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1.
Carolina Reyes Dominik Schneider Marko Lipka Andrea Thürmer Michael E. Böttcher Michael W. Friedrich 《Marine biotechnology (New York, N.Y.)》2017,19(2):175-190
In this study, we analysed metagenomes along with biogeochemical profiles from Skagerrak (SK) and Bothnian Bay (BB) sediments, to trace the prevailing nitrogen pathways. NO3 ? was present in the top 5 cm below the sediment-water interface at both sites. NH4 + increased with depth below 5 cm where it overlapped with the NO3 ? zone. Steady-state modelling of NO3 ? and NH4 + porewater profiles indicates zones of net nitrogen species transformations. Bacterial protease and hydratase genes appeared to make up the bulk of total ammonification genes. Genes involved in ammonia oxidation (amo, hao), denitrification (nir, nor), dissimilatory NO3 ? reduction to NH4 + (nfr and otr) and in both of the latter two pathways (nar, nap) were also present. Results show ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) are similarly abundant in both sediments. Also, denitrification genes appeared more abundant than DNRA genes. 16S rRNA gene analysis showed that the relative abundance of the nitrifying group Nitrosopumilales and other groups involved in nitrification and denitrification (Nitrobacter, Nitrosomonas, Nitrospira, Nitrosococcus and Nitrosomonas) appeared less abundant in SK sediments compared to BB sediments. Beggiatoa and Thiothrix 16S rRNA genes were also present, suggesting chemolithoautotrophic NO3 ? reduction to NO2 ? or NH4 + as a possible pathway. Our results show the metabolic potential for ammonification, nitrification, DNRA and denitrification activities in North Sea and Baltic Sea sediments. 相似文献
2.
Tomato growth was examined in solution culture under constant pH and low levels of NH4+ or NO3?. There were five nitrogen treatments: 20 mmoles m?3 NH4+, 50 mmoles m?3 NO3?, 100 mmoles m?3 NH4+ 200 mmoles m?3 NO3?, and 20 mmoles m?3 NH4++ 50 mmoles m?3 NO3?. The lower concentrations (20 mmoles m?3 NH4+ and 50 mmoles m?3 NO3?) were near the apparent Km for net NH4+ and NO3? uptake; the higher concentrations (100 mmoles m?3 NH4+ and 200 mmoles m?3 NO3?) were near levels at which the net uptake of NH4+ or NO3? saturate. Although organic nitrogen contents for the higher NO3? and the NH4++ NO3? treatments were 22.2–30.3% greater than those for the lower NO3? treatment, relative growth rates were initially only 10–15% faster. After 24 d, relative growth rates were similar among those treatments. These results indicate that growth may be only slightly nitrogen limited when NH4+ or NO3? concentrations are held constant over the root surface at near the apparent Km concentration. Relative growth rates for the two NH4+ treatments were much higher than have been previously reported for tomatoes growing with NH4+ as the sole nitrogen source. Initial growth rates under NH4+ nutrition did not differ significantly (P≥ 0.05) from those under NO3? or under combined NH4++ NO3?. Growth rates slowed after 10–15 d for the NH4+ treatments, whereas they remained more constant for the NO3? and mixed NH4++ NO3? treatments over the entire observation period of 24–33 d. The decline in growth rate under NH4+ nutrition may have resulted from a reduction in Ca2+, K+, and/or Mg2+ absorption. 相似文献
3.
The dependence of substrate saturated uptake of 15NH4+, 15NO3?, 32PO43?, and 14CO2 on photosynthetic photon flux density (PPFD or photsynthetically active radiation, 400–700 nm) was characterized seasonally in oligotrophic Flathead Lake, Montana. PO43? uptake was not dependent upon PPFD at any time of the year, whereas NH4+, NO3?, and CO2 uptake were consistently dependent on PPFD over all seasons. Maximal rates of NH4+, NO3? and CO2 uptake usually occurred near 40% of surface PPFD, which corresponded to about 5 m in the lake; inhibition was evident at PPFD levels greater than 40%. NH4+, NO3? and PO43? were incorporated in the dark at measurable rates most of the year, whereas dark CO2 uptake was always near 0 relative to light uptake. CO2 and NO3? uptake were more strongly influenced by PPFD than was NH43? uptake. The PPFD dependence of PO43?, NH4+, NO3? and CO2 uptake may affect algal growth and nutrient status by influencing the balance in diel and seasonal C:N:P uptake ratios. 相似文献
4.
