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1.
Natural colloids are abundant in seawater and are an intermediary in the fate, transport and bioavailability of many trace elements. Knowledge of the pathways and mechanisms of the biological uptake of colloidal Fe and other Fe species is of paramount importance in understanding Fe limitation on marine phytoplankton and thus carbon sequestration in the ocean. Whether the natural colloids serve as a source for the biological Fe requirements of marine phytoplankton, or just as a sink for particle-reactive metals in the oceans remains largely unknown. This study examined the bioavailability of Fe bound with colloids from different regions to a coastal diatom (Thalassiosira pseudonana). Natural colloids were isolated by cross-flow ultrafiltration and radiolabeled with 59Fe before being exposed to phytoplankton. Control experiments were conducted to ensure that 59Fe radiolabeled onto the colloids remained mostly in the colloidal phase. Both the natural oceanic and coastal colloidal organic matter complexed Fe (1 nm–0.2 μm) can be biologically available to the marine diatom even though its uptake was lower than the low molecular weight counterparts. By comparing the measured Fe internalization fluxes and the calculated maximum diffusive uptake fluxes, it is evident that ligand exchange kinetics on the cell surface may control the internalization of macromolecular Fe. The calculated concentration factors under dark and light conditions were generally comparable. Colloidal Fe, as an important intermediary phase, can be actively involved in the planktonic food web transfer through biological uptake and regeneration processes. The bioavailable fraction of Fe may be substantially underestimated by only considering the truly dissolved Fe or overestimated when using the external fluxes, such as aerosol Fe, as the bioavailable fraction.  相似文献   

2.
Dissolved Fe and ligand concentrations and the Fe-binding strength of the organic ligands were measured in samples from the upper water column (150 m) of the oligotrophic waters of the Canary Basin (eastern North Atlantic Ocean). Concentrations of major nutrients, phytoplankton abundance and photosynthetic characteristics were also measured in the same samples.The concentrations of dissolved Fe and dissolved organic ligands were low with mean values of 0.31 ± 0.18 nM Fe and 1.79 ± 0.73 nEq of M Fe(n = 47), respectively. The conditional binding constant varied between 1019.8–1022.7 (n = 47). The largest variation with depth in the ligand concentrations (between 4.78 and 1.1 nEq of M Fe) was observed in the upper layer, above the Deep Chlorophyll Maximum (DCM located between 80 and 100 m), with high surface values in stations at 18 and 34.At the DCM where Fe was depleted, the ligand concentrations were still relatively high showing the same trend with depth as the amount of phytoplankton cells. Here 62% of the vertical variation in ligand concentrations can be explained by parameters describing phytoplankton cell abundance or biomass and orthosilicic acid concentration, which could reflect diatom growth. Ligand concentrations below the maximum of the DCM (n = 4) showed good linear positive relationships with the total phytoplankton biomass as well as with 2 out of 4 distinguished groups of phytoplankton (Synechococcus and pico-eukaryote I).In the maximum of the DCM and below this maximum the phytoplankton origin of the dissolved organic ligands of Fe is very probable. Data suggest a release of ligands by cell lysis and not by an active production. However, the origin in the surface layer is more difficult to explain. Although the amount of phytoplankton cells in the surface layer is reduced, it is still  25% of the cell concentration observed in the DCM. High concentrations of organic ligands could then be a remnant of past blooms or present production under nutrient depleted conditions. Input of Sahara dust can be another source of ligands.  相似文献   

3.
The biogeochemistry of trivalent iron, manganese, and cobalt in the oceans is dominated by soluble complexes formed with high-affinity organic ligands that are believed to be microbial siderophores or similar biogenic chelating agents. Desferrioxamine B (DFOB), a trihydroxamate siderophore found in both terrestrial and marine environments, has served as a useful model for a large class of microbial siderophores in studies of 1:1 complexes formed with trivalent iron and manganese. However, no data exist concerning DFOB complexes with Co(III), which we hypothesize should be as strong as those with Fe(III) and Mn(III) if the current picture of the ocean biogeochemistry of the three trivalent metals is accurate. We investigated the complexation reaction between DFOB and Co(III) in aqueous solution at seawater pH using base and redox titrations, and then characterized the resulting 1:1 complex Co(III)HDFOB+ using X-ray absorption, resonance Raman spectroscopy, and quantum mechanical structural optimizations. We found that the complex stability constant for Co(III)HDFOB+ (log K [Co(III)HDFOB+] = 37.5 ± 0.4) is in fact five and seven orders of magnitude larger than that for Fe(III)HDFOB+ (log K[Fe(III)HDFOB+] = 32.02) and Mn(III)HDFOB+ (log K[Mn(III)HDFOB+] = 29.9), respectively. Spectroscopic data and the supporting theoretical structural optimizations elucidated the molecular basis for this exceptional stability. Although not definitive, our results nevertheless are consistent with the evolution of siderophores as a response by bacteria to oxygenation, not only because of sharply decreasing concentrations of Fe(III), but also of Co(III).  相似文献   

