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1.
The results of the experiments discussed here present changes in the chemical composition of xylem sap of tomato seedlings cultivated in hydroponics on media containing 5 mmol HCO3
– and an N-source given as NO3
–, NH4
+ or these two forms in different proportions. The occurrence of free NH4
+ in the xylem sap of NH4
+-seedlings and in NO3
–-seedlings indicates that the process of N-assimilation was not only confined to roots. The application of HCO3
– to the medium effected a decrease in the concentration of NH4
+ in the xylem sap of NH4
+-seedlings, having no effect on changes in the concentration of NO3
– or NH4
+ in NO3
–-seedlings. Malate, citrate, fumarate, and succinate were identified in the xylem sap. The concentration of carboxylates in NO3
–-seedlings exceeded by about 50% that recorded in NH4
+-seedlings. The highest concentration of malate constituting from 80% to 93.5% of this fraction, was determined in this group of compounds. The enrichment of the medium with HCO3
– ions induced an increase in the content of carboxylates, chiefly of malate. In these experimental conditions an increase in the malate concentration in the xylem sap of NO3
– and NH4
+-seedlings reached relative values of 100% and 36%, respectively. The total concentration of amides and amino acids was about 2.6 times higher in the xylem sap of NH4
+-seedlings than in NO3
–-seedlings. Amide glutamine was the main component of this fraction in xylem sap and its total concentration was about 3.3 times higher in NH4
+-seedlings than that determined in NO3
–-seedlings. Glutamine, glutamate, aspargine, and aspartate constituted from 69% to 77% of this fraction. The concentration of the remaining amino acids varied from 0.6% to 7%. The enrichment of the medium with HCO3
– ions also effected an increase in the concentration of amides and amino acids in the xylem sap by about 17% and 56% in the case of NO3
– and NH4
+-seedlings, respectively, in comparison with the respective controls (without HCO3
–).
Abbreviations: DAG – days after germination; DIC – dissolved inorganic carbon; GOGAT – glutamine:2-oxoglutarate aminotransferase; GS – glutamine synthetase; PAR – photosynthetically active radiation; PEPc – phosphoenolpyruvate carboxylase 相似文献
2.
The seasonal dynamics of amino acids and other nutrients in Alaskan Arctic tundra soils 总被引:4,自引:0,他引:4
Past research strongly indicates the importance of amino acids in the N economy of the Arctic tundra, but little is known about the seasonal dynamics of amino acids in tundra soils. We repeatedly sampled soils from tussock, shrub, and wet sedge tundra communities in the summers of 2000 and 2001 and extracted them with water (H2O) and potassium sulfate (K2SO4) to determine the seasonal dynamics of soil amino acids, ammonium (NH4+), nitrate (NO3–), dissolved organic nitrogen (DON), dissolved organic carbon (DOC), and phosphate (PO42–). In the H2O extractions mean concentrations of total free amino acids (TFAA) were higher than NH4+ in all soils but shrub. TFAA and NH4+ were highest in wet sedge and tussock soils and lowest in shrub soil. The most predominant amino acids were alanine, arginine, glycine, serine, and threonine. None of the highest amino acids were significantly different than NH4+ in any soil but shrub, in which NH4+ was significantly higher than all of the highest individual amino acids. Mean NO3– concentrations were not significantly different from mean TFAA and NH4+ concentrations in any soil but tussock, where NO3– was significantly higher than NH4+. In all soils amino acid and NH4+ concentrations dropped to barely detectable levels in the middle of July, suggesting intense competition for N at the height of the growing season. In all soils but tussock, amino acid and NH4+ concentrations rebounded in August as the end of the Arctic growing season approached and plant N demand decreased. This pattern suggests that low N concentrations in tundra soils at the height of the growing season are likely the result of an increase in soil N uptake associated with the peak in plant growth, either directly by roots or indirectly by microbes fueled by increased root C inputs in mid-July. As N availability decreased in July, PO42– concentrations in the K2SO4 extractions increased dramatically in all soils but shrub, where there was a comparable increase in PO42– later in the growing season. Previous research suggests that these increases in PO42– concentrations are due to the mineralization of organic phosphorus by phosphatase enzymes associated with soil microbes and plant roots, and that they may have been caused by an increase in organic P availability. 相似文献
3.
