Fertilizer nitrogen budget of Na15NO3 and (15NH4)2SO4 split-applied to winter wheat in microplots on a loam soil

Labelled fertilizer N applied to winter wheat as Na¹⁵NO₃ and (¹⁵NH₄)₂SO₄ at a total N dressing of 100kg ha⁻¹ was used in a microplot balance study to investigate the fate of each split fraction at three growth stages: end of tillering, heading and beginning of flowering. Results indicated that while the percentage utilization of the applied N by the grain and total crop increased considerably from the first to the third split application, these values diminished steadily in the straw. Grain recovery values for the first, second and third split applications were 34.2%, 51.5% and 55.7% for the NO₃ and 32.3%, 48.4% and 52.5% for the NH₄ carrier, respectively. The corresponding recovery values for the whole plant were 54.6%, 67.8% and 69.9% for the NO₃ and 51.7%, 63.5% and 66.1% for the NH₄ carrier. A greater proportion of the fertilizer N applied at the end of tillering stage was found in the vegetative plant components as compared with the grain. The reverse occurred for the N applied at the heading and at the beginning of the flowering stages. The residual fertilizer N found in the soil amounted to 18.0%, 10.4% and 11.6% of the applied NO₃−N and to 22.5%, 12.7% and 15.2% of the applied NH₄−N for the respective split applications. No differences were found for each split application between the two carriers as far as the unaccounted fertilizer N was concerned. The losses were 26.6%, 22.3% and 18.6% of the applied N for the three split applications, respectively. The application of fertilizer N did not lead to any increase in soil N uptake by the crop.     

The kinetics of NH4 + and NO3 − uptake by Douglas fir from single N-solutions and from solutions containing both NH4 + and NO3 −

The kinetics of NH₄ ⁺ and NO₃ ⁻ uptake in young Douglas fir trees (Pseudotsuga menziesii [Mirb.] Franco) were studied in solutions, containing either one or both N species. Using solutions containing a single N species, the V_max of NH₄ ⁺ uptake was higher than that of NO₃ ⁻ uptake. The K_m of NH₄ ⁺ uptake and K_m of NO₃ ⁻ uptake differed not significantly. When both NH₄ ⁺ and NO₃ ⁻ were present, the V_max for NH₄ ⁺ uptake became slightly higher, and the K_m for NH₄ ⁺ uptake remained in the same order. Under these conditions the NO₃ ⁻ uptake was almost totally inhibited over the whole range of concentrations used (10–1000 μM total N). This inhibition by NH₄ ⁺ occurred during the first two hours after addition. ei]{gnA C}{fnBorstlap}     

Nitrate reductase activity and nitrogen compounds in xylem exudate of Juglans nigra seedlings: relation to nitrogen source and supply

Nitrogen (N) limits plant productivity and its uptake and assimilation may be regulated by N source, N availability, and nitrate reductase activity (NRA). Knowledge of how these factors interact to affect N uptake and assimilation processes in woody angiosperms is limited. We fertilized 1-year-old, half-sib black walnut (Juglans nigra L.) seedlings with ammonium (NH₄ ⁺) [as (NH₄)₂SO₄], nitrate (NO₃ ⁻) (as NaNO₃), or a mixed N source (NH₄NO₃) at 0, 800, or 1,600 mg N plant⁻¹ season⁻¹. Two months following final fertilization, growth, in vivo NRA, plant N status, and xylem exudate N composition were assessed. Specific leaf NRA was higher in NO₃ ⁻-fed and NH₄NO₃-fed plants compared to observed responses in NH₄ ⁺-fed seedlings. Regardless of N source, N addition increased the proportion of amino acids (AA) in xylem exudate, inferring greater NRA in roots, which suggests higher energy cost to plants. Root total NRA was 37% higher in NO₃ ⁻-fed than in NH₄ ⁺-fed plants. Exogenous NO₃ ⁻ was assimilated in roots or stored, so no difference was observed in NO₃ ⁻ levels transported in xylem. Black walnut seedling growth and physiology were generally favored by the mixed N source over NO₃ ⁻ or NH₄ ⁺ alone, suggesting NH₄NO₃ is required to maximize productivity in black walnut. Our findings indicate that black walnut seedling responses to N source and level contrast markedly with results noted for woody gymnosperms or herbaceous angiosperms.     

