首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Cyanobacteria are ubiquitous in marine waters. These prokaryotic cells are of particular interest in areas of the ocean where the availability of iron may be limiting for cell growth since these organisms commonly excrete iron-specific organic ligands (siderophores) in response to low levels of iron. It is generally considered that the production of siderophores provides a competitive advantage over the competing microorganisms that do not produce these ligands.In order to ascertain the influence of iron availability on the physiology of picoplanktonic cyanobacteria we performed a series of experiments on the coastal coccoid cyanobacterium, Synechococcus sp. PCC 7002. Physiological responses were examined in cells grown in a continuous cuture system with influx media containing a range of iron concentrations (from 4.2 × 10−5 to 5.1 × 10−9 M FeCl3). Steady-state growth rates, combined with growth data from batch cultures demonstrated a non-linear response between iron availability and cell proliferation: cell yields were considerably higher in the lowest-iron chemostats than predicted based on the yields in the higher-iron chemostats. The higher yields during low-iron growth corresponded with the production of the extracellular siderophores and the induction of the specific iron-siderophore membrane transport proteins. A comparison of iron transport and carbon acquisition rates between the low-iron grown cells and the high-iron grown cells indicates that under low-iron growth conditions, iron and carbon acquisition meets the growth demands of the cells, whereas growth at higher iron levels enabled excessive (luxury) carbon acquisition and storage. We conclude that cyanobacteria are efficiently adapted to grow in low-iron environments (providing sufficient light for photosynthesis is available) and the luxury-uptake of carbon may serve as the source material for the extracellular ligands released by these cells. Since the release of siderophores was at iron levels in excess of the levels that induce the siderophore-mediated transport of iron, cyanobacteria growing in an environment with varying levels of iron may contribute substantial amounts of their stored carbon reserves into the DOC as iron-specific ligands.  相似文献   

2.
To elucidate iron regeneration and organic iron(III)-binding ligand formation during microzooplankton and copepod grazing on phytoplankton, incubation experiments were conducted in the western subarctic Pacific. During 8 days of dark incubation of ambient water and that amended with plankton concentrate, dissolved iron and organic iron(III)-binding ligands accumulated, approximately proportionally to the decrease in chlorophyll a. The observed increases in dissolved iron concentration were much greater than those expected from the consumption of phytoplankton biomass and previously reported Fe:C value of cultured algal cells, suggesting resolution from colloidal or particulate iron adsorbed onto the algal cell surface. When copepods were added to the ambient water, organic iron(III)-binding ligands accumulated more rapidly than in the control receiving no copepod addition, although consumed phytoplankton biomass was comparable between the two treatments. Bioassay experiment using filtrates collected from the incubation experiment showed that organic ligands formed during microzooplankton grazing reduced the iron bioavailability to phytoplankton and suppressed their growth. Moreover, picoplankton Synechococcus sp. and Micromonas pusilla were more suppressed by the organic ligands than the diatom Thalassiosira weissflogii. In conclusion, through microzooplankton and copepod grazing on phytoplankton, organic iron(III)-binding ligands as well as regenerated iron are released into the ambient seawater. Because the ligands lower iron bioavailability to phytoplankton through complexation and the degree of availability reduction varies among phytoplankton species, grazing by zooplankton can shift phytoplankton community structure in iron-limited waters.  相似文献   

