Influence of the nitrogen source and concentration on N fractions and free amino acid levels of grape vine explants

The influence of the source of inorganic nitrogen (KNO₃, (NH₄)₂SO₄ and NH₄NO₃) and its concentration (5, 10, 20 and 30 mM N) on total N incorporation, as well as on N distribution into different fractions (amminiacal, amino, amide and protein) and on free amino acid levels has been determined in grape vine explants cultured in vitro.Increasing concentrations of the nitrogen source resulted in increased total N content in tissues. This effect was small for KNO₃, higher for (NH₄)₂SO₄ and maximal for NH₄NO₃. In addition, nitrate promoted an increase in amino-N only, whereas ammonium increased both the ammoniacal-N and the amino-N fractions. Incorporation of N into amide-N and protein-N were not affected significantly by the N sources tested.The application of increasing quantities of N enhanced the accumulation of most free amino acids, especially arginine, alanine and proline, but to different extents, depending on both the N source and its concentration. The combination of ammonium and nitrate resulted in a higher accumulation of amino acids than that observed with either one of the two forms alone.     

Biological role of mycorrhizal fungi on the assimilation and transportation of carbon and nitrogen to Anacamptis palustris and Anacamptis laxiflor

Fungal is a physiological trail and its understanding in the assimilation with the transfer of carbon (C) cum nitrogen (N) or (C/N) to orchid-seedlings have not been determined. Labelled stable isotopes ¹³C and ¹⁵N were used to plan the flow of C and N between orchid plants and mycorrhizal connotations in-terms of bulk transfer for C/N. This study attends to comprehend the mechanism, supporting mycorrhizal fungi which influences on orchid-seedling growth. Determined integration and transfer of C/N from amino acids (AA), ammonium nitrate (NH₄NO₃) and sugar for orchid-plant may lead to understand these mechanisms. This current study tries to estimate the importance of organic compounds as a source for C/N over the inorganic-NH₄NO₃. Generally, after begging of germination and when it is found to be associated to the nutrient resource, organic compound enhance the biomass accumulation of two orchid species. AA significantly increase the mass of ¹³C assimilated by two species. With amino acids the concentration of ¹³C in two species was greater than with NH₄NO₃ and sugar. At another phase, amount of ¹⁵N content shoots was a higher value in Anacamptis laxiflora shoots assimilated substantially additional of ¹⁵N with NH₄NO₃ plus sugar compared with ammonium nitrate only. This study showed that two terrestrial orchids species are reliant on organic compounds as a source of carbon and nitrogen more than inorganic compounds.     

The effect of CuSO4 for establishing in vitro culture,and the role nitrogen and iron sources in in vitro multiplication of Corylus avellana L. cv. Tonda Gentile Romana

Abstract

In the present work, we have used copper sulphate (CuSO₄·5H₂O) enriched medium for effective control of visible and latent contamination. Among the different concentrations used, 1.25–2.5?mg/L resulted the most appropriate. In addition, the role of different nitrogen source and concentrations (NH₄NO₃ and KNO₃), as different iron source (FeEDTA and FeEDDHA) has been investigated in the proliferation and rooting phases of European hazelnut (cv. Tonda Gentile Romana). The normal concentration of nitrogen present in Murashige and Skoog medium is too high for hazelnut micropropagation cv. Tonda Gentile Romana. A reduction of total nitrogen, accompanied by a reduction of ammonium forms, resulted in a better quality of the shoots. Similar results have been obtained when the common iron source FeEDTA has been replaced by the same concentration of FeEDDHA. An increase in rooting occurs when the amount of nitrogen was reduced in the rooting medium, particularly when the NH₄NO₃ was not present.     

Nitrogen metabolism of Spirodela oligorrhiza

Summary Spirodela oligorrhiza grown in axenic culture was able to use either ammonium, nitrate, or nitrite as sole source of nitrogen, although the morphology of the plants was affected. Plants utilizing ammonium contained higher levels of NH₄, arginine, asparagine and glutamine than did those utilizing NO₃, whereas concentrations of other amino acids were similar.The utilization of NH₄ inhibited that of NO₃ by inhibiting, at least partially, NO₃ uptake, and by inhibiting almost completely the reduction of NO₃ to NO₂. NO₂ also inhibited the utilization of NO₃. NH₄ and NO₂ were taken up and assimilated simultaneously when they were supplied together in the medium.     

