pH Compensation Point Research Articles

Effects of increased pH and inorganic carbon on growth and photosynthesis in the macroalga Gracilaria lemaneiformis (Gigartinales, Rhodophyta)

ABSTRACT The marine red macroalga Gracilaria lemaneiformis usually experiences a changing carbonate system during mariculture. Thalli of G. lemaneiformis collected from Nanao Island, Shantou, China, were cultured in six treatments, with two inorganic carbon (Ci) levels (ambient-Ci, AC; elevated-Ci, EC) and three pH levels (8.2, 9.0, and 9.4), to examine the influence of increased Ci concentrations and high seawater pH on growth and photosynthesis in this farmed algal species. The capacity to extract HCO3 − from seawater was relatively stable, as pH compensation points of G. lemaneiformis remained unchanged (9.54–9.59) in the six treatments. Relative growth rate (RGR) and net photosynthetic rate (Pn) of G. lemaneiformis showed no significant differences between treatments of AC and EC at pH 8.2. However, RGR and Pn were higher at EC than at AC at pH 9.4. In addition, RGR and Pn at AC treatments were 67% ± 12% and 76% ± 6% lower at pH 9.4 than at pH 8.2, respectively. At AC, total pigment content, effective quantum yield of PSII (Yield), and maximum relative electron transport rate (rETRm) were all lower at pH 9.4 than at 8.2. However, reductions of these parameters were significantly ameliorated when thalli of G. lemaneiformis were cultured at EC conditions. We conclude that increasing atmospheric CO2 is conducive to the aquaculture of G. lemaneiformis through the decline of pH and the concurrent increase of Ci in seawater.

Photosynthetic behaviors in response to intertidal zone and algal mat density in Ulva lactuca (Chlorophyta) along the coast of Nan'ao Island, Shantou, China.

Intertidal macroalgae suffer different environmental conditions and mat densities during growing period. In the present study, Ulva lactuca Linnaeus were collected from high, intermediate, and low tidal zones at Nan'ao Island, China. These algal photosynthetic pigments and photosynthesis behaviors with different mat densities were measured. The aim is to examine how the physiological responses and acclimation match the representative tidal distribution and algal mat density. The photosynthetic pigment (chlorophyll a and carotenoid) contents and irradiance-saturated maximum photosynthetic rates (Pmax) were greater in low zone-grown U. lactuca compared with the algae grown at high and intermediate zones. Under low algal mat density, the Pmax, apparent photosynthetic efficiency (α), and dark respiration rate (Rd) of U. lactuca grown at low zone were increased, whereas the irradiance saturation points (Ik) were decreased, compared with the algae grown at higher zone. However, the Pmax of high and intermediate zone-grown U. lactuca at high algal mat density were greater than at low density. Moreover, the pH compensation point of low zone-grown thalli (9.98) was lower than the higher zone-grown thalli (more than 10.15); however, the chlorophyll fluorescence parameters (reflect photosynthetic system activity) of the thalli collected from the three different zones were similar. Therefore, we proposed that the effects of varied densities on the photosynthetic rates of these three tidal zone-grown U. lactuca thalli were different, which might be related with different capacity of HCO3- utilization of macroalgae at their zonations.

Physiological response of a red tide alga (Skeletonema costatum) to nitrate enrichment, with special reference to inorganic carbon acquisition

A classical red tide alga Skeletonema costatum was cultured under various nitrate levels to investigate its physiological response to nitrate enrichment combined with CO2 limitation. The higher nitrate levels increased content of photosynthetic pigments (Chl a and Chl c), electron transport rate in photosystem II, photosynthetic O2 evolution, and thus growth rate in S. costatum. On the other hand, the lower CO2 levels (3.5–4.4 μmol kg−1 seawater) and higher pH (8.56–8.63) values in seawater were observed under higher nitrate conditions. Redox activity of plasma membrane and carbonic anhydrase in S. costatum was enhanced to address the reduced CO2 level at higher nitrate levels. In addition, the pH compensation point was enhanced and direct HCO3− use was induced at higher nitrate levels. These findings indicate that nitrate enrichment would stimulate the breakout of S. costatum dominated red tides via enhancing its photosynthetic performances, and maintain a quick growth rate under CO2 limitation conditions through improving its inorganic carbon acquisition capability. Our study sheds light on the mechanisms of S. costatum defeating CO2 limitation during algal bloom.

