Alga Ulva Prolifera Research Articles

Ocean warming enhances the competitive advantage of Ulva prolifera over a golden tide alga, Sargassum horneri under eutrophication

Recent years have seen the Ulva green tide and Sargassum golden tide become commonplace in the coastal waters of China. However, little is known on how the combination of ocean warming and eutrophication would affect the interaction of green and golden tides. In this study, we cultured the green tide alga Ulva prolifera and the golden tide alga Sargassum horneri under different temperatures (5, 10, 15, 20, 25, and 30°C) and two nutrient concentrations (Low nutrient, LN: 5 μM-nitrate and 0.5 μM-phosphate; High nutrient, HN: 500 μM-N and 50 μM-P) in both monoculture and coculture systems to investigate the physiological responses and their competitive relationships. In monocultures, the growth of U. prolifera and S. horneri, along with pigment concentrations and photosynthesis, increased with rising temperature, reaching a plateau at 15 - 25°C. However, when the temperature increased to 30°C, the growth of U. prolifera and S. horneri decreased abruptly, with S. horneri even suffering death. In coculture, the growth of both U. prolifera and S. horneri was inhibited compared to the monoculture, with the greatest decline observed in S. horneri at 25°C under two nutrient conditions. Our results show that U. prolifera would outcompete S. horneri under high temperature in coculture, suggesting that ocean warming would enhance the competitive advantage of green tide over golden tide under eutrophication in the future.

Effects of ocean acidification and eutrophication on the growth and photosynthetic performances of a green tide alga Ulva prolifera

With the impact of fossil fuel burning and industrialization, atmospheric CO2 concentration will reach about 1000 ppmv in 2100, and more and more CO2 will be absorbed by ocean, resulting in ocean acidification. The Chinese coastal waters are showing unexpectedly high levels of acidification due to a combination of global ocean acidification and severe regional eutrophication, which is caused by natural accumulation or human activities such as aquacultural tail water input, potentially affecting macroalgal blooms. However, little is known about the combined effects of ocean acidification and entrophication on the eco-physiology of bloom-forming macroalgae. This study investigated Ulva prolifera, a dominant species causing green tide in the South Yellow Sea, and explored its growth and physiological responses under the combination conditions of ocean acidification and enriched nutrients. In this study, U. prolifera thalli were cultured under two CO2 conditions (air and 1000 μatm) and two nutrient conditions (High Nutrient, HN, 135 μmol L-1 N and 8.5 μmol L-1 P; Normal Nutrient, NN, 27 μmol L-1 N and 1.7 μmol L-1 P). The results showed that eutrophication conditions obviously enhanced the relative growth rate and photosynthetic performance of U. prolifera. Elevated pCO2 had no significant effect on U. prolifera growth and photosynthetic performance under normal nutrient conditions. However, under eutrophication conditions elevated pCO2 inhibited U. prolifera growth. Moreover, eutrophication conditions markedly improved the contents of chlorophyll a, chlorophyll b and nitrate reductase activity and inhibited the soluble carbohydrate content, but elevated pCO2 had no significant effect on them under nutrient-replete conditions. In addition, elevated pCO2 significantly reduced the carotenoid content under eutrophication conditions and had no effect on it under normal nutrient conditions. These findings indicate that seawater eutrophication would greatly accelerate U. prolifera bloom, which may also be suppressed to a certain extent by ocean acidification in the future. The study can provide valuable information for predicting the future outbreaks of U. prolifera green tide in nearshore regions.

Biomass and species composition of green macroalgae in the Binhai Harbor intertidal zone of the Southern Yellow Sea

Green tides have occurred in the Southern Yellow Sea (SYS) for 16 consecutive years, causing widespread concern. Attached and floating green macroalgae have been observed in Binhai Harbor, Jiangsu Province, China, in the SYS. This study used morphological analysis, and internal transcribed spacers and rps2-trnL molecular identification methods, to analyze the species composition and biomass of green macroalgae along the Binhai Harbor coast. Six species of green tide algae (Ulva prolifera, Ulva meridionalis, Ulva linza, Ulva flexuosa, Ulva californica, and Ulva intestinalis) were identified, in addition to Blidingia sp. The discovery of U. californica is the first report of this species off the coast of Jiangsu Province. The floating green macroalgae along the Binhai Harbor coast originated from attached green macroalgae in Binhai Harbor, and a small number of the attached algae were closely related to the large-scale floating U. prolifera in the SYS. Moreover, in December 2021, February 2022, and April 2022, the total biomass of attached green macroalgae in Binhai Harbor was 25.600, 10.767, and 25.867 t, respectively, of which the U. prolifera biomass was 10.697, 8.709, and 4.185 t, respectively. This study proved Binhai Harbor may not be an important source of green tide in the SYS.

