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1.
Ditylum brightwellii grown on NO2- as a nitrogen source took up and assimilated NO2- only in the light, apparently via a photosynthetic nitrite reductase. Assimilation was inhibited by dichlorophenyldimethylurea (DCMU), KCN, partially by 2,4 dinitrophenol, and by NO3-. Kinetics of inhibition of NO2- assimilation by NO3- appeared to be “competitive.” D. brightwellii cells grown on NO2- took up NO3- in both light and dark and in both cases the uptake was inhibited by p-chloromercuribenzoate, but not by DCMU, KCN, or by NO2-. Most of the NO3- taken up in the dark was recovered unchanged from the cells. However only 40% of NO3- taken up in light was recovered from the cells and no NO2- was found. This suggests that a photosynthetic nitrate reduction mechanism was active in these cells. DCMU inhibited the light-induced NO3- reduction. This mechanism of NO3- reduction is distinct from that involving NADH nitrate reductase in D. brightwellii since the concentration of the latter enzyme is very low in cells grown on NO2-. Saturation kinetics were observed for NO2- and NO3- uptake. Half-saturation concentrations (Ksvalues) were 4 and 2 μM, respectively. These values are compared with those obtained for NO2- and NO3- assimilation by other unicellular algae. The comparisons show lower Ksvalues in oceanic species compared with tide-pool or freshwater algae and they support the idea that Ksvalues for NO3- assimilation may provide a key to understanding species succession when this is due to declining: nitrate concentrations in the sea. 相似文献
2.
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
3.
Short-term (within 5 min) and long-term (≤2 h) rates of nitrate uptake were determined for the marine diatoms, Nitschiella longissima (Cleve), Skeletonema costatum (Greville) Cleve and Asterionella japonica (Cleve). Pigment levels, cell carbon, nitrogen and cell volume were also determined for cells in the logarithmic and stationary phases of growth. For each species, one clone isolated from oligotrophic coastal water and one clone isolated from eutrophic coastal water were compared. Long-term NO3? uptake typically followed saturation kinetics describable by the Michaelis-Menten expression. Under experimental conditions, half-saturation constants ranged from 0.6 to 2.2 μM NO3?. Generally, the oligotrophic clones had lower Ks and Vmax (on a per cell basis) than their eutrophic counterparts, though this was only statistically significant in one pair of clones. Eutrophic and oligotrophic clones also differed in their short-term response to nutrient addition; oligotrophic clones showed greatest rate of uptake at the lowest nitrate addition while uptake by eutrophic clones increased with increasing nitrate concentration. However, all clones had very similar Vmax values expressed on a dry weight basis. Under N-starvation, cellular C and pigment levels (and N to a lesser extent) generally declined more in eutrophic than in oligotrophic clones. While the differences between inshore and offshore clones were not great, the results are consistent with the hypothesis that eutrophic waters support algae which grow faster and are less conservative biochemically than cells in oligotrophic waters. 相似文献
4.
Rates of NH4+ and NO3? uptake were determined by accumulation of 15N in plant tissue and by disappearance of nutrient from the medium. Agreement between rates calculated by the two methods was good, averaging 82.7% (SD = 15.8%) and 91.2% (SD = 13.7%) for NH4+ and NO3? uptake, respectively. An average of 93.4 and 96.0% of added 15NH4+ and 15NO3? was recovered from the medium and /or plant tissue at the end of the incubations. Both bacterial uptake and regeneration of NH4+ may contribute to discrepancies between NH4+ uptake rates calculated by 15N accumulation and disappearance of NH4+ from the medium. The influence of tissue composition on uptake of NH4+, NO3? and PO43- by Enteromorpha prolifera (Müller) J. Agardh was examined. For NH4+ uptake, Vmax was 188 μmol NH4+. g dry wt?1. h?1 and Ks ranged from 9.3 to 13.4 μM, but there was no correlation between kinetic parameters and tissue nitrogen content. For NO3?, both kinetic parameters were higher for plants with low tissue nitrogen than for plants with high tissue nitrogen. Maximum rates were 169 and 75.4 μmol NO3?. g dry wt?1. h?1, and Ks was 13.3 and 2.31 μM for low and high tissue nitrogen plants, respectively. Estimates of uptake in the field suggested that NH4+ accounted for 65% and NO3? for up to 35% of total nitrogen uptake during the summer. Nutrient uptake rates of field-collected plants also indicated that E. prolifera in Yaquina Bay, Oregon was not likely to have been nitrogen-limited, but may have been phosphorus-limited. 相似文献
5.