Interactive effects of elevated CO2 and nitrogen–phosphorus supply on the physiological properties of Pyropia haitanensis (Bangiales, Rhodophyta)

The ongoing increases in atmospheric CO2 concentrations and coastal eutrophication have affected the coastal environment and marine macroalgae. In this study, the interactive effects of CO2 (390 and 1000 μL L−1) and nutrient levels (nitrogen and phosphorus supplied simultaneously) on the physiological properties of the maricultured macroalga Pyropia haitanensis (Bangiales, Rhodophyta) were investigated. The results showed that elevated CO2 significantly enhanced P. haitanensis growth and NO3 − uptake, but lowered the pH compensation points, regardless of nutrient levels, and enhanced photosynthesis and apparent photosynthetic efficiency (α) when the nutrient levels were high. However, CO2 had little effect on photosynthetic rates at low nutrient levels. At each nutrient level, CO2 elevation lowered both the phycobiliproteins (PB) and soluble protein contents, but enhanced biomass accumulation. Chlorophyll a (Chl a) and carotenoid (Car) contents were markedly increased by high CO2 concentrations at low nutrient levels. Increasing nutrient supply significantly enhanced growth, pH compensation points, and photosynthesis in P. haitanensis at each CO2 level, but the differences of the effects between intermediate and high nutrient levels on this alga were not significant for photosynthesis, pigment content, and nutrient uptake, regardless of CO2 levels. Our results suggest that the growth and physiological responses of P. haitanensis to CO2 levels are largely dependent on the supplement of nutrients. However, the interactive effects of elevated CO2 and nitrogen–phosphorus supplies on the physiological properties of P. haitanensis were limited through respective regulation by the CO2 levels in the atmosphere and the nutrient concentrations in the seawater.

Comparative research on inorganic carbon acquisition by the macroalgae Ulva prolifera (Chlorophyta) and Pyropia yezoensis (Rhodophyta)

The red macroalga Pyropia/Porphyra is one of the most important marine crops in the world; Pyropia cultivation is severely affected by the green macroalga Ulva spp., a fouling organism. In this study, growth competition and acquisition of dissolved inorganic carbon (Ci) by Ulva prolifera and Pyropia yezoensis were investigated to understand the physiological characteristics of the two species. Competition experimental results showed that the relative growth rate of U. prolifera was not affected, whereas the growth rate of P. yezoensis was significantly inhibited. U. prolifera exhibited a competitive advantage when these two species were cultured together. The two algal species displayed high pH compensation points, suggesting that U. prolifera and P. yezoensis can photosynthesize by using HCO3 −; the utilization ability of U. prolifera is stronger than that of P. yezoensis. The net photosynthetic rates of P. yezoensis and U. prolifera were significantly inhibited by the carbonic anhydrase (CA) inhibitors acetazolamide and 6-ethoxyzolamide indicating that CA is implicated in carbon-concentrating mechanisms (CCM). 4,4′-diisothiocyano-stilbene-2,2′-disulfonate (DIDS), another inhibitor that prevents direct HCO3 − uptake, did not significantly affect U. prolifera. Conversely, DIDS can sharply decrease the photosynthetic rate of P. yezoensis, particularly at high pH. U. prolifera and P. yezoensis also showed CO2-limited photosynthesis by which the half-saturating concentration of Ci exceeds that of seawater. U. prolifera did not show active HCO3 − uptake; instead, U. prolifera used HCO3 − via extracellular CA for photosynthetic carbon fixation. U. prolifera also utilizes extracellular CA-mediated HCO3 − absorption to a higher extent than P. yezoensis. By contrast, P. yezoensis shows active HCO3 − uptake and extracellular CCMs for photosynthetic carbon fixation. Therefore, these two algal species can survive in changing environments with high pH and low Ci concentration because of the action of CCMs.

