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Unicellular C4 photosynthesis in a marine diatom
Abstract
Nearly 50 years ago, inorganic carbon was shown to be fixed in microalgae as the C3 compound phosphoglyceric acid. The enzyme responsible for C3 carbon fixation, ribulose-1,5-bisphosphate carboxylase (Rubisco), however, requires inorganic carbon in the form of CO2 (ref. 2), and Rubisco enzymes from diatoms have half-saturation constants for CO2 of 30-60 microM (ref. 3). As a result, diatoms growing in seawater that contains about 10 microM CO2 may be CO2 limited. Kinetic and growth studies have shown that diatoms can avoid CO2 limitation, but the biochemistry of the underlying mechanisms remains unknown. Here we present evidence that C4 photosynthesis supports carbon assimilation in the marine diatom Thalassiosira weissflogii, thus providing a biochemical explanation for CO2-insensitive photosynthesis in marine diatoms. If C4 photosynthesis is common among marine diatoms, it may account for a significant portion of carbon fixation and export in the ocean, and would explain the greater enrichment of 13C in diatoms compared with other classes of phytoplankton. Unicellular C4 carbon assimilation may have predated the appearance of multicellular C4 plants.
... Il y a de fortes preuves soutenant que beaucoup de diatomées possèdent un MCC biophysique qui pourrait aider à surmonter la limitation en carbone (Hopkinson et al. 2011 ;Matsuda et al. 2017). Cependant, en 2000, un article marquant, mais controversé a été publié par Reinfelder et al. (2000), affirmant que la diatomée marine centrique Thalassiosira weissflogii (maintenant connue sous le nom de Conticriba weissflogii) réalisait une photosynthèse C4. Les auteurs ont observé une augmentation de l'activité de la PEPC lorsque cette diatomée croissait à basse concentration en CO 2 , par rapport à l'activité lorsqu'elle était soumise à de hautes concentrations en CO 2 . ...
... Plus encore, une augmentation de l'activité de la PEPC a aussi été observée dans des cellules limitées en Zn (avec 6 pM de Zn), des conditions qui altèrent l'anhydrase carbonique, un composant essentiel pour les MMC biophysiques et biochimiques (voir chapitres 3 et 6), et par conséquent l'accumulation de carbone inorganique chez cette diatomée. De même, en présence d'un inhibiteur d'AC, l'activité de la PEPC est augmentée (Reinfelder et al. 2000). Des expériences de pulse-chase ont aussi montré qu'une partie du carbone venant du CO2 était incorporé en malate plutôt qu'en 3-phosphoglycerate, suggérant aussi la présence d'un type C 4 (Reinfelder et al. 2000) ou d'un mécanisme de type intermédiaire C 3 -C 4 (Roberts et al. 2007) dans cette diatomée. ...
... De même, en présence d'un inhibiteur d'AC, l'activité de la PEPC est augmentée (Reinfelder et al. 2000). Des expériences de pulse-chase ont aussi montré qu'une partie du carbone venant du CO2 était incorporé en malate plutôt qu'en 3-phosphoglycerate, suggérant aussi la présence d'un type C 4 (Reinfelder et al. 2000) ou d'un mécanisme de type intermédiaire C 3 -C 4 (Roberts et al. 2007) dans cette diatomée. Les mesures de l'activité des enzymes C 4 à haut et bas CO 2 sont cohérentes avec la photosynthèse C 4 chez cette espèce (Clement et al. 2017). ...
Planète bleue, photosynthèse rouge et verte décrit les mécanismes qui permettent aux organismes photosynthétiques aquatiques de contribuer pour moitié à la productivité primaire nette, d’atténuer les changements climatiques en séquestrant le dioxyde de carbone et, par la production d’oxygène, d’avoir transformé l’atmosphère anoxique originelle de la Terre au cours de l’évolution.La photosynthèse aquatique est réalisée par une grande diversité d’organismes, impliquant majoritairement des cyanobactéries et des algues issues de la « lignée rouge », contrairement à la productivité primaire terrestre qui est restreinte aux plantes de la « lignée verte ».Cet ouvrage présente comment, afin de maximiser la productivité, les producteurs aquatiques primaires ont développé des structures et des mécanismes qui augmentent l’apport de dioxyde de carbone à l’enzyme Rubisco qui est responsable de la fixation du dioxyde de carbone. L’analyse s’étend des mécanismes moléculaires impliqués dans l’absorption du carbone aquatique aux conséquences globales de la modification de la planète bleue par l’Homme.
... Except showing some functional similarities, the CCMs in diatoms also show a distinct feature from C. reinhardtii and cyanobacteria that some species, for instance, T. weissflogii has been shown to perform a biochemical CCM, or at least produce C4 intermediates during photosynthesis (Reinfelder et al., 2000;Roberts et al., 2007b). Such biochemical CCM has not yet been reported in C. reinhardtii and cyanobacteria. ...
... However, there are only a few reports on C4 photosynthesis in algae, for instance, the marine, macroscopic green alga Udotea flabellum (Reiskind et al., 1988;Reiskind & Bowes, 1991). In marine diatom Thalassiosira weissflogii, observations of principal intracellular C4 compounds (malate) after 14 CO2 labeling and 14 C transfer from malate to phosphoglyceric acid (PGA) in CO2 stressed cells; the higher activity of phosphoenolpyruvate carboxylase (PEPC) at low CO2 than high CO2 concentrations suggest the existence of a biochemical CCM in this species (Reinfelder et al., 2000). Indications of C4 photosynthesis in diatoms is not only limited to T. weissflogii, some biochemical and molecular data also suggest C4-assisted photosynthesis in T. pseudonana and P. tricornutum (Beardall et al., 1976;McGinn & Morel, 2008;Kustka et al., 2014). ...
... PEPCs in green algae have been shown to be involved in non-photosynthetic anaplerotic functions (Schuller et al., 1990;Huppe & Turpin, 1994;Norici et al., 2002;Mamedov et al., 2005). In diatoms, the PEPCs were proposed to be involved in photosynthesis (Reinfelder et al., 2000;Reinfelder et al., 2004). C4 photosynthesis has evolved many times independently during the evolution of land plants (Sage, 2004), and photosynthetic PEPCs have independently evolved from non-photosynthetic PEPCs (Sage, 2004). ...
... Recently, the presence of a C 4 pathway has been reported in some diatom and green algae species through genome annotations and/or other biochemical approaches (Reinfelder et al., 2000;Derelle et al., 2006;Li et al., 2020). Unlike the typical C 4 land plants where the C 4 biochemistry is split between two effectively collaborating cell types (bundle sheath and mesophyll), the C 4 pathway in unicellular phytoplankton relies on the phosphoenolpyruvate carboxylase (PEPC) to fix HCO 3 À into oxaloacetic acid (OAA) in cytoplasm (McGinn and Morel, 2008) and phosphoenolpyruvate carboxykinase (PEPCK) to release CO 2 (from OAA) around RubisCO in chloroplast (Reinfelder et al., 2000). ...
... Recently, the presence of a C 4 pathway has been reported in some diatom and green algae species through genome annotations and/or other biochemical approaches (Reinfelder et al., 2000;Derelle et al., 2006;Li et al., 2020). Unlike the typical C 4 land plants where the C 4 biochemistry is split between two effectively collaborating cell types (bundle sheath and mesophyll), the C 4 pathway in unicellular phytoplankton relies on the phosphoenolpyruvate carboxylase (PEPC) to fix HCO 3 À into oxaloacetic acid (OAA) in cytoplasm (McGinn and Morel, 2008) and phosphoenolpyruvate carboxykinase (PEPCK) to release CO 2 (from OAA) around RubisCO in chloroplast (Reinfelder et al., 2000). The C 4 pathway in diatoms functions not only to fix and accumulate carbon (Reinfelder et al., 2004;Kustka et al., 2014) but also helps the cells to dissipate excess light energy and maintain the internal pH homeostasis (Haimovich-Dayan et al., 2013). ...
... As the bloom proceeds, the content of malate remained relatively stable in the AB system but increased significantly in the NAB system (Fig. 6F). Short-term 14 C labeling experiments also reveal that malate is part of the major initial product of C 4 photosynthesis in diatoms and more 14 C is incorporated into malate at low CO 2 conditions (Reinfelder et al., 2000;Roberts et al., 2007). As the physiological characteristics of P. donghaiense and other environmental conditions were almost the same between the NAB and AB systems, the increased amounts of malate in the NAB system partially reflected the highly expressed induction of the C 4 pathway under low CO 2 during the bloom period. ...
Dinoflagellates are important primary producers and major causative agents of harmful algal blooms in the global ocean. Despite the great ecological significance, the photosynthetic carbon acquisition by dinoflagellates is still poorly understood. The pathways of photosynthetic carbon assimilation in a marine dinoflagellate Prorocentrum donghaiense under both in situ and laboratory‐simulated bloom conditions were investigated using a combination of metaproteomics, qPCR, stable carbon isotope and targeted metabolomics approaches. A rapid consumption of dissolved CO2 to generate high biomass was observed as the bloom proceeded. The carbon assimilation genes and proteins including intracellular carbonic anhydrase 2, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase and RubisCO as well as their enzyme activities were all highly expressed at the low CO2 level, indicating that C4 photosynthetic pathway functioned in the blooming P. donghaiense cells. Furthermore, δ13C values and content of C4 compound (malate) significantly increased with the decreasing CO2 concentration. The transition from C3 to C4 pathway minimizes the internal CO2 leakage and guarantees efficient carbon fixation at the low CO2 level. This study demonstrates the existence of C4 photosynthetic pathway in a marine dinoflagellate and reveals its important complementary role to assist carbon assimilation for cell proliferation during the bloom period. This article is protected by copyright. All rights reserved.
... In biochemical CCMs, the enzyme phosphoenolpyruvate carboxylase (PEPC) works as a primary carboxylase in the cytoplasm, forming oxaloacetate (C4) from phosphoenolpyruvate (C3) and HCO 3 − ( Figure 1B). This C4 acid is then transported into the chloroplast and releases CO 2 in the vicinity of Rubisco by action of the enzyme phosphoenolpyruvate carboxykinase (PEPCK) (Reinfelder et al., 2000(Reinfelder et al., , 2004Roberts et al., 2007a,b;and references therein). The process of decarboxylation can also be performed by the malic enzyme (ME). ...
... This strengthens the fact that diatoms are capable of maintaining a high CO 2 :O 2 ratio in the vicinity of Rubisco through active DIC pumping systems (Reinfelder, 2011). The main evolutionary diversification in marine diatoms took place during the time when atmospheric CO 2 levels dropped significantly (Reinfelder et al., 2000) and therefore diatoms among the other phytoplankton groups are likely to have developed the most efficient CCMs and Rubisco type (Young et al., 2012). This type ID Rubisco from red algal lineage can perform its highest activity under low CO 2 :O 2 ratio and demands low nutrients as well as energy investment in a CCM; this was likely to be the key factor for mass expansion of diatoms and coccolithophores in the Phanerozoic oceans under very high O 2 and low CO 2 levels (Rickaby and Hubbard, 2019). ...
... There are many experimental studies on marine diatoms showing the expression of all C4 enzymes (Reinfelder et al., 2000, 2004, Reinfelder, 2011Roberts et al., 2007b), however their active functioning was not confirmed. The negative correlation between gene expression levels of ME and pCO 2 /fugacity (as well as the positive correlation with pH) suggests that under CO 2 limitation the diatoms are likely to use this enzyme (except in the largest size fraction). ...
Marine diatoms, the most successful photoautotrophs in the ocean, efficiently sequester a significant part of atmospheric CO2 to the ocean interior through their participation in the biological carbon pump. However, it is poorly understood how marine diatoms fix such a considerable amount of CO2, which is vital information toward modeling their response to future CO2 levels. The Tara Oceans expeditions generated molecular data coupled with in situ biogeochemical measurements across the main ocean regions, and thus provides a framework to compare diatom genetic and transcriptional flexibility under natural CO2 variability. The current study investigates the interlink between the environmental variability of CO2 and other physicochemical parameters with the gene and transcript copy numbers of five key enzymes of diatom CO2 concentration mechanisms (CCMs): Rubisco activase and carbonic anhydrase (CA) as part of the physical pathway, together with phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, and malic enzyme as part of the potential C4 biochemical pathway. Toward this aim, we mined >200 metagenomes and >220 metatranscriptomes generated from samples of the surface layer of 66 globally distributed sampling sites and corresponding to the four main size fractions in which diatoms can be found: 0.8–5 μm, 5–20 μm, 20–180 μm, and 180–2,000 μm. Our analyses revealed that the transcripts for the enzymes of the putative C4 biochemical CCM did not in general display co-occurring profiles. The transcripts for CAs were the most abundant, with an order of magnitude higher values than the other enzymes, thus implying the importance of physical CCMs in diatom natural communities. Among the different classes of this enzyme, the most prevalent was the recently characterized iota class. Consequently, very little information is available from natural diatom assemblages about the distribution of this class. Biogeographic distributions for all the enzymes show different abundance hotspots according to the size fraction, pointing to the influence of cell size and aggregation in CCMs. Environmental correlations showed a complex pattern of responses to CO2 levels, total phytoplankton biomass, temperature, and nutrient concentrations. In conclusion, we propose that biophysical CCMs are prevalent in natural diatom communities.
... As far as biochemical CCMs are concerned, the findings in diatoms are far from clear. Observations of principal 14 C-labelled intracellular C 4 compounds (malate), 14 C transfer from malate to 3-phosphoglyceric acid (PGA) and sugar in CO 2 -limited cells, and the high activity of phosphoenolpyruvate carboxylase (PEPC) at low CO 2 concentrations, indicate the existence of a biochemical CCM in the marine diatom Thalassiosira weissflogii (Reinfelder et al., 2000). Some biochemical and molecular data also suggest a C 4 -assisted photosynthesis in other diatoms, such as Thalassiosira pseudonana and Phaeodactylum tricornutum. ...
... It has been debated for a long time whether there is a C 4 -like photosynthetic pathway in diatoms (Beardall et al., 1976;Reinfelder et al., 2000Reinfelder et al., , 2004McGinn & Morel, 2008;Kustka et al., 2014). While the genes for enzymes required for such a pathway were identified more than a decade ago in the model diatoms P. tricornutum and T. pseudonana (Kroth et al., 2008), their intracellular locations argue against the involvement of the enzymes in a biochemical CCM (Tanaka et al., 2014;Ewe et al., 2018). ...
Photosynthetic carbon fixation is often limited by CO2 availability, which led to the evolution of CO2 concentrating mechanisms (CCMs). Some diatoms possess CCMs that employ biochemical fixation of bicarbonate, similar to C4 plants, but whether biochemical CCMs are commonly found in diatoms is a subject of debate.
