Inorganic Carbon Utilization Research Articles

Optimal algae species inoculation strategy for algal-bacterial granular sludge: Sludge characteristics, performance and microbial community

The algal-bacterial granular sludge (ABGS) system is emerging as a promising technology for future wastewater treatment. This study assessed the impact of different algae species inoculation on granulation, performance, and microbial communities within ABGS systems. The experimental setup included single-species inoculations (Chlorella sp. (R1), Scenedesmus sp. (R2), and Desmodesmus sp. (R3)) and a mixed-species inoculation strategy (R4). Results revealed that R4 achieved the fastest completed granulation process (15 days) with the largest average granule diameter (772.93 μm) and highest physical strength (2.24 ± 0.26%) in the end of the experiment. The relative abundance of extracellular polymeric substances secreting bacteria of R4 maintained high level in whole operation time. Algae assimilation capacity and the abundance of functional bacteria can also influence removal performance. In mature stage, only the average effluent total nitrogen (3.15 ± 2.87 mg/L), total phosphorus (0.37 ± 0.27 mg/L), chemical oxygen demand (25.25 ± 2.98 mg/L) concentration in R4 was lower than that of Grade I discharge standard of municipal wastewater treatment plants in China. The best inorganic carbon utilization and lipid production ability were observed in R4 and R3, respectively. The choice of inoculated algae species was identified as a key factor for bacterial community dynamics. Overall, above results demonstrated that mixed algae species inoculation can be selected as the optimal algae inoculation strategy due to its excellent granulation, performance, and acceptable carbon utilization and lipid production.

Aluminium bioavailability and toxicity disrupted chloroplast structure and inhibited inorganic carbon utilization and nutrient uptake in Vallisneria natans at acidic and alkaline pH

Vallisneria natans, as submerged aquatic plants, face significant threats from aluminium (Al) toxicity. While the effects of Al at low pH on terrestrial plants have been extensively studied, there is a lack of research on the impacts of both low and high pH on chloroplast ultrastructure and nutrient uptake in submerged plants. This research is important as it aims to fill this gap by exposing the leaves of Vallisneria natans to 100 μM Al at varying pH levels (4.5, 5.5, 7.5, and 9.5) for 48 hours. The results showed that inorganic carbon (CT), CO2, and HCO3 content increased at extreme pH levels (4.5 and 9.5), suggesting decreased inorganic carbon utilization under Al stress. Additionally, photosystem II efficiency and electron transport rate were significantly reduced at extreme pH levels, highlighting the sensitivity of V. natans to Al. Chlorophyll a and total chlorophyll content were significantly lower at pH 4.5 compared to pH 7.5. Chloroplast structural disruptions were evident at extreme pH levels coupled with Al exposure, whereas minimal injury was observed at pH 5.5 and 7.5. The study also noted vacuole enlargement, altered plasma membrane permeability, and hematoxylin staining, indicating Al accumulation in leaves. ICP analysis revealed increased Al content at extreme pH levels, underscoring heightened Al bioavailability and toxicity. Significant reductions in macro and micronutrient content (P, Mg, K, Fe, Zn, B, Mn) were observed, likely due to Al-induced root and cell damage and altered nutrient uptake. These findings emphasize the complex interplay between Al exposure, pH fluctuations, and their cascading effects on the physiology and elemental composition of Vallisneria natans, highlighting the need for further research and environmental management strategies.

Inorganic carbon utilization strategies of plateau aquatic plants in response to native habitats.

Aquatic plants are a crucial component of the aquatic ecosystem in the Tibetan Plateau region. Researching the adaptability of plateau aquatic plants in photosynthesis to the plateau environment can enhance understanding of the operational mechanisms of plateau ecosystems, thereby providing a scientific basis for the protection and management of plateau aquatic ecosystems. This study presents an investigation of photosynthetic inorganic carbon utilization strategies and photosynthetic efficiency of 17 aquatic plants under natural growing conditions in Niyang River basin on the Tibetan Plateau. In pH-drift experiments, 10 of 17 species were able to utilize HCO3-, and environmental factors like water pH were shown to have a significant effect on the ability of the tested species to utilize HCO3-. Titratable acidity in the leaves of Stuckenia filiformis, Zannichellia palustris, Batrachium bungei, and Myriophyllum spicatum showed significant diurnal fluctuations at certain sampling sites, indicating the presence of CAM. In B. bungei, water pH positively correlated with CAM activity, while CO2 concentration negatively correlated with CAM activity. The chlorophyll fluorescence analysis revealed that aquatic plants inhabiting the Tibetan Plateau exhibited photosynthetic adaptations. In conclusion, the aquatic plants on the Tibetan Plateau employ diverse strategies for utilizing inorganic carbon during photosynthesis, exhibiting their flexible adaptability to the native high-altitude habitats of the Tibetan Plateau.