4.
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   

5.
Iron coordination and redox reactions in synthetic and coastal seawater were investigated at nanomolar concentrations using 59Fe radiometry and ion-pair solvent extraction of iron chelated by sulfoxine (8-hydroxyquinoline-5-sulfonate) and BPDS (bathophenanthroline disulfonate). Using sulfoxine, we determined the rate at which the monomeric Fe(III) hydroxide species present in seawater of pH 8 are complexed by the microbial siderophore deferriferrioxamine B and the synthetic chelator EDTA (ethylenediaminetetraacetic acid). Forward rate constants of 2 × 106M−1s−1 and 20 M−1s−1, respectively, were obtained. The kinetics of these reactions have not been measured previously at pH values near that of seawater. Conditional equilibrium constants measured for the Fe(III)-EDTA system are consistent with published stability constants for EDTA complexes and for Fe(III) hydrolytic equilibria minus the neutral Fe(OH)3o species, suggesting it is not quantitatively significant near pH 8. Commercial humic acid was found to have sufficient affinity for iron to compete with Fe(III) hydrolysis in seawater, and limited evidence was obtained for an interaction with dissolved organic matter in coastal seawater.In our investigations of redox reactions using BPDS to trap Fe(II) produced in the medium, we observed enhanced photoreduction of Fe(III) by humic acid as well as reduction induced by solutes released from phytoplankton in seawater of pH 8. Although the method is sensitive enough to work at near-oceanic levels of iron, the difficulty in distinguishing Fe(II) generated by Fe(III)-BPDS interactions from Fe(II) produced by other means limits its utility. This analytical ambiguity may be generalizable to other methods which measure ferrous iron in seawater using Fe(II)-specific ligands.  相似文献   

6.
《Marine Chemistry》2001,73(2):83-95
More than half of the dissolved iron in rain collected in Wilmington, NC, USA, occurred as Fe(II)(aq). More than 80% of the dissolved iron in marine rain from several marine storms in both North Carolina and New Zealand was Fe(II)(aq). In almost all rain events Fe(II)(aq) was in excess of Fe(III)(aq). Rainwater is a significant source of iron to surface seawater and contributes approximately 1010 mol year−1 of dissolved plus particulate iron to surface seawater on a global scale, which is more than 30 times the amount of iron resident in the surface 10 m of seawater. The length of time atmospherically deposited dissolved iron remains in surface seawater is critical to its role as a phytoplankton nutrient because it is predominately the soluble form of Fe that is bioavailable. Earlier studies have demonstrated that Fe(II)(aq) oxidizes rapidly in seawater. Our experiments utilizing authentic rainwater with ambient concentrations and speciation of iron clearly demonstrate, however, that rainwater Fe(II)(aq) is stabilized against oxidation for more than 4 h in seawater and rainwater Fe(III)(aq) is protected against rapid precipitation when added to coastal or oligotrophic seawater. These results are significant because they show rainwater deposited Fe does not behave as previously thought based on earlier kinetic work on non-rainwater Fe(II) oxidation in seawater. Rainwater, therefore, is an important source of soluble, stable Fe(II)(aq) to surface seawater.  相似文献   

7.
Under the artificial condition the 59Fe morphology in sea water, its concentration in sediment and phytoplankton, its distribution and metabolism in tissue organs of marine animals were studied. The results showed that the morphology of 59Fe was in a particulate state in sea water. The adsorption rule of 59Fe by three kinds of sediments was similar. The concentration ability of 59Fe by phytoplankton was very strong. The critical concentration organs of S9Fe by marine animals were viscera. The gross radioactivity of 59Fe was mainly concentrated in protein. The concentration factor of 59Fe by DNA was the highest one. After excretion experiment, 59Fe of all the tissue organs was not detected. Small part of59Fe remained in the organic acid and protein state. There was a redistribution process in sediment for59Fe.  相似文献   