Genome Sequence of the Edible Green Alga Ulva prolifera, Originating from the Yoshinogawa River in Japan.

ABSTRACTWe report the genome sequence of Ulva prolifera, which originated from the Yoshinogawa River in Japan, using Oxford Nanopore Technologies MinION and Illumina sequencing reads. The genome assembly size is 103.8 Mbp, consisting of 142 scaffolds with an N50 value of 4.11 Mbp.

A new assessment of the algal biomass of green tide in the Yellow Sea

The annually recurring Yellow Sea green tide causes significant economic, social, and ecological impacts in China. Currently, the magnitude of Yellow Sea green tide is usually evaluated according to the snap shot maximum algal coverage area or artificially removed algal biomass. However, this method ignores growth of the alga Ulva prolifera and thus needs improvement. We build a model to predict algal growth in drifting from upstream and the potential muaximum biomass of green tide. The results suggest that the potential maximum biomass is significantly higher than those estimated merely from maximum algal coverage area, particularly for years with extended period of algal loading in the upstream. Our method improves the evaluation of the magnitude of green tide and provides a scientific basis for developing effective countermeasures to reduce the persistent disaster.

Impacts of low pH and low salinity induced by acid rain on the photosynthetic activity of green tidal alga Ulva prolifera

Acid rain is a serious environmental problem and has obvious impacts on the growth, reproduction, and photosynthesis of terrestrial plants. Ulva prolifera, a main blooming species of green tides, was studied on its physiological response to acid rain. The photosynthetic parameters were determined under different conditions (salinity: 1, 10, 30‰; pH: 3.0, 3.5, 4.5; duration: 0.5, 1.0, 2.0 h) followed by 24-h recovering under natural conditions. Results showed 1-h treatment with pH 3.5 caused 50-70% reduction in the maximal quantum yield of PSII photochemistry (Fv/Fm) and effective quantum yield of PSII photochemistry (ФPSII) at normal salinity but when the low pH was combined with a salinity of 10‰ or lower, PSII activity was almost completely inhibited. Moreover, the low salinity (1‰ and 10‰) reduced the degree of photoprotection under low pH (3.5) conditions. Finally, we speculated if the pH of acid rain ≤ 3.5, with 1‰ salinity and 2-h rainfall time, the amount of U. prolifera and the scale of green tides would decrease.

Elevated CO2 influences competition for growth, photosynthetic performance and biochemical composition in Neopyropia yezoensis and Ulva prolifera

The occurrence of various marine macroalgae in the same niche will inevitably lead to interspecific competition due to similar environmental requirements. With the increasing global atmospheric CO2 concentration, the resulting ocean acidification can potentially influence competition among macroalgae in the future. Neopyropia yezoensis (Rhodophyta, formerly Pyropia yezoensis) and the epiphytic alga Ulva prolifera (Chlorophyta) were selected for investigating competition among macroalgae grown under different CO2 conditions. The results showed that when cultured with U. prolifera, N. yezoensis' growth rate was significantly inhibited along with a sharp decrease in net photosynthetic rate. Although CO2 decreased the growth rate of N. yezoensis, it enhanced the resistance of the alga to the allelopathic effect of U. prolifera. While no difference was found between U. prolifera grown in monoculture and biculture, strong competitive ability was observed. CO2 could enhance this ability with higher net photosynthetic rate. However, CO2 significantly inhibited the carotenoid synthesis in both plants. This inhibition in N. yezoensis was more pronounced in the presence of U. prolifera. Biculture promoted the accumulation of soluble protein in N. yezoensis while it inhibited the process in U. prolifera. In addition, it enhanced the inhibitory effect of acidification on soluble carbohydrates of both plants. Elevated CO2 levels alleviated the competition between N. yezoensis and U. prolifera, but the latter can become the more competitive epiphytic alga which can impact the future of nori culture.

