Posts Tagged 'photosynthesis'

Combined effects of simulated acidification and hypoxia on the harmful dinoflagellate Amphidinium carterae

Hypoxia and acidification frequently co-occur in coastal marine ecosystems, and will likely become more intense and persistent with anthropogenic climate change. Although the separate effects of these stressors have previously been described, their combined effects on marine phytoplankton are currently unknown. In this novel study, multi-stressor incubation experiments using the harmful dinoflagellate, Amphidinium carterae, examined the effects of acidification and hypoxia both individually and in combination. Long-term (7 days) and short-term (6 h) experiments under controlled carbon dioxide (CO2) and oxygen (O2) conditions examined the interactive effects of the stressors and the physiological mechanisms driving their interaction. In the long-term experiment, synergistically negative effects were observed for A. carterae growth, photosynthesis, carbon fixation, nitrate uptake, and photosynthetic efficiency (Fv/Fm) under combined high CO2 (low pH) and low O2 conditions. In the short-term experiment, delayed recovery of photosystem II (PSII) reaction centers was observed following photoinhibition, suggesting that high CO2 and low O2 conditions negatively affect photosynthesis in A. carterae even after relatively short exposures. Although high CO2, low O2 conditions should decrease photorespiration and favor carbon fixation by the key photosynthetic enzyme ribulose-1,5-bisphosphate-carboxylase/oxygenase (RuBisCO), these findings demonstrate that the affinity of RuBisCO for CO2 relative to O2 alone does not predict phytoplankton responses to CO2 and O2 conditions in vivo, complicating predictions of phytoplankton community responses to hypoxia and acidification. Results of these experiments suggest that the combination of low pH and O2 concentrations may negatively impact the growth of some harmful dinoflagellates in coastal marine ecosystems.

Continue reading ‘Combined effects of simulated acidification and hypoxia on the harmful dinoflagellate Amphidinium carterae’

Limited response of a spring bloom community inoculated with filamentous cyanobacteria to elevated temperature and pCO2

Temperature and CO2 levels are projected to increase in the future, with consequences for carbon and nutrient cycling in brackish environments, such as the Baltic Sea. Moreover, filamentous cyanobacteria are predicted to be favored over other phytoplankton groups under these conditions. Under a 12-day outdoor experiment, we examined the effect on a natural phytoplankton spring bloom community of elevated temperature (from 1°C to 4°C) and elevated pCO2 (from 390 to 970 μatm). No effects of elevated pCO2 or temperature were observed on phytoplankton biovolumes, but a significantly higher photosystem II activity was observed at elevated temperature after 9 days. In addition, three species of diazotrophic filamentous cyanobacteria were inoculated to test their competitive capacity under spring bloom conditions. The toxic cyanobacterium Nodularia spumigena exhibited an average specific growth rate of 0.10 d−1 by the end of the experiment, indicating potential prevalence even during wintertime in the Baltic Sea. Generally, none of the inoculated cyanobacteria species were able to outcompete the natural phytoplankton species at temperatures ≤4°C. No direct effects were found on heterotrophic bacteria. This study demonstrates the highly efficient resistance towards short-term (12 days) changes in abiotic factors by the natural Baltic Sea spring bloom community.

Continue reading ‘Limited response of a spring bloom community inoculated with filamentous cyanobacteria to elevated temperature and pCO2’

Temporal effects of ocean warming and acidification on coral–algal competition

While there is an ever-expanding list of impacts on coral reefs as a result of ocean warming and acidification, there is little information on how these global changes influence coral–algal competition. The present study assessed the impact of business-as-usual ocean warming and acidification conditions on the survivorship, calcification, photosynthesis and respiration of the coral–algal interaction between the macroalga Halimeda heteromorpha and the coral Acropora intermedia over 8 weeks in two seasons. The physiological responses of A. intermedia and H. heteromorpha were highly dependent on season, with both organisms demonstrating optimal rates of calcification and photosynthesis under present-day conditions in summer. Contact with H. heteromorpha did not influence A. intermedia survivorship, however did reduce long-term calcification rates. Photosynthetic rates of A. intermedia were influenced by algal contact temporally in opposing directions, with rates reduced in winter and increased in summer. Enhanced photosynthetic rates as a result of algal contact were not enough to offset the combined effects of ocean warming and acidification, which regardless of coral–algal contact, reduced survivorship, calcification and photosynthesis of A. intermedia and the calcification rates of H. heteromorpha. These findings provide experimental support for the idea that the effects of coral–algal competition are temporally variable, and help improve our understanding of how future ocean warming and acidification may alter the dynamics of coral–algal interactions.

