Gracilariopsis Lemaneiformis Research Articles

Evaluation of Ethanolic Extract of Red Seaweed (Gracilariopsis lemaneiformis) on Growth and Haematological Parameters of Nile Tilapia (Oreochromis niloticus)

ABSTRACTSeaweed is multicellular marine macroalgae that enhances the immunity of aquatic organisms. The study was designed to assess the ethanolic extract (EtOH) extracted from red seaweed (Gracilariopsis lemaneiformis) on Nile tilapia (Oreochromis niloticus) to evaluate growth, immunity and haematological parameters. The EtOH was applied with fish feed in four treatments such as T1‐control (0% EtOH), T2 (5% w/v EtOH), T3 (10% w/v EtOH) and T4 (15% w/v EtOH) each with three replicates. The initial average weight of the fish was 17.53 ± 2.1 g. Results showed that the growth increased gradually with the percentage of red seaweed extract, whereas the mean weight gain was found significantly higher in T4 (51.5 ± 4.2) than in the control. The specific growth rate (%) and survival rate (%) were found higher in T4 at the lowest FCR compared to other treatments (p < 0.05). The blood haemoglobin level of Nile tilapia was higher in T4 (11.5 g/dL) and lowest recorded in T1 (7.5 g/dL). However, the level of blood glucose interacted inversely with blood haemoglobin. The plasma protein level was also varied among the treatments (p > 0.05). The blood parameters, refractive index (RI) and spleen somatic index (SSI) were significantly different among the treatments. The RI of blood plasma and SSI were found to be better in T4 treatment. The research indicated that red seaweed extracts significantly enhanced the growth and boosted the immunity level of Nile tilapia.

Seaweed burial mitigated the release of organic carbon and nutrients by regulating microbial activity

Seaweed debris is susceptible to being buried in sediments due to natural environmental changes and human activities. So far, the effect of buried seaweeds on the environment and its decomposition mechanism remains unclear. This study simulated the decomposition of seaweed Gracilariopsis lemaneiformis for 180 days with different burial depths (0 cm and 10 cm) and burial weights (10 g and 20 g). Our findings revealed that compared with Gracilariopsis decomposition on the sediment surface, the seaweed buried in sediment slowed down the release of N, P, and dissolved organic carbon (DOC) by enhancing the activity of diverse anaerobic microbes (i.e. Draconibacterium, Desulfuromusa, Sediminispirochaeta), which were associated with organic matter decomposition. The enhanced burial quantity of Gracilariopsis resulted in a 3.28 % increase in sediment OC and enriched the humification degree of DOC in seawater. These results highlight the role of seaweed burial in enhancing OC sequestration in marine environments.

Photosynthetic performance and antioxidant activity of Gracilariopsis lemaneiformis are sensitive to phosphorus deficiency in elevated temperatures

Photosynthetic performance and antioxidant activity of Gracilariopsis lemaneiformis are sensitive to phosphorus deficiency in elevated temperatures

Photosynthetic performance of the red algae Gracilariopsis lemaneiformis under high seawater pH: Excess reactive oxygen production due to carbon limitation.

The red algae Gracilariopsis lemaneiformis is extensively cultivated at high densities, leading to significant increases in regional seawater pH due to its photosynthetic removal of inorganic carbon. We conducted a study on G. lemaneiformis cultured under various pH conditions (normal pH, pH 9.3, and pH 9.6) and light levels (dark and 100 μmol photons m-2 s-1) to investigate how high pH seawater environments affect the metabolic processes of G. lemaneiformis. The high pH did not directly damage the photosynthetic light reactions or the Calvin cycle. Instead, the observed reduction in photosynthetic rates was primarily due to CO2 limitation. However, under illuminated conditions, a high pH environment leads to a decrease in electron transport efficiency (ETo/RC) and reaction center density (RC/CSo), while simultaneously increasing the levels of hydrogen peroxide (H2O2), malondialdehyde (MDA), and the activity of antioxidant enzymes. Under illuminated conditions, the limitation of inhibit the photosynthetic electron transport process, leading to energy imbalance and excessive production of reactive oxygen species, which in turn resulted in lipid peroxidation of the cell membrane. This might be one of the inducing factors responsible for the bleaching in sea-farmed G. lemaneiformis plants.