3.
To test the iron hypothesis in the subarctic Pacific Ocean, an in situ iron-enrichment experiment (SEEDS) was performed in the western subarctic gyre in July–August 2001. About 350 kg of iron (as acidic iron sulfate) and 0.48 mol of the inert chemical tracer sulfur hexafluoride were introduced into a 10-m deep surface mixed layer over an 80 km2 area. This single iron infusion raised dissolved iron levels to 2.9 nM initially. Dissolved iron concentrations rapidly decreased after the infusion, but levels remained close to 0.15 nM even at the end of the 14-day experimental period. During SEEDS there were iron-mediated increases in chlorophyll a concentrations (up to 20 μg l−1), primary production rates, biomass and photosynthetic energy conversion efficiency relative to waters outside the iron-enriched patch. The rapid and very high accumulation of phytoplankton biomass in response to the iron addition appeared to be partly attributable to shallow mixed-layer depth and moderate water temperature in the western subarctic Pacific. However, the main reason was a floristic shift to fast-growing centric diatom Chaetoceros debilis, unlike the previous iron-enrichment experiments in the equatorial Pacific and the Southern Ocean, in both of which iron stimulated the growth of pennate diatoms. The iron-mediated blooming of diatoms resulted in a marked consumption of macronutrients and drawdown of pCO2. Biological and physiological measurements indicate that phytoplankton growth in the patch became both light- and iron-limited, making phytoplankton biomass relatively constant after day 9. The increase in microzooplankton grazing rate after day 9 also influenced the net growth rate of phytoplankton. There was no significant increase in the export flux of carbon to depth during the 14-day occupation of the experimental site. The export flux between day 4 and day 13 was estimated to be only 13% of the integrated primary production in the iron-enriched patch. The major part of the carbon fixed by the diatom bloom remained in the surface mixed layer as biogenic particulate matter. Our findings support the hypothesis that iron limits phytoplankton growth and biomass in a ‘bottom up’ manner in this area, but the fate of algal carbon remains unknown.  相似文献   

4.
The chemical speciation of iron was determined in the Southern Ocean along a transect from 48 to 70°S at 20°E. Dissolved iron concentrations were low at 0.1–0.6 nM, with average concentrations of 0.25±0.13 nM. Organic iron complexing ligands were found to occur in excess of the dissolved iron concentration at 0.72±0.23 nM (equivalent to an excess of 0.5 nM), with a complex stability of log KFeL′=22.1±0.5 (on the basis of Fe3+ and L′). Ligand concentrations were higher in the upper water column (top 200 m) suggesting in situ production by microorganisms, and less at the surface consistent with photochemical breakdown. Our data are consistent with the presence of stable organic iron-complexing ligands in deep global ocean waters at a background level of ∼0.7 nM. It has been suggested that this might help stabilise iron at levels of ∼0.7 nM in deep ocean waters. However, much lower iron concentrations in the waters of the Southern Ocean suggest that these ligands do not prevent the removal of iron (by scavenging or biological uptake) to well below the concentration of these ligands. Scavenging reactions are probably inhibited by such ligand competition, so it is likely that biological uptake is the chief cause for the further removal of iron to these low levels in waters that suffer from very low iron inputs.  相似文献   

5.
The first iron (Fe) – fertilization experiment in the western North Pacific was carried out using SF6 to trace the Fe-fertilized water mass. A solution in 10,800 liters of seawater of 350 kg of Fe and 0.48 M of SF6 tracer was released into the mixed layer over a 8 × 10 km area. On the first underway transects through the patch after the Fe release, we observed a significant increase of dissolved Fe (ave. 2.89 nM). The fertilized patch was traced for 14 days by on-board SF6 analysis. A Lagrangian frame of reference was maintained by the use of a drogued GPS buoy released at the center of the patch. The patch moved westward at a rate of 6.8 km d−1. Mixed layer depth increased from 8.5 to 15 m during the experiment. Horizontal diffusivity was determined by the change of SF6 concentration in the patch. The horizontal diffusivity increased during the experiment. We evaluate here the fate of Fe in a Fe-fertilized patch using the dilution rate determined from sulphur hexafluoride (SF6) concentration. Dissolved Fe concentrations subsequently decreased rapidly to 0.15 nM on Day 13. However, the dissolved Fe half-life of 43 h was relatively longer than in previous Fe-enrichment studies, and we observed a larger increase of the centric diatom standing stock and corresponding drawdown of macro-nutrients and carbon dioxide than in the previous studies. The most important reason for the larger response was the phytoplankton species in the western North Pacific. In addition, the smaller diffusivity and shallower mixed layer were effective to sustain the higher dissolved Fe concentration compared to previous experiments. This might be one reason for the larger response of diatoms in SEEDS.  相似文献   

