The role of iron species on the competition of two coastal diatoms , Skeletonema costatum and Thalassosira weissflogii

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Introduction
Diatoms tend to dominate phytoplankton communities in well-mixed coastal and upwelling regions (Bowler et al., 2008).Marine diatoms greatly influence marine food webs, global climate, atmospheric carbon dioxide concentration, and marine ecosystem function (Armbrust, 2009).Coastal diatoms are often exposed to N, P, and Fe enrichment (Bizsel and Uslu, 2000;Wells and Trick, 2004).An understanding of diatoms species composition in coastal ecosystems and the processes that select for blooms Introduction

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Full of certain species were still limited, in spite of the importance of diatom competition in coastal ecosystem dynamics.Macronutrient inputs into coastal waters continue to rise (Turner and Rabalais, 1994;Cai et al., 2011).Coastal eutrophication results in a wide variety of changes in the structure and function of coastal marine ecosystems, metal sorption, bioaccumulation and species distribution (Li et al., 2007(Li et al., , 2009;;Li and Zheng, 2011) and protecting these systems from the many adverse effects of eutrophication is extremely important (Smith, 2003).
Dissolved-Fe availability (Sunda and Huntsman, 1997;Takeda, 1998;Hutchins and Bruland, 1998) and siderophore-and porphyrin-complexed Fe (Hutchins et al., 1999) play a critical role in controlling diatom growth, but we have a very restricted knowledge of the role of phytoplankton in controlling Fe species distribution in coastal water, because only phytoplankton blooms have been studied (Nishioka et al., 2001;Christopher et al., 2002;Öztürk et al., 2003), at the same time, it is important to distinguish Fe absorption (intracellular uptake) and adsorption (cellular surface uptake) (Li and Zheng, 2011).Fe bioavailability or toxicity, biogeochemical fates, and ecological effects are quite different between absorbed and adsorbed Fe by marine phytoplankton, because: after absorption (i.e., assimilation) by algal cells, Fe can combine with organic compounds such as proteins and enzymes, and then accumulate through the aquatic food chain; whereas adsorbed Fe by cell surfaces can be partly desorbed into the seawater, and then exist as inorganic compounds transfer to seawater.There is surprisingly little information available on the quantitative and qualitative effect of N, P, and Fe additions on Fe speciation distribution and it subsequent influence on the species competition.
Skeletonema costatum, as a non-toxic coastal diatom, has been responsible for large-scale bloom events (ca. 10 000 km 2 ) in Yangtze River estuary and the adjacent East China Sea in recent years (Zhou et al., 2003).Thalassiosira weissflogii, a nontoxic coastal centric diatom, is used as a model of marine algae (Qu et al., 2000).In this study, we have investigated the interspecific competition of S. costatum and T. weissflogii for iron speciation distribution for the first time.These two species of non-toxic Introduction

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Full coastal diatom were exposed to a four-day macronutrient and iron enrichment.How these exposures influence on Fe biogeochemical cycle, Fe speciation distribution, and competition of diatom were examined.
Sterile trace element clean techniques were applied for culturing and experimental manipulations (Shi et al., 2010).Reagents for this study were made in acid-washed lowdensity polyethylene (LDPE) bottles.The acid cleaning procedure for reagent bottles included a 6 M HCl soak for one month and 0.7 M HNO 3 storage for another month.Sample bottles (100 mL LDPE, Bel-Art) and eluate bottles (8 mL LDPE, Nalgene) were cleaned by heating overnight in 3 M HCl and then heating again overnight in 4 M HNO 3 Introduction

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Full ( Biller and Bruland, 2012).Each new lot of vials was tested before use to ensure that there was no biological or trace element contamination.