Denitrification and nitrous oxide effluxes in boreal, eutrophic river sediments under increasing nitrate load: a laboratory microcosm study 总被引:1,自引:0,他引:1
Hanna Silvennoinen Anu Liikanen Jouni Torssonen C. Florian Stange Pertti J. Martikainen 《Biogeochemistry》2008,91(2-3):105-116
Intact sediment cores from rivers of the Bothnian Bay (Baltic Sea) were studied for denitrification based on benthic fluxes of molecular nitrogen (N2) and nitrous oxide (N2O) in a temperature controlled continuous water flow laboratory microcosm under 10, 30, 100, and 300 μM of 15N enriched nitrate (NO3 ?, ~98 at. %). Effluxes of both N2 and N2O from sediment to the overlying water increased with increasing NO3 ? load. Although the ratio of N2O to N2 increased with increasing NO3 ? load, it remained below 0.04, N2 always being the main product. At the NO3 ? concentrations most frequently found in the studied river water (10–100 μM), up to 8% of the NO3 ? was removed in denitrification, whereas with the highest concentration (300 μM), the removal by denitrification was less than 2%. However, overall up to 42% of the NO3 ? was removed by mechanisms other than denitrification. As the microbial activity was simultaneously enhanced by the NO3 ? load, shown as increased oxygen consumption and dissolved inorganic carbom efflux, it is likely that a majority of the NO3 ? was assimilated by microbes during their growth. The 15N content in ammonium (NH4 +) in the efflux was low, suggesting that reduction of NO3 ? to NH4 + was not the reason for the NO3 ? removal. This study provides the first published information on denitrification and N2O fluxes and their regulation by NO3 ? load in eutrophic high latitude rivers. 相似文献
5.
Nitrogen retention in soil organic matter (SOM) is a key process influencing the accumulation and loss of N in forest ecosystems, but the rates and mechanisms of inorganic N retention in soils are not well understood. The primary objectives of this study were to compare ammonium (NH4+), nitrite (NO2?), and nitrate (NO3?) immobilization among soils developed under different tree species in the Catskill Mountains of New York State, and to determine the relative roles of biotic or abiotic processes in soil N retention. A laboratory experiment was performed, where 15N was added as NH4+, NO2?, or NO3? to live and mercury‐treated O horizon soils from three tree species (American beech, northern red oak, sugar maple), and 15N recoveries were determined in the SOM pool. Mercuric chloride was used to treat soils as this chemical inhibits microbial metabolism without significantly altering the chemistry of SOM. The recovery of 15N in SOM was almost always greater for NH4+ (mean 20%) and NO2? (47%) than for NO3? (10%). Ammonium immobilization occurred primarily by biotic processes, with mean recoveries in live soils increasing from 9% at 15 min to 53% after 28 days of incubation. The incorporation of NO2? into SOM occurred rapidly (<15 min) via abiotic processes. Abiotic immobilization of NO2? (mean recovery 58%) was significantly greater than abiotic immobilization of NH4+ (7%) or NO3? (7%). The incorporation of NO2? into SOM did not vary significantly among tree species, so this mechanism likely does not contribute to differences in soil NO3? dynamics among species. As over 30% of the 15NO2? label was recovered in SOM within 15 min in live soils, and the products of NO2? incorporation into SOM remained relatively stable throughout the 28‐day incubation, our results suggest that NO2? incorporation into SOM may be an important mechanism of N retention in forest soils. The importance of NO2? immobilization for N retention in field soils, however, will depend on the competition between incorporation into SOM and nitrification for transiently available NO2?. Further research is required to determine the importance of this process in field environments. 相似文献
6.