Bicarbonate concentration influences carbon utilization rates and biochemical profiles of freshwater and marine microalgae.

Selecting the optimal microalgal strain for carbon capture and biomass production is crucial for ensuring the commercial viability of microalgae-based biorefinery processes. This study aimed to evaluate the impact of varying bicarbonate concentrations on the growth rates, inorganic carbon (IC) utilization, and biochemical composition of three freshwater and two marine microalgal species. Parachlorella kessleri, Vischeria cf. stellata, and Porphyridium purpureum achieved the highest carbon removal efficiency (>85%) and biomass production at 6gL-1 sodium bicarbonate (NaHCO3), while Phaeodactylum tricornutum showed optimal performance at 1gL-1 NaHCO3. The growth and carbon removal rate of Scenedesmus quadricauda increased with increasing NaHCO3 concentrations, although its highest carbon removal efficiency (∼70%) was lower than the other species. Varying NaHCO3 levels significantly impacted the biochemical composition of P. kessleri, S. quadricauda, and P. purpureum but did not affect the composition of the remaining species. The fatty acid profiles of the microalgae were dominated by C16 and C18 fatty acids, with P. purpureum and P. tricornutum yielding relatively high polyunsaturated fatty acid content ranging between 14% and 30%. Furthermore, bicarbonate concentration had a species-specific effect on the fatty acid and chlorophyll-a content. This study demonstrates the potential of bicarbonate as an effective IC source for microalgal cultivation, highlighting its ability to select microalgal species for various applications based on their carbon capture efficiency and biochemical composition.

Effects of HCO3− and CO2 conversion rates on carbon assimilation strategies in marine microalgae: Implication by stable carbon isotope analysis of fatty acids

Marine microalgae are an essential component of marine plankton and critical primary producers, playing a vital role in marine ecosystems. The seawater carbonate system is a dynamic equilibrium system, and changes in any component can alter the carbonate balance. In CO2-concentrating mechanisms (CCMs), carbonic anhydrase (CA) regulates CO2 concentration by catalyzing the interconversion between CO2 and HCO3−. Therefore, limiting the activity of extracellular carbonic anhydrase (exCA) alters the rate at which carbonate equilibrium is reached and further affects the carbon assimilation process in microalgae. In this study, two different microalgae, Phaeodactylum tricornutum and Nannochloropsis oceanica, were selected to investigate the effects of changes in the carbonate system on photosynthetic carbon assimilation in microalgae by inhibiting exCA activity with acetazolamide (AZ). Inhibition of exCA activity reduces specific growth rates and photosynthetic efficiency of microalgae. The total alkalinity, HCO3− concentration, and CO2 concentration of the cultures increased with the decrease of pH, but the changes of the ribulose 1,5- bisphosphate carboxylase/oxygenase (Rubisco) activities of the two microalgae were different. In addition, the two microalgae possessed different lipid and carbohydrate synthesis strategies, but both restricted triacylglycerol (TAG) synthesis. Meanwhile, the microalgal cells had to utilize more 13CO2 when HCO3− and CO2 conversion rates were limited and restricted. This led to the continuous accumulation of 13C in fatty acids and the elevation of δ13CFAs. In conclusion, our study provides a new perspective on the role of microalgae in correlating carbonate changes with photosynthetic carbon assimilation strategies under mechanistic constraints on inorganic carbon utilization.

