Photosynthetic Oxygen Production Research Articles

Effects of reduced dissolved oxygen concentrations on physiology and fluorescence of hermatypic corals and benthic algae

While shifts from coral to seaweed dominance have become increasingly common on coral reefs and factors triggering these shifts successively identified, the primary mechanisms involved in coral-algae interactions remain unclear. Amongst various potential mechanisms, algal exudates can mediate increases in microbial activity, leading to localized hypoxic conditions which may cause coral mortality in the direct vicinity. Most of the processes likely causing such algal exudate induced coral mortality have been quantified (e.g., labile organic matter release, increased microbial metabolism, decreased dissolved oxygen availability), yet little is known about how reduced dissolved oxygen concentrations affect competitive dynamics between seaweeds and corals. The goals of this study were to investigate the effects of different levels of oxygen including hypoxic conditions on a common hermatypic coral Acropora yongei and the common green alga Bryopsis pennata. Specifically, we examined how photosynthetic oxygen production, dark and daylight adapted quantum yield, intensity and anatomical distribution of the coral innate fluorescence, and visual estimates of health varied with differing background oxygen conditions. Our results showed that the algae were significantly more tolerant to extremely low oxygen concentrations (2–4 mg L−1) than corals. Furthermore corals could tolerate reduced oxygen concentrations, but only until a given threshold determined by a combination of exposure time and concentration. Exceeding this threshold led to rapid loss of coral tissue and mortality. This study concludes that hypoxia may indeed play a significant role, or in some cases may even be the main cause, for coral tissue loss during coral-algae interaction processes.

Cellular Cycling, Carbon Utilization, and Photosynthetic Oxygen Production during Bicarbonate-Induced Triacylglycerol Accumulation in a Scenedesmus sp.

Microalgae are capable of synthesizing high levels of triacylglycerol (TAG) which can be used as precursor compounds for fuels and specialty chemicals. Algal TAG accumulation typically occurs when cellular cycling is delayed or arrested due to nutrient limitation, an environmental challenge (e.g., pH, light, temperature stress), or by chemical addition. This work is a continuation of previous studies detailing sodium bicarbonate-induced TAG accumulation in the alkaline chlorophyte Scenedesmus sp. WC-1. It was found that upon sodium bicarbonate amendment, bicarbonate is the ion responsible for TAG accumulation; a culture amendment of approximately 15 mM bicarbonate was sufficient to arrest the cellular cycle and switch the algal metabolism from high growth to a TAG accumulating state. However, the cultures were limited in dissolved inorganic carbon one day after the amendment, suggesting additional carbon supplementation was necessary. Therefore, additional abiotic and biotic experimentation was performed to evaluate in- and out-gassing of CO2. Cultures to which 40–50 mM of sodium bicarbonate were added consumed DIC faster than CO2 could ingas during the light hours and total photosynthetic oxygen production was elevated as compared to cultures that did not receive supplemental inorganic carbon.

Modelling microalgal activity as a function of inorganic carbon concentration: accounting for the impact of pH on the bicarbonate system

The aim of this study is to develop a generic model that can predict algal photosynthetic activity as a function of total inorganic carbon and pH, which will assist in the design and operation of algal culture systems. This is important as the availability of inorganic carbon plays a critical role in algal growth and product accumulation, and in practice, pH is not constant in an algal culture. Hence, such a model will assist in predicting and understanding carbon limitation in algae growth and product accumulation systems. The model builds on published work on inorganic carbon uptake in natural algal systems and extends it to systematically account for wide pH and total inorganic carbon ranges. This study develops and validates a simple model which integrates a summative carbon dioxide and bicarbonate Monod kinetic relationship with inorganic carbon equilibrium chemistry. This is the first time that the algal photosynthetic oxygen production rate has been described as a function of both total inorganic carbon and pH. The model was tested against published and experimental data over an extended pH and total inorganic carbon range. Kinetic parameters estimated by the model match those presented in the literature. The Chlorella alga tested in the experiments showed little affinity for bicarbonate which agrees with previous observations for this alga.