Preference for NH4+ or NO3− nutrition by the perennial legume Sesbania sesban (L.) Merr. was assessed by supplying plants with NH4+ and NO3− alone or mixed at equal concentrations (0.5 mM) in hydroponic culture. In addition, growth responses of S. sesban to NH4+ and NO3− nutrition and the effects on root nodulation and nutrient and mineral composition of the plant tissues were evaluated in a hydroponic setup at a range of external concentration of NH4+ and NO3− (0, 0.1, 0.2, 0.5, 2 and 5 mM). Seedlings of S. sesban grew equally well when supplied with either NH4+ or NO3− alone or mixed and had high relative growth rates (RGRs) ranging between 0.19 and 0.21 d−1. When larger plants of S. sesban were supplied with NH4+ or NO3− alone, the RGRs and shoot elongation rates were not affected by the external concentration of inorganic N. At external N concentrations up to 0.5 mM nodulation occurred and contributed to the N nutrition through fixation of gaseous N2 from the atmosphere. For both NH4+ and NO3−-fed plants the N concentration in the plant tissues, particularly water-extractable NO3−, increased at high supply concentrations, and concentrations of mineral cations generally decreased. It is concluded that S. sesban can grow without an external inorganic N supply by fixing atmospheric N2 gas via root nodules. Also, S. sesban grows well on both NH4+ and NO3− as the external N source and the plant can tolerate relatively high concentrations of NH4+. This wide ecological amplitude concerning N nutrition makes S. sesban very useful as a N2-fixing fallow crop in N deficient areas and also a candidate species for use in constructed wetland systems for the treatment of NH4+ rich waters. 相似文献
4.
The effects of inorganic nutrient (ammonium [NH4 + ] and nitrate [NO3 − ]) and amino acid (glutamate [glu] and glutamine [gln]) additions on rates of N2 fixation, N uptake, glutamine synthetase (GS) activity, and concentrations of intracellular pools of gln and glu were examined in natural and cultured populations of Trichodesmium. Additions of 1 μM glu, gln, NO3 − , or NH4 + did not affect short-term rates of N2 fixation. This may be an important factor that allows for continued N2 fixation in oligotrophic areas where recycling processes are active. N2 fixation rates decreased when nutrients were supplied at higher concentrations (e.g. 10 μM). Uptake of combined N (NH4 + , NO3 − , and amino acids) by Trichodesmium was stimulated by increased concentrations. For NO3 − , proportional increases in NO3 − uptake and decreases in N2 fixation were observed when additions were made to cultures before the onset of the light period. GS activity did not change much in response to the addition of NH4 + , NO3 − , glu, or gln. GS is necessary for N metabolism, and the bulk of this enzyme pool may be conserved. Intracellular pools of glu and gln varied in response to 10 μM additions of NH4 + , glu, or gln. Cells incubated with NH4 + became depleted in intracellular glu and enriched with intracellular gln. The increase in the gln/glu ratio corresponded to a decrease in the rate of N2 fixation. Although the gln/glu ratio decreased in cells exposed to the amino acids, there was only a corresponding decrease in N2 fixation after the gln addition. The results presented here suggest that combined N concentrations on the order of 1 μM do not affect rates of N2 fixation and metabolism, although higher concentrations (e.g. 10 μM) can. Moreover, these effects are exerted through products of NH4 + assimilation rather than exogenous N, as has been suggested for other species. These results may help explain how cultures of Trichodesmium are able to simultaneously fix N2 and take up NH4 + and how natural populations continue to fix N2 once combined N concentrations increase within a bloom. 相似文献
5.
