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 and ammonium as nitrogen sources for lupins prior to nodulation

Two cultivars of Lupinus angustifolius L. were grown in a glasshouse in solutions containing NO₃ ^-, NH₄ ⁺ or NH₄NO₃ with a total nitrogen concentration of 2.8 M m^-3 in each treatment. One cultivar chosen (75A-258) was relatively tolerant to alkaline soils whereas the other (Yandee) was intolerant to alkalinity. Controlled experiments were used to assess the impact of cationic vs. anionic forms of nitrogen on the relative performance of these cultivars. Relative growth rates (dry weight basis) were not significantly different between the two cultivars when grown in the presence of NO₃ ^-, NH₄ ⁺ or NH₄NO₃. However, when NO₃ ^- was supplied, there was a modest decline in relative growth rates in both cultivars over time. When plants grown on the three sources of nitrogen for 9 days were subsequently supplied with ¹⁵NH₄NO₃ or NH₄ ¹⁵NO₃ for 30 h, NH₄ ⁺ uptake was generally twice as fast as NO₃ ^- uptake, even for plants grown in the presence of NO₃ ^-. Low rates of NO₃ ^- uptake accounted for the decrease in growth rates over time when plants were grown in the presence of NO₃ ^-. It is concluded that the more rapid growth of 75A-258 than Yandee in alkaline conditions was not due to preferential uptake of NH₄ ⁺ and acidification of the external medium. In support of this view, acidification of the root medium was not significantly different between cultivars when NH₄ ⁺ was the sole nitrogen source.     

Utilization of Ammonium as a Nitrogen Source : Effects of Ambient Acidity on Growth and Nitrogen Accumulation by Soybean

Dry matter accumulation of plants utilizing NH₄⁺ as the sole nitrogen source generally is less than that of plants receiving NO₃⁻ unless acidity of the root-zone is controlled at a pH of about 6.0. To test the hypothesis that the reduction in growth is a consequence of nitrogen stress within the plant in response to effects of increased acidity during uptake of NH₄⁺ by roots, nonnodulated soybean plants (Glycine max [L.] Merr. cv Ransom) were grown for 24 days in flowing nutrient culture containing 1.0 millimolar NH₄⁺ as the nitrogen source. Acidities of the culture solutions were controlled at pH 6.1, 5.1, and 4.1 ± 0.1 by automatic additions of 0.01 n H₂SO₄ or Ca(OH)₂. Plants were sampled at intervals of 3 to 4 days for determination of dry matter and nitrogen accumulation. Rates of NH₄⁺ uptake per gram root dry weight were calculated from these data. Net CO₂ exchange rates per unit leaf area were measured on attached leaves by infrared gas analysis. When acidity of the culture solution was increased from pH 6.1 to 5.1, dry matter and nitrogen accumulation were reduced by about 40% within 14 days. Net CO₂ exchange rates per unit leaf area, however, were not affected, and the decreased growth was associated with a reduction in rates of appearance and expansion of new leaves. The uptake rates of NH₄⁺ per gram root were about 25% lower throughout the 24 days at pH 5.1 than at 6.1. A further increase in solution acidity from pH 5.1 to 4.1 resulted in cessation of net dry matter production and appearance of new leaves within 10 days. Net CO₂ exchange rates per unit leaf area declined rapidly until all viable leaves had abscised by 18 days. Uptake rates of NH₄⁺, which were initially about 50% lower at pH 4.1 than at 6.1, continued to decline with time of exposure until net uptake ceased at 10 days. Since these responses also are characteristic of the sequence of responses that occur during onset and progression of a nitrogen stress, they corroborate our hypothesis.     