Investigating nanoparticle formation and the metabolic response of Ulva prolifera to gold ions

With the application of AuNPs in cancer treatment and targeted drug delivery, algae have been proposed as potential eco-friendly nanofactories for the synthesis of AuNPs. Unfortunately, little is known about how HAuCl4 is converted to AuNPs, and the toxicity of HAuCl4 affects the mechanisms underlying metabolite shifts in algae. The aim of this work is to systematically study the cellular metabolism profile of the green alga Ulva prolifera upon exposure to HAuCl4 by using metabolomics based on nontargeted liquid chromatography and mass spectrometry. The results showed that the metabolite profiles of UpAu (treatment) and UpC (control) were clearly separated, as revealed by PCA and PLS-DA. A total of 200 metabolites and 16 specific metabolic pathways were significantly altered by exposure to HAuCl4, many of which are associated with the cellular stress response and AuNP synthesis. Importantly, the expression levels of crotonobetaine, ascorbic acid, jasmonic acid, ubiquinol, and vitamin D3 involve in stress-related metabolites increased, and those of secondary metabolites such as diosgenin and hecogenin terpendole G, and steroids, as reducers, were also all significantly increased. In addition, the downregulated metabolites included linoleic acid, stearidonic acid and arachidonic acid, which affect membrane composition and stability. Importantly, a metabolic analysis identified some novel metabolic pathways that are specifically regulated by HAuCl4, including linoleic acid metabolism, arachidonic acid metabolism, porphyrin and chlorophyll metabolism, steroid biosynthesis, and biosynthesis of secondary metabolites regulated by HAuCl4. In summary, the manifestation of differential metabolic profiles combined with SEM analysis of exposure to HAuCl4 provided evidence of damage to photosynthesis and membranes. These results provide holistic information about complex disturbances in the metabolite profiles of U. prolifera exposed to HAuCl4 and provide new insights into the mechanisms of HAuCl4 toxicity and AuNP synthesis in macroalgae.

Characterization of a broad substrates specificity acyl-CoA: diacylglycerol acyltransferase 1 from the green tide alga Ulva prolifera

Triacylglycerols (triglycerides, TAGs) are the major carbon and energy storage forms in various organisms, and important components of cellular membranes and signaling molecules; they have essential functions in multiple physiological processes and stress regulation. Acyl-CoA: diacylglycerol acyltransferase (DGAT) catalyzes the final and only committed acylation step in the synthesis of TAGs in eukaryotes. The present work identified and isolated a novel gene, UpDGAT1, from the green tide alga Ulva prolifera. The activity of UpDGAT1 was confirmed by heterologous expression in a Saccharomyces cerevisiae TAG-deficient quadruple mutant. Results of thin-layer chromatography and BODIPY staining indicated that UpDGAT1 was able to restore TAG synthesis and lipid body formation in the yeast. Lipid analysis of yeast cells revealed that UpDGAT1 showed broad substrate specificity, accepting saturated as well as mono- and polyunsaturated acyl-CoAs as substrates. High salinity and high temperature stresses increased UpDGAT1 expression and TAG accumulation in U. prolifera. The present study provides clues to the functions of UpDGAT1 in TAG accumulation in, and stress adaptation of, U. prolifera.

Extracts of the green algae Ulva prolifera possess antioxidant and antibacterial activities in vitro

Macroalgae are currently being explored as novel and sustainable sources of bioactive compounds. Ulva prolifera is a major member of the green algae, as it includes various bioactive compounds, including carotenoids, fucoidans, and phlorotannins, with various biological activities in pharmaceutical, nutraceutical, cosmeceutical, and functional foods industries. In the current work, the rbcL gene products were utilized in identifying U. prolifera molecularly. The antibacterial and antioxidant activities of the hexane, ethyl acetate, and methanol extracts of U. prolifera were carried out In vitro. The total antioxidant capacity method was utilized in assessing the antioxidant activity. Estimation of nutritional value of U. prolifera showed 5.4±0.04%, 1.7±0.04% and 43±0.5% dry weight for total proteins, lipids, and carbohydrates, respectively. The total antioxidant capacity of algal hexane, ethyl acetate, and methanol extract was 0.97±0.09, 1.23±0.04 and 1.63±0.09 mg equivalent ascorbic acid/gdw, respectively. Investigation of the antibacterial activity of U. prolifera against Staphylococcus aureus and Aeromonas hydrophila showed that the recorded diameter of the inhibition zones for the methanolic extract was 1.1cm. The antibacterial effect of hexane extract against Edwardsiella tarda was high which had a diameter of 1.5cm. Of interest, the ethyl acetate extract of U. prolifera showed potent antibacterial activity against the three bacteria, including Vibrio anguillarum, Aeromonas hydrophila, and Edwardsiella tarda. These results indicate that macroalgae U. prolifera contain bioactive substances with potential antioxidant and antibacterial effects.