Nitrogen metabolism by heterotrophic bacterial assemblages in Antarctic coastal waters 总被引:4,自引:0,他引:4
Field studies to examine the in situ assimilation and production of ammonium (NH4
+) by bacterial assemblages were conducted in the northern Gerlache Strait region of the Antarctic Peninsula. Short term incubations of surface waters containing 15N-NH4
+ as a tracer showed the bacterial population taking up 0.041–0.128 g-atoms Nl–1d–1, which was 8–25% of total NH4
+ uptake rates. The large bacterial uptake of NH4
+ occurred even at low bacterial abundance during a rich phytoplankton bloom. Estimates of bacterial production using 3H-leucine and -adenine were l.0gCl–1 d–1 before the bloom and 16.2 g Cl–1 d–1 at the bloom peak. After converting bacterial carbon production to an estimate of nitrogen demand, NH4
+ was found to supply 35–60% of bacterial nitrogen requirements. Bacterial nitrogen demand was also supported by dissolved organic nitrogen, generally in the form of amino acids. It was estimated, however, that 20–50% of the total amino acids taken up were mineralized to NH4
+. Bacterial production of NH4
+ was occurring simultaneously to its uptake and contributed 27–55% of total regenerated NH4
+ in surface waters. Using a variety of 15N-labelled amino acids it was found that the bacteria metabolized each amino acid differently. With their large mineralization of amino acids and their relatively low sinking rates, bacteria appear to be responsible for a large portion of organic matter recycling in the upper surface waters of the coastal Antarctic ecosystem. 相似文献
6.
The use of macroalgae as biological indicators of dissolved nutrient source and availability in the water column was investigated. Total tissue nitrogen (N) content, pigments, and amino acids of the red alga Gracilaria edulis (Gmelin) Silva were compared to N source and availability in laboratory and field incubations to identify responses that would serve as bioindicators of N. Field-collected algae were preincubated (6–8 wk) in low-nutrient seawater to deplete their luxury reserves ofN. Incubations were then conducted for periods of 3 d in laboratory aquaria (N-spiked seawater) and in the field using macroalgal incubation chambers. After incubation in different N sources (NH4+, NO3?, and urea) in laboratory aquaria, photosynthetic pigments (phycoerythrin and chlorophyll a) and total tissue N increased, in response to increasing [NH4+] but not to [NO3?] or [urea]. Incubation in two ranges of [NH4+], one from 0 to 80 μM and the other from 0 to 800 μM, in laboratory aquaria increased the total amino acid pool. Citrulline concentrations were the most responsive to [NH4+] (r2= 0. 84). NH4+ source treatments produced increases in citrulline, phenylalanine, serine, and free NH4+ and decreases in alanine; NO3? treatments produced increases in glutamic acid, citrulline, and alanine; and urea treatments produced increases in free NH4+ and decreases in phenylalanine and serine. The observed variations in amino acid content facilitated the development of an index for each N source based on relative concentrations of various amino acids (i. e. metabolic profiling). Gracilaria edulis was incubated along a field N gradient in the Brisbane River (three sites) and Moreton Bay (four sites), Queensland, Australia. Both phycoerythrin and tissue N appeared to respond equally to NH4+ and NO3? availability in the field. N source indices, based on amino acid concentration, were effective predictors of both [NH4+] and [NO3?] over a wide range of concentrations along the field gradient. Macroalgal physiological responses, particularly amino acid content, to changes in source and availability of N appear to be useful as sensitive bioindicators of N. 相似文献
7.
Solutes contributing to osmotic adjustment in cultured plant cells adapted to water stress 总被引:17,自引:7,他引:10
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Osmotic adjustment was studied in cultured cells of tomato (Lycopersicon esculentum Mill cv VFNT-Cherry) adapted to different levels of external water potential ranging from −4 bar to −28 bar. The intracellular concentrations of reducing sugars, total free amino acids, proline, malate, citrate, quaternary ammonium compounds, K+, NO3−, Na+, and Cl− increased with decreasing external water potential. At any given level of adaptation, the maximum contribution to osmotic potential was from reducing sugars followed by potassium ions. The sucrose levels in the cells were 3- to 8-fold lower than reducing sugar levels and did not increase beyond those observed in cells adapted to −16 bar water potential. Concentrations of total free amino acids were 4- to 5-fold higher in adapted cells. Soluble protein levels declined in the adapted cell lines, but the total reduced nitrogen was not significantly different after adaptation. Uptake of nitrogen (as NH4+ or NO3−) from the media was similar for adapted and unadapted cells. Although the level of quaternary ammonium compounds was higher in the nonadapted cells than that of free proline, free proline increased as much as 500-fold compared to only a 2- to 3-fold increase observed for quaternary ammonium compounds. Although osmotic adjustment after adaptation was substantial (up to −36 bar), fresh weight (volume increase) was restricted by as much as 50% in the adapted cells. Altered metabolite partitioning was evidenced by an increase in the soluble sugars and soluble nitrogen in adapted cells which occurred at the expense of incorporation of sugar into cell walls and nitrogen into protein. Data indicate that the relative importance of a given solute to osmotic adjustment may change depending on the level of adaptation. 相似文献
8.