丛枝菌根真菌和施加不同形态氮肥对杉木幼苗养分吸收的影响

为了解丛枝菌根真菌(AMF)和不同形态氮对杉木(Cunninghamia lanceolata)生长和养分吸收的影响,以1 a生杉木幼苗接种摩西球囊霉(Glomus mosseae)和添加不同形态氮(NH₄⁺-N和NO₃^–-N),对其养分元素和生长状况的变化进行研究。结果表明,AMF显著提高了杉木的苗高和生物量,促进了杉木对N、P、K、Ca、Mg、Fe和Na的吸收,AMF对微量元素Fe、Na的促进作用总体上要强于大量元素K、Ca。与NO₃^–-N相比,AMF显著提高了NH₄⁺-N处理杉木的生物量、总C和N、Ca、Mg、Mn含量,而且这种显著性在叶中普遍高于根和茎。接种AMF可以促进杉木幼苗的生长和对养分元素的吸收,且添加NH₄⁺-N处理的促进作用要强于NO₃^–-N。     

Dissolved Nitrogen Uptake by a Cyanobacterial Bloom (Anabaena flos-aquae) in a Subarctic Lake

Uptake of dissolved nitrogen (NH₄⁺ + NO₃^- + urea + N₂) by a cyanobacterial [Anabaena flos-aquae (Lyngb.)] De Brèb population in Smith Lake, Alaska, was measured every 2 to 4 days during the spring of 1990. Total dissolved nitrogen uptake ranged from 0.34 to 24.75 μmol liter^-1 h^-1, with a mean of 5.75 μmol liter^-1 h^-1; the euphotic zone accounted for 91% of the uptake. The mean turnover time for dissolved combined nitrogen (NH₄⁺ + NO₃^- + urea) in the euphotic zone was less than 14 h, and that for NH₄⁺ was only 3.6 h. The mean relative preference indices for NH₄⁺ (2.4), NO₃^- (0.4), and urea (0.5) established NH₄⁺ as the preferred nitrogenous nutrient. The uptake rates were apparently dependent on biomass, temperature, and light. Regeneration, probably due to zooplankton excretion and bacterial remineralization of dissolved organic nitrogen, was the main source of NH₄⁺ for the cyanobacterial growth. The high half-saturation constant for NH₄⁺ with low ambient NH₄⁺ concentration nevertheless resulted in the simultaneous utilization of several forms of nitrogen.     

不同氮素水平对油麦菜栽培效果的综合评价分析

为探讨不同氮素水平的硝态氮与铵态氮对油麦菜(Lactuca sativa L.)生长及品质的影响,自主设计并制作了适合蔬菜水培的立体管道栽培系统,配制了NO3-：NH4+=10：0,NO3-：NH4+=7：1,NO3-：NH4+=7：3的营养液,通过模糊数学原理,采用层次分析法(AHP)确定品质的权重值,综合评价了不同氮素水平对油麦菜的栽培效果。结果表明,以NO3-：NH4+=7：3营养液的栽培效果最好,其次是NO3-：NH4+=7：1。当营养液的NO3-：NH4+=7：3时,油麦菜的产量最高,叶片叶绿素、可溶性糖、可溶性蛋白质含量最高,硝酸盐含量最少,其综合品质最好。层次分析法对油麦菜不同氮素水平营养液的栽培效果的综合评价有较好的适用性,有助于获得南方设施管道栽培油麦菜最佳的营养液配方。     

Nitrification and Denitrification in Lake and Estuarine Sediments Measured by the 15N Dilution Technique and Isotope Pairing

The transformation of nitrogen compounds in lake and estuarine sediments incubated in the dark was analyzed in a continuous-flowthrough system. The inflowing water contained ¹⁵NO₃^-, and by determination of the isotopic composition of the N₂, NO₃^-, and NH₄⁺ pools in the outflowing water, it was possible to quantify the following reactions: total NO₃^- uptake, denitrification based on NO₃^- from the overlying water, nitrification, coupled nitrification-denitrification, and N mineralization. In sediment cores from both lake and estuarine environments, benthic microphytes assimilated NO₃^- and NH₄⁺ for a period of 25 to 60 h after darkening. Under steady-state conditions in the dark, denitrification of NO₃^- originating from the overlying water accounted for 91 to 171 μmol m^-2 h^-1 in the lake sediments and for 131 to 182 μmol m^-2 h^-1 in the estuarine sediments, corresponding to approximately 100% of the total NO₃^- uptake for both sediments. It seems that high NO₃^- uptake by benthic microphytes in the initial dark period may have been misinterpreted in earlier investigations as dissimilatory reduction to ammonium. The rates of coupled nitrification-denitrification within the sediments contributed to 10% of the total denitrification at steady state in the dark, and total nitrification was only twice as high as the coupled process.     