Abstract A 16-channel fully automated microcomputer-based system was designed to measure the disappearance of NO?3 NO?2 and NH+4 simultaneously from uptake solutions. The analyses were done using high-performance liquid chromatography. Statistical procedures were used to generate transport kinetics and interactions amongst NO?3, NO?2 and NH+4 by intact wheat seedlings. The simultaneous analysis of NO?3, NO?2 and NH+4 at real-time; the accommodation of varying sampling intervals; the capability to study up to 16 experimental units in synchrony; and the analysis of the data with a microcomputer, make this a powerful system for studying transport kinetics and interactions. 相似文献
7.
Gaston E. Small James B. Cotner Jacques C. Finlay Rebecca A. Stark Robert W. Sterner 《Hydrobiologia》2014,731(1):95-108
The capacity of a lake to remove reactive nitrogen (N) through denitrification has important implications both for the lake and for downstream ecosystems. In large oligotropic lakes such as Lake Superior, where nitrate (NO3 ?) concentrations have increased steadily over the past century, deep oxygen penetration into sediments may limit the denitrification rates. We tested the hypothesis that the position of the redox gradient in lake sediments affects denitrification by measuring net N-fluxes across the sediment–water interface for intact sediment cores collected across a range of sediment oxycline values from nearshore and offshore sites in Lake Superior, as well as sites in Lake Huron and Lake Erie. Across this redox gradient, as the thickness of the oxygenated sediment layer increased from Lake Erie to Lake Superior, fluxes of NH4 + and N2 out of the sediment decreased, and sediments shifted from a net sink to a net source of NO3 ?. Denitrification of NO3 ? from overlying water decreased with thickness of the oxygenated sediment layer. Our results indicate that, unlike sediments from Lake Erie and Lake Huron, Lake Superior sediments do not remove significant amounts of water column NO3 ? through denitrification, likely as a result of the thick oxygenated sediment layer. 相似文献
8.
Nitrification and Denitrification in Lake and Estuarine Sediments Measured by the 15N Dilution Technique and Isotope Pairing 总被引:1,自引:0,他引:1
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Sren Rysgaard Nils Risgaard-Petersen Lars Peter Nielsen Niels Peter Revsbech 《Applied microbiology》1993,59(7):2093-2098
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. 相似文献
9.
Influence of bioturbation on denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in freshwater sediments 总被引:2,自引:0,他引:2
Intensive agriculture leads to increased nitrogen fluxes (mostly as nitrate, NO3 ?) to aquatic ecosystems, which in turn creates ecological problems, including eutrophication and associated harmful algal blooms. These problems have focused scientific attention on understanding the controls on nitrate reduction processes such as denitrification and dissimilatory nitrate reduction to ammonium (DNRA). Our objective was to determine the effects of nutrient-tolerant bioturbating invertebrates (tubificid oligochaetes) on nitrogen cycling processes, specifically coupled nitrification–denitrification, net denitrification, DNRA, and biogeochemical fluxes (O2, NO3 ?, NH4 +, CO2, N2O, and CH4) in freshwater sediments. A mesocosm experiment determined how tubificid density and increasing NO3 ? concentrations (using N15 isotope tracing) interact to affect N cycling processes. At the lowest NO3 ? concentration and in the absence of bioturbation, the relative importance of denitrification to DNRA was similar (i.e., 49.6 and 50.4 ± 8.1 %, respectively). Increasing NO3 ? concentrations in the control cores (without fauna) stimulated denitrification, but did not enhance DNRA, which significantly altered the relative importance of denitrification compared to DNRA (94.6 vs. 5.4 ± 0.9 %, respectively). The presence of tubificid oligochaetes enhanced O2, NO3 ?, NH4 + fluxes, greenhouse gas production, and N cycling processes. The relative importance of denitrification to DNRA shifted towards favoring denitrification with both the increase in NO3 ? concentrations and the increase of bioturbation activity. Our study highlights that understanding the interactions between nutrient-tolerant bioturbating species and nitrate contamination is important for determining the nitrogen removal capacity of eutrophic freshwater ecosystems. 相似文献
10.