In the diatom Phaeodactylum tricornutum, phosphoenolpyruvate carboxylase (PEPC) is present in two isoforms, PEPC1 in the plastids and PEPC2 in the mitochondria. We used real‐time quantitative polymerase chain reaction, Western blots, and enzymatic assays to examine PEPC expression and PEPC activity, under low and high concentrations of dissolved inorganic carbon (DIC).
We generated and analyzed individual knockout cell lines of PEPC1 and PEPC2, as well as a PEPC1/2 double‐knockout strain. While we could not detect an altered phenotype in the PEPC1 knockout strains at ambient, low or high DIC concentrations, PEPC2 and the double‐knockout strains grown under ambient air or lower DIC availability conditions showed reduced growth and photosynthetic affinity for DIC while behaving similarly to wild‐type (WT) cells at high DIC concentrations. These mutants furthermore exhibited significantly lower ¹³C/¹²C ratios compared to the WT.
Our data imply that in P. tricornutum at least parts of the CCM rely on biochemical bicarbonate fixation catalyzed by the mitochondrial PEPC2.
... Generally, the fixation of HCO 3 − and phosphoenolpyruvate (PEP) into oxaloacetate (OAA, a C4 compound) by phosphoenolpyruvate carboxylase (PEPC) is thought to be the first step of the biochemical CCM (also called the C4-like pathway or C4-type CCM), and then, the OAA formed is directly decarboxylated by a phosphoenolpyruvate carboxykinase (PEPCK) or reduced to malate (MAL) or aspartate (ASP) by malate dehydrogenase (MDH) or aspartate aminotransferase (AAT), respectively, which follows decarboxylation to CO 2 by NADP-dependent malic acid (ME) or NADdependent ME, respectively; the CO 2 then enters the Calvin cycle. To date, a single-cell C4-like pathway has been clearly found in the diatom Thalassiosira weissflogii [7], and an atypical "closed-loop biochemical model" C4-like pathway has been found in Thalassiosira pseudonana [4], while the existence of the C4 pathway in the other model diatom species, Phaeodactylum tricornutum, remains somewhat controversial. ...
... Data are expressed as means ± SD of three replicates. PK: pyruvate kinase; PYC: pyruvate carboxylase; PDH: pyruvate dehydrogenase complex; PDC: pyruvate decarboxylase; CS:citrate synthase; GAPDH: glyceraldehyde 3-phosphate dehydrogenase; NC: normal CO 2 ; LC: low CO 2 ; HC: high CO 2 C4 pathway in higher plants [26], and also different from the PEPCK-dependent C4-like pathway reported in the diatom T. weissflogii [7]. Kustka et al. [4] previously proposed that diatom Thalassiosira pseudonana operates a "closed-loop biochemical model" in response to LC conditions, in which the generation and the subsequent decarboxylation of the C4 acid (OAA) were brought out by plastid-localized PEPC2 and PYC, respectively, and the regeneration of PEP from PYR was in a glycine decarboxylase-dependent manner instead of the PPDKmediated manner. ...
Background
Diatoms are well known for high photosynthetic efficiency and rapid growth rate, which are not only important oceanic primary producer, but also ideal feedstock for microalgae industrialization. Their high success is mainly due to the rapid response of photosynthesis to inorganic carbon fluctuations. Thus, an in-depth understanding of the photosynthetic carbon fixation mechanism of diatoms will be of great help to microalgae-based applications. This work directed toward the analysis of whether C4 photosynthetic pathway functions in the model marine diatom Phaeodactylum tricornutum , which possesses biophysical CO 2 -concentrating mechanism (CCM) as well as metabolic enzymes potentially involved in C4 photosynthetic pathway.
Results
For P. tricornutum , differential proteome, enzyme activities and transcript abundance of carbon metabolism-related genes especially biophysical and biochemical CCM-related genes in response to different concentrations of CO 2 were tracked in this study. The upregulated protein abundance of a carbonic anhydrases and a bicarbonate transporter suggested biophysical CCM activated under low CO 2 (LC). The upregulation of a number of key C4-related enzymes in enzymatic activity, transcript and protein abundance under LC indicated the induction of a mitochondria-mediated CCM in P. tricornutum . Moreover, protein abundance of a number of glycolysis, tricarboxylic acid cycle, photorespiration and ornithine–urea cycle related proteins upregulated under LC, while numbers of proteins involved in the Calvin cycle and pentose phosphate pathway were downregulated. Under high CO 2 (HC), protein abundance of most central carbon metabolism and photosynthesis-related proteins were upregulated.
Conclusions
The proteomic and biochemical responses to different concentrations of CO 2 suggested multiple carbon metabolism strategies exist in P. tricornutum . Namely, LC might induce a mitochondrial-mediated C4-like CCM and the improvement of glycolysis, tricarboxylic acid cycle, photorespiration and ornithine–urea cycle activity contribute to the energy supply and carbon and nitrogen recapture in P. tricornutum to cope with the CO 2 limitation, while P. tricornutum responds to the HC environment by improving photosynthesis and central carbon metabolism activity. These findings can not only provide evidences for revealing the global picture of biophysical and biochemical CCM in P. tricornutum , but also provide target genes for further microalgal strain modification to improve carbon fixation and biomass yield in algal-based industry.
... ween CO 2 and D-ribulose-1,5-bisphosphate (RuBP). However, RuBisCO is also capable of fixing O 2 into RuBP during a process known as photorespiration. The two reactions are competitive since, at a high CO 2 concentration (and low O 2 concentration), the enzyme performs carbon fixation instead of photorespiration, and vice versa (Parker et al., 2004). Reinfelder et al. (2000 found that the C3-and C4-pathways can occur simultaneously in diatoms thanks to their different cellular location, namely the chloroplast and cytosol, respectively. During the C4 pathway, bicarbonate (HCO 3 À ) is first fixed in the cytosol into OAA and then into malate that is transported into the chloroplast. The reactions of C3-and C ...
... This enzyme catalyses the conversion of HCO 3 À into CO 2 , and so increases the concentration of the latter near the catalytic site of RuBisCO. The C4 pathway also increases the efficiency of RuBisCO, particularly when there is a problem with the CCM (Reinfelder et al., 2000). ...
Diatoms are microalgae well known for their high variability and high primary productivity, being responsible for about 20% of the annual global carbon fixation. Moreover, they are interesting as potential feedstocks for the production of biofuels and high-value lipids and carotenoids. Diatoms exhibit trophic flexibility and, under certain conditions, they can grow mixotrophically by combing photosynthesis and respiration. So far, only a few species of diatoms have been tested for their mixotrophic metabolism; in some cases, they produced more biomass and with higher lipid content when grown under this condition. Phaeodactylum tricornutum is the most studied diatom species for its mixotrophic metabolism due to available genome sequence and molecular tools. However, studies in additional species are needed to better understand the conservation of this process in diatoms and its potential in industrial applications. Here, we describe the photosynthetic and respiratory pathways involved in mixotrophy and provide an overview of the trophic variability in diatoms. This review also highlights promising areas of industrial applications for diatoms when cultivated under mixotrophy.
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... CCM可以分为生物物理机制以及 生 物 化 学 机 制 . 生 物 物 理 机 制 主 要 通 过 碳 酸 酐 酶 (carbonic anhydrase, CA) [11] [14] . 近年来, Reinfelder等人 [14,15] 运用同位素标记方法和实时荧光 定 量 P C R 方 法 , 证 明 在 单 细 胞 硅 藻 威 氏 海 链 藻 (Thalassiosira weissflogii)中含有C 4 途径的中间代谢 产物及PEPC, PEPCK. ...
... 生 物 物 理 机 制 主 要 通 过 碳 酸 酐 酶 (carbonic anhydrase, CA) [11] [14] . 近年来, Reinfelder等人 [14,15] 运用同位素标记方法和实时荧光 定 量 P C R 方 法 , 证 明 在 单 细 胞 硅 藻 威 氏 海 链 藻 (Thalassiosira weissflogii)中含有C 4 途径的中间代谢 产物及PEPC, PEPCK. 研究还发现, 在限制CO 2 浓度 或抑制CA活性(对CCM的生物物理机制进行抑制)时, PEPC和PEPCK的转录本也出现了表达量增加的情 况 [16,17] , 表明C 4 活动在该条件下有所加强. ...
... Thus, in the absence of CO 2 concentrating mechanisms (CCMs), growth of diatoms could be CO 2 limited at high pH/low pCO 2 (Riebesell et al., 1993;Giordano et al., 2005). Thalassiosira weissflogii, as a model diatom, has been suggested to possess a CCM based on C 4 (Reinfelder et al., 2000) or C 3 -C 4 intermediate photosynthesis (Roberts et al., 2007). There is limited knowledge about the growth and photosynthesis responses of T. weissflogii to seawater alkalization, but varied results have been reported, with reports that growth was unaltered (Burkhardt et al., 1999a;Milligan et al., 2004;Reinfelder, 2012;Goldman et al., 2017), or enhanced (Milligan et al., 2009), by lowered pCO 2 compared to current or higher pCO 2 levels. ...
... This species could utilize CO 2 and HCO À 3 at approximately the same rate at current pCO 2 level, and a decrease in the CO 2 : HCO À 3 uptake ratio was observed at low pCO 2 (Burkhardt et al., 2001). Marine diatoms are suggested to utilize bicarbonate indirectly through the activity of extracellular carbonic anhydrase (CA) (Martin and Tortell, 2008) or directly via specific plasmalemma-located transporters (Nakajima et al., 2013), though T. weisflogii appears use a biochemical rather than a biophysical CCM ( Reinfelder et al., 2000;Roberts et al., 2007). Both extracellular and intracellular CA activities of T. weissflogii were markedly enhanced by low pCO 2 and half-saturation concentration of DIC for photosynthesis was decreased with decreasing pCO 2 (Burkhardt et al., 2001), Figure 3. Percentage changes of maximum photochemical quantum yields (F v /F m , a), relative maximum electron transport rate (rETR max , b), apparent photon transfer efficiency (a, c), and light saturation point (I k , d) (%) of T. weissflogii cells grown at different pCO 2 levels (relative to 400 matm treatment). ...
Increasing atmospheric pCO2 leads to seawater acidification, which has attracted considerable attention due to its potential impact on the marine biological carbon pump and function of marine ecosystems. Alternatively, phytoplankton cells living in coastal waters might experience increased pH/decreased pCO2 (seawater alkalization) caused by metabolic activities of other photoautotrophs, or after microalgal blooms. Here we grew Thalassiosira weissflogii (diatom) at seven pCO2 levels, including habitat-related lowered levels (25, 50, 100, and 200 µatm) as well as present-day (400 µatm) and elevated (800 and 1600 µatm) levels. Effects of seawater acidification and alkalization on growth, photosynthesis, dark respiration, cell geometry, and biogenic silica content of T. weissflogii were investigated. Elevated pCO2 and associated seawater acidification had no detectable effects. However, the lowered pCO2 levels (25 ∼ 100 µatm), which might be experienced by coastal diatoms in post-bloom scenarios, significantly limited growth and photosynthesis of this species. In addition, seawater alkalization resulted in more silicified cells with higher dark respiration rates. Thus, a negative correlation of biogenic silica content and growth rate was evident over the pCO2 range tested here. Taken together, seawater alkalization, rather than acidification, could have stronger effects on the ballasting efficiency and carbon export of T. weissflogii.
... We focused here on the latter possibility, and analysis of KEGG pathways in the predicted proteome of KR01-identified genes that may be involved in a biochemical CCM. We do not expect, however, that the putative KR01 biochemical CCM would strictly follow the canonical version present in algae and plants (e.g., Kroth et al., 2008;Ouyang et al., 2013;Reinfelder et al., 2000;Stutz et al., 2014;Xu et al., 2012) due to its earlier stage of evolution. To explore the predicted functions of target genes identified in our study, we generated RNA-seq data from cultures incubated under different light and CO 2 conditions for 6 h. ...
The photosynthetic amoeba, Paulinella provides a recent (ca. 120 Mya) example of primary plastid endosymbiosis. Given the extensive data demonstrating host lineage‐driven endosymbiont integration, we analysed nuclear genome and transcriptome data to investigate mechanisms that may have evolved in Paulinella micropora KR01 (hereinafter, KR01) to maintain photosynthetic function in the novel organelle, the chromatophore. The chromatophore is of α‐cyanobacterial provenance and has undergone massive gene loss due to Muller's ratchet, but still retains genes that encode the ancestral α‐carboxysome and the shell carbonic anhydrase, two critical components of the biophysical CO2 concentrating mechanism (CCM) in cyanobacteria. We identified KR01 nuclear genes potentially involved in the CCM that arose via duplication and divergence and are upregulated in response to high light and downregulated under elevated CO2. We speculate that these genes may comprise a novel CO2 delivery system (i.e., a biochemical CCM) to promote the turnover of the RuBisCO carboxylation reaction and counteract photorespiration. We posit that KR01 has an inefficient photorespiratory system that cannot fully recycle the C2 product of RuBisCO oxygenation back to the Calvin‐Benson cycle. Nonetheless, both these systems appear to be sufficient to allow Paulinella to persist in environments dominated by faster‐growing phototrophs.
... Freshwater plants like Hydrilla verticillata, Egeria densa, Elodia canadensis Sagittaria subulata, and Orcuttia viscida perform facultative C4 photosynthesis within a single cell (de Groote and Kennedy 1977;Keeley 1998;Casati et al. 2000;Bowes et al. 2002). Marine macroalgae and diatom Udotea flabellum and Thalassiosira weissfloggi also show C4 metabolism (Reiskind & Bowes 1991;Reinfelder et al. 2000;Johnston et al. 2001). Extensive studies were done on H. verticillata to characterize the single-cell system Estavillo et al. 2007;Miyao et al. 2011). ...
Plant physiologists set about comprehending the genesis of the C4 photosynthetic pathway after its discovery by Hatch and Slack. They discovered that a sophisticated combination of morphological and biochemical adaptations allowed the plant to concentrate CO 2 around RuBisCO to achieve maximum efficiency. We categorize the evolutionary events leading to C4 photosynthesis, beginning with anoxygenic photosynthesis and the evolution of RuBisCO to the cooling of Earth by the Great Oxygenation Event that led to the oxygenic photosynthesis. The evolutionary descent of the C4 plants is a phenomenon that occurred around 30 million years ago. Due to industrialization and population growth, improved photosynthetic efficiency and carbon fixation of C4 plants could contest the current global scenario of rising CO 2 concentration. C3 crops engineered with C4 traits, implemented on a large scale, could impact the climate globally. Here we discuss the various strategies used to introduce C4 traits in the C3 plants and the potential techniques to be considered for successful hybridization.
... Carbon acquisition processes, carbonic anhydrase (CA), 47 stress, degradation, and signaling proteins were upregulated in diatoms exposed to Ca(OH) 2 treatment, corroborating previous evidence that CCM during C 4 photosynthesis is vital in T. weissflogii metabolism. 48 Furthermore, metabolic inhibition abolished calcium and silica deposition, a photosynthesis-dependent process. This result suggests that Ca 2+ calcification most probably enters the cell down its electrochemical gradient via a Ca 2+ permeable channel. ...
