Carbon isotope ratio and photosynthetic activity of phytoplankton in the eutrophic Mikawa Bay,Japan

Primary production by phytoplankton in the eutrophic Mikawa Bay, Japan, was studied by simultaneous measurements of natural carbon isotope ratio (δ ¹³C) and short-term carbon uptake rates (¹³C tracer study) of size-fractionated nannoplankton (<10 μm) and net plankton (>10 μm) samples. Short-term photosynthetic rates, which represent the physiological state of algae, were variable regardless of standing stock sizes. Theδ ¹³C values of particulate organic carbon (POC) in June and July displayed horizontal variations for both the net plankton fraction (−19.8 to −12.7‰) and the nannoplankton fraction (−22.0 to −12.8‰). For both fractions, low concentrations of POC had more negativeδ ¹³C values (−22 to −18‰). Highδ ¹³C values for the net plankton were found when POC concentrations were much higher, due to red tide. This suggests that the increase in algal standing crop for the net plankton fraction resulted from accelerated photosynthetic activity. However the nannoplankton fractions with higher POC values have relatively lowδ ¹³C values.     

Iron deficiency-induced changes in carbon fixation and leaf elemental composition of sugar beet (Beta vulgaris) plants

In this experiment we (i) tested the hypothesis that, besides decreasing leaf C fixation, lime induced iron (Fe) deficiency increases root C fixation via PEP carboxylase and (ii) assessed the Fe-induced modifications in the elemental composition of plant tissues. Sugar beet plants were grown in nutrient solutions with Fe (45 M Fe-EDTA; +Fe control) or in a similar nutrient solution without Fe (–Fe) and in presence of CaCO₃ (1.0 gL^–1), either labelled with ¹³C (20 at. %) or unlabelled. After 7 and 17 days from treatment imposition, plants were harvested and single organs analysed for total O, C, H, macro and micronutrients. ¹³C abundance was also assessed in control, unlabelled and labelled –Fe plants. Iron deficiency caused significant growth reductions; chlorophyll and net photosynthesis decreased markedly in Fe-deficient plants when compared to the controls, whereas leaf transpiration rates and stomatal conductance were not affected by Fe deficiency. Iron deficient plants had leaf biomass with lower C (2 to 4%) and higher O (3 to 5%) concentrations than +Fe plants. The ¹³C was higher (less negative) in +Fe than in –Fe unlabelled plants. Iron deficient plants grown in the nutrient solution enriched with labelled CaCO₃ absorbed a relatively small amount of labelled C, which was mainly recovered in the fine roots and accounted for less than 2% of total C gain in the 10 d treatment period. Evidences suggest that iron deficient sugar beets grown in the presence of CaCO₃ do not markedly shift their C fixation from leaf RuBP to root PEPC.     

Relationship between photosynthetic and respiratory carbon metabolism in freshwater phytoplankton

Measurements of algal carbon metabolism in the light and the dark were conducted in (1) short-term (3-h) light and dark incubations, (2) a diel (24-h) experiment, and (3) a longer-term (4-d) carbon accumulation experiment to examine the relationship between photosynthetic rates, photosynthetic carbon metabolism in the light, and respiration and carbon metabolism in the ensuing dark period in natural assemblages of freshwater phytoplankton. High rates of photosynthesis and polysaccharide synthesis in the light were followed by high rates of respiration and polysaccharide utilization in the dark. Polysaccharide was the major respiratory substrate in the dark, and small molecular weight metabolites, lipids, and protein were less important sources of metabolic energy. The protein pool accumulated carbon during dark incubations, but more slowly than during active photosynthesis in the light. Because the intracellular macromolecular pools turn over at very different rates (polysaccharide > protein and lipid), patterns of short-term photosynthetic carbon metabolism are not necessarily indicative of the biochemical composition of the phytoplankton.     