桧叶白发藓对不同氮源胁迫的形态和生理响应

桧叶白发藓(Leucobryum juniperoideum)在我国东南部常见,被认为是一种理想的、适用于庭院栽培的苔藓植物,而氮是植物必需的矿质元素,但过量摄入会对其造成伤害,近年来氮沉降水平的提高对苔藓植物的多样性造成了严重影响。该研究为揭示氮沉降加剧对桧叶白发藓的影响,以经6个月断茎培养的桧叶白发藓配子体为材料,用Ca(NO3)2、NH4HCO3和NH4NO3代表三种氮源,设置2、4、8、16gN·m-2 4个水平,以喷洒去离子水为对照,进行不同氮源的胁迫试验。结果表明:氮处理浓度的增加引起组织氮含量的显著提高,增加幅度分别为69.1%、25.7%和43.1%;同时引起植株坏死率显著上升,增加幅度分别为16.5%、12.5%和13.9%。三种氮源处理对株高和净重的影响有显著差异,低浓度的铵态氮(4gN·m-2)引起株高和净重的显著增加,而硝态氮和混合态氮处理差异不显著;加氮浓度的进一步提高,引起株高和净重的减低,硝态氮处理的减低幅度最大,铵态氮的降低幅度最小。三种氮源处理均引起叶绿素含量先上升后下降,但同一水平铵态氮处理的叶绿素含量要高于其它两种氮处理,而且引起叶绿素含量下降的处理浓度要高于其它两种氮源;三种氮源均引起SOD活性显著增加、可溶性蛋白和脯氨酸含量先升后降,但不同氮源间生理指标的变化不同步。这说明桧叶白发藓对硝态氮胁迫的响应比铵态氮敏感,硝态氮的增加对桧叶白发藓造成严重危害,而少量的铵态氮(4gN·m-2)则能促进桧叶白发藓的生长。研究结果可作为桧叶白发藓繁殖与生产的氮源。     

The Influence of Nitrate and Ammonium Nutrition on the Growth of Wheat (Triticum aestivum) and Maize (Zea mays) Plants

The effects of NO^-₃ and NH⁺₄ nutrition on hydroponically grownwheat (Triticum aestivum L.) and maize (Zea mays L.) were assessedfrom measurements of growth, gas exchange and xylem sap nitrogencontents. Biomass accumulation and shoot moisture contents ofwheat and maize were lower with NH⁺₄ than with NO^-₃ nutrition.The shoot:root ratios of wheat plants were increased with NH⁺₄compared to NO^-₃ nutrition, while those of maize were unaffectedby the nitrogen source. Differences between NO^-₃ and NH⁺₄-fedplant biomasses were apparent soon after introduction of thenitrogen into the root medium of both wheat and maize, and thesedifferences were compounded during growth. Photosynthetic rates of 4 mM N-fed wheat were unaffected bythe form of nitrogen supplied whereas those of 12 mM NH⁺₄-fedwheat plants were reduced to 85% of those 12 mM NO^-₃-fed wheatplants. In maize supplied with 4 and 12 mM NH⁺₄ the photosyntheticrates were 87 and 82% respectively of those of NO^-₃-fed plants.Reduced photosynthetic rates of NH⁺₄ compared to NO^-₃-fed wheatand maize plants may thus partially explain reduced biomassaccumulation in plants supplied with NH⁺₄ compared to NO^-₃ nutrition.Differences in the partitioning of biomass between the shootsand roots of NO^-₃-and NH⁺₄-fed plants may also, however, arisefrom xylem translocation of carbon from the root to the shootin the form of amino compounds. The organic nitrogen contentof xylem sap was found to be considerably higher in NH⁺₄- thanin NO^-₃-fed plants. This may result in depletion of root carbohydrateresources through translocation of amino compounds to the shootin NH⁺₄-fed wheat plants. The concentration of carbon associatedwith organic nitrogen in the xylem sap of maize was considerablyhigher than that in wheat. This may indicate that the shootand root components of maize share a common carbon pool andthus differences induced by different forms of inorganic nitrogenare manifested as altered overall growth rather than changesin the shoot:root ratios.Copyright 1993, 1999 Academic Press Triticum aestivum, wheat, Zea mays, maize, nitrogen, growth, photosynthesis, amino acids, xylem     

Negative effect of ammonium nitrate as nitrogen source on the production of water-soluble red pigments by Monascus sp.