Benthic metabolism and nitrogen dynamics in an urbanised tidal creek: Domination of DNRA over denitrification as a nitrate reduction pathway

Benthic oxygen and nutrient fluxes and nitrate reduction rates were determined seasonally under light and dark conditions at three sites in a micro-tidal creek within an urbanised catchment (Saltwater Creek, Australia). It was hypothesized that stormwater inputs of organic matter and inorganic nitrogen would stimulate rates of benthic metabolism and nutrient recycling and preferentially stimulate dissimilatory nitrate reduction to ammonium (DNRA) over denitrification as a pathway for nitrate reduction. Stormwaters greatly influenced water column dissolved inorganic nitrogen (DIN) and suspended solids concentrations with values following a large rainfall event being 5–20-fold greater than during the preceding dry period. Seasonally, maximum and minimum water column total dissolved nitrogen (TDN) and DIN concentrations occurred in the summer (wet) and winter (dry) seasons. Creek sediments were highly heterotrophic throughout the year, and strong sinks for oxygen, and large sources of dissolved organic and inorganic nitrogen during both light and dark incubations, although micro-phytobenthos (MPB) significantly decreased oxygen consumption and N-effluxes during light incubations due to photosynthetic oxygen production and photoassimilation of nutrients. Benthic denitrification rates ranged from 3.5 to 17.7 μmol N m2 h−1, denitrification efficiencies were low (<1–15%) and denitrification was a minor process compared to DNRA, which accounted for ∼75% of total nitrate reduction.Overall, due to the low denitrification efficiencies and high rates of N-regeneration, Saltwater Creek sediments would tend to increase rather than reduce dissolved nutrient loads to the downstream Gold Coast Broadwater and Moreton Bay systems. This may be especially true during wet periods when increased inputs of particulate organic nitrogen (PON) and suspended solids could respectively enhance rates of N-regeneration and decrease light availability to MPB, reducing their capacity to ameliorate N-effluxes through photoassimilation.

Effects of Biofloc Reduction on Microbial Dynamics in Minimal‐exchange, Superintensive Shrimp, Litopenaeus vannamei, Culture Systems

The microbial community in minimal‐exchange, superintensive culture systems should be managed to cycle nutrients and enhance production. This paper explores the effects of biofloc concentration reduction and a fish‐free diet on several microbial community characteristics. In 16, 3.5‐m diameter, 71‐cm deep outdoor tanks, shrimp were stocked at 460/m3. Eight of the tanks received a fish‐free, plant‐based feed and eight received a conventional feed containing fishmeal and fish oil. Within each diet type, biofloc concentration was reduced in four of the tanks and was not reduced in the other four tanks. Photosynthetically active radiation (PAR) extinction coefficients, photosynthetic oxygen production, chlorophyll‐a (chl‐a) concentrations, pheophytin‐a (pheo‐a) concentrations, and the sum of odd and branched chain fatty acid concentrations as a bacterial abundance indicator (BAI) were measured. Biofloc reduction significantly (P≤ 0.003) decreased PAR extinction coefficients, chl‐a concentration, pheo‐a concentration, and BAI concentration, while significantly increasing photosynthetic oxygen production. Diet did not significantly affect (P &gt; 0.05) any of these measured parameters. The observed changes in microbial community characteristics corresponded with, and may help to explain, significantly improved shrimp feed conversion ratios, growth rate, final weight, and biomass yield in the tanks with biofloc reduction.

Photoacclimation of cultured strains of the cyanobacteriumMicrocystis aeruginosato high-light and low-light conditions

The cyanobacterium Microcystis aeruginosa forms blooms that can consist of colonies. We have investigated how M.aeruginosa acclimatizes to changing light conditions such as can occur during blooms. Three different strains were exposed to two irradiance levels: lower (LL) and higher (HL) than the irradiance-onset saturation parameter. We measured the photosynthetic pigment concentrations, PSII photochemical efficiency, electron transport rate (ETR), irradiance-saturated ETR and ETR efficiency. The relationship between ETR and photosynthetic oxygen production and the excess in PSII capacity were also studied for one strain. Higher values of chlorophyll a and phycocyanin and lower values of total carotenoids were found under LL conditions in the three strains. The strains showed clear differences in the irradiance-saturated ETR and in ETR efficiency under both LL and HL treatments. No differences were found in the linear relationship between ETR and photosynthetic oxygen production under both irradiance treatments. LL-acclimated cells showed higher PSII excess capacity than HL ones, possibly because their higher pigment content could result in a higher light stress than HL cells when forming surface blooms. The fact that the genetically different strains show different photosynthetic physiologies suggests that the very dynamic light climate observed in lakes may allow their coexistence.

Photochemical performance of the acidophilic red alga Cyanidium sp. in a pH gradient.