6.
Variations in the speciation of iron in the northern North Sea were investigated in an area covering at least two different water masses and an algal bloom, using a combination of techniques. Catalytic cathodic stripping voltammetry was used to measure the concentrations of reactive iron (FeR) and total iron (FeT) in unfiltered samples, while dissolved iron (FeD) was measured by GFAAS after extraction of filtered sea water. FeR was defined by the amount of iron that complexed with 20 μM 1-nitroso-2-napthol (NN) at pH 6.9. FeT was determined after UV-digestion at pH 2.4. Concentrations of natural organic iron complexing ligands and values for conditional stability constants, were determined in unfiltered samples by titration. Mean concentrations of 1.3 nM for FeR, 10.0 nM for FeT and 1.7 nM for FeD were obtained for the area sampled. FeR concentrations increased towards the south of the area investigated, as a result of the increased influence of continental run off. FeR concentrations were found to be enhanced below the nutricline (below 40 m) as a result of the remineralisation of organic material. Enhanced levels of FeT were observed in some surface samples and in samples collected below 30 m at stations in the south of the area studied, thought to be a result of high concentrations of biogenic particulate material and the resuspended sediments respectively. FeD concentrations varied between values similar to those of FeT in samples from the north of the area to values similar to those of FeR in the south. The bloom was thought to have influenced the distribution of both FeR and FeT, but less evidence was observed for any influence on FeR and FeD. The concentration of organic complexing ligands, which could possibly include a contribution from adsorption sites on particulate material, increased slightly in the bloom area and in North Sea waters. Iron was found to be fully (99.9%) complexed by the organic complexing ligands at a pH of 6.9 and largely complexed (82–96%) at pH 8. The ligands were almost saturated with iron suggesting that the ligand concentration could limit the concentration of iron occurring as dissolved species.  相似文献   

7.
The coastline near Chañaral in Northern Chile is one of the most highly Cu-contaminated zones in the world due to discharges from mining activities for more than 60 years. The speciation of Cu has been studied to determine the importance of organic complexation in highly contaminated areas, and to assess the likely physiological impacts of Cu on marine organisms. Dissolved Cu concentrations of up to 500 nM were measured, completely saturating organic ligands and leading to free Cu2+ concentrations in excess of 10− 8 M. These values are higher than those reported in any other marine environment, and because they occur over an extensive area, provide a unique opportunity to study the effects of Cu on marine ecosystems and to see how Cu behaves when its speciation is predominantly inorganic. We found strong gradients in free Cu2+ between Chañaral and adjacent areas with lower Cu, where speciation is dominated by organic complexation. There is also a significant increase in the partitioning of Cu onto suspended particles in the contaminated areas, consistent with previous studies that showed that organic ligands stabilize Cu in the dissolved phase, whilst “excess” Cu is rapidly scavenged. Those high dissolved Cu concentrations persist in spite of solid phase partitioning and advective processes along this open-ocean coastline, suggesting that Cu inputs into the system are still very large. Measurements were made using anodic stripping voltammetry with a thin mercury film coated with Nafion, which previous workers have shown can mitigate ambiguity in the data arising from inadvertent reduction of organic complexes. Our findings suggest that this is a useful methodology for contaminated systems.  相似文献   

8.
Pore water aliquots were taken with an in situ close interval sampler: the “Peeper”.We report here the pore water concentration profiles of TCO2, SO4, TH2S, Ca and the trace metals Mn, Cu, Pb, Cd and Cr from sediments of a relatively polluted area, the Villefranche Bay, on the French Riviera (close to Nice).We investigated the major ion concentrations in order to establish geochemical mass balances of organic matter oxidation. ΔTCO2/ΔSO4 was <−2.0, reflecting the precipitation of calcite as confirmed by the calcium profile. Reduction of sulfate led to increasing sulfide concentrations with depth.Trace metal interstitial water concentrations decreased from 63 to 5 nM, 18 to 4 nM and 6.6 to less than 2 nM for Cu, Pb and Cr, respectively. Cd showed a different pattern with top and deep values of 0.7 nM and a minimum of 0.27 nM.Thermodynamic calculations were performed which suggest the potential formation of mineral phases such as sulfides.  相似文献   