The effects of severe carbon limitation on the green seaweed, Ulva conglobata (Chlorophyta)

Low inorganic carbon (Ci) concentrations in seawater are usually an important factor controlling photosynthesis and growth of seaweeds. The green seaweed, Ulva conglobata Kjellm, collected from a rock pool in a middle intertidal zone located at Nanao Island, Shantou, China, were cultured under low Ci level for several days, to examine the effect of severe carbon limitation on photosynthesis. The rather high pH compensation points obtained from the pH-drift experiments indicated that U. conglobata was capable of acquiring HCO3− from surrounding seawater as its Ci source for photosynthesis. However, thalli of U. conglobata cultured in Ci-starved seawater exhibited a decline of biomass, showing that the realistic photosynthetic carbon gain could not compensate for the respiratory carbon consumption in the thalli under severe Ci limitation during laboratory culture. Compared with ambient Ci conditions, the culture under severe Ci limitation significantly had an increased pigment content, but a lower maximum quantum yield and photosynthetic electron transport rate. Additionally, the maximum carbon-saturating photosynthesis rate and the apparent photosynthetic conductance of U. conglobata thalli increased in cultures with severe Ci limitation compared with ambient Ci in low N-grown thalli. The results suggest that under severe Ci limitation, U. conglobata thalli increased capacities of both light absorption processes and carbon fixation pathways.

Enhanced production of green tide algal biomass through additional carbon supply.

Intensive algal cultivation usually requires a high flux of dissolved inorganic carbon (Ci) to support productivity, particularly for high density algal cultures. Carbon dioxide (CO2) enrichment can be used to overcome Ci limitation and enhance productivity of algae in intensive culture, however, it is unclear whether algal species with the ability to utilise bicarbonate (HCO3 −) as a carbon source for photosynthesis will benefit from CO2 enrichment. This study quantified the HCO3 − affinity of three green tide algal species, Cladophora coelothrix, Cladophora patentiramea and Chaetomorpha linum, targeted for biomass and bioenergy production. Subsequently, we quantified productivity and carbon, nitrogen and ash content in response to CO2 enrichment. All three species had similar high pH compensation points (9.7–9.9), and grew at similar rates up to pH 9, demonstrating HCO3 − utilization. Algal cultures enriched with CO2 as a carbon source had 30% more total Ci available, supplying twenty five times more CO2 than the control. This higher Ci significantly enhanced the productivity of Cladophora coelothrix (26%), Chaetomorpha linum (24%) and to a lesser extent for Cladophora patentiramea (11%), compared to controls. We demonstrated that supplying carbon as CO2 can enhance the productivity of targeted green tide algal species under intensive culture, despite their clear ability to utilise HCO3 −.