Chronic Atmospheric NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> Deposition Does Not Induce NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> Use by <Emphasis Type="Italic">Acer saccharum</Emphasis> Marsh.

The ability of an ecosystem to retain anthropogenic nitrogen (N) deposition is dependent upon plant and soil sinks for N, the strengths of which may be altered by chronic atmospheric N deposition. Sugar maple (Acer saccharum Marsh.), the dominant overstory tree in northern hardwood forests of the Lake States region, has a limited capacity to take up and assimilate NO₃⁻. However, it is uncertain whether long-term exposure to NO₃⁻ deposition might induce NO₃⁻ uptake by this ecologically important overstory tree. Here, we investigate whether 10 years of experimental NO₃⁻ deposition (30 kg N ha⁻¹ y⁻¹) could induce NO₃⁻ uptake and assimilation in overstory sugar maple (approximately 90 years old), which would enable this species to function as a direct sink for atmospheric NO₃⁻ deposition. Kinetic parameters for NH₄⁺ and NO₃⁻ uptake in fine roots, as well as leaf and root NO₃⁻ reductase activity, were measured under conditions of ambient and experimental NO₃⁻ deposition in four sugar maple-dominated stands spanning the geographic distribution of northern hardwood forests in the Upper Lake States. Chronic NO₃⁻ deposition did not alter the V _max or K _m for NO₃⁻ and NH₄⁺ uptake nor did it influence NO₃⁻ reductase activity in leaves and fine roots. Moreover, the mean V _max for NH₄⁺ uptake (5.15 μmol ¹⁵N g⁻¹ h⁻¹) was eight times greater than the V _max for NO₃⁻ uptake (0.63 μmol ¹⁵N g⁻¹ h⁻¹), indicating a much greater physiological capacity for NH₄⁺ uptake in this species. Additionally, NO₃⁻ reductase activity was lower than most values for woody plants previously reported in the literature, further indicating a low physiological potential for NO₃⁻ assimilation in sugar maple. Our results demonstrate that chronic NO₃⁻ deposition has not induced the physiological capacity for NO₃⁻ uptake and assimilation by sugar maple, making this dominant species an unlikely direct sink for anthropogenic NO₃⁻ deposition.     

Effect of activated charcoal and 6-benzyladenine on in vitro nitrogen uptake by Lagerstroemia indica

A sterile hydroponic culture system suitable for studying nitrogen (N) uptake ofLagerstroemia indica L.in vitro was developed. Four different treatments were assayed: with and without activated charcoal (AC and NAC, respectively), with and without 50 μM of 6-benzyladenine (+BA and −BA, respectively). Medium pH, electrical conductivity (EC), NO₃ ⁻ and NH₄ ⁺ concentrations were measured weekly. At the end of the culture, propagules were sampled and SPAD indices, and shoot and root fresh weights were determined. Explants grown in media with activated charcoal were able to take up both NO₃ ⁻ and NH₄ ⁺, although NH₄ ⁺ uptake was lower. Subsequently the pH of the media was maintained between 5.5–6.0. In treatments with no addition of activated charcoal, NH₄ ⁺ uptake was preferential and the pH dropped to 3.1. Explants in these conditions were unable to raise the pH by taking up NO₃ ⁻, especially when root morphogenesis was inhibited by addition of BA. Supply of this PGR produced root growth inhibition, which was almost complete in the treatment without activated charcoal. This component significantly reduced the inhibitory effect of 50 μM BA on root growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