Kinetic parameters of nitrate uptake by different catch crop species: effects of low temperatures or previous nitrate starvation 总被引:8,自引:0,他引:8
The pollution of aquifers by NO?3 in temperate environments is aggravated by farming practices that leave the ground bare during winter. The use of catch crops during this time may decrease nitrate loss from the soil. Nitrate uptake by several catch crop species (Brassica napus L., Sinapis alba L., Brassica rapa L., Raphanus sativus L., Trifolium alexandrinum L., Trifolium incarnatum L., Phacelia tanacetifolia Benth., Lolium perenne L., Lolium multiflorum Lam. and Secale cereale L.) was here studied in relation to transpiration rate and low temperatures applied to the whole plant or to roots only. The Michaelis constant (Km), maximum uptake rate (Vmax), time of induction and contributions of inducible and constitutive mechanisms were estimated from measurements of NO?3 depletion in the uptake medium. There were large differences between species, with Km (μM) values ranging between 5.12 ± 0.64 (Trifolium incarnatum) and 36.4 ± 1.97 (Lolium perenne). Maximum NO?3 uptake rates expressed per unit root weight were influenced by ageing, temperature and previous NO?3 nutrition. They were also closely correlated with water flow through the roots and with shoot/root ratio of these species. The combined results from all species and treatments showed that Vmax increased with shoot/root ratio, suggesting a regulatory role for the shoots in NO?3 uptake. Overall, the results showed a great diversity in NO?3 uptake characteristics between species in terms of kinetic parameters, contribution of the constitutive system (100% of total uptake in ryegrass, nil in Fabaceae) and time of induction. 相似文献
6.
The modelling of ion uptake by plants requires the measurement of kinetic and growth parameters under specific conditions.
The objective of this study was to evaluate the effect of nine NH
inf4
sup+
:NO
inf3
sup−
ratios on onions (Allium cepa L.). Twenty-eight to 84 day-old onion plants were treated with NH
inf4
sup+
:NOf3/sup− ratios ranging from 0 to 100% of each ionic species in one mM solutions in a growth chamber. Maximum N influx (Imax) was assessed using the N depletion method. Except at an early stage, ionic species did not influence significantly Imax, the Michaelis constant (Km) and the minimum concentration for net uptake (Cmin). Imax for ammonium decreased from 101 to 59 pmole cm-2 s-1 while Imax for nitrate increased from 26 to 54 pmole cm-2 s-1 as the plant matured. On average, Km and Cmin values were 14.29 μM, and 5.06 μM for ammonium, and 11.90 μM and 4.54 μM for nitrate, respectively. In general, the effect of NH4
+:NO3
- ratios on root weight, shoot weight and total weight depended on plant age. At an early stage, maximum plant growth and N
uptake were obtained with ammonium as the sole source of N. At later stages, maximum plant growth and N uptake were obtained
as the proportion of nitrate increased in the nutrient solution. The was no apparent nutrient deficiency whatever NH4
+:NO3
- ratio was applied, although ammonium reduced the uptake of cations and increased the uptake of phosphorus.
The research was supported by the Natural Sciences and Engineering Research Council of Canada. 相似文献
7.