Garnett Trevor P. Shabala Sergey N. Smethurst Philip J. Newman Ian A. 《Plant and Soil》2001,236(1):55-62
Knowledge of the preferred source of N for Eucalyptus nitens will lead to improved fertiliser management practices in plantations. Ion selective microelectrodes were used non-invasively to measure simultaneously net fluxes of NH4
+, NO3
– and H+ along the tap root of solution-cultured E. nitens. Measurements were conducted in solutions containing 100 m NH4NO3. The pattern of fluxes was such that there was a large influx of NH4
+, a smaller influx of NO3
– and large H+ efflux. The ratio of these fluxes was constant, according to the ratio 3:1:–6 (NH4
+:NO3
–:H+). Within the region 20–60 mm from the root apex of E. nitens seedlings there was spatial and temporal variation in fluxes but flux patterns remained constant. Root hair density did not affect fluxes nor did proximity to lateral roots. Variation was less than that found in previous studies of localised root fluxes using similar high-resolution measurement techniques. It was concluded that small-scale spatial variation in fluxes may have confounded previous studies. There were associations between fluxes of all three ions, the strongest associations being between NH4
+ and H+, and NH4
+ and NO3
–. Overall, these results are consistent with NH4
+ being the preferred source N for E. nitens. 相似文献
9.
Western red cedar (Thuja plicata Donn.), western hemlock (Tsuga heterophylla Raf. Sarge) and salal (Gaultheria shallon Pursh) are the main species growing in cedar–hemlock forests on Vancouver Island, Canada. Based on the dominance of organic N in these systems, we tested the hypotheses that: (1) organic N can be utilized by the three plant species; and (2) salal, which is ericoid mycorrhizal and has high tannin concentration in its tissues, would absorb more N from the complex organic N compounds than the other two species. The abilities of cedar, hemlock and salal to take up 15N,13C-labelled glutamic acid were measured and the capacities of the three species to use nitrate (NO3–), ammonium (NH4+), glutamic acid, protein and protein–tannin N were compared over a 20-day period. Based on 13C enrichment, all three species absorbed at least a portion of glutamic acid intact. Cedar, hemlock and salal also showed similar patterns of N uptake from the NO3–, NH4+, glutamic acid, protein and protein–tannin treatments. The largest proportions of applied N were taken up from the NO3– and NH4+ treatments while smaller amounts of N were absorbed from the organic N compounds. Thus organic N was accessed to a modest degree by all three species, and salal did not have a greater capacity to utilize protein and protein–tannin–N. 相似文献
10.
Changes in the size of intracellular nitrogen pools and the potential feedback by these pools on maximum N uptake (NH4+ and NO3?) rates were determined for Chaetomorpha linum (Müller) Kützing grown sequentially under nutrient-saturating and nutrient-limiting conditions. The size of individual pools in N-sufficient algae could be ranked as residual organic N (RON) comprised mainly of amino acids and amino compounds > protein N > NO3? > NH4+ > chlorophyll N. When the external N supply was removed, growth rates remained high and individual N pools were depleted at exponential rates that reflected both dilution of existing pools by the addition of new biomass from growth and movement between the pools. Calculated fluxes between the tissue N pools showed that the protein pool increased throughout the N depletion period and thus did not serve a storage function. RON was the largest storage reserve; nitrate was the second largest, but more temporary, storage pool that was depleted within 10 days. Upon N resupply, the RON pool increased 3 × faster than either the inorganic or protein pools, suggesting that protein synthesis was the rate-limiting step in N assimilation and caused a buildup of intermediate storage compounds. Maximum uptake rates for both NH4+ and NO3? varied inversely with macroalgal N status and appeared to be controlled by changes in small intracellular N pools. Uptake of NO3? showed an initial lag phase, but the initial uptake of NH4+ was enhanced and was present only when the intracellular NH4+ pool was depleted in the absence of an external N supply. A strong negative correlation between the RON pool size and maximum assimilation uptake rates for both NH4+ and NO3? suggested a feedback control on assimilation uptake by the buildup and depletion of organic compounds. Enhanced uptake and the accumulation of N as simple organic compounds or nitrate both provide a temporary mechanism to buffer against the asynchrony of N supply and demand in C. linum. 相似文献
11.