The growth of Salvinia molesta D.S. Mitchell was studied in a greenhouse using controlled-temperature water-baths at 16, 19 and 22°C and 4 different nitrogen compounds (NO3?, NH4+, NH4NO3 and urea) at levels up to 60 mg N l?1. Little growth occurred at 16°C even if 20 mg N l?1 was supplied together with other nutrients including phosphorus (2 mg H2PO4-P l?1). The highest relative growth rate and total dry matter production occurred at 22°C when plants were supplied with 20 mg NH4-N l?1. At this temperature, the NH4+ ion was superior to the NO3? ion or urea as a nitrogen source (almost doubling the biomass), but was not significantly better than NH4NO3. Over a period of 19 days for plants receiving 0.02 mg NH4-N l?, biomass increased 4-fold at 16°C, 9-fold at 19°C and 10-fold at 22°C. In contrast, for plants receiving 20 mg NH4-N l?1, biomass increased 4-fold at 16°C, 18-fold at 19°C and 38-fold at 22°C. 相似文献
11.
The mechanisms of action of the known inhibitors of gastric acid secretion such as SCN?, OCN?, NO2?, and NH4+ (M. E. LeFevre, E. J. Gohmann, Jr. and W. S. Rehm, 1964, Amer. J. Physiol.207, 613–618) were investigated using isolated pig gastric microsomal vesicles as a model system. The gastric microsomal vesicles enriched in (H+ + K+)-ATPase have previously been demonstrated to accumulate H+ in exchange for K+. The vesicular accumulation of acridine orange, which is a measure of H+ uptake, shows sigmoidal kinetics in the presence of increasing K+ with a Hill coefficient of 2.27 and a S50 of 19.05 mm. None of those agents affects the microsomal (H+ + K+)-ATPase activity, although they inhibit vesicular H+ transport in a dose-dependent manner; the order of efficacy being NH4+ > SCN? > OCN? > NO2?. The inhibitory effects of NH4+ on vesicular H+ transport appear to be due to neutralization of the transported H+ by freely permeable NH3 generated from the dissociation of NH4+ in the bulk medium. SCN?, OCN?, and NO2? appear to work by a different mechanism. These agents do not act as protonophores. Our data demonstrate that the presence of SCN?, OCN?, and NO2? within the vesicle interior are essential for exerting their inhibitory effects. Furthermore, the inhibitory effects of SCN? and OCN? on vesicular H+ transport could be reversed by an elevation of intravesicular K+. Our data strongly suggest that the effects of SCN?, OCN?, and NO2? are exerted by interfering with a low-affinity K+ site (S50 = 19.05 mm) within the domain of the gastric ATPase complex. This low-affinity K+ site is accessible only from the vesicle interior and appears to be essential for the vectorial transport of H+ by the gastric microsomal (H+ + K+)-ATPase system. 相似文献
12.
NH4+ and NO3? uptake were measured by continuous sampling with an autoanalyzer. For Hypnea musciformis (Wulfen) Lamouroux, NO3?up take followed saturable kinetics (K2=4.9 μg-at N t?1, Vmax= 2.85 μg- at N, g(wet)?1. h?1. The ammonium uptake data fit a trucatd hyperbola, i.e., saturation was not reach at the concentrations used. NO3? uptake was reduced one-half in the presence of NH4+, but presence of NO3? had no effect on NH4+ uptake. Darkness reduced both NO3? and NH4+ uptake by one-third to one-half. For Macrocystis pyrufera (L) C. Agardh, NO3? uptake followed saturable kinetices: K2=13.1 μg-at N. l?1. Vmax=3.05 μg-at N. g(wet)?1. h?1.NH4+ uptake showed saturable kinetics at concentration below 22 μg-at N l -1 (K2=5.3 μg-at N.1–1, Vmax= 2.38 μg-at N G (wet)?1.h?1: at higher concentration uptake increased lincarly with concentrations. NO3?and NH4+ were taken up simulataneously: presence of one form did not affect uptake of the other. 相似文献
13.