A role for mitochondrial carbonic anhydrase in limiting CO2 leakage from low CO2-grown cells of Chlamydomonas reinhardtii

A model is presented which quantifies a possible role for the carbonic anhydrase in the mitochondrial matrix of Chlamydomonas reinhardtii which incorporates the observation that the expression of this enzyme is increased under growth conditions in which the expression of the carbon dioxide-concentrating mechanism is increased. It is assumed that the inorganic carbon enters the cytosol from the medium, and leaves the cytosol to the plastids, as HCO₃⁻ and that there is negligible carbonic anhydrase activity in the cytosol. The role of the mitochondrial carbonic anhydrase is suggested to be the conversion to HCO₃^– of the CO₂ produced in the mitochondria in the light from tricarboxylic acid cycle activity and from decarboxylation of glycine in any photorespiratory carbon oxidation cycle activity which is not suppressed by the carbon concentrating mechanism. If there is a HCO₃⁻ channel in the inner mitochondrial membrane then almost all of the inorganic carbon leaves the mitochondria as HCO₃⁻, thus limiting the potential for CO₂ leakage through the plasmalemma. This mechanism could increase inorganic C supply to ribulose bisphosphate carboxylase-oxygenase by some 10% at the energetic expense of less than 1% of the total ATP generation by plastids plus mitochondria.     

Monochromatic ultraviolet light induced damage to Photosystem II efficiency and carbon fixation in the marine diatom Thalassiosira pseudonana (3H)

Low light adapted cultures of the marine diatom Thalassiosira pseudonana (3H) were cultured and incubated for 30 min under different ultraviolet (UV) wavelengths of near monochromatic light with and without background photosynthetically active radiation (PAR, 380–700 nm). Maximum damage to the quantum yield for stable charge separations was found in the UVB (280-320 nm) wavelengths without background PAR light while the damage under PAR was 30% less. UV induced damage to carbon fixation in the cells was described by a function similar to non-linear functions of inhibiting irradiance previously published with the exception that damage was slightly higher in the UVA (320–380). Various measurements of fluorescent transients were measured and the results indicate localised damage most likely on the acceptor side of the Photosystem II reaction center. However, dark adapted measurements of fluorescence transients with and without DCMU do not result in similar functions. This is also true for the relationships between fluorescence transients and carbon fixation for this species of marine diatom. The correlation between the weightings _H from measurements of carbon fixation and the quantum yield for stable charge separation as calculated from induction curves with DCMU and without DCMU is R ² 0.44 and R ² 0.78, respectively. The slopes of the two measurements are 3.8 and 1.4, respectively. The strong correlation between the weightings of the induction curves without DCMU and carbon fixation are due to a loss of electron transport from the reaction center to plastoquinone. Under these experimental conditions of constant photon flux density (PFD) this is manifested as a strong linear relationship between the decrease in the operational quantum yield of Photosystem II and carbon fixation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Gas exchange and carbon isotope discrimination in lichens: Evidence for interactions between CO2-concentrating mechanisms and diffusion limitation