Role of cytokinin in enhanced productivity of maize supplied with NH4 + and NO3 −

Supplying both N forms (NH₄ ⁺+NO₃ ⁻) to the maize (Zea mays L.) plant can optimize productivity by enhancing reproductive development. However, the physiological factors responsible for this enhancement have not been elucidated, and may include the supply of cytokinin, a growth-regulating substance. Therefore, field and gravel hydroponic studies were conducted to examine the effect of N form (NH₄ ⁺+NO₃ ⁻ versus predominantly NO₃ ⁻) and exogenous cytokinin treatment (six foliar applications of 22 μM 6-benzylaminopurine (BAP) during vegetative growth versus untreated) on productivity and yield of maize. For untreated plants, NH₄ ⁺+NO₃ ⁻ nutrition increased grain yield by 11% and whole shoot N content by 6% compared with predominantly NO₃ ⁻. Cytokinin application to NO₃ ⁻-grown field plants increased grain yield to that of NH₄ ⁺+NO₃ ⁻-grown plants, which was the result of enhanced dry matter partitioning to the grain and decreased kernel abortion. Likewise, hydroponically grown maize supplied with NH₄ ⁺+NO₃ ⁻ doubled anthesis earshoot weight, and enhanced the partitioning of dry matter to the shoot. NH₄ ⁺+NO₃ ⁻ nutrition also increased earshoot N content by 200%, and whole shoot N accumulation by 25%. During vegetative growth, NH₄ ⁺+NO₃ ⁻ plants had higher concentrations of endogenous cytokinins zeatin and zeatin riboside in root tips than NO₃ ⁻-grown plants. Based on these data, we suggest that the enhanced earshoot and grain production of plants supplied with NH₄ ⁺+NO₃ ⁻ may be partly associated with an increased endogenous cytokinin supply.     

RETRACTED ARTICLE: Effect of root-zone salinity and form of N on photosynthate partitioning in wheat (Triticum aestivum L.)

Carbon-14 pulse labeling technique was used to study the effect of rooting medium salinity and form and availability of N on growth and rhizodeposition of wheat (Triticum aestivum L.). Thirty days old plants grown in continuously aerated Arnon and Hoagland nutrient solution were subjected to ¹⁴C pulse labeling for 24 h and transferred to aqueous rooting medium containing 0, 150, and 300 mM NaCl in all combinations with different forms (calcium nitrate, ammonium sulphate, and ammonium nitrate) and amounts (0.5, 1.0, 1.5, and 2.0 times the standard N concentration (150 ppm) of Arnon and Hoagland plant growth medium). Plant samples immediately after pulse labeling, following 7 days of growth under different rooting medium conditions, and the freeze-dried rooting medium were analyzed for total C and ¹⁴C. Length and fresh/dry weight of root and shoot portions and calculated values of unaccounted ¹⁴C were determined. Presence of NaCl in the rooting medium led to a decrease in root and shoot portions. However, NO₃ ⁻-fed plants showed better growth than NH₄ ⁺-fed plants at all the three salinity levels. Salinity in rooting medium led to higher rhizodeposition and lower loss of ¹⁴C. Relatively higher proportion of ¹⁴C was released as rhizodeposits and retained in root/shoot portions of plants fed with NH₄ ⁺ or NH₄ ⁺+NO₃ ⁻, than those with NO₃ ⁻, while less was respired. The specific activity of the rhizodeposits (kBq ¹⁴C g⁻¹ C) was also higher under saline conditions. The rhizodeposits in NH₄ ⁺-fed plants were more highly labeled as compared to NO₃ ⁻-plants.     

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.     

Ammonium nutrition increases photosynthesis rate under water stress at early development stage of rice (Oryza sativa L.)