The influence of nitrogen concentration and ammonium/nitrate ratio on N-uptake,mineral composition and yield of citrus 总被引:9,自引:0,他引:9
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. 相似文献
12.
Growth and solute composition of the salt-tolerant kallar grass [Leptochloa fusca (L.) Kunth] as affected by nitrogen source 总被引:1,自引:0,他引:1
A study was conducted to elucidate the effect of N form, either NH4
+ or NO3
–, on growth and solute composition of the salt-tolerant kallar grass [Leptochloa fusca (L.) Kunth] grown under 10 mM or 100 mM NaCl in hydroponics. Shoot biomass was not affected by N form, whereas NH4
+ compared to NO3
– nutrition caused an almost 4-fold reduction in the root biomass at both salinity levels. Under NH4
+ nutrition, salinity had no effect on the biomass yield, whereas under NO3
– nutrition, increasing salinity from 10 mM to 100 mM caused 23% and 36% reduction in the root and shoot biomass, respectively. The reduced root growth under NH4
+ nutrition was not attributable to impaired shoot to root C allocation since N form did not affect the overall root sugar concentration and the starch concentration was even higher under NH4
+ compared to NO3
– nutrition. The low NH4
+ (2 mM) and generally higher amino-N concentrations in NH4
+- compared to NO3
–-fed plants indicated that the grass was able to effectively detoxify NH4
+. Salinity had no effect on Ca2+ and Mg2+ levels, whereas their concentration in shoots was lower under NH4
+ compared to NO3
– nutrition (over 66% reduction in Ca2+; over 20% reduction in Mg2+), but without showing deficiency symptoms. Ammonium compared to NO3
– nutrition did not inhibit K+ uptake, and the K+-Na+ selectivity either remained unaffected or it was higher under NH4
+ than under NO3
– nutrition. Results suggested that while NH4
+
versus NO3
– nutrition substantially reduced root growth, and also strongly modified anion concentrations and to a minor extent concentrations of divalent cations in shoots, it did not influence salt tolerance of kallar grass. 相似文献
13.
Responses to excessive ammonium (NH4
+) were compared between two Arabidopsis ecotypes (Col-0, JA22) with respect to different photoperiods in hydroponics. In this study, we showed that external extra
NH4
+ led to severe growth suppression, accumulations of free NH4
+ and amino acids and increased the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in shoots of
the two Arabidopsis ecotypes. However, the levels of free NH4
+ and total amino acids increased, whereas the activities of GS, NADH-dependent glutamate synthase and GDH decreased under
the continuous light when compared with the light (16 h)–dark (8 h) cycle photoperiod. Statistical analyses suggested that
strong correlations exist among the growth reduction, accumulations of free NH4
+, total amino acids and levels of GS activity in shoots under the high NH4
+ stress regardless of the photoperiod regimes. Interestingly, under the continuous light, Col-0 showed more resistant to such
growth reduction and maintained about onefold higher capability of converting excess free NH4
+ into amino acids, with onefold higher GS activity induced by the external NH4
+ when compared with JA22. In contrast, these differences were abolished between Col-0 and JA22 under the light–dark cycle
condition. Taken together, our results conclude that the sensitivity to NH4
+ of Col-0 and JA22 is changed between the continuous light and the light–dark cycle photoperiod, which is correlative to the
alteration of the GS activity in shoots. 相似文献
14.
Nitrate Reduction in a Groundwater Microcosm Determined by 15N Gas Chromatography-Mass Spectrometry 总被引:1,自引:0,他引:1
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Aerobic and anaerobic groundwater continuous-flow microcosms were designed to study nitrate reduction by the indigenous bacteria in intact saturated soil cores from a sandy aquifer with a concentration of 3.8 mg of NO3−-N liter−1. Traces of 15NO3− were added to filter-sterilized groundwater by using a Darcy flux of 4 cm day−1. Both assimilatory and dissimilatory reduction rates were estimated from analyses of 15N2, 15N2O, 15NH4+, and 15N-labeled protein amino acids by capillary gas chromatography-mass spectrometry. N2 and N2O were separated on a megabore fused-silica column and quantified by electron impact-selected ion monitoring. NO3− and NH4+ were analyzed as pentafluorobenzoyl amides by multiple-ion monitoring and protein amino acids as their N-heptafluorobutyryl isobutyl ester derivatives by negative ion-chemical ionization. The numbers of bacteria and their [methyl-3H]thymidine incorporation rates were simultaneously measured. Nitrate was completely reduced in the microcosms at a rate of about 250 ng g−1 day−1. Of this nitrate, 80 to 90% was converted by aerobic denitrification to N2, whereas only 35% was denitrified in the anaerobic microcosm, where more than 50% of NO3− was reduced to NH4+. Assimilatory reduction was recorded only in the aerobic microcosm, where N appeared in alanine in the cells. The nitrate reduction rates estimated for the aquifer material were low in comparison with rates in eutrophic lakes and coastal sediments but sufficiently high to remove nitrate from an uncontaminated aquifer of the kind examined in less than 1 month. 相似文献
15.