Ammonium salts, especially ammonium nitrate, have been used as nitrogen sources for production of traditional water-insoluble Monascus pigments. However, we noted that defined media employing NH₄NO₃ as the sole nitrogen source in fermentations supported only poor pigment production by Monascus sp., and the pigments produced were mainly cell-bound. NH₄NO₃ was found not to (a) repress pigment synthase formation, (b) enhance synthase decay, or (c) serve as a nitrogen source for pigment production by resting cells; it had a weak inhibitory effect on the action of pigment synthase(s). The high level of cell-bound did not exert a feedback effect on the further synthesis of pigments. These observations indicate that the reason why NH₄NO₃ supports only low pigment production during fermentations is the poor ability of NH₄NO₃ to donate nitrogen in the Schiff-base reaction converting orange pigments to red ones.     

The Effect of Several Protein Amino Acids and Some Inorganic Nitrogen Sources on the Growth of Sphagnum nemoreum

The nitrogen metabolism of a bog moss, Sphagnum nemoreum Scop., has been studied in aseptic cultures. The effect of several protein amino acids, especially those found in peat, has been investigated. NH₄NO₃ (1.25 mM) was the best nitrogen source but NH₄⁺ ions were more effectively utilized than NO₃⁻ ions when given as the only nitrogen source. Some of the amino acids (2.5 mM) allowed fairly satisfactory growth (arginine and alanine) when given as the only nitrogen source, but some of them were not utilized at all (leucine, lysine, isoleucine and methionine). Given at low concentrations (0.001 and 0.25 mM) together with NH₄NO₃ (2.5 mM), most of the protein amino acids failed to reveal any growth-promoting or -inhibiting effect. Only lysine (0.25 mM) clearly inhibited growth under these conditions. The nitrogen metabolism of Sphagnum nemoreum seems to be rather flexible and this species is more tolerant of organic nitrogen, especially hydroxyproline, than the higher plants.     

The effect of copper and nitrogen on the amino acid composition of oat straw

Summary The effect of fertilization with nitrogen and copper on the amino acid composition of oat straw has been studied.The plants (Avena sativa cv Yielder) were grown in peat with a very low copper content and supplied with two levels of nitrogen (NH₄ or NO₃) and three levels of copper sulphate.The higher level of nitrogen stimulated growth only when copper was added, whereas, without copper, it had an adverse effect on growth and prevented grain formation altogether. The higher level of nitrogen increased the nitrogen content of the straw at all levels of copper, but particularly in plants receiving no copper.Total amino acids in the straw hydrolysate of copper sufficient oats accounted for about 50% of the total N and was about 20% higher in copper-deficient tissues. The addition of copper caused a decrease in the amounts of all amino acids. The relative proportions of most of the amino acids to glycine remained fairly constant. Threonine, serine, alanine, iso-leucine, histidine and arginine showed small significant differences with copper treatment, whereas valine, tyrosine, phenylalanine, proline, lysine and cysteic acid (derived from cysteine and cystine) showed no differences. The proportion of aspartic acid relative to glycine in the straw hydrolysate was greatly increased in copper deficient plants supplied with the higher level of nitrogen, particularly as ammonium. The proportion of glutamic acid was also increased by the higher level of nitrogen, but showed no effect of added copper. Most of the difference in aspartic acid could be accounted for as free asparagine. The possible reasons for higher proportions of asparagine are discussed in relation to the metabolism of the oat plant.     