Marine heatwaves alter competition between the cultured macroalga Gracilariopsis lemaneiformis and the harmful bloom alga Skeletonema costatum

Seaweed cultivation can inhibit the occurrence of red tides. However, how seaweed aquaculture interactions with harmful algal blooms will be affected by the increasing occurrence and intensity of marine heatwaves (MHWs) is unknown. In this study, we run both monoculture and coculture systems to investigate the effects of a simulated heatwave on the competition of the economically important macroalga Gracilariopsis lemaneiformis against the harmful bloom diatom Skeletonema costatum. Coculture with G. lemaneiformis led to a growth decrease in S. costatum. Growth and photosynthetic activity (Fv/Fm) of G. lemaneiformis was greatly reduced by the heatwave treatment, and did not recover even after one week. Growth and photosynthetic activity of S. costatum was also reduced by the heatwave in coculture, but returned to normal during the recovery period. S. costatum also responded to the stressful environment by forming aggregates. Metabolomic analysis suggests that the negative effects on S. costatum were related to an allelochemical release from G. lemaneiformis. These findings show that MHWs may enhance the competitive advantages of S. costatum against G. lemaneiformis, leading to more severe harmful algal blooms in future extreme weather scenarios.

Rotation Culture of Macroalgae Based on Photosynthetic Physiological Characteristics of Algae

Seaweed farming has made outstanding contributions to food supply and the restoration of the ecological environment despite the limitations in production and ecological effects due to the current intensive farming of single algae species. These limitations can be overcome by selecting suitable algal species based on their physiological characteristics and by constructing a large-scale seaweed rotation model. This study carried out a trial culture in aquaculture sea areas, and performed in situ monitoring of the environmental conditions and physiological characteristics of Saccharina japonica, Hizikia fusiformis, and Gracilariopsis lemaneiformis. Additionally, a comparative analysis of the three macroalgae at different times was conducted to determine their response characteristics to environmental factors. The results showed that: (1) The three macroalgae had varying light tolerance. The effective quantum yield of Hizikia fusiformis and Gracilariopsis lemaneiformis remained unchanged during the changes in light environment, while that of Saccharina japonica first decreased and then recovered. (2) The relative electron transport rates of the three macroalgae were significantly different under different temperature conditions. Hizikia fusiformis and Saccharina japonica exhibited the highest relative electron transport rates (70.45 and 106.75, respectively) in May (20.3 °C). Notably, Gracilariopsis lemaneiformis demonstrated good growth and exhibited the highest relative electron transport rate (93.07) in September (27.5 °C). These findings collectively support the feasibility of establishing a macroalgae rotation model. Based on the combined environmental conditions of the seas in Shandong, Zhejiang, and Fujian, a macroalgae rotation model was proposed. The application of this model in the construction of artificial seaweed farms in marine ranches can provide a stable output of large-scale seaweed production and ecological benefits.

Analysis of Hyperosmotic Tolerance Mechanisms in Gracilariopsis lemaneiformis Based on Weighted Co-Expression Network Analysis.

We conducted transcriptome sequencing on salt-tolerant mutants X5 and X3, and a control (Ctr) strain of Gracilariopsis lemaneiformis after treatment with artificial seawater at varying salinities (30‱, 45‱, and 60‱) for 3 weeks. Differentially expressed genes were identified and a weighted co-expression network analysis was conducted. The blue, red, and tan modules were most closely associated with salinity, while the black, cyan, light cyan, and yellow modules showed a close correlation with strain attributes. KEGG enrichment of genes from the aforementioned modules revealed that the key enrichment pathways for salinity attributes included the proteasome and carbon fixation in photosynthesis, whereas the key pathways for strain attributes consisted of lipid metabolism, oxidative phosphorylation, soluble N-ethylmaleimide-sensitive factor-activating protein receptor (SNARE) interactions in vesicular transport, and porphyrin and chlorophyll metabolism. Gene expression for the proteasome and carbon fixation in photosynthesis was higher in all strains at 60‱. In addition, gene expression in the proteasome pathway was higher in the X5-60 than Ctr-60 and X3-60. Based on the above data and relevant literature, we speculated that mutant X5 likely copes with high salt stress by upregulating genes related to lysosome and carbon fixation in photosynthesis. The proteasome may be reset to adjust the organism's proteome composition to adapt to high-salt environments, while carbon fixation may aid in maintaining material and energy metabolism for normal life activities by enhancing carbon dioxide uptake via photosynthesis. The differences between the X5-30 and Ctr-30 expression of genes involved in the synthesis of secondary metabolites, oxidative phosphorylation, and SNARE interactions in vesicular transport suggested that the X5-30 may differ from Ctr-30 in lipid metabolism, energy metabolism, and vesicular transport. Finally, among the key pathways with good correlation with salinity and strain traits, the key genes with significant correlation with salinity and strain traits were identified by correlation analysis.

Temporal variations of biological nitrogen fixation and diazotrophic communities associated with artificial seaweed farms

Diazotrophic communities contribute inorganic nitrogen for the primary productivity of the marine environment by biological nitrogen fixation (BNF). They play a vital role in the biogeochemical cycle of nitrogen in the marine ecological environment. However, there is still an incomplete understanding of BNF and diazotrophs in artificial seaweed farms. Therefore, this study comprehensively investigated the temporal variations of BNF associated with Gracilariopsis lemaneiformis, as well as the diazotrophic communities associated with macroalgae and its surrounding seawater. Our results revealed that a total of 13 strains belonging to Proteobacteria and Bacteroidetes were identified as N2-fixing bacteria using azotobacter selective solid medium and nifH gene cloning. Subsequently, BNF and diazotrophic communities were characterized using the acetylene reduction method and high-throughput sequencing of the nifH gene, respectively. The results showed that nitrogenase activity and nifH gene abundance of epiphytic bacteria on G. lemaneiformis varied significantly among four different cultivation periods, i.e., Cultivation Jan. (CJ), Cultivation Feb. (CF), Cultivation Mar. (CM), Cultivation Apr. (CA). Among them, the nitrogenase activity and nifH gene abundance of epiphytic bacteria on G. lemaneiformis in CM were significantly higher than those in CJ, CF, and CA, indicating that the BNF of eiphytic bacteria on G. lemaneiformis was markedly enhanced. Combined with the data on environmental factors, it was found that the low concentration of nitrogen and phosphorus in CM might considerably boost the BNF of epiphytic bacteria in G. lemaneiformis. The sequencing results of the nifH gene showed that the α-diversity of diazotrophic communities associated with G. lemaneiformis and seawater in CM was higher than that in other cultivation periods. In addition, the diazotrophic communities on G. lemaneiformis were significantly different in CJ, CF, CM, and CA, and they were significantly diverse from diazotrophic communities in seawater. LEfSe analysis indicated that Rhodobacterales, Hyphomonadaceae, Robiginitomaculum, and Robiginitomaculum antarcticum within α-proteobacteria played a remarkable role in BNF in response to nitrogen nutrient deficiency. Taken together, these results provide a unique insight into the interaction between macroalgae and its epiphytic bacteria and lay a foundation for further research on the mechanism of action of nitrogen-cycling microorganisms associated with macroalgae.

Physiological, Transcriptome, and Metabolome Analyses Reveal the Tolerance to Cu Toxicity in Red Macroalgae Gracilariopsis lemaneiformis.

Heavy metal copper (Cu) will inevitably impact the marine macroalgae Gracilariopsis lemaneiformis (G. lemaneiformis), which is a culture of economic importance along China's coastline. In this study, the detoxification mechanism of Cu stress on G. lemaneiformis was revealed by assessing physiological indicators in conjunction with transcriptome and metabolome analyses at 1 d after Cu stress. Our findings revealed that 25 μM Cu stimulated ROS synthesis and led to the enzymatic oxidation of arachidonic acid residues. This process subsequently impeded G. lemaneiformis growth by suppressing photosynthesis, nitrogen metabolism, protein synthesis, etc. The entry of Cu ions into the algae was facilitated by ZIPs and IRT transporters, presenting as Cu2+. Furthermore, there was an up-regulation of Cu efflux transporters HMA5 and ABC family transporters to achieve compartmentation to mitigate the toxicity. The results revealed that G. lemaneiformis elevated the antioxidant enzyme superoxide dismutase and ascorbate-glutathione cycle to maintain ROS homeostasis. Additionally, metabolites such as flavonoids, 3-O-methylgallic acid, 3-hydroxy-4-keto-gama-carotene, and eicosapentaenoic acid were up-regulated compared with the control, indicating that they might play roles in response to Cu stress. In summary, this study offers a comprehensive insight into the detoxification mechanisms driving the responses of G. lemaneiformis to Cu exposure.

Identification of Indicator Genes for Agar Accumulation in Gracilariopsis lemaneiformis (Rhodophyta).

Agar, as a seaweed polysaccharide mainly extracted from Gracilariopsis lemaneiformis, has been commercially applied in multiple fields. To investigate factors indicating the agar accumulation in G. lemaneiformis, the agar content, soluble polysaccharides content, and expression level of 11 genes involved in the agar biosynthesis were analysed under 4 treatments, namely salinity, temperature, and nitrogen and phosphorus concentrations. The salinity exerted the greatest impact on the agar content. Both high (40‱) and low (10‱, 20‱) salinity promoted agar accumulation in G. lemaneiformis by 4.06%, 2.59%, and 3.00%, respectively. The content of agar as a colloidal polysaccharide was more stable than the soluble polysaccharide content under the treatments. No significant correlation was noted between the two polysaccharides, and between the change in the agar content and the relative growth rate of the algae. The expression of all 11 genes was affected by the 4 treatments. Furthermore, in the cultivar 981 with high agar content (21.30 ± 0.95%) compared to that (16.23 ± 1.59%) of the wild diploid, the transcriptional level of 9 genes related to agar biosynthesis was upregulated. Comprehensive analysis of the correlation between agar accumulation and transcriptional level of genes related to agar biosynthesis in different cultivation conditions and different species of G. lemaneiformis, the change in the relative expression level of glucose-6-phosphate isomerase II (gpiII), mannose-6-phosphate isomerase (mpi), mannose-1-phosphate guanylyltransferase (mpg), and galactosyltransferase II (gatII) genes was highly correlated with the relative agar accumulation. This study lays a basis for selecting high-yield agar strains, as well as for targeted breeding, by using gene editing tools in the future.

A contagious disease caused serious damage to Gracilariopsis lemaneiformis cultivation in China

A contagious disease caused serious damage to Gracilariopsis lemaneiformis cultivation in China

Extraction, Isolation and Biological Activity of Two Glycolipids from Bangia fusco-purpurea.

In order to explore the extraction and activity of macroalge glycolipids, six macroalgae (Bangia fusco-purpurea, Gelidium amansii, Gloiopeltis furcata, Gracilariopsis lemaneiformis, Gracilaria sp. and Pyropia yezoensis) glycolipids were extracted with five different solvents firstly. Considering the yield and glycolipids concentration of extracts, Bangia fusco-purpurea, Gracilaria sp. and Pyropia yezoensis were selected from six species of marine macroalgae as the raw materials for the extraction of glycolipids. The effects of the volume score of methanol, solid-liquid ratio, extraction temperature, extraction time and ultrasonic power on the yield and glycolipids concentration of extracts of the above three macroalgae were analyzed through a series of single-factor experiments. By analyzing the antioxidant activity in vitro, moisture absorption and moisturizing activity, the extraction process of Bangia fusco-purpurea glycolipids was further optimized by response surface method to obtain suitable conditions for glycolipid extraction (solid-liquid ratio of 1:27 g/mL, extraction temperature of 48 °C, extraction time of 98 min and ultrasonic power of 450 W). Bangia fusco-purpurea extracts exhibited a certain scavenging effect on DPPH free radicals, as well as good moisture-absorption and moisture retaining activities. Two glycolipids were isolated from Bangia fusco-purpurea by liquid-liquid extraction, silica gel column chromatography and thin-layer chromatography, and they showed good scavenging activities against DPPH free radicals and total antioxidant capacity. Their scavenging activities against DPPH free radicals were about 60% at 1600 µg/mL, and total antioxidant capacity was better than that of Trolox. Among them, the moisturizing activity of a glycolipid was close to that of sorbierite and sodium alginate. These two glycolipids exhibited big application potential as food humectants and antioxidants.

Study on the enhancement of salt tolerance of Gracilariopsis lemaneiformis through addition of exogenous substances based on transcriptome analysis

Gracilariopsis lemaneiformis is an economic red macroalga whose cultivation is affected by salinity. To investigate the molecular mechanism of G. lemaneiformis response to salt stress, transcriptome sequencing was used to analyze the differentially expressed genes of wild G. lemaneiformis cultured at low (10‰), normal (30‰) and high (40‰) salinities. After the algae were treated for seven days at 10‰ and 40‰ salinity, a total of 1016 and 1231 differently expressed genes were discovered, respectively. Through GO and KEGG pathway analysis, the transcription of genes involved in lysine biosynthesis, ascorbic acid biosynthesis and TCA cycling were up-regulated significantly under low salt stress. The transcription of genes related to glycogen degradation and ABC transporters pathway was significantly up-regulated under high salt stress. Meanwhile, the transcription of genes related to lignin and trehalose biosynthesis, which can enhance plant stress resistance, was up-regulated significantly under both low and high salt stress. Based on the transcriptome results, lysine, ascorbic acid, and trehalose were added to the culture system of G. lemaneiformis. The results showed that the addition of certain concentrations of exogenous lysine and trehalose enhanced the growth and salt stress tolerance of wild G. lemaneiformis. This study investigates the molecular mechanism of salt response of G. lemaneiformis and provides an experimental basis to improve the salt tolerance of G. lemaneiformis by adding exogenous substances.

Review on recent advances of Gracilariopsis lemaneiformis (Rhodophyta)

Gracilariopsis lemaneiformis is an economical red algae that is an important raw material for agar production. Although researchers have obtained several high-yield cultivars (e.g., 981 and 2007), their growth is still limited and influenced by several environmental factors such as heat stress and nitrogen restriction. In recent years, agar metabolism, photosynthesis, and tetrasporophyte development in G. lemaneiformis have emerged as prominent areas of research for investigators to unravel the molecular mechanism in development and reproduction. In addition, with the development of genomics and transcriptomics, more regulatory factors have been revealed, and the emergence of gene editing technology has also brought new possibilities for the genetic breeding of G. lemaneiformis. We have summarized the information here and provided an invaluable resource for future studies on G. lemaneiformis.

Transcriptome analysis reveals ABA involved in the detoxification mechanism of macroalga Gracilariopsis lemaneiformis to cadmium toxicity

IntroductionCadmium (Cd) is a significant threat environmental pollutant in the marine ecological environment offshore. The macroalga, Gracilariopsis lemaneiformis, of significant economic value, is widely cultivated along China’s coastline. Yet, little is known about the molecular mechanisms underlying Cd tolerance in macroalga.MethodsHere, we examined the transcriptome of G. lemaneiformis exposed to Cd to identify the responses to Cd stress.Results and discussionOur findings revealed that Cd led to the retardation of growth rate in G. lemaneiformis, accompanied by a notable reduction in the content of photosynthetic pigments and a decrease in the expression of genes associated with the photosynthetic system and nitrogen metabolism. When exposed to Cd, there was a rapid increase in Cd levels through the upregulation of genes encoding GlZIP6 and GlIRT1. Additionally, the expression of Cd efflux transporters, GlZIP1 and GlABCG22, and the ABCC7 transporter for compartmentation to the vacuole, was induced to mitigate Cd toxicity. Cd also activated crucial genes involved in the ABA biosynthesis and enhanced ABA content, thereby inducing ABA signaling pathway. Furthermore, exogenous ABA reduced the growth inhibition of G. lemaneiformis under Cd stress. Redox homeostasis was adjusted to adapt to Cd toxicity, with thioredoxin, glutaredoxin cycle and ascorbate-glutathione cycle identified as playing significant in maintaining reactive oxygen species homeostasis. Moreover, transcription factors such as several MYBs, signal transmission factors G protein and heat shock proteins (sHSPs, HSP 40, HSP 90, HSP101) were involved in the detoxification of Cd. Collectively, this study provided a comprehensive understanding of the molecular mechanisms underpinning the of responses of macroalga G. lemaneiformis to Cd exposure.

Phosphorus deficiency regulates the growth and photophysiology responses of an economic macroalga Gracilariopsis lemaneiformis to ocean acidification and warming

Phosphorus deficiency regulates the growth and photophysiology responses of an economic macroalga Gracilariopsis lemaneiformis to ocean acidification and warming

Diversity and ecological function of urease-producing bacteria in the cultivation environment of Gracilariopsis lemaneiformis

Urease-producing bacteria (UPB) provide inorganic nitrogen for primary producers by hydrolyzing urea, and play an important role in marine nitrogen cycle. However, there is still an incomplete understanding of UPB and their ecological functions in the cultivation environment of the red macroalgae Gracilariopsis lemaneiformis. This study comprehensively analyzed the diversity of culturable UPB and explored their effects on urea uptake by G. lemaneiformis. A total of 34 isolates belonging to four main bacterial phyla i.e. (Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria) were identified through 16S rRNA sequencing and were screened for UPB by urea agar chromogenic medium assay and ureC gene cloning. Our data revealed that only 8 strains contained urease. All of these UPB exhibited different urease activities, which were determined by the Berthelot reaction colorimetry assay. Additionally, the UPB strain (G13) isolated from G. lemaneiformis with higher urease activity was selected for co-culture with G. lemaneiformis to explore its role in promoting or inhibiting nitrogen uptake by macroalgae. The results showed a significant increase in urea consumption in the culture medium and the total cellular nitrogen in G. lemaneiformis in the UPB-co culture group compared to the sterile group. This suggests that the selected UPB strain positively influences nitrogen uptake by G. lemaneiformis. Similarly, isotopic assays revealed that the δ15N content of G. lemaneiformis was significantly higher in the UPB-co culture than in the control group, where δ15N-urea was the only nitrogen source in the culture medium. This indicates that the UPB helped G. lemaneiformis to absorb more nitrogen from urea. Moreover, the highest content of δ15N was found in G. lemaneiformis with epiphytic bacteria compared to sterilized (i.e. control), showing that epiphytic bacteria, along with UPB, have a compound effect in helping G. lemaneiformis absorb more nitrogen from urea. Taken together, these results provide unique insight into the ecological role of UPB and suggest that urease from macroalgae environment-associated bacteria might be an important player in marine nitrogen cycling.

Administration of Gracilariopsis lemaneiformis polysaccharide attenuates cisplatin-induced inflammation and intestinal mucosal damage in colon-26 carcinoma tumor-bearing mice.

Our preliminary research revealed that the polysaccharide GP90 from Gracilariopsis lemaneiformis enhanced the antitumor effect of cisplatin, indicating that GP90 may increase the chemotherapeutic sensitivity. However, it is still necessary to fully understand whether GP90 can also improve the intestinal barrier dysfunction and systemic inflammation induced by cisplatin. GP90 has been demonstrated to inhibit the excessive release of nitirc oxide, interleukin (IL)-6, IL-1β and tumor necrosis factor (TNF)-α induced by lipopolysaccharide in RAW264.7 cells. In vivo, GP90 effectively ameliorated the decrease in the serum CD4+ /CD8+ T-cell ratio induced by cisplatin and significantly reduced the increase in the inflammatory cytokines, CD4+ Foxp3+ , CD4+ granzyme B+ and CD4+ TNF-α induced by cisplatin. Furthermore, when combined with cisplatin, GP90 increases the protein expression levels of mucin-2 and zonula occludens-1 in the mouse small intestine. Additionally, GP90 combined with cisplatin has a modulatory effect on the intestinal microbiota by elevating the Firmicutes-to-Bacteroidetes ratio and the relative abundance of beneficial microorganisms (Lachnospiraceae bacterium), at the same time as reducing the abundance of cisplatin specific Bacteroides acidifaciens and elevating the content of butyric acid and isobutyric acid. Collectively, these findings indicate that GP90 potentially mitigates inflammation and protects the intestinal barrier in tumor-bearing organisms undergoing chemotherapy. © 2024 Society of Chemical Industry.

Light intensity influences the glycerolipid remodeling of Gracilariopsis lemaneiformis in response to short-term high temperature stress

Temperature and light are two pivotal environmental factors for the growth of marine photosynthetic organisms. While the responses of Gracilariopsis lemaneiformis to individual high temperature or light stress have been explored, our understanding of its combined stress responses remains limited. This study aimed to investigate the combined effects of short-term high temperature (33 °C, 8 h) and different light intensities, that is, low light (LL, 50 μmol photon m−2 s−1), medium light (ML, 150 μmol photon m−2 s−1), and high light (HL, 300 μmol photon m−2 s−1), on the physiological responses and lipid remodeling of G. lemaneiformis. Results demonstrated that short-term exposure to either high temperature or high light stress led to a reduction in maximum (Fv/Fm), effective photochemical efficiency (Fv'/Fm') and maximum relative electron transfer rate (rETRmax), and the combination of these stresses exerted a more pronounced inhibitory effect on photosystem II efficiency. Short-term exposure to heat stress led to an increase in superoxide dismutase (SOD) activity, as well as a rise in glutathione (GSH) and ascorbate (Asc) contents under LL, while the activities of antioxidant enzymes (SOD, peroxidase, and ascorbate peroxidase) and levels of non-enzymatic antioxidants (GSH and Asc) were reduced under ML and HL. Additionally, short-term heat stress induced the accumulations of phosphatidylcholine (PC), phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerol, sulfoquinovosyldiacylglycerol, and triacylglycerol (TAG) under LL, while heat-induced lipid accumulation decreased under ML and HL. Furthermore, heat stress increased the accumulation of saturated or unsaturated PC species under LL. Specifically, there was an increase in the levels of saturated or monounsaturated acyl chain–containing PC species, whereas the levels of polyunsaturated acyl chain-containing PC species declined under ML and HL. Correspondingly, a significant increase in TAG species with polyunsaturated acyl chains was observed, particularly under LL conditions, suggesting a potential lipid turnover between PC and TAG. These results showed that the lipid metabolic plasticity of G. lemaneiformis enabled it to rapidly adapt to fluctuating environmental conditions, and the light environment regulated its heat stress response.

High nutrient availability modulates photosynthetic performance and biochemical components of the economically important marine macroalga Kappaphycus alvarezii (Rhodophyta) in response to ocean acidification

Increased atmospheric CO2 concentrations not only change the components of inorganic carbon system in seawater, resulting in ocean acidification, but also lead to decreased seawater pH, resulting in ocean acidification. Consequently, increased inorganic carbon concentrations in seawater provide a sufficient carbon source for macroalgal photosynthesis and growth. Increased domestic sewage and industrial wastewater discharge into coastal areas has led to nutrient accumulation in coastal seawaters. Combined with elevated pCO2 (1200 ppmv), increased nutrient availability always stimulates the growth of non-calcifying macroalgae, such as red economical macroalga Gracilariopsis lemaneiformis. Here, we evaluated the interactive effects of nutrients with elevated pCO2 on the economically important marine macroalga Kappaphycus alvarezii (Rhodophyta) in a factorial 21-day coupling experiment. The effects of increased nutrient availability on photosynthesis and photosynthetic pigments of K. alvarezii were greater than those of pCO2 concentration. The highest Fv/Fm values (0.660 ± 0.019 and 0.666 ± 0.030, respectively) were obtained at 2 μmol L−1 of NO3–N at two pCO2 levels. Under the elevated pCO2 condition, the Chl-a content was lowest (0.007 ± 0.004 mg g−1) at 2 μmol L−1 of NO3–N and highest (0.024 ± 0.002 mg g−1) at 50 μmol L−1 of NO3–N. The phycocyanin content was highest (0.052 ± 0.012 mg g−1) at 150 μmol L−1 of NO3–N under elevated pCO2 condition. The malondialdehyde content declined from 32.025 ± 4.558 nmol g−1 to 26.660 ± 3.124 nmol g−1 with the increased nutrients at under low pCO2. To modulate suitable adjustments, soluble biochemical components such as soluble carbohydrate, soluble protein, free amino acids, and proline were abundantly secreted and were likely to protect the integrity of cellular structures under elevated nutrient availability. Our findings can serve as a reference for cultivation and bioremediation methods under future environmental conditions.