9.
The chemical speciation of Cu and Zn was investigated by voltammetric titration methods in the surface waters (10 m) of the western Black Sea during an Istanbul–Sevastopol cruise conducted in November 1998. Supporting parameters (temperature (T), salinity (S), pH, alkalinity (Alk), suspended particulate matter (SPM) and dissolved and particulate 234Th) were obtained in order to distinguish hydrographic features against involvement of the metals in biogeochemical processes. In the Turkish continental slope region, the cruise track intersected a narrow vein of colder water originating on the western shelf. The core of this cold water vein was characterised by a relatively low salinity, higher specific alkalinity and higher metal (especially Cu) and metal-binding ligand concentrations.A very large portion of Cu (93–99.8%) and Zn (82–97%) was organically complexed. The degree of complexation was highest in shelf waters and lowest in the central gyre. Titration data for Cu were modelled by two classes of organic binding ligands characterised by (CL1=3–12 nM, log K1′=13.1–13.9) and (CL2=20–70 nM, log K2′=9.4–11.2). These ligands occurred mainly in the ‘dissolved’ phase, as defined by 0.4-μm filtration. The stronger Cu-binding ligand seemed to be produced in situ in response to Cu concentration, whereas the weaker Cu-binding ligand appeared to be derived from terrestrial sources and/or reducing shelf sediments. Titration results for Zn were generally represented by one class of ligands (CL1=8–23 nM, log K1′=9.4–10.2), which were almost uniformly distributed between the ‘dissolved’ (78±8%) and the particulate phase (22±8%). The concentration of these strong Zn-binding ligands showed a very good correlation with SPM (r2=0.64), which improved when the dissolved ligands alone were considered (r2=0.78). It is hypothesised that these ligands were produced in situ by the bacterial breakdown of particulate organic matter.  相似文献   

10.
The organic matter released by the marine phytoplankton species Dunaliella tertiolecta and its physico-chemical interaction with cadmium and copper ions were studied by electrochemical methods (differential pulse anodic stripping voltammetry (DPASV) and a.c. polarography). The interactions with cadmium and copper were studied at the model interface (mercury electrodesolution) and in the bulk phase by measuring the complexing ability of the released organic material.The axenic cultures were grown on different growth media, without and with trace metals and chelators. Culture media were analyzed 10 days after inoculation, containing 5 × 105−1.2 × 106 cells cm−3 when untreated or after separation of cells by gentle centrifugation.It was found that the content and type of the released surface-active material and complexing ligands depend on the initial composition of the growth media. In all cases, strong interaction of excreted organic substances with copper in the bulk phase and with cadmium at the model interface were observed.A rather high value of the complexing capacity, 9.5 × 10−7 mol Cu2+ dm−3, was found in the culture grown on medium without trace metals and chelators (medium I) whereas the surface activity of this culture was not high (0.2 mg dm−3 equivalent to Triton-X-100). Higher contents of surface-active material (0.8 and 1.0 mg dm−3) were found in cultures grown in media with trace metals and without chelators (II and III), accompanied by a high content of complexing ligands (5.8 × 10−7 and 9.5 × 10−7 mol Cu2+ dm−3). However, if the complexing capacity is calculated per cell the values obtained for cultures grown in media II and III (0.79 × 10−15 and 0.98 × 10−15 mol Cu2+ dm−3) are lower than for cultures grown on medium I (1.8 × 10−15 mol Cu2− dm−3). The exceptional adsorption effects and the copper complexing capacity for medium 1, and the presence of cells with degenerative symptoms can be ascribed to stressed growth conditions, and, particularly, to deficiency of metals. A qualitatively similar behaviour has been observed in natural samples of estuarine waters, indicating the existence of stressed conditions during the mixing of fresh and saline waters.  相似文献   