The Influence of Nitrate and Chloride Uptake on Expressed Sap pH, Organic Acid Synthesis, and Potassium Accumulation in Higher Plants 总被引:10,自引:8,他引:2
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The influence of NO3− uptake and reduction on ionic balance in barley seedlings (Hordeum vulgare, cv. Compana) was studied. KNO3 and KCl treatment solutions were used for comparison of cation and anion uptake. The rate of Cl− uptake was more rapid than the rate of NO3− uptake during the first 2 to 4 hours of treatment. There was an acceleration in rate of NO3− uptake after 4 hours resulting in a sustained rate of NO3− uptake which exceeded the rate of Cl− uptake. The initial (2 to 4 hours) rate of K+ uptake appeared to be independent of the rate of anion uptake. After 4 hours the rate of K+ uptake was greater with the KNO3 treatment than with the KCl treatment, and the solution pH, cell sap pH, and organic acid levels with KNO3 increased, relative to those with the KCl treatment. When absorption experiments were conducted in darkness, K+ uptake from KNO3 did not exceed K+ uptake from KCl. We suggest that the greater uptake and accumulation of K+ in NO3−-treated plants resulted from (a) a more rapid, sustained uptake and transport of NO3− providing a mobile counteranion for K+ transport, and (b) the synthesis of organic acids in response to NO3− reduction increasing the capacity for K+ accumulation by providing a source of nondiffusible organic anions. 相似文献
8.
Louise T. Kregting Catriona L. Hurd Conrad A. Pilditch Craig L. Stevens 《Journal of phycology》2008,44(2):320-330
The influence of seawater velocity (1.5–12 cm · s?1) on inorganic nitrogen (N) uptake by the soft‐sediment perennial macroalga Adamsiella chauvinii (Harv.) L. E. Phillips et W. A. Nelson (Rhodophyta) was determined seasonally by measuring uptake rate in a laboratory flume. Regardless of N tissue content, water velocity had no influence on NO3? uptake in either winter or summer, indicating that NO3?‐uptake rate was biologically limited. However, when thalli were N limited, increasing water velocity increased NH4+ uptake, suggesting that mass‐transfer limitation of NH4+ is likely during summer for natural populations. Uptake kinetics (Vmax, Ks) were similar among three populations of A. chauvinii at sites with different mean flow speeds; however, uptake rates of NO3? and NH4+ were lower in summer (when N status was generally low) than in winter. Our results highlight how N uptake can be affected by seasonal changes in the physiology of a macroalga and that further investigation of N uptake of different macroalgae (red, brown, and green) during different seasons is important in determining the relative influence of water velocity on nutrient uptake. 相似文献
9.
Comparative Kinetics and Reciprocal Inhibition of Nitrate and Nitrite Uptake in Roots of Uninduced and Induced Barley (Hordeum vulgare L.) Seedlings 总被引:9,自引:5,他引:4
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Nitrate and NO2− transport by roots of 8-day-old uninduced and induced intact barley (Hordeum vulgare L. var CM 72) seedlings were compared to kinetic patterns, reciprocal inhibition of the transport systems, and the effect of the inhibitor, p-hydroxymercuribenzoate. Net uptake of NO3− and NO2− was measured by following the depletion of the ions from the uptake solutions. The roots of uninduced seedlings possessed a low concentration, saturable, low Km, possibly a constitutive uptake system, and a linear system for both NO3− and NO2−. The low Km system followed Michaelis-Menten kinetics and approached saturation between 40 and 100 micromolar, whereas the linear system was detected between 100 and 500 micromolar. In roots of induced seedlings, rates for both NO3− and NO2− uptake followed Michaelis-Menten kinetics and approached saturation at about 200 micromolar. In induced roots, two kinetically identifiable transport systems were resolved for each anion. At the lower substrate concentrations, less than 10 micromolar, the apparent low Kms of NO3− and NO2− uptake were 7 and 9 micromolar, respectively, and were similar to those of the low Km system in uninduced roots. At substrate concentrations between 10 and 200 micromolar, the apparent high Km values of NO3− uptake ranged from 34 to 36 micromolar and of NO2− uptake ranged from 41 to 49 micromolar. A linear system was also found in induced seedlings at concentrations above 500 micromolar. Double reciprocal plots indicated that NO3− and NO2− inhibited the uptake of each other competitively in both uninduced and induced seedlings; however, Ki values showed that NO3− was a more effective inhibitor than NO2−. Nitrate and NO2− transport by both the low and high Km systems were greatly inhibited by p-hydroxymercuribenzoate, whereas the linear system was only slightly inhibited. 相似文献
10.