... In this case, most of the light energy absorbed by the pigment is dissipated. Miller et al. found that under carbon-restricted constant culture conditions, cyanobacterial Synechococcus cells had a half-saturation concentration of 3 nmol/L at fixed CO 2 and confirmed a CO 2 concentration mechanism (CCM) between the extracellular environment and the Rubisco perimeter [22,23]. ...
Phytoplankton have a crucial role in the conversion of greenhouse gas sources and sinks in natural water bodies, such as lakes, rivers, and oceans. In response to environmental changes, phytoplankton adapt by altering their carbon utilization strategies, which affect carbon sequestration rates and carbon fluxes at the water–air interface. This paper classifies and summarizes the main carbon utilization strategies of phytoplankton in terms of carbon acquisition, carbon metabolism, and carbon emission. Their carbon acquisition strategy determines their carbon uptake rate, while their carbon metabolism strategy affects their carbon sequestration potential. Moreover, their carbon emission strategy determines the final net carbon sequestration. A systematic study of phytoplankton carbon utilization strategies is important for the development of phytoplankton-based wastewater treatment technologies, understanding of algal greenhouse gas fixation, and assessment of greenhouse gas sources and sinks in natural water bodies. This article provides a comprehensive understanding of the ecological role of phytoplankton in natural water bodies and offers valuable references for related research. Furthermore, our research sheds light on the carbon metabolism and emission processes of phytoplankton. By analyzing the carbon metabolism and emission of phytoplankton under different carbon utilization strategies, we can more accurately evaluate the impact of phytoplankton on the carbon cycle in natural water bodies, which can contribute to environmental protection and sustainable development.
... The SiO 3 2− content in Daya Bay increased due to the increase in precipitation, which was attributed to SiO 3 2− from the land contributed by stormwater runoff. In addition, the length of daylight has a significant effect on SiO 3 2− as diatoms in seawater photosynthesize under sunlight [33]. The life activity of diatoms is influenced by photosynthesis. ...
This study explored the variations in the characteristics of the trophic structure of Daya Bay island waters over the last four decades based on the survey findings and research data on biogenic elements (dissolved inorganic nitrogen (DIN), NO2−, NO3−, NH4+, PO43−, and SiO32−) in Daya Bay during 1985–2021. At this time, the DIN concentration increased from 21.14 µg·L−1 to 558.42 µg·L−1 (26.41-fold increase), whereas the SiO32− concentration increased by only 3.6-fold. The PO43− concentrations attained a peak in 2004 and experienced a steady decline over the rest of the survey period. The fractions of NH4+, NO3−, and NO2− in DIN changed from 0.45, 0.40, and 0.15 in 1986 to 0.26, 0.74, and 0.003 in 2021, respectively. Overall, the mean values of NH4+, NO3−, and NO2− accounted for 45.2%, 42.5%, and 12.3%, respectively. The N/P(DIN/PO43−) ratio in Daya Bay increased from 28.08 in the 1980s to 51.63 in the 2010s. Meanwhile, the nutrient limitation conditions showed a gradual shift from N-limited to P-limited conditions. According to the nutrient quality index (NQI) analysis, the trophic state level of Daya Bay waters fell into the oligotrophic category 30 years ago (1985–2002, NQI < 2), whereas it increased from the mesotrophic level in 2005 (NQI = 2.03) to the eutrophic level in 2019 (NQI = 3.33) over the last 20 years. The results based on the eutrophication index (EI) of Daya Bay waters were generally consistent with those based on the NQI, displaying that the trophic level of Daya Bay waters indicated an increasing trend from 2005 to 2019. Moreover, the assessment data in 2021 indicated a decrease in the NQI to 0.90, thereby attaining the oligotrophic level again. This may be related to the decrease in aquacultural area in the bay over the last two years. The correlation analysis among the DIN, PO43−, and nutrient levels of Daya Bay waters indicated that the input of nitrogen and phosphorus was the primary reason for the higher nutrient levels in the water bodies; among them, municipal sewage discharge, aquaculture, and atmospheric deposition from industry are the main factors for the over importation. This indicates that the changes in the biogenic element concentrations led to variations in the trophic structure and level of Daya Bay and may be attributed to population growth and the development of the seaside industry and agriculture in the region.
... Hence, the upregulation of genes coding photosynthetic apparatus was in line with the increase in Fv/Fm value and the content of photosynthetic pigments. Similar to some other microalgae, such as Chromochloris zofingiensis [31] and Thalassiosira weissflogii [33], both the C 4 cycle and Calvin-Benson cycle for CO 2 fixation exist in C. sorokiniana FZU60. As shown in Fig. 5b, the expression level of RBCS gene in the Calvin-Benson cycle, responsible for fixing CO 2 into glycerate, was significantly upregulated after the shift to photoautotrophy (0 and 12 h). ...
Background
Chlorella sorokiniana FZU60 is a promising lutein producing microalga. A mixotrophy/photoautotrophy two-stage strategy can achieve high biomass concentration at stage 1 and high lutein content at stage 2, leading to excellent lutein production efficiency in C. sorokiniana FZU60. However, the underlying molecular mechanisms are still unclear, restraining the further improvement of lutein production.
Results
In this study, physiological and biochemical analysis revealed that photochemical parameters (Fv/Fm and NPQ) and photosynthetic pigments contents increased during the shift from mixotrophy to photoautotrophy, indicating that photosynthesis and photoprotection enhanced. Furthermore, transcriptomic analysis revealed that the glyoxylate cycle and TCA cycle were suppressed after the shift to photoautotrophy, leading to a decreased cell growth rate. However, the gene expression levels of photosynthesis, CO2 fixation, autophagy, and lutein biosynthesis were upregulated at the photoautotrophy stage, demonstrating that microalgal cells could obtain more precursor to synthesize lutein for enhancing photosynthesis and reducing reactive oxygen species.
Conclusions
The findings help to elucidate the molecular mechanisms for high lutein production efficiency of C. sorokiniana FZU60 under the mixotrophy/photoautotrophy strategy, identify key functional genes responsible for lutein biosynthesis, and shed light on further improvement of lutein production by genetic or metabolic engineering in future studies.
... Most diatoms studied to date possess a biophysical CCM that uses a compartment (pyrenoid) capable of elevating CO 2 around the CO 2 fixing enzyme, RuBisCO (Roberts et al. 2007;Hopkinson et al. 2016). Some diatoms may also possess a biochemical CCM (e.g., a C4 pathway) but this is still open for debate (Reinfelder et al. 2000;Morel et al. 2002;Roberts et al. 2007;Clement et al. 2016) and is not the focus of this study. While pyrenoids are common in diatoms, the mechanism by which the CCM elevates CO 2 around RuBisCO varies among species. ...
Marine diatoms are key primary producers across diverse habitats in the global ocean. Diatoms rely on a biophysical carbon concentrating mechanism (CCM) to supply high concentrations of CO 2 around their carboxylating enzyme, RuBisCO. The necessity and energetic cost of the CCM are likely to be highly sensitive to temperature, as temperature impacts CO 2 concentration, diffusivity, and the kinetics of CCM components. Here, we used membrane inlet mass spectrometry (MIMS) and modeling to capture temperature regulation of the CCM in the diatom Phaeodactylum tricornutum (Pt). We found that enhanced carbon fixation rates by Pt at elevated temperatures were accompanied by increased CCM activity capable of maintaining RuBisCO close to CO 2 saturation but that the mechanism varied. At 10 and 18 °C, diffusion of CO 2 into the cell, driven by Pt's 'chloroplast pump' was the major inorganic carbon source. However, at 18 °C, upregulation of the chlo-roplast pump enhanced (while retaining the proportion of) both diffusive CO 2 and active HCO 3 − uptake into the cytosol, and significantly increased chloroplast HCO 3 − concentrations. In contrast, at 25 °C, compared to 18 °C, the chloroplast pump had only a slight increase in activity. While diffusive uptake of CO 2 into the cell remained constant, active HCO 3 − uptake across the cell membrane increased resulting in Pt depending equally on both CO 2 and HCO 3 − as inorganic carbon sources. Despite changes in the CCM, the overall rate of active carbon transport remained double that of carbon fixation across all temperatures tested. The implication of the energetic cost of the Pt CCM in response to increasing temperatures was discussed.
... Notably, symbionts in A32 also upregulated genes encoding transporters and enzymes associated with algal CCMs, including SLC4 inorganic carbon (Ci) transporters and those key enzymes (PEPCK, NADP-ME, and PPDK) involved in C4 pathway, thus indicating a certain degree of cooperation between algal and host CCMs in photosynthetic Ci acquisition ( Figure 6). Although the unicellular algae lack the typical Kranz anatomy (bundle sheath and mesophyll cells) for the spatial separation of Ci fixation and release, the performance of a C4-like pathway and photosynthesis is commonly recognized in diatoms and dinoflagellates, including Symbiodiniaceae from cnidarians (Reinfelder et al., 2000;Tytler et al., 1986;Zhang et al., 2021). The co-upregulation of PEPCK and NADP-ME subtypes in A32 suggests higher efficiency in the carboxylation process to enrich CO 2 in the vicinity of Rubisco and suppress the oxygenase function of Rubisco and the photorespiratory activity (Timm & Hagemann, 2020). ...
Thermal priming of reef corals can enhance their heat tolerance, however, the legacy effects of heat stress during parental brooding on larval resilience remain understudied. This study investigated whether preconditioning adult coral Pocillopora damicornis to high temperatures (29°C and 32°C) could better prepare their larvae for heat stress. Results showed that heat‐acclimated adults brooded larvae with reduced symbiont density and shifted thermal performance curves. Reciprocal transplant experiments demonstrated higher bleaching resistance and better photosynthetic and autotrophic performance in heat‐exposed larvae from acclimated adults compared to unacclimated adults. RNA‐seq revealed strong cellular stress responses in larvae from heat‐acclimated adults that could have been effective in rescuing host cells from stress, as evidenced by the widespread upregulation of genes involved in cell cycle and mitosis. For symbionts, a molecular coordination between light harvesting, photoprotection and carbon fixation was detected in larvae from heat‐acclimated adults, which may help optimize photosynthetic activity and yield under high temperature. Furthermore, heat acclimation led to opposing regulations of symbiont catabolic and anabolic pathways and favored nutrient translocation to the host and thus a functional symbiosis. Notwithstanding, the improved heat tolerance was paralleled by reduced light‐enhanced dark respiration, indicating metabolic depression for energy saving. Our findings suggest that adult heat acclimation can rapidly shift thermal tolerance of brooded coral larvae and provide integrated physiological and molecular evidence for this adaptive plasticity, which could increase climate resilience. However, the metabolic depression may be maladaptive for long‐term organismal performance, highlighting the importance of curbing carbon emissions to better protect corals.
... The widespread CCMs in marine phytoplankton are processes of increasing the CO 2 level at the site of Rubisco through transporters and carbonic anhydrases (CAs), which accelerate the otherwise slow interconversion between HCO 3and CO 2 [24][25][26] . The possible influences of biochemical CCMs involving C4-type photosynthesis on δ 13 C phyto have been suggested in some species of marine phytoplankton 27,28 but not yet proven 29,30 . Not all of the factors are necessarily relevant under natural conditions in the field, and only a few are likely to exert primary control on δ 13 C phyto at most times and location 31 . ...
The stable carbon isotopic composition of marine particulate organic matter (δ ¹³ C POM ) varies with source and environmental conditions. Dissolved carbon dioxide (CO 2 ) concentration is thought to influence δ ¹³ C POM more than temperature, but this relationship is poorly constrained in marginal seas. Here we present δ ¹³ C POM , hydrographic and carbonate system variables at the deep chlorophyll maxima of the southern Yellow Sea in late summer 2017. We find δ ¹³ C POM values varied between stable and cyclonic gyre regions, but indicated autochthonous organic matter production and were more strongly correlated with temperature than dissolved CO 2 concentration throughout. We find that the relationship between temperature and δ ¹³ C POM was independent of CO 2 concentration, whereas the relationship between δ ¹³ C POM and CO 2 concentration was dependent on temperature also being correlated with CO 2 concentration. We suggest that temperature is the primary determinant of marine δ ¹³ C POM due to temperature-dependent metabolism in phytoplankton, irrespective of inorganic carbon acquisition mode.
... The three other paleoenvironmental time series used were 13 C, 87 Sr/ 86 Sr, and 34 S isotopic ratios, following Cárdenas and Harries (13). 13 C reflects variations in not only primary productivity and burial of organic matter (photosynthetic reduction of CO 2 in organic matter) but also weathering, hydrothermal degassing, clathrates, and volcanism (40)(41)(42). Here, we used the 13 C time series as an environmental proxy of oceanic productivity. ...
Biodiversity on Earth is shaped by abiotic perturbations and rapid diversifications. At the same time, there are arguments that biodiversity is bounded and regulated via biotic interactions. Evaluating the role and relative strength of diversity regulation is crucial for interpreting the ongoing biodiversity changes. We have analyzed Phanerozoic fossil record using public databases and new approaches for identifying the causal dependence of origination and extinction rates on environmental variables and standing diversity. While the effect of environmental factors on origination and extinction rates is variable and taxon specific, the diversity dependence of the rates is almost universal across the studied taxa. Origination rates are dependent on instantaneous diversity levels, while extinction rates reveal delayed diversity dependence. Although precise mechanisms of diversity dependence may be complex and difficult to recover, global regulation of diversity via negative diversity dependence of lineage diversification seems to be a common feature of the biosphere, with profound consequences for understanding current biodiversity crisis.
... Due to anthropogenic climate change driven by increased CO 2 emissions, average surface seawater temperatures are predicted to increase 1-6 °C by 2100 [64]. As a result, the ecophysiology of marine biota is likely to be altered due to changes to metabolic function and changes in seawater chemistry and nutrient availability [65][66][67]. Such changes have the potential to exert damaging effects on ecosystem functioning. ...
The ocean faces an era of change, driven in large by the release of anthropogenic CO 2 , and the unprecedented entry of pollutants into the water column. Nanomaterials, those particles < 100 nm, represent an emerging contaminant of environmental concern. Research on the ecotoxicology and fate of nanomaterials in the natural environment has increased substantially in recent years. However, commonly such research does not consider the wider environmental changes that are occurring in the ocean, i.e ., ocean warming and acidification, and occurrence of co-contaminants. In this review, the current literature available on the combined impacts of nanomaterial exposure and (i) ocean warming, (ii) ocean acidification, (iii) co-contaminant stress, upon marine biota is explored. Here, it is identified that largely co-stressors influence nanomaterial ecotoxicity by altering their fate and behaviour in the water column, thus altering their bioavailability to marine organisms. By acting in this way, such stressors, are able to mitigate or elevate toxic effects of nanomaterials in a material-specific manner. However, current evidence is limited to a relatively small set of test materials and model organisms. Indeed, data is biased towards effects upon marine bivalve species. In future, expanding studies to involve other ecologically significant taxonomic groups, primarily marine phytoplankton will be highly beneficial. Although limited in number, the available evidence highlights the importance of considering co-occurring environmental changes in ecotoxicological research, as it is likely in the natural environment, the material of interest will not be the sole stressor encountered by biota. As such, research examining ecotoxicology alongside co-occurring environmental stressors is essential to effectively evaluating risk and develop effective long-term management strategies.