Optimization of nitrogen removal and microbial mechanism of a hydrogen-based membrane biofilm reactor

ABSTRACT The hydrogen-based membrane biofilm reactor (H2-MBfR) is an emerging biological nitrogen removal technology characterized by high efficiency, energy-saving capability, and environmental friendliness. The technology achieves denitrification and denitrogenation of microorganisms by passing hydrogen as an electron donor from inside to outside through the hollow fibre membrane module, and eventually the hydrogen reachs the biofilm attached to the surface of the fibre membrane. H2-MBfR has obtained favourable outcomes in the treatment of secondary biochemical effluent and low concentration nitrogen polluted water source. The experiment was optimized by s single-factor testing and response surface methodology-based optimization (RSM), and the optimal operational conditions were obtained as follows: an influent flow rate of 2 mL/min, hydrogen pressure of 0.04 MPa, and influent nitrate concentration of 24.29 mg/L. Under these conditions, a high nitrate removal rate of 98.25% was achieved. In addition, Proteobacteria and Bacteroidetes were the dominant bacteria in all stages, and the genus Hydrogenophaga was sufficiently enriched, occurring at 13.0%–49.0% throughout the reactor operation. Furthermore, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway for nitrate reduction and inorganic carbon utilization by microorganisms in the H2-MBfR was explored through comparison with the KEGG database. The results provided a mechanistic explanation for the denitrification and carbon sequestration capacity of the H2-MBfR.

Enhanced Food Waste Chain Elongation for Caproate Production: Role of Inorganic Carbon and Optimization Strategies

In this study, the role of inorganic carbon in chain elongation fermentation was investigated by examining its effects at different carbonate concentrations. The results demonstrated that higher yield of caproate (6.3±0.3 g/L - 7.4±0.2 g/L) was achieved with a NaHCO3 concentration of 2.5-5.0 g/L. Building upon these findings, a chain elongation process for food waste was developed. The caproate productions of control, CO2 and Na2CO3 trials were 4.6±0.2 g/L, 7.3±0.1 g/L, and 8.3±0.2 g/L, respectively. Chain elongation fermentation of food waste (1t TS) with Na2CO3 enhancement could synthesize 116.9 kg of caproate and 72.5 kg of carbon could be converted in caproate, accounting for 15.5% of the total organic carbon in the food waste. This study provided a comprehensive exploration of the chain elongation process for food waste, offering insights for further optimization and enhancement of food waste chain elongation performance coupling inorganic carbon utilization.

Diversity of CO2 Concentrating Mechanisms in Macroalgae Photosynthesis: A Case Study of Ulva sp.

Many algae respond to the CO2 limitation in seawater by inducing a CO2 concentrating mechanism (CCM) to obtain sufficient inorganic carbon to meet their photosynthetic needs, and Ulva sp. is a model population suitable for studying the ecological adaptability of macroalgae. As the dominant species of green tide disaster, Ulva sp. often faces strong inorganic carbon restriction due to its rapid growth and high population density and must have evolved a variety of carbon acquisition strategies, such as CCM, to overcome these limitations. This paper briefly summarizes the position and function of the important components of CCM (inorganic carbon transporters, carbonic anhydrase, Rubisco, and pyrenoid) and introduces several indexes suitable for evaluating the relative function of CCMs in macroalgae from the aspects of affinity between photosynthesis and Rubisco for CO2, and carbonic anhydrase inhibitor. The methods of judging the carbon sequestration pathway of Ulva sp., the CCM responses of diversity under different carbon sources, and the related genes that may be involved in the operation of CCMs were summarized. This work could provide a reference for revealing the CCMs of macroalgae and lay a foundation for further research on the inorganic carbon utilization strategy of the Ulva sp.

Enhanced direct gaseous CO2 fixation into higher bio-succinic acid production and selectivity