INORGANIC NITROGEN NUTRITION OF THE SEEDLINGS OF THE ORCHID,CATTLEYA

When grown in vitro in a medium containing NH₄NO₃ as the sole source of nitrogen, seeds ro the orchid, Cattleya (C. labiata ‘Wonder’ X C. labiata ‘Treasure'), germinated readily and proceeded to form small plantlets. Development of the embryos was accompanied by an increase in their total nitrogen and a decline in the percent dry weight. Growth responses of the seedlings in other ammonium salts like (NH₄)₂SO₄, (NH₄)₂HPO₄, NH₄Cl, ammonium acetate and ammonium oxalate were similar to that in NH₄NO₃. However, when grown in a medium containing NaNO₃, development of the seedlings was drastically inhibited; KNO₃, Ca(NO₃)₂, KNO₂ and NaNO₂ also were poor nitrogen sources. Attempts to grow the seedlings in NaNO₃ by changing the pH or by addition of kinetin, molybdenum or ascorbic acid as supplements were completely unsuccessful. When seedlings growing in NH₄NO₃ for varying periods were transferred to NaNO₃, it was found that those plants allowed to grow for 60 or more days in NH₄NO₃ could resume normal growth thereafter in NaNO₃. Determination of the nitrate reductase activity in seedlings of different ages grown in NaNO₃, after NH₄NO₃, showed that the ability of the seedlings to assimilate inorganic nitrogen was paralleled by the appearance of the enzyme.     

NH4 + and NO3 − requirement for wheat somatic embryogenesis

The influence of three nitrogen salts: NH₄NO₃, KNO₃ and NH₄Cl on wheat in vitro cultures was investigated. Both NO ₃ ⁻ and NH ₄ ⁺ ions were indispensable for proliferation of embryogenic calli and development of wheat somatic embryos. It is possible to obtain wheat somatic embryos when the medium is enriched with NH₄NO₃ only as a source of inorganic nitrogen. The results of the statistical analysis showed that the level of NH₄NO₃ and KNO₃ in the medium had a great influence on the efficiency of somatic embryogenesis. We observed tendency that calli on media containing 50 mM NH₄NO₃ and 0 to 20 mM KNO₃ turned out to be more embryogenic than on control MS medium. High concentrations of KNO₃- 100 mM inhibited somatic embryogenesis, while 100 mM NH₄NO₃ did not. The level of total N did not have significant influence on wheat somatic embryogenesis. Ratio NO ₃ ⁻ :NH ₄ ⁺ also turned out to be not substantial. We observed that mutual connection of concentration levels between NH₄NO₃ and KNO₃ and between NH₄Cl and KNO₃ was more important. The efficiency of somatic embriogenesis obtained in the experiment with NH₄Cl and KNO₃ was significantly lower than in experiment with NH₄NO₃ and KNO₃.     

Distribution and recovery of15N after fertilization of Douglas-fir saplings with different nitrogen sources

Summary Four-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) saplings planted in pots with a sand and peat mix (11) were fertilized at the rate of 200 kg N/ha of (¹⁵NH₂)₂CO (U-15),¹⁵NH₄NO₃ (A-15) and NH₄ ¹⁵NO₃(An-15). They were placed in a shadehouse and watered regularly to maintain soil moisture at field capacity over periods of one and two years. Quantity of¹⁵N in foliage generally increased from old to current growth, irrespective of the nitrogen source. Utilization of¹⁵N fertilizers by saplings after the first and second growing seasons following fertilization was greatest with nitrate labelled ammonium nitrate AN-15, and nearly equal for urea U-15 and ammonium labelled ammonium nitrate A-15. The soil immobilized more fertilizer nitrogen-15 from U-15 and A-15 than from AN-15. Data from the present study, in which leaching losses of fertilizer were minimized, demonstrated that in terms of nitrogen uptake by the saplings the nitrate fertilizer was superior to ammonium fertilizer.     

The uptake and translocation of macro- and microelements in rape and wheat seedlings as affected by selenium supply level

Plant growth in saline soils may be increased by fertilisation, but little is known about the effect of different forms of N on wheat growth in soils with different salinity levels. The aim of this study was to investigate the response of wheat (Triticum aestivum L., cv Krichauff) to (NH₄)₂SO₄ or KNO₃ or NH₄NO₃ at 0 (N0), 50 (N50), 100 (N100) and 200 (N200) mg N?kg^?1 soil in a saline sandy loam. Salinity was induced using Na⁺ and Ca²⁺ salts to achieve three EC_e levels, 2.8, 6.6 and 11.8 dS m^?1 denoted S1, S2 and S3, respectively, while maintaining a low SAR (>1). Dry weights of shoot and root were reduced by salinity in all N treatments. Addition of N significantly increased shoot and root dry weights with significant differences between N forms. Under non-saline conditions (S1), addition of NO₃???N at rates higher than N50 had a negative effect, while N100 as NH₄???N or NH₄NO₃???N increased shoot and root dry weights. At N100, shoot concentrations of N and K were higher and P, Ca, Fe, Mn, Cu and Zn were lower with NO₃???N than with NH₄???N nutrition. The concentration of all nutrients however fell in ranges did not appear to be directly associated with poor plant growth with NO₃???N. At all N additions, calculations indicated that soil salinity was highest with N addition as NO₃???N and decreased in the following order: NO₃?N > NH₄?N > NH₄NO₃?N. Addition of greater than N50 as NO₃???N, compared to NH₄???N or NH₄???NO_3, increased soil salinity and reduced micronutrient uptake both of which likely limited plant growth. It can be concluded that in saline soils addition of 100 mg N?kg^?1 as NH₄???N or NH₄NO₃???N is beneficial for wheat growth, whereas NO₃???N can cause growth depression.     