... We hypothesized that (i) primary producer abundance and primary production are mainly influenced by DIC, salinity and nutrients, and that enhancing DIC could alleviate the salinity constraint on primary production; and (ii) the taxonomic compositions of microbial primary producers would change with enhanced DIC and salinity. Diatoms, for example, may play a key role in primary production, particularly in high-salt lakes, due to their strong resistance to salinity Kong et al. 2012) and high efficiency in carbon concentrating mechanisms (CCMs) (Reinfelder, Kraepiel andMorel 2000, Reinfelder, Milligan andMorel 2004;Tozzi, Schofield and Falkowski 2004). To test these hypotheses, we determined the primary production rate (PPR) using 13 C-labeling incubation experiments in lake waters. ...
Climate change globally accelerates the shrinkage of inland lakes, resulting in increases in both water salinity and dissolved inorganic carbon (DIC). The increases of salinity and DIC generate contrasting effects on microbial primary producers and primary production, however, their combined effects remain unclear in aquatic ecosystems. We hypothesized that increased DIC mitigates the constraints of enhanced salinity on microbial primary producers and primary production. To test this, we employed isotope labeling and molecular methods to explore primary production and four dominant types of microbial primary producers (form IA, IB, IC and ID) in lakes on the Tibetan Plateau. Results showed that DIC was positively correlated with the abundance of the form IAB and ID microbial primary producers and primary production (all P < 0.001) and offset salinity constraints. Structural equation models elucidated that DIC substantially enhanced primary production by stimulating the abundance of form ID microbial primary producers. The abundance of form ID primary producers explained more variations (14.6%) of primary production than form IAB (6%) and physicochemical factors (6.8%). Diatoms (form ID) played a determinant role in primary production in the lakes by adapting to high DIC and high salinity. Our findings suggest that inland lakes may support higher primary productivity in future climate change scenarios.
... The transport of HCO − 3 to the chloroplast could support photosynthesis by the C4 pathway, a scenario consistent with the up-regulation of phosphoenolpyruvate carboxylase (PEPC) (Ausenhus and O'Leary, 1992;Reinfelder et al., 2000). With the action of PEPC, CO 2 reacts with phosphoenolpyruvate (PEP) to produce the C4 compound oxaloacetate (OAA) and phosphate ( Figure 3F). ...
Global warming is expected to cause decreases in nutrient availability, photosynthesis, and potentially carbon export in the ocean. But how, and by what molecular mechanisms, nutrient limitation affects biological pump (BP) efficiency of phytoplankton are poorly understood. Here, using transcriptomics, miRNAomics, and physiological measurements, we report that phosphorus (P)-limitation increased cellular carbon and calcium contents and sinking rate of the cosmopolitan phytoplankton Emiliania huxleyi. Under P-limitation, when photosynthesis was depressed, there were substantial increases in cellular organic (3.4-fold) and inorganic (fivefold) carbon contents due to cell division arrest and, as our transcriptomic data suggest, CO2 incorporation into C4 compounds. Furthermore, calcification was increased by 46% through transcriptional and epigenetic regulations. An increase in sinking rate by 37-44% was detected. Although calcification releases equivalent amounts of CO2, the considerable increase in cellular carbon content and sinking rate far outweighed the CO2 release, leading to an elevated efficiency of carbon export by E. huxleyi, which would partially offset the decrease in BP capacity resulting from lower growth rate under P deficiency. However, how the observed sinking rate and its increase under P limitation on the laboratory cultures will translate into BP efficiency still requires further examination using in situ or mesocosm experiments.
... Suda yasayan bazı angiospermlerde (Hydrilla verticillata ve Egeria densa) ve Thalassiosira weisslogi gibi diatomların fotosentetik hücrelerinde C4 döngüsü olduğu bildirilmiştir (Reiskind, 1991;Reinfelder, 2000). Sucul bitkilerde C4 fotosentezinin keşfi ilk defa George Bowes tarafından Hydrilla verticillata'da gerçekleştirilmiştir (Holaday ve Bowes, 1980;Salvucci ve Bowes, 1981;Salvucci ve Bowes, 1983). ...
Tek hücre C4 fotosentezi moleküler, biyokimyasal, anatomik özelliklerin bir bütünüdür. C4 fotosentezinin yaklaşık 25-30 milyon önce Oligosen’de CO2 seviyesindeki azalmaya bağlı olarak ortaya çıktığı tahmin edilmektedir. Yüksek yapılı bitkilerde, yüksek sıcaklıklarda fotosentezin verimliliği, Rubisco (Ribuloz 1,5 bisfosfat karboksilaz/oksijenaz) enziminin oksijenaz aktivitesi ile sınırlanmaktadır. Karasal bitkilerin bazıları fotorespirasyon ile kaybedilen karbon miktarını en aza indirmek için Rubisco’nun CO2 tutması için arttırıcı mekanizmalar geliştirmiştir ve tek hücre C4 fotosentezi Kranz anatomi olarak isimlendirilen mezofil ve demet kını adı verilen iki farklı hücre tipinde evrimleşmiştir. C4 fotosentezi dimorfik kloroplast yapısı, Kranz anatomi ve C4 yolunun biyokimyası olarak çeşitlilik göstermektedir. Karasal bitkilerde tek hücre C4 fotosentezi 1960’ların ortalarında Chenopodiaceae familyasına ait dört türde (Bienertia aralospica, Bienertia cycloptera, Bienertia sinuspersici, Bienertia kavirense), sucul ve fakültatif (hem oksijenli hem de oksijensiz ortamda yaşayan) tek çenekli bir bitki olan Hydrilla verticillata’ da keşfedilmiştir. Son yıllarda C4 bitkilerinin özelliklerinin ortaya konması için birçok çalışma yapılmaya devam edilmektedir. Bu derlemede, karasal ve sucul bitkilerde tek hücre C4 fotosentezi, C4 fotosentezinin mekanizması, kimyası gibi konuların incelenmesi amaçlanmıştır.
... The photosynthesis in algal cell performed by the solar energy in the form of packet of photons is biologically transduced to ATP energy and reductant NADPH. Both are mandatory to convert CO 2 to reduced 3-carbon sugar compounds by Calvin cycle (Reinfelder et al. 2000). Various algal cell strains have been exposed in the lab for the generation of biomass, with the lipid biomass primarily triacylglycerides (TAGs), also known as triglycerides, being the anticipated starting material for biofuels (Hu et al. 2008). ...
... The C4 pathway is well understood in higher plants. Although the existence of a C4 pathway has been reported in the marine diatom Thalassiosira weissflogii, C3 photosynthesis is predominant in algae [80,81]. ...
The rising concentration of global atmospheric carbon dioxide (CO2) has severely affected our planet's homeostasis. Efforts are being made worldwide to curb carbon dioxide emissions, but there is still no strategy or technology available to date that is widely accepted. Two basic strategies are employed for reducing CO2 emissions, viz. (i) a decrease in fossil fuel use, and increased use of renewable energy sources; and (ii) carbon sequestration by various biological, chemical, or physical methods. This review has explored microalgae's role in carbon sequestration, the physiological apparatus , with special emphasis on the carbon concentration mechanism (CCM). A CCM is a specialized mechanism of microalgae. In this process, a sub-cellular organelle known as pyrenoid, containing a high concentration of Ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), helps in the fixation of CO2. One type of carbon concentration mechanism in Chlamydomonas reinhardtii and the association of pyrenoid tubules with thylakoids membrane is represented through a typical graphical model. Various environmental factors influencing carbon sequestration in microalgae and associated techno-economic challenges are analyzed critically.
... PEPCase was significantly downregulated in the context of the C 4 pathway in ET and ETOA (Fig. 4a), suggesting that it may influence carbon fixation under elevated temperature. Genomic studies suggest that PEPCase is involved in the C 4 metabolism in F. kawagutii and catalyzes the carboxylation of phosphoenolpyruvic acid in the C 4 pathway that uses HCO 3 − as an inorganic carbon substrate in oxaloacetic acid, which is catalyzed by phosphoenolpyruvate carboxykinase into CO 2 for fixation by RuBisCo (Fig. 5) (Reinfelder et al., 2000). PEPCase inhibition in the diatom Thalassiosira weissflogii (Reinfelder et al., 2004) and Bowes, 1991) results in a 70%-90% decrease in photosynthesis, highlighting the important role of PEPCase in carbon fixation. ...
Climate change causes ocean warming and acidification, which threaten coral reef ecosystems. Ocean warming and acidification cause bleaching and mortality, and decrease calcification in adult corals, leading to changes in the composition of coral communities; however, their interactive effects on coral larvae are not comprehensively understood. To examine the underlying molecular mechanisms of larval responses to elevated temperature and pCO2, we examined the physiological performance and protein expression profiles of Pocillopora damicornis at two temperatures (29 and 33 °C) and pCO2 levels (500 and 1000 μatm) for 5 d. Extensive physiological and proteomic changes were observed in coral larvae. The results indicated a significant decrease in net photosynthesis (PNET) and autotrophic capability (PNET/RD) of larvae exposed to elevated temperature but a marked increase in PNET and PNET/RD of larvae exposed to high pCO2 levels. Elevated temperature significantly reduced endosymbiont densities (to approximately 70%) and photochemical efficiency, indicating that warming impaired host-symbiont symbiosis. Expression of photosynthesis-related proteins, the photosystem (PS) I reaction center subunits IV and XI as well as oxygen-evolving enhancer 1, was downregulated at higher temperatures in symbionts, whereas expression of the PS I iron‑sulfur center protein was increased under high pCO2 conditions. Furthermore, expression of phosphoribulokinase (involved in the Calvin cycle) and phosphoenolpyruvate carboxylase (related to the C4 pathway) was downregulated in symbionts under thermal stress; this finding suggests reduced carbon fixation at high temperatures. The abundance of carbonic anhydrase-associated proteins, which are predicted to exert biochemical roles in dissolved inorganic carbon transport in larvae, was reduced in coral host and symbionts at high temperatures. These results elucidate potential mechanisms underlying the responses of coral larvae exposed to elevated temperature and acidification and suggest an important role of symbionts in the response to warming and acidification.
... We hypothesized that (i) primary producer abundance and primary production are mainly influenced by DIC, salinity and nutrients, and that enhancing DIC could alleviate the salinity constraint on primary production; and (ii) the taxonomic compositions of microbial primary producers would change with enhanced DIC and salinity. Diatoms, for example, may play a key role in primary production, particularly in high-salt lakes, due to their strong resistance to salinity Kong et al. 2012) and high efficiency in carbon concentrating mechanisms (CCMs) (Reinfelder, Kraepiel andMorel 2000, Reinfelder, Milligan andMorel 2004;Tozzi, Schofield and Falkowski 2004). To test these hypotheses, we determined the primary production rate (PPR) using 13 C-labeling incubation experiments in lake waters. ...
... Another method includes addition of HCO 3 to the media (Lohman et al., 2015;Mokashi et al., 2016), which is a cheaper and more suitable inorganic carbon alternative to the CO 2 . Diatoms, including Phaeodactylum, possesses biophysical and/or biochemical CO 2 -concentrating mechanism (CCM) (Reinfelder et al., 2000;Roberts et al., 2007;Hopkinson et al., 2011;Matsuda et al., 2011). Biophysical CCMs involve active transport of CO 2 or HCO 3 and CA maintains equilibrium between the two species by catalyzing the reversible interconversion of CO 2 and water into HCO 3 and protons. ...
Diatoms are photoautotrophic unicellular algae and are among the most abundant, adaptable, and diverse marine phytoplankton. They are extremely interesting not only for their ecological role but also as potential feedstocks for sustainable biofuels and high-value commodities such as omega fatty acids, because of their capacity to accumulate lipids. However, the cultivation of microalgae on an industrial scale requires higher cell densities and lipid accumulation than those found in nature to make the process economically viable. One of the known ways to induce lipid accumulation in Phaeodactylum tricornutum is nitrogen deprivation, which comes at the expense of growth inhibition and lower cell density. Thus, alternative ways need to be explored to enhance the lipid production as well as biomass density to make them sustainable at industrial scale. In this study, we have used experimental and metabolic modeling approaches to optimize the media composition, in terms of elemental composition, organic and inorganic carbon sources, and light intensity, that boost both biomass quality and quantity of P. tricornutum. Eventually, the optimized conditions were scaled-up to 2 L photobioreactors, where a better system control (temperature, pH, light, aeration/mixing) allowed a further improvement of the biomass capacity of P. tricornutum to 12 g/L.
... The increasing amount of anthropogenic greenhouse gas emission has resulted significant changes in the physical and chemical properties of the global ocean that have intense implications to the marine ecosystem (Pörtner et al., 2014). It is assumed that the warming ocean will enhance the nutrient stratification and modulates the ecophysiology of marine organisms (Reinfelder et al., 2000). A recent report described increasing sea surface temperature (SST), and depletion of nutrients affects the phytoplankton community resulting in 6% global biomass decrease by the end of this century (Chust et al., 2014). ...
Global warming is expected to reduce the nutrient concentration in the upper ocean and affect the physiology of marine diatoms, but the underlying molecular mechanisms controlling these physiological changes are currently unknown. To understand these mechanisms, here we investigated iTRAQ based proteomic profiling of diatom Skeletonema dohrnii in a multifactorial experimental with a combining change of temperature and silicate concentrations. In total, 3369 differently abundant proteins were detected in four different environmental conditions, and the function of all proteins was identified using Gene Ontology and KEGG pathway analysis. For discriminating the proteome variation among samples, multivariate statistical analysis (PCA, PLS-DA) was performed by comparing the protein ratio differences. Further, performing pathway analysis on diatom proteomes, we here demonstrated downregulation of photosynthesis, carbon metabolism, and ribosome biogenesis in the cellular process that leads to decrease the oxidoreductase activity and affects the cell cycle of the diatom. Using PLS-DA VIP score plot analysis, we identified 15 protein biomarkers for discriminating studied samples. Of these, five proteins or gene (rbcL, PRK, atpB, DNA-binding, and signal transduction) identified as key biomarkers, induced by temperature and silicate stress in diatom metabolism. Our results show that proteomic finger-printing of S. dohrnii with different environmental conditions adds biological information that strengthens marine phytoplankton proteome analysis.