The acidophilic red alga Cyanidium sp. is one of the dominant mat-forming species in the highly acidic waters of Río Tinto, Spain. The culture of Cyanidium sp., isolated from a microbial mat sample collected at Río Tinto, was exposed to 9 different pH conditions in a gradient from 0.5 to 5 for 24h and its physiological status evaluated by variable chlorophyll a fluorescence kinetics measurements. Maximum quantum yield was determined after 30min, 1h, 2h, 4h, 6h and 24h of exposure after 15min dark adaptation. The effect of pH on photochemical activity of Cyanidium sp. was observable as early as 30min after exposure and the pattern remained stable or with only minor modifications for 24h. The optimum pH ranged from 1.5 to 2.5. A steep decrease of the photochemical activity was observed at pH below 1 even after 30min of exposure. Although the alga had tolerated the exposure to pH = 1 for at least 6h, longer (24h) exposure resulted in reduction of the photochemical activity. At pH above 2.5, the decline was more moderate and its negative effect on photochemistry was less severe. According to the fluorescence measurements, the red alga Cyanidium sp. is well-adapted to prevailing pH at its original locality at Río Tinto, i.e. pH of 1 to 3. The short-term survival in pH < 1.5 may be adaptation to rare exposures to such low pH in the field. The tolerance of pH above 3 could be caused by adaptation to the microenvironment of the inner parts of microbial mats in which Cyanidium sp. usually dominates and where higher pH could occur due to photosynthetic oxygen production.

Acoustic detection of gas bubbles in saturated sands at high spatial and temporal resolution

Small gas bubbles embedded near the surface of submerged sand affect physical, chemical, and biological processes, and so their detection and characterization is important. So far, a noninvasive method for the detection of such bubbles has not been available. We developed a portable acoustic detection technique that offers high spatial and temporal resolution. The measuring system consists of a hand‐held ultrasonic transmitterreceiver that we operated with transducers generating 1 MHz and 2.27 MHz pulses. Bubble detection was based on changes in amplitude and travel time of backscatter data collected from bubbles that were either manually injected into sediment or created by sedimentary microalgal photosynthesis. Laboratory experiments showed that individual bubbles of 6 mm diameter can be detected as deep as 60 mm beneath the sediment‐water interface. Vertical and horizontal resolutions of 0.4–1 mm and 8–13 mm were achieved, depending on the transducer used. Measurements in a coastal bay demonstrated that our technique discriminates between sands with and without bubbles and locates embedded gas. We found that gas accumulations develop in the upper 10 mm of shallow sandy sediment in shallow water during daytime, revealing that the combination of photosynthetic oxygen production and porewater transport in permeable sands can lead to bubble generation below the photosynthetically active layer.

Modeling the dynamic modulation of light energy in photosynthetic algae

An integrated cell-based dynamic mathematical model that take into account the role of the photon absorbing process, the partition of excitation energy, and the photoinactivation and repair of photosynthetic units, under variable light and dissolved inorganic carbon (DIC) availability is proposed. The modeling of the photon energy absorption and the energy dissipation is based on the photoadaptive changes of the underlying mechanisms. The partition of the excitation energy is based on the relative availability of light and DIC to the cell. The modeling of the photoinactivation process is based on the common aspect that it occurs under any light intensity and the modeling of the repair process is based on the evidence that it is controlled by chloroplast and nuclear-encoded enzymes. The present model links the absorption of photons and the partitioning of excitation energy to the linear electron flow and other quenchers with chlorophyll fluorescence emission parameters, and the number of the functional photosynthetic units with the photosynthetic oxygen production rate. The energy allocation to the LEF increases as DIC availability increases and/or light intensity decreases. The rate of rejected energy increases with light intensity and with DIC availability. The resulting rate coefficient of photoinactivation increases as light intensity and/or as DIC concentration increases. We test the model against chlorophyll fluorescence induction and photosynthetic oxygen production rate measurements, obtained from cultures of the unicellular green alga Scenedesmus obliquus, and find a very close quantitative and qualitative correspondence between predictions and data.