The characteristics of gas exchange and carbon isotope discrimination were determined for a number of lichen species, representing contrasting associations between fungal (mycobiont) and photosynthetic (photobiont) organism. These parameters were evaluated with regard to the occurrence of any CO₂-concentrating mechanism (CCM) expressed specifically by the green algal (phycobiont) or cyanobacterial (cyanobiont) partner. Carbon isotope discrimination () fell into three categories. The highest , found in lichens comprising a phycobiont plus cyanobacteria limited to pockets in the thallus (known as cephalodia), ranged from 24 to 28, equivalent to a carbon isotope ratio (¹³C) of around -32 to-36 vs. Pee Dee Belemnite (PDB) standard. Further evidence was consistent with CO₂ supply to the carboxylating system entirely mediated by diffusion rather than a CCM, in that thallus CO₂ compensation point and online instantaneous were also high, in the range normally associated with C₃ higher plants. For lichens consisting of phycobiont or cyanobiont alone, organic material formed two distinct ranges around 15 (equivalent to a ¹³C of -23%.). Thallus compensation point and instantaneous were lower in the cyanobiont group, which also showed higher maximum rates of net photosynthesis, whether expressed on the basis of thallus dry weight, chlorophyll content or area. These data provide additional evidence for the activity of a CCM in cyanobiont lichens, which only show photosynthetic activity when reactivated with liquid water. Rates of net CO₂ uptake were lower in both phycobiont associations, but were relatively constant across a wide working range of thallus water contents, usually in parallel with on-line . The phycobiont response was consistent whether photosynthesis had been reactivated with liquid water or water vapour. The effect of diffusion limitation could generally be seen with a 3–4 decrease in instantaneous at the highest water contents. The expression of a CCM in phycobiont algae, although reduced compared with that in cyanobacteria, has already been related to the occurrence of pyrenoids in chloroplasts. In view of the inherent requirement of cyanobacteria for some form of CCM, and the smaller pools of dissolved inorganic carbon (DIC = CO₂ + HCO _inf3 ^su– + CO _inf3 ^su2– ) associated with phycobiont lichens, it appears that characteristics provide a good measure of the magnitude of any CCM, albeit tempered by diffusion limitation at the highest thallus water contents.Abbreviations ANOVA analysis of variance - CCM CO₂-concentrating mechanism - cyanobiont cyanobacterium - DIC CO₂ + HCO _inf3 ^su– + CO _inf3 ^su2– (dissolved inorganic carbon) - photobiont photosynthetic organism present in the association - phycobiont green alga - phycobiont + cephalodia green algae + cyanobacteria in cephalodia - Pmax maximum photosynthetic rate - PPFD photosynthetic photon flux density, 400–700 nm - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - carbon isotope discrimination () - ¹³C carbon isotope ratio () We would like to thank Dr. Enrico Brugnoli (CNR, Porano, Italy) and E.C. Smith (University of Newcastle) for many helpful discussions. Dr. Kristin Palmqvist (Department of Plant Physiology, University of Umeå, Sweden) kindly provided the samples of Peltigera apthosa. In particularly, Cristina Máguas would like to thank to Prof. Fernando Catarino (University of Lisbon) for his support throughout this study. Cristina Máguas has been supported by JNICT-Science Programme studentship (BD/153/90-RN).     

Vertical and seasonal variations of inorganic carbon allocation into macromolecules by phytoplankton population in a brown-colored and a clear-water lake

The aim of this study was to asses vertical and seasonal variations of inorganic carbon allocation into macromolecules by phytoplankton population in an humic and acidic lake (Lake Vassivière) and in a clearwater lake (Lake Pavin). Biochemical fractionation was done by consecutive differential extractions in order to separate proteins, polysaccharides, lipids and low molecular weight compounds (LMW) by virtue of their relative solubilities in different extraction solvents.Independent of depth and season, the principal photosynthetic end products were polysaccharides followed by proteins, LMW and lipids. However, inorganic carbon allocation into macromolecules varied, in these two lakes, with depth and with the taxonomic composition of phytoplankton. Carbon allocation into polysaccharides decreased with increasing depth, especially in the brown-colored humic lake, and Diatoms, showed high C incorporation into polysaccharides.     

Modeling and experimental validation of carbon dioxide evolution in alkalophilic cultures

The chemical reactions involving carbon dioxide in mineral culture media are considered. A mathematic model is set up, based on published data, which is valid at pH values below 9, and in which the nonideality of the solution is taken into account. The crucial parameter is the constant expressing the equilibrium between carbon dioxide and bicarbonate, K(1).The reactions were studied in three different aqueous solutions: water, mineral salt medium, and a suspension with nongrowing bacterial cells. For each situation, three methods were compared for the determination of the bicarbonate concentration in the solution: equilibrium state total carbon analysis, dynamic monitoring of the rate of acid or alkali addition, and dynamic measurement of the carbon dioxide gas phase mole fraction.In a batch-stirred tank reactor, the equilibrium constant K(1) agreed with the published value, and the three bicarbonate analysis methods give the same results. If the nonideality is not taken into account, the result significantly differed from the published value and is likely to be incorrect.A real alkalophilic process, using Acinetobacter calcoaceticus in a continuous stirred tank reactor at steady state, also gave results that are in accord with the literature. However, the results do not allow validation of the equation expressing the nonideality.The steady state in the batch system and in continuous culture can be well described with the mathematical model. However, in the transient state there are some unexplained differences between simulation and measurement.     