Growth,chemical composition,and nitrate reductase activity of Rumex species in relation to form and level of N supply

Growth, chemical composition, and nitrate reductase activity (NRA) of hydroponically cultured Rumex crispus, R. palustris, R. acetosa, and R. maritimus were studied in relation to form (NH₄ ⁺, NO₃ ^-, or both) and level of N supply (4 mM N, and zero-N following a period of 4mM N). A distinct preference for either NH₄ ⁺ or NO₃ ^- could not be established. All species were characterized by a very efficient uptake and utilization of N, irrespective of N source, as evident from high concentrations of organic N in the tissues and concurrent excessive accumulations of free NO₃ ^- and free NH₄ ⁺. Especially the accumulation of free NH₄ ⁺ was unusually large. Generally, relative growth rate (RGR) was highest with a combination of NH₄ ⁺ and NO₃ ^-. Compared to mixed N supply, RGR of NO₃ ^-- and NH₄ ⁺-grown plants declined on average 3% and 9%, respectively. Lowest RGR with NH₄ ⁺ supply probably resulted from direct or indirect toxicity effects associated with high NH₄ ⁺ and/or low Ca²⁺ contents of tissues. NRA in NO₃ ^- and NH₄NO₃ plants was very similar with maxima in the leaves of ca 40 μmol NO₂ ^- g^-1 DW h^-1. ‘Basal’ NRA levels in shoot tissues of NH₄ ⁺ plants appeared relatively high with maxima in the leaves of ca 20 μmol NO₂ ^- g^-1 DW h^-1. Carboxylate to organic N ratios, (C-A)/N_org, on a whole plant basis varied from 0.2 in NH₄ ⁺ plants to 0.9 in NO₃ ^- plants. After withdrawal of N, all accumulated NO₃ ^- and NH₄ ⁺ was assimilated into organic N and the organic N redistributed on a large scale. NRA rapidly declined to similar low levels, irrespective of previous N source. Shoot/root ratios of -N plants were 50–80% lower than those from +N plants. In comparison with +N, RGR of -N plants did not decline to a large extent, decreasing by only 15% in -NH₄ ⁺ plants due to very high initial organic-N contents. N-deprived plants all exhibited an excess cation over anion uptake (net proton efflux), and whole-plant (C-A)/N_org ratios increased to values around unity. Possible difficulties in interpreting the (C-A)/N_org ratio and NRA of plants in their natural habitats are briefly discussed.     

不同氮处理下速生柳对水体氮的吸收、分配及生理响应

采用水培法,研究了旱柳苗在外源添加不同氮水平(贫氮、中氮、富氮、过氮)的铵态氮(NH+4-N)和硝态氮(NO-3-N)的生长、氮吸收、分配和生理响应。结果表明:一定范围氮浓度的增加能够促进旱柳苗的生长,但过量氮会抑制其生长,且NH+4-N的抑制作用大于NO-3-N;两种氮处理下,旱柳表现出对NH+4-N的吸收偏好,在同一氮水平时,旱柳各部位氮原子百分含量Atom%15N(AT%)、15N吸收量和来自氮源的N%(Ndff%)均为NH+4-N处理大于NO-3-N处理,且随着氮浓度的增加,差异增大,且在旱柳各部位的分布为根﹥茎﹥叶;2种氮素过量和不足均会对旱柳根和叶生理指标产生不同的影响,其中在过氮水平时,NH+4-N和NO-3-N处理下根系活力比对照减少了50.61%和增加了19.53%;在过氮水平时,NH+4-N处理柳树苗根总长、根表面积、根平均直径、根体积和侧根数分别对照下降了30.92%、29.48%、19.44%、27.01%和36.41%,NO-3-N处理柳树苗相应的根系形态指标分别对对照下降了1.66%、5.65%、1.49%、5.06%和25.72%。可见,高浓度NH+4-N对旱柳苗的胁迫影响大于NO-3-N,在应用于水体氮污染修复时可通过改变水体无机氮的比例,削弱其对旱柳的影响,从而提高旱柳对水体氮污染的修复效果。     