... However, distribution of EPS in different microorganisms may show heterogeneity 24 . Cooksey reported that diatoms embellish themselves on steel and glass after few hours of exposure which follows increased growth due to photosynthetic activity 25,26 . Furthermore, colonization on OPEN Update 03 February 2021 The version of this Article previously published quoted an incorrect email address for Vandana Vinayak. ...
Abstract In the present study, embellishment or beautification of diatoms on substrates like plastics, polydimethylsiloxane, graphite, glass plate, and titanium dioxide, triggered by exopolysaccharides was examined under laboratory conditions. Exopolysaccharides are secreted mainly by primary colonisers, bacteria, which is succeeded by secondary colonisers i.e. diatoms. Both diatom (Nitzschia sp.4) and bacteria (Bacillus subtilis) were exposed with substrates separately for 30 days. Diatoms adhere on substrates strongly, not only because of surface roughness of different substrates but also the nanoporous architecture of diatoms which enhanced their embellishment. This study attempted to identify the substrates that adhere to diatoms strongly and was mainly analyzed by scanning electron microscope and further the observations are well supported by math work software (MATLAB). The variation of diatom’s binding on different substrates is due to the influence of marine litters on diatom population in ocean beds where they undergo slow degradation releasing macro, micro and nanoparticles besides radicals and ions causing cell death. Therefore a proof-of-concept model is developed to successfully deliver a message concerning benefit of using different diatom species.
... A dominant route in the CCMs is that intra-or extracellular dehydration of HCO 3 − is catalyzed by carbonic anhydrases (CA) to release CO 2 to increase reactions at the Rubisco site (Fig. 1a). Although traditionally associated with more advanced terrestrial plants, in recent decades a C 4 or C 4 -like pathway has been discovered in the green alga Udotea flabellum 6 and the marine diatom Thalassiosira weissflogii 7,8 , in which transmembrane HCO 3 − is not only catalyzed via CA to generate CO 2 but also involves C 4 enzymesphosphoenolpyruvate carboxylase (PEPCase) and PEPCase kinase (PEPCKase). CO 2 incorporated in this manner eventually enters the C 3 cycle to increase reactions at the Rubisco site (Fig. 1b). ...
Most marine algae preferentially assimilate CO 2 via the Calvin-Benson Cycle (C 3) and cat-alyze HCO 3 − dehydration via carbonic anhydrase (CA) as a CO 2-compensatory mechanism, but certain species utilize the Hatch-Slack Cycle (C 4) to enhance photosynthesis. The occurrence and importance of the C 4 pathway remains uncertain, however. Here, we demonstrate that carbon fixation in Ulva prolifera, a species responsible for massive green tides, involves a combination of C 3 and C 4 pathways , and a CA-supported HCO 3 − mechanism. Analysis of CA and key C 3 and C 4 enzymes, and subsequent analysis of δ 13 C photosynthetic products showed that the species assimilates CO 2 predominately via the C 3 pathway, uses HCO 3 − via the CA mechanism at low CO 2 levels, and takes advantage of high irradiance using the C 4 pathway. This active and multi-faceted carbon acquisition strategy is advantageous for the formation of massive blooms, as thick floating mats are subject to intense surface irradiance and CO 2 limitation.
... Biochemical CCMs are characterized by the carboxylation of C3 compounds to form C4 compounds and providing CO 2 via decarboxylating C4 compounds in close proximity to Rubisco. It is generally considered that C4-like metabolism can function as biochemical CCMs in the marine centric diatom Thalassiosira weissflogii (Reinfelder et al. 2000;Roberts et al. 2007). However, the existence of biochemical CCMs in another marine centric diatom Thalassiosira pseudonana is still controversial. ...
Differential responses of diatoms, an important group of marine primary producers to ocean acidification, have been well documented. However, studies so far are based on limited representative strains from key species. Investigation of strain level responses will help us better understand the contrasting discrepancy in diatom responses to ocean acidification. Here, we selected four strains of the model diatom Phaeodactylum tricornutum isolated from different regions of the global ocean, representing all genotypes based on internal transcribed spacer 2 sequences, and investigated strain-specific responses to ocean acidification. In response to ocean acidification, changes in carbon metabolism varied among strains, although no significant effects of ocean acidification on growth rates or pigments were observed in any strains. The expression of genes encoding plasma membrane bicarbonate transporters was downregulated in strain Pt4, reflecting a potential decrease in active (Formula presented.) uptake, which was not observed in the other strains. Reduction of CO2 concentrating mechanism efficiency was also indicated by the regulated expression of genes encoding carbonic anhydrases that catalyze the interconversion of (Formula presented.) and CO2 in the pyrenoids and pyrenoid-penetrating thylakoid, which exhibited different patterns among the strains. Under ocean acidification conditions, C4-like metabolism appeared to redistribute carbon flux to gluconeogenesis in strain Pt1, and lipid synthesis in strains Pt8 and Pt11, rather than participating in net photosynthetic carbon fixation. These variations were incompletely correlated with phylogenetic relationship in different strains, implying that the habitat-adapted imprints of the different strains could also be responsible for their differential responses to ocean acidification. © 2020 Association for the Sciences of Limnology and Oceanography
The increasing concentration of carbon dioxide (CO2) in the Earth's atmosphere has had a profound impact on the planet's balance. There is presently no approved technique or method for reducing CO2 emissions, despite attempts being conducted on a global scale. To reduce CO2 emissions, two primary strategies are being used, but in this present review we tried to focus on carbon capture via biological technique. The present study analyses i) the physiological processes of microalgae and focuses on their
function in carbon capture, paying particular attention to the carbon concentration mechanism (CCM). ii) The RuBisCo (“Ribulose-1,5-bisphosphate carboxylase-oxygenase”)-rich subcellular organelle known as the pyrenoid, which is an essential component of CCM in microalgae and vital role of Carbonic
Anhydrase (CA) for CO2 conversion into HCO3 and its utilization by maintaining the pH in algal cells.iii) Also compare the economic viability of different CO2 capture technologies with the help of their estimated cost.
The increasing concentration of carbon dioxide (CO2) in the Earth's atmosphere has had a profound impact on the planet's balance. There is presently no approved technique or method for reducing CO2 emissions, despite attempts being conducted on a global scale. To reduce CO2 emissions, two primary strategies are being used, but in this present review we tried to focus on carbon capture via biological technique. The present study analyses i) the physiological processes of microalgae and focuses on their function in carbon capture, paying particular attention to the carbon concentration mechanism (CCM). ii) The RuBisCo ("Ribulose-1,5-bisphosphate carboxylase-oxygenase")-rich subcellular organelle known as the pyrenoid, which is an essential component of CCM in microalgae and vital role of Carbonic Anhydrase (CA) for CO2 conversion into HCO3-and its utilization by maintaining the pH in algal cells.iii) Also compare the economic viability of different CO2 capture technologies with the help of their estimated cost.
Phosphoenolpyruvate carboxykinase (PEPCK) catalyzes the reversible reaction of decarboxylation and phosphorylation of oxaloacetate (OAA) to generate phosphoenolpyruvate (PEP) and CO2 playing mainly a gluconeogenic role in green algae. We found two PEPCK isoforms in Chlamydomonas reinhardtii and we cloned, purified and characterized both enzymes. ChlrePEPCK1 is more active as decarboxylase than ChlrePEPCK2. ChlrePEPCK1 is hexameric and its activity is affected by citrate, phenylalanine and malate, while ChlrePEPCK2 is monomeric and it is regulated by citrate, phenylalanine and glutamine. We postulate that the two PEPCK isoforms found originate from alternative splicing of the gene or regulated proteolysis of the enzyme. The presence of these two isoforms would be part of a mechanism to finely regulate the biological activity of PEPCKs.
Starch is by far the major storage compound accumulated by plants and algae, one of the most abundant polysaccharides present on earth and principal source of dietary calories in the human and animal diet. Starch synthesis occurs during the day, using global outputs of photosynthesis and its degradation starts as night falls to sustain energy-demanding cellular functions. Little is known about the regulatory mechanisms governing starch metabolism in microalgae and current knowledge is lim-ited to factors impacting starch accumulation under adverse environmental conditions such as nitro-gen limitation. A link between light perception and starch accumulation has been suggested in the case of higher plants: Mutants devoid of Phytochrome have a reduced CO2 uptake but over-accumulate daytime sucrose and starch while PHOT has been found to mediate starch degradation in guard cells in the light to energize stomatal opening. Light perception and metabolism have not been associated in microalgae. Here we present a detailed PHOT-dependent signalling cascade, linking blue light perception with starch accumulation in the green microalga Chlamydomonas reinhard-tii:Pathway 1: Blue light, via PHOT, represses the bHLH domain-containing transcription factor (TF) GAPr4, an activator of GAP1, (glyceraldehyde-3-phosphate dehydrogenase, involved in glycolysis and in photosynthetic CO2 fixation). Both the PHOT knock-out mutant phot and GAP1 over-expressing lines accumulate high amounts of starch.Pathway 2: Blue light, via PHOT, activates the RWP5 TF (belonging to the RWP-K family of TFs), a re-pressor of starch accumulation in a GAP1-independent manner.Pathway 3: PHOT-dependent phosphorylation of the serine/threonine kinase Blue Starch Kinase 1 (BSK1; orthologue of the Arabidopsis HT1 kinase that controls stomatal movements in response to CO2) mediates GAP1 and starch accumulation levels in a GAPr4-independent manner.Our work advances the current understanding of how light signaling controls metabolism in microal-gae. It also adds one more aspect in the multifaceted role of PHOT so far reported to control gameto-genesis at low nitrogen, expression of genes encoding chlorophyll and carotenoid biosynthesis, the size of the eyespot and photoprotection.
The productivity of terrestrial plants can be limited by water supply and high temperature, but these factors are often replaced in aquatic plants by low light and restricted inorganic carbon supply. Furthermore, oxygen concentrations in water can be over two times greater than air‐equilibrium and low diffusion will restrict losses from the chloroplast to the environment. These conditions can cause underwater photosynthesis to be carbon‐limited, promoting photorespiration and favoring the possession of a CO 2 concentrating mechanism (CCM). Crassulacean acid metabolism (CAM) is similar to C 4 metabolism since the first product of carbon fixation in both pathways leads to the formation of C 4 organic acids. Future research could increase the number of aquatic species studied since only a fraction has been investigated for possessing a biochemical CCM. Detailed mechanistic studies, which are beginning to be carried out on marine diatoms, should be applied to a wider range of aquatic photoautotrophs.
Diatoms (Bacillarophyceae) are the most abundant and diverse phytoplankton in oceans. They can produce several valuable metabolic products (e.g., lipids) that can be potential feedstocks for many commercial products (e.g., biofuels). Enhancing the yield of such metabolic products requires deep understanding and genetic manipulations of diatoms metabolism. Genome-scale metabolic modeling is a useful tool to explore metabolisms in terms of extra- and intra-cellular fluxes, theoretical yields, and feasibility of knockout and knock-in mutants. This chapter provides a comprehensive overview of current advances in the construction of diatom GEMs and their potential advantages for studying and engineering diatom metabolism. Using some examples, we also highlighted how GEMs could provide insights in understanding the metabolic exchanges between diatoms and surrounding organisms in marine ecosystems.
Diatoms represent one of the most successful groups of marine phytoplankton and are major contributors to ocean biogeochemical cycling. They have colonized marine, freshwater and ice environments and inhabit all regions of the World’s oceans, from poles to tropics. Their success is underpinned by a remarkable ability to regulate their growth and metabolism during nutrient limitation and to respond rapidly when nutrients are available. This requires precise regulation of membrane transport and nutrient acquisition mechanisms, integration of nutrient sensing mechanisms and coordination of different transport pathways. This review outlines transport mechanisms involved in acquisition of key nutrients (N, C, P, Si, Fe) by marine diatoms, illustrating their complexity, sophistication and multiple levels of control.
Extensive studies have documented the responses of diatoms to environmental drivers in the context of climate change. However, bloom dynamics are usually ignored in most studies. Here, we investigated the effects of the initial pCO2 on the bloom characteristics of two cosmopolitan diatoms, Skeletonema costatum and Thalassiosira weissflogii. Batch cultures with two initial pCO2 conditions (LC: 400 μatm; HC: 1000 μatm) were used to investigate bloom dynamics under current and ocean acidification scenarios. The simulated S. costatum bloom was characterized by fast accumulation, a rapid decline in biomass, and a shorter stationary phase. The T. weissflogii bloom had a longer stationary phase, and cell density remained at high levels after culturing for 19 days. The physiological performances of the two diatoms varied significantly in the different bloom phases. We found that the initial pCO2 has modulating effects on biomass accumulation and bloom dynamics for these two diatoms. The higher initial pCO2 enhanced the specific growth rate of T. weissflogii by 6% in the exponential phase, leading to higher cell densities, while 86% higher decay rates were observed in the HC cultures of S. costatum. Overall, ocean acidification may alter the dynamics of diatom blooms and may have profound impacts on the biological carbon pump.
Here, we demonstrate that phloroglucinol, a growth promoter in higher plants, also increases growth and fucoxanthin synthesis in the microalga Thalassiosira pseudonana and therefore may have substantial practical application for industrial fucoxanthin production. Phloroglucinol treatment also induced the synthesis of cis -zeatin and brassinolide in T. pseudonana , and the cis -zeatin and brassinolide signaling pathways were implicated in the phloroglucinol-driven increases in T. pseudonana growth and fucoxanthin synthesis.
Primary biological aerosol particles and microorganisms are ubiquitous in the atmosphere. Investigations of airborne chemical markers and microbial communities are critical for identifying sources, transport and transformation processes of aerosols. One potential major source of airborne chemical compounds and microbial communities (e.g. L- and D-amino acids, Flavobacteria) could be related to phytoplankton blooms that occur during the spring season in Arctic fjord systems. Here, we conducted a field study in a polar environment to investigate the occurrence in coarse and fine particles of water-soluble compounds (major ions, carboxylic acids and free L- and D-amino acids) and airborne bacterial communities in aerosol samples. The sampling was conducted with a 6 day sampling frequency at the Gruvebadet observatory, close to Ny-Ålesund (Svalbard Islands). Glycine, D-amino acids and C4- organic acids increased during the exponential phase of a marine bloom that occurred in Kongsfjorden and started to drop at the beginning of the main-bloom phase. On the other hand, Polaribacter together with free L-amino acids overlapped with the Chlorophyll a peak and the subsequent decline, and thus might constitute a useful marker for the main-bloom phase.