Stable carbon isotope fractionation by marine phytoplankton during photosynthesis

Abstract. In the marine environment, the range of values of carbon isotope fractionation between particulate tissue of phytoplankton and inorganic carbon can be more than 20‰ (− 35‰ < δ¹³C < − 14‰). This review considers the influence of seawater temperature, lipid content of phytoplanktonic cells, kinetic fractionation, and carbon pathway on δ¹³C values observed at sea.
In order to study the contribution of carboxylases (RUBISCO and the β-carboxylases phosphoenolpyruvate carboxylase, phosphoenoplpyruvate carboxykinase and pyruvate carboxylase) to variations of particulate δ¹³C values at sea, we present results obtained simultenously on carboxylase activities and δ¹³C in various environmental conditions. The lowest δ¹³C values are clearly associated with predominance of ribulose-1.5-bisphosphate carboxylase activity, but it was more difficult to explain the high δ¹³C values. Different hypotheses are discussed.     

Allometric scaling of maximum population density: a common rule for marine phytoplankton and terrestrial plants

A primary goal of macroecology is to identify principles that apply across varied ecosystems and taxonomic groups. Here we show that the allometric relationship observed between maximum abundance and body size for terrestrial plants can be extended to predict maximum population densities of marine phytoplankton. These results imply that the abundance of primary producers is similarly constrained in terrestrial and marine systems by rates of energy supply as dictated by a common allometric scaling law. They also highlight the existence of general mechanisms linking rates of individual metabolism to emergent properties of ecosystems.     

The Effect of Atmospheric Carbon Dioxide Elevation on Plant Growth in Freshwater Ecosystems

We developed a dynamic model to investigate the effect of atmospheric carbon dioxide (CO₂) increase on plant growth in freshwater ecosystems. Steady-state simulations were performed to analyze the response of phytoplankton and submerged macrophytes to atmospheric CO₂ elevation from 350 to 700 ppm. We studied various conditions that may affect this response, such as alkalinity, the air–water exchange rate of CO₂, the community respiration rate, and the phosphorus (P) supply rate. The increase in atmospheric CO₂ could affect submerged plant growth only under relatively eutrophic conditions and at a low community respiration rate. Alkalinity had little effect on the response of the different species. When the air–water exchange was low, the proportional effect of the CO₂ increase on plant growth was higher. Under eutrophic conditions, algae and macrophytes using CO₂ and HCO₃^– may double their growth rate due to atmospheric CO₂ elevation, while the growth of macrophytes restricted to CO₂ assimilation may be threefold. The differences in response of the species under various conditions indicate that the elevation of atmospheric CO₂ may induce drastic changes in the productivity and species dominance in freshwater systems.     

中国热带天然林变迁对大气CO2的影响及经济损益评估

我国目前保存较好的热带天然林（包括热带原始林、结构良好的天然更新林,而不包括疏林、残次林、灌木林等）面积约１１８７万ｈｍ２,其中云南南部约有６０万ｈｍ２,海南中南部山区约有５８７万ｈｍ２。在过去的４５年中,我国的热带原始林面积减少了５０％（约１１０ｈｍ２）。在海南岛尖峰岭的实例结果表明,热带原始林的生态系统的Ｃ素库为３４２ｔ／ｈｍ２（其中,森林群落Ｃ素库为２３４ｔ／ｈｍ２,土壤为１０５ｔ／ｈｍ２,凋落物层为３ｔ／ｈｍ２）,系统每年净固定ＣＯ２量为１３３６ｔ／ｈｍ２,折合Ｃ量为０３７３ｔ／ｈｍ２;热带天然更新林生态系统每年净固定ＣＯ２量为７２１３ｔ／ｈｍ２,折合成Ｃ量为１９７ｔ／ｈｍ２。在我国现有的热带天然林生态系统中,森林植被层的Ｃ素库为１４４８亿ｔ,土壤中的Ｃ素库为１４２２亿ｔ,与植被层Ｃ库相当。在减少的热带森林中,Ｃ素库减少了约２２３１亿ｔ、ＣＯ２净同化量减少了０１８３亿ｔ,其经济损益高达２２００亿元。最后从森林与ＣＯ２的关系方面探讨了热带林可持续经营的问题。     

