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1.
Photosynthetic CO2-fixation, chlorophyll content, growth rate and nitrate reductase activity were used to examine the influence of NH+4-N and NO3-N on Sphagnum magellanicum cultivated under defined conditions in phytotrons. NO3-concentrations up to 322 μ M were found to be favourable. Increased NH+4 concentrations, however, resulted in growth inhibition and decreased chlorophyll content at concentrations ≧ 255 μ M ; e.g. 600 μ M NH+4 caused a 20% reduction of nitrate reductase activity and net photosynthesis. For raised bog Sphagna an improved standard nutrient solution is proposed with the following ion concentrations (μ M ): 55 Na+; 17 K+; 95 NH+4; 22 Ca2+; 22 Mg2+; 2 Fe3+; 20 Cl; 100 NO3; 57 SO2-4; 7.4 H2PO4; trace elements: A-Z solution (Hoagland) 50 μl 1000 ml−1; pH 5.8.  相似文献   

2.
The immediate and posteffects of various concentrations of NaNO2 on ion uptake of wheat ( Triticum aestivum L. cv. GK Öthalom) seedlings were studied at different pH values. Without pretreatment, the higher the concentration of NaNO2 the greater was the decrease in uptake of K+ into the roots, both at pH 4 and pH 6. At pH 6 but not at pH 4 the reverse was true when the seedlings were pretreated with NaNO2. Due to the high Na+ content of the roots, an effect of Na+ in this process cannot be excluded. Nitrite was taken up by the roots more rapidly than nitrate. Nitrite at 0.1 m M in the medium induced the development of an uptake system for both NO2 and NO3 in wheat roots. At higher concentrations pretreatment with NO2 decreased NO3 uptake by the roots, but NO3 did not inhibit the uptake of NO2. The toxic effect of NO2 was strongly pH dependent. Lower pH of the external solution led to an increased inhibition by NO2 of both ion uptake and growth of seedlings. The inhibitory effect of NO2 differed considerably for roots and shoots. The roots and especially the root hairs were particularly sensitive to NO2 treatment.  相似文献   

3.
Inhibition of electron transport through photosystem II (PS II) by formate (HCO2) or nitrite (NO2) in the presence or absence of chloride ions was studied. The inhibition induced by HCO2 or NO2 is overcome by HCO3 more in the presence, than in the absence of Cl. The data on electron transport are supported by chlorophyll a fluorescence measurements. In experiments. In experiments in which water oxidation was blocked. Cl was found to facilitate electron transport between bound quinone A (QA) and the plastoquinone (PQ) pool. It can thus be concluded that in addition to the well known site of action of Cl on water oxidation, another site of Cl action is between QA and the PQ pool.  相似文献   

4.
Two-month-old jack pine ( Pinus banksiana Lamb.) seedlings were placed in a greenhouse where both nitrogen source and light level were varied. After 4 months, whole seedling biomass, leaf biomass and relative growth rate were greatest in seedlings grown with NH+4/NO/NO3-N and full light (FL) and least in seedlings grown with NO 3-N and low light (LL). NO 3-seedlings grown under full light and NH+4/NO3-seedlings grown under low light were approximately equal. This indicates that the extra carbon costs of assimilating only NO3-N were similar to the reduction of carbon fixation resulting from a 50% decrease in photon flux density. Percentage and total nitrogen content of needles were greater in seedlings grown under low light independent of nitrogen fertilization. Percentage and total nitrogen content of roots were higher under low light and lower when fertilized with NO3.
Nitrate reductase (NR) activity was higher in roots than in needles, while glutamine synthetase (GS) activity was higher in needles than in roots. Low light resulted in decreased NR activity (mg N)−1 in needles, but not in roots. However, no nitrate was detected in the needles in any treatment. GS activity, on the other hand, was greater under low light in both needles and roots. GS activity in needles is most likely involved with the reassimilation rather than the initial assimilation of ammonium. Some implications of these shifts in enzymatic activity for ecological phenomena in forests are discussed.  相似文献   