11.
A sensitive method for iron determination in seawater has been adapted on a submersible chemical analyser for in situ measurements. The technique is based on flow injection analysis (FIA) coupled with spectrophotometric detection. When direct injection of seawater was used, the detection limit was 1.6 nM, and the precision 7%, for a triplicate injection of a 4 nM standard. At low iron concentrations, on line preconcentration using a column filled with 8-hydroxyquinoline (8HQ) resin was used. The detection limit was 0.15 nM (time of preconcentration = 240 s), and the precision 6%, for a triplicate determination of a 1 nM standard, allowing the determination of Fe in most of the oceanic regimes, except the most depleted surface waters. The effect of temperature, pressure, salinity, copper, manganese, and iron speciation on the response of the analyser was investigated. The slope of the calibration curves followed a linear relation as a function of pressure (Cp = 2.8 × 10− 5P + 3.4 × 10− 2 s nmol− 1, R2 = 0.997, for Θ = 13 °C) and an exponential relation as a function of temperature (CΘ = 0.009e0.103Θ, R2 = 0.832, for P = 3 bar). No statistical difference at 95% confidence level was observed for samples of different salinities (S = 0, 20, 35). Only very high concentration of copper (1000 × [Fe]) produced a detectable interference. The chemical analyser was deployed in the coastal environment of the Bay of Brest to investigate the effect of iron speciation on the response of the analyser. Direct injection was used and seawater samples were acidified on line for 80 s. Dissolved iron (DFe, filtered seawater (0.4 μm), acidified and stored at pH 1.8) corresponded to 29 ± 4% of Fea (unfiltered seawater, acidified in line at pH 1.8 for 80 s). Most of Fea (71 ± 4%) was probably a fraction of total dissolvable iron (TDFe, unfiltered seawater, acidified and stored at pH 1.8).  相似文献   

12.
Evidence for organic complexation of iron in seawater   总被引：1，自引：0，他引：1  
Iron occurs at very low concentrations in seawater of oceanic origin and its low abundance is thought to limit primary production in offshore waters (Martin and Fitzwater, 1988). A new electrochemical method, cathodic stripping voltammetry (CSV), is used here to determine the speciation of iron in seawater originating from the Western Mediterranean taking advantage of ligand competition of an added electroactive ligand with the natural organic complexing matter to evaluate whether iron is organically complexed. The measurements indicate that iron occurs 99% (or 99.9% depending on which value is selected for αFe′) complexed by organic complexing ligands throughout the water column of the Western Mediterranean and by analogy probably also in other oceanic waters. The composition of the organic complexing ligands is as yet unknown, but the data indicate a major source from microorganisms (bacteria or phytoplankton) in and immediately below the fluorescence maximum in the upper water column. The organic complexes are apparently reversible releasing iron when the competing ligand is added and binding more iron when its concentration is increased. The organic complexing ligands occur at concentrations well above those of iron ensuring full complexation of this biologically essential element, and buffer the free iron concentration at a very low level against fluctuations as a result of removal by primary producers or inputs from atmospheric sources. The new data indicate that a re-evaluation of the concept of the bioavailable fraction of iron is required.  相似文献   

13.
The solubility of iron in oxic waters is so low that iron can be a limiting nutrient for phytoplankton growth in the open ocean. In order to mimic low iron concentrations in algal cultures, Ethylenediaminetetraacetate (EDTA) is commonly used. The presence of EDTA enables culture experiments to be performed at a low free metal concentration, while the total metal concentrations are high. Using EDTA provides for a more reproducible medium. In this study Fe speciation, as defined by EDTA in culture media, is compared with complexation by natural organic complexes in ocean water where Fe is thought to be limited. To grow oceanic species into iron limitation, a concentration of at least 10−4 M EDTA is necessary. Only then does the calculated [Fe3+] concentrations resemble those found in natural sea water, where the speciation is governed by natural dissolved organic ligands at nanomolar concentrations. Moreover, EDTA influences the redox speciation of iron, and thus frustrates research on the preferred source of Fe-uptake, Fe(III) or Fe(II), by algae. Nowadays, one can measure the extent of natural organic complexation in sea water, as well as the dissolved Fe(II) state, and can use ultra clean techniques in order to prevent contamination. Therefore, it is advisable to work with more natural conditions and not use EDTA to create iron limitation. This is especially important when the biological availability of the different chemical fractions of iron are the subject of research. Typically, many oceanic algae in the smallest size classes can still grow at very low ambient Fe and are not easily cultivated into limitation under ambient sea water conditions. However, the important class of large oceanic algae responsible for the major blooms and the large scale cycling of carbon, silicon and other elements, commonly has a high Fe requirement and can be grown into Fe limitation in ambient seawater.  相似文献   