Ludwigia grandiflora and L. peploides Onagraceae – Water primroses

<i>Ludwigia grandiflora</i> and <i>L. peploides</i> Onagraceae – Water primroses

Seasonal microphytobenthos on the hypoxic ­northern Gulf of Mexico continental shelf

The presence of photosynthetic organisms on the seafloor may indicate whether oxy- gen evolution contributes to the bottom water oxygen pool in the hypoxic area of the northern Gulf of Mexico. We sampled 3 stations (depth: 14, 20 and 23 m) 100 km west of the mouth of the Mississippi River over 3 hypoxic annual cycles to determine whether microphytobenthos or settled phytoplankton existed on the sediment surface. Microscopy and high-performance liquid chro- matography were used to determine the presence and composition, and to estimate the biomass of microphytobenthos and phytoplankton in surface and bottom waters and sediments. The sedi- ment community (cells >3 µm) found during hypoxia differed from those in the water column and were primarily benthic (58 to 88%). Settled pelagic phytoplankton (1 to 36%) and tychopelagic phytoplankton (5 to 10%) were also present. The settled phytoplankton were mostly present on the sediment during fall and winter. The abundance of benthic cells was directly correlated with light levels on the seafloor and sediment chlorophyll a values. Picocyanobacteria, pennate diatoms and filamentous cyanobacteria dominated the sediment community (by density for all cells 0.2 to 8.0 µm in diameter) during summer. The presence of a viable community of microphytobenthos during hypoxia indicates that the potential for photosynthetic oxygen production exists and may influence the oxygen dynamics in the hypoxic zone.

Crystal structure of the TL29 protein from Arabidopsis thaliana: An APX homolog without peroxidase activity

TL29 is a plant-specific protein found in the thylakoid lumen of chloroplasts. Despite the putative requirement in plants for a peroxidase close to the site of photosynthetic oxygen production, and the sequence homology of TL29 to ascorbate peroxidases, so far biochemical methods have not shown this enzyme to possess peroxidase activity. Here we report the three-dimensional X-ray crystal structure of recombinant TL29 from Arabidopsis thaliana at a resolution of 2.5Å. The overall structure of TL29 is mainly alpha helical with six longer and six shorter helical segments. The TL29 structure resembles that of typical ascorbate peroxidases, however, crucial differences were found in regions that would be important for heme and ascorbate binding. Such differences suggest it to be highly unlikely that TL29 functions as a peroxidase.

The impact of cell-specific absorption properties on the correlation of electron transport rates measured by chlorophyll fluorescence and photosynthetic oxygen production in planktonic algae

Photosynthesis-irradiance (P-E)-curves describe the photosynthetic performance of autotrophic organisms. From these P-E-curves the photosynthetic parameters α-slope, P(max), and E(k) can be deduced which are often used to characterize and to compare different organisms or organisms in acclimation to different environmental conditions. Particularly, for in situ-measurements of P-E curves of phytoplankton the analysis of variable chlorophyll fluorescence proved its potential as a sensitive and rapid method. By using Chlorella vulgaris (Trebouxiophyceae), Nannochloropsis salina (Eustigmatophyceae), Skeletonema costatum and Cyclotella meneghiniana (Bacillariophyceae), the present study investigated the influence of cellular bio-optical properties on the correlation of the photosynthetic parameters derived from fluorescence-based P-E-curves with photosynthetic parameters obtained from the measurement of oxygen evolution. It is demonstrated that small planktonic algae show a wide range of cellular absorptivity which was subject to species-specifity, growth stage and environmental conditions, e.g. nutrient limitation. This variability in bio-optical properties resulted in a great deviation of relative electron transport rates (rETRs) from oxygen-based photosynthesis rates. Thus, the photosynthetic parameters α-slope and P(max) derived from rETRs strongly depend on the specific cellular absorptivity and cannot be used to compare the photosynthetic performance of cells with different optical properties. However, it was shown that E(k) is independent of cellular absorptivity and could be used to compare samples with unknown optical properties.

