Posts Tagged 'photosynthesis'

Future CO2-induced ocean acidification enhances resilience of a green tide alga to low-salinity stress

To understand how Ulva species might respond to salinity stress during future ocean acidification we cultured a green tide alga Ulva linza at various salinities (control salinity, 30 PSU; medium salinity, 20 PSU; low salinity, 10 PSU) and CO2 concentrations (400 and 1000 ppmv) for over 30 days. The results showed that, under the low salinity conditions, the thalli could not complete its whole life cycle. The specific growth rate (SGR) of juvenile thalli decreased significantly with reduced salinity but increased with a rise in CO2. Compared to the control, medium salinity also decreased the SGR of adult thalli at low CO2 but did not affect it at high CO2. Similar patterns were also found in relative electron transport rate (rETR), non-photochemical quenching, saturating irradiance, and Chl b content. Although medium salinity reduced net photosynthetic rate and maximum rETR at each CO2 level, these negative effects were significantly alleviated at high CO2 levels. In addition, nitrate reductase activity was reduced by medium salinity but enhanced by high CO2. These findings indicate that future ocean acidification would enhance U. linza’s tolerance to low salinity stress and may thus facilitate the occurrence of green tides dominated by U. linza.

Continue reading ‘Future CO2-induced ocean acidification enhances resilience of a green tide alga to low-salinity stress’

Continuous photoperiod of the Arctic summer stimulates the photosynthetic response of some marine macrophytes


• Long photoperiods increase the photosynthetic activity of certain subarctic macrophytes.

• Increased CO2 had no effect on tested macrophytes.

• Highest increases of photosynthetic activity of A. nodosum and Z. marina at long day lengths; smaller increase for F. vesiculosus.

• Subarctic macrophytes, expanding as sea ice retreats, will benefit from long summer days.


Subarctic macrophytes are predicted to expand in the Arctic as a result of on-going global climate change. This will expose them to 24 h of light during the Arctic summer while pCO2 levels are predicted to rise globally. Here, we tested the photosynthetic activity of two brown macroalgae (Ascophyllum nodosum, Fucus vesiculosus) and one seagrass (Zostera marina) from subarctic Greenland, measuring their relative maximum electron transport rate (rETRmax), photosynthetic efficiency (α) and saturating irradiance (Ik) after 3 days of incubation at different photoperiods (12:12 h, 15:09 h, 18:06 h, 21:03 h and 24:00 h, light:dark) with ambient values of pCO2 (200 ppm, characteristic of current subarctic surface waters) and increased pCO2 (400 and 1000 ppm). The photosynthetic parameters rETRmax and Ik increased significantly with longer photoperiods and increased, however insignificantly, with increased pCO2. Responses differed between species. A. nodosum and Z. marina showed the highest increase of rETRmax and Ik from 12 h to 24 h while the increase of F. vesiculosus was smaller. Our results suggest that as subarctic macrophytes expand in the Arctic in response to retracting sea ice, the long summer days will stimulate the productivity of the species tested here, while the effect of high-CO2 environment needs further research.

Continue reading ‘Continuous photoperiod of the Arctic summer stimulates the photosynthetic response of some marine macrophytes’