14.
During late winter and spring of 2002 and 2003, 24 two- to three-day cruises were conducted to Dabob Bay, Washington State, USA, to examine the grazing, egg production, and hatching success rates of adult female Calanus pacificus and Pseudocalanus newmani. Here, we discuss the results of our grazing experiments for P. newmani. Each week, we conducted traditional microzooplankton dilution experiments and “copepod dilution” experiments, each from two different layers. Grazing was measured by changes in chlorophyll concentration and direct cell counts. Clearance rates on individual prey species, as calculated by cell counts, showed that Pseudocalanus are highly selective in their feeding, and may have much higher grazing rates on individual taxa than calculated from bulk chlorophyll disappearance. The grazing rates of the copepods, however, are typically an order of magnitude lower than the grazing rates of the microzooplankton community, or the growth rates of the phytoplankton. P. newmani ingested diatoms, but, at certain times fed preferentially on microzooplankton, such as ciliates, tintinnids, and larger dinoflagellates. Removal of the microzooplankton may have released the other phytoplankton species from grazing pressure, allowing those species’ abundance to increase, which was measured as an apparent “negative” grazing on those phytoplankton species. The net result of grazing on some phytoplankton species, while simultaneously releasing others from grazing pressure resulted in bulk chlorophyll-derived estimates of grazing which were essentially zero or slightly negative; thus bulk chlorophyll disappearance is a poor indicator of copepod grazing. Whether copepods can significantly release phytoplankton from the grazing pressure by microzooplankton in situ, thus causing a trophic cascade, remains to be verified, but is suggested by our study.  相似文献   

15.
An iron enrichment experiment, EisenEx, was performed in the Atlantic sector of the Southern Ocean during the Antarctic spring of 2000. Deck incubations of open ocean water were performed to investigate the influence of ultraviolet B (UVB: 280–315 nm) and ultraviolet A (UVA: 315–400 nm) on the speciation of iron in seawater, using an addition of the radioisotopes 59Fe(III) (1.25 nM) or 55Fe(III) (0.5 nM). Seawater was sampled inside and outside the iron-enriched region. The radioisotopic Fe(II) concentration was monitored during daylight under three different light conditions: the full solar spectrum (total), total minus UVB, and total minus UVB+UVA. A distinct diel cycle was observed with a clear distinction between the three different light regimes. A clear linear relationship was found for the concentration of radioisotopic Fe(II) versus irradiance. UVB produced most of the Fe(II) followed by UVA and visible light (VIS: 400–700 nm), respectively. UVB produced 4.89 and 0.69 pM m2 W−1 radioisotopic Fe(II) followed by UVA with 0.33 and 0.10 pM m2 W−1 radioisotopic Fe(II) and VIS with 0.04 and 0.03 pM m2 W−1 radioisotopic Fe(II).  相似文献   

16.
Catalytic cathodic stripping voltammetry (CSV) preceded by adsorptive collection of complexes of 1-nitroso-2-napthol (NN) can be used to determine iron in seawater. It is shown here that iron(II) is effectively masked in the presence of 2,2-dipyridyl (Dp) so that iron(III) is measured selectively. The concentration of iron(II) is then calculated as the difference between the concentrations of reactive iron (FeR) in the absence and presence of 2 μM Dp, FeR being defined as that which was complexed by 20 μM NN at pH 6.9 in the presence of 1.8 mM H2O2 and 5 ppm sodium dodecyl sulphate. A 30 min reaction time was allowed for Dp to react with iron(II) in seawater prior to the determination of reactive iron(III) using the same conditions as used for FeR. Detection limits of 0.08 nM, 0.077 nM and 0.12 nM were obtained for FeR, iron(III) and iron(II), respectively, using a 60 s deposition time.The method was utilised to determine the redox speciation of iron in the northern North Sea. Concentrations of FeR ranged between 0.8 and 3.5 nM with nutrient-like depth profiles. Iron(II) was found to be present at concentrations up to 1.2 nM, the highest concentrations occurring in the upper 20 m of the water column.  相似文献   