两种浒苔无机碳利用对温度响应的机制

PDF HTML阅读 XML下载 导出引用 引用提醒 两种浒苔无机碳利用对温度响应的机制 DOI: 10.5846/stxb201304200756 作者: 作者单位: 淮海工学院海洋学院,淮海工学院海洋学院,淮海工学院海洋学院,淮海工学院海洋学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（41106093）；江苏省自然科学基金资助项目（BK2011400）；国家海洋局海洋公益性行业科研专项资助项目（201205010）；江苏高校优势学科建设工程资助项目 The mechnism of the characters of inorganic carbon acquisition to temperature in two Ulva species Author: Affiliation: School of Marine Science ＆ Technology,Huaihai Institute of Technology,Lianyungang,Jiangsu,China,School of Marine Science ＆ Technology,Huaihai Institute of Technology,Lianyungang,Jiangsu,China,School of Marine Science ＆ Technology,Huaihai Institute of Technology,Lianyungang,Jiangsu,China,School of Marine Science ＆ Technology,Huaihai Institute of Technology,Lianyungang,Jiangsu,China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了探讨温度对大型海藻无机碳利用机制的影响，选择了潮间带常见的绿藻缘管浒苔 （Ulva linza）和浒苔（Ulva prolifera）为实验材料，研究了碳酸酐酶抑制剂乙酰唑磺胺（AZ）和己氧苯并噻唑磺胺（EZ）在不同的温度下对藻体光合作用的影响。实验设置6个温度梯度（5、10、15、20、25和30℃）。结果表明，缘管浒苔和浒苔都有很强的无机碳利用能力，而温度对此有显著的影响。但他们之间存在明显的种间差异。缘管浒苔对温度的依赖性要强于浒苔，其对温度的适应范围要窄于浒苔，尤其是在高温下（30℃），缘管浒苔的最大光合作用能力与最适温度相比下降了56%，而浒苔仅为20%，这表明在高温的情况下，浒苔比缘管浒苔具有更强的生存适应能力，这是浒苔能够在绿潮藻占有绝对优势的原因之一。对缘管浒苔来说，在低温（5℃）和高温（30℃）时，无机碳的转运主要是通过胞外碳酸酐酶的催化作用，而在15℃时，加入胞外碳酸酐酶的抑制剂对无机碳的转运没有明显的影响，这表明在此温度下其他无机碳转运形式可以有效补偿胞外碳酸酐酶的作用。在其他的温度下，胞外碳酸酐酶和其他无机碳转运方式各占一定的比例。而对于浒苔来说，在低温5℃时，其他无机碳转运形式占主要作用，而从10℃开始，胞外碳酸酐酶作用比例显著增加，并且保持在相同的水平上。 Abstract:The intertidal green macroalgae Ulva linza and Ulva prolifera were selected to study the effects of carbonic anhydrase inhibitors AZ and EZ on the photosynthesis of the thalli under different temperatures. Six temperature levels were set (5, 10, 15, 20, 25 and 30℃) in the experiment. Our results showed that the values of pH compensation point of both Ulva linza and Ulva prolifera was as high as 10. This suggested that the both the two Ulva species possessed rather high ability of photosynthetic acquisition of inorganic carbon. The ability of inorganic carbon acquisition in both the two species were significantly affected by temperature, and this temperature responses were species-specific. Compared with Ulva prolifera, Ulva linza was more sensitive to temperature, suggesting that the optimum range of temperature for photosynthesis was narrower in Ulva linza than Ulva prolifera. At high temperature (30℃), the net photosynthetic rate of Ulva linza was decreased by 56%, while only by 20% in Ulva prolifera, compared with the rate at optimum temperature. These results suggested that Ulva prolifera possessed stronger ability to endure high temperature than Ulva linza did. This might be one of the most possilble physiological reasons that the dominant species in green tide bloom is Ulva prolifera. For Ulva linza, the transport of inorganic carbon was predominantly carried out by catalysis of extracellular carbonic anhydrase at temperatures of 5℃ and 30℃. However, no significant effect was found in the transport of inorganic carbon at temperature of 15℃ when the extracellular carbonic anhydrase inhibitor AZ was added. This implied that, at 15℃, another way of transport of inorganic carbon might eliminate the effect of the inhibition of extracellular carbonic anhydrase. Over the temperature rang of 20-25℃, extracellular carbonic anhydrase-mediated inorganic carbon transport and the other patterns of inorganic carbon transport operated as a fixed proportion, respectively. For Ulva prolifera, the primary pattern of the transport of inorganic carbon was not due to the catalysis of extracellular carbonic anhydrase at temperature of 5℃, and another pattern of inorganic carbon transport might operate at this temperature. However, as temperature rose to 10℃, the action of catalysis of extracellular carbonic anhydrase increased significantly, and this action maintained the same levels with further rising of temperature. 参考文献 相似文献 引证文献

Acquisition of inorganic carbon by Endarachne binghamiae (Scytosiphonales, Phaeophyceae)

Photosynthetic acquisition of inorganic carbon was studied in the brown seaweed Endarachne binghamiae J. Agardh. Photosynthesis was saturated at 245 µmol photons m−2 s−1 and photoinhibition did not occur at an irradiance as high as 750 µmol photons m−2 s−1. The dependence of O2 evolution on inorganic carbon (Ci) concentration demonstrated that the normal Ci composition in natural seawater was not saturating for irradiance-saturated photosynthesis. Three lines of evidence demonstrated that E. binghamiae was able to acquire as a source of Ci for photosynthesis: (i) the high value of photosynthetic conductance for CO2 (220.6 µm s−1); (ii) the high pH compensation point of 9.7; and (iii) the measured photosynthetic rates being in excess of the theoretical maximum rates supported solely by the CO2 supply from the spontaneous dehydration of in the bulk seawater. In order to establish the mechanism of Ci acquisition, specific inhibitors and a proton buffer were applied to examine their inhibitory effects on photosynthesis. No inhibitory effects were found for the proton buffer tris(hydroxymethyl)aminomethane and the anion exchanger inhibitor, 4,4′-diisothiocyano-stilbene-2,2′-disulphonate. By contrast, photosynthetic O2 evolution in natural seawater was significantly depressed by the extracellular carbonic anhydrase (CA) activity inhibitor, acetazolamide, and the plasma membrane P-type H+-ATPase inhibitor, vanadate. These results suggested that carbon acquisition from the natural seawater was mostly through the external CA-mediated dehydration mechanism, and that P-type H+-ATPase (proton pump) in the plasma membrane simultaneously functioned in photosynthesis of E. binghamiae. Additional experiments on the O2 exchange versus pH value relationship indicated that, in contrast to photosynthesis, dark respiration of E. binghamiae was insensitive to the change of pH in the seawater, which resulted in a decreasing instantaneous balance between net carbon gain and respiratory carbon loss at high pH values in seawater.