Utilizing CO2 for bio-succinic acid production is an attractive approach to achieve carbon capture and recycling (CCR) with simultaneous production of a useful platform chemical. Actinobacillus succinogenes and Basfia succiniciproducens were selected and investigated as microbial catalysts. Firstly, the type and concentration of inorganic carbon concentration and glucose concentration were evaluated. 6 g C/L MgCO3 and 24 g C/L glucose were found to be the optimal basic operational conditions, with succinic acid production and carbon yield of over 30 g/L and over 40%, respectively. Then, for maximum gaseous CO2 fixation, carbonate was replaced with CO2 at different ratios. The “less carbonate more CO2” condition of the inorganic carbon source was set as carbonate: CO2 = 1:9 (based on the mass of carbon). This condition presented the highest availability of CO2 by well-balanced chemical reaction equilibrium and phase equilibrium, showing the best performance with regarding CO2 fixation (about 15 mg C/(L·hr)), with suppressed lactic acid accumulation. According to key enzymes analysis, the ratio of phosphoenolpyruvate carboxykinase to lactic dehydrogenase was enhanced at high ratios of gaseous CO2, which could promote glucose conversion through the succinic acid path. To further increase gaseous CO2 fixation and succinic acid production and selectivity, stepwise CO2 addition was evaluated. 50%-65% increase in inorganic carbon utilization was obtained coupled with 20%-30% increase in succinic acid selectivity. This was due to the promotion of the succinic acid branch of the glucose metabolism, while suppressing the pyruvate branch, along with the inhibition on the conversion from glucose to lactic acid.

Different photosynthetic inorganic carbon utilization strategies in the heteroblastic leaves of an aquatic plant Ottelia ovalifolia.

The leaves of the heteroblastic aquatic plant Ottelia ovalifolia faces submerged and aerial environments during its life history. However, the acclimation of the submerged leaves and floating leaves to these two environments in morphology, physiology, and biochemistry remain unclear. In the present study, we investigated the acclimation of the CO2-concentrating mechanisms in these two types of leaves. We found that the submerged leaves were longer, narrower, and thinner than the floating leaves, which increased the specific surface area of the leaves and lead to better absorption of the inorganic carbon underwater. Meanwhile, the floating leaves absorbed atmospheric CO2 directly through the stomata to acclimate to the aerial environment. Both the leaf types had the ability to use , but the capacity in submerged leaves was stronger than that in floating leaves. The extracellular carbonic anhydrase and anion exchanger were responsible for the use in both types of leaves. The higher ratio of chlorophyll a/b and content of anthocyanin in floating leaves than that in submerged leaves indicated that the acclimation of aerial and submerged photosynthesis depended on changes in the photosynthetic pigments. Based on the stable carbon isotope ratio, key enzyme activities of the C4 pathway indicated that submerged leaves might have the ability to perform C4 metabolism while floating leaves only performed C3 metabolism. In summary, O. ovalifolia acclimates to submerged and aerial environments through changes in morphology, physiology, and biochemistry during different growth stages.

The Predominance of Ammonia-Oxidizing Archaea in an Oceanic Microbial Community Amended with Cyanobacterial Lysate.

When the oligotrophic microbial community was amended with Synechococcus-derived dissolved organic matter (SDOM) and incubated under the dark condition, archaea relative abundance was initially very low but made up more than 60% of the prokaryotic community on day 60, and remained dominant for at least 9 months. The archaeal sequences were dominated by Candidatus Nitrosopumilus, the Group I.1a Thaumarchaeota. The increase of Thaumarchaeota in the dark incubation corresponded to the period of delayed ammonium oxidation upon an initially steady increase in ammonia, supporting the remarkable competency of Thaumarchaeota in energy utilization and fixation of inorganic carbon in the ocean. IMPORTANCE Thaumarchaeota, which are ammonia-oxidizing archaea (AOA), are mainly chemolithoautotrophs that can fix inorganic carbon to produce organic matter in the dark. Their distinctive physiological traits and high abundance in the water column indicate the significant ecological roles they play in the open ocean. In our study, we found predominant Thaumarchaeota in the microbial community amended with cyanobacteria-derived lysate under the dark condition. Furthermore, Thaumarchaeota remained dominant in the microbial community even after 1 year of incubation. Through the ammonification process, dissolved organic matter (DOM) from cyanobacterial lysate was converted to ammonium which was used as an energy source for Thaumarchaeota to fix inorganic carbon into biomass. Our study further advocates the important roles of Thaumarchaeota in the ocean's biogeochemical cycle.