17.
Freshwater concentrations confirm the pristine character of the Lena River environment as already pointed-out in a previous study with a limited set of data (Martin et al., 1993). Total dissolved concentrations of the freshwater are 13.8 ± 1.6 nM, Cu, 4.4 ± 0.1 nM, Ni, 0.054 ± 0.047 nM, Cd, 642 ± 208 nM, Fe, 0.2–0.3 nM Pb and 1.2 ± 1.0 nM, Zn. For Zn and Pb, a simple mixing of the Lena River waters with the Arctic waters is observed. Relationships with salinity suggest that for Cu, Ni and Cd, there is a mobilization of the dissolved fraction from the suspended matter, with an increase of the dissolved concentration of 1.5, 3 and 6 times, respectively. For Fe, the total dissolved concentrations follow an exponential decrease in the mixing zone and 80% of the total “dissolved” Fe is removed from the solution. For Cu, Ni, Cd and Fe, the riverine end-members are 20 nM, 12 nM, 0.3 nM and 47 nM, respectively. When considering the input of total dissolved metals to the Arctic Ocean, the fraction attributed to the freshwaters from the Arctic rivers appears to be small (4% of the input of dissolved metal to the Arctic Ocean for Cd, 27% for Cu, 11 % for Ni and 2% for Zn). Metal concentrations in the Laptev Sea and Arctic Ocean are very similar, indicating a generally homogeneous distribution in the areas sampled.  相似文献   

18.
  相似文献   

19.
Marine ecosystems, like terrestrial biological communities, are generally considered to depend, regarding their structure and functioning, upon the trophic and sexual relationships between organisms, either “horizontally”, between individuals at the same level, or “vertically”, all the way down the various levels of the food chains. Nevertheless, the functioning of biosystems is mostly governed by their structure, i.e., the qualitative and quantitative distribution of individuals within biocenoses, as well as the relationships with one another and with the environment. Therefore, it is vital to get to know how these connections work in order to outline the main causes of microbiological equilibrium in the sea. Actually, the major problem remains that of communication between individuals in biocenoses. This is a general problem as far as life is concerned, but it proves especially acute when it comes to microbial life because of its importance in the oceanic cycles.Data available in the literature, together with the results of our own studies in this field, led us to the assumption that some of the dissolved organic substances present in seawater might well be responsible for the control of the relationships between species. These substances would be active at various degrees of concentration, after they have been released into the medium by certain species. This theory, already adumbrated by Lucas (1938, 1947, 1955), Nigrelli (1958) and Fontaine (1970) concerning direct relationships between marine species or groups of organisms, was resumed and generalized by M. Aubert (1971) who called these substances “telemediators”.Such chemical communication plays a major role in a variety of fields including sexual behaviour, nutrition and predation, as well as defense mechanisms, mobility and migration.Remote connection of two organisms through a chemical mediation involves a sequence of actions and reactions which raises a number of problems of biochemical microecology. The organism that produces the telemediator must synthesize it — either spontaneously or in an induced way — and release it into the medium, during its active growth or after cell lysis. Next, the mediator is conveyed to the remote receiving organism, which it should reach without being degraded or chemically modified (or after such a modification. Its concentration must remain equal to or higher than its activity threshold. The receptor detects it, with or without absorption, and reacts by modifying its own metabolism or behaviour. This may go as far as causing the receptor the receptor to die. In even more complex situations, another mediator will be synthesized and released into the medium.Theoretical as it may be, such a pattern is a useful guide to explain the microbial interactions in a marine environment. It involves a number of complex microecological phenomena, some phases of which begin to be known. One specific problem is chemoreception in microorganisms, hence chemotaxis. Telemediator activity threshold and turnover in the natural environment must also be investigated.One should also take account of the physical context in which the phenomena take place. For instance, it is a known fact that an important fraction of the bacterial flora in the sea is adsorbed on solid or particulate substrates. Thus, the relationships with which they are concerned are much more probable in a sphere of a few fractions of a millimeter: this emphasizes the significance of the biochemical processes which cause the microorganisms to colonize substrates and to compete with one another in so doing. Another point of interest is how they modify the substrate until they are replaced by higher organisms.In the microbial field, communication between species has been described at various levels. Horizontally, it can take place between different bacteria or between various species of algae. Vertically, it may involve bacteria and planktonic algae, bacteria and protozoa, or algae and zooplanktonic organisms.Besides, the communication may be “positive”, if the mediator enhances the growth of the receiving organism — then, it is used as a source of carbon or nitrogen, or as a growth factor — or “negative” whenever the mediator is toxic (antibiotic, antiseptic or toxin) or induces a lethal metabolic modification in the receiver.In fact, there are various telemediation mechanisms, which correspond to increasing degrees of complexity in the biological systems: a primary mechanism, in which the mediator is synthetized by a species and controls (or modifies) the metabolism of another species in one step, and a secondary mechanism, where the mediator is synthetized by a species, and modifies the metabolism of another species; the latter, in turn, releases a primary mediator which controls the functions of a third species. This might be a longer sequence, involving a higher number of species.If the mechanism becomes cyclic, feedback may occur: as far as we know, such feedback may be either positive or negative ecologically, depending on whether it speeds up or slows down a biological process.A conception of a marine universe whose equilibrium would be controlled by the interaction of organisms within a more or less dense biotic network, with meshes made up of the relationship functions as a whole, is highly suggestive of an homology with cybernetic structures. Then, each marine organism can be considered as a separate functional unit characterized by some particular properties, its functions, which govern its activity. These units are involved in the functioning of complex and varying systems in which they intervene locally to channel up the flow of energy and matter to a given extent and in a given direction.The analogy is still more pronounced as there are feedbacks, which can control various sectors of the system. In a series of studies based on biological systems regulated by various chemical mediators, authors were able to demonstrate that the introduction of varied chemical pollutants into the marine environment entails modifications in the structure of the biological components of seawater and results in either the modification or the destruction of the mediating metabolites or “signals”. The result could be a more or less pronounced ecological drift, that varies according to the activity of the pollutant.  相似文献   