An hydroponic experiment with a simulated water stress induced by PEG (6000) was conducted in a greenhouse to study the effects of nitrate (NO₃ ⁻), ammonium (NH₄ ⁺) and the mixture of NO₃ ⁻ and NH₄ ⁺, on water stress tolerance of rice seedlings. Rice (Shanyou 63) was grown under non- or simulated water stress condition (10% (w/v) PEG, MW6000) with the 3 different N forms during 4 weeks. Under non-stressed condition no difference was observed among the N treatments. Under simulated water stress, seedlings grown on N-NO₃ ⁻ were stunted. Addition of PEG did not affect rice seedling growth in the treatment of only NH₄ ⁺ supply but slightly inhibited the rice seedling growth in the treatment of mixed supply of NO₃ ⁻ and NH₄ ⁺. Simulated water stress, when only N-NH₄ ⁺ was present, did not affect leaf area and photosynthesis rate, however, both parameters decreased significantly in the NO₃ ⁻ containing solutions. Under water stress, Rubisco content in newly expanded leaves significantly increased in the sole NH₄ ⁺ supplied plants as compared to that in plants of the other two N treatments. Under water stress, the ratio of carboxylation efficiency to Rubisco content was, respectively, decreased by 13 and 23% in NH₄ ⁺ and NO₃ ⁻ treatments, respectively. It is concluded that, water stress influenced the Rubisco activity than stomatal limitation, and this effects could be regulated by N forms. Responsible Editor: Herbert Johannes Kronzucker. Shiwei Guo and Gui Chen contributed equally to this paper.     

Functional role of DNRA and nitrite reduction in a pristine south Chilean <Emphasis Type="Italic">Nothofagus</Emphasis> forest

Nitrite (NO₂ ⁻) is an intermediate in a variety of soil N cycling processes. However, NO₂ ⁻ dynamics are often not included in studies that explore the N cycle in soil. Within the presented study, nitrite dynamics were investigated in a Nothofagus betuloides forest on an Andisol in southern Chile. We carried out a ¹⁵N tracing study with six ¹⁵N labeling treatments, including combinations of NO₃ ⁻, NH₄ ⁺ and NO₂ ⁻. Gross N transformation rates were quantified with a ¹⁵N tracing model in combination with a Markov chain Monte Carlo optimization routine. Our results indicate the occurrence of functional links between (1) NH₄ ⁺ oxidation, the main process for NO₂ ⁻ production (nitritation), and NO₂ ⁻ reduction, and (2) oxidation of soil organic N, the dominant NO₃ ⁻ production process in this soil, and dissimilatory NO₃ ⁻ reduction to NH₄ ⁺ (DNRA). The production of NH₄ ⁺ via DNRA was approximately ten times higher than direct mineralization from recalcitrant soil organic matter. Moreover, the rate of DNRA was several magnitudes higher than the rate of other NO₃ ⁻ reducing processes, indicating that DNRA is able to outcompete denitrification, which is most likely not an important process in this ecosystem. These functional links are most likely adaptations of the microbial community to the prevailing pedo-climatic conditions of this Nothofagus ecosystem.     

Effect of nitrogen forms on growth,cell composition and N<Subscript>2</Subscript> fixation of <Emphasis Type="Italic">Cylindrospermopsis raciborskii</Emphasis> in phosphorus-limited chemostat cultures