Kinetics of nitrate uptake by freshwater algae 总被引:2,自引:2,他引:0
The kinetics of nitrate (NO3
–) uptake, the maximum uptake velocity (Vm) and the half-saturation constant (Ks), were determined for 18 species of batch-cultured freshwater algae grown without nitrogen limitation. Values of Ks ranged from 0.25 to 6.94 µM l–1
Chlorella pyrenoidosa Chick, and Navicula pelliculosa (Breb.) Hilse, respectively. Values of Vm ranged from 0.51 to 5.07 µM l–1 h–1 for Anabaena A7214 and Nitzschia W-32 O'Kelley, respectively. The mean positive values of Ks for Chlorophyta, Cyanophyta and Chrysophyta were 1.89, 3.67 and 4.07 µM l–1, respectively. The mean values of Vm for the same phyla were 1.61, 1.02 and 2.97 µM l–1 h–1 105 cells–1, respectively. The ranges of these kinetic parameters encompass values of kinetic parameters for marine and freshwater species in batch culture, for freshwater algae grown in N-limited chemostats and for natural populations of freshwater phytoplankton. Thus, in spite of variability between species, uptake parameters for both marine and freshwater algae are identical. 相似文献
11.
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
12.
《Harmful algae》2011,10(6):531-539
Temporal and spatial variability in the kinetic parameters of uptake of nitrate (NO3−), ammonium (NH4+), urea, and glycine was measured during dinoflagellate blooms in Changjiang River estuary and East China Sea coast, 2005. Karenia mikimotoi was the dominant species in the early stage of the blooms and was succeeded by Prorocentrum donghaiense. The uptake of nitrogen (N) was determined using 15N tracer techniques. The results of comparison kinetic parameters with ambient nutrients confirmed that different N forms were preferentially taken up during different stages of the bloom. NO3− (Vmax 0.044 h−1; Ks 60.8 μM-N) was an important N source before it was depleted. NH4+ (Vmax 0.049 h−1; Ks 2.15 μM-N) was generally the preferred N. Between the 2 organic N sources, urea was more preferred when K. mikimotoi dominated the bloom (Vmax 0.020 h−1; Ks 1.35 μM-N) and glycine, considered as a dominant amino acid, was more preferred when P. donghaiense dominated the bloom (Vmax 0.025 h−1; Ks 1.76 μM-N). The change of N uptake preference by the bloom-forming algae was also related to the variation in ambient N concentrations. 相似文献
13.
Pithophora oedogonia (Mont.) Wittr. biomass in Surrey Lake, Indiana was greater in the littoral than in the pelagial region. Although mean soluble reactive phosphorus concentrations did not differ between the two areas, nitrate concentrations were almost six times higher in the cove than in the open water. Using laboratory cultures of Pithophora, the half saturation constant (Ks at 20° C relating filament growth to external concentrations of nitrate-nitrogen was determined to be 1.23 mg L?1 (=88 μM)and for phosphate-phosphorus, 0.1 mg L?1 (=3.22 μM). These values were used to calculate a NO3-N/PO4-P atomic ratio of 27.6. Comparison of this value with NO3-N/PO4-P ratios in Surrey Lake showed that nitrogen limiting conditions were prevalent in the open water section of the lake. Alkaline phosphatase and dark ammonia uptake analyses on field collected filaments from the shallow and deep water sections confirmed the hypothesis that nitrate is the major factor limiting growth of Pithophora in Surrey Lake. 相似文献
14.