Inorganic carbon utilization: A target of silver nanoparticle toxicity on a submerged macrophyte

Submerged macrophytes play an important role in the global carbon cycle through diversified pathways of inorganic carbon (Ci) utilization distinct from terrestrial plants. However, the effects of silver nanoparticles (AgNPs), an emerging contaminant, were unknown on the Ci utilization of submerged macrophytes. In Ottelia alismoides, the only known submerged macrophyte with three pathways of Ci utilization, before absorption, AgNPs inhibited the external carbonic anhydrase activity thus reducing the capacity of the plant to use HCO3−. After entering the plant, AgNPs mainly aggregated at the cell wall and in the chloroplast. The internalized AgNPs inhibited ribulose 1,5-bisphosphate carboxylase-oxygenase (Rubisco) activity blocking CO2 fixation and disturbed C4 and crassulacean acid metabolism (CAM) by inhibiting phosphoenolpyruvate carboxylase (PEPC), pyruvate phosphate dikinase (PPDK), and NAD-dependent malic enzyme (NAD-ME) activities to alter intracellular malate biosynthesis and decarboxylation. Overall, our findings indicate that the Ci utilization of the submerged macrophyte is a target of AgNPs toxicity that might affect the carbon cycle in aquatic systems.

The mechanism of carbon source utilization by microalgae when co-cultivated with photosynthetic bacteria

Microalgae-photosynthetic bacteria (PSB) co-culture, which is promising for wastewater treatment and lipid production, is lacking of study. In this work, the combinations of 3 microalgae and 3 PSB strains were firstly screened and then different inoculation ratios of the co-cultures were investigated. It was found the best promotion was Chlorella pyrenoidosa/Rhodobacter capsulatus co-culture (1:1), where the biomass productivity, acetate assimilation rate and lipid productivity were 1.64, 1.61 and 2.79 times than that of the sum of pure microalgae and PSB cultures, respectively. Meanwhile, the inoculation ratio significantly affected the growth rate and lipid productivity of co-culture systems. iTRAQ analysis showed that PSB played a positive effect on acetate assimilation, TCA cycle and glyoxylate cycle of microalgae, but decreased the carbon dioxide utilization and photosynthesis, indicating PSB promoted the microalgae metabolism of organic carbon utilization and weakened inorganic carbon utilization. These findings provide in-depth understanding of carbon utilization in microalgae-PSB co-culture.

Effects of nutrients on the utilization pattern of photosynthetic inorganic carbon of the tropical <italic>Thalassia hemprichii</italic>

<p indent="0mm">Studies on the utilization strategy of photosynthetic inorganic carbon of seagrass can reveal its ecological adaptation mechanism. <italic>Thalassia hemprichii</italic>, a widely distributed seagrass species in the Indo-Pacific and Atlantic coastal seas, needs to evolve several utilization patterns of inorganic carbon to adapt different environments and meet its growth, development and reproduction. However, the effect of nutrient on the photosynthetic inorganic carbon utilization strategy in seagrass is still unknown and further research is urgently needed. Therefore, using oxygen electrode technology, chlorophyll fluorescence technology, and non-invasive micro-test technology, this study examined the similarity and difference in the utilization patterns of photosynthetic inorganic carbon of <italic>T</italic>.<italic> hemprichii </italic>from two typical tropical seagrass beds (Tanmen, Hainan Island, and Yongxing Island, Xisha), that were affected by varying degrees of human activity. Experiments showed that the photosynthetic oxygen release rate, maximum relative electron transfer rate, and half-saturated light intensity of <italic>T</italic>.<italic> hemprichii</italic> in Yongxing Island waters were 24.95%, 24.54%, and 28.73% higher than the corresponding in Tanmen, Hainan Island. This indicated that the growth status of <italic>T</italic>.<italic> hemprichii</italic> in the waters of Yongxing Island was better with higher photosynthetic efficiency. The addition of acetazolamide (AZ) and ethoxyzolamide (EZ) significantly reduced the photosynthetic oxygen release rate of <italic>T</italic>.<italic> hemprichii</italic>, with an insignificant difference in the inhibition between AZ and EZ. This indicated that it mainly absorbed HCO₃⁻ via extracellular carbonic anhydrase catalysis. Meanwhile, hydroxymethyl (Tris) inhibited the photosynthetic oxygen release of <italic>T</italic>.<italic> hemprichii</italic> in Tanmen by up to 100% and decreased the maximum relative electron transfer rate and the H⁺ inward flow rate, implying a synergistic H⁺/HCO₃⁻ transport mode. On the other hand, the rate of photosynthetic oxygen release and the maximum electron transfer rate of <italic>T</italic>.<italic> hemprichii</italic> in Xisha did not change significantly with the addition of AZ and EZ, while Tris buffer inhibited photosynthetic oxygen release by up to 100% and significantly reduced the maximum electron transfer rate. This suggested <italic>T</italic>.<italic> hemprichii </italic>in Xisha mainly relied on the H⁺/HCO₃⁻ synergistic transport. Therefore, <italic>T</italic>.<italic> hemprichii </italic>could uptake inorganic carbon in an environment with greater anthropogenic activity, larger nutrient load and lower light availability on Hainan Island by catalyzing HCO₃⁻ into CO₂ with extracellular carbonic anhydrase and the H⁺/HCO₃⁻ synergistic transport. In contrast, <italic>T</italic>.<italic> hemprichii</italic> in an environment with less anthropogenic activity, lower nutrient loading, and greater light availability, relied chiefly on H⁺/HCO₃⁻ synergistic transport. Facing a relatively unfavorable high-nutrient and low-light growth environment, <italic>T</italic>.<italic> hemprichii</italic> could increase the photosynthetic inorganic carbon utilization strategy (such as the activity of extracellular carbonic anhydrase) to improve its utilization ability of inorganic carbon to overcome stress and growth limitation. This suggested that <italic>T</italic>.<italic> hemprichii</italic> could adjust its inorganic carbon utilization patterns according to its geographical environment. With the continuous development of technology, it is urgent to study the utilization mechanism of inorganic carbon of seagrass by applying seagrass omics technology and stable isotope tracing to deepen the understanding of the carbon sink function of seagrass.