Effects of elevated CO2 on the red seaweed Gracilaria lemaneiformis (Gigartinales, Rhodophyta) grown at different irradiance levels

Zou D. and Gao K. 2009. Effects of elevated CO2 on the red seaweed Gracilaria lemaneiformis (Gigartinales, Rhodophyta) grown at different irradiance levels. Phycologia 48: 510–517. DOI: 10.2216/08-99.1.The red seaweed Gracilaria lemaneiformis (Bory) Weber-van Bosse (Gigartinales, Rhodophyta) from Nanao Island, Shantou, China, was cultured at 370 and 700 µl l−1 CO2 in aeration and at intermediate (160 µmol photons m−2 s−1) and low (30 µmol photons m−2 s−1) irradiance levels in order to examine the influences of the elevated atmospheric CO2 concentrations on growth, photosynthetic performance and some biochemical components in this commercially important species. Relative growth rate (RGR) was significantly higher in G. lemaneiformis thalli grown using CO2-enriched air with respect to nonenriched air when the algae were subjected to intermediate irradiance. However, RGR was similar between these two CO2 treatments when the algae were grown under the low-irradiance condition. Extra CO2 in the culture decreased phycobiliprotein (PB, including phycoerythrin, PE, and phycocyanin, PC) contents of G. lemaneiformis thalli at the higher growth irradiance. However, chlorophyll a (Chl a) and soluble protein contents were unchanged by the CO2 levels in culture. Both PB and Chl a contents were higher in G. lemaneiformis thalli grown at the lower irradiance than at the higher irradiance, regardless of the CO2 levels in culture. The parameters for photosynthetic responses to irradiance and inorganic carbon were mostly not altered with the increase of CO2 concentrations in culture. However, light-saturated photosynthetic rates (Pmax) and apparent carboxylating efficiencies (ACE), expressed per unit Chl a, were significantly higher in algae grown at the intermediate irradiance compared to the low irradiance. Photosynthetic rate was reduced by an increase in pH of seawater from 8.2 to 9.1, and it was also strongly inhibited by the external carbonic anhydrase inhibitor acetazolamide (AZ) in G. lemaneiformis thalli grown at each CO2 and irradiance condition. Moreover, pH compensation points were not affected by the growth conditions. These results suggested that G. lemaneiformis under both growth conditions had a similar capacity of the photosynthetic utilization of external pool in seawater. However, ACE decreased in G. lemaneiformis thalli grown at the low irradiance with respect to the higher irradiance implied that the transport of Ci towards Rubisco within the cell was weakened. Taken together, the data showed that an increase of CO2 was less effective on G. lemaneiformis than the irradiance levels. We concluded that CO2 affected photosynthesis and growth performance when light was not the limiting factor.

Evidence for K+-dependent HCO3- utilization in the marine diatom Phaeodactylum tricornutum.

Photosynthetic utilization of inorganic carbon in the marine diatom Phaeodactylum tricornutum was investigated by the pH drift experiment, measurement of K(1/2) values of dissolved inorganic carbon (DIC) with pH change, and comparison of the rate of photosynthesis with the rate of the theoretical CO(2) formation from uncatalyzed HCO(3)(-) conversion in the medium. The higher pH compensation point (10.3) and insensitivity of the photosynthetic rate to acetazolamide indicate that the alga has good capacity for direct HCO(3)(-) utilization. The photosynthetic rate reached 150 times the theoretical CO(2) supply rate at 100 micromol L(-1) DIC (pH 9.0) in the presence of 10 mmol L(-1) K(+) and 46 times that in the absence of K(+), indicating that for pH 9.4-grown P. tricornutum, HCO(3)(-) in the medium is taken up through K(+)-dependent and -independent HCO(3)(-) transporters. The K(1/2) (CO(2)) values at pH 8.2 were about 4 times higher than those at pH 9.0, whereas the K(1/2) (HCO(3)(-)) values at pH 8.2 were slightly lower than those at pH 9.0 whether without or with K(+), providing further evidence for the presence of the two HCO(3)(-) transport patterns in this alga. Photosynthetic rate and affinity for HCO(3)(-) in the presence of K(+), respectively, were about 2- and 7-fold higher than those in the absence of K(+), indicating that K(+)-dependent HCO(3)(-) transport is a predominant pattern of HCO(3)(-) cellular uptake in low DIC concentration. However, as P. tricornutum was cultured at pH 7.2 or 8.0, photosynthetic affinities to HCO(3)(-) were not affected by K(+), implying that K(+)-dependent HCO(3)(-) transport is induced when P. tricornutum is cultured at high alkaline pH.