Effects of reduced pH on health biomarkers of the seagrass Cymodocea nodosa

Ocean acidification is a growing problem that may affect many marine organisms in the future. Within 100 years the pH of the ocean is predicted to decrease to 7.8, from the current ocean pH of around 8.1. Using phenolic acid levels as a stress indicator as well as respiration and chlorophyll content as a measure of health, the effect of lowering pH was tested on the seagrass, Cymodocea nodosa, in a controlled environment. Plant samples, water, and soil were taken from the Bay of Cádiz, Spain, and placed in aquaria in a temperature-controlled room. One control group was left untreated with a pH of approximately 8.1, while experimental groups maintained pH levels of 7.8 and 7.5. Using High Performance Liquid Chromatography (HPLC), concentration of the phenol rosmarinic acid was quantified in the plants. Average concentration for the control group was 1.7 μg g-1, while it was 2.9 μg g-1 for pH group 7.8, and 10.1g g-1 for pH group 7.5. To evaluate the overall health of C. nodosa within the three groups, chlorophyll concentration and photosynthesis/respiration rates were determined. A one-tailed ANOVA test was conducted using the chlorophyll concentrations of the three groups. With an F-value of 1.360 and a p-value of 0.287, the differences between the groups were not statistically significant. Although the raw data shows a slight decrease in chlorophyll content between the control group and the pH group 7.5, these discrepancies might have been larger or smaller due to sampling or experimental error. Additionally, the average values with their respective standard deviations were calculated for the respiration rates and oxygen production of each group. A one-tailed ANOVA was also used to determine the relationship between rosmarinic acid content and pH levels between the groups, with an F-value of 5.1423 and a p-value of 0.050.

Continue reading ‘Effects of reduced pH on health biomarkers of the seagrass Cymodocea nodosa’

pH affects growth, physiology and agar properties of agarophyte Gracilaria changii (Rhodophyta) under low light intensity from Morib, Malaysia

• The highest and the lowest growth rates of G. changii was at pH 6.61 and pH 9.30, respectively.
• G. changii survived poorly under high pH with partial thallus degradation.
• Photosynthetic pigments and agar production were significantly affected by pH.


Changes in coastal water pH alter inorganic carbon chemistry and impose abiotic stress on photosynthetic marine organisms. The red algal cell wall contains sulfated agar which protects them against environmental stresses. In this study, we investigated the effects of three different pHs (6.61, 8.04 and 9.30) on Gracilaria changii cultured in artificial seawater for 3 and 6 days, respectively. The growth rate of G. changii was the highest and the lowest at pH 6.61 and pH 9.30, respectively. Partial thallus degradation was observed in seaweeds treated at pH 9.30. Upon a 3-day treatment, the levels of allophycocyanin, total phycobilins in G. changii cultured at pH 6.61, and all photosynthetic pigments in G. changii cultured at pH 9.30, were significantly lower than those cultured at pH 8.04. G. changii exposed to pH 9.30 for 6 days also had significantly lower levels of chlorophyll a and allophycocyanin than those treated at pH 8.04. A six-day treatment at pH 6.61 caused a decline in the content of chlorophyll a and carotenoids, but an increase in the levels of phycoerythrin, phycocyanin, and total phycobilins, compared to those treated at pH 8.04. G. changii samples treated at pH 6.61 and pH 9.30 have a higher agar content compared to those cultured at 8.04. Gel strength was significantly lower in seaweed cultured at pH 9.30, compared to those cultured at pH 8.04. Gelling temperature and 3,6-anhydrogalactose content of agar were significantly affected by different pHs, but no significant changes were found in the melting temperature, gel syneresis and sulfate content of agar upon treatments. These information enhance our knowledge on physiological response and agar production in G. changii at different pHs, and useful for optimization of seaweed cultivation system in future.

Continue reading ‘pH affects growth, physiology and agar properties of agarophyte Gracilaria changii (Rhodophyta) under low light intensity from Morib, Malaysia’

Seasonal interactive effects of pCO2 and irradiance on the ecophysiology of brown macroalga Fucus vesiculosus L.