M. Scott Smith 《Applied microbiology》1982,43(4):854-860
Dissimilatory reduction of NO2− to N2O and NH4+ by a soil Citrobacter sp. was studied in an attempt to elucidate the physiological and ecological significance of N2O production by this mechanism. In batch cultures with defined media, NO2− reduction to NH4+ was favored by high glucose and low NO3− concentrations. Nitrous oxide production was greatest at high glucose and intermediate NO3− concentrations. With succinate as the energy source, little or no NO2− was reduced to NH4+ but N2O was produced. Resting cell suspensions reduced NO2− simultaneously to N2O and free extracellular NH4+. Chloramphenicol prevented the induction of N2O-producing activity. The Km for NO2− reduction to N2O was estimated to be 0.9 mM NO2−, yet the apparent Km for overall NO2− reduction was considerably lower, no greater than 0.04 mM NO2−. Activities for N2O and NH4+ production increased markedly after depletion of NO3− from the media. Amendment with NO3− inhibited N2O and NH4+ production by molybdate-grown cells but not by tungstate-grown cells. Sulfite inhibited production of NH4+ but not of N2O. In a related experiment, three Escherichia coli mutants lacking NADH-dependent nitrite reductase produced N2O at rates equal to the wild type. These observations suggest that N2O is produced enzymatically but not by the same enzyme system responsible for dissimilatory reduction of NO2− to NH4+. 相似文献
16.
We compared growth kinetics of Prorocentrum donghaiense cultures on different nitrogen (N) compounds including nitrate (NO3
−), ammonium (NH4
+), urea, glutamic acid (glu), dialanine (diala) and cyanate. P. donghaiense exhibited standard Monod-type growth kinetics over a range of N concentraions (0.5–500 μmol N L−1 for NO3
− and NH4
+, 0.5–50 μmol N L−1 for urea, 0.5–100 μmol N L−1 for glu and cyanate, and 0.5–200 μmol N L−1 for diala) for all of the N compounds tested. Cultures grown on glu and urea had the highest maximum growth rates (μm, 1.51±0.06 d−1 and 1.50±0.05 d−1, respectively). However, cultures grown on cyanate, NO3
−, and NH4
+ had lower half saturation constants (Kμ, 0.28–0.51 μmol N L−1). N uptake kinetics were measured in NO3
−-deplete and -replete batch cultures of P. donghaiense. In NO3
−-deplete batch cultures, P. donghaiense exhibited Michaelis-Menten type uptake kinetics for NO3
−, NH4
+, urea and algal amino acids; uptake was saturated at or below 50 μmol N L−1. In NO3
−-replete batch cultures, NH4
+, urea, and algal amino acid uptake kinetics were similar to those measured in NO3
−-deplete batch cultures. Together, our results demonstrate that P. donghaiense can grow well on a variety of N sources, and exhibits similar uptake kinetics under both nutrient replete and deplete conditions. This may be an important factor facilitating their growth during bloom initiation and development in N-enriched estuaries where many algae compete for bioavailable N and the nutrient environment changes as a result of algal growth. 相似文献
17.