Diatoms are the most recent major algal lineage added to the geological record, appearing more than 200 million years ago. They are stramenopile protists resulting from a secondary endosymbiotic event that yielded the only photosynthetic protistan lineage expressing external siliceous cell wall structures called frustules. Many diatoms also have large internal vacuoles, and a common assumption in the literature is that success of the diatoms is largely attributable to these two morphological inventions: the frustule for defense and vacuole for luxury nutrient uptake. Here, we revisit the evolution of these inventions, propose sequential steps in frustule development, replace luxury nutrient uptake with predator defense and buoyancy control as the driver of vacuole expansion, and suggest that perhaps the greatest significance of the frustule for diatom evolution is the secondary consequence of enhancing sexual reproduction. In this synthesis, we emphasize a distinction between the “general” success of diatoms and the success of “bloom‐forming” species, as the physiological and morphological drivers of these successes differ. Importantly, the bloom‐forming species are responsible for the major role of diatoms in aquatic biogeochemical cycles. The bloom‐forming habit we ascribe to specific physiological attributes that, at their core, revolve around influencing the balance between diatom growth and losses to predators. We propose that these physiological adaptations are linked to size‐dependent maximum division rates in bloom‐forming diatoms, because of size scaling of predator–prey interactions. The existence of these bloom‐forming species yields an apparent allometric relationship that has previously been interpreted in terms of nutrient acquisition. Our analysis yields insights into species successions during blooms, considers the fundamental benefit of blooming (and subsequent sinking) from a reproductive standpoint, and provides some reinterpretation of diatoms success over geologic time and in the modern ocean.
This chapter describes the role of phosphoenolpyruvate carboxylase in C4 photosynthesis and its activity assay protocols based on the measurement of oxaloacetate-dependent NADH oxidation.
Rising atmospheric CO2 concentrations are causing ocean acidification (OA) with significant consequences for marine organisms. Because CO2 is essential for photosynthesis, the effect of elevated CO2 on phytoplankton is more complex and the mechanism is poorly understood. Here we applied RNA-seq and iTRAQ proteomics to investigate the impacts of CO2 increase (from ∼400 to 1000 ppm) on the temperate coastal marine diatom Skeletonema marinoi. We identified 32,389 differentially expressed genes (DEGs) and 1,826 differentially expressed proteins (DEPs) from elevated CO2 conditions, accounting for 48.5% of total genes and 25.9% of total proteins we detected, respectively. Elevated pCO2 significantly inhibited the growth of S. marinoi, and the ‘omic’ data suggested that this might be due to compromised photosynthesis in the chloroplast and raised mitochondrial energy metabolism. Furthermore, many genes/proteins associated with nitrogen metabolism, transcriptional regulation, and translational regulation were markedly up-regulated, suggesting enhanced protein synthesis. In addition, S. marinoi exhibited higher capacity of ROS production and resistance to oxidative stress. Overall, elevated pCO2 seems to repress photosynthesis and growth of S. marinoi, and through massive gene expression reconfiguration induce cells to increase investment in protein synthesis, energy metabolism and antioxidative stress defense, likely to maintain pH homeostasis and population survival. This survival strategy may deprive this usually dominant diatom in temperate coastal waters of its competitive advantages in acidified environments.
Importance
Rising atmospheric CO2 concentrations are causing ocean acidification with significant consequences for marine organisms. Chain-forming centric diatoms of Skeletonema is one of the most successful groups of eukaryotic primary producers with widespread geographic distribution. Among the recognized 28 species, S. marinoi can be a useful model for investigating the ecological, genetic, physiological, and biochemical characteristics of diatoms in temperate coastal regions. In this study, we found that the elevated pCO2 seems to repress photosynthesis and growth of S. marinoi, and through massive gene expression reconfiguration induce cells to increase investment in protein synthesis, energy metabolism and antioxidative stress defense, likely to maintain pH homeostasis and population survival. This survival strategy may deprive this usually dominant diatom in temperate coastal waters of its competitive advantages in acidified environments.
The active species of “CO2”, i.e. CO2 or HCO3⁻, utilized in the ribulose diphosphate carboxylase reaction was determined with the use of homogeneous preparations of the spinach enzyme. Employing an assay system predicated upon the observation that the hydration of CO2 requires more than 60 sec to reach equilibrium at temperatures below 15°, data were obtained which are quite compatible with those expected if CO2 is the active species.
The active species of "CO2," i.e. CO2 or HCO3⁻, utilized in the pyruvate carboxylase and phosphoenolypruvate carboxylase reaction have been determined with an assay predicated upon the fact that the hydration of CO2 is a kinetically slow and measurable reaction. The results of these assays in both cases are in reasonable agreement with those expected if HCO3⁻ is assumed to be the functional species utilized by both enzymes.
Routine geodetic measurements are made at only a few dozen of the world's 600 or so active volcanoes, even though these measurements have proven to be a reliable precursor of eruptions. The pattern and rate of surface displacement reveal the depth and rate of pressure increase within shallow magma reservoirs. This process has been demonstrated clearly at Kilauea and Mauna Loa, Hawaii; Long Valley caldera, California; Campi Flegrei caldera, Italy; Rabaul caldera, Papua New Guinea; and Aira caldera and nearby Sakurajima, Japan. Slower and lesser amounts of surface displacement at Yellowstone caldera, Wyoming, are attributed to changes in a hydrothermal system that overlies a crustal magma body. The vertical and horizontal dimensions of eruptive fissures, as well as the amount of widening, have been determined at Kilauea, Hawaii; Etna, Italy; Tolbachik, Kamchatka; Krafla, Iceland; and Asal-Ghoubbet, Djibouti, the last a segment of the East Africa Rift Zone. Continuously recording instruments, such as tiltmeters, extensometers, and dilatometers, have recorded horizontal and upward growth of eruptive fissures, which grew at rates of hundreds of meters per hour, at Kilauea; Izu-Oshima, Japan; Teishi Knoll seamount, Japan; and Piton de la Fournaise, Réunion Island. In addition, such instruments have recorded the hour or less of slight ground movement that preceded small explosive eruptions at Sakurajima and presumed sudden gas emissions at Galeras, Colombia. The use of satellite geodesy, in particular the Global Positioning System, offers the possibility of revealing changes in surface strain both local to a volcano and over a broad region that includes the volcano.
Algae have adopted two primary strategies to maximize the performance of Rubisco in photosynthetic CO2 fixation. This has included either the development of a CO2-concentrating mechanism (CCM), based at the level of the chloroplast, or the evolution of the kinetic properties of Rubisco. This review examines the potential diversity of both Rubisco and chloroplast-based CCMs across algal divisions, including both green and nongreen algae, and seeks to highlight recent advances in our understanding of the area and future areas for research. Overall, the available data show that Rubisco enzymes from algae have evolved a higher affinity for CO2 when the algae have adopted a strategy for CO2 fixation that does not utilise a CCM. This appears to be true of both Green and Red Form I Rubisco enzymes found in green and nongreen algae, respectively. However, the Red Form I Rubisco enzymes present in nongreen algae appear to have reduced oxygenase potential at air level of O-2 This has resulted in a photosynthetic physiology with a reduced potential to be inhibited by O-2 and a reduced need to deal with photorespiration. In the limited number of microalgae that have been examined, there is a strong correlation between the existence of a high-affinity CCM physiology and the presence of pyrenoids in all algae, highlighting the potential importance of these chloroplast Rubisco-containing bodies. However, in macroalgae, there is greater diversity in the apparent relationships between pyrenoids and chloroplast features and the CCM physiology that the species shows. There are many examples of microalgae and macroalgae with variations in the presence and absence of pyrenoids as well as single and multiple chloroplasts per cell. This occurs in both green and nongreen algae and should provide ample material for extending studies in this area. Future research into the function of the pyrenoid and other chloroplast features, such as thylakoids, in the operation of a chloroplast-based CCM needs to be addressed in a diverse range of algal species. This should be approached together with assessment of the coevolution of Rubisco, particularly the evolution of Red Form I Rubisco enzymes, which appear to achieve superior kinetic characteristics when compared with the Rubisco of C-3 higher plants, which are derived from green algal ancestors.
We analysed 92 interferograms produced using ERS1 SAR images taken on Etna between May 1992 and October 1993. Nineteen show a local subsidence in the eastern flank of the volcano, correlated with the location of the 30 October 1986-1 March 1987 and 27 September-9 October 1989 lava flows. Using fringe unwrapping and data gridding techniques, and assuming that over the sampled time-window, deformation was a linear function of time, we derive a map of a long range rate of motion. The correlation between the deformation field and the area covered by recent lavas suggests that compaction of the lava flows continues several years after the eruptions. The area of maximum subsidence (47 mm/yr.) is localised at the narrowing of the 1989 flow, between 1500 and 1700 m a.s.l.. We observe that subsidence extends outside the lava flows, accounting for at least 12 mm/yr. Assuming a relaxation process of the substrate in response to loading produced by recent lavas, a simple 1D Maxwell visco-elastic model predicts a maximum subsidence rate of 25 mm/yr and a relaxation time of about 3.5 years. The relaxation time agrees with those derived from post-eruptive displacements observed by levelling on Etna and Piton de la Fournaise after several eruptions. We conclude that at the time of our measurements, 25 to 50% of the deformation was related to relaxation of the substrate and the other part due to compaction of the lava flows.
Fernandina Volcano, the most active of Galapagos volcanoes and the one most directly overlying the Galapagos hotspot, is one of a small number of active, plume-related oceanic island volcanoes with a well-documented recent eruptive record. Whole rock and glass analyses of lava and tephra from all 12 known eruptions from 1958 to the present show them to be evolved (Mg#(=Mg/Mg+Fe2+) of 0.47-0.56), plagioclase-phyric, clinopyroxene-and olivine-bearing tholeiites. Thermodynamic modeling indicates that this phase assemblage erupted at 1100-1130°C and is stable only at low pressures (
The movements produced by the 1992 earthquake in Landers, California are mapped using SAR interferometry. An interferogram is constructed by combining topographic information with SAR images obtained by the ERS-1 satellite before and after the earthquake. It is shown that the observed changes in the range from the ground surface to the satellite agree well with the slip measured in the field, with the displacements measured by surveying, and with the results of Okada's (1985) elastic dislocation model. This interferogram provides a denser spatial sampling than surveying methods and a better precision than earlier space imaging techniques.
Galapagos magmas evolve by fractional crystallization at systematically different depths in the crust and mantle, which results in strikingly different volcano morphologies. Every Galapagos volcano has erupted some lavas that are saturated with olivine + plagioclase + augite, especially those magmas with MgO <6 wt.%. Magmas of the central volcanoes cool and fractionate below the Moho at pressures >5 kbar, resulting in transient chambers and no calderas. In the western Galapagos, magmas equilibrate in the crust, at pressures between 1 and 3 kbar. The withdrawal of magma from these shallow chambers results in calderas, and there appears to be a direct relation between the depth of fractionation and caldera morphology. Magmas of the volcanoes with deep calderas stage and fractionate at very shallow depths. Magmas of the volcanoes with broad, shallow calderas cool and crystallize in the lower crust. There is no evidence for high- or low-18O sources in the Galapagos plume, as have been observed at other hotspot volcanoes. A combination of O-isotope, He-isotope, and trace-element data indicates that assimilation of oceanic crust is not an important process in the evolution of Galapagos magmas, either in terms of total mass of assimilated material or in producing the characteristic chemistry of the lavas. We suggest two possible explanations for the systematic differences in the depths at which Galapagos magmas cool and fractionate. First, the depth of the magma chambers may be due to the magma supply rate. A second potential control on the depth at which Galapagos magmas cool and crystallize is the regional difference in the lithospheric structure. The lithosphere thickens to the west across a sharp discontinuity at about 90°30′W which approximately separates the western islands with shallow fractionation and the central islandds with deep fractionation.
We have applied two Monte Carlo optimization techniques, simulated annealing and random cost, to the inversion of deformation data for fault and magma chamber geometry. These techniques involve an element of randomness that permits them to escape local minima and ultimately converge to the global minimum of misfit space. We have tested the Monte Carlo algorithms on two synthetic data sets. We have also compared them to one another in terms of their efficiency and reliability. We have applied the bootstrap method to estimate confidence intervals for the source parameters, including the correlations inherent in the data. Additionally, we present methods that use the information from the bootstrapping procedure to visualize the correlations between the different model parameters. We have applied these techniques to GPS, tilt, and leveling data from the March 1997 earthquake swarm off of the Izu Peninsula, Japan. Using the two Monte Carlo algorithms, we have inferred two sources, a dike and a fault, that fit the deformation data and the patterns of seismicity and that are consistent with the regional stress field.
PROCESSES that control carbon uptake by marine phytoplankton are
important in the global carbon cycle11-3. Uptake of
CO2 itself may be limited by diffusion4.
Bicarbonate uptake may be limited by zinc as HCO-3
transport appears to involve the zinc metallo-enzyme carbonic
anhydrases5,6and the concentration of inorganic zinc in
seawater7is low enough to limit the growth of certain
phytoplankton in culture8,9. Here we show that
HCO-3 uptake by the marine diatom Thalassiosira
weissflogii is modulated by the partial pressure of CO2 and
by the concentration of inorganic Zn (for which Cd and Co may substitute
in carbonic anhydrase). This result leads naturally to a 'zinc
hypothesis' which, like the standing 'iron hypothesis10,
posits that Zn (Fe) may limit oceanic production and influence the
global carbon cycle. Because of the large13C enrichment of
HCO-3 over CO2, our results may be
important for the interpretation of δ13C measurements
in seawater and sediments.
Geophysical applications of radar inter-ferometry to measure changes in the Earth's surface have exploded in the early 1990s. This new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times. The resulting interferogram is a contour map of the change in distance between the ground and the radar instrument. These maps provide an unsurpassed spatial sampling density (100 pixels km 2), a competitive pre-cision (1 cm), and a useful observation cadence (1 pass month 1). They record movements in the crust, pertur-bations in the atmosphere, dielectric modifications in the soil, and relief in the topography. They are also sensitive to technical effects, such as relative variations in the radar's trajectory or variations in its frequency standard. We describe how all these phenomena contribute to an interferogram. Then a practical summary explains the techniques for calculating and manipulating interfero-grams from various radar instruments, including the four satellites currently in orbit: ERS-1, ERS-2, JERS-1, and RADARSAT. The next chapter suggests some guide-lines for interpreting an interferogram as a geophysical measurement: respecting the limits of the technique, assessing its uncertainty, recognizing artifacts, and dis-criminating different types of signal. We then review the geophysical applications published to date, most of which study deformation related to earthquakes, volca-noes, and glaciers using ERS-1 data. We also show examples of monitoring natural hazards and environ-mental alterations related to landslides, subsidence, and agriculture. In addition, we consider subtler geophysical signals such as postseismic relaxation, tidal loading of coastal areas, and interseismic strain accumulation. We conclude with our perspectives on the future of radar interferometry. The objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intu-ition necessary to interpret it.