The aim of this research was to test whether NH₄ ⁺ and NO₃ ⁻ affect the growth, P demand, cell composition and N₂ fixation of Cylindrospermopsis raciborskii under P limitation. Experiments were carried out in P-limited (200 μg l⁻¹ PO₄-P) chemostat cultures of C. raciborskii using an inflowing medium containing either 4,000 μg l⁻¹ NH₄-N, 4,000 μg l⁻¹ NO₃-N or no combined N. The results showed the cellular N:P and C:P ratios of C. raciborskii decreased towards the Redfield ratio with increasing dilution rate (D) due to the alleviation of P limitation. The cellular C:N and carotenoids:chlorophyll-a ratios also decreased with D, predominantly as a result of an increase in the chlorophyll-a and N content. The NH₄ ⁺ and NO₃ ⁻ supply reduced the P maintenance cell quota of C. raciborskii. Consequently, the biomass yield of the N₂-grown culture was significantly lower. The maximum specific growth rate of N₂-grown culture was also the lowest observed. It is suggested that these differences in growth parameters were caused by the P and energy requirement for heterocyte formation, nitrogenase synthesis and N₂ fixation. N₂ fixation was partially inhibited by NO₃ ⁻ and completely inhibited by NH₄ ⁺. It was probably repressed through the high N content of cells at high dissolved N concentrations. These results indicate that C. raciborskii is able to grow faster and maintain a higher biomass under P limitation where a sufficient supply of NH₄ ⁺ or NO₃ ⁻ is maintained. Information gained about the species-specific nutrient and pigment stoichiometry of C. raciborskii could help to access the degree of nutrient limitation in water bodies. Handling editor: Luigi Naselli-Flores     

NO<Subscript>3</Subscript><Superscript>−</Superscript>-Driven SO<Subscript>4</Subscript><Superscript>2−</Superscript> Production in Freshwater Ecosystems: Implications for N and S Cycling

Massive anthropogenic acceleration of the global nitrogen (N) cycle has stimulated interest in understanding the fate of excess N loading to aquatic ecosystems. Nitrate (NO₃ ⁻) is traditionally thought to be removed mainly by microbial respiratory denitrification coupled to carbon (C) oxidation, or through biomass assimilation. Alternatively, chemolithoautotrophic bacterial metabolism may remove NO₃ ⁻ by coupling its reduction with the oxidation of sulfide to sulfate (SO₄ ²⁻). The NO₃ ⁻ may be reduced to N₂ or to NH₄ ⁺, a form of dissimilatory nitrate reduction to ammonium (DNRA). The objectives of this study were to investigate the importance of S oxidation as a NO₃ ⁻ removal process across diverse freshwater streams, lakes, and wetlands in southwestern Michigan (USA). Simultaneous NO₃ ⁻ removal and SO₄ ²⁻ production were observed in situ using modified “push-pull” methods in nine streams, nine wetlands, and three lakes. The measured SO₄ ²⁻ production can account for a significant fraction (25–40%) of the overall NO₃ ⁻ removal. Addition of ¹⁵NO₃ ⁻ and measurement of ¹⁵NH₄ ⁺ production using the push–pull method revealed that DNRA was a potentially important process of NO₃ ⁻ removal, particularly in wetland sediments. Enrichment cultures suggest that Thiomicrospira denitrificans may be one of the organisms responsible for this metabolism. These results indicate that NO₃ ⁻-driven SO₄ ²⁻ production could be widespread and biogeochemically important in freshwater sediments. Removal of NO₃ ⁻ by DNRA may not ameliorate problems such as eutrophication because the N remains bio-available. Additionally, if sulfur (S) pollution enhances NO₃ ⁻ removal in freshwaters, then controls on N processing in landscapes subject to S and N pollution are more complex than previously appreciated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Yield and nitrogen uptake of rapessed (Brassica campestris L.) with ammonium and nitrate