Inter-strain variability in the photosynthetic use of inorganic carbon, exemplified by the pH compensation point, in the cyanobacterium Microcystis aeruginosa

Inter-strain variability in pH compensation point (pH c) in the cyanobacterium Microcystis aeruginosa has been investigated. The pH c allows one to discriminate whether the organism is able to take up HCO 3 − as inorganic carbon (C i) source in photosynthesis. Eight subgroups were found according to the pH c value, ranging from 10.44 ± 0.22 to 11.67 ± 0.05. The high variability in pH c (and consequently, in the capacity to use HCO 3 − as C i source) suggested that different HCO 3 − use mechanisms could occur in M. aeruginosa and, from an evolutionary point of view, this trait is not under high natural selective pressure.

The photosynthetic performance of the tropical seagrass Halophila ovalis in the upper intertidal

Some ecophysiological adaptation strategies of the tropical seagrass Halophila ovalis were investigated with respect to this plant's ability to grow in the upper intertidal in either monospecific pools (but not together with other intertidal species) or emergent and exposed to high temperatures and irradiances during several hours every day. It was found that Halophila ovalis could raise the pH in simulated pools to 8.6, while the two other major (biomass wise) intertidal seagrasses raised the pH to 8.8 ( Cymodocea rotundata) and 9.2 ( Thalassia hemprichii). In situ, midday pH values of 8.5, 8.7 and 9.0 were recorded in pools inhabiting the three species, respectively. It was further found that photosynthetic electron transport rates (ETR) measured continuously in situ for one leaf during a diurnal cycle followed the irradiance up to a daily maximal value of 2200 μmol photons m −2 s −1, but dropped by ca. 50% when the leaf became air exposed just before noon. This drop in ETR upon emergence was verified by “point measurements”, while ETRs of leaves that grew in small pools formed as the tide receded followed the irradiance more closely. Similarly, F v/ F m measured after 15 min of dark adaptation decreased by ca. 50% in emergent leaves during midday, but maintained higher daily values in the submerged leaves. Based on the above results, we suggest that Halophila ovalis can not grow in intertidal pools together with the other major intertidal species because the latter raise the pH above its pH compensation point, thus restricting its utilisation of inorganic carbon. For emergent leaves, while F v/ F m values drop during the day, ETRs are still high enough so as to contribute significantly to the daily photosynthetic production of Halophila ovalis. The drop in F v/ F m indicates photoinhibition during midday, especially in emergent leaves, but this is a dynamic process that apparently repairs itself during the late afternoon.

HABITAT MATTERS FOR INORGANIC CARBON ACQUISITION IN 38 SPECIES OF RED MACROALGAE (RHODOPHYTA) FROM PUGET SOUND, WASHINGTON, USA1

Measurements of pH drift were used to assess the ability of 38 red algal seaweeds to use bicarbonate and to deplete the dissolved inorganic carbon pool (DIC) from seawater medium. Subtidal algae were typically restricted to the use of DIC in the form of dissolved CO2, reducing the initial DIC by only 9%. Intertidal species used both dissolved CO2 and bicarbonate and reduced initial DIC by as much as 70%. DIC reductions and pH compensation points for the intertidal species tested were strongly correlated with their vertical zonation on the rocky shoreline (analysis of variance). DIC acquisition efficiency increased with tidal height, but species from the upper edge of the intertidal demonstrated a reversal of this trend. This general pattern associated with tidal height was observed not only among intertidal red algae in general, but also among four species of the genus Porphyra (P. torta V. Krishnamurthy, P. papenfussii Krishnamurthy, P. perforata J. Agardh, P. fucicola Krishnamurthy) and among four populations of the broadly distributed species Mastocarpus papillatus (C. Agardh). The Mastocarpus observations suggest either that individuals of this species may be able to express alternate strategies for carbon acquisition or that intertidal height may select for survivorship of genotypes with different carbon acquisition strategies. Taken together, these data suggest that the carbon acquisition strategy of intertidal red algae may be an important physiological set of adaptations that is under active evolutionary selection. These physiological differences were not related to phylogeny, tested as membership in red algal families and orders.