Differential Responses of Nitrate/Ammonium Use to Bicarbonate Supply in Two Brassicaceae Species under Simulated Karst Habitat

In the karst habitats with nitrate-abundant and ammonium-rare soil, the bicarbonate supply plays a crucial role in both inorganic carbon and nitrogen assimilation in various plant species. Consequently, two carbon sources, carbon dioxide (CO2) and bicarbonate (HCO3−), and two nitrogen sources, namely nitrate (NO3−) and ammonium (NH4+) are available for plants. However, variations in the absorption and utilization of nitrate, ammonium, and inorganic carbon during bicarbonate supply in different plants are not well-depicted. In this study, we evaluated the nitrate/ammonium use efficiency and their contributions to the total nitrogen assimilation/utilization capacity at different bicarbonate levels using a bidirectional stable nitrogen isotope tracer approach. The inorganic carbon assimilation, such as the photosynthesis, carbon/nitrogen enzymatic activities, carbon/nitrogen content, nitrogen assimilation/utilization capacity, and nitrate/ammonium contributions to plant growth, were also evaluated to decipher the responses of both carbon and nitrogen metabolism to bicarbonate supply in karst habitats. With the increasing bicarbonate level, Orychophragmus violaceus (Ov) was found to be more available for nitrate to total nitrogen assimilation and utilization than Bn (Brassica napus). Further, it enhanced the contributions of nitrate and nitrogen accumulation/utilization capacity and inorganic carbon assimilation, increasing photosynthesis, carbon/nitrogen enzymatic activities, and carbon accumulation, and promoted the growth in Ov. Though the highest bicarbonate level was conducive to ammonium utilization and water use efficiency in both Ov and Bn, it inhibited total inorganic carbon and nitrogen assimilation, leading to growth suppression in Bn compared to Ov. Moreover, considering the optimistic responses of both carbon and nitrogen assimilation to the high bicarbonate supply in nitrate-abundant, as well as ammonium-rare, environments, we conclude that Ov was more adaptable to the karst habitats. This study provides a novel approach to elucidate the responses of nitrate/ammonium utilization and inorganic carbon assimilation to bicarbonate. Furthermore, the current study reveals the complex interactions among different carbon–nitrogen metabolism pathways in various plants and their adaptations to karst habitats.