The effect of copper toxicity on the contents of nitrogen compounds in Silene vulgaris (Moench) Garcke

The effect of copper on the uptake of nitrogen and the tissue contents of inorganic nitrogen, amino acids and proteins were studied in cooper-sensitive Silene vulgaris (Moench) Garcke, grown at different nitrogen sources (NH₄ ⁺ or NO₃ ^-). All the toxic copper levels tested, i.e. 4, 8, 16 M Cu²⁺, strongly inhibited the uptake of nitrogen, especially of NO₃ ^-, and decreased the content of NO₃ ^-, amino acids and proteins. Especially at 4 and 8 M Cu²⁺, NH₄ ⁺ accumulated in the plants, suggesting that the conversion of NH₄ ^- into amino acids was inhibited.     

Nitrate reductase activity of two leafy vegetables as affected by nickel and different nitrogen forms

The author studied the effect of different nickel concentrations (0, 0.4, 40 and 80 μM Ni) on the nitrate reductase (NR) activity of New Zealand spinach (Tetragonia expansa Murr.) and lettuce (Lactuca sativa L. cv. Justyna) plants supplied with different nitrogen forms (NO₃ ⁻–N, NH₄ ⁺–N, NH₄NO₃). A low concentration of Ni (0.4 μM) did not cause statistically significant changes of the nitrate reductase activity in lettuce plants supplied with nitrate nitrogen (NO₃ ⁻–N) or mixed (NH₄NO₃) nitrogen form, but in New Zealand spinach leaves the enzyme activity decreased and increased, respectively. The introduction of 0.4 μM Ni in the medium containing ammonium ions as a sole source of nitrogen resulted in significantly increased NR activity in lettuce roots, and did not cause statistically significant changes of the enzyme activity in New Zealand spinach plants. At a high nickel level (Ni 40 or 80 μM), a significant decrease in the NR activity was observed in New Zealand spinach plants treated with nitrate or mixed nitrogen form, but it was much more marked in leaves than in roots. An exception was lack of significant changes of the enzyme activity in spinach leaves when plants were treated with 40 μM Ni and supplied with mixed nitrogen form, which resulted in the stronger reduction of the enzyme activity in roots than in leaves. The statistically significant drop in the NR activity was recorded in the aboveground parts of nickel-stressed lettuce plants supplied with NO₃ ⁻–N or NH₄NO₃. At the same time, there were no statistically significant changes recorded in lettuce roots, except for the drop of the enzyme activity in the roots of NO₃ ⁻-fed plants grown in the nutrient solution containing 80 μM Ni. An addition of high nickel doses to the nutrient solution contained ammonium nitrogen (NH₄ ⁺–N) did not affect the NR activity in New Zealand spinach plants and caused a high increase of this enzyme in lettuce organs, especially in roots. It should be stressed that, independently of nickel dose in New Zealand spinach plants supplied with ammonium form, NR activity in roots was dramatically higher than that in leaves. Moreover, in New Zealand spinach plants treated with NH₄ ⁺–N the enzyme activity in roots was even higher than in those supplied with NO₃ ⁻–N.     

Effect of nitrogen form and phosphorus source on the growth,nutrient uptake and rhizosphere soil property of Camellia sinensis L.