Stochastic upwelling of seawater in the Baltic Sea from the deep, anoxic bottoms may bring low-pH water rich in CO2 close to the surface. Such events may become more frequent with climate change and ongoing ocean acidification (OA). Photoautotrophs, such as macroalgae, which are important foundation species, have been proposed to benefit from increased carbon availability due to reduced energetic cost in carbon acquisition. However, the exact effects of CO2 fertilization may depend on the ambient light environment, as photosynthesis rates depend on available irradiance. In this experimental study, interacting effects of CO2 addition and irradiance on the habitat-forming macroalga Fucus vesiculosus were investigated during two seasons – winter and summer – in the northern Baltic Sea. Growth rates remained unaffected by CO2 or irradiance during both seasons, suggesting that direct effects of elevated CO2 on mature F. vesiculosus are small. Increases in CO2 affected algal elemental ratios by increasing carbon and decreasing nitrogen content, with resulting changes in the C:N ratio, but only in winter. In summer, chlorophyll a content increased under low irradiance. Increases in CO2 caused a decline in light-harvesting efficiency (decrease in Fv/Fm and α) under high irradiance in summer, and conversely increased α under low irradiance. High irradiance caused increases in the maximum relative electron transport rate (rETRmax) in summer, but not in winter. Differences between winter and summer indicate that F. vesiculosus responses to CO2 and irradiance are season-specific. Increases in carbon content during winter could indicate slightly positive effects of CO2 addition in the long run if the extra carbon gained may be capitalized in growth. The results of this study suggest that increases in CO2, either through upwelling or OA, may have positive effects on F. vesiculosus, but these effects are probably small.

Continue reading ‘Seasonal interactive effects of pCO2 and irradiance on the ecophysiology of brown macroalga Fucus vesiculosus L.’

Physiological responses of a coccolithophore to multiple environmental drivers

• Coccolithophores were more stressful in the higher solar UV irradiance exposures.

• The cells increased their functional antennae sizes under the future ocean conditions.

• Coccolithophores photosynthesized more in the high CO2 and warming ocean.

• Synergistical or antagonistic interactions were observed among multiple drivers.

Ocean acidification is known to affect primary producers differentially in terms of species and environmental conditions, with controversial results obtained under different experimental setups. In this work we examined the physiological performances of the coccolithophore Gephyrocapsa oceanica that had been acclimated to 1000 μatm CO2 for ~400 generations, and then exposed to multiple drivers, light intensity, light fluctuating frequency, temperature and UV radiation. Here, we show that increasing light intensity resulted in higher non-photochemical quenching and the effective absorption cross-section of PSII. The effective photochemical efficiency (Fv′/Fm′) decreased with increased levels of light, which was counterbalanced by fluctuating light regimes. The greenhouse condition acts synergistically with decreasing fluctuating light frequency to increase the Fv′/Fm′ and photosynthetic carbon fixation rate. Our data suggest that the coccolithophorid would be more stressed with increased exposures to solar UV irradiances, though its photosynthetic carbon fixation could be enhanced under the greenhouse condition.

Continue reading ‘Physiological responses of a coccolithophore to multiple environmental drivers’

Future CO2-induced seawater acidification mediates the physiological performance of a green alga Ulva linza in different photoperiods

Photoperiods have an important impact on macroalgae living in the intertidal zone. Ocean acidification also influences the physiology of macroalgae. However, little is known about the interaction between ocean acidification and photoperiod on macroalgae. In this study, a green alga Ulva linza was cultured under three different photoperiods (L: D = 8:16, 12:12, 16:8) and two different CO2 levels (LC, 400 ppm; HC, 1,000 ppm) to investigate their responses. The results showed that relative growth rate of U. linza increased with extended light periods under LC but decreased at HC when exposed to the longest light period of 16 h compared to 12 h. Higher CO2 levels enhanced the relative growth rate at a L: D of 8:16, had no effect at 12:12 but reduced RGR at 16:8. At LC, the L: D of 16:8 significantly stimulated maximum quantum yield (Yield). Higher CO2 levels enhanced Yield at L: D of 12:12 and 8:16, had negative effect at 16:8. Non-photochemical quenching (NPQ) increased with increasing light period. High CO2 levels did not affect respiration rate during shorter light periods but enhanced it at a light period of 16 h. Longer light periods had negative effects on Chl a and Chl b content, and high CO2 level also inhibited the synthesis of these pigments. Our data demonstrate the interactive effects of CO2 and photoperiod on the physiological characteristics of the green tide macroalga Ulva linza and indicate that future ocean acidification may hinder the stimulatory effect of long light periods on growth of Ulva species.

Continue reading ‘Future CO2-induced seawater acidification mediates the physiological performance of a green alga Ulva linza in different photoperiods’

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Ocean acidification in the IPCC AR5 WG II

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