Macduff J.H. Abberton M.T. Raistrick N. Michaelson-Yeates T.P.T. 《Plant and Soil》2002,238(2):191-204
The nitrogen relations of an inbred line of white clover (Trifolium repens L.) thought to exhibit an abnormally low capacity for NO3
– uptake (line LNU) were compared with a line regarded as normal with respect to NO3
– uptake (line NNU). Growth, nodulation, N2 fixation and NO3
– uptake were measured over 7 weeks in flowing solution culture (Experiment 1) by plants dependent for N acquisition on either (i) NO3
– uptake, (ii) NO3
– uptake +N2 fixation, or (iii) N2 fixation only. Effects of plant N status on the short-term uptake and translocation of 15NH4
+ and 15NO3
– were also investigated (Experiment 2). Nitrate uptake per plant by –fix/+NO3
– line LNU was 50% of uptake by line NNU over 35 days, and there were significant differences in specific uptake rates of NO3
– between the lines over the first 24 days. The `low NO3
– uptake' phenotype was indistinct under +fix/+NO3
– treatment. Nitrate lowered specific rates of nitrogen fixation by line NNU but had no effect on line LNU. Only low N status line LNU plants had lower short-term rates of NH4
+ and NO3
– uptake than line NNU. It is concluded that the `low NO3
– uptake' phenotype of line LNU is inconsistently expressed. Circumstantial evidence points to increased NO3
– efflux and decreased xylem translocation of NO3
– as possible explanations for the lower NO3
– uptake by line LNU. 相似文献
18.
In vitro weathering of phlogopite by ectomycorrhizal fungi 总被引:1,自引:0,他引:1
Oxalate accumulation in external medium under hyphal mats of two ectomycorrhizal species is strongly stimulated (1.7 to 35 fold) by a simultaneous depletion of available K+ and Mg2+. Pisolithus tinctorius strain 441 accumulates oxalate both on NH4–N and on NO3–N whereas Paxillus involutus strain COU only accumulates oxalate on NO3–N. On NO3–N, under a simultaneous K+ and Mg2+ deficiency, P. involutus COU is a very active oxalate producer compared to P. tinctorius 441. The present results could explain the various mineralogical evolutions of a phlogopite mica previously recorded under P. involutus COU or P. tinctorius 441 and suggest a key role for fungal oxalic acid during mineral weathering in response to nutrient deficiency. 相似文献
19.
Summary Soybean plants were grown in nutrient culture solutions containing 150 ppm of N either as an equal concentration of NH4
+ or NO3
–, or all NO3
–. At the R2 stage of growth for some plants, the N form was changed to either all NO3
– or all NH4
+, but at the same total N concentration as before. Highest seed yield was obtained with all NO3
– over the entire growth period, the poorest when the N form was switched from an equal ratio of NH4
+ and NO3
– to all NH4
+ at the R2 stage. Kjeldahl N concentrations in the plant leaves and seed were highest when NH4
+ was part or all of the N source in the nutrient solution. These results may partially explain why the literature is inconsistent on the effect of added fertilizer N on soybean seed yield, and may pose a problem in using leaf Kjeldahl N concentration to determine plant N sufficiency. 相似文献
20.
Nitrous Oxide Emission Associated with Autotrophic Ammonium Oxidation in Acid Coniferous Forest Soil 总被引:4,自引:3,他引:1
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Pertti J. Martikainen 《Applied microbiology》1985,50(6):1519-1525
Aerobic N2O production was studied in nitrifying humus from urea-fertilized pine forest soil. Acetylene and nitrapyrin inhibited both NH4+ oxidation and N2O production, indicating that N2O production was closely associated with autotrophic NH4+ oxidation. N2O production was enhanced by low soil pH; it was negligible above pH 4.7. When soil pH decreased from 4.7 to 4.1, the relative amount of N2O-N produced from NH4+-N oxidized increased exponentially to 20%. There was also some evidence that N2O formation was stimulated by salts (potassium sulfate and sodium phosphates). The maximum rate of N2O-N production was 0.17 μg of N2O-N per g of soil per h. When humus was treated with NO2−, N2O evolved immediately, indicating chemical formation, but no N2O was formed on the addition of NO3−. The amount of N2O-N evolved was 0.6 to 4.6% of NO2−-N added. A high concentration of NO2− and low soil pH enhanced chemical production of N2O. There was no accumulation of NO2− during nitrification. The calculations indicated that chemical formation of N2O was not the main source of N2O during NH4+ oxidation. After the addition of inhibitors of NH4+ oxidation the soils contained NO3−, but no N2O was produced. The results suggest that enhanced autotrophic NH4+ oxidation is a potential source of N2O in fertilized acid forest soil. 相似文献