Jerry A. Topinka Bigelow 《Journal of phycology》1978,14(3):241-247
Ammoniun, nitrate and nitrite update by Fucus spiralis L. from the Massachusetts coast was examined. Uptake of all appeared to follow saturation type nutrient uptake kinetics, with uptake often restricted at ambient nutrient concentrations. Although only relatively large difference in K8 values could be easily distinguished, K8 values for NO3? and NH4+ were generally similar and low compared with NO2?. There was also some suggestion that K8 was reduced at lower temperatures. At 15 C. Vmax for light and dark uptake for both NH4+ and NO3?, and light uptake of N02? were similar, suggesting comparable potential use at higher concentrations. Ammonium and NO3?uptake decreased at lower temperatures giving Qro values of 1.8 and 1.6, respectively, between 5 and 15°C. Nitrate and NH4+ were taken up together and high levels of NH4+ did not inhibit NO3? uptake. Light did not affect uptake of either but did stimulate NO2? uptake. Ammonium and NO3? uptake were highest in apical frond and whole young plants, and lowest in slower growing, older frond and stipe. On a relative basis. NO3?, NH4+ and NO2? were estimated to have contributed ca. 59, 39 and 2% respectively, to the yearly N uptake by apical frond. During winter, NO3? would provide ca. twice the N to F. spiralis as would, NH4+. From summer to early fall, when NO3? levels are lower, NO3? and NH4+ would be used in comparable amounts. 相似文献
15.
The toxigenic diatom Pseudo‐nitzschia cuspidata, isolated from the U.S. Pacific Northwest, was examined in unialgal batch cultures to evaluate domoic acid (DA) toxicity and growth as a function of light, N substrate, and growth phase. Experiments conducted at saturating (120 μmol photons · m?2 · s?1) and subsaturating (40 μmol photons · m?2 · s?1) photosynthetic photon flux density (PPFD), demonstrate that P. cuspidata grows significantly faster at the higher PPFD on all three N substrates tested [nitrate (NO3?), ammonium (NH4+), and urea], but neither cellular toxicity nor exponential growth rates were strongly associated with one N source over the other at high PPFD. However, at the lower PPFD, the exponential growth rates were approximately halved, and the cells were significantly more toxic regardless of N substrate. Urea supported significantly faster growth rates, and cellular toxicity varied as a function of N substrate with NO3?‐supported cells being significantly more toxic than both NH4+‐ and urea‐supported cells at the low PPFD. Kinetic uptake parameters were determined for another member of the P. pseudodelicatissima complex, P. fryxelliana. After growth of these cells on NO3? they exhibited maximum specific uptake rates (Vmax) of 22.7, 29.9, 8.98 × 10?3 · h?1, half‐saturation constants (Ks) of 1.34, 2.14, 0.28 μg‐at N · L?1, and affinity values (α) of 17.0, 14.7, 32.5 × 10?3 · h?1/(μg‐at N · L?1) for NO3?, NH4+ and urea, respectively. These labo‐ratory results demonstrate the capability of P. cuspidata to grow and produce DA on both oxidized and reduced N substrates during both exponential and stationary growth phases, and the uptake kinetic results for the pseudo‐cryptic species, P. fryxelliana suggest that reduced N sources from coastal runoff could be important for maintenance of these small pennate diatoms in U.S. west coast blooms, especially during times of low ambient N concentrations. 相似文献
16.