Water culture, growth chamber, greenhouse and field experiments were conducted to compare the effect of NH₄−N and NO₃−N on yield and N uptake of rapeseed (Brassica campestris L.). In water culture, the yields of 28-day old rapeseed plants grown at 14 μg N ml⁻¹ were double with NO₃ compared to NH₄, but N uptake was little affected. There was no such effect when concentration was reduced to 3.5 or 7 μg N ml⁻¹. The yield and N uptake of 26-day old rapeseed grown on six soils (pH 4.6 to 6.5) in pots in a growth chamber were much greater with NO₃ than with NH₄, although N concentration was more in the NH₄- than the NO₃-grown plants. In a greenhouse experiment with rapeseed grown on 12 potted soils, the N uptake of applied N was greater with NO₃ than with NH₄ on all soils. Averages were 63% with NH₄ and 78% with NO₃. However, NH₄-fixation capacities of the soils were only weakly correlated with yield from the two sources of N (r=0.48) and the relation was similar with N uptake. In contrast to the behavior of water culture, growth chamber and greenhouse experiments, the 33 field experiments did not show consistent difference in seed yield with NH₄ and NO₃ applied at time of seeding. In nine field experiments where band application was used for Ca(NO₃)₂, (NH₄)₂ SO₄, NH₄ NO₃, yield tended to be greatest for (NH₄)₂SO₄. However, in 19 experiments on acid soils with and without lime, yields in most cases were similar with (NH₄)₂SO₄ and NH₄ NO₃. Nitrification inhibitors were added to spring banded NH₄-based fertilizers in five experiments, but the yields were not influenced. Scientific Paper No. 558, Lacombe Research Station, Agriculture Canada.     

Epidemiology of wheat take-all as influenced by soil pH and temporal changes in inorganic soil N

Summary Soil pH, NH ₄ ⁺ and NO ₃ ⁻ concentrations in soil, and take-all root rot of winter wheat grown in the field were measured concurrently from sowing to anthesis in order to relate disease development to liming and N fertilization practices. Experimental variables included soil pH (5.5 and 6.0) and three N sources (NH₄NO₃, (NH₄)₂SO₄, NH₄Cl) banded with the seed at sowing in factorial combination with the same three N sources topdressed in the spring. Take-all severity was increased by increasing soil pH and by fertilization with NO ₃ ⁻ . Disease severity on crown roots increased exponentially following spring N fertilization and was affected more by soil pH and N-form than was severity on seminal roots. Grain yield ranged from 4.70 Mgha⁻¹ with spring NH₄NO₃ at soil pH 6.0 to 7.65 Mgha⁻¹ with spring NH₄Cl at soil pH 5.5. Sixty-six percent of the variability in grain yield was explained by the number of take-all infected crown roots per tiller at anthesis. Oregon Agric. Exp. Stn. technical paper no. 7707.     

Alleviation of nickel toxicity by ammonium supply to sunflower plants

Phytotoxicity of nickel (Ni) varies within plant species and cultivars as well as with the concentration of Ni in the rooting medium. Moreover, it is known that several nutrients can modify the plant response to excess Ni. Nitrogen can be absorbed by plants as different N forms and because N metabolism and Ni are closely related, a hydroponic experiment was conducted to study the effect of Ni toxicity on the growth, nutrient status of the different plant parts and leaf chlorophyll concentrations in sunflower plants (Helianthus annuus L.) cv Quipu grown with different forms of N supply. The plants were grown under controlled conditions for 35 days. Depending on the N source supplied, there were significant differences in the sensitivity of sunflower plants to excess Ni. Tolerance was lowest when grown with NO₃ ⁻ alone. A high Ni and NO₃ ⁻ as the only N source resulted in reduced dry weight and significant decreases in nutrient concentration. Plants supplied with a mixture of NO₃ ⁻ and NH₄ ⁺ absorbed in the presence of Ni in solution about three times less Ni than those supplied with NO₃ ⁻ alone. Consequently, there were great differences in Ni concentrations between treatments. With a N nutrition of 100% NO₃ ⁻-N, Ni supply led to severe growth inhibition. Just contrary, simultaneous supply of NO₃ ⁻ and NH₄ ⁺ not only reduced Ni toxicity, but growth was even stimulated by Ni if supplied to plants fed with NO₃ ⁻ and NH₄ ⁺. This indicates the significant role of the N form supplied in the behaviour of Ni toxicity in sunflower plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> stress on oxidative damage,antioxidant enzymes activities and polyamine contents in roots of grafted and non-grafted tomato plants