Photosynthetic use of exogenous inorganic carbon in the agarophyte Gracilaria lemaneiformis (Rhodophyta)

Oxygen evolution characteristics of the agarophyte Gracilaria lemaneiformis (Bory) Weber-van Bosse (Rhodophyta) were examined to establish the mechanism of photosynthetic use of exogenous inorganic carbon (Ci). Oxygen evolution in seawater of pH 8.0 was sharply reduced with the increase of pH. However, the rates of O 2 evolution at pH 8.0 and above exceeded the theoretical calculated maximum rates supported solely by the CO 2 supply from the spontaneous dehydration of HCO 3 − in the bulk seawater. In addition, G. lemaneiformis exhibited a high pH compensation point (9.58). These data indicate that G. lemaneiformis was able to use HCO 3 − as a source of Ci for photosynthesis. Both external and internal carbonic anhydrase (CA) activities, which could be detected potentiometrically, were essential for photosynthesis at alkaline pH values (8.0 and 9.0), because O 2 evolution was inhibited with the addition of CA inhibitors acetazolamide (AZ) and ethoxyzolamide (EZ). By contrast, the anion exchanger inhibitor, 4,4′-diisothiocyano-stilbene-2,2′-disulfonate (DIDS) had no inhibitory effects on photosynthetic O 2 evolution at neither acidic nor alkaline pH values. Therefore, the experiments with CA inhibitors would suggest that the mechanism of extracellular dehydration of HCO 3 − into CO 2 mediated by external CA activity was involved in HCO 3 − use by G. lemaneiformis. The relationship between photosynthetic O 2 evolution rates and Ci concentrations showed that the normal Ci composition in natural seawater could fully saturate photosynthesis of G. lemaneiformis at pH 8.0 or lower. However, the affinity for Ci and the carbon-saturated maximum photosynthesis were dramatically reduced at pH 9.0.

Photosynthetic utilisation of inorganic carbon and its regulation in the marine diatom Skeletonema costatum.

Photosynthetic uptake of inorganic carbon and regulation of photosynthetic CO2 affinity were investigated in Skeletonema costatum (Grev.) Cleve. The pH independence of K1/2(CO2) values indicated that algae grown at either ambient (12 μmol L-1) or low (3 μmol L-1) CO2 predominantly took up CO2 from the medium. The lower pH compensation point (9.12) and insensitivity of photosynthetic rate to di-isothiocyanatostilbene disulfonic acid (DIDS) indicated that the alga had poor capacity for direct HCO3- utilisation. Photosynthetic CO2 affinity is regulated by the concentration of CO2 rather than HCO3-, CO32- or total dissolved inorganic carbon (DIC) in the medium. The response of photosynthetic CO2 affinity to changes in CO2 concentration was most sensitive within the range 3-48 μmol L-1 CO2. Light was required for the induction of photosynthetic CO2 affinity, but not for its repression, when cells were shifted between high (126 μmol L-1) and ambient (12 μmol L-1) CO2. The time needed for cells grown at high CO2 (126 μmol L-1) to fully develop photosynthetic CO2 affinity at ambient CO2 was approximately 2 h, but acclimation to low or very low CO2 levels (3 and 1.3 μmol L-1, respectively) took more than 10 h. Cells grown at low CO2 (3 μmol L-1) required approximately 10 h for repression of all photosynthetic CO2 affinity when transferred to ambient or high CO2 (12 or 126 μmol L-1, respectively), and more than 10 h at very high CO2 (392 μmol L-1).

PHOTOSYNTHETIC UTILIZATION OF INORGANIC CARBON IN THE ECONOMIC BROWN ALGA, HIZIKIA FUSIFORME (SARGASSACEAE) FROM THE SOUTH CHINA SEA1