The culture medium Aquil has been designed for studying trace metal physiology in algae. We describe recent modifications in the preparation of Aquil and discuss processes that affect its trace metals and their physiological effects. The major changes in Aquil preparation are purification of the Chelex column to avoid contamination by chelating agents, use of alternative sterilization procedures, and increases in the concentration of trace metal buffers. During growth, phytoplankton take up trace metals, thus continuously reducing their concentrations in the medium. Algae can also modify the redox state and degree of organic complexation of trace metals through the direct and indirect activity of cell surface enzymes and the release of metabolites. Illumination of the culture medium necessary to promote photosynthesis also promotes a variety of photochemical reactions that alter the chemistry of the medium and maintain it in a state of disequilibrium. In particular, light absorption by FeEDTA leads to reduction of the iron and oxidation of the EDTA. Rapid reoxidation of Fe (II) leads to a high steady-state inorganic Fe (III) concentration. Slow coordination kinetics with chelating agents contribute to maintaining the disequilibrium conditions promoted by cellular and photochemical processes. Kinetic processes rather than pseudo-equilibrium conditions are now the focus in the study of trace metal-phytoplankton interactions.
We present a map of the coseimic displacement field resulting from the Landers, California, June 28, 1992, earthquake derived using data acquired from an orbiting high-resolution radar system. We achieve results more accurate than previous space studies and similar in accuracy to those obtained by conventional field survey techniques. Data from the ERS 1 synthetic aperture radar instrument acquired in April, July, and August 1992 are used to generate a high-resolution, wide area map of the displacements. The data represent the motion in the direction of the radar line of sight to centimeter level precision of each 30-m resolution element in a 113 km by 90 km image. Our coseismic displacement contour map gives a lobed pattern consistent with theoretical models of the displacement field from the earthquake. Fine structure observed as displacement tiling in regions several kilometers from the fault appears to be the result of local surface fracturing. Comparison of these data with Global Positioning System and electronic distance measurement survey data yield a correlation of 0.96; thus the radar measurements are a means to extend the point measurements acquired by traditional techniques to an area map format. The technique we use is (1) more automatic, (2) more precise, and (3) better validated than previous similar applications of differential radar interferometry. Since we require only remotely sensed satellite data with no additioanl requirements for ancillary information. the technique is well suited for global seismic monitoring and analysis.
Interferometric synthetic aperture radar observations provide a means for obtaining high-resolution digital topographic maps from measurements of amplitude and phase of two complex radar images. The phase of the radar echoes may only be measured modulo 2 pi; however, the whole phase at each point in the image is needed to obtain elevations. An approach to 'unwrapping' the 2 pi ambiguities in the two-dimensional data set is presented. It is found that noise and geometrical radar layover corrupt measurements locally, and these local errors can propagate to form global phase errors that affect the entire image. It is shown that the local errors, or residues, can be readily identified and avoided in the global phase estimation. A rectified digital topographic map derived from the unwrapped phase values is presented.
1. Mesophyll and parenchyma-sheath chloroplasts of maize leaves were separated by density fractionation in non-aqueous media. 2. An investigation of the distribution of photosynthetic enzymes indicated that the mesophyll chloroplasts probably contain the entire leaf complement of pyruvate,P(i) dikinase, NADP-specific malate dehydrogenase, glycerate kinase and nitrite reductase and most of the adenylate kinase and pyrophosphatase. The fractionation pattern of phosphopyruvate carboxylase suggested that this enzyme may be associated with the bounding membrane of mesophyll chloroplasts. 3. Ribulose diphosphate carboxylase, ribose phosphate isomerase, phosphoribulokinase, fructose diphosphate aldolase, alkaline fructose diphosphatase and NADP-specific ;malic' enzyme appear to be wholly localized in the parenchyma-sheath chloroplasts. Phosphoglycerate kinase and NADP-specific glyceraldehyde phosphate dehydrogenase, on the other hand, are distributed approximately equally between the two types of chloroplast. 4. After exposure of illuminated leaves to (14)CO(2) for 25sec., labelled malate, aspartate and 3-phosphoglycerate had similar fractionation patterns, and a large proportion of each was isolated with mesophyll chloroplasts. Labelled fructose phosphates and ribulose phosphates were mainly isolated in fractions containing parenchyma-sheath chloroplasts, and dihydroxyacetone phosphate had a fractionation pattern intermediate between those of C(4) dicarboxylic acids and sugar phosphates. 6. These results indicate that the mesophyll and parenchyma-sheath chloroplasts have a co-operative function in the operation of the C(4)-dicarboxylic acid pathway. Possible routes for the transfer of carbon from C(4) dicarboxylic acids to sugars are discussed.
Small subunit ribosomal RNA (ssu rRNA) coding regions from 30 diatoms, nine other heterokont algae, three oomycetes, one thraustochytrid and one heterotrophic flagellate were used to construct a molecular clock from maximum-likelihood trees, and from linearized trees using a neighbor-joining analysis. Taxa with fast and/or aberrantly evolving ssu rRNAs were not included in our molecular clock calculations. First appearance dates of diatom taxa from the fossil record were regressed against their corresponding branch lengths to infer the average and earliest possible age for the origin of the heterokont algae. The earliest age estimates (based on the median-evolving diatom taxon in the maximum-likelihood tree or on the average branch length in a linearized tree) suggest that the secondary endosymbiotic event leading to the divergence of pigmented heterokonts from their non-pigmented ancestors is unlikely to have occurred much before the Permian-Triassic boundary. The trees also show that the diatoms, one of the major groups of pigmented heterkonts, must have inherited their diplont life cycle and the ability to form resting stages from the last common ancestor shared with the oomycetes and the other pigmented heterokonts. We hypothesize that non-pigmented, diploid heterokonts, capable of forming resting stages and of stably maintaining a photosynthetic organism within their cytoplasm, had an adaptive advantage over other organisms during the intense climatic tectonic and geochemical changes that led to a mass extinction close to this boundary. After the mass extinction, many niches in the marine and aquatic realms were opened and the heterokont algae, including the diatoms, appear to have diverged after this time.
In 1952, Steemann Nielsen (1) introduced the ‘C-14 technique’ for measuring primary productivity in aquatic systems. The extent to which the technique has been used over the past 28 years bears testimony to its importance. In a real sense, use of the radioisotope provided a very sensitive and convenient method of measuring the rate at which photosynthetic cells, floating in an illuminated layer of water, convert inorganic carbon to cell material.
The distribution of slopes on the six basaltic shield voicanoes in the Western Galapagos Islands is investigated using a digital elevation model derived from airborne interferometric radar (TOPSAR) data. These measurements have a spatial sampling of 10 m/pixel, a vertical accuracy of 3 to 5 m, and constitute the highest resolution, most complete, topographic data set available for the islands. Volcano heights are determined to range from 1,124 m (Sierra Negra) to 1,710 m (Wolf). Over extensive areas of each volcano, slopes exceed 25°, with the highest slopes being ∼37° on Wolf and ∼36° on Fernandina. We confirm that two morphologic subgroups exist: Cerro Azul, Fernandina, and Wolf, with deep calderas (depth between 40-60% of the subaerial height of the volcano) and steep (>20°) maximum slopes at elevations between ∼60 and 80% of the volcano height; and Alcedo, Darwin, and Sierra Negra, with shallow calderas (depth <25% of subaerial height) and slopes that remain <15° until ∼90% of the total height is reached. Our data show that steep slopes are not uniquely correlated with the occurrence of arcuate fissures at the summit, leaving the origin of the steep slopes unresolved.
Marine diatoms play a predominant role in the biological carbon pump¹ transferring carbon dioxide from surface to deep waters. Laboratory studies show that a number of species take up HCO3⁻ and concentrate inorganic carbon intracellularly allowing rapid growth despite low CO2 availability²,³. In contrast, many oceanographers, particularly when interpreting carbon isotope data⁴,⁵, have made the assumption that diatoms do not utilize the abundant HCO3⁻ in seawater but rather take up CO2 by diffusion⁶. This has led to the hypothesis that large diatoms may be CO2-limited in the oceans⁷. We now demonstrate active uptake of HCO3⁻ in the field and a carbon-concentrating mechanism in coastal Atlantic diatoms. By manipulating PCO2 we show that growth of large diatoms in the California upwelling is not limited by CO2 availability.
An accessible text for the study of numerical methods for solving least squares problems remains an essential part of a scientific software foundation. Feedback that we have received from practicing engineers and scientists, as well as from educators and students in numerical analysis, indicates that this book has served this purpose. We were pleased when SIAM decided to republish the book in their Classics in Applied Mathematics series.
The main body of the book remains unchanged from the original book that was published by Prentice-Hall in 1974, with the exception of corrections to known errata. Appendix C has been edited to reflect changes in the associated software package and the software distribution method. A new Appendix D has been added, giving a brief survey of the many new developments in topics treated in the book during the period 1974–1995. Appendix D is organized into sections corresponding to the chapters of the main body of the book and includes a bibliography listing about 230 publications from 1974 to 1995.
Until now it has been considered that the positioning of magma conduits, dykes and eruption sites on Mt Etna is controlled by stresses set up by regional tectonism. It is also likely that gravitational stresses have some influence on the subsurface path taken by Etnean magmas prior to eruption. An additional effect discussed here is based mainly on convincing field evidence gathered over a number of years. It is proposed that fracturing of the surface and changes in the stress pattern due to loading by recent lava flows may strongly influence the siting of eruptions. Detailed field observations are presented, showing that cracks and fumaroles have consistently appeared round the edges of recent lava flows, and that these cracks are sometimes later used by erupting lavas. Eruption statistics indicate that since 1970, 50% of new eruptive vents have appeared within 80 m of a recent flow edge, and field measurements show that downward flexure is still occurring at the edges of lava flows more than sixteen years old. Simple theoretical modelling indicates that this effect is strongest at the surface, with gravitational and regional tectonic control of eruption sites dominating at progressively deeper levels.
We used stable isotope measurements to investigate the possible nutritional importance of diatoms for consumers in planktonic food webs. Several lines of evidence indicated that rapidly growing diatoms had C-13-rich isotopic compositions in the Georges Bank (USA) ecosystem. Diatoms in spring blooms and in well-mixed summer waters were relatively rich in C-13, with delta-C-13 values in the -15 to -19 parts per thousand range, while other phytoplankton and most particulate organic matter collected over a 13 mo period had C-13-depleted values of -21 to -25 parts per thousand. Culture experiments with nutrient-enriched seawater performed on Georges Bank and in Woods Hole Harbor (MA, USA) also showed a C-13 distinction between fast-growing diatoms with C-13-rich contents and other algae that were depleted in C-13. Zooplankton from central Georges Bank where diatoms are abundant had relatively high delta-C-13 values, consitent with an important nutritional role for C-13 diatoms. We estimate that a minimum of 40% of the carbon present in zooplankton consumers of central Georges Bank is derived from diatoms. Bloom diatoms from the North Atlantic, northeastern Pacific, and the nearshore Gulf of Mexico also had C-13-rich compositions, indicating that diatoms can be a source of C-13-rich carbon in many marine food webs.
Sierra Negra is the most voluminous of the western Galapagos shields and exhibits many unusual morphologic features: extensive lower flank apron, steep upper flanks, a broad summit plateau, a large complex caldera, ubiquitous occurrence of aa, and radial and circumferential fissures. A field-based investigation of the volcano was conducted in order to establish the distribution and characteristics of eruptive zones and associated flow fields and to construct a volcano-wide surface flow stratigraphy. The volcano has undergone over 90% resurfacing in the past 4500 yr. -from Authors
Volcán Alcedo is one of the seven western Galápagos shields and is the only active Galápagos volcano known to have erupted rhyolite as well as basalt. The volcano stands 4 km above the sea floor and has a subaerial volume of 200 km3, nearly all of which is basalt. As Volcán Alcedo grew, it built an elongate domal shield, which was partly truncated during repeated caldera-collapse and partial-filling episodes. An outward-dipping sequence of basalt flows at least 250 m thick forms the steepest (to 33°) flanks of the volcano and is not tilted; thus a constructional origin for the steep upper flanks is favored. About 1 km3 of rhyolite erupted late in the volcano's history from at least three vents and in 2–5 episodes. The most explosive of these produced a tephra blanket that covers the eastern half of the volcano. Homogeneous rhyolitic pumice is overlain by dacite-rhyolite commingled pumice, with no stratigraphic break. The tephra is notable for its low density and coarse grain size. The calculated height of the eruption plume is 23–30 km, and the intensity is estimated to have been 1.2x108 kg/s. Rhyolitic lavas vented from the floor of the caldera and from fissures along the rim overlie the tephra of the plinian phase. The age of the rhyolitic eruptions is ≤120 ka, on the basis of K-Ar ages. Between ten and 20 basaltic lava flows are younger than the rhyolites. Recent faulting resulted in a moat around part of the caldera floor. Alcedo most resently erupted sometime between 1946 and 1960 from its southern flank. Alcedo maintains an active, transient hydrothermal system. Acoustic and seismic activity in 1991 is attributed to the disruption of the hydrothermal system by a regional-scale earthquake.
This is a remarkable reference for researchers interested in volcanic hazards and silicic volcanism. Because of long repose and often obscure shapes and large size calderas are a volcanic type less obvious and less well studied. Because they represent potentially highly dangerous and highly explosive volcanos which could have large-scale and even global impact when they erupt, it is very important to understand their behavior. This new volume represents an extensive effort at compiling real observations at earth's calderas. The authors manage to incorporate a very impressive list of original references that go far beyond standard volcanological literature and also often extend back many centuries to include the perspective of longer historic time at some calderas. If volcanologists are serious about eruption forecasting, they must be willing to dig out and absorb the lessons of historic observations as well as design instruments and make good measurements. There is an initial introductory chapter of 27 pages which attempts to lead the way to interpretation of various patterns of caldera unrest, based on synthesis of the various individual cases. The meat of the volumes is in sections on the individual calderas, enriched with many maps and figures documenting the caldera unrest. A valuable asset of the compilation is its broad scope, which incorporates the activity of related or possibly related cones, domes, solfataras, etc., with the parent ( ) caldera.
THE supply of dissolved inorganic carbon (DIC) is not considered to limit oceanic primary productivity1, as its concentration in sea water exceeds that of other plant macronutrients such as nitrate and phosphate by two and three orders of magnitude, respectively. But the bulk of oceanic new production2 and a major fraction of vertical carbon flux is mediated by a few diatom genera whose ability to use DIG components other than CO2, which comprises < 1% of total DIC3, is unknown4. Here we show that under optimal light and nutrient conditions, diatom growth rate can in fact be limited by the supply of CO2. The doubling in surface water pCO2 levels since the last glaciation from 180 to 355 p.p.m.5,6 could therefore have stimulated marine productivity, thereby increasing oceanic carbon sequestration by the biological pump.
The utilization of inorganic carbon by three species of marine diatom, Skeletonema costatum (Grev.) Cleve. Ditylum brightwellii (West) Grun., and Chaetoceros calcitrans Paulsen was investigated using an inorganic carbon isotopic disequilibnum technique and inorganic carbon dose-response curves. Stable carbon isotope data of the diatoms are also presented. Observed rates of photosynthetic oxygen evolution were greater than could be accounted for by the theoretical rate of CO2 supply from the uncatalyzed dehydration of HCO3− in the external medium, suggesting use of HCO3− as an inorganic carbon source. Data from the isotopic disequilibrium experiment demonstrate the use of both HCO3− and CO2 for photosynthesis. Carbon isotope discrimination values support the use of HCO3− by the diatoms.