Continue reading ‘Temporal effects of ocean warming and acidification on coral–algal competition’

Responses of seaweeds that use CO2 as their sole inorganic carbon source to ocean acidification: differential effects of fluctuating pH but little benefit of CO2 enrichment

Laboratory studies that test the responses of coastal organisms to ocean acidification (OA) typically use constant pH regimes which do not reflect coastal systems, such as seaweed beds, where pH fluctuates on diel cycles. Seaweeds that use CO2 as their sole inorganic carbon source (non-carbon dioxide concentrating mechanism species) are predicted to benefit from OA as concentrations of dissolved CO2 increase, yet this prediction has rarely been tested, and no studies have tested the effect of pH fluctuations on non-CCM seaweeds. We conducted a laboratory experiment in which two ecologically dominant non-CCM red seaweeds (Callophyllis lambertii and Plocamium dilatatum) were exposed to four pH treatments: two static, pHT 8.0 and 7.7 and two fluctuating, pHT 8.0 ± 0.3 and 7.7 ± 0.3. Fluctuating pH reduced growth and net photosynthesis in C. lambertii, while P. dilatatum was unaffected. OA did not benefit P. dilatatum, while C. lambertii displayed elevated net photosynthetic rates. We provide evidence that carbon uptake strategy alone cannot be used as a predictor of seaweed responses to OA and highlight the importance of species-specific sensitivity to [H+]. We also emphasize the importance of including realistic pH fluctuations in experimental studies on coastal organisms.

Continue reading ‘Responses of seaweeds that use CO2 as their sole inorganic carbon source to ocean acidification: differential effects of fluctuating pH but little benefit of CO2 enrichment’

Responses to ocean acidification and diurnal temperature variation in a commercially farmed seaweed, Pyropia haitanensis (Rhodophyta)

To investigate carbon and nitrogen metabolism in Pyropia haitanensis in response to the combined conditions of ocean acidification and diurnal temperature variation, maricultured thalli were tested in acidified culture under different temperature treatments. The results showed a combined effect of ocean acidification and diurnal temperature difference on the C and N metabolism and growth of P. haitanensis. In acidifed culture, algal growth, maximum photosynthetic rate, nitrate reductase (NR) activity, amino acid (AA) content and AA score (AAS) were more significantly enhanced in seaweed under diurnal temperature variation than in seaweed at constant temperature. In acidified seawater, soluble carbohydrates in P. haitanensis increased due to greater dissolved inorganic carbon (DIC), whereas soluble proteins decreased. Under the diurnal temperature treatment, higher temperature during the light period enhanced accumulation of algal photosynthates, whereas lower temperature in the dark period reduced energy consumption, resulting in enhanced algal growth, AA content and AAS. We concluded that suitable diurnal temperature difference would be conducive to C fixation and N assimilation under ocean acidification. However, excessively high temperatures would depress algal photosynthesis and increase energy consumption, thereby exerting a negative effect on algal growth.

Continue reading ‘Responses to ocean acidification and diurnal temperature variation in a commercially farmed seaweed, Pyropia haitanensis (Rhodophyta)’

Responses of carbonic anhydrases and Rubisco to abrupt CO2 changes of seawater in two marine diatoms

Diatoms are experiencing striking fluctuations in seawater carbonate chemistry in the natural marine environment, especially in coastal seawaters. Here, we show that the diatoms Thalassiosira weissflogii and Phaeodactylum tricornutum, which utilize different carbon acquisition mechanisms, respond differently to short-term changes in seawater carbonate chemistry. Our results showed that T. weissflogii showed significantly higher photosynthetic oxygen evolution rates than that of P. tricornutum at low levels of CO2 or HCO3−. This suggests that T. weissflogii had higher affinities for CO2 or HCO3− when their concentrations were not sufficient to support saturated growth and photosynthesis. While the activity of Rubisco in P. tricornutum positively correlated with carbonic anhydrases (CA), we observed negative relationship between Rubisco and CA activity in the diatom T. weissflogii. These contrasting physiological responses of diatoms with varied carbon acquisition mechanisms indicate different abilities to cope up with abrupt changes in seawater carbonate chemistry. We propose that the ability to respond to varying carbonate chemistry may act as one determinant of the diatom distributions and phytoplankton community structures.

Continue reading ‘Responses of carbonic anhydrases and Rubisco to abrupt CO2 changes of seawater in two marine diatoms’

Diverse responses of sporophytic photochemical efficiency and gametophytic growth for two edible kelps, Saccharina japonica and Undaria pinnatifida, to ocean acidification and warming

Highlights

• Increased pCO2 enhanced sporophytic photosynthesis of S. japonica and U. pinnatifida.
• Increased pCO2 inhibited gametophytic growth of these two kelps.
• Ocean acidification and warming represent major threats to kelp mariculture.
• U. pinnatifida showed higher productivity in warmer ocean than S. japonica.

Abstract

Ocean acidification and warming represent major environmental threats to kelp mariculture. In this study, sporophytic photochemical efficiency and gametophytic growth of Saccharina japonica and Undaria pinnatifidawere evaluated under different pCO2 levels (360, 720, and 980 ppmv) and temperatures (5, 10, 15, and 20 °C for sporophytes; 15 and 20 °C for gametophytes). Sporophytic photochemical efficiencies of both kelps were significantly greater at 720 ppmv than at 360 and 980 ppmv. Female gametophytes of both kelps grew significantly better at 360 ppmv than at higher pCO2 levels. The growth of U. pinnatifida gametophytes was significantly greater at 20 °C than at 15 °C, while no significant difference was observed for the growth of S. japonica. These results indicate that increased pCO2 stimulated sporophytic photochemical efficiency while inhibited gametophytic growth of these kelps, which might negatively affect their seedling cultivation. U. pinnatifida exhibited higher productivity in warmer ocean than S. japonica.

Continue reading ‘Diverse responses of sporophytic photochemical efficiency and gametophytic growth for two edible kelps, Saccharina japonica and Undaria pinnatifida, to ocean acidification and warming’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book