5.
Ecosystem flux measurements using the eddy covariance (EC) technique were undertaken in 4 subsequent years during summer for a total of 562 days in an arctic wet tundra ecosystem, located near Cherskii, Far-Eastern Federal District, Russia. Methane (CH4) emissions were measured using permanent chambers. The experimental field is characterized by late thawing of permafrost soils in June and periodic spring floods. A stagnant water table below the grass canopy is fed by melting of the active layer of permafrost and by flood water. Following 3 years of EC measurements, the site was drained by building a 3 m wide drainage channel surrounding the EC tower to examine possible future effects of global change on the tundra tussock ecosystem. Cumulative summertime net carbon fluxes before experimental alteration were estimated to be about +15 g C m−2 (i.e. an ecosystem C loss) and +8 g C m−2 after draining the study site. When taking CH4 as another important greenhouse gas into account and considering the global warming potential (GWP) of CH4 vs. CO2, the ecosystem had a positive GWP during all summers. However CH4 emissions after drainage decreased significantly and therefore the carbon related greenhouse gas flux was much smaller than beforehand (475 ± 253 g C-CO2-e m−2 before drainage in 2003 vs. 23 ± 26 g C-CO2-e m−2 after drainage in 2005).  相似文献   

6.
A model describing the transport of elements through the xylem vessels into the leaf of a red cherry tomato ( Lycopersicon esculentum Mill cv. Tiny Tim) in a non-steady state situation is presented. The model describes the upward movement of ions as a mass-flow of the xylem fluid with dissolved elements, with lateral ion escape represented by a first-order process. The model is fitted to data obtained in an experiment in which 15 elements were applied in a solution to a cut stem part with attached leaf and were measured simultaneously by gamma-ray spectroscopy. The model is in good agreement with the transport into the leaf of K+ Na+, Rb+, Cs+, Yb3+, Sm3+ Zn2+, Co2+, Cu2+, Sb(SO4)2 AsO3+4, WO2+4; and Mo7O6+24.
Only indirect data could be obtained for Cd2+ and La3+ because of their apparently high affinity for charged sites in the cell walls and high escape constant, respectively. The escape constants were relatively low for all anions, probably due to the presence of a large number of negative charges in the cell walls.  相似文献   

7.
Abstract The interactions occuring between populations of a nitrate-respiring Vibrio sp. and autotrophic nitrifying bacteria belonging to the genera Nitrosomonas and Nitrobacter have been investigated in a compound bi-directional flow diffusion chemostat at a dilution rate of 0.025 h−1 and a temperature of 25°C. When grown under NO3 limitation, the Vibrio sp. produced NH+4 as the principal end-product of nitrate respiration, and there was a corresponding significant increase in cell numbers of the Nitrosomonas sp. population, which derived energy by the oxidation of NH+4 to NO2. Nitrite in turn was used by the Nitrobacter sp. population as an energy source with the concomitant regeneration of NO3. Under NO3 excess growth conditions the Vibrio sp. produced NO2 rather than NH+4 as the major product of NO3 dissimilation, and growth of the Nitrobacter population was stimulated as increased quantities of NO2 became available. In contrast, the Nitrosomonas sp. population declined sharply as the energy source NH+4 became limiting. These data demonstrate that defined mixed populations of obligately aerobic nitrifying bacteria and facultatively anaerobic nitrate respiring bacteria can co-exist for extended time periods and operate an internal nitrogen cycle which is energetically beneficial to both populations.  相似文献   

8.
Growth and mineral status of 9 Taraxacum microspecies were studied under mineral stress conditions, using a flowing solution of low nutrient concentration. Relative growth rate of (whole) plant dry weight, leaf area, and (whole) plant tissue water were used to describe growth. For 4 microspecies, specific uptake rates of NO3, H2PO4, K+, Mg2+ and Ca2+ were investigated.
The applied nutrient condition clearly discriminated between the studied Taraxacum microspecies. With respect to relative growth rate, 3 groups of microspecies could be distinguished: T. nordstedtii > T. lancidens, T. adamii, T. hollandicum, T. taeniatum > T. sellandii, T. eudontum, T. ekmanii, T. ancistrolobum . These categories coincided well with the mineral ecology of the microspecies, going from infertile to fertile sites.
T. nordstedtii , a microspecies of infertile sites, was most efficient in absorbing NO3, H2PO4 and K+. T. sellandii and T. eudontum , both occurring in fertile grasslands, showed poor uptake performances for all studied ions. In all Taraxacum microspecies studied, except T. eudontum , internal N concentration appeared to limit growth. Efficiencies in N use, at sub-optimal internal N concentrations, varied with the mineral habitat of the microspecies studied. T. nordstedtii , from infertile sites, and T. sellandii , from fertile sites, were established as high and low extremes, respectively.  相似文献   