8.
The distribution of dissolved iron and its chemical speciation (organic complexation and redox speciation) were studied in the northeastern Atlantic Ocean along 23°W between 37 and 42°N at depths between 0 and 2000 m, and in the upper-water column (upper 200 m) at two stations further east at 45°N10°W and 40°N17°W in the early spring of 1998. The iron speciation data are here combined with phytoplankton data to suggest cyanobacteria as a possible source for the iron binding ligands. The organic Fe-binding ligand concentrations were greater than that of dissolved iron by a factor of 1.5–5, thus maintaining iron in solution at levels well above it solubility. The water column distribution of the organic ligand indicates in-situ production of organic ligands by the plankton (consisting mainly of the cyanobacteria Synechococcus sp.) in the euphotic layer and a remineralisation from sinking biogenic particles in deeper waters. Fe(II) concentrations varied from below the detection limit (<0.1 nM) up to 0.55 nM but represented only a minor fraction of 0% to occasionally 35% of the dissolved iron throughout the water column. The water column distribution of the Fe(II) suggests biologically mediated production in the deep waters and photochemical production in the euphotic layer. Although there was no evidence of iron limitation in these waters, the aeolian iron input probably contributed to a shift in the phytoplankton assemblage towards increased Synechococcus growth.  相似文献   

9.
赵玉颖  孙军  魏玉秋 《海洋科学》2020,44(10):121-132
当前全球气候变化下的上层海洋变暖与酸化对以浮游植物为主的海洋生态系产生了重大影响，理解此背景下的海洋浮游植物生理生态响应，对我们理解和抑制全球气候变化具有重要意义。在全球大气二氧化碳分压（pCO2）升高情景下，浮游植物通过光合作用、微生物循环等过程，通过不同功能群对海洋生源要素循环模式的改变，进而影响区域及全球海洋的生物地球化学循环。研究全球浮游植物对海洋酸化生理生态的响应使得我们对生物地球化学系统的认识更加全面、系统。  相似文献   

10.
To clarify the nature of organic metal complexes dissolved in seawater, a ligand exchange reaction between ligands of natural origin and an aminopolycarboxylic acid (EDTA) was used to determine the conditional stability constants of organic metal complexes. The results indicate that more than two organic molecules complexed with copper and zinc exist in surface seawater. It is found that the conditional stability constants of these naturally-occurring organic metal complexes are 1–3 orders of magnitude higher than those of EDTA-Cu and EDTA-Zn complexes. These estimates of the conditional stability constants for the dominant species of organic copper and zinc complexes are 1011.8 and 109.3, respectively, at pH 8.1. The results indicate that these naturally-occurring organic metal complexes are stable species and not easily dissociated or displaced with others in the marine environment.  相似文献   

11.
Recent electrochemical measurements have shown that iron (Fe) speciation in seawater is dominated by complexation with strong organic ligands throughout the water column and have provided important thermodynamic information about these compounds. Independent work has shown that iron exists in both soluble and colloidal fractions in the Atlantic Ocean. Here we have combined these approaches in samples collected from a variety of regimes within the Atlantic Ocean. We measured the partitioning of Fe between soluble (< 0.02 μm) and colloidal (0.02 to 0.4 μm) size classes and characterized the concentrations and conditional stability constants of Fe ligands within these size classes. Results suggest that equilibrium partitioning of Fe between soluble and colloidal ligands is partially responsible for the distribution of Fe between soluble and colloidal size classes. However, a significant fraction of the colloidal Fe was inert to ligand exchange as soluble Fe concentrations were generally lower than values predicted by a simple equilibrium partitioning model.In surface waters, strong ligands with conditional stability constants of 1013 relative to total inorganic Fe appeared to dominate speciation in both the soluble and colloidal fractions. In deep waters these ligands were absent, and instead we found ligands with stability constants 12–15 fold smaller that were predominantly in the soluble pool. Nevertheless, significant levels of colloidal Fe were found in these samples, which we inferred must be inert to coordination exchange.  相似文献   

12.
1995年改进了浮游植物表面积的酸碱滴定测定法，其中应用改进BET方程对酸滴定曲线拟合求最大表面酸量，由此测定了18种海洋浮游植物（包括8种绿藻，7种硅藻，2种甲藻，1种红藻）的细胞表面积。结果表明，该方法精密度为15．2％，所测定的18种海洋浮游植物的表面积为2．78×10-8—6．9×10-6m2，变异系数为0．9％—31．3％，较传统的用光／电子显微镜粗略估算的方法，更为精确，并且设备简单，操作方便。  相似文献   