The effects of Ca(NO₃)₂ stress on biomass production, oxidative damage, antioxidant enzymes activities and polyamine contents in roots of grafted and non-grafted tomato plants were investigated. Results showed that when exposed to 80 mM Ca(NO₃)₂ stress, the biomass production reduction in non-grafted plants was more significant than that of grafted plants. Under Ca(NO₃)₂ stress, superoxide anion radical (O₂•⁻) producing rate, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) contents of non-grafted plants roots were significantly higher than those of grafted plants, however, nitrate (NO₃ ⁻), ammonium (NH₄ ⁺) and proline contents, superoxide dismutase (SOD, EC1.15.1.1), peroxidase (POD, EC1.11.1.7), catalase (CAT, EC1.11.1.6) and arginine decarboxylase (ADC, EC 4.1.1.19) activities of grafted plants roots were significantly higher than those of non-grafted plants. Regardless of stress, free, conjugated and bound polyamine contents in roots of grafted plants were significantly higher than those of non-grafted plants. The possible roles of antioxidant enzymes, prolines and polyamines in adaptive mechanism of tomato roots to Ca(NO₃)₂ stress were discussed. Gu-Wen Zhang and Zheng-Lu Liu contributed equally to this work.     

Effects of Al on nitrogen (NH 4 + and NO 3 − ) uptake,nitrate reductase activity and proton release in two sorghum cultivars differing in Al tolerance

After growth for 17 to 36 days on nutrient solutions with NH₄NO₃ as nitrogen source (pH 4.2) dry matter of sorghum genotype SC0283 was much less affected by Al (1.5 and 3.0 ppm) than that of genotype NB9040. In the absence of Al both cultivars released protons into the nutrient solution as a result of an excess of cationic nutrients taken up. When Al was present, this proton efflux per unit dry weight increased drastically, especially with the sensitive genotype NB9040. Chemical analysis of plant material and continuous analyses of NO ₃ ⁻ and NH ₄ ⁺ in the nutrient solution indicated, that the Al-induced shift in H⁺-balance of both genotypes could almost completely be attributed to a decreased NO ₃ ⁻ /NH ₄ ⁺ uptake ratio. In vivo nitrate reductase activity (NRA) was reduced in the shoot of NB9040 and to a lesser degree in SC0283. Al-induced decrease in NRA was accompanied by similar percentual decreases in NO ₃ ⁻ tissue concentrations. Therefore this decrease is interpreted as being indirect,i.e., the consequence of the reduced NO ₃ ⁻ uptake of the plants. A direct repression of NRA by Al seems also unlikely because nitrate reductase activity of the roots (where cellular Al-concentrations should be higher than in shoots) was not affected in Al-treated plants of either genotype.     

The influence of nitrogen concentration and ammonium/nitrate ratio on N-uptake,mineral composition and yield of citrus