9.
Calcification in aquatic plants   总被引:1,自引:0,他引:1  
Abstract. The CaCO3 deposits of aquatic plants may be intra-, inter- and extracellular. Calcification is mainly the result of photosynthetic CO2 or HCO3 assimilation. This raises the local pH and CO2−3 concentration resulting from shifts in the dissolved inorganic carbon equilibrium, due to either net CO2 depletion as in Halimeda or localized OH efflux (or H+ influx) as in Chara. The plant cell wall may be important in CaCO3 nucleation by acting as an epitaxial substratum or template, or by creating a microenvironment enriched in Ca2+ compared to Mg2+. Hypotheses on the reason for the lack of calcification in many aquatic plants are presented.  相似文献   

10.
Processing tomato ( Lycopersicon esculentum Mill. cv. UC82B) plants were subjected to moderate levels of water deficit and salinity (Na2SO4/CaCl2) in sand culture. Fruit water content and the relative contributions of organic and inorganic constituents to fruit solute potential (Ψ) and soluble solids content were determined throughout development. Fruit Ψ averaged –0.63, –0.86 and –0.77 MPa in the control, salinity and water deficit plants, respectively. Reduced net water import and maintenance of solute accumulation, irrespective of water import, accounted for the reductions in Ψ of stressed fruits. Mineral ions (Na+, K+, Ca2+, Mg2+, Cl and SO2-4) contributed –0.31 MPa to Ψ in salinized fruit, compared with –0.19 MPa in control and water deficit treatments. Changes in net carbon accumulation were not observed among treatments, despite considerable differences in fruit K+ status. Starch accumulation in immature fruit was increased and hexose accumulation was decreased by both salinity and water deficit. Maximum starch levels were negatively correlated with total fruit Ψ, but were independent of fruit K+. Organic acid levels were generally higher throughout development in salinized plants, relative to control plants, and correlated with increased inorganic cation rather than anion accumulation in these fruits.  相似文献   

11.
It has long been assumed that Al3+ is an important rhizotoxic ion in acid soils around the world, but the toxicity of Al3+ relative to mononuclear hydroxy-Al [AlOH2+ and Al(OH)+2] has been examined in detail only for an Al-sensitive wheat variety ( Triticum aestivum L. cv. Tyler). That plant appears to be sensitive to Al3+ but not to AlOH2+ and Al(OH)+2. New experiments, and reanalyses of previously published experiments, provide evidence that dicotyledonous species may be sensitive to mononuclear hydroxy-Al and that Al3+ may be nontoxic, or less toxic, to those plants. Despite these consistently measured differences between wheat and the dicotyledons, the determination of relative toxicities (Al3+ vs mononuclear hydroxy-Al) may be an intractable problem. Because of hydrolysis equilibria, (AlOH2+) and (Al(OH)+2) are equivalent to (Al3+)k1(H+)−1 and (l3+)k2(H+)−2, respectively, in which k1 and k2 are the first and second hydrolysis constants (braces denote activities). Thus, any expression of root elongation as a function of mononuclear hydroxy-Al can be alternatively expressed as a function of (Al3+) and (H+). Toxicity attributed to mononuclear hydroxy-Al may actually be Al3+ toxicity that increases as pH rises (i.e. Al3+ toxicity ameliorated by H+).  相似文献   