Differential responses of root uptake kinetics of NH4+ and NO3− to enriched atmospheric CO2 concentration in field-grown loblolly pine

The nitrogen requirement of plants is predominantly supplied by NH₄⁺ and/or NO₃^? from the soil solution, but the energetic cost of uptake and assimilation is generally higher for NO₃^? than for NH₄⁺. We found that CO₂ enrichment of the atmosphere enhanced the root uptake capacity for NO₃^?, but not for NH₄⁺, in field-grown loblolly pine saplings. Increased preference for NO₃^? at the elevated CO₂ concentration was accompanied by increased carbohydrate levels in roots. The results have important implications for the potential consequences of global climate change on plant-and ecosystem-level processes in many temperate forest ecosystems.     

Interactive effect of salt (NaCl) and nitrogen form on growth, water relations and photosynthetic capacity of sunflower (Helianthus annum L.)

The effects of the ammonium (NH₄⁺) and nitrate (NO₃^-) forms of nitrogen and NaCl on the growth, water relations and photosynthesis performance of sunflower (Helianthus annuus L.) were examined under glasshouse conditions. Eight-day-old plants of cv. Hisun 33 were subjected for 21 days to Hoagland's nutrient solution containing 8 mol m^-3N as NH₄⁺or NO₃^-, and salinised with 0, 60, or 120 mol m^-3NaCl. Fresh weights of shoots and roots, and leaf area of NO₃^-supplied non-salinised plants were significantly greater than those of NH₄⁺-supplied non-salinised plants. But addition of NaCl to the rooting medium of these plants had more inhibitory effect on the growth of NO₃^--supplied plants than on NH₄⁺-supplied plants. Both leaf water and osmotic potentials of plants grown with NH₄⁺were lower than those of plants given NO₃^-under both non-saline and saline conditions. Chlorophylls a and b concentrations were higher in plants grown with NH₄⁺than N0₃^--supplied plants at the lower two levels of salinisation. The rate of photosynthesis in plants was considerably higher in non-salinised plants grown with NO₃^-than with NH₄⁺, but with increase in salinisation the photosynthesis rate decreased in NO₃^--supplied plants, but not in those given NH₄⁺. The rate of transpiration was increased significantly by salinisation in NO₃^--supplied plants, but not consistently so in NH₄⁺-supplied plants. The stomatal conductances were much higher in plants given NO₃^-than with NH₄⁺when grown under non-saline conditions, but not when salinised. As a consequence, water-use efficiency in NO₃^--supplied control plants was better than in NH₄⁺-supplied under non-saline conditions, but worse under saline conditions. The different forms of nitrogen and the addition of NaCl to the growing medium did not affect the relative intercellular concentrations of CO₂ (C_i/C_a). Overall, the NH₄⁺form of nitrogen inhibited the growth of sunflowers under non-saline conditions, but NO₃^-and NaCl interacted to inhibit growth more than did NH₄⁺under saline conditions.     