Adaptation of inorganic carbon utilization strategies in submerged and floating leaves of heteroblastic plant Ottelia cordata

During the life history, the aquatic heteroblastic plant undergoes submerged-leaf and floating/emerged-leaf phases, with dramatic changes in their surrounding environments. However, little is known about the physiological and biochemical changes of the two types of leaves adapting to submerged and aerial environments. In the present study, a heteroblastic plant Ottelia cordata was chosen to investigate the variations in morphology, anatomy, physiology, and biochemistry between the two types of leaves. The results showed that the floating leaf developed stomate to absorb atmospheric CO 2 for photosynthesis to adapt to the aerial habitat, while the submerged leaf showed longer, narrower, and thinner to maximize inorganic carbon uptake underwater. Through external carbonic anhydrase catalysis, both types of leaves could use HCO 3 - as an extra carbon source, and it was stronger in submerged leaves. Besides HCO 3 - use, the δ 13 C and the activity of C4 process key enzymes supported that the submerged leaf could perform C4 metabolism, while the floating leaves only carried on C3 metabolism. This is the first time to report an aquatic plant transiting from the C4 process underwater to the C3 process in the air. Based on the discrimination of stable carbon isotope, in the field, the main carbon source was atmospheric CO 2 for floating leaves and the free CO 2 underwater for submerged leaves. Additionally, HCO 3 - could approximately support 16% carbon source for underwater photosynthesis, which was the second important carbon source for submerged leaves. All our data indicated the heteroblastic aquatic plant adapts to underwater and aerial environments in morphology, anatomy, physiology, and biochemistry for completing life history and maintaining the population in the field. • Morphology and anatomy differed between submerged and floating leaves of O. cordata. • Both types of leaves could use HCO 3 - via external CA mediation for photosynthesis. • Submerged leaf performed C4 metabolism, floating leaf only carried on C3 metabolism. • Atmospheric CO 2 was the main carbon source for floating leaf. • Soluble CO 2 and HCO 3 - underwater were the two main carbon sources for submerged leaf.

Constraints on coccolithophores under ocean acidification obtained from boron and carbon geochemical approaches

Ocean acidification (OA) appears to have diverse impacts on calcareous coccolithophores, but the cellular processes underlying these responses are not well understood. Here we use stable boron and carbon isotopes, B/Ca ratios, as well as inorganic and organic carbon production rates to investigate the carbon utilization and the internal pH regulation at the site of calcification in Emiliania huxleyi, Calcidiscus leptoporus and Pleurochrysis carterae cultured over a wide pCO2 range (180–1000 μatm). Despite large variability, the geochemistry data indicate species-specific modes of pH control and differences in the utilization of inorganic carbon. Boron isotope data suggest that all three species generally upregulate the pH of the calcification fluid (pHCF) compared to surrounding seawater, which coincides with relatively constant growth rates and cellular ratios of inorganic to organic carbon. Furthermore, species exhibit different strategies in regulating their pHCF, i.e., two species maintain homeostasis (pHCF = ∼8.7), while one species shows a constant offset to the surrounding seawater (ΔpH = ∼0.6 units) over the entire tested pCO2 range. In addition to these different strategies, carbon isotope data suggests that high plasticity in the utilization of dissolved inorganic carbon might be an explanation for species-specific differences in coccolithophore responses to OA.

Approaches and involved principles to control pH/pCO2 stability in algal cultures

Experimental cultures of both microalgae and macroalgae are commonly carried out by phycologists or environmental biologists to look into morphological, physiological, and molecular responses to aquatic environmental changes. However, the species of inorganic carbon in algae cultures is often altered by algal photosynthetic CO2 removal and/or bicarbonate utilization. The pH changes associated with altered carbonate chemistry in cultures impact physiological processes in microalgae and macroalgae even at their exponential growth phases, since extra energy is required to sustain intracellular acid–base homeostasis. Usually, pH increases during light period due to inorganic carbon uptake and utilization for photosynthesis and decreases during dark period because of respiratory CO2 release. Therefore, to obtain relevant data aimed for physiological and/or molecular responses of algae to changed levels of environmental factors, stability of pH/pCO2 in the cultures should be considered and controlled to rule out impacts of carbonate chemistry and pH changes. In this work, principles involved in changing pH processes in algal cultures are mechanistically analyzed and several approaches to control pH and pCO2 are introduced. In order to sustain stability of pH/pCO2, the principles underline the following key points: (1) maintaining the rate of photosynthetic C removal less than or equal to the rate of CO2 dissolution into the cultures which are aerated; or (2) sustaining dilute cultures with very low cell density without aeration, so that photosynthetic C removal is small enough not to cause significant pH/pCO2 changes; or (3) stabilizing the changes in micro-environments surrounding the cells or thallus. To maintain pH drift < 1% in growing typical unicellular microalgae, the recommended cell concentration ranges from 50 × 103 to 200 × 103 mL−1 with aeration (air replacement rate of ca 500–1000 mL L−1 min−1) in semi-continuous cultures of < 1 L, and it ranges from 100 to 5000 cells mL−1 for diatoms and from 100 to 100 × 103 cells mL−1 for coccolithophores in dilute cultures without aeration, respectively. For macroalgae, maintaining the thalli in flowing through- system or in semi-continuous cultures (continuously control algal biomass density) is recommended.

Anthropogenic and Climatic Contributions to Observed Carbon System Trends in the Northeast Pacific

AbstractThe ocean absorbs anthropogenic carbon, slowing atmospheric CO2 increase but driving ocean acidification. Long‐term changes in the carbon system are typically assessed from single‐point time series or from hydrographic sections spaced by decades. Using higher resolution observations (1–3 year−1) from the Line P time series, we investigate processes modulating trends in the carbon system of the northeast subarctic Pacific. Dissolved inorganic carbon (DIC) and apparent oxygen utilization (AOU) from 1990 to 2019 reveal substantial trends over most of the upper water column along the 1,500 km coastal to open ocean transect. At the surface, an increasing trend in salinity‐normalized DIC (sDIC33) (+0.5 ± 0.4 μmol kg−1 yr−1) is associated with a decrease in pH (0.01–0.02 decade−1) and a decrease in aragonite saturation state (0.04–0.08 decade−1). These observed trends are driven by anthropogenic CO2 uptake, partially offset by trends in surface salinity or temperature. Stratification associated with recent marine heat waves appears to have caused anomalously low surface pCO2. sDIC33 trends of similar magnitude were found below the seasonal thermocline on the 26.7–26.8 isopycnals (150–300 m), which are ventilated in the western Pacific. Roughly, a third (20%–50%) of the subsurface sDIC33 trend is driven by increased remineralization, likely caused by long‐term decreases in ventilation in the western Pacific. Bidecadal oscillations in the ventilation of the 26.7–26.8 isopycnals arising from the Lunar Nodal Cycle cause oscillations in sDIC33 and AOU at the offshore end of our transect. We trace the oscillations to alternating periods of higher anthropogenic carbon uptake or higher carbon remineralization.

The Mid-Atlantic Bight Dissolved Inorganic Carbon System Observed in the March 1996 DOE Ocean Margins Program (OMP)—A Baseline Study

The United States Department of Energy (DOE)’s Ocean Margins Program (OMP) cruise EN279 in March 1996 provides an important baseline for assessing long-term changes in the carbon cycle and biogeochemistry in the Mid-Atlantic Bight (MAB) as climate and anthropogenic changes have been substantial in this region over the past two decades. The distributions of O2, nutrients, and marine inorganic carbon system parameters are influenced by coastal currents, temperature gradients, and biological production and respiration. On the cross-shelf direction, pH decreases seaward, but carbonate saturation state (ΩArag) does not exhibit a clear trend. In contrast, ΩArag increases from north to south, while pH has no clear spatial patterns in the along-shelf direction. In order to distinguish between the effects of physical mixing of various water masses and those of biological activities on the marine inorganic carbon system, we use the potential temperature-salinity diagram to identify water masses, and differences between observations and theoretical mixing concentrations to measure the non-conservative (primarily biological) effects. Our analysis clearly shows the degree to which ocean margin pH and ΩArag are regulated by biological activities in addition to water mass mixing, gas exchange, and temperature. The correlations among anomalies in dissolved inorganic carbon, phosphate, nitrate, and apparent oxygen utilization agree with known biological stoichiometry. Biological uptake is substantial in nearshore waters and in shelf-slope mixing areas. This work provides valuable baseline information to assess the more recent changes in the marine inorganic carbon system and the status of coastal ocean acidification.