Posts Tagged 'photosynthesis'

Interactive effects of seawater carbonate chemistry, light intensity and nutrient availability on physiology and calcification of the coccolithophore Emiliania huxleyi

Rising atmospheric carbonate dioxide (CO2) levels lead to increasing CO2 concentration and declining pH in seawater, as well as ocean warming. This enhances stratification and shoals the upper mixed layer (UML), hindering the transport of nutrients from deeper waters and exposing phytoplankton to increased light intensities. In the present study, we investigated combined impacts of CO2 levels (410 μatm (LC) and 925 μatm (HC)), light intensities (80–480 μmol photons m−2 s−1) and nutrient concentrations [101 μmol L−1 dissolved inorganic nitrogen (DIN) and 10.5 μmol L−1 dissolved inorganic phosphate (DIP) (HNHP); 8.8 μmol L−1 DIN and 10.5 μmol L−1 DIP (LN); 101 μmol L−1 DIN and 0.4 μmol L−1 DIP (LP)] on growth, photosynthesis and calcification of the coccolithophore Emiliania huxleyi. HC and LN synergistically decreased growth rates of E. huxleyi at all light intensities. High light intensities compensated for inhibition of LP on growth rates at LC, but exacerbated inhibition of LP at HC. These results indicate that the ability of E. huxleyi to compete for nitrate and phosphate may be reduced in future oceans with high CO2 and high light intensities. Low nutrient concentrations increased particulate inorganic carbon quotas and the sensitivity of maximum electron transport rates to light intensity. Light-use efficiencies for carbon fixation and calcification rates were significantly larger than that of growth. Our results suggest that interactive effects of multiple environmental factors on coccolithophores need to be considered when predicting their contributions to the biological carbon pump and feedbacks to climate change.

Continue reading ‘Interactive effects of seawater carbonate chemistry, light intensity and nutrient availability on physiology and calcification of the coccolithophore Emiliania huxleyi’

The effects of warming and ocean acidification on growth, photosynthesis, and bacterial communities for the marine invasive macroalga Caulerpa taxifolia

Caulerpa taxifolia is a pantropical green benthic marine macroalga, and one of the best known marine invasive species in temperate coastal habitats. In Australia, this species has been introduced to seven estuaries along New South Wales and one in South Australia. How this alga will perform under future climate change scenarios is however not well defined. This study experimentally assessed the effects of ocean acidification and global warming on the growth, photosynthetic performance and the bacterial community on two populations of C. taxifolia, one native and one invasive. A range of complex significant interactive effects between pH, temperature, and initial plant size on the growth of C. taxifolia were observed, but no effect of population origin and photosystem II (PSII) fluorescence quantum yield parameters were detected. No significant effects of the treatment combinations were observed on bacterial community richness or diversity. Only one bacterial species out of 1087 present on the algae showed significant changes between pH treatments at high temperature (24°C). This bacterium belonged to the genus Planctomyces and its relative abundance was more than 10 times higher in samples with low pH compared to the control. Higher plant growth was observed under all higher pCO2 and lower pH conditions suggesting that C. taxifolia will benefit from climate change, posing a potential higher risk in invaded locations.

Continue reading ‘The effects of warming and ocean acidification on growth, photosynthesis, and bacterial communities for the marine invasive macroalga Caulerpa taxifolia’

Photosynthesis and mineralogy of Jania rubens at low pH/high pCO2: a future perspective

Highlights

• Calcifying red algae may show species-specific response to ocean acidification (OA).
• Photosynthesis and mineralogy (biosphere) were assessed after a three-week transplant.
• Field carbon chemistry (hydrosphere) and irradiance (atmosphere) were also considered.
• Photosynthesis decreased while calcification was maintained under future pH conditions.
• The calcifying Jania rubens may survive but reducing the fitness under OA.

Abstract

Corallinales (Rhodophyta) are high Mg-calcite macroalgae and are considered among the most vulnerable organisms to ocean acidification (OA). These sensitive species play fundamental roles in coastal systems as food source and settlement promoters as well as being involved in reef stabilization, and water carbonate balance. At present only a few studies are focused on erect calcifying macroalgae under low pH/high pCO2 and the contrasting results make difficult to predict the ecological consequences of the OA on the coralline algae. In this paper the physiological reasons behind the resistance of Jania rubens, one of the most common calcareous species, to changing ocean pH are analysed. In particular, we studied the photosynthetic and mineralogical response of J. rubens after a three-week transplant in a natural CO2 vent system. The overall results showed that J. rubens could be able to survive under predicted pH conditions even though with a reduced fitness; nevertheless physiological limits prevent the growth and survival of the species at pH 6.7. At low pH (i.e. pH 7.5), the maximum and effective PSII efficiency decreased even if the increase of Rubisco expression suggests a compensation effort of the species to cope with the decreased light-driven products. In these circumstances, a pH-driven bleaching phenomenon was also observed. Even though the photosynthesis decreased at low pH, J. rubens maintained unchanged the mineralogical composition and the carbonate content in the cell wall, suggesting that the calcification process may also have a physiological relevance in addition to a structural and/or a protective role. Further studies will confirm the hypotheses on the functional and evolutionary role of the calcification process in coralline algae and on the ecological consequences of the community composition changes under high pCO2 oceans.