Vibha Sinha N. Arul Manikandan Rakhi Chaturvedi 《International journal of phytoremediation》2017,19(11):1007-1016
Discharge of wastewater from electroplating and leather industries is a major concern for the environment due to the presence of toxic Cr6+ and other ions, such as sulfate, nitrate, phosphate, etc. This study evaluated the potential of Tradescantia pallida, a plant species known for its Cr bioaccumulation, for the simultaneous removal of Cr6+, SO42?, NO3?, and PO43?. The effect of different co-ions on Cr6+ removal by T. pallida was examined following the Plackett-Burman design of experiments carried out under batch hydroponics conditions. The results revealed a maximum removal of 84% Cr6+, 87% SO42?, 94% NO3? and 100% PO43? without any phytotoxic effect on the plant for an initial Cr6+ concentration in the range 5–20 mg L?1. SO42? and NO3? enhanced Cr uptake at a high initial Cr concentration (20 mg L?1), whereas PO43? did not affect Cr uptake both at high and low initial Cr concentrations. The Cr6+ removal kinetics in the presence of different ions was well described by the pseudo-second-order kinetic model which revealed that both biosorption and bioaccumulation of the metal played an important role in Cr6+ removal. Increase in the total carbohydrate and protein content of the plant following Cr6+ and co-ions exposure indicated a good tolerance of the plant toward Cr6+ toxicity. Furthermore, enhancement in the lipid peroxidation and catalase activity in T. pallida upon Cr6+ exposure revealed a maximum stress-induced condition in the plant. Overall, this study demonstrated a very good potential of the plant T. pallida for Cr6+ removal from wastewater even in the presence of co-ions. 相似文献
14.
In the presence of purified nitrate reductase (NR) and 1 mM NADH, illuminated pea chloroplasts catalysed reduction of NO3? to NH3 with the concomitant evolution of O2. The rates were slightly less than those for reduction of NO2? to NH3 and O2, evolution by chloroplasts in the absence of NR and NADH (ca 6 μg atoms N/mg Chl/hr). Illuminated chloroplasts quantitatively reduced 0.2 mM oxaloacetate (OAA) to malate. In the presence of an extrachloroplast malate-oxidizing system comprised of NAD-specific malate dehydrogenase (NAD-MDH), NAD, NR and NO3?, illuminated chloroplasts supported OAA-dependent reduction of NO3? to NH3 with the evolution of O2. The reaction did not proceed in the absence of any of these supplements or in the dark but malate could replace OAA. The results are consistent with the reduction of NO3?by reducing equivalents from H2O involving a malate/OAA shuttle. The ratios for O2, evolved: C4-acid supplied and N reduced: C4-acid supplied in certain experiments imply recycling of the C4-acids. 相似文献
15.