Photosynthetic energy supply for NO3− assimilation in Scenedesmus

NO₃^?-dependent O₂ in synchronous Scenedesmus obtusiusculus Chod. in the absence of CO₂ is stoichiometric with NH₄⁺ excretion, indicating a close coupling of NO₃^? reduction to non-cyclic electron flow. Also in the presence of CO₂, NO₃^? stimulates O₂ evolution as manifested by an increase in the O₂/CO₂ ratio from 0.96 to 1.11. This quotient was increased to 1.36 by addition of NO₂^?, without competitive interaction with CO₂ fixation, indicating that the capacity for non-cyclic electron transport at saturating light is non-limiting for simultaneous reduction of NO₃^? and CO₂ at high rates. During incubation with NO₃^?+ CO₂, no NH₄⁺ is released to the outer medium, whereas during incubation with NO₂^?+ CO₂, excess NH₄⁺ is formed and excreted. NO₃^? uptake is stimulated by CO₂, and this stimulation is also significant when the cellular energy metabolism is restricted by moderate concentrations of carbonyl cyanide-p-trifluoromethoxyphenylhydrazone, whereas NO₃^? uptake in the absence of CO₂ is severely inhibited by the uncoupler. Also under energy-restricted conditions NO₃^? uptake is not competitive with CO₂ fixation. Antimycin A is inhibitory for NO₃^? uptake in the absence of CO₂, and there is no enhancement of NO₃^? uptake by CO₂ in the presence of antimycin A. It is assumed that the energy demand for NO₃^? uptake is met by energy fixed as triosephosphates in the Calvin cycle. Antimycin A possibly affects the transfer of reduced triose phosphates from the chloroplast to the cytoplasm. Active carbon metabolism also seems to exert a control effect on NO₃^? assimilation, inducing complete incorporation of all NO₃^? taken up into amino acids. This control effect is not functional when NO₂^? is the nitrogen source. Active carbon metabolism thus seems to be essential both for provision of energy for NO₃^? uptake and for regulation of the process.     

SHORT TERM UPTAKE OF NUTRIENTS BY ENTEROMORPHA PROLIFERA (CHLOROPHYCEAE)1

Rates of NH₄⁺ and NO₃^? uptake were determined by accumulation of ¹⁵N in plant tissue and by disappearance of nutrient from the medium. Agreement between rates calculated by the two methods was good, averaging 82.7% (SD = 15.8%) and 91.2% (SD = 13.7%) for NH₄⁺ and NO₃^? uptake, respectively. An average of 93.4 and 96.0% of added ¹⁵NH₄⁺ and ¹⁵NO₃^? was recovered from the medium and /or plant tissue at the end of the incubations. Both bacterial uptake and regeneration of NH₄⁺ may contribute to discrepancies between NH₄⁺ uptake rates calculated by ¹⁵N accumulation and disappearance of NH₄⁺ from the medium. The influence of tissue composition on uptake of NH₄⁺, NO₃^? and PO₄^3- by Enteromorpha prolifera (Müller) J. Agardh was examined. For NH₄⁺ uptake, V_max was 188 μmol NH₄^+. g dry wt^?1. h^?1 and K_s ranged from 9.3 to 13.4 μM, but there was no correlation between kinetic parameters and tissue nitrogen content. For NO₃^?, both kinetic parameters were higher for plants with low tissue nitrogen than for plants with high tissue nitrogen. Maximum rates were 169 and 75.4 μmol NO₃^?. g dry wt^?1. h^?1, and K_s was 13.3 and 2.31 μM for low and high tissue nitrogen plants, respectively. Estimates of uptake in the field suggested that NH₄⁺ accounted for 65% and NO₃^? for up to 35% of total nitrogen uptake during the summer. Nutrient uptake rates of field-collected plants also indicated that E. prolifera in Yaquina Bay, Oregon was not likely to have been nitrogen-limited, but may have been phosphorus-limited.     

The Influence of Ammonium Nitrate,pH and Indole Butyric Acid on Root Induction and Survival in Soil of Micropropagated <Emphasis Type="Italic">Eucalyptus globulus</Emphasis>

Rooting of Eucalyptus globulus shoots was influenced by the concentration of the indole butyric acid (IBA) and NH₄ ⁺ in the root-induction medium. Optimum plantlet vigor and survival were achieved using low concentrations (1 – 2.5 μM) of IBA and when NH₄NO₃ was removed. Removal of NH₄ ⁺ also had a significant effect on medium pH, its presence caused a decrease in pH as the culture period proceeded. When different nitrate compounds (excluding NH₄NO₃) were used as the nitrogen source, the medium pH was more stable and this was associated with higher root production. The higher root production, in association with appropriate IBA concentrations, produced plantlets with higher survival and better growth on transfer to soil. This revised version was published online in July 2006 with corrections to the Cover Date.     