The effects of nitrogen form and phosphorus source on the growth, nutrient uptake and rhizosphere soil property of tea (Camellia sinensis L.) were investigated in a pot experiment. The experiment was performed with a compartmental cropping device, which enables the collection of rhizosphere soil at defined distances from the root of tea plant. Nitrogen was supplied as nitrate or ammonium in combination with soluble phosphorus as Ca(H₂PO₄)₂ or insoluble P as rock phosphate. The leaf dry matter production of tea was significantly greater in the treatments with NH₄ ⁺ than NO₃ ^-, whereas dry matter production of root and stem was not significantly affected. Addition of phosphorus as either source did not influence the dry matter production. The concentrations of K in root, Mg and Ca in both the shoot and root supplied with NO₃ ^- were significantly higher than in NH₄ ⁺ and influence of P sources was minor. On the contrary, Al and Mn concentrations were significantly larger in NH₄ ^--fed plants which could be attributed to remarkably increased availability of Al and Mn caused by acidification of the rhizosphere soil (the first 1-mm soil section from the root surface) with NH₄–N nutrition. The concentration of N in shoot was also significantly higher in NH₄- than in NO₃-fed plants, indicating higher use efficiency of NH₄–N. Whatever the phosphate source, rhizosphere pH declined in ammonium compared to in nitrate treatment. The pH decrease was much larger when no P or soluble P were applied and reached 0.85–1.30 units which extended to 3–5 mm away from the root surface. Exchangeable acidity, content of exchangeable Al and Mn were also considerably higher in the rhizosphere soils of NH₄ ⁺ fed tea plants. Significant amounts of P dissolved from rock phosphate accumulated in rhizosphere of NH₄ ⁺, not NO₃ ^-, suggesting that the dissolution of rock phosphate was induced by the proton excreted by tea root fed with ammonium. With soluble P addition, shoot and root P concentrations were greater in NH₄ ⁺ than in NO₃ ^- treatment and it appeared that this difference could not be sufficiently explained by the available P content in soil which was only slightly higher in NH₄ ⁺ treatment. With rock phosphate addition, the shoot and root P concentrations were hardly affected by nitrogen form, although the available P content was much higher and accumulated in the rhizosphere soil supplied with ammonium. The reason for this was discussed with regard to the inter-relationship of Al with P uptake. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nitrogen metabolism inErica and soybean,two species differing by their sensitivity to inorganic N source

Growth of soybean was not altered, whatever the inorganic N-source (NO₃, NH₄ or a NO₃/NH₄ mixture); conversely, growth of Erica x darleyensis plants in vitro decreased more in. NH₄ medium than in a NO₃ medium, compared to a NO₃/NH₄ medium. The GS/GOGAT pathway (in NH₄ medium), the nitrate and nitrite reductase activities (in NO₃ medium), as the contents in free nitrogenous forms and total nitrogen (in NO₃ and NH₄ media) were not more altered in Erica than in soybean, compared to a NO₃/NH₄ medium. PEPCase activity was the highest in soybean irrespective of the N-treatments; the involvement of PEPCase in N-metabolism could be explained by its function in ionic and osmotic balances rather than its function in supplying carboxylates as acceptors for NH₄-assimilation.     

Nitrate and ammonium in the rhizosphere of wheat crops and concurrent observations of take-all

Summary In 1973 the concentration of nitrate nitrogen in the rhizosphere of winter wheat (NO₃-N _r , extracted withN-K₂SO₄ from soil from within 5 mm of the roots) growing in slightly acid, flintly loam decreased progressively from January until early April, when it became less than that of ammonium nitrogen in the rhizosphere (NH₄-N _r , extracted withN-K₂SO₄). An April application of ammonium nitrate (as Nitro-chalk) augmented NO₃-N _r more than NH₄-N _r , but because NH₄-N _r was depleted less quickly it exceeded NO₃-N _r from early June onwards. From January to April pH _r remained between 6.9–7.2, but then decreased progressively to a minimum of 6.3 in June. The differences in soil pH and forms of N amongst plots that had grown three, six or fourteen consecutive cereal crops susceptible to take-all were small; a first wheat crop differed only in having less extreme changes in NO₃-N _r during April-June.First winter wheat crops were grown on a similar soil in 1974–5, either with farmyard manure applied in autumn (FYM plot, bulk soil pH 7.4) or Nitro-chalk applied in April (NPK plot, pH _b 6.7). Soil nitrate decreased considerably in May and to a lesser extent in June and was always at a lower concentration in the rhizosphere. NH₄-N _r was more than NO₃-N _r in water extracts after May in the FYM plot and after June in the NPK plot, but NH₄-N _b never exceeded NO₃-N _b .There was, therefore, a tendency for more of the dwindling mineral N to exist as NH₄-N close to roots in spring and summer unless temporarily disrupted by spring fertilizer. Take-all developed against this background was mostly slight and never severe. In 1973 it was least in the first wheat, and most in the third, but the differences were small and disease increased steadily in all plots after mid-February. In 1975 it developed quickest and most in the FYM plot. re]19760928     