The mechanism of inorganic carbon (Ci) acquisition by the economic brown macroalga, Hizikia fusiforme (Harv.) Okamura (Sargassaceae), was investigated to characterize its photosynthetic physiology. Both intracellular and extracellular carbonic anhydrase (CA) were detected, with the external CA activity accounting for about 5% of the total. Hizikia fusiforme showed higher rates of photosynthetic oxygen evolution at alkaline pH than those theoretically derived from the rates of uncatalyzed CO2 production from bicarbonate and exhibited a high pH compensation point (pH 9.66). The external CA inhibitor, acetazolamide, significantly depressed the photosynthetic oxygen evolution, whereas the anion‐exchanger inhibitor 4,4′‐diisothiocyano‐stilbene‐2,2′‐disulfonate had no inhibitory effect on it, implying the alga was capable of using HCO3− as a source of Ci for its photosynthesis via the mediation of the external CA. CO2 concentrations in the culture media affected its photosynthetic properties. A high level of CO2 (10,000 ppmv) resulted in a decrease in the external CA activity; however, a low CO2 level (20 ppmv) led to no changes in the external CA activity but raised the intracellular CA activity. Parallel to the reduction in the external CA activity at the high CO2 was a reduction in the photosynthetic CO2 affinity. Decreased activity of the external CA in the high CO2 grown samples led to reduced sensitiveness of photosynthesis to the addition of acetazolamide at alkaline pH. It was clearly indicated that H. fusiforme, which showed CO2‐limited photosynthesis with the half‐saturating concentration of Ci exceeding that of seawater, did not operate active HCO3− uptake but used it via the extracellular CA for its photosynthetic carbon fixation.

Photosynthetic bicarbonate utilization inPorphyra haitanensis (Bangiales, Rhodophyta)

The activities of carbonic anhydrase (CA) and photosynthesis ofPorphyra haitanensis were investigated in order to see its photosynthetic utilization of inorganic carbon source. Both intra- and extra-cellular CA activities existed in the thallus. CA inhibitors, acetazolamide (AZ) and ethoxy-zolamide (EZ), remarkably depressed the photosynthetic oxygen evolution in seawater of pH 8.2 and 10.0, and EZ showed stronger inhibition than AZ. The observed net photosynthetic rate in seawater of pH 8.2 was much higher than that of CO2 supply theoretically derived from spontaneous dehydration of HCO3 −.P. haitanensis also showed a rather high pH compensation point (9.9). The results demonstrated thatP. haitanensis could utilize bicarbonate as the external inorganic carbon source for photosynthesis. The bicarbonate utilization was closely associated with HCO3 − dehydration catalyzed by extracellular CA activity. The inorganic carbon composition in seawater could well saturate the photosynthesis ofP. haitanensis. The low Km value and compensation points for inorganic carbon reflected the existence of CO2-concentrating mechanism in this alga.

Photosynthetic bicarbonate utilization in Porphyra haitanen-sis (Bangiales, Rhodophyta)

The activities of carbonic anhydrase (CA) and photosynthesis of Porphyra haitanensis were investigated in order to see its photosynthetic utilization of inorganic carbon source. Both intra- and extra-cellular CA activities existed in the thallus. CA inhibitors, acetazolamide (AZ) and ethoxy- zolamide (EZ), remarkably depressed the photosynthetic oxygen evolution in seawater of pH 8.2 and 10.0, and EZ showed stronger inhibition than AZ. The observed net pho- tosynthetic rate in seawater of pH 8.2 was much higher than that of CO 2 supply theoretically derived from spontaneous dehydration of HCO 3 - . P. haitanensis also showed a rather high pH compensation point (9.9). The results demonstrated that P. haitanensis could utilize bicarbonate as the external inorganic carbon source for photosynthesis. The bicarbonate utilization was closely associated with 3 HCO - dehydration catalyzed by extracellular CA activity. The inorganic carbon composition in seawater could well saturate the photosynthe- sis of P. haitanensis. The low K m value and compensation points for inorganic carbon reflected the existence of CO 2 - concentrating mechanism in this alga.

PHOTOSYNTHETIC BICARBONATE UTILIZATION BY A TERRESTRIAL CYANOBACTERIUM, NOSTOC FLAGELLIFORME (CYANOPHYCEAE)

The photosynthetic characteristics of the terrestrial cyanobacterium, Nostoc flagelliforme, after complete recovery by rewetting, was investigated to see whether it could use bicarbonate as the external inorganic carbon source when submerged. The photosynthesis–pH relationship and high pH compensation point suggested that the terrestrial alga could use bicarbonate to photosynthesize when submerged. The photosynthetic oxygen evolution rates were significantly inhibited in Na+‐free and Na++ Li+ media but were not affected by the absence of Cl−, implying that the bicarbonate uptake was associated with Na+/ HCO3− symport rather than Cl−/HCO3− exchange system.