北亚热带3种典型森林群落对降水中氮、磷、硫的截留及分配特征

森林群落在净化空气、截留沉降污染物、改善地表水质等方面具有重要作用。本研究以北亚热带地区3种典型森林群落（毛竹林、杉木林、青冈阔叶林）为研究对象,通过分析沉降污染物（NH₄⁺-N、NO₃^--N、NO₂^--N、TP和SO₄^2-）在大气降水、林内穿透雨、树干茎流、枯透水和地表径流中的浓度和通量变化特征,探讨不同森林群落对氮、磷、硫的截留净化作用和分配特征。结果表明,该区域大气降水中NH₄⁺-N、NO₃^--N、NO₂^--N、TP和SO₄^2-年均浓度分别为1.06、0.61、0.04、0.07、1.84 mg/L,其年均pH为5.88;各森林群落林冠层能够调升降雨的pH且全年稳定,对TP和NH₄⁺-N均有吸附作用,截留率分别为79.09%-84.68%和30.88%-69.36%;而枯落物层则是林下氮、磷、硫的主要释放源,对NH₄⁺-N、NO₃^--N、TP和SO₄^2-均具有淋溶作用;此外,由地表径流（输出）与大气降水（输入）的对比分析可知,各林地对沉降污染物中氮、磷、硫的截留率均超过98%;3种森林群落对沉降污染物中氮、磷、硫的截留能力依次为：青冈阔叶林 > 毛竹林 > 杉木林,阔叶林对沉降污染物的净化能力要高于毛竹林及针叶的杉木林。     

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.     

The influence of NO3 - and NH4 + nutrition on the carbon and nitrogen partitioning characteristics of wheat (Triticum aestivum L.) and maize (Zea mays L.) plants

The carbon and nitrogen partitioning characteristics of wheat (Triticum aestivum L.) and maize (Zea mays L.) grown hydroponically at a constant pH on either 4 mM or 12 mM NO₃ ^- or NH₄ ⁺ nutrition were investigated using either ¹⁴C or ¹⁵N techniques. Greater allocation of ¹⁴C to amino-N fractions occurred at the expense of allocation of ¹⁴C to carbohydrate fractions in NH₄ ⁺-compared to NO₃ ^--fed plants. The [¹⁴C]carbohydrate:[¹⁴C]amino-N ratios were 1.5-fold and 2.0-fold greater in shoots and roots respectively of 12 mM NO₃ ^--compared to 12 mM NH₄ ⁺-fed wheat. In both 4 mM and 12 mM N-fed maize the [¹⁴C]carbohydrate:[¹⁴C]amino-N ratios were approximately 1.7-fold and 2.0-fold greater in shoots and roots respectively of NO₃ ^--compared to NH₄ ⁺-fed plants. Similar results were observed in roots of wheat and maize grown in split-root culture with one root-half in NO₃ ^--and the other in NH₄ ⁺-containing nutrient media. Thus the allocation of carbon to the amino-N fractions occurred at the expense of carbohydrate fractions, particularly within the root. Allocation of ¹⁴N and ¹⁵N within separate sets of plants confirmed that NH₄ ^--fed plants accumulated more amino-N compounds than NO₃ ^--fed plants. Wheat roots supplied with ¹⁵NH₄ ⁺ for 8 h were found to accumulate ¹⁵NH₄ ⁺ (8.5 g ¹⁵N g^-1 h^-1) whereas in maize roots very little ¹⁵NH₄ ⁺ accumulated (1.5 g ¹⁵N g^-1 h^-1)It is proposed that the observed accumulation of ¹⁵NH₄ ⁺ in wheat roots in these experiments is the result of limited availability of carbon within the roots of the wheat plants for the detoxification of NH₄ ⁺, in contrast to the situation in maize. Higher photosynthetic capacity and lower shoot: root ratios of the C₄ maize plants ensure greater carbon availability to the root than in the C₃ wheat plants. These differences in carbon and nitrogen partitioning between NO₃ ^--and NH₄ ⁺-fed wheat and maize could be responsible for different responses of wheat and maize root growth to NO₃ ^- and NH₄ ⁺ nutrition.     