Effects of mixing and silica enrichment on phytoplankton seasonal succession

During the summer of 1983, cryptophytes, diatoms, cyanophytes, and the dinoflagellate, Ceratium hirundinella were most prominant among the phytoplankton of Eau Galle Reservoir. In the open water, cryptophytes and diatoms peaked in the spring, cyanophytes were most successful in the early summer, and Ceratium was dominant from mid-July until early August. In general, the sequence of events corresponded quite closely to the model of seasonal succession developed by the Plankton Ecology Group of the International Society of Limnology. To a large extent, the same pattern held in four experimental water columns. Departures from the model involved the roles of specific nutrients in diatom and cyanophyte periodicity. Diatoms began to yield to cyanophytes in late spring despite intermittent mixing and silica enrichment. Although capable of buoyancy regulation and thus well adapted to stable water columns, cyanophytes had greater increases in biomass in mixed columns, and in those columns, were most successful during a period of intermittent mixing. Cyanophyte success varied inversely with TN : TP ratios during the period of intermittent mixing, but not subsequently. By mid-July, Ceratium dominated the phytoplankton of every column except that of a mixed column in which conditions favored cyanophytes and large diatom species.     

Silicate availability, vertical mixing and grazing control of phytoplankton blooms in mesocosms

Lake Sempach, located in the central part of Switzerland, has a surface area of 14 km², a maximum depth of 87 m and a water residence time of 15 years. Restoration measures to correct historic eutrophication, including artificial mixing and oxygenation of the hypolimnion, were implemented in 1984. By means of the combination of external and internal load reductions, total phosphorus concentrations decreased in the period 1984–2000 from 160 to 42 mg P m^–3. Starting from 1997, hypolimnion oxygenation with pure oxygen was replaced by aeration with fine air bubbles. The reaction of the plankton has been investigated as part of a long-term monitoring program. Taxa numbers, evenness and biodiversity of phytoplankton increased significantly during the last 15 years, concomitant with a marked decline of phosphorus concentration in the lake. Seasonal development of phytoplankton seems to be strongly influenced by the artificial mixing during winter and spring and by changes of the trophic state. Dominance of nitrogen fixing cyanobacteria (Aphanizomenon sp.), causing a severe fish kill in 1984, has been correlated with lower N/P-ratio in the epilimnion. Buoyant algae such as Planktothrix rubescens (syn. Oscillatoria rubescens) increased in abundance due to enlargement of the trophogenic layer and extended mixing depth during winter. The interactions between zoo- and phytoplankton seemed to be depressed as a result of restoration measures. Zooplankton composition changed to more carnivorous and less herbivorous species. Oxygenation of the hypolimnion induced bioturbation of sediments, mainly by oligochaetae worms, and stimulated germination of spores and cysts and hatching of resting eggs.     

Mutualistic relationships between phytoplankton and bacteria caused by carbon excretion from phytoplankton

For the competition system of phytoplankton and bacteria through inorganic phosphorus, our mathematical model showed that mutualistic relationships between them could occur due to production and consumption of extracellular organic carbon by phytoplankton and bacteria. In our model, phytoplankton are limited in their growth by light and phosphorus, and bacteria are limited in their growth by phosphorus and carbon released from phytoplankton. We adopted permanence as a criterion of the coexistence in mathematical analysis, and led necessary conditions of permanence in the model. Under these coexistence conditions, we estimated the strength of total effects of interactions between phytoplankton and bacteria at the steady state by press perturbation method. The results of this estimation indicated the mutualistic interactions between phytoplankton and bacteria. This suggests that mutualistic situation could occur due to the introduction of carbon flow from phytoplankton to bacteria, even if phytoplankton and bacteria compete with each other through common resource, inorganic phosphorus.     

Observations on carbon dioxide fixation in the Nant-y-moch reservoir,Ceredigion, Wales

High rates of carbon dioxide fixation, both in the light and the dark have been observed in Nant-y-Moch Mountain reservoir; these are surprising because of the sparse algal population. The values of CO₂-carbon fixed in the light per milligramme of Chlorophyll a per hour, ranged from 0.1167 mgC/ mg Chl a/hr. to infinity and are much higher than any recorded previously. The uptake of ¹⁴C-sucrose and ¹⁴C glucose was also determined. Factors which might possibly account for these observations, either alone or in combination are discussed. Possible CO₂ fixing agencies include detritus, flagellates and other organisms capable of obtaining energy by dark reactions (chemotrophs).     