Greenhouse-grown cut flower roses are often irrigated with moderately saline irrigation water. The salt/ballast ions are either present initially in poor quality raw water or reclaimed municipal water, or accumulated in greenhouse irrigation water that is captured and reused. Such ions can inhibit root absorption of essential nutrients. The objective of this work was to quantify the influence of NaCl concentration on the uptake of nitrate and potassium by roses and develop a predictive model of uptake inhibition based on NaCl, NO3 ?, and K+ concentration. One year-old rose plants (Rosa spp. ‘Kardinal’ on ‘Natal Briar’ rootstock) were moved into growth chambers where nitrogen and potassium depletion were monitored during 6 days. Eight different initial NaCl treatments varying from zero to 65 mol m?3 were used and within these there were two initial NO3 ? and K+ concentrations: high concentration (HC, 7.0 mol m?3 and 2.6 mol m?3 NO3 ? and K+ respectively) or low concentration (LC, 3.5 mol m?3 and 1.3 mol m?3 NO3 ? and K+ respectively). Plant NO3 ? uptake was negatively affected by NaCl concentration. NO3 ? maximum influx (Imax) declined from 5.1 µmol to 2.5 µmol per gram of plant dry weight per hour as NaCl concentration increased from zero to 65 mol m?3. A modified Michaelis–Menten (M–M) equation taking into account inhibition by NaCl provided the best fit for NO3 ? uptake in response to varying NaCl concentration. K+ uptake was unaffected by NaCl concentration. A M–M equation that did not include inhibition was suitable for describing K+ uptake at varying NaCl concentration. The resulting empirical models could assist with decision making, such as: adjustment of NO3 ? fertilization based on NaCl concentration, necessity of water desalinization, or determination of the desired leaching fraction. 相似文献
17.
《Plant and Soil》2000,220(1-2):107-117
The contribution of influx and efflux of NO3
- on NO3
- net uptake has been studied in excised mycorrhizae of 18–20 week old beech (Fagus sylvatica L.) trees. Net uptake rates of NO3
- followed uniphasic Michaelis-Menten kinetics in the concentration range between 10 μM and 1.0 mM external NO3
-, with an apparent Km of 88±7 μM, and a Vmax of 110±7 nmol g-1 root f.wt. h-1. The relative xylem loading of N, i.e. the portion of NO3
- taken up that was loaded into the xylem vessels as NO3
- plus reduced N, was constant over the concentration range tested (4.6–7.7%). NO3
- influx proceeded linearly with increasing external NO3
- supply. When the assumed regulators of net NO3
- uptake, i.e. NH4
+ or L-glutamate, were applied together with NO3
-, net uptake rates of NO3
- decreased. This inhibitory effect was caused by a reduction of NO3
- influx rather than an enhanced efflux. The comparison of the present data with a recent study with non-mycorrhizal beech
roots (Kreuzwieser et al., 1997; J. Exp. Bot. 48, 1431–1438) revealed that mycorrhization leads to reduced rates of NO3
- net uptake. This effect is caused by reduced influx plus enhanced efflux of NO3
- as compared with non-mycorrhizal beech roots.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
18.
A comparative kinetic analysis of nitrate and ammonium influx in two early-successional tree species of temperate and boreal forest ecosystems 总被引:6,自引:1,他引:6
Xiangjia Min M. Yaeesh Siddiqi Robert D. Guy Anthony D. M. Glass & Herbert J. Kronzucker 《Plant, cell & environment》2000,23(3):321-328
Root NO3 ? and NH4 + influx systems of two early‐successional species of temperate (trembling aspen: Populus tremuloides Michx.) and boreal (lodgepole pine: Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) forest ecosystems were characterized. NO3 ? and NH4 + influxes were biphasic, consisting of saturable high‐affinity (HATS) and constitutive non‐saturable low‐affinity transport systems (LATS) that were evident at low and relatively high N concentrations, respectively. NO3 ? influx via HATS was inducible (IHATS); nitrate pre‐treatment resulted in 8–10‐fold increases in the Vmax for influx in both species. By contrast, HATS for NH4 + were entirely constitutive. In both species, Vmax values for NH4 + influx were higher than those for NO3 ? uptake; the differences were larger in pine (6‐fold) than aspen (1·8‐fold). In aspen, the Km for NH4 + influx by HATS was approximately 3‐fold higher than for IHATS NO3 ? influx, while in pine the Km for IHATS NO3 ? influx was approximately 3‐fold higher than for NH4 + influx. The aspen IHATS for NO3 ? influx appeared to be more efficient than that of pine (Vmax values for aspen being approximately 10‐fold higher and Km values being approximately 13‐fold lower than for pine). By contrast, only small differences in values for the NH4 + HATS were evident between the two species. The kinetic parameters observed here probably result from adaptations to the N availabilities in their respective natural habitats; these may contribute to the distribution and niche separation of these species. 相似文献
19.