Seawater sample
Coastal seawater was collected from Zhangzhou Bay, Fujian Province, China.The salinity of the seawater was 33.1 ± 0.05 psu.The N and P concentrations were measured three times using a flow injection analyzer (FIA), and the background concentrations were 47.5 µmol L −1 for N (as nitrate) and 0.250 µmol L −1 for P (as reactive P).
The background concentrations of Fe were 0.40 µmol L −1 measured by ICP-MS, similar to that reported by Öztürk et al. (2003).The detection limit of Fe by ICP-MS was 0.4 nmol L −1 .The amounts of Fe in seawater were determined three times and the relative standard deviation was 1.1 %.Subsequently, this coastal seawater, with both Fe and macronutrient enrichment, could be used for experiments related to Fe sorption by bloom-forming speciation and Fe species distribution in seawater.
Clean seawater used for the experiments on the competition between two dominant bloom-forming species was collected 10 km offshore in Zhangzhou Bay, Fujian Introduction

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Full State, China.The background concentration of Fe in the seawater was measured using ICP-MS, and the iron concentration was 0.165 nmol L −1 .The N and P concentrations were measured using FIA, and the background concentrations were 7.66 µmol L −1 and 0.05 µmol L −1 for N (as nitrate) and P (as reactive P), respectively.The seawater was considered to be remoted from anthropogenic activities.
All the seawater was stored at 4 • C for about 6 months, filtered through acid-washed Pall Acropak Supor capsule 0.22 µm filters, and sterilized before use.

Algal culture
Unialgal cultures of S. costatum and T. weissflogii were obtained from the State Key Laboratory for Marine Environmental Science, Xiamen University.They were maintained in seawater (with 21.1 mmol L −1 Si added as Na 2 SiO 3 • H 2 O, but without trace metals) at different N (added as NaNO 3 ) and P (added as Na 2 HPO 4 ) concentrations with different species of Fe at 19 • C sterile conditions, and with the light illumination of 140 µmol photons m −2 s −1 by a light : dark cycle as 14 h : 10 h.The algal suspensions were stirred at 100 rpm during the irradiation experiments and dark controls to simulate the current of seawater and to reduce the adsorption of Fe by vessel.A relatively large volume of culture vessel (5 L) was used to decrease the thickness of the marine phytoplankton suspension for avoiding the light limitation.The difference of light illuminaton on the surface and the bottom of marine phytoplankton suspension could be ignored.

Iron absorption and adsorption by the bloom-forming species under different nutrient regimes
Exponentially growing cells of S. costatum or T. weissflogii cells were filtered and transferred to new medium every 1-2 days, to ensure that the cells were acclimated to the experment.After 4 transfers, the cells were again filtered and added into 1000 mL of filtered seawater (0.22 µm) in acid-cleaned polycarbonate bottles, at a cell concentration Introduction

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Full of 1 × 10 4 cells m L −1 .For N and P, a two-factor experiment was performed to examine the effect of N and P on Fe absorption, adsorption and bioconcentration by the cells.The experimental macronutrient treatments included: total N concentrations of 8, 16, 32, and 64 µmol L −1 , respectively, at a total P concentration of 1.0 µmol L −1 ; and total P concentrations of 1.5, 2.0, and 2.5 µmol L −1 , respectively, at total N concentration of 8 µmol L −1 .These experiments were replicated (n = 3).The N, P, and Fe concentrations (1.8 µmol L −1 ) were maintained in the cultures through compensating addition daily of NaNO 3 , Na 2 HPO 4 , and Fe 2 (SO 4 ) 3 salt for 3 days after determination of N, P, and Fe in the medium, i.e., semi-continuous culture was adopted.
After cultured for 4 days, iron absorption, adsorption, and uptake by the diatom species, S. costatum and T. weissflogii were measured, and the cell density was counted microscopically.The cell diameter of S. costatum was 6-18 µm.The cell length and width of T. weissflogii was 15-22 µm and 9-14 µm, respectively.The cells contained in 600 mL of the medium were collected on a 3.0 µm membrane filter, rinsed with clean natural seawater with 0. water.Fe (III)-EDTA was chosen to simulate Fe chelation by organic substances such as humic and fulvic acids, which occur naturally in the environment.

Statistical approaches
Analysis of variance was calculated by using SASPROC MIXED (Littell et al., 1996).For all analyses, significance was assigned at the P < 0.05 level.Analytical data was tested for homogeneity of variance (Bartlett's Test).All data was log10 transformed to meet assumptions of normality.Univariate data was analysed using Statistica Version 18.1.Correlations between measured parameters were also performed using Statistica Version 18.1 (Templeman et al., 2010).

Accuracy and detection limits of iron determination
Iron determination using microwave-assisted digestion and ICP-MS was evaluated by analyzing certified reference materials, including NIES-03 (green algae, Chlorella Kessleri) and NASS-5 (standard seawater).Limit of detection (LOD, calculated as three times of the standard deviation of 3 reagent blank replicates analysed at different time intervals between samples) was 2.84 µg g −1 ; limit of quantification (calculated as 3.3 times LOD) was 9.37 µg g −1 .Found value in NIES-03 and NASS-5 were 1.82 ± 0.023 mg g −1 and 0.207±0.023ng g −1 , respectively, the results of these analyses in good agreement with certified concentration in both CRMs (1.85±0.092mg g −1 ) and NASS-5 (0.240 ± 0.035 ng g −1 ).The method described was applicable for the determination of low levels (ng g −1 or µg L −1 ) of Fe in coastal seawater and marine organisms.Introduction

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Iron adsorption on the cells of T. weissflogii and S. costatum under different nutrient regimes
Extracellular adsorption of Fe by T. weissflogii and S. costatum maintained at different N and P concentrations in a semi-continuous culture is shown in Fig. 1.Except at the concentration of N 64 µmol L −1 , Fe adsorption by T. weissflogii per cell was increased with increasing macronutrient concentration of N concentration from 8 to 32 µmol L −1 .The minimum (0.07 fmol cell −1 ) and the maximum (1.96 fmol cell −1 ) adsorption of Fe was observed at concentrations of 8 µmol L −1 N/2.5 µmol L −1 P and 32 µmol L −1 N/1 µmol L −1 P, respectively.The maximum adsorption was 28 times of the minimum.The influence of macronutrient concentration on the Fe adsorption by S. costatum per cell was more significant.The maximum adsorption (7.74 fmol cell −1 ) was 38.7 times of the minimum (0.2 fmol cell −1 ).Thus, the influence of macronutrient addition on the adsorption of Fe was obviously dependent on algal species.Marine algae adsorb and coordinate Fe with basic functional groups on their cell surface (Zuo and Hoigné, 1993;Li et al., 2009).Iron adsorption by S. costatum per cell was higher than that T. weissflogii per cell under various macronutrient regimes, although the surface area S. costatum per cell (28-254 µm 2 ) was less than that of T. weissflogii (154-804 µm 2 ).The Fe speciation in the culture solution was controlled by the species of marine phytoplankton and the concentrations of N and P. The amount of basic functional groups on the cell's surface and the cell size are both affected by the concentrations of N and P (Zuo and Hoigné, 1992;Liu et al., 2014).Iron diffusion decrease (or an increase) with a decreasinge (or increasing) of cell size.The degree of influence of macronutrient additions on the cell size of S. costatum was more significant than that of T. weissflogii, so the effect of macronutrient additions on Fe adsorption by S. costatum was more obvious than that by T. weissflogii.Fe adsorption was most likely to be affected by the following five factors: (1) the amount of surface basic groups on the cell surface, (2) the cell size, (3) the species and concentration of Fe, (4) the Introduction

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Full affinity constant between Fe and surface basic groups on the cell surface, and ( 5) the concentrations of N and P through their effects on the above four factors.

Influence of N and P addition on iron absorption by the cells of T. weissflogii and S. costatum
Different species of marine algae have different, growth rate and biochemical composition of marine alga, including the contents of carbohydrate, protein, chlorophyll, and surface basic groups, and the requirement of Fe (Zuo and Hoigné, 1992).The biochemical composition of marine alga affects iron absorption ability and other bioactivities.Macronutrient addition may influence both the growth rate and biochemical composition of marine algae (Liu et al., 2014).Figure 2

Comparison of iron adsorption and absorption by T. weissflogii and S. costatum cells under different nutrient regimes
Iron absorption is not simply diffusion, but results in the internalization of iron by the marine phytoplankton.The iron internalization strategies are highly species-dependent (Völker and Wolf-Gladrow, 1999).In the marine environment, eukaryotic phytoplankton utilizes mainly a reductive strategy to absorb iron (Shaked and Lis, 2012).The rates of iron reduction are inversely proportional to the ratio of the stability constants of their Fe (III) and Fe(II) complexes.The stability constants of iron complexes in the medium are different for different species of marine alga because the ligands of organically bound iron complexes are controlled by the excretion of marine phytoplankton (Wells and Trick, 2004).The activities of cell surface ferric reductases can be relevant to phytoplankton nutrition (Hutchins et al., 1998).
Iron absorption might be influenced by the species and concentration of Fe on the cellular surfaces (Li et al., 2013) (i.e., Fe adsorption, e.g.although the influences of N and P addition on Fe absorption and adsorption by T. weissflogii were the same, the bioactivity and cellular biochemical composition of the marine phytoplankton was different (e.g., Fe-transporter or transport systems for Fe (III) siderophore complexes).Because the effect of P addition on Fe absorption and adsorption was alga-specific, the addition of P could affect the Fe internalization strategy.

Total sorption under different nutrient regimes
Total Fe uptake by marine phytoplankton, including Fe absorption and adsorption by all of the algal cells, is important for depletion of Fe in seawater.Total Fe uptake, adsorption, and absorption by all T. weissflogii and S. costatum cells under different nutrient regimes are shown in Fig. 3.With increasing N concentration from 8 to 32 µmol L −1 , the total Fe uptake, adsorption, and absorption by S. costatum cells were more than that by T. weissflogii cells.It was mainly due to the difference between the cell densities achieved by S. costatum and T. weissflogii.The influence of the species of marine phy-Introduction

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Full toplankton, including the diatom species, on the depletion of Fe in seawater was obvious.Total Fe uptake by T. weissflogii cells was increased with increasing N concentration from 8 to 32 µmol L −1 .A similar result was observed in S. costatum cells, that was, total Fe uptake was increased with increasing N concentration from 8 to 32 µmol L −1 and decreased with increasing P concentration from 1 to 2.5 µmol L −1 .Macronutrient enrichment in coastal ecosystems could cause an increase in the depletion of Fe in seawater by the non-toxic coastal diatom (Li et al., 2013).Total adsorption and absorption by all T. weissflogii and S. costatum cells was increased with increasing N concentration from N concentration from 8 to 32 µmol L −1 .
With increasing P concentration from 1.5 to 2.5 µmol L −1 , total adsorption and absorption by all both T. weissflogii and S. costatum cells was decreased.
The P value was 0.530 for total iron uptake, 0.0348 for total iron adsorption, and 0.541 for total iron absorption, so the influence of different species of marine alga on the total adsorption was statistically significant, but total iron uptake and absorption was statistically non-significant.While the influence of different concentrations of macronutrient on total iron uptake, adsorption, and absorption was statistically non-significant, because the P value 0.858 for total iron uptake, 0.268 for total iron adsorption, and 0.855 for total iron absorption.

Distribution of iron species in seawater under different nutrient regimes
Marine algae produce extracellular organic compounds including polysaccharides, proteins, peptides, and small organic acids (Zuo and Hoigné, 1992;Chen and Wang, 2001).Some of these organic molecules may form stable complexes with iron.Several studies have indeed observed extremely high conditional stability constants (log K FeL = 20 ∼ 23) for iron and organic ligands during an algal bloom, especially in the final stage of a phytoplankton bloom in estuarine and coastal waters at similar salinities (Gobler et al., 2002;Rose and Waite, 2003;Rijkenberg et al., 2006).On the other hand, macronutrient addition may affect the production of extracellular organic compounds and their composition by marine algae, and subsequently influence Introduction

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Full the complex formation, speciation and solubility of iron (Li et al., 2013).Thus, it is important to examine the effects of macronutrients on the solubility of iron in the algae cultures.To test these effectes, Fe 2 (SO 4 ) 3 salt was added into the culture medium as a compensating daily addition.The results are shown in Table 1.
With N concentration from 8 to 32 µmol L −1 , its influence on the concentration of dissolved Fe and particulate Fe from T. weissflogii was similar, but reverse for colloidal Fe, i.e., increasing for dissolved Fe and particulate Fe and decreasing for colloidal Fe, but the effect of P addition from 1.5 to 2.5 µmol L −1 on the concentration of dissolved, colloidal and particulate Fe from T. weissflogii was similar.The colloidal Fe from S. costatum was increased with increasing P concentration from 1.5 to 2.5 µmol L −1 .Except for this relationship between macronutrient addition and colloidal Fe, no other trends were observed for S. costatum.
According to P value analyis, the distribution of iron species under the same culture medium was extremely statistically significant, and the P value for T. weissflogii (4.94 × 10 −4 ) was lower than that for S. costatum (4.15 × 10 −3 ), but the influence of algal species and macronutrient addition on the same iron species was statistically non-significant.The date is shown in Table 2.There were significant inter-species relationships between different algal species and macronutrient addition, although these patterns were not always consistent (Table 3).There was a positive correlation between dissolved Fe and N : P (r = 0.706) from T. weissflogii.Colloidal and particulate Fe from S. costatum (r = 0.710) were also positively correlated in different macronutrient additions.In contrast, all species from S. costatum had significant negatively correlations with macronutrient addition.All the dissolved, colloidal and particulate Fe from T. weissflogii and S. costatum were used as the sources of Fe.The percentages of dissolved Fe (PDI), colloidal Fe (PCI) or particulate Fe (PPI) over the total Fe (< 3.0 µm) in the culture medium of T. weissflogii and S. costatum under different N and P concentration (µmol L −1 ) could be calculated from the results listed in Table 3.For the mixed culture of T. weissflogii and S. costatum were done, the theoretic value of the total cell density of T. weissflogii and S. costatum (i.e.C1, C2, C3, and C4) under different macronutrient regimes could be calculated obtained from the cell density presented in Figs. 3 and 4 using dissolved, colloidal and particulate Fe.The influence of N and P on cell density of T. weissflogii and S. costatum was similar, and the growth was controlled by N/P ratio and the concentrations of N and P.However, the growth was affected by Fe speciation not obvious.With N addition from 8.0 to 64.0 µmol L −1 , the value of C1 / C2 was increased but C3 / C4 was decreased; When P concentration was increased from 1.5 to 2.5 µmol L −1 , the value of C1 / C2 was increased but the change of the value of C3 / C4 wasn't obvious.Hence, an alga-specific influence of N and P addition on cell density was observed.According to the value of C2 / C1, C3 / C4, C3 / C1, C4 / C2, and C3 / C2, algal exudates could promote diatom growth itself, such promotion on S. costatum was more obvious than that on T. weissflogii, which would be beneficial to S. costatum during an interspecific competition.According to P value analyis, iron species and macronutrient addition could extremely significantly effect the growth of both T. weissflogii and S. costatum, and the influence of Fe species was more significant than macronutrient addtion.The data is showed in Tables 4 and 5.

Effect of macronutrient additions on the interspecific competition between T. weissflogii and S. costatum
In coastal environment, S. costatum was coexistence with T. weissflogii, their cell density ratios were 5.57-7.03times, indicating that S. costatum was more competitive than T. weissflogii, Fe was a key determinant for the interspecific competition, because: (1) under N addition from 8 µmol L −1 to 32 µ mol L −1 , the adsorption and absorption of Fe Introduction

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Full  waters, Mar. Chem., 86, 1-13, 2004.Zhou, M. J., Yan, T., and Zou, J. Z.: Preliminary analysis of the characteristics of red tide areas in Changjiang River estuary and its adjacent sea, Chin.J. Appl. Ecol., 14, 1031-1038, 2003.Zuo, Y. and Hoigné, J.: Formation of hydrogen peroxide and depletion of oxalic acid in atmospheric water by photolysis of Fe(III)-oxalato complexes, Environ.Sci.Technol., 26, 1014- Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 16 nmol L −1 Fe twice, resuspended into 25 mL of trace metals clean reagent, stirred for 1 h to remove surface-bound Fe, and filtered on a 3.0 µm membrane filter.The filtrate was added into a closed vessel with mixed acid (HNO 3 : H 2 O 2 , v: v = 2 : 1), microwave digested for 7 min at 1.01 × 10 6 Pa, and then used for determining the concentration of Fe adsorbed by S. costatum or T. weissflogii cells.After removing surface sorbed Fe, the S. costatum or T. weissflogii cells were microwave-digested, and then used for determining the concentration of Fe absorbed by S. costatum or T. weissflogii cells.Fe adsorption or absorption per cell was calculated.Total Fe adsorption or absorption by S. costatum or T. weissflogii cells was the product of Fe adsorption or absorption per cell and the cell density.Discussion Paper | Discussion Paper | Discussion Paper | 2.6 Distribution of iron in seawater with S. costatum or T. weissflogii under different nutrient regimes After 4 days culture, the cross-flow ultra-filtration devices used in this study were a Millipore Pellicon 2 System.With the Pellicon 2, the filters have cut-offs of 3.0, 0.22 µm and 1 kDa.The filter material of the 3.0 and 0.22 µm filter was hydrophobic polyvinylidene fluoride.All materials were carefully acid-rinsed, and filters were kept refrigerated before use.Initially, every new filter was rinsed with deionised water and then with a NaOH and HCl rinse programme before use.The same procedure was repeated after every filtration and before every new sampling occasion.All the retentates and permeates were collected and analysed.The recovery was calculated as R% = {((particulate Fe) + (colloidal Fe) + (dissolved Fe))/(total Fe in culture medium)} × 100.The recovery data for the ultrafilters used in this study were in the range 92-110 %.Particulate Fe (3.0-0.22 µm), colloidal Fe (0.22 µm-1 kDa), and dissolved Fe (< 1 kDa, probably still containing a fraction of smaller colloids) was added into a closed vessel with mixed acid (HNO 3 : H 2 O 2 , v : v = 2 : 1), microwave digested for 7 min at 1.01 × 10 6 Pa, and then used for the determination of the concentration of Fe.The concentrations of Fe in different size fractions were determined by ICP-MS.Particulate Fe, colloidal Fe, and dissolved Fe were used for the cultures of S. costatum and T. weissflogii for examining their influence on the interspecific competition.To statistically analyse the effects of N, P and different species of Fe additions on the competition between S. costatum and T. weissflogii, a three-way factorial experimental design was used.The macronutrient treatments were the same as previous describe and different species of Fe at 1.8 µmol L −1 were added into the clean seawater for the cultures of S. costatum and T. weissflogii.Six species of Fe were used, including dissolved, colloidal, and particulate Fe from S. costatum or T. weissflogii.The background concentration of Fe in the clean seawater was only 0.165 µmol L −1 , and thus could be ignored.Fe was complexed with EDTA at a ratio of 1 : 1.1 before spiking into the sea-Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | showed the absorption of iron by P. donghaiense and S. costatum per cell at seven different N and P concentrations.N addition affected the absorption of Fe by both S. costatum and T. weissflogii per cell in the same way: (1) the minimum Fe absorption (17.67 fmol cell −1 for T. weissflogii and 24.91 fmol cell −1 for S. costatum) was at an N concentration of 64 µmol L −1 and an N : P ratio of 64; (2) Fe absorption was increased with increasing N concentration from 8 to 32 µmol L −1 , with the maximum absorption of Fe (33.16 fmol cell −1 for T. weissflogii and 709.23 fmol cell −1 for S. costatum).With increasing P concentration from 1 to 2.5 µmol L −1 , Fe absorption was decreased in both S. costatum and T. weissflogii, so the value of Fe absorption at concentration of 8 µmol L −1 N/2.5 µmol L −1 P was the minimum (113.44 fmol cell −1 and 68.31 fmol cell −1 ) for T. weissflogii and S. costatum, respectively.The content of Fe absorbed by S. costatum cells was more than that by T. weissflogii under the regimes with N ≥ 8 µmol L −1 , but this situation was reversed when P concentration from 1.5 to 2.5 µmol L −1 .Hence, a non-alga-specific influence of N addition on Fe absorption was observed, but the influence of P addition on Fe absorption was species-dependent.Under studied nutrient regimes, the maximum absorption of iron was 27.2 times and 28.5 times of the minimum absorption for T. weissflogii and Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

3. 7
Influence of the additions of macronutrient and different species of iron on the growth of T. weissflogii and S. costatum With the addition of macronutrient, eight species of Fe, including Fe(III)-EDTA, Fe(OH) 3 , and dissolved, colloidal and particulate Fe from the cultured medium of S. costatum or T. weissflogii, were used to inquire their combined effect on the growth of Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |