Posts Tagged 'light'

Effects of CO2 supply on growth and photosynthetic ability of young sporophytes of the economic seaweed Sargassum fusiforme (Sargassaceae, Phaeophyta)

Young sporophytes of Sargassum fusiforme were cultured at decreased CO2 (20 μatm), ambient CO2 (400 μatm), and high CO2 (1000 μatm), and then the quantum efficiency of open photosystem II (Fv′/Fm′), initial slope of the rapid light curves (α), and relative maximum photosynthetic electron transport rate (rETRm) of the algae under different temperatures and light levels were measured. The study aimed to investigate how the decreased CO2 and high CO2 supply affected the growth and photosynthetic functions of S. fusiforme young sporophytes. While both lowered and increased CO2 supply significantly reduced the growth rates of the alga, greater declines were observed under decreased CO2. The Fv′/Fm′, α, and rETRm of alga remained stable after short-term (120 min) exposures to 18, 22, and 26 °C, as well as to highlight (300 μmol photons m−2 s−1), with no significant difference among the three CO2 supply treatments. Hence, neither decreased nor increased CO2 affected the photosynthetic responses of S. fusiforme young sporophytes to temperature and high light. However, the Fv′/Fm′ of the three CO2 treatments declined by 72% under 60 μmol photons m−2 s−1, suggesting its sensitivity to short-term low light. These observations are crucial for the improved management of S. fusiforme for commercial farming, while ensuring its sustainable production and supply amid seawater pH shifts brought about by global climate change.

Continue reading ‘Effects of CO2 supply on growth and photosynthetic ability of young sporophytes of the economic seaweed Sargassum fusiforme (Sargassaceae, Phaeophyta)’

The role of irradiance and C-use strategies in tropical macroalgae photosynthetic response to ocean acidification

Fleshy macroalgae may increase photosynthesis with greater CO2 availability under ocean acidification (OA) and outcompete calcifying macroalgae important for tropical reef accretion. Macroalgae use energy-dependent carbon concentrating mechanisms (CCMs) to take up HCO3, the dominant inorganic carbon for marine photosynthesis, but carbon-use strategies may depend on the pCO2, pH and irradiance. We examined photosynthesis in eight tropical macroalgae across a range of irradiances (0–1200 μmol photon m−2 s−1), pH levels (7.5–8.5) and CO2 concentrations (3–43 μmol kg−1). Species-specific CCM strategies were assessed using inhibitors and δ13C isotope signatures. Our results indicate that the log of irradiance is a predictor of the photosynthetic response to elevated pCO2 (R2 > 0.95). All species utilized HCO3, exhibited diverse C-use pathways and demonstrated facultative HCO3 use. All fleshy species had positive photosynthetic responses to OA, in contrast to a split amongst calcifiers. We suggest that shifts in photosynthetically-driven tropical macroalgal changes due to OA will most likely occur in moderate to high-irradiance environments when CCMs are ineffective at meeting the C-demands of photosynthesis. Further, facultative use of HCO3 allows greater access to CO2 for photosynthesis under OA conditions, particularly amongst fleshy macroalgae, which could contribute to enhance fleshy species dominance over calcifiers.

Continue reading ‘The role of irradiance and C-use strategies in tropical macroalgae photosynthetic response to ocean acidification’

A three-dimensional niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica: reconciling observations with projections (update)

Coccolithophore responses to changes in carbonate chemistry speciation such as CO2 and H+ are highly modulated by light intensity and temperature. Here, we fit an analytical equation, accounting for simultaneous changes in carbonate chemistry speciation, light and temperature, to published and original data for Emiliania huxleyi, and compare the projections with those for Gephyrocapsa oceanica. Based on our analysis, the two most common bloom-forming species in present-day coccolithophore communities appear to be adapted for a similar fundamental light niche but slightly different ones for temperature and CO2, with E. huxleyi having a tolerance to lower temperatures and higher CO2 levels than G. oceanica. Based on growth rates, a dominance of E. huxleyi over G. oceanica is projected below temperatures of 22 °C at current atmospheric CO2 levels. This is similar to a global surface sediment compilation of E. huxleyi and G. oceanica coccolith abundances suggesting temperature-dependent dominance shifts. For a future Representative Concentration Pathway (RCP) 8.5 climate change scenario (1000 µatm fCO2), we project a CO2 driven niche contraction for G. oceanica to regions of even higher temperatures. However, the greater sensitivity of G. oceanica to increasing CO2 is partially mitigated by increasing temperatures. Finally, we compare satellite-derived particulate inorganic carbon estimates in the surface ocean with a recently proposed metric for potential coccolithophore success on the community level, i.e. the temperature-, light- and carbonate-chemistry-dependent CaCO3 production potential (CCPP). Based on E. huxleyi alone, as there was interestingly a better correlation than when in combination with G. oceanica, and excluding the Antarctic province from the analysis, we found a good correlation between CCPP and satellite-derived particulate inorganic carbon (PIC) with an R2 of 0.73, p < 0.01 and a slope of 1.03 for austral winter/boreal summer and an R2 of 0.85, p < 0.01 and a slope of 0.32 for austral summer/boreal winter.

Continue reading ‘A three-dimensional niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica: reconciling observations with projections (update)’

Ocean acidification conditions increase resilience of marine diatoms

The fate of diatoms in future acidified oceans could have dramatic implications on marine ecosystems, because they account for ~40% of marine primary production. Here, we quantify resilience of Thalassiosira pseudonana in mid-20th century (300 ppm CO2) and future (1000 ppm CO2) conditions that cause ocean acidification, using a stress test that probes its ability to recover from incrementally higher amount of low-dose ultraviolet A (UVA) and B (UVB) radiation and re-initiate growth in day–night cycles, limited by nitrogen. While all cultures eventually collapse, those growing at 300 ppm