On-line estimation of O<Subscript>2</Subscript> production,CO<Subscript>2</Subscript> uptake,and growth kinetics of microalgal cultures in a gas-tight photobioreactor

Growth of the green algae Chlamydomonas reinhardtii and Chlorella sp. in batch cultures was investigated in a novel gas-tight photobioreactor, in which CO₂, H₂, and N₂ were titrated into the gas phase to control medium pH, dissolved oxygen partial pressure, and headspace pressure, respectively. The exit gas from the reactor was circulated through a loop of tubing and re-introduced into the culture. CO₂ uptake was estimated from the addition of CO₂ as acidic titrant and O₂ evolution was estimated from titration by H₂, which was used to reduce O₂ over a Pd catalyst. The photosynthetic quotient, PQ, was estimated as the ratio between O₂ evolution and CO₂ up-take rates. NH₄ ⁺, NO₂ ⁻, or NO₃ ⁻ was the final cell density limiting nutrient. Cultures of both algae were, in general, characterised by a nitrogen sufficient growth phase followed by a nitrogen depleted phase in which starch was the major product. The estimated PQ values were dependent on the level of oxidation of the nitrogen source. The PQ was 1 with NH₄ ⁺ as the nitrogen source and 1.3 when NO₃ ⁻ was the nitrogen source. In cultures grown on all nitrogen sources, the PQ value approached 1 when the nitrogen source was depleted and starch synthesis became dominant, to further increase towards 1.3 over a period of 3–4 days. This latter increase in PQ, which was indicative of production of reduced compounds like lipids, correlated with a simultaneous increase in the degree of reduction of the biomass. When using the titrations of CO₂ and H₂ into the reactor headspace to estimate the up-take of CO₂, the production of O₂, and the PQ, the rate of biomass production could be followed, the stoichiometrical composition of the produced algal biomass could be estimated, and different growth phases could be identified.     

氮素形态及配比对5个种源菘蓝的生物碱类成分和多糖的影响

以5份不同种源的菘蓝为材料,采用田间小区试验,设置不施氮(CK)、硝态氮(NO3--N)、铵态氮(NH4+-N)、NH4+-N/NO3--N=75/25、NH4+-N/NO3--N=50/50、NH4+-N/NO3--N=25/75和酰胺态氮等7个处理,分析比较了不同种源植株的靛蓝、靛玉红和总生物碱含量、(R,S)-告依春及多糖含量等指标的差异,为菘蓝栽培生产中氮素的高效利用提供理论参考。结果表明:氮素处理有利于提高山西运城菘蓝和陕西商洛菘蓝叶内靛蓝含量,以及安徽亳州菘蓝和陕西商洛菘蓝叶内的总生物碱含量;NH4+-N/NO3--N=50/50处理对山西运城菘蓝,以及酰胺态氮处理对山西运城菘蓝和陕西商洛菘蓝叶内生物碱类成分的积累均有促进作用;与对照相比,氮素处理亦能有效地提高甘肃张掖菘蓝和陕西商洛菘蓝根内的(R,S)-告依春及安徽亳州菘蓝根内的多糖含量;安徽阜阳菘蓝(R,S)-告依春含量在任一氮处理下均远远高于其他种质菘蓝。研究表明,不同种源菘蓝对氮素处理的响应存在较大的差异,建议生产中综合考虑菘蓝的来源和需肥规律,采用经济有效的施氮组合,以提高其活性成分含量。