Extraction and identification of toxic organic substances from decaying green alga Ulva prolifera

In this study, the extraction, identification, and antialgal activity of toxic organic substances from decaying green alga Ulva prolifera, a disaster-causing alga on green tides in the Yellow Sea, were investigated. The toxic organic substances of U. prolifera were isolated by a sequence of procedures, namely, liquid-liquid extraction (LLE), silica gel chromatography column separation (SGCC), C18 solid phase extraction (C18 SPE), and acid-alkali separation (AAS) and their antialgal activities were tested against diatom Skeletonema costatum. The results showed that the 96h-EC50 value in each procedure was 57.00 mg•L−1, 12.14 mg•L−1, 11.70 mg•L−1, and 6.31 mg•L−1 in turn. Additionally, the initial (ethyl acetate extract in LLE) and final (Organic phase A in AAS) yield of toxic organics were 318 mg•kg−1 and 9 mg•kg−1 (the wet weight of U. prolifera). The final active fractions were preliminary identified as five 16- and 18-carbon fatty acids and four enols using GC–MS. The study may further evaluate the effect of bioactive substances on marine life after U. prolifera green tides bloom.

Absorptive process and biological activity of Ulva prolifera and algal bioremediation of coking effluent

The concentrates of coking effluents are toxic and technically challenging to treat. Environmental protection demands an efficient and cost-effective technique for coking wastewater treatment. The intertidal marine macro alga Ulva prolifera has a high tolerance to various environmental stresses. In this study, U. prolifera was collected from an intertidal field and tested in a laboratory-scale photobioreactor for potential bioremediation of coking effluent concentrate. Algal physiology and water quality were measured. During treatment, the quantum yield Fv/Fm and effective quantum yield Y(II) values showed 12% and 15% decreases in 24 h, respectively, and a complete recovery in 168 h. The algal physiological characteristics indicated that light irradiance provided in a sine pattern of enhanced algal growth by 53% in the coking concentrate. The removal efficiency for total nitrogen and total phosphorus was up to 26.1% and 68.5% in 24 h, respectively. It also showed high removal efficiencies for some heavy metals, chemical oxygen demand, biological oxygen demand, and nutrients within 24 h. The feasibility of using U. prolifera for coking concentrate treatment was also considered. This study provided a possible bioremediation technique for wastewater treatment, especially for concentrates of coking effluent, in the coking industry.

The complete mitochondrial genome sequence of Bryopsis plumosa

In 2015, a novel macroalgae began to bloom in Qinhuangdao on the coast of the Bohai Sea, Northern China. Bryopsis plumosa, a green macroalga, is one of the causal species of the macroalgae blooms, which have severely affected the environment and ecosystem on the coast of Qinhuangdao. In the present study, we sequenced the mitochondrial genome of B. plumosa for the first time (GenBank accession number MN853874). It was found that the ring-shaped genome was made up of 110,912 base pairs, including 29 protein-coding genes, 23 tRNAs, and 2 rRNAs. Phylogenetic analysis showed B. plumosa had close genetic relationships with algae Ulva prolifera, Ulva linza, and Ulva flexuosa. The present data will provide important information on the phylogenetics and molecular evolution of Bryopsis species.

Reproductive strategy of the floating alga Ulva prolifera in blooms in the Yellow Sea based on a combination of zoid and chromosome analysis

Green algal blooms have occurred in the Yellow Sea for 13 consecutive years since 2007. However, little is known about the reproductive strategy of the dominant species Ulva prolifera in the field. In particular, it is not clear whether the floating Ulva species are sporophytes or gametophytes, and if their life history is sexual or asexual. In this study, the life history type was determined based on the size, phototactic response, and flagella number for the zoids in at least two successive generations. In addition, chromosome observations were conducted to distinguish the gametophytes and sporophytes in the floating Ulva species. The results showed that the floating Ulva species were all sporophytes with sexual reproductive patterns, thereby indicating that this Ulva species always maintains vegetative growth from April to June during the early stage of the blooms. In addition, we found that the chromosome numbers were 18 for the diploid sporophytes and nine for the haploid male and female gametophytes. These results provide useful information to help understand the explosive growth of these green algal blooms.

Ulvibacterium marinum gen. nov., sp. nov., a novel marine bacterium of the family Flavobacteriaceae, isolated from a culture of the green alga Ulva prolifera.

A Gram-stain negative, aerobic, rod-shaped, and non-motile bacterium, designated strain CCMM003T, was isolated from a culture of the green alga Ulva prolifera. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain CCMM003T belongs to the family Flavobacteriaceae and exhibits a close relationship to Pseudozobellia thermophila DSM 19858T (92.5%). Optimal growth occurred in the presence of 4% (w/v) NaCl, at pH 7.0 and 30°C. The polar lipids of strain CCMM003T consisted of phosphatidylethanolamine and six unidentified lipids. The predominant isoprenoid quinone was MK-6. The major fatty acids were iso-C15:0, iso-C15:1 G, iso-C17:0 3-OH and summed feature 3 (C16:1ω7c and/or iso-C15:0 2-OH). The DNA G + C content of strain CCMM003T calculated on the basis of the genome sequence was 41.2mol% and the genome size was 5.9 Mbp. On the basis of data from this polyphasic study, strain CCMM003T is considered to represent a novel genus and species of the family Flavobacteriaceae, for which the name Ulvibacterium marinum gen. nov., sp. nov. is proposed. The type strain is CCMM003T (= MCCC 1K03244T =KCTC52639T).

Algihabitans albus gen. nov., sp. nov., isolated from a culture of the green alga Ulva prolifera.

A bacterial strain, designated HHTR 118T, was isolated from a culture of the green alga Ulvaprolifera obtained from offshore seawater of Qingdao, Shandong Province, China. Cells of strain HHTR 118T were rod-shaped and motile with a single flagellum, and approximately 0.3-0.4 µm wide and 0.8-1.4 µm long. The strain was Gram-stain-negative, strictly aerobic, catalase-negative and oxidase-positive. Optimal growth was observed at 30 °C, at pH 8.0 and with 1 % (w/v) NaCl. Nitrate was not reduced. Sucrose, sodium citrate and l-leucine stimulated growth, but not lactose, fructose, xylose, d-mannose, glucose, raffinose, rhamnose, ornithine or lysine. The DNA G+C content of strain HHTR 118T calculated on the basis of the genome sequence was 64.9 mol% and the genome size is 4.6 Mbp. The major quinone was ubiquinone 10 and the predominant cellular fatty acids (>10 % of total fatty acids) were summed feature 8 (C18 : 1ω6c and/or C18 : 1ω7c). The predominant polar lipids were phosphatidylglycerol, one unidentified phospholipid, two unidentified aminolipids and three unidentified polar lipids. Phylogenetic analysis, based on 16S rRNA gene sequences, demonstrated that strain HHTR 118T was affiliated with the family Rhodospirillaceae. On the basis of the 16S rRNA gene sequence data as well as physiological and biochemical characteristics, we concluded that strain HHTR 118T represents a novel species of a novel genus. We propose the name of Algihabitans albus gen. nov., sp. nov. for this novel species. The type strain of the novel species is strain HHTR 118T (=KCTC 62395T=MCCC 1K03486T).

Differential gene expression for carotenoid biosynthesis in a green alga Ulva prolifera based on transcriptome analysis

BackgroundCarotenoids are widely distributed in plants and algae, and their biosynthesis has attracted widespread interest. Carotenoid-related research has mostly focused on model species, and there is a lack of data on the carotenoid biosynthetic pathway in U. prolifera that is the main species leading to green tide, a harmful plague of floating green algae.ResultsThe carotenoid content of U. prolifera samples, that is the main species leading to green tide, a harmful plague of floating green algae at different temperatures revealed that its terpenoid was highest in the samples subjected to high temperature at 28 °C (H), followed by the samples subjected to low temperature at 12 °C (L). Its terpenoid was lowest in the samples subjected to medium temperature at 20 °C (M). We conducted transcriptome sequencing (148.5 million raw reads and 49,676 unigenes in total) of samples that were subjected to different temperatures to study the carotenoid biosynthesis of U. prolifera. There were 1125–3164 significant differentially expressed genes between L, M and H incubation temperatures, of which 11–672 genes were upregulated and 453–3102 genes were downregulated. A total of 3164 genes were significantly differentially expressed between H and M, of which 62 genes were upregulated and 3102 genes were downregulated. A total of 2669 significant differentially expressed genes were observed between L and H, of which 11 genes were upregulated and 2658 genes were downregulated. A total of 13 genes were identified to be involved in carotenoid biosynthesis in U. prolifera, and the expression levels of the majority were highest at H and lowest at M of incubation temperature. Both the carotenoid concentrations and the expression of the analysed genes were lowest in the normal temperature group, while low temperature and high temperature seemed to activate the biosynthesis of carotenoids in U. prolifera.ConclusionsIn this study, transcriptome sequencing provided critical information for understanding the accumulation of carotenoids and will serve as an important reference for the study of other metabolic pathways in U. prolifera.