13.
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   

14.
腐殖质是地表普遍存在的天然有机物,对海洋中重要的微量营养元素-铁（Fe）的分布及生物地球化学循环具有重要的影响作用。本文对腐殖质的来源、分布及对海水中溶解态铁的迁移转化的影响做了总结,特别论述了其在河口及沿岸水域的行为。大量研究表明河口、沿岸及开放海水中溶解态铁分布的变化可以用腐殖质的浓度及其铁结合能力的变化来解释。腐殖质的络合作用不仅能够阻止溶解态铁（DFe）在河口、沿岸等水域被去除,而且能够通过洋流将DFe迁移至外海及大洋区域,此外还能增加铁的溶解度及对海水中浮游植物的生物可利用性,并且促进铁的氧化还原循环。研究还发现两者之间的络合强度受到盐度、pH等理化因素的影响。盐度是影响HS与DFe配合能力的重要影响因素,盐度增加,导致HS中可以与Fe配合的位点数量降低,配合总量呈现指数降低,而pH的增加可以增加HS与DFe的配合量。另外HS还能影响海水中DFe的氧化还原,并以此影响浮游植物对DFe的吸收利用。因此腐殖质对溶解态铁的有机络合作用是影响其海洋生物地球化学循环的一个重要参数,进一步研究海水中腐殖质的浓度和分布具有重要的意义。  相似文献   

15.
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   

16.
The relationship between total and chemically labile Fe has been studied in estuarine, coastal and shelf waters of the Gulf of Maine, U.S.A. Measurements of the labile fraction of total Fe, defined by complexation with 8-hydroxyquinoline in 1 h, correlate with the availability of Fe to marine phytoplankton and therefore can be used to estimate Fe availability in seawater. The results show that the relative lability (=labile/total) of Fe in seawater varied both spatially and temporally from near-zero to 100%. Although particulate Fe (>0.45 μm) was generally less labile than dissolved Fe (<0.45 μm), the particulate fraction often contributed substantially to labile Fe concentrations overall. Conversely, as much as 75% of ‘dissolved’ Fe was non-labile, and therefore was probably not available to phytoplankton. In seawater/river-water mixing experiments, aggregation diminished the relative lability of Fe by 30%, even though much of it remained in the ‘dissolved’ fraction. Considering phytoplankton nutrition, these results demonstrate that equating dissolved Fe concentrations with ‘available’ metal can be misleading. Furthermore, the large variability observed in the labile proportion of total Fe in seawater indicates that Fe availability to phytoplankton cannot be estimated by applying fixed lability-ratios to total Fe concentrations.  相似文献   

17.
We have developed an ecosystem model including two nitrogen isotopes (14N and 15N), and validated this model using an actual data set. A study of nitrogen isotopic ratios (δ15N) using a marine ecosystem model is thought to be most helpful in quantitatively understanding the marine nitrogen cycle. Moreover, the model study may indicate a new potential of δ15N as a tracer. This model has six compartments: phytoplankton, zooplankton, particulate organic nitrogen, dissolved organic nitrogen, nitrate and ammonium in a two-box model, and has biological processes with/without isotopic fractionation. We have applied this model to the Sea of Okhotsk and successfully reproduced the δ15N of nitrate measured in seawater and the seasonal variations in δ15N of sinking particles obtained from sediment trap experiments. Simulated δ15N of phytoplankton are determined by δ 15N of nitrate and ammonium, and the nitrogen f-ratio, defined as the ratio of nitrate assimilation by phytoplankton to total nitrogenous nutrient assimilation. Detailed considerations of biological processes in the spring and autumn blooms have demonstrated that there is a significant difference between simulated δ15N values of phytoplankton, which assimilates only nitrate, and only ammonium, respectively. We suggest that observations of δ 15N values of phytoplankton, nitrate and ammonium in the spring and autumn blooms may indicate the ratios of nutrient selectivity by phytoplankton. In winter, most of the simulated biogeochemical fluxes decrease rapidly, but nitrification flux decreases much more slowly than the other biogeochemical fluxes. Therefore, simulated δ15N values and concentrations of ammonium reflect almost only nitrification. We suggest that the nitrification rate can be parameterized with observations of δ15N of ammonium in winter and a sensitive study varying the parameter of nitrification rate.  相似文献   