Energy Budget for the Cultured, Zooxanthellate Octocoral Sinularia flexibilis

The zooxanthellate octocoral Sinularia flexibilis is a producer of potential pharmaceutically important metabolites such as antimicrobial and cytotoxic substances. Controlled rearing of the coral, as an alternative for commercial exploitation of these compounds, requires the study of species-specific growth requirements. In this study, phototrophic vs. heterotrophic daily energy demands of S. flexibilis was investigated through light and Artemia feeding trials in the laboratory. Rate of photosynthetic oxygen by zooxanthellae in light (≈200 μmol quanta m⁻² s⁻¹) was measured for the coral colonies with and without feeding on Artemia nauplii. Respiratory oxygen was measured in the dark, again with and without Artemia nauplii. Photosynthesis-irradiance curve at light intensities of 0, 50, 100, 200, and 400 μmol quanta m⁻² s⁻¹ showed an increase in photosynthetic oxygen production up to a light intensity between 100 and 200 μmol quanta m⁻² s⁻¹. The photosynthesis to respiration ratio (P/R > 1) confirmed phototrophy of S. flexibilis. Both fed and non-fed colonies in the light showed high carbon contribution by zooxanthellae to animal (host) respiration values of 111-127%. Carbon energy equivalents allocated to the coral growth averaged 6-12% of total photosynthesis energy (mg C g⁻¹ buoyant weight day⁻¹ and about 0.02% of the total daily radiant energy. "Light utilization efficiency (ε)" estimated an average ε value of 75% 12 h⁻¹ for coral practical energetics. This study shows that besides a fundamental role of phototrophy vs. heterotrophy in daily energy budget of S. flexibilis, an efficient fraction of irradiance is converted to useable energy.

Assessing the influence of the carbon oxidation-reduction state on organic pollutant biodegradation in algal–bacterial photobioreactors

The influence of the carbon oxidation-reduction state (CORS) of organic pollutants on their biodegradation in enclosed algal-bacterial photobioreactors was evaluated using a consortium of enriched wild-type methanotrophic bacteria and microalgae. Methane, methanol and glucose (with CORS -4, -2 and 0, respectively) were chosen as model organic pollutants. In the absence of external oxygen supply, microalgal photosynthesis was not capable of supporting a significant methane and methanol biodegradation due to their high oxygen demands per carbon unit, while glucose was fully oxidized by photosynthetic oxygenation. When bicarbonate was added, removal efficiencies of 37 ± 4% (20 days), 65 ± 4% (11 days) and 100% (2 days) were recorded for CH(4,) CH(3)OH and C(6)H(12)O(6), respectively due to the additional oxygen generated from photosynthetic bicarbonate assimilation. The use of NO(3)(-) instead of NH(4)(+) as nitrogen source (N oxidation-reduction state of +5 vs. -3) resulted in an increase in CH(4) degradation from 0 to 33 ± 3% in the absence of bicarbonate and from 37 ± 4% to 100% in the presence of bicarbonate, likely due to a decrease in the stoichiometric oxygen requirements and the higher photosynthetic oxygen production. Hypothetically, the CORS of the substrates might affect the CORS of the microalgal biomass composition (higher lipid content). However, the total lipid content of the algal-bacterial biomass was 19 ± 7% in the absence and 16 ± 2% in the presence of bicarbonate.

Geological constraints on the origin of oxygenic photosynthesis

This article examines the geological evidence for the rise of atmospheric oxygen and the origin of oxygenic photosynthesis. The evidence for the rise of atmospheric oxygen places a minimum time constraint before which oxygenic photosynthesis must have developed, and was subsequently established as the primary control on the atmospheric oxygen level. The geological evidence places the global rise of atmospheric oxygen, termed the Great Oxidation Event (GOE), between ~2.45 and ~2.32Ga, and it is captured within the Duitschland Formation, which shows a transition from mass-independent to mass-dependent sulfur isotope fractionation. The rise of atmospheric oxygen during this interval is closely associated with a number of environmental changes, such as glaciations and intense continental weathering, and led to dramatic changes in the oxidation state of the ocean and the seawater inventory of transition elements. There are other features of the geologic record predating the GOE by as much as 200-300 million years, perhaps extending as far back as the Mesoarchean-Neoarchean boundary at 2.8Ga, that suggest the presence of low level, transient or local, oxygenation. If verified, these features would not only imply an earlier origin for oxygenic photosynthesis, but also require a mechanism to decouple oxygen production from oxidation of Earth's surface environments. Most hypotheses for the GOE suggest that oxygen production by oxygenic photosynthesis is a precondition for the rise of oxygen, but that a synchronous change in atmospheric oxygen level is not required by the onset of this oxygen source. The potential lag-time in the response of Earth surface environments is related to the way that oxygen sinks, such as reduced Fe and sulfur compounds, respond to oxygen production. Changes in oxygen level imply an imbalance in the sources and sinks for oxygen. Changes in the cycling of oxygen have occurred at various times before and after the GOE, and do not appear to require corresponding changes in the intensity of oxygenic photosynthesis. The available geological constraints for these changes do not, however, disallow a direct role for this metabolism. The geological evidence for early oxygen and hypotheses for the controls on oxygen level are the basis for the interpretation of photosynthetic oxygen production as examined in this review.