Ammonium under solution culture alleviates aluminum toxicity in rice and reduces aluminum accumulation in roots compared with nitrate

Al stress and ammonium–nitrogen nutrition often coexist in acidic soils due to their low pH and weak nitrification ability. Rice is the most Al-resistant species among small grain cereal crops and prefers NH₄ ⁺ as its major inorganic nitrogen source. This study investigates the effects of NH₄ ⁺ and NO₃ ^? on Al toxicity and Al accumulation in rice, and thereby associates rice Al resistance with its NH₄ ⁺ preference. Two rice subspecies, indica cv. Yangdao6 and japonica cv. Wuyunjing7, were used in this study. After treatment with or without Al under conditions of varying NH₄ ⁺ and NO₃ ^? supply, rice seedlings were harvested for the determination of root elongation, callose content, biomass, Al concentration and medium pH. The results indicated that Wuyunjing7 was more Al-resistant and NH₄ ⁺-preferring than Yangdao6. NH₄ ⁺ alleviated Al toxicity in two cultivars compared with NO₃ ^?. Both NH₄ ⁺-Al supply and pretreatment with NH₄ ⁺ reduced Al accumulation in roots and root tips compared with NO₃ ^?. NH₄ ⁺ decreased but NO₃ ^? increased the medium pH, and root tips accumulated more Al with a pH increase from 3.5 to 5.5. Increasing the NO₃ ^? concentration enhanced Al accumulation in root tips but increasing the NH₄ ⁺ concentration had the opposite effect. These results show NH₄ ⁺ alleviates Al toxicity for rice and reduces Al accumulation in roots compared with NO₃ ^?, possibly through medium pH changes and ionic competitive effects. Making use of the protective effect of NH₄ ⁺, in which the Al resistance increases, is advised for acidic soils, and the hypothesis that rice Al resistance is associated with the preferred utilization of NH₄ ⁺ is suggested.     

Contrasting nitrogen uptake by diatom and Phaeocystis-dominated phytoplankton assemblages in the North Sea

This paper documents ambient concentrations of nutrients in the Belgian coastal waters of the North Sea during the spring of 1996 and 1997. The paper elaborates the differences of uptake rates of oxidised nitrogen (NO₃⁻) and reduced nitrogen (NH₄ and urea) by Phaeocystis and diatoms. The nitrogen concentrations were dominated by NO₃⁻ with a maximum concentration of 30 μM (January 1997) and 40 μM (March 1996). In 1996, Phaeocystis dominated the spring biomass with a maximum of 521 μg C l⁻¹, while maximum diatom biomass was 174 μg C l⁻¹. In 1997, the maximum Phaeocystis spring biomass was 1600 μg C l⁻¹ and diatom maximum biomass was below 100 μg C l⁻¹. A maximum bacteria biomass of about 55 μg C l⁻¹ was observed in mid-May 1996. The maximum nitrogen uptake rates were recorded during spring and were dominated by NO₃⁻ (0.005 h⁻¹ in 1996 and 0.032 h⁻¹ in 1997). Maximum specific NH₄ uptake rates were between 0.005 h⁻¹ in May 1996 and 0.006 h⁻¹ in April 1997. The NO₃⁻ uptake rates displayed exponential decrease versus increasing ambient reduced nitrogen concentrations (ammonium and urea), whereas the reduced nitrogen uptake increased but never compensated the decreased nitrate uptake. The NH₄ uptake kinetics of diatoms displayed lower v_max compared to Phaeocystis. Consequently, Phaeocystis showed ability to increase their NH₄ uptake capacity when more NH₄ became available while diatoms failed to do so, after ammonium had exceeded their saturation concentration (>1 μM). Although reduced nitrogen has a negative effect on the uptake of NO₃⁻, Phaeocystis have more advantage than diatoms on the uptake of ammonium. This might be contributing to the biomass domination shown by Phaeocystis over extended periods in spring.