Posts Tagged 'growth'

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Divergent responses of an armored and an unarmored dinoflagellate to ocean acidification

Published 24 December 2024 Science Closed
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Highlights

  • An armored and an unarmored dinoflagellate exhibited divergent responses to OA.
  • The unarmored species presented a higher ability to withstand OA stress.
  • Cell wall structure may play essential roles in response to OA stress.
  • Unarmored dinoflagellates may have significant advantages in acidic oceans.

Abstract

Dinoflagellates, both armored and unarmored, with distinct cell wall difference, are being affected by elevated CO2-induced ocean acidification (OA). However, their specific responses to OA are not well understood. In this study, we investigated the physiological and molecular response of the armored species Prorocentrum obtusidens and the unarmored species Karenia mikimotoi to OA over a 28-day period. The results show that the two species responded differently to OA. Cell growth rate, particulate organic carbon (POC) content, and the activities of C4 pathway enzymes decreased in P. obtusidens under future acidified ocean condition (pH 7.8, 1000 μatm pCO2), but the activities of carbonic anhydrase (CA), ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), and superoxide dismutase (SOD) increased. Whereas cell growth rate, contents of Chl a and PON, and SOD activity altered insignificantly in K. mikimotoi, but contents of POC and total carbohydrate, and the activity of RubisCO increased while the activities of CA and C4 pathway enzymes decreased. Transcriptomic analysis indicates that genes associated with antioxidative response, heat shock protein, proteasome, signal transduction, ribosome, and pH regulation were up-regulated in P. obtusidens but down-regulated in K. mikimotoi. Notably, the synthesis of soluble organic matter (i.e., spermidine and trehalose) was enhanced in K. mikimotoi, thereby regulating intracellular pH and improving stress resistance. This study highlights the divergent response of the armored and unarmored dinoflagellates to OA, with the unarmored dinoflagellate exhibiting a higher ability to withstand this stressor. Therefore, caution should be exercised when predicting the behavior and the eventual fate of dinoflagellates in the future acidified ocean.

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Long-term warming and acidification interaction drives plastic acclimation in the diatom Pseudo-nitzschia multiseries

Published 17 December 2024 Science Closed
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Highlights

  • Temperature shows stronger effects than CO2 on P. multiseries growth and stress reponses.
  • Multi-omics analysis reveals phenotypic plasticity and molecular adaptations under long-term warming and acidification.
  • Short-term experiments effectively predict long-term P. multiseries responses to combined temperature and CO2 changes.

Abstract

Ocean warming (OW) and acidification (OA) are expected to interactively impact key phytoplankton groups such as diatoms, but the underlying mechanisms, particularly under long-term acclimation, remain poorly understood. In this study, we investigated the responses of the toxic diatom Pseudo-nitzschia multiseries to combined changes in temperature (20 °C and 30 °C) and CO2 concentration (pCO2 400 μatm and 1000 μatm) using a multi-omics approach over an acclimation period of at least 251 generations. Physiological data suggest that elevated temperature, either alone or in combination with CO2, reduced the net photosynthesis and nitrate uptake rate, thus inhibiting P. multiseries growth. Conversely, elevated CO2 alone stimulated P. multiseries growth. Comparative genome analysis revealed the phenotypic plasticity in response to temperature and pCO2 variations, even after more than 251 generations acclimation period. Temperature was identified as the dominant environmental factor, showing stronger effects than CO2. Transcriptomic profiles indicated that genes involved in stress- and intracellular homeostasis such as Hsps, ubiquitination process and antioxidant defense were mostly down-regulated under long-term warming acclimation. This study demonstrates that P.multiseries responds similarly to both short-term and long-term experimental selection, suggesting that short-term experiments can be used to predict long-term responses.

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Interactive effects of CO2, temperature, and nitrate limitation on the growth and physiology of strain CCMP 1334 of the marine cyanobacterium Synechococcus (Cyanophyceae)

Published 13 December 2024 Science Closed
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The marine cyanobacterium Synecococcus sp. (CCMP 1334) was grown in a continuous culture system on a 12:12 h light:dark cycle at all combinations of low and high pCO2 (400 and 1000 ppmv, respectively), nutrient availability (nitrate-limited and nutrient-replete conditions), and temperatures of 21, 24, 28, 32, and 35°C. The maximum nutrient-replete growth rate was ~1.15 day−1 at 32–35°C. Median nutrient-replete growth rates were higher at 1000 ppmv than at 400 ppmv pCO2 at all temperatures. Carbon:nitrogen ratios were independent of pCO2 at a fixed relative growth rate (i.e., growth rate ÷ nutrient-replete growth rate) but decreased with increasing temperature. Carbon:chlorophyll a ratios were decreased monotonically with increasing temperature and were higher under nitrate-limited than nutrient-replete conditions. Ratios of phycoerythrin to chlorophyll a were independent of growth conditions. Productivity indices were independent of temperature and nutrient limitation but were consistently higher at 1000 ppmv than 400 ppmv pCO2. Both growth rates and dark respiration rates were positively correlated with temperature, and the associated Q10 values were 2.2 and 2.3, respectively. A model of phytoplankton growth in which cellular carbon is allocated to structure, storage, or the light or dark reactions of photosynthesis accounted for the general patterns of cell composition and growth rate. This strain of Synechococcus appears well suited to changes in environmental conditions that are expected as the climate warms in response to anthropogenic emissions of CO2.

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Differential impacts of pH on growth, physiology, and elemental stoichiometry across three coccolithophore species

Published 10 December 2024 Science Closed
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Coccolithophores are pivotal players in ocean biogeochemistry, yet the impact of changing pH on the physiology of different species remains unclear as there has been a dominant focus on Gephyrocapsa huxleyi. Meta-analyses of existing experimental data are challenging due to the differences in multidimensional culture conditions. This study investigated the response of three species—Gephyrocapsa huxleyi, Coccolithus braarudii, and Chrysotila carterae—under varying CO2 conditions (via pH). The sensitivity to pH differed between species, but all species showed reduced growth rates under the highest CO2 (lowest pH) treatment possibly due to high [H+]-related inhibition. Low pH impacted cellular physiology and elemental stoichiometry, while the impact of high pH was less adverse. The changes in elemental production induced by low pH could exert a negative influence on the contribution of coccolithophores to nutrient and carbon export, especially for biogeochemically relevant open-ocean species. pH also affected coccolith formation, especially in C. braarudii, through CO2 limitation at high pH and low calcite saturation state at low pH. Contrasting species-specific pH sensitivities highlighted the potential for species like G. huxleyi to further outperform others like C. braarudii in an acidic ocean. Literature synthesis showed that coccolithophores show a broad CO2 optimum, although growth rates and particulate inorganic carbon to particulate organic carbon ratios consistently declined with increasing CO2. Strain-specific CO2 optima partly contributed to the variability within responses of individual species, giving the misleading perception of a broad species-level CO2 optimum. Strain-specific optima exist possibly due to their adaptation to carbonate chemistry conditions at the place of origin.

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The important role of the antioxidant stress capacity in the response of Prochlorococcus to increased CO2 under varying iron and light conditions

Published 9 December 2024 Science Closed
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Highlights

  • Low-light-adapted Prochlorococcus ecotypes have stronger low-iron adaptation capacity
  • Fe limitation in Prochlorococcus is enhanced under both low growth-limiting light and high photo-inhibitory light
  • High CO2 promotes the growth of low-light-adapted Prochlorococcus ecotypes due to a reduction in cellular oxidation stress

Abstract

Ocean acidification caused by the ongoing increase in atmospheric carbon dioxide (CO2) is expected to impact the growth of marine phytoplankton. Additionally, CO2-driven climate change influences light intensity and iron (Fe) availability in surface seawaters, two critical factors for marine phytoplankton carbon fixation and growth due to their central role in regulating photosynthesis. The cyanobacterium Prochlorococcus often dominates marine productivity in oligotrophic oceans with low but variable Fe concentrations and light intensities. However, the combined effects of light intensity, Fe availability and CO2 concentration on the growth and photosynthesis of Prochlorococcus remain unclear. In this study, we found that the high-light-adapted Prochlorococcus strain MED4, isolated from shallower depths, required much higher Fe concentrations and light intensities to grow than the low-light-adapted strain NATL1A, isolated from deeper depths. Increased CO2 had no effect on the growth of strain MED4 under any light or Fe conditions. In contrast, increased CO2 caused a 29% increase in the growth of strain NATL1A under low Fe coupled with high photo-inhibitory light condition, owing to a reduction in cellular oxidative stress. The varying antioxidant stress capacities of different Prochlorococcus strains appeared to influence their responses to increased CO2. These results indicate complex interactions among light intensity, Fe limitation, and CO2 concentration, which may affect the species distributions and productivities of marine phytoplankton, including Prochlorococcus, in a future high-CO2 ocean.

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Ocean acidification enhances the tolerance of dinoflagellate Prorocentrum donghaiense to nanoplastic-induced oxidative stress by modulating photosynthetic performance

Published 28 November 2024 Science Closed
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Introduction: The impact of ocean acidification (OA) and nanoplastics (NPs) on harmful algal blooms (HAB) has emerged as a major global concern. However, the combined effects of OA and NPs on the HAB species are poorly understood.

Methods: In this study, dinoflagellate Prorocentrum donghaiense, a typical HAB species, was exposed to varying concentrations of NPs (108.15 ± 8.52 nm) (0, 5, 10, and 15 mg L−1) and CO2 (low CO2: 417 ppm, pH: 8.00 and high CO2: 1045 ppm, pH: 7.73) for seven days to investigate the combined effects of OA and NPs.

Results and discussion: The findings revealed that NPs inhibited the growth of P. donghaiense by inducing oxidative stress, as indicated by elevated malondialdehyde (MDA) content and decreased carotenoid/chlorophyll-a ratio, even though photochemical efficiency (φP0, ψ0, and φE0), rETRmax and α were enhanced in response to NPs stress. However, OA promoted the growth and alleviated the adverse effects of NPs on P. donghaiense by increasing photochemical efficiency (φP0, ψ0, and φE0) and energy flux (RC/CS0, TR0/CS0, ET0/CS0) and enhancing the antioxidant ability (increased superoxide dismutase, and decreased MDA). P. donghaiense showed enhanced tolerance to NPs under simulated OA conditions. These findings enhance our knowledge of the HAB species response to NPs pollution under future OA scenarios.

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Phytoplankton responses to changing irradiance and carbon fertilization

Published 25 November 2024 Science Closed
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Phytoplankton play a crucial role in marine ecosystems due to their innate ability to fix carbon. As atmospheric CO2 levels continue to rise from fossil fuel combustion, the resulting increase in dissolved CO2 and the concurrent decrease in ocean pH are likely to impact the phytoplankton community. The response of phytoplankton to elevated CO2 can vary significantly among species and environmental conditions (e.g. light, temperature, nutrient availability). To address these variations, an experiment was conducted using a controlled photobioreactor system, maintaining high and low light, constant temperature, nutrient levels, and two pCO2 concentrations. This study focused on two regionally relevant phytoplankton in the northern Gulf of Mexico. Skeletonema (a diatom) increased growth rates with the combination of high light and high carbon, but this was not accompanied by increases in particulate organic carbon and nitrogen (POC/N). In contrast, Micromonas commoda (a green alga) did not show changes in growth rate or POC/PON but allocated more energy towards photosynthesis. Additionally, Skeletonema displayed a decoupling between growth rate and silicification, leading to higher biogenic silica content per cell in elevated pCO2 environments. These results highlight the necessity for genera specific and regionally focused research, as the physiological plasticity among phytoplankton can vary.

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Genomic signals of adaptation to a natural CO2 gradient over a striking microgeographic scale

Published 14 November 2024 Science Closed
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Highlights

  • Arbacia lixula populations near CO2 vents show tolerance to acidification despite their vulnerable calcified structure.
  • A. lixula population reveal genetic divergence and substructure in response to small-scale pH variation.
  • Acidification potentially affects specific genes linked to growth, development, and calcification.
  • lixula exhibits adaptability and plasticity to acidification, suggesting its potential resilience to cope with OA.

Abstract

Our study explores genomic signs of adaptation in A. lixula to different water pH conditions. To achieve this, we analysed the genomics variation of A. lixula individuals living across a natural pH gradient in Canary Islands, Spain. We use a 2b-RADseq protocol with 74 samples from sites with varying pH levels (from 7.3 to 7.9 during low tide) and included a control site. We identified 14,883 SNPs, with 432 identified as candidate SNPs under selection to pH variations through redundancy analysis. While all SNPs indicated genomic homogeneity, the 432 candidate SNPs under selection displayed genomic differences among sites and along the pH gradient. Out of these 432 loci, 17 were annotated using published A. lixula transcriptomes, involved in biological functions such as growth. Therefore, our findings suggest local adaptation in A. lixula populations to acidification in CO2 vents, even over short distances of 75 m, underscoring their potential resistance to future Ocean Acidification.

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Effects of CO2 on the nitrogen isotopic composition of marine diazotrophic cyanobacteria

Published 13 November 2024 Science Closed
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Biological N2 fixation has been crucial for sustaining early life on Earth. Very negative δ15N values detected in Archean sediments, which are not observed in present-day environments, have been attributed to the low efficiency of proto-nitrogenases. Alternatively, variations in early atmospheric CO2 may also play a role. Here we examine the effects of CO2 concentrations on the biomass δ15N signatures of the diazotrophs Trichodesmium erythraeum and Crocosphaera watsonii, which utilize Mo-Fe nitrogenase (the most common form of the enzyme). Our results show that these organisms produce biomass with δ15N values up to ∼3‰ lower under both decreased and elevated CO2 concentrations compared to modern levels (∼380 μatm). These deviations from modern CO2 levels reduce nitrogenase enzyme efficiency, leading to increased organismal isotopic fractionation during N2 fixation. This study offers an alternative explanation for the observed fluctuations in geological δ15N records and provides new insights into the past nitrogen cycle on Earth.

Key Points

  • The effects of CO2 on the biomass δ15N signatures of the diazotrophs Trichodesmium erythraeum and Crocosphaera watsonii are examined
  • Both species produce biomass with δ15N values lower under both decreased and elevated CO2 concentrations compared to modern CO2 levels
  • CO2-controlled nitrogenase efficiency significantly influences organismal isotopic fractionation during N2 fixation

Plain Language Summary

The isotope effect of biological N2 fixation is crucial for understanding the nitrogen cycle, but its regulation under different atmospheric CO2 levels as appeared in Earth’s history is not well understood. Our research shows that CO2 levels significantly influence the nitrogen isotope composition in the biomass of the diazotrophic cyanobacteria Trichodesmium and Crocosphaera by affecting the nitrogenase efficiency and thus the growth rate. This study sheds light on the geological changes in the δ15N records and provides new insights into the historical nitrogen cycle on Earth.

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Environmental behavior and toxic effects of micro(nano)plastics and engineered nanoparticles on marine organisms under ocean acidification: a review

Published 5 November 2024 Science Closed
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Ocean acidification (OA) driven by human activities and climate change presents new challenges to marine ecosystems. At the same time, the risks posed by micro(nano)plastics (MNPs) and engineered nanoparticles (ENPs) to marine ecosystems are receiving increasing attention. Although previous studies have uncovered the environmental behavior and the toxic effects of MNPs and ENPs under OA, there is a lack of comprehensive literature reviews in this field. Therefore, this paper reviews how OA affects the environmental behavior of MNPs and ENPs, and summarizes the effects and the potential mechanisms of their co-exposure on marine organisms. The review indicates that OA changes the marine chemical environment, thereby altering the behavior of MNPs and ENPs. These changes affect their bioavailability and lead to co-exposure effects. This impacts marine organisms’ energy metabolism, growth and development, antioxidant systems, reproduction and immunity. The potential mechanisms involved the regulation of signaling pathways, abnormalities in energy metabolism, energy allocation, oxidative stress, decreased enzyme activity, and disruptions in immune and reproductive functions. Finally, based on the limitations of existing research, actual environment and hot issues, we have outlined future research needs and identified key priorities and directions for further investigation. This review deepens our understanding of the potential effects of MNPs and ENPs on marine organisms under OA, while also aiming to promote further research and development in related fields.

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Chapter 3 – Effects of ocean acidification on the growth and development of marine mollusks

Published 21 October 2024 Science Closed
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Ocean acidification (OA) induced by seawater pH decline and the resulting changes in carbonate chemical systems have had impacts on various organisms in marine ecosystems. Shelled mollusks, as a representative biological group in marine ecosystems, have a certain ability to regulate acid-base balance. However, they are easily affected by OA due to they belong to calcified organisms. In the previous investigations about the responses of mollusks to OA, it can be found that OA can affect the entire life cycle and almost most physiological processes of mollusks, especially growth and development in their early life cycle stages. To fully understand the effects of OA on these physiological processes, this chapter summarizes and interprets the effects of OA on the growth and development of marine mollusks in the embryonic, larval and juvenile stages, as well as the underlying molecular mechanisms behind mollusk responses. The impacts of ocean acidification on some specific physiological processes such as calcification and shell growth of shelled mollusks are also highlighted in this chapter. This chapter is respected to provide theoretical reference for the further study of the effects of OA on marine mollusks.

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Ecophysiology and ocean acidification in marine mollusks: from molecule to behavior

Published 17 October 2024 Science Closed
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Ecophysiology and Ocean Acidification in Marine Mollusks: From Molecule to Behavior provides an extensive overview of the latest research on the various ecophysiological effects of ocean acidification on marine mollusks. This book synthesizes historical information and recent findings on the effects of environmental change, ocean warming, and acidification on key mollusks and their life-history. It also discusses the underlying mechanisms underpinning the effects of ocean warming and acidification. Written by internationally recognized experts in the field of marine biology, this book systematically examines the effects of ocean acidification on the reproduction, growth and development, physiological metabolism, immunity, and behavior of marine mollusks.

The book concludes by discussing the implications of current research, acknowledging data limitations in the field, and proposing future research directions, providing a better understanding of the potential impacts of ocean acidification on mollusks and the global aquaculture industry and inspiring new thinking for future research practices. It will be an indispensable resource for researchers, practitioners, undergraduate and graduate students, conservationists, and aquaculturists alike who are interested in marine environmental change, ecology, physiology, and marine biology.

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Energy budget as a tool to assess the effects of environmental stressors: a study on whiteleg shrimp (Penaeus vannamei) exposed to variations in salinity and ocean acidification

Published 10 October 2024 Science Closed
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Our goal was to use the energy budget as a tool to evaluate the effects of salinity (20, 25, 30, 35 or 40‰) and ocean acidification (pH 8.0 or 7.3) in Penaeus vannamei. We assessed the energy budget a range of physiological processes (ingestion, defecation, growth, metabolism, excretion, energy substrate, hepatosomatic index, and osmoregulation). In general, salinity had an accentuated effect than pH, as it altered nearly all physiological parameters, including the energy channeled into growth (up to −56%). Reduced pH also affected the energy budget: increased energy lost in feces (25 and 40‰: +21% and 13%, respectively), excretion (25‰: +55%), and metabolism (20‰: +58%). Furthermore, acidified pH increased oxygen consumption by 60%, which may be related to higher energy expenditure. In conclusion, the energy budget can be a valuable tool for assessing the impacts of environmental stressors and the salinity has an accentuated effect than the ocean acidification predicted.

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Elevated pCO2 may increase the edible safety risk of clams exposed to toxic Alexandrium spp.

Published 2 October 2024 Science Closed
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Highlights

  • High pCO2 diversely affects PSTs production of various Alexandrium spp.
  • Elevated pCO2 alters PSTs composition and toxicity in clams than in algae.
  • High pCO2 is beneficial to bioaccumulation of highly toxic PST in clams.
  • Elevated pCO2 inhibits elimination of highly toxic PST components in clams.
  • High pCO2 enhances PSTs toxicity in clams exposed to different Alexandrium spp.

Abstract

Toxic harmful algal blooms (HABs) have received increasing attention owing to their threat to the health of aquatic life and seafood consumers. This study evaluated the impacts of elevated atmospheric partial pressure of CO2 (pCO2) on the production of paralytic shellfish toxins (PSTs) in different Alexandrium spp. strains, together with its further effects on the bioaccumulation/elimination dynamics of PSTs in bivalves contaminated with PSTs from toxic dinoflagellates. Our results showed that elevated pCO2 stimulated the growth of the two Alexandrium spp. (A. catenella and A. pacificum) isolated from the northern and southern coastal areas of China, respectively, and affected PST production including content and toxicity of the two strains differently. Further PSTs bioaccumulation/elimination in PSTs-contaminated Manila clam, Ruditapes philippinarum under high pCO2 also occurred. It is worth noting the biotransformation of neosaxitoxin (NEO) with high toxicity through trophic transfer with effect of elevated pCO2. When in microalgae cultured under the control (410 ppm) and elevated pCO2 conditions (495 and 850 ppm), the proportion of NEO in the PST content produced by A. catenella was reduced from 11.1 to 6.4 and 2.6 %, while the proportion of NEO in A. pacificum was increased from 3.1 to 3.6 and 4.7 %, respectively. NEO accounted for >50 % of total PST contents in clams, which were biotransformed via transfer from dinoflagellates and higher pCO2 enhanced this biotransformation leading to increased NEO accumulation. The negatively affected elimination of PSTs, especially NEO, in clams fed with A. catenella or A. pacificum, indicates that the detoxification of PSTs-contaminated clams may be more difficult under elevated pCO2. This study provides reference for developing models to assess the safety of bivalves under the co-stress of environmental change and toxic HABs, suggesting that ocean acidification may lead to the higher safety risk of Manila clams exposed to toxic HAB dinoflagellates.

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Long-term study of the combined effects of ocean acidification and warming on the mottled brittle star Ophionereis fasciata

Published 27 September 2024 Science Closed
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The global ocean is rapidly changing, posing a substantial threat to the viability of marine populations due to the co-occurrence of multiple drivers, such as ocean warming (OW) and ocean acidification (OA). To persist, marine species must undergo some combination of acclimation and adaptation in response to these changes. Understanding such responses is essential to measure and project the magnitude and direction of current and future vulnerabilities in marine ecosystems. Echinoderms have been recognised as a model in studying of OW-OA effects on marine biota. However, despite their global diversity, vulnerability, and ecological importance in most marine habitats, brittle stars (ophiuroids) are poorly studied. A long-term mesocosm experiment was conducted on adult mottled brittle star (Ophionereis fasciata) as a case study to investigate the physiological response and trade-offs of marine organisms to ocean acidification, ocean warming and the combined effect of both drivers. Long-term exposure of O. fasciata to high temperature and low pH affected survival, respiration and regeneration rates, growth rate, calcification/dissolution, and righting response. Higher temperatures increased stress and respiration and decreased regeneration and growth rates as well as survival. Conversely, changes in pH had more subtle or no effect affecting only respiration and calcification. Our results indicate that exposure to a combination of high temperature and low pH produces complex responses for respiration, righting response and calcification. We address the knowledge gap of the impact of a changing ocean on ophiuroids in the context of echinoderm studies, proposing this class as an ideal alternative echinoderm for future research.

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Impact of low pH/high pCO2 on the physiological response and exopolysaccharide content in cyanobacteria Trichodesmium erythraeum

Published 26 September 2024 Science Closed
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The acidification of the ocean caused by the diffusion of anthropogenic carbon dioxide (CO2) into seawater has been believed to threaten the stability of the marine ecosystem. As one of the major contributors to the primary production in oligotrophic oceans, the response of Trichodesmium to the acidification of the ocean has attracted a lot of attention. Therefore, in this study, we applied physiological and biochemical methods to identify the influences of high pCO2 and low pH conditions on the growth of T. erythraeum. Our results showed that the low pH during the acidification of the ocean was the main factor inhibiting the growth of T. erythraeum. In addition, low pH caused oxidative stress to T. erythraeum, as evidenced by the increase of the reactive oxygen species and antioxidant enzyme’s activities. The activity of carbonic anhydrase (CA) enzyme is dually regulated by pCO2 and pH, and T. erythraeum can adapt to different levels of pCO2 and pH in seawater by flexibly adjusting CA enzyme activity. We also discovered that the stimulatory effect of high pCO2 on the exopolysaccharide (EPS) content of T. erythraeum outweighed the inhibitory effect of low pH during the process of ocean acidification. In conclusion, this study systematically revealed the effects of high pCO2 and low pH caused by the acidification of the ocean on the growth and EPS of T. erythraeum. These results provide new insights into the response mechanisms of T. erythraeum in the acidified ocean under future climate conditions.

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Effects of ocean acidification and temperature coupling on photosynthetic activity and physiological properties of Ulva fasciata and Sargassum horneri

Published 25 September 2024 Science Closed
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Simple Summary

Macroalgae in natural marine areas play an important role in mitigating ocean climate change. The complexity of natural conditions also makes it necessary to study macroalgae not only by considering the effects of changes in a single factor but also by exploring the coupled effects of different environmental conditions on macroalgae. Therefore, in this study, two species of macroalgae were used as experimental subjects to observe their growth processes under different co-treatments of temperature and CO2 concentration. The results of this study can provide a reference for how natural macroalgae can cope with future changes in ocean climate.

Abstract

To investigate the ecological impacts of macroalgae in the framework of shifting global CO2 concentrations, we conducted a study utilizing Ulva fasciata and Sargassum horneri specimens sourced from the Ma’an Archipelago in Zhejiang Province on how ocean acidification (OA) and temperature changes interact to affect the photosynthetic physiological responses of macroalgae. The results of the study showed that OA reduced the tolerance of U. fasciata to bright light at 20 °C, resulting in more pronounced photoinhibition, while 15 °C caused significant inhibition of U. fasciata, reducing its growth and photosynthetic activity, but OA alleviated the inhibition and promoted the growth of the alga to a certain extent. The tolerance of S. horneri to bright light was also reduced at 20 °C; the inhibition was relieved at 15 °C, and the OA further improved the algal growth. The Relative Growth Rate (RGR), photosynthetic pigment content, and the release of the dissolved organic carbon (DOC) of U. fasciata were mainly affected by the change in temperature; the growth of the alga and the synthesis of metabolites were more favored by 20 °C. A similar temperature dependence was observed for S. horneri, with faster growth and high metabolism at 15 °C. Our results suggest that OA reduces the tolerance of macroalgae to high light at suitable growth temperatures; however, at unsuitable growth temperatures, OA effectively mitigates this inhibitory effect and promotes algal growth.

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Effects of ocean acidification on nitrogen metabolism of Skeletonema costatum

Published 16 September 2024 Science Closed
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Ocean acidification (OA), caused by the rising concentration of atmospheric CO2, leads to changes in the marine carbonate system. This, in turn, affects the physiological processes of phytoplankton. In response to increased pCO2 levels, marine microalgae modulate their physiological responses to meet their energy and metabolic requirements. Nitrogen metabolism is a critical metabolic pathway, directly affecting the growth and reproductive capacity of marine microorganisms. Understanding the molecular mechanisms that regulate nitrogen metabolism in microalgae under OA conditions is therefore crucial. This study aimed to investigate how OA affects the expression profiles of key genes in the nitrogen metabolic pathway of the marine diatom Skeletonema costatum. Our findings indicate that OA upregulates key genes involved in the nitrogen metabolic pathway, specifically those related to nitrate assimilation and glutamate metabolism. Moreover, pCO2 has been identified as the predominant factor affecting the expression of these genes, with a more significant impact than pH variations in S. costatum. This research not only advances our understanding of the adaptive mechanisms of S. costatum in response to OA but also provides essential data for predicting the ecological consequences of OA on marine diatoms.

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Effects of ocean acidification and nitrogen limitation on the growth and photophysiological performances of marine macroalgae Gracilariopsis lemaneiformis

Published 11 September 2024 Science Closed
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To investigate the effects of ocean acidification (OA) and nitrogen limitation on macroalgae growth and photophysiological responses, Gracilariopsis lemaneiformis was cultured under two main conditions: ambient (Low CO2, LC, 390 μatm) and CO2 enriched (High CO2, HC, 1000 μatm), with low (LN, 7 μmol L-1) and high (HN, 56 μmol L-1) nitrate. High CO2 levels decreased growth under both LN and HN treatments. HC reduced Chl a, carotenoids, phycoerythrin (PE), and phycocyanin (PC) under HN conditions, while only Chl a decreased under LN conditions. NO3– uptake rate was restricted under LN compared to HN, while HC enhanced it under HN. Net photosynthetic O2 evolution rates did not differ between CO2 and nitrate treatments. Dark respiration rates were higher under HN, further boosted by HC. The stimulated effective quantum yield (Y(II)) corresponded to decreased non-photochemical quenching (NPQ) under HN conditions. Nitrate, not CO2, showed significant effects on the relative electron transport rate (rETRmax), light use efficiency (α) and saturation light intensity (Ik) that with lowered rETRmax and α under LN culture. Our results indicate that OA may negatively affect Gracilariopsis lemaneiformis growth and alter its photophysiological performance under different nutrient conditions.

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Effects of pH/pCO2 fluctuation on photosynthesis and fatty acid composition of two marine diatoms, with reference to consequence of coastal acidification

Published 30 August 2024 Science Closed
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Coastal waters are impacted by a range of natural and anthropogenic factors, which superimpose on effects of increasing atmospheric CO2, resulting in dynamically changing seawater carbonate chemistry. Research on influences of dynamic pH/pCO2 on marine ecosystem is still in its infancy, although effects of ocean acidification have been extensively studied. In the present study, we manipulated the culturing pH/pCO2 to investigate physiological performance and fatty acid (FA) composition of two coastal diatoms Skeletonema costatum and Thalassiosira weissflogii in both steady and fluctuating pH/pCO2 regimes. Generally, seawater acidification and pH variability showed neutral or positive effects on specific growth rate, chlorophyll a, and biogenic silica contents of two species. Elevated pCO2 inhibited net photosynthetic rate by 27 % and enhanced mitochondrial respiration rate of S. costatum by 36 % in the steady pH regime, while these rates were unaltered by elevated pCO2 in the fluctuating regime. Elevated pCO2 leaded to 21 % lower saturated FA and twofold increase in polyunsaturated FA proportions of T. weissflogii. Our results indicate that costal acidification could affect primary production in a different way from ocean acidification. Together with the altered nutritional quality of prey for higher trophic levels, coastal acidification might have far-reaching consequence for marine ecosystem functioning.

Continue reading ‘Effects of pH/pCO2 fluctuation on photosynthesis and fatty acid composition of two marine diatoms, with reference to consequence of coastal acidification’

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