Pervasive oxygenation along late Archaean ocean margins

The photosynthetic production of oxygen in the ocean is thought to have begun at least 2.7 billion years ago. The geochemistry of marine sediments deposited 2.6 billion years ago suggests that ocean margins were oxygenated at least 100 million years before the first significant increase in atmospheric oxygen concentrations.

Ecosystem functioning in a disturbance-recovery context: Contribution of macrofauna to primary production and nutrient release on intertidal sandflats

Although many ecologists have described relationships between biodiversity and ecosystem functioning, changes in functioning after disturbance and during recovery are not well documented. Diversity–functioning theory predicts a decline in functioning with decreased diversity (e.g., following disturbance) and a gradual increase in functioning coincident with biotic recovery. We tested this theory empirically by measuring primary production and nutrient release (indices of sandflat functioning) at three sites at the beginning, middle and end of a year-long recovery period. Although microphytobenthos stock (sediment chlorophyll a content) recovered quickly, rates of gross photosynthetic oxygen production were reduced in disturbed plots, relative to controls, in 7 of 9 comparisons. Plots with high macrofaunal richness had enhanced ammonium efflux, and greater efflux of ammonium likely increased rates of primary production. The site with the highest bioturbation potential, which was dominated by large bivalves, exhibited the largest decline in functioning immediately after disturbance. This site also had the most persistent treatment–control differences during recovery, probably because the large bivalves remained at low abundance in treated plots throughout the year-long experiment.

Dissolved oxygen and its response to eutrophication in a tropical black water river

The Siak is a typical, nutrient-poor, well-mixed, black water river in central Sumatra, Indonesia, which owes its brown color to dissolved organic matter (DOM) leached from surrounding, heavily disturbed peat soils. We measured dissolved organic carbon (DOC) and oxygen concentrations along the river, carried out a 36-h experiment in the province capital Pekanbaru and quantified organic matter and nutrient inputs from urban wastewater channels into the Siak. In order to consider the complex dynamic of oxygen in rivers, a box-diffusion model was used to interpret the measured data. The results suggest that the decomposition of soil derived DOM was the main factor influencing the oxygen concentration in the Siak which varied between approximately 100 and 140 micromol l(-1). Additional DOM input caused by wastewater discharges appeared to reduce the oxygen concentrations by approximately 20 micromol l(-1) during the peak-time in household water use in the early morning and in the early evening. Associated enhanced nutrient inputs appear to reduce the impact of the anthropogenic DOM by favoring the photosynthetic production of oxygen in the morning. A reduction of 20 micromol l(-1), which although perhaps not of great significance in Pekanbaru, has strong implications for wastewater management in the fast developing areas downstream Pekanbaru where oxygen concentrations rarely exceed 20 micromol l(-1).

Changes in physiological activity of algae Desmodesmus quadricauda after active bioaccumulation of newly prepared and characterized Fe(III) complexes with pyridine-3-carboxamide (pca) by living algal cells

The study characterized five iron(III) complexes with heterocyclic N-donor ligand pyridine-3-carboxamide (pca) [FeCl 3(pca) 3], [Fe(H 2O) 2(pca) 3](ClO 4) 3, [Fe 2O(ac) 2(pca) 6]Cl 2·3H 2O, [Fe(NO 3) 3(pca) 3]·3H 2O, [Fe(Cl 2ac) 3(pca) 3] (ac = acetate, Cl 2ac = dichloroacetate) and their effects on biomass, chlorophylls ( a, b), photosynthetic oxygen production and iron biosorption in algae Desmodesmus quadricauda. The effects of Fe(III) complexes were compared with control and those of FeCl 3·6H 2O . While pca coordination to iron atom through the nitrogen atom of its heterocyclic ring mostly increased iron inhibitory effect on algal biomass and chlorophylls production, oxygen production was enhanced. The exceptions were observed only for [Fe 2O(ac) 2(pca) 6]Cl 2·3H 2O complex effect on biomass and oxygen production and [Fe(H 2O) 2(pca) 3](ClO 4) 3 complex effect on chlorophylls production. Complexation increased iron biosorption in algal biomass and iron accumulated amount in algae was 2.8–20 times higher than that from FeCl 3·6H 2O with maximal accumulation from dimeric complex [Fe 2O(ac) 2(pca) 6]Cl 2·3H 2O.