Empirical relations involving seismic moment M_o, magnitude M_S, energy E_S and fault dimension L (or area S) are discussed on the basis of an extensive set of earthquake data (M_S ≧ 6) and simple crack and dynamic dislocation models. The relation between log S and log M_o is remarkably linear (slope ∼ 2/3) indicating a constant stress drop Δσ; Δσ = 30, 100 and 60 bars are obtained for inter-plate, intra-plate and “average” earthquakes, respectively. Except for very large earthquakes, the relation M_S ∼ (2/3) log M_o ∼ 2 log L is established by the data. This is consistent with the dynamic dislocation model for point dislocation rise times and rupture times of most earthquakes. For very large earthquakes M_S ∼ (1/3) log M_o ∼ log L ∼ (1/3) log E_S. For very small earthquakes M_S ∼ log M_o ∼ 3 log L ∼ log E_S. Scaling rules are assumed and justified. This model predicts log E_S ∼ 1.5 M_S ∼ 3 log L which is consistent with the Gutenberg-Richter relation. Since the static energy is proportional to σ̅L^3, where σ̅ is the average stress, this relation suggests a constant apparent stress ησ̅ where η is the efficiency. The earthquake data suggest ησ̅ ~ 1/2 Δσ. These relations lead to log S ∼ M_S consistent with the empirical relation. This relation together with a simple geometrical argument explains the magnitude-frequency relation log N ∼ − M_S.
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 K1/2(CO2) in the range 1.0 to 4.0mmol m−3 and O2− 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.
Volcn Ecuador (002S, 9135W) consists of two strongly contrasting components: the eroded and vegetated remnant of a once-circular main volcano with a probable caldera, and a prominent rift zone extending to the northeast that is neither strongly eroded nor weathered. There are about 20 young-looking flows and vents on this caldera floor but only one on the higher remnant of the main volcano. The southwest half of the main volcano is faulted into the ocean. The main part of Volcn Ecuador possesses steep erosional slopes (average 30–40) that cut into a sequence of flows that dip radially outward at
) erupted from circumferential vents near the summit. These flows are nearly an order of magnitude smaller in volume than
the predominantly aa flows erupted from radial eruptive fissures near the break in slope (0.06–0.1 km3). The differences in volume and flow morphology with altitude are due to slower eruption rates from summit vents than from
flank vents, which, in turn, are attributable to the different heights the magmas must ascend from shallow reservoirs. These
observations support the contention that the steep upper flanks were constructed by the buildup of short lava flows rather
than by the structural deformation of originally gently dipping flanks. In addition to the higher eruption rates, a subdued
lower flank geometry is promoted by the deposition of lava deltas onto the shallow Galápagos platform on the western, northern,
and eastern flanks of the volcano. 40Ar/39Ar geochronology and volume estimates show that, despite their morphologic differences, the growth of the western Galápagos
shields has been nearly synchronous, precluding an evolutionary model for their development. The wide variations in elevation,
volume, area, and the distribution of slope angles among the western volcanoes can be linked instead to different long-term
eruption rates and, to a lesser degree, the position of each volcano relative to the edge of the Galápagos platform.
The carbon-fixation patterns of freshly isolated zooxanthellae from the hermatypic coral Acropora formosa were examined during a 15 min exposure to sodium mosa were examined during a 15 min exposure to sodium [14C]bicarbonate. The labelling pattern during the first 60 s exposure showed that the C3 carbon-fixation pathway is the major route for photosynthetic carbon fixation in Symbiodinium sp. 3-Phosphoglyceric acid, which constituted >50% of the label after 5 s, steadily decreased over the first 60 s. Hexose phosphates, aspartate, malate and glucose were the other main products during the first 60 s. Over longer periods, significant amounts of the organic acids succinate, aspartate and glutamate were found in the extract along with glucose; but no glycerol.
The 1998 eruption of Volcan Cerro Azul, Isla Isabela, Galápagos Islands, was observed in near real-time by the Geostationary
Operational Environmental Satellite-8 (GOES-8) weather satellite. Due to the remote location of the eruption site, 3.9-μm
radiance values derived from GOES band 2 provide the best timing of the start and termination of the eruption, which occurred
on 15 Sept. and 21 Oct., respectively. Throughout the 36-day long eruption, a total of 1335 thermal infrared images were collected,
of which 851 were cloud-free and permitted the thermal anomaly to be detected. A detailed chronology including 77 separate
events was assembled from the GOES data and field observations. Numerous attributes of the eruption were observed from the
GOES data, including the sizes and dispersal of seven eruption plumes and the occurrence and timing of intra-caldera effusive
activity. The growth of a lava flow on the SE flank, the formation of smoke and volcanic haze from the flank vent, and burning
of vegetation caused by lava flows entering vegetated areas were monitored both on the ground and with the satellite data.
In most cases GOES images were processed as they were received every 30 min and were then distributed over the Internet within
minutes of reception. These data provided timely high-temporal information to field parties as well as enabled the documentation
of the eruption. The GOES observations of Cerro Azul serve as a further example of the way in which the remote sensing community
and field volcanologists can collaborate during future eruptions, and permit the temporal and spatial resolution requirements
for future satellites systems to be better defined.
In recent years (1970–72 and 1982–84) two inflation episodes took place in the Campi Flegrei caldera (Italy), characterized by significant ground uplift and gravity variations. An elastic half-space model with vertical density stratification is employed to compute the displacement field and the gravity variations produced by the deformation of buried layers, following the inflation of a spherically symmetric deformation source. Contributions to gravity variations are produced by dilation/contraction of the medium, by the displacements of density interfaces (the free surface and subsurface layers) and of source boundaries and, possibly, by new mass input from remote distances into the source volume. Three cases were examined in detail: In case I, the magma chamber is identified as the deformation source and volume and pressure increase in the magma chamber is due to input of new magma from remote distances; in case II deformation is due to magma differentiation within the magma chamber (deformation source with constant mass); in case III the geothermal system is identified as the deformation source and a pressure increase, possibly driven by the exsolution of high temperature and high pressure volatiles in the magma chamber, is assumed to play a dominant role. From the comparison between measured and computed gravity residuals (free-air-corrected gravity variations) we can assess that, in case I, an inflation source with constant density would predict gravity residuals compatible with observations, whereas an expansion at constant mass (case II) would predict gravity residuals much lower than observed. The resolving power of gravity data however prevents accurate assessment of the density of the emplaced material. In case III, the pervasive density increase of the geothermal fluids induced by pressure increase is assumed to be the main source of gravity variations. The average porosity value required for this model to match both the ground deformation and the gravity residuals is found to be ~10%, a value which is compatible with measured porosity values at Campi Flegrei in deep wells. The subsidence phases following both inflation episodes and the gravity residuals during subsidence lead us to consider case III as more plausible, even if a suitable combination of cases I and III cannot be discarded.
The functioning of the biological pump during spring blooms was assessed with biogeochemical data from JGOFS (Joint Global Ocean Flux Study) process studies in the NE Atlantic during 1989 and 1990. A comparison of the integrated primary productivity signal (estimated by the 14C technique and from changes in ambient surface-water [tCO2] and [NO3−]s during the spring blooms of the two years revealed close similarities. These observations suggest that the magnitude of the biological drawdown of CO2 via photosynthetic activity during these periods was comparable. However, despite similarities in the magnitudes of these and other surface rate processes, sediment trap particulate organic carbon (POC) fluxes at 3100 m representing the spring bloom settlement events were 1.8 times greater in 1989 than in 1990. Taking into account the spatial and temporal resolutions of pelagic and deep trap datasets, these observations suggest that the coupling between organic carbon production in surface waters and its transfer to the deep ocean was stronger in the period studied in 1989 than in 1990. That is, the biological pump was more efficient in 1989. The size of the dominant phytoplankton species was observed to be the principal difference between the two spring bloom data sets. The potential influence of the observed algal size differences on the vertical POC flux was quantified from size-fractionated productivity data in conjuction with a food web-vertical flux model. The derived POC fluxes from the surface layer were two times greater in spring 1989 than in the bloom period in 1990, and a comparison of these flux estimates with those from other methods is favourable. Extrapolation of these derived shallow POC fluxes to 3100 m with existing empirical algorithms yields deep POC fluxes that are consistent with those collected by sediment traps at this depth. Differences in algal size between the two spring blooms can thus account for the observed interannual differences in deep-water POC fluxes without the need to invoke interannual differences in unmeasured mid-water processes. This work provides a clear demonstration that although observations of oceanic productivity may yield the input to the biological pump, they cannot, on annual timescales, reliably provide information on the efficiency of the pump in transferring carbon to the deep ocean.
New records of the abundance of in marine organic matter have been compiled for (i) the later Neoproterozoic, from 800 to 543 Ma (346 analyses), (ii) the Cambrian through the Jurassic (1616 analyses), and (iii) the Cretaceous and Cenozoic (2493 analyses). Comparison of these to existing compilations of the abundance of in sedimentary carbonates has allowed development of a record of the isotopic fractionation (≡εTOC) accompanying the production and burial of organic material. Over time, globally averaged values of εTOC have fallen in three ranges: (i) greater than 32‰ and apparently indicative of significant inputs from sulfide-oxidizing or other chemoautotrophic bacteria, notably during late Proterozoic interglacials at 752, 740–732, and 623–600 Ma; (ii) between 28 and 32‰ and indicative of maximal fractionation of carbon isotopes by phytoplanktonic producers, during the Neoproterozoic from 800 to 750 and from 685 to 625 Ma and during the Phanerozoic up to the early Oligocene; and (iii) less than 28‰, probably reflecting a reduction of primary fractionation by some combination of low levels of CO2, rapid rates of growth, and high ratios of cellular volume to surface area during Neoproterozoic glaciations (740, 720, and 575 Ma) and since the early Oligocene. Evidence of similar variations during the Ordovician and Gondwanan glaciations is absent. The decline in εTOC since the early Oligocene, from 30 to 22‰, has been nearly linear. The structure of the record of εTOC suggests that the maximal isotopic fractionation between dissolved CO2 and primary biomass has consistently been 25‰. Overall, the records provide compelling evidence that values of εTOC have varied widely and that the long-term average fractionation is roughly 30‰.
C4 and CAM phtosynthesis are evolutionarily derived from C3 photosynthesis. The morphological and biochemical modifications necessary to acheive either C4 or CAM photosynthesis are thought to have independently arisen numerous times within different higher plant taxa. It is though that C4 photsynthesis evolved in response to the low atmospheric CO2 concentrations that arose sometime after the end of the Cretaceous. Low CO2 concentrations result in significant increases in photorespiration of C3 plants, reducing productivity; both C3-C4 intermediate and C4 plants exhibit photorespiration rates. In contrast, it may be argued that CAM arose either in response to selection of increased water efficiency or for increased carbon gain. Globally, all three pathways are widely distributed today, with a tendency toward ecological adaptation of C4 plants into warm, monsoonal climates and CAM plants into water-limited habitats. In an anthropogenically altered CO2 environment, C4 plants, may lose their competitive advantage.
Lava flows continue to move after they have been emplaced by flow mechanisms. This movement is largely vertical and can be detected using differential synthetic aperture radar (SAR) interferometry. There are three main components to this motion: (1) movement of surface scatterers, resulting in radar phase decorrelation, (2) measurable subsidence of the flow surface due to thermal contraction and clast repacking, and (3) time-dependent depression of the flow substrate. These effects act in proportion to the thickness of the lava flow and decay with time, although there is a time lag before the third component becomes significant. We explore these effects using SAR data from the ERS satellites over the Etna volcano, Sicily. Phase decorrelation on young, thick a'a lava flows persists for a few years and probably results from surface block rotations during flow contraction. Maximum measured subsidence rates of the 1991–1993 lava flow over a period of 70 days are about 0.7 mm day−1, but are potentially greater in areas of data decorrelation. These rates fall to <2.7 × 10−2 mm day−1 after about 20 years in flows about 50 m thick, sooner for thinner flows. Comparison with measured subsidence rates on Kilauean lava lakes suggests that thermal contraction only accounts for about one third of the observed subsidence. The remaining motion is thought to come from surface clast repacking during cooling and from creep mechanisms in the flow substrate. Measurements of postemplacement surface movement provide new constraints on the thermomechanical properties of lava flows and have cautionary implications for the interpretation of interferometric SAR data of volcanoes.
噴火の際に火山周辺の地殻が著しく変動することは,古く1910年の有珠山の噴火の場合に大森博士によつて精密水準測泣が行われて以来,主な噴火について同様の測量が実施されて,次第に明らかになつて来た.これらの火山周辺の地殻変動に関する研究は必ずしも少なくないけれども,火山の噴火の機構との関係としてその火山学的意味を吟味したものはほとんど見られない.本論文ではこれまでに得られた測量の結果を調べて地殻変動の特性及び,噴火現象との関係を明らかにすることを試みた.
In addition to the normal carboxylation reaction, phosphoenolpyruvate carboxylase from Zea mays catalyzes a HCO3(-)-dependent hydrolysis of phosphoenolpyruvate to pyruvate and Pi. Two independent methods were used to establish this reaction. First, the formation of pyruvate was coupled to lactate dehydrogenase in assay solutions containing high concentrations of L-glutamate and aspartate aminotransferase. Under these conditions, oxalacetic acid produced in the carboxylation reaction was efficiently transaminated, and decarboxylation to form spurious pyruvate was negligible. Second, sequential reduction of oxalacetate and pyruvate was achieved by initially running the reaction in the presence of malate dehydrogenase with NADH in excess over phosphoenolpyruvate. After the reaction was complete, lactate dehydrogenase was added, thus giving a measure of pyruvate concentration. At pH 8.0 in the presence of Mg2+, the rate of phosphoenolpyruvate hydrolysis was 3-7% of the total reaction rate. The hydrolysis reaction catalyzed by phosphoenolpyruvate carboxylase was strongly metal dependent, with rates decreasing in the order Ni2+ greater than Co2+ greater than Mn2+ greater than Mg2+ greater than Ca2+. These results suggest that the active site metal ion binds to the enolate oxygen, thus stabilizing the proposed enolate intermediate. The more stable the enolate, the less reactive it is toward carboxylation and the greater the opportunity for hydrolysis.
The active species of "CO2," i.e. CO2 or HCO3-, utilized in the pyruvate carboxylase and phosphoenolypruvate carboxylase reaction have been determined with an assay predicated
upon the fact that the hydration of CO2 is a kinetically slow and measurable reaction. The results of these assays in both cases are in reasonable agreement with
those expected if HCO3- is assumed to be the functional species utilized by both enzymes.