L. Adamec 《Biologia Plantarum》1997,39(4):599-606
The uptake of K+ by the leafy shoots of four submersed higher aquatic plants (Elodea canadensis, Ranunculus aquatilis, R. trichophyllus, and
Callitriche hamulata) with different HCO3
- affinity was measured in successive 2-h periods under the conditions of high or low photosynthetic rates (i.e. at pH 7.5
or 10). At pH 7.5 the uptake of K+ by species with the higher HCO3
- affinity (E. canadensis, R. trichophyllus) was significantly faster than that by species with a lower HCO3
- affinity (R. aquatilis, C. hamulata). In the former group of species, the K+ uptake rate at pH 7.5 was 1.7 - 3.5 times higher than at pH 10. At pH 10, the soft-water species, R. aquatilis, had the lowest
net photosynthetic rate (PN) of the three HCO3
- users but, in contrast to the relative hard-water species, R. trichophyllus, showed a small K+ efflux (47 nmol kg-1 s-1). Thus, K+ uptake by shoots was not strictly correlated with PN. A significant K+ efflux (73 - 86 nmol kg-1 s-1) occurred from all HCO3
- users in darkness. The relatively low K+ uptake by the strict CO2 user, C. hamulata, was quite independent of PN and light or darkness. It may be suggested that uptake of K+ by shoots of submersed plants depends on their HCO3
- affinity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
The nitrogen uptake and growth capabilities of the potentially harmful, raphidophycean flagellate Heterosigma akashiwo (Hada) Sournia were examined in unialgal batch cultures (strain CCMP 1912). Growth rates as a function of three nitrogen substrates (ammonium, nitrate and urea) were determined at saturating and sub-saturating photosynthetic photon flux densities (PPFDs). At saturating PPFD (110 μE m−2 s−1), the growth rate of H. akashiwo was slightly greater for cells grown on NH4+ (0.89 d−1) compared to cells grown on NO3− or urea, which had identical growth rates (0.82 d−1). At sub-saturating PPFD (40 μE m−2 s−1), both urea- and NH4+-grown cells grew faster than NO3−-grown cells (0.61, 0.57 and 0.46 d−1, respectively). The N uptake kinetic parameters were investigated using exponentially growing batch cultures of H. akashiwo and the 15N-tracer technique. Maximum specific uptake rates (Vmax) for unialgal cultures grown at 15 °C and saturating PPFD (110 μE m−2 s−1) were 28.0, 18.0 and 2.89 × 10−3 h−1 for NH4+, NO3− and urea, respectively. The traditional measure of nutrient affinity—the half saturation constants (Ks) were similar for NH4+ and NO3− (1.44 and 1.47 μg-at N L−1), but substantially lower for urea (0.42 μg-at N L−1). Whereas the α parameter (α = Vmax/Ks), which is considered a more robust indicator for substrate affinity when substrate concentrations are low (<Ks), were 19.4, 12.2 and 6.88 × 10−3 h−1/(μg-at N L−1) for NH4+, NO3− and urea, respectively. These laboratory results demonstrate that at both saturating and sub-saturating N concentrations, N uptake preference follows the order: NH4+ > NO3− > urea, and suggests that natural blooms of H. akashiwo may be initiated or maintained by any of the three nitrogen substrates examined. 相似文献