12.
The effect of the nitrogen source on carbohydrate and protein contents and on several enzymatic activities involved in the carbon and nitrogen metabolism was studied in Anabaena variabilis ATCC 29413 cells grown under a constant supply of either N, NO3 or NH+4 at different concentrations. An enhancement of protein content accompanied by a parallel decrease of carbohydrates was observed with increasing NO3 or NH+4 concentrations in the medium. In cultures containing 0.1 m M NO3 or 0.1 m M NH+4 nitrogenase (EC 1.18.6.1) activity was 74 and 66%, respectively, of that found in N2-grown cells. This activity was still present with 1 m M NO3 or 1 m M NH+4 in the medium and even with 10 m M NO3, but it was completely inhibited by 5 m M NH+4. Ferredoxin-nitrate reductase (EC 1.7.7.2) activity was detected only in NO3 grown cells and simultaneously with nitrogenase activity. Increasing concentrations of combined nitrogen in the medium, especially NH+4, promoted a concomitant decline of glutamine synthetase (EC 6.3.1.2), NADP+-isocitrate dehydrogenase (EC 1.1.1.42), and NAD+-malate dehydrogenase (EC 1.1.1.37) activities, suggesting that these enzymes play an important role in the regulation of carbon-nitrogen metabolism in cyanobacteria.  相似文献   

13.
Twenty‐day‐old sunflower plants ( Helianthus annuus L. cv. Sun‐Gro 380) grown in nutrient solutions with different KCl levels were used to study the effects of K+ status of the root and of abcisic acid (ABA) on the exudation rate (Jv), the hydraulic conductivity of the root (Lp), the fluxes of exuded K+ and Na+ (JK and JNa), and the gradient of osmotic pressure between the xylem and the external medium. Jv and Lp increased in direct proportion to the K+ starvation of the root. Also addition of ABA (4 µ M ) at the onset of exudation in the external medium made Jv and Lp rise, and this effect also increased with the degree of K+ starvation. Similarly, K+ starvation and ABA promoted both the flux of exuded Na+ and the accumulation of Na+ in the root. We suggest that ABA acts as a regulating signal for the radial transport of water across the root, and that potassium may be an effector of this mechanism.  相似文献   

14.
Abstract. Rates of proton extrusion and potassium (86Rb) influx by intact roots of barley ( Hordeum vulgare cvs . Fergus, Conquest and Betzes) plants were simultaneously measured in short-term (15min) experiments. The nature and extent of apparent coupling between these ion fluxes was explored by manipulating conditions of temperature, pH and cation composition and concentration during flux determinations. In addition, the influence of salt status upon these fluxes was examined. At low K+ concentrations (0.01 to 1 mol m−3), H+ efflux and K+ influx were strongly correlated in both low- and high-K+ roots, although K+: H+ exchange stoichiometries were almost consistently greater than 2:1. At higher concentrations (1 to 5 mol m−3), H+ efflux was either reduced or remained unchanged while K+ influxes increased. In the presence of Na2SO4, rates of H+ extrusion demonstrated similar cation dependence, although below 10 mol m−3 Na2SO4, H+ fluxes were generally 50% lower than in equivalent concentrations of K2SO4. These observations are considered in the context of current hypotheses regarding the mechanisms of k+/H+ exchange.  相似文献   

15.
1. The annual dynamics of methane (CH4) in a temporarily flooded meadow, mire bank, lacustrine sedge fen, temporarily and continuously inundated sedge ( Carex sp.) and reed ( Phragmites australis ) marshes were studied from June to November in the humic mesoeutrophic Lake Mekrijärvi and in eutrophicated parts of the mesotrophic Lake Heposelkä in the southern part of East Finland. The effects of water level and temperature on littoral CH4 fluxes were determined. Vegetation zonation along the moisture gradient, and associated CH4 fluxes, were evaluated.
2. The CH4 flux increased along the moisture gradient from –0.2 to 14.2 mg CH4 m–2 h–1, and was highest in the permanently inundated marshes. The duration of anoxia in the sediment caused differences in the CH4 flux. Estimated emissions for the period 1 June – 30 September in continuously inundated sparse reed and sedge marshes, drying sedge marsh, and lacustrine sedge fen were 13, 11 and 6 g CH4 m–2, respectively.
3. In continuously inundated vegetation, the fluxes were highest in late July/early August. The seasonal CH4 flux pattern suggested that the fluxes were regulated by the supply of organic matter during the course of the summer and the water level. In the temporarily flooded zone, the seasonal CH4 flux dynamics was greatly affected by changes in the lake water level, the fluxes being highest during the spring flood in early June.  相似文献   