Marinicaulis aureum sp. nov., isolated from a culture of the green alga Ulva prolifera, and emended description of the genus Marinicaulis.

A Gram-stain negative, facultatively anaerobic, rod-shaped motile bacterium with a single polar flagellum, designed strain HHTR114T, was isolated from a culture of the green alga Ulva prolifera obtained from offshore seawater at Qingdao, China. Optimum growth occurred in the presence of 2-3% (w/v) NaCl, at pH 7.0-8.0 and 30°C. The major fatty acids (> 10% of total fatty acids) were C16:0 (24.7%), C18:1ω7c 11-methyl (24.3%) and summed feature 3 (C16:1ω6c and/or C16:1ω7c, 19.7%). The major polar lipids were phosphatidylethanolamine, glycolipid and four unidentified polar lipids. The DNA G + C content of strain HHTR114T calculated on the basis of the genome sequence was 58.2% and the genome size is 4.1Mbp. The predominant isoprenoid quinone was Q-10. The estimated DNA-DNA hybridization values were 21.4% [18.6-24.4%] between strain HHTR114T and Marinicaulis flavus SY-3-19T. On the basis of polyphasic analysis, strain HHTR114T is considered to represent a novel species, for which the name Marinicaulis aureum sp. nov. is proposed. The type strain of the type species is HHTR114T (= KCTC 62394T = MCCC 1K03481T).

Photoperiod mediates the effects of elevated CO2 on the growth and physiological performance in the green tide alga Ulva prolifera

Ulva spp., an increasingly important food, are the dominant species of the large-scale green tides. In this study, both the growth and the physiological responses of the Ulva prolifera were studied after cultured in three different light and dark regimes (12:12, 14:10 and 16:8-h light/dark) in combination with current (420 μatm; LC) and increased (1000 μatm; HC) levels of atmospheric CO2. Grown rate of U. prolifera was significantly enhanced by increased CO2 under the three light:dark regimes, especially under 16:8 h-light:dark, indicating that growth was C-unsaturated at present CO2 levels. U. prolifera showed a significantly higher growth rate and lower dark respiration rate (Rd) at 16:8 h-light:dark treatment than at 12:12 h-light/dark treatment, regardless of the CO2 treatment. The photochemical performance was largely unaffected by elevated CO2 and daylength. These results suggest that U. prolifera in a future CO2 enriched coastal water, seems to be resilient to higher CO2 concentrations, and this could be enhanced by longer daylength.

Nitrogen uptake and assimilation preferences of the main green tide alga Ulva prolifera in the Yellow Sea, China

The successive outbreak of large-scale Ulva prolifera green tides in the Yellow Sea, China, from 2007 to 2017, is a serious regional environmental issue that attracts worldwide attention. The competitive advantage in nitrogen uptake and utilization is an important factor, making U. prolifera the dominant green-tide-forming seaweed. However, the detailed preference characteristics of U. prolifera for nitrogen uptake and assimilation in common inorganic and organic nitrogen sources is poorly understood and is studied using stable nitrogen isotope (15N) analysis. Our results reveal that various nitrogen sources can be simultaneously and directly taken up by U. prolifera. The uptake rates are in the sequence of NO3− (nitrate) > NH4+ (ammonium) > CO(NH2)2 (urea) > C2H5NO2 (glycine) and C3H7NO2 (alanine). In other words, U. prolifera mostly prefers inorganic nitrogen, such as nitrate and ammonium, although it can also utilize different organic nitrogen sources simultaneously. Moreover, the assimilation of NH4+ is inhibited and its uptake cannot be fitted by the Michaelis–Menten equation when the alga is exposed to multiple nitrogen sources. We propose that at the early and middle stages of green tides the rich inorganic nitrogen sources (especially NO3−) in seawater are very important to support the fast growth of U. prolifera, while at the later stage of green tides, when inorganic nitrogen sources have been exhausted, organic nitrogen sources may contribute importantly to maintaining the growth of U. prolifera, thus lengthening the duration of green tides.