20.
Concentrations of thiol compounds, copper-complexing ligands, and total dissolved copper were followed over the course of 1 year (October 2002 until September 2003) in the Elizabeth River, Virginia to evaluate seasonality. Copper-complexing ligand concentrations were determined by competitive ligand equilibration-adsorptive cathodic stripping voltammetry (CLE/ACSV). Thiol detection was carried out by high performance liquid chromatography (HPLC) and calibration using a suite of nine thiol compounds (cysteine, glutathione, mercaptoacetic acid, 2-mercaptoethanesulfonic acid, 2-mercaptoethanol, 2-mercaptopropionic acid, 3-mercaptopropionic acid, mercaptosuccinic acid, and monothioglycerol). Total dissolved copper concentrations reached a January low of 13.1 nM to a June high of 24.7 nM and were found to vary seasonally with higher concentrations occurring from June to September. With a low of 26 nM during April to a high of 56 nM in October, copper-complexing ligand (average log K′CuL of 12.0 ± 0.2) concentrations displayed a similar seasonal pattern to that of total dissolved copper. Free cupric ion concentrations remained below 1.5 pM for a majority of the year except during March, April, and December when values reached pM levels greater than 1.5. Six of the nine thiol compounds surveyed were detected in the Elizabeth River samples and ranged in concentration from below detectable concentrations (< 5 nM) to individual highs ranging from 25.3 to168.5 nM. The thiol compound concentrations displayed a clear seasonality fluctuating at below detection limits during November to February then increasing with increasing surface water temperatures from March to July. CLE/ACSV was used to assess whether or not the suite of thiol compounds detected by HPLC could contribute to the copper-complexing ligand pool. Conditional stability constants for each one of six thiol standards (average log K′CuL  12.1 ± 0.5) were found to be statistically equivalent to the naturally occurring copper-complexing ligands (average log K′CuL  12.0 ± 0.2). This suggests that these thiol compounds could act as copper-complexing ligands in natural samples and could contribute to the copper-complexing ligand pool detected by CLE/ACSV. This study involving seasonality of copper-complexing ligands and thiols in an industrialized, urban estuary underscored several points that have to be substantiated in future research efforts including copper-complexing ligands sources and the role that thiol compounds as well as other unidentified organic compounds play in the copper-complexing ligand pool.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号