Michael W. Lomas Patricia M. Gilbert Gry M. Berg Michele Burford 《Journal of phycology》1996,32(6):907-916
Nitrogen uptake studies were conducted during an aestival “brown tide” bloom in Shinnecock Bay, Long Island, New York. The same station was sampled in late July and mid-August 1995 when Aureococcus anophagefferens composed >90% and 30–40% of the total cell density, respectively. Experiments were designed to examine the effect of incubation duration on the uptake kinetics, and the effect of light and temperature dependencies of NH4+, urea, and NO3? uptake. Maximum specific uptake rates (V'max) decreased in the order NH4+, urea, NO3? and were nonlinear with time for NH4+ and urea, both of which exhibited an exponential decline between 1 and 10 min and then did nut significantly change for 60 min. Nitrogen uptake kinetic experiments exhibited a typical hyperbolic response for urea and NO3?. Half-saturation constants. (Ks) were calculated to he 0.03 and 0.12 μmol · L?1 for urea and NO3?; respectively, but could not be calculated for NH4+ under these experimental conditions. Nutrient uptake rate versus, irradiance (NI) experiments showed that maximum uptake rates occurred at ≤% of incident irradiance on both sampling dates and that values of V′max-cell (NH4+) were on average 30% greater than V′max-cell (urea). A7°–9°C temperature decrease in incubation temperature between the two NI experiments in August resulted in a 30% decrease in V′max-cell(NH4+), no change in V′max-cell(urea), and a 3–4-fold decrease in calculated Klt values for both NH4+ and urea. The results from these experiments demonstrate that A. anophagefferens has a higher affinity for NH4+ and urea than for NO3? and that this particular species is adapted to use these substrates at low irradiances and concentrations. The data presented in this study are also consistent with the hypothesis that A. anophagefferens may be an oceanic clone that was displaced by an anomalous oceanographic event. 相似文献
16.
Hydrogeochemical evolution and risk assessment of human health in a riverbank filtration site,northeastern China 总被引:1,自引:0,他引:1
Intensive agriculture and industrial activities have resulted in contamination in rivers and groundwater quality, which threatens human health. In this study, we used comprehensive physiochemical indicators to assess the quality of groundwater used for drinking and irrigation in addition to the potential risks to local residents in a riverbank filtration site. Human health risks through drinking water intake and dermal contact were also estimated. Moreover, we analyzed the spatial distribution regularities of health risk values in a riverbank filtration site. The assessment results revealed that NH4–N, NO2–N, F?, Mn, and As are main contaminants affecting groundwater quality and that 62% of the total samples is suitable for a variety of purposes. All groundwater in the study area is suitable for irrigation based on the sodium adsorption ratio (SAR), residual sodium carbonate (RSC), Na percentage (%Na), and U.S. Salinity Laboratory (USSL) and Wilcox diagrams. The health risk assessment suggests that residents in the study area are at high health risk, and women and children face higher risk than men in both non-carcinogenic and carcinogenic risks. The spatial distribution regularities of health risk values suggest that the human health risk value of each groundwater sample is different in the study area and has certain regularity. Therefore, effective measurements must be taken to address the groundwater contamination and to reduce the human health risks. 相似文献
17.
A. M. Enitan-Folami N. Mutileni J. O. Odiyo F. M. Swalaha J. N Edokpayi 《人类与生态风险评估》2020,26(8):2044-2058
Abstract Potential effects of anthropogenic activities on different boreholes around Thulamela Municipality, South Africa, were evaluated by quantifying the bacteria indicators and physicochemical parameters during summer, autumn, and winter. The purpose was to determine whether the borehole water in this region is safe for domestic use across the seasons. The concentrations of physicochemical (Temperature, pH, electrical conductivity (EC), turbidity, and nitrate) and bacteriological (both Escherichia coli and Enterococcus faecalis) contaminants in the borehole water samples were determined using standard microbiology methods. The mean concentration of NO3 for most of the boreholes failed to comply with the recommended guidelines throughout the season. High microbial load of E. coli (2.0?×?101 – 4.6?×?103 CFU/100?ml) and E. faecalis (2.0?×?10° – 6.0?×?102 CFU/100?ml) was recorded in the wet season than in the dry season (0.0 – 7.0?×?102 and 0.0 – 1.0?×?101 CFU/100?ml, respectively). Sanitary inspection and water source classification showed that most boreholes are prone to chemical contaminants during summer and autumn due to rainfall and this correlates with the measured microbial contamination. The result is significantly important because water from these boreholes is used for domestic purposes without treatment and could pose major public health risks to the consumers. 相似文献
18.
