd对照相比,Cd 1 mg/kg处理水平下,全铵、全硝、硝铵和尿素处理的小白菜可食部分鲜重分别下降了31%、16%、21%和26%;Cd 3 mg/kg处理水平下分别下降了58%、28%、35%和39%;Cd 5 mg/kg处理水平下分别下降了83%、38%、52%和69%。全硝和硝铵处理间小白菜Cd耐受系数（TICd）差异不显著,但均高于全铵和尿素处理。2）与无Cd对照相比,Cd 1 mg/kg处理下,全铵、全硝、硝铵和尿素处理小白菜叶片的光合速率分别下降了14%、10%、12%和13%;Cd 3 mg/kg处理分别下降了33%、22%、25%和40%;Cd 5 mg/kg处理分别下降了53%、42%、41%和56%。与无Cd对照相比,1 mg/kg Cd浓度时全铵、全硝、硝铵和尿素处理小白菜叶片的丙二醛含量分别增加了11%、4%、9%和11%;超氧自由基产生速率分别增加了5%、1%、2%和4%,综合比较,以全硝处理下小白菜受Cd的光合抑制及氧化胁迫相对最小。3）3个Cd处理水平,均以施用全铵和尿素处理的小白菜体内Cd含量最高,硝铵处理次之,全硝处理最低。【结论】在供试菜园土上,小白菜施用铵态氮和尿素易引起Cd在小白菜体内的积累。施用硝态氮可缓解Cd诱导的光合抑制和氧化胁迫,减轻Cd对小白菜的生长胁迫,降低作物体内Cd的含量。     

Absorption and translocation of foliar applied triazone‐n as compared to other nitrogen sources in tomato

Absorption and translocation of foliar applied ¹⁵N labeled S‐tetrahydrotriazone (triazone), as compared to other N forms, was evaluated in tomato plants. Triazone‐N was taken up into leaf tissue in quantities similar to urea, ammonium, and nitrate‐N when applied at a N concentration of 0.35% w/v. Although >40% of the ¹⁵N label was exported from the treated leaf after 7 days, nearly 50% of the translocated triazone ¹⁵N label accumulated in non‐treated leaf tissue as compared to only 10% or less for the other N sources. The largest percentage of the translocated urea‐, ammonium‐, and nitrate‐¹⁵N label accumulated within developing fruit tissue. Multiple (3) foliar applications of triazone and urea at concentrations of 0.94% or higher and 1.0% N (w/v), respectively, enhanced both leaf and fruit tissue N concentrations. No growth responses to foliar applied N were observed.     

不同供氮形态下油菜幼苗对盐胁迫的响应

为比较不同供氮形态下油菜对盐胁迫的响应,通过供应铵态氮和硝态氮,探讨盐胁迫对油菜幼苗生物量、 光合作用、 离子含量等的效应。结果表明: 非盐胁迫条件下的硝态氮处理的植株生物量和叶片光合参数均显著高于其它处理; 在盐胁迫条件下,两种供氮形态处理油菜的生长和光合均受到明显抑制,其中铵态氮处理表现的抑制效应较显著,且其光合抑制主要来自气孔限制。在两种供氮条件下,盐胁迫使得植株Na+浓度均显著增加,其中铵态氮处理的叶片和叶柄中Na+浓度的增幅大于硝态氮处理,而其根中Na+浓度则小于硝态氮处理。盐胁迫导致两种供氮形态下整株和叶柄中K+浓度均显著降低,而在根中,则只造成硝态氮处理的K+浓度的显著降低。在整株水平上,盐胁迫下铵态氮处理的K+ 、 Na+的选择性比率（SK,Na）要显著低于硝态氮处理。综上,在盐胁迫条件下,硝态氮处理对K+吸收维持较高的相对选择性是其耐盐性高于铵态氮处理的重要原因。     

Nutrient uptake by wheat seedlings that differ in response to mixed nitrogen nutrition 1

In hydroponics, cereal crop growth is usually enhanced when the nutrient media contains both nitrate and ammonium compared to either form separately. Identification of genotypic variation between two spring wheat cultivars (Triticum aestivum cv. Len, and Triticum durum cv. Inbar) in their magnitude of growth response to mixed N permits a comparative evaluation of metabolic processes underlying enhanced growth from utilization of N mixtures. The objective of this study was to determine if the additional mixed N‐induced growth, and the difference in response between cultivars, is associated with the uptake or partitioning of N, P, or K during the seedling stage of development. Plants of Len and Inbar were grown hydroponicaily for 21 days in nutrient solutions containing N either as all nitrate or as a 50/50 mixture of nitrate and ammonium. The mean of three experiments showed that whole plant dry weight increased 19% for Len and 41 % for Inbar when the plants were supplied with the N mixture compared to only nitrate. With the N mixture, the increase in biomass was almost entirely due to enhanced shoot production, which was mainly the result of greater tiller formation. Both cultivars absorbed more N, P, and K when grown with mixed N, and the additional N and K uptake of appeared to be associated with the enhanced growth. This conclusion is based on the observation that Inbar absorbed proportionately more N and K, but less P, than Len when grown with mixed N nutrition. These data suggest that the increased dry matter production from the utilization of mixed N nutrition is not directly related to the additional absorption of P, but may be associated with enhanced N and K uptake.