In short-term water culture experiments with different ¹⁵N labeled ammonium or nitrate concentrations, citrus seedlings absorbed NH₄ ⁺ at a higher rate than NO₃ ^–. Maximum NO₃ ^– uptake by the whole plant occurred at 120 mg L^–1 NO₃ ^–-N, whereas NH₄ ⁺ absorption was saturated at 240 mg L^–1 NH₄ ⁺-N. ¹⁵NH₄ ⁺ accumulated in roots and to a lesser degree in both leaves and stems. However, ¹⁵NO₃ ^– was mostly partitioned between leaves and roots.Adding increasing amounts of unlabeled NH₄ ⁺ (15–60 mg L^–1 N) to nutrient solutions containing 120 mg L^–1 N as ¹⁵N labeled nitrate reduced ¹⁵NO₃ ^– uptake. Maximum inhibition of ¹⁵NO₃ ^– uptake was about 55% at 2.14 mM NH₄ ⁺ (30 mg L^–1 NH₄ ⁺-N) and it did not increase any further at higher NH₄ ⁺ proportions.In a long-term experiment, the effects of concentration and source of added N (NO₃ ^– or NH₄ ⁺) on nutrient concentrations in leaves from plants grown in sand were evaluated. Leaf concentration of N, P, Mg, Fe and Cu were increased by NH₄ ⁺ versus NO₃ ^– nutrition, whereas the reverse was true for Ca, K, Zn and Mn.The effects of different NO₃ ^–-N:NH₄ ⁺-N ratios (100:0, 75:25, 50:50, 25:75 and 0:100) at 120 mg L^–1 total N on leaf nutrient concentrations, fruit yield and fruit characteristics were investigated in another long-term experiment with plants grown in sand cultures. Nitrogen concentrations in leaves were highest when plants were provided with either NO₃ ^– or NH₄ ⁺ as a sole source of N. Lowest N concentration in leaves was found with a 75:25 NO₃ ^–-N/NH₄ ⁺-N ratio. With increasing proportions of NH₄ ⁺ in the N supply, leaf nutrients such as P, Mg, Fe and Cu increased, whereas Ca, K, Mn and Zn decreased. Yield in number of fruits per tree was increased significantly by supplying all N as NH₄ ⁺, although fruit weight was reduced. The number of fruits per tree was lowest with the 75:25 NO₃ ^–-N:NH₄ ⁺-N ratio, but in this treatment fruits reached their highest weight. Rind thickness, juice acidity, and colour index of fruits decreased with increasing NH₄ ⁺ in the N supply, whereas the % pulp and maturity index increased. Percent of juice in fruits and total soluble solids were only slightly affected by NO₃ ^–:NH₄ ⁺ ratio.     

The growth and some physiological responses of rice to Cd toxicity as affected by nitrogen form

A hydroponic experiment was conducted to examine the effect of Cd stress on anti-oxidative enzyme activities at heading stage, yield components, root exudation and Cd and N uptake of rice plants grew in different N source i.e. (NH₄)₂SO₄, NH₄NO₃ and Ca(NO₃)₂. The results show that the effect of Cd stress on all measured parameters were N source dependent. Cd stress (1 μM) caused a remarkable reduction in grain yield and shoot biomass, an increase in root exudation, glutathione content, Cd concentration and catalase (CAT) and peroxidase (POD) activities of rice plants. In the plants under the control (without Cd addition) N source had no distinctive effect on the above measured parameters, but the differences among the three N forms in these parameters became significant when plants were exposed to Cd stress. Cd stress significantly increased POD and CAT activities, and gultathione content, with Ca(NO₃)₂-fed plants having the greatest POD and CAT activities and lowest glutathione content, and (NH₄)₂SO₄-fed plants being just opposite. Moreover, organic acid exudation varied also with N form for the Cd-stressed plants. In comparison with other two N forms, (NH₄)₂SO₄,-treated plants had higher grain yield, N concentration and lower Cd concentration in plants. The current results indicated that (NH₄)₂SO₄ is a better fertilizer for use in Cd contaminated soil.     

Avocado shoot culture, plantlet development and net CO2 assimilation in an ambient and CO2 enhanced environment

Summary The proliferation and survival of avocado nodal cultures of juvenile origin were affected by the form and concentration of nitrogen. Optimum growth was achieved on modified Murashige and Skoog medium containing 67% KNO₃ and 33% NH₄NO₃ with total N of 40 mM supplemented with 100 mg l⁻¹ myo-inositol, 1 mg l⁻¹ thiamine HCl, 30 g l⁻¹ sucrose, and 4.44 μM BA with a 16-h photoperiod (120–150 μmol m⁻² s⁻¹). Proliferating shoots and plantlets were photosynthetically active. Better shoot growth and accumulation of higher biomass occurred in a CO₂-enriched environment than under ambient CO₂ conditions. CO₂ assimilation efficiency, however, was higher under the latter conditions than in a CO₂-enhanced environment, e.g., 31±7 and 17±2 μmol CO₂ m⁻² s⁻¹, respectively. The net CO₂ assimilation rates of in vitro grown plantlets were comparable to those of seedlings ex vitro.