Continue reading ‘Photosynthesis and mineralogy of Jania rubens at low pH/high pCO2: a future perspective’

Ocean acidification and nutrient limitation synergistically reduce growth and photosynthetic performances of a green tide alga Ulva linza

Large-scale green tides have been invading the coastal zones of the western Yellow Sea annually since 2008. Meanwhile, oceans are becoming more acid due to continuous absorption of anthropogenic carbon dioxide and intensive seaweed cultivation in Chinese coastal areas is leading to severe regional nutrient limitation. However, little is known the combined effects of global and local stressors on the eco-physiology of bloom-forming algae. We cultured Ulva linza under two levels of pCO2 (400 and 1000 μatm) and four treatments of nutrient (nutrient repletion, N limitation, P limitation, and N & P limitation) to investigate the physiological responses of this green tide alga to the combination of ocean acidification and nutrient limitation. For both sporelings and adult plants, elevated pCO2 did not affect the growth rate when cultured under nutrient replete conditions but reduced it under P limitation; N or P limitation by themselves reduced growth rate. P limitation resulted in a larger inhibition in growth for sporelings compared to adult plants. Sporelings under P limitation did not reach the mature stage after 16 days of culture while those under P repletion became mature by day 11. Elevated pCO2 reduced net photosynthetic rate for all nutrient treatments but increased nitrate reductase activity and soluble protein content under P replete conditions. N or P limitation reduced nitrate reductase activity and soluble protein content. These findings indicate that ocean acidification and nutrient limitation would synergistically reduce the growth of Ulva species and may thus hinder the occurrence of green tides in a future ocean environment.

Continue reading ‘Ocean acidification and nutrient limitation synergistically reduce growth and photosynthetic performances of a green tide alga Ulva linza’

Impact of ocean acidification and warming on the productivity of a rock pool community

Highlights

• Fleshy algae drive the response of assemblages.
• The response of coralline algae to global change depend on the season.
• Rock pool assemblages are robust to ocean acidification and warming.

Abstract

This study examined experimentally the combined effect of ocean acidification and warming on the productivity of rock pool multi-specific assemblages, composed of coralline algae, fleshy algae, and grazers. Natural rock pool communities experience high environmental fluctuations. This may confer physiological advantage to rock pool communities when facing predicted acidification and warming. The effect of ocean acidification and warming have been assessed at both individual and assemblage level to examine the importance of species interactions in the response of assemblages. We hypothesized that rock pool assemblages have physiological advantage when facing predicted ocean acidification and warming. Species exhibited species-specific responses to increased temperature and pCO2. Increased temperature and pCO2 have no effect on assemblage photosynthesis, which was mostly influenced by fleshy algal primary production. The response of coralline algae to ocean acidification and warming depended on the season, which evidenced the importance of physiological adaptations to their environment in their response to climate change. We suggest that rock pool assemblages are relatively robust to changes in temperature and pCO2, in terms of primary production.

Continue reading ‘Impact of ocean acidification and warming on the productivity of a rock pool community’

Inorganic carbon is scarce for symbionts in scleractinian corals

Ocean acidification and changing sea surface temperatures stand to affect the interactions of corals and their Symbiodinium symbionts with regard to the inorganic carbon used for photosynthesis. However, there have been few investigations on the availability of dissolved inorganic carbon (DIC) for algal symbionts in hospite. This study compared the DIC-associated photosynthetic kinetic parameters of three Caribbean corals and their freshly isolated symbionts, as well as components of the DIC concentrating systems of both corals and symbionts. Species level differences were found in the extent of inorganic carbon saturation among the coral taxa studied. Only Orbicella faveolata was photosynthesizing at maximum rates under current seawater conditions, while Porites astreoides and Siderastrea radians were at or below half DIC saturation. O. faveolata also had significantly more external carbonic anhydrase activity, indicating that this species could produce more CO2 at the coral surface than P. astreoides or S. radians. In contrast and despite differences in Symbiodinium type, the symbionts of all the corals had a similar, very low DIC half saturation constant for photosynthesis and high levels of internal carbonic anhydrase activity, showing that they live in a carbon scarce environment and invest a great deal of energy in concentrating carbon at the site of photosynthesis. Considering the diffusional dynamics of the system and the relationship of host to symbiont kinetic parameters, the most likely cause of this scarcity is host regulation of DIC delivery to the symbionts.

Continue reading ‘Inorganic carbon is scarce for symbionts in scleractinian corals’

Physiological stress response associated with elevated CO2 and dissolved iron in a phytoplankton community dominated by the coccolithophore Emiliania huxleyi

We exposed a natural phytoplankton community to combined present (390 µatm, low carbon [LC]) and future CO2 levels predicted for the year 2100 (900 µatm, high carbon [HC]), and ambient (4.5 nM, -DFB [desferoxamine B]) and high (12 nM, +DFB) dissolved iron (dFe) levels, for 25 d in mesocosms. We report on the physiological response of the community dominated by the coccolithophore Emiliania huxleyi. The community structure shifted on Day 10, leading to 2 different phases (1 and 2), i.e. before and after Day 10, respectively. We focussed on the massive bloom of E. huxleyi that developed in Phase 2, in the LC+DFB treatment. In high dFe conditions, pigments and photosynthetic parameters increased compared to the control (LC-DFB). Cell death was only detected during the community shift (Days 10-12) and mostly increased in the presence of high CO2. The accumulation of reactive oxygen species (ROS) decreased under high dFe, pointing to an efficient, rather than a stressed, metabolism. DNA lesions, caused by excess irradiance, were minimised under high Fe. E. huxleyi is known for its low Fe requirements for growth. However, we demonstrate that Fe is essential to E. huxleyi for DNA repair and ROS management, and to maintain optimal functioning of the photosynthetic machinery, with implications for carbon cycling and future ecosystem functioning.

Continue reading ‘Physiological stress response associated with elevated CO2 and dissolved iron in a phytoplankton community dominated by the coccolithophore Emiliania huxleyi’


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Ocean acidification in the IPCC AR5 WG II

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