16.
Addition of NO3 rapidly induced senescence of root nodules in alfalfa ( Medicago sativa L. cv. Aragon). Loss of nodule dry matter began at the lowest NO3 concentration (10 m M ) but degradation of bacteroid proteins was only detected when nodules were supplied with NO3 concentrations above 20 m M .
Bacteroids from Rhizobium meliloti contained high specific activities of nitrate reductase (NR) and nitrite reductase (NiR). Both enzymes were presumably substrate-induced although substantial enzyme activities were present in the absence of NO3 Typical specific activities for soluble NR and NiR of bacteroids under NO3 free conditions were 1.2 and 1.4 μmol (mg protein)−1h−1, respectively. In the presence of NO3, the specific activity of NR was considerably greater than that of NiR, thus causing NO2 accumulation in bacteroids. Nitrite levels in the bacteroids were linearly correlated with specific activities of NR and NiR, indicating that NO2 is formed by bacteroid NR and that this NO2 in turn, induces bacteroid NiR. Accumulation of NO2 within bacteroids also indicates that NO2 inhibits nodule activity after feeding plants with NO3  相似文献   

17.
The effects of perturbation and excision on net NO-3, uptake, influx and efflux in roots of 8-day-old barley ( Hordeum vulgare L.) seedlings induced with NO-3 or NO-2 were determined. Perturbation was simulated by mechanically striking the intact roots with a glass rod. Perturbation or excision of roots and subsequent division into small segments had little effect on NO-3 influx, but briefly inhibited net uptake which recovered within a few min. While in perturbed roots net uptake rates recovered to the same level as in control roots, full recovery did not occur in excised roots. Inhibition of net uptake was due to stimulation of NO-3 efflux. The recovery time and level of inhibition of net NO-3 uptake and/or stimulation of efflux were a function of extent of perturbation, or the number of segments following excision, and root NO-3 concentration. NO-3 efflux was further stimulated when roots were perturbed after cytoplasmic NO-3 had been depleted, indicating that both the plasmalemma and tonoplast may be affected. In excised roots both NO-3 influx and efflux decreased with age due to depletion of energy sources. The results indicate that root perturbation and excision had no effect on NO-3 influx but inhibited net uptake by stimulating efflux.  相似文献   

18.
The uptake of the auxin type herbicide 2,4-D into rice seedlings ( Oryza sativa L. cv. Dunghan Shali) and its effects on the K+, NH+4 and NO3 ion uptake and the K+ content were investigated at different pH values. A short incubation of the roots in 0.01 m M 2,4-D caused a marked ion uptake inhibition only at low pH. The non-auxin type herbicide benthiocarb did not produce such an inhibitory effect. Lowering of the pH in the external medium led to an increased 2,4-D uptake by the roots. These results can be explained by the increased H+ permeability of the membranes, allowing a more rapid entrance of 2,4-D into the root cells, thereby inhibiting the active ion uptake. Rice roots not subjected to 2,4-D treatment responded to H+ stress with an increased anomalous K+ uptake and a decreased K+ content. With reference to the effects of pH changes on the ion and 2,4-D uptake, possible transport mechanism of NH+4 and 2,4-D are briefly discussed.  相似文献   

19.
Abstract. Net NO3 uptake by NO3 deficient Chara cells was used to calculate [NO3]c assuming that the cytoplasm occupies 10% total volume and that nitrate reduction and storage are negligible (i.e. maximum [NO3]c was calculated). A linear relationship was found between NO3 efflux and [NO3]c. There was an initial burst of NO3 efflux when NH+4 was added, followed by a slower efflux rate which matched influx rate such that net NO3 uptake was zero. Over 50% of NO3 that had been taken up in 2 h was lost within the first 5 min of NH+4 addition. The Nernst equation was used to predict the direction of the electrochemical driving force for NO3 entry. Under the experimental conditions used NO3 efflux is actively transported. The differential involvement of both NO3 influx and NO3 efflux in the regulation of NO3 uptake is discussed and a model is proposed to account for these results which envisages discrete NO3 influx and NO3 efflux carriers.  相似文献   

20.
Abstract The kinetic parameters of NH+4-uptake in yeast cells were determined by a method that is based on the following changes in the external NH+4 concentration in cell suspensions by using NADH-dependent glutamate formation from NH+4 and 2-oxoglutarate. The kinetics of the observed NADH oxidation were analyzed by computer and enabled an estimation of V max and K m of the NH+4-uptake system of the cells.  相似文献   

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