18.
Phytoplankton cultures occurring in disphotic zone water were conducted to examine dissolved organic carbon (DOC) for possible controlling agent of the initial lag period and growth rate. Culture media of various concentrations of DOC were prepared by mixing low DOC disphotic zone water with high DOC surface water. Natural phytoplankton populations showed strong correlations in their lag period with DOC concentrations in the range from 0.75 mgC·I–1 to 1.2 mgC·I–1 in the water (r=–0.833,n=8) and in their population growth rate () (r=0.899,n=8). Similar tendencies were confirmed with a marine diatom (Skeletonema costatum) dominating in the present disphotic zone water by culture experiments. By reducing DOC concentrations in seawater samples by pretreatments of ultraviolet radiation, charcoal adsorption and Amberlite XAD-2 resin adsorption, lag periods ofS. costatum increased in every case, but their population growth rates were almost identical. These results obviously show that prolonged lag period at least occurs in low DOC water, which can explain the observations by Barber and Ryther (1969) that low photosynthetic carbon uptake rate occurs in newly upwelled low DOC water. It is found that the essential substance to shorten lag periods of phytoplankton cultured in disphotic zone water is a portion of dissolved organic matter, which is poor in disphotic zone water and rich in surface water, and the effect of the substance analogous to Na2EDTA strongly suggests that the substances are organic ligands.  相似文献   

19.
According to the principle of photosythesis with sunlight and CO2 by phytoplankton supplying food for marine organisms, while the nitrogenous compounds excreted by marine animals are transferred by bacteria into the nitrate for the use of phytoplankton, an artificial microhabitat is built to investigate comprehensively distributive relationship of 127Cs, 134Cs, 65Zn, 60Co, 50Fe, 54Mn In the parts of the microhabitat. The results show that 78% of the 134Cs and 137Cs in ion state are present in sea water, with 28 % of them nearly homogenous envolved in the exchanging processes of the suspensates and organisms, and that 80% of 59Fe, 54Mn, 65Zn, 60Co were concentrated by solid substance, whose motion was mainly controlled by biological processes. The factors affecting the distribution of nuclides in each composition are discussed. As another type of research on the controlled ecological system which is a subject currently studied in the world, the present paper is of reference value for studying quantitativ  相似文献   

20.
I present here a review of my work concerning nitrogen assimilation by marine phytoplankton. This opportunity was provided to me as the recipient of the Okada Prize for 1990 from the Oceanographical Society of Japan. Assimilation of nitrogenous nutrients by phytoplankton has received considerable research effort since it is an essential process in organic matter production in the sea surface. The use of15N technique is necessary for tracing nitrogen assimilation by natural marine phytoplankton, but nitrogen metabolism of heterogenous natural populations significantly complicates flow of isotope. Dilution of15N isotope by heterotrophic regeneration of ammonium causes underestimates of uptake rates. I made an evaluation of isotope dilution effects in available data sets of15N-ammonium uptake experiments in literature. Incorporated15N in particulates might revert back to dissolved organic or inorganic nitrogen. I conducted pulse-chase experiments which can quantify such loss of tracer. From these studies, a short term experiment with sufficient amount of tracer enrichment is found to overwhelm these problems. In such an experiment, however, the elevation of nutrient concentration by tracer addition may likely perturb the uptake process. An initial rapid uptake is expected if the population is nitrogen deficient, but I found that this phenomenon is not common to surface oligotrophic open oceans. Uptake rate from such an experiment, or capacity of nitrogen uptake, was obtained using surface waters from an extended area in the North Pacific, and its regional variability was discussed. In addition to overall15N uptake, time series analysis of intracellular15N partitioning between hot ethanol soluble and insoluble fractions was found to be useful. When15N-ammonium is added to nitrogen deficient cells of phytoplankton,15N is accumulated in the ethanol soluble fraction. Using cultured strains of marine phytoplankton, this accumulation was proved to be caused by the difference of rates of nitrogen uptake and nitrogenous macromolecule synthesis. Uptake rate per cell is relatively constant irrespective of nutritional status, but macromolecule synthesis decreases with nitrogen deficiency. This accumulation of15N in the ethanol soluble fraction was used as an index of nutritional status with respect to nitrogen of the natural populations of phytoplankton from the western North Pacific. The uptake capacity of nitrate was observed to be higher than that of ammonium in the regional upwelling around Izu Islands and during the spring bloom in Alaskan coastal water. The15N partitioning technique revealed that nitrate taken up was rapidly incorporated in the macromolecule fraction. This suggests that ammonium uptake is suppressed to be smaller than intracellular nitrogen assimilation, rather than that nitrate is taken up in excess and accumulates within the cell. Regulation of nitrate uptake by light intensity was also discussed in detail for the Alaskan data. Several other studies currently conducted are also mentioned.  相似文献   

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