Regulation of the induction of bicarbonate uptake by dissolved CO2 in the marine diatom, Phaeodactylum tricornutum

Physiological properties of photosynthesis were determined in the marine diatom, Phaeodactylum tricornutum UTEX640, during acclimation from 5% CO₂ to air and related to H₂CO₃ dissociation kinetics and equilibria in artificial seawater. The concentration of dissolved inorganic carbon at half maximum rate of photosynthesis (K_0·5[DIC]) value in high CO₂‐grown cells was 1009 mmol m ^{? 3} but was reduced three‐fold by the addition of bovine carbonic anhydrase (CA), whereas in air‐grown cells K_0·5[DIC] was 71 mmol m ^{? 3}, irrespective of the presence of CA. The maximum rate of photosynthesis (P_max) values varied between 300 and 500 μ mol O₂ mg Chl ^{? 1} h ^{? 1} regardless of growth pCO₂. Bicarbonate dehydration kinetics in artificial seawater were re‐examined to evaluate the direct HCO₃ ^? uptake as a substrate for photosynthesis. The uncatalysed CO₂ formation rate in artificial seawater of 31·65°/_oo of salinity at pH 8·2 and 25 °C was found to be 0·6 mmol m ^{? 3} min ^{? 1} at 100 mmol m ^{? 3} DIC, which is 53·5 and 7·3 times slower than the rates of photosynthesis exhibited in air‐ and high CO₂‐grown cells, respectively. These data indicate that even high CO₂‐grown cells of P. tricornutum can take up both CO₂ and HCO₃ ^? as substrates for photosynthesis and HCO₃ ^? use improves dramatically when the cells are grown in air. Detailed time courses were obtained of changes in affinity for DIC during the acclimation of high CO₂‐grown cells to air. The development of high‐affinity photosynthesis started after a 2–5 h lag period, followed by a steady increase over the next 15 h. This acclimation time course is the slowest to be described so far. High CO₂‐grown cells were transferred to controlled DIC conditions, at which the concentrations of each DIC species could be defined, and were allowed to acclimate for more than 36 h. The K_0·5[DIC] values in acclimated cells appeared to be correlated only with [CO_2(aq)] in the medium but not to HCO₃ ^? , CO₃^{2 ?} , total [DIC] or the pH of the medium and indicate that the critical signal regulating the affinity of cells for DIC in the marine diatom, P. tricornutum, is [CO_2(aq)] in the medium.     

Photosynthetic inorganic carbon uptake and accumulation in two marine diatoms

Some physiological characteristics of photosynthetic inorganic carbon uptake have been examined in the marine diatoms Phaeodactylum tricornutum and Cyclotella sp. Both species demonstrated a high affinity for inorganic carbon in photosynthesis at pH7.5, having K_1/2(CO₂) in the range 1.0 to 4.0mmol m^?3 and O_2? and temperature-insensitive CO₂ compensation concentrations in the range 10.8 to 17.6 cm³ m^?3. Intracellular accumulation of inorganic carbon was found to occur in the light; at an external pH of 7.5 the concentration in P. tricornutum was twice, and that in Cyclotella 3.5 times, the concentration in the suspending medium. Carbonic anhydrase (CA) was detected in intact Cyclotella cells but not in P. tricornutum, although internal CA was detected in both species. The rates of photosynthesis at pH 8.0 of P. tricornutum cells and Cyclotella cells treated with 0.1 mol m^?3 acetazolamide, a CA inhibitor, were 1.5- to 5-fold the rate of CO₂ supply, indicating that both species have the capacity to take up HCO₃^? as a source of substrate for photosynthesis. No Na⁺ dependence for HCO₃^? could be detected in either species. These results indicate that these two marine diatoms have the capacity to accumulate inorganic carbon in the light as a consequence, in part, of the active uptake of bicarbonate.