Xiao Fan Dong Xu Yitao Wang Xiaowen Zhang Shaona Cao Shanli Mou Naihao Ye 《Journal of applied phycology》2014,26(1):537-544
The green-tide macroalga, Ulva prolifera, was tested in the laboratory to determine its nutrient uptake and photosynthesis under different conditions. In the nutrient concentration experiments U. prolifera showed a saturated uptake for nitrate but an escalating uptake in the tested range for phosphorus. Both N/P and NO3 ?/NH4 + ratios influenced nutrient uptake significantly (p?<?0.05) while the PSII quantum yield [Y(II)] (p?>?0.05) remained unaffected. The maximum N uptake rate (33.9?±?0.8 μmol g?1 DW h?1) and P uptake rate (11.1?±?4.7) was detected at N/P ratios of 7.5 and 2.2, respectively. U. prolifera preferred NH4 +-N to NO3 ?-N when the NO3 ?-N/NH4 +-N ratio was less than 2.2 (p?<?0.05). But between ratios of 2.2 and 12.9, the uptake of NO3 ?-N surpassed that of NH4 +-N. In the temperature experiments, the highest N uptake rate and [Y(II)] were observed at 20 °C, while the lowest rates were detected at 5 °C. P uptake rates were correlated with increasing temperature. 相似文献
19.
Fu-Cang Zhang Shao-Zhong Kang Fu-Sheng Li Jian-Hua Zhang 《植物学报(英文版)》2007,49(4):455-462
In the present study, we investigated whether growth and main nutrient ion concentrations of cabbage (Brassica campestris L.) could be increased when plants were subjected to different NH4^+/NO3- ratios. Cabbage seedlings were grown in a greenhouse in nutrient solutions with five NH4^+/NO3- ratios (1:0; 0.75:0.25; 0.5:0.5; 0.25:0.75; and 0:1). The results showed that cabbage growth was reduced by 87% when the proportion of NH4^+-N in the nutrient solution was more than 75% compared with a ratio NH4^+/NO3- of 0.5:0.5 35 d after transplanting, suggesting a possible toxicity due to the accumulation of a large amount of free ammonia in the leaves. When the NH4+/NO3- ratio was 0.5:0.5, fresh seedling weight, root length, and H2PO4- (P), K^+, Ca^2+, and Mg^2+ concentrations were all higher than those in plants grown under other NH4^+/NO3- ratios. The nitrate concentration in the leaves was the lowest in plants grown at 0.5: 0.5 NH4^+/NO3-. The present results indicate that an appropriate NH4^+/NO3- ratio improves the absorption of other nutrients and maintains a suitable proportion of N assimilation and storage that should benefit plant growth and the quality of cabbage as a vegetable. 相似文献
20.
A planktonic alga similar in general morphology and pigments to Aureococcus anophagefferens Hargraves and Sieburth has caused persistent and ecologically damaging blooms along the south Texas coast. Experiments using 100 μM NO3?, NO2?, and NH4+ demonstrated that the alga could not use NO3? for growth but could use NO2? and NH4+. Doubling iron or trace metal concentrations did not permit growth on NO3?. Chemical composition data for cultures grown in excess NO3? or NH4+, respectively, were as follows: N·cell?1 (0.88 vs. 1.3 pg), C:N ratio (25:1 vs. 6.4:1), C:chlorophyll a (chl a) (560:1 vs. 44:1), and chl a·cell?1 (0.033 vs. 0.16 pg). These data imply that cells supplied with NO3? were N-starved. Culture addition of 10 mM final concentration chlorate (a nitrate analog) did not affect the Texas isolate while NO3? utilizing A. anophagefferens was lysed, suggesting that the NO3? reductase of the Texas isolate is nonfunctional. Rates of primary productivity determined during a dense bloom indicated that light-saturated growth rates were ca. 0.45 d?1, which is similar to maximum rates determined in laboratory experiments (0.58 d?1± 0.16). However, chemical composition data were consistent with the growth rate of these cells being limited by N availability (C:N 28, C:chl a 176, chl a·cell?1 0.019). Calculations based on a mass balance for nitrogen suggest that the bloom was triggered by an input of ca. 69 μM NH4+ that resulted from an extensive die-off of benthos and fish. 相似文献