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Blooms of microalgal red tides and macroalgae (e.g., green and golden tides caused by Ulva and Sargassum) have caused widespread problems around China in recent years, but there is uncertainty around what triggers these blooms and how they interact. Here, we use 30 years of monitoring data to help answer these questions, focusing on the four main species of microalgae Prorocentrum donghaiense, Karenia mikimotoi, Noctiluca scintillans, and Skeletonema costatum) associated with red tides in the region. The frequency of red tides increased from 1991 to 2003 and then decreased until 2020, with S. costatum red tides exhibiting the highest rate of decrease. Green tides started to occur around China in 1999 and the frequency of green tides has since been on the increase. Golden tides were first reported to occur around China in 2012. The frequency of macroalgal blooms has a negative linear relationship with the frequency and coverage of red tides around China, and a positive correlation with total nitrogen and phosphorus loads as well as with atmospheric CO2 and sea surface temperature (SST). Increased outbreaks of macroalgal blooms are very likely due to worsening levels of eutrophication, combined with rising CO2 and SST, which contribute to the reduced frequency of red tides. The increasing grazing rate of microzooplankton also results in the decline in areas affected by red tides. This study shows a clear shift of algal blooms from microalgae to macroalgae around China over the past 30 years driven by the combination of eutrophication, climate change, and grazing stress, indicating a fundamental change in coastal systems in the region. [ABSTRACT FROM AUTHOR]

The effects of ocean warming on phytoplankton have been extensively studied, but little has been documented on responses of differently sized diatoms to changes of temperature over wide ranges. We grew three diatom species, Thalassiosira pseudonana, Thalassiosira weissflogii, and Thalassiosira punctigera, with cell volumes of 199, 1805, and 13,599 μm3, respectively, at seven temperatures (5, 10, 15, 20, 25, 30, and 35°C) over 15 generations, and investigated their physiological responses. The optimum growth temperature (Topt), maximum growth rates (μmax), and thermal niche width (w) decreased by 16%, 48%, and 29% per order of magnitude in cell size increment, respectively. The cell volume of each species diminished significantly and linearly with increased temperatures, by 22% in T. punctigera, 17% in T. weissflogii, and 11% in T. pseudonana, respectively. However, the cellular biogenic silica (BSi) contents increased with rising temperature till the optimum growth temperature for growth, with the sensitivity of BSi to temperature changes (Q10BSi) ranging from 1.4 in the largest to 3.4 in the smallest diatom. The largest diatom T. punctigera showed the highest deactivation energy and succumbed to warmer conditions over its Topt, while the smallest was the most tolerant of warming. Although the moderate increase in growth temperature increased the diatoms' BSi levels, warming to temperatures higher than the optimum temperature for growth significantly reduced it. Our results suggest that diatoms acclimated to warmer conditions diminish their cell size but increase their mineralization of silica, which has profound significance in ocean carbon and silica biogeochemical cyclings. [ABSTRACT FROM AUTHOR]

Macroalgae, playing a crucial role in coastal marine ecosystems, are subject to multiple environmental challenges due to tidal and seasonal alterations. In this work, we investigated the physiological responses of Pyropia yezoensis to ocean acidification (ambient CO2 (AC: 400 μatm) and elevated CO2 (HC: 1000 μatm)) under changing salinity (20, 30 psu) and light intensities (50, 100 μmol photons m−2 s−1) by measuring the growth, pigment content, chlorophyll fluorescence, and soluble sugar content. The key results are the following: (1) P. yezoensis exhibited better growth under normal salinity (30 psu) compared to hyposaline conditions (20 psu). (2) Intermediate light intensity increased phycoerythrin content, ultimately enhancing thalli growth without significant changes to the contents of chlorophyll a and carotenoids. (3) Ocean acidification alleviated hyposaline stress by enhancing pigment production in P. yezoensis only at a salinity of 20 psu, highlighting the complex interplay of these environmental factors. These findings indicate that higher light intensities and elevated pCO2 levels could mitigate the stress caused by low salinity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

With the introduction of potassium species, the catalytic oxidation performance over the Pt1/CeO2 catalyst was significantly enhanced, where potassium ions acted as structural and electronic promoters, and formed Pt–O–K interactions with Pt to directly regulate the coordination environment and electronic state of Pt and the metal-support interaction between Pt and CeO2. [ABSTRACT FROM AUTHOR]

The effect of different CO2 concentrations and their subsequent light changes on the photosynthetic characteristics of Porphyra yezoensis are not well understood. The relationship between the availability of CO2 and light to physiological traits of the thalli could help understand the response and adaptation mechanisms of P. yezoensis to extreme weather changes. In this study, the photosynthetic response of P. yezoensis to light changes at different CO2 concentrations was determined. Under low light intensity, the high CO2 concentration promoted the relative growth rate (RGR) of P. yezoensis by 22.79% compared to that of ambient CO2 treatment. The net photosynthetic rate and phycoerythrin (PE) content under high CO2 were also significantly greater than those under ambient CO2 treatment at low light therapy. Under high light intensity, high CO2 exacerbated the inhibitory effect of light on the RGR of thalli. The net photosynthetic rate and PE content were significantly reduced by 12.53% and 14.06% at elevated CO2 concentration under a high light intensity, respectively. Furthermore, the net photosynthetic rate was significantly decreased when the light intensity was rapidly reduced, especially under simultaneously elevated CO2 concentrations. These findings indicate that elevated CO2 concentration increased the RGR and PE content at low light intensity of P. yezoensis. In addition, this study provides a theoretical basis for the response and adaptation mechanism of P. yezoensis to extreme weather changes. [ABSTRACT FROM AUTHOR]

Lipid and polyunsaturated fatty acids (PUFA) from microalgae can be used as biodiesel and health care products. How to enhance their productivity is crucial for successful commercial production. In this study, a two-stage model was used to stimulate the production of lipids and PUFA in a bloom-forming marine diatom Skeletonema costatum. Cells were cultured in ambient air (0.04% CO2) in the first stage and transferred to two high CO2 levels (5% and 10%) in the second stage. The medium CO2 level (5%) increased both specific growth rate and lipid content and hence almost doubled lipid productivity compared to 0.04% CO2 level. Although a 10% CO2 level induced the highest lipid content, it had negative effects on the specific growth rate and soluble carbohydrate synthesis, and the lipid productivity was not as high as 5% CO2. Neither CO2 level affected the cell size, chlorophyll a content, or soluble protein content. High CO2 levels also increased the synthesis of PUFA, e.g., eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Although high CO2 levels increased iodine value and decreased the cetane number of oil exacted from S. costatum, they fall in the range of the European standard, suggesting its suitability for biodiesels. These findings indicate that a two-stage model with high CO2 induction is an effective approach for the production of biodiesel and PUFA from S. costatum, which could be used in both biofuel and health care markets. [ABSTRACT FROM AUTHOR]

While intertidal macroalgae are exposed to drastic changes in solar photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) during a diel cycle, and to ocean acidification (OA) associated with increasing CO2 levels, little is known about their photosynthetic performance under the combined influences of these drivers. In this work, we examined the photoprotective strategies controlling electron flow through photosystems II (PSII) and photosystem I (PSI) in response to solar radiation with or without UVR and an elevated CO2 concentration in the intertidal, commercially important, red macroalgae Pyropia (previously Porphyra) yezoensis. By using chlorophyll fluorescence techniques, we found that high levels of PAR alone induced photoinhibition of the inter-photosystem electron transport carriers, as evidenced by the increase of chlorophyll fluorescence in both the J- and I-steps of Kautsky curves. In the presence of UVR, photoinduced inhibition was mainly identified in the O2-evolving complex (OEC) and PSII, as evidenced by a significant increase in the variable fluorescence at the K-step (F k) of Kautsky curves relative to the amplitude of F J− F o (Wk) and a decrease of the maximum quantum yield of PSII (F v/ F m). Such inhibition appeared to ameliorate the function of downstream electron acceptors, protecting PSI from over-reduction. In turn, the stable PSI activity increased the efficiency of cyclic electron transport (CET) around PSI, dissipating excess energy and supplying ATP for CO2 assimilation. When the algal thalli were grown under increased CO2 and OA conditions, the CET activity became further enhanced, which maintained the OEC stability and thus markedly alleviating the UVR-induced photoinhibition. In conclusion, the well-established coordination between PSII and PSI endows P. yezoensis with a highly efficient photochemical performance in response to UVR, especially under the scenario of future increased CO2 levels and OA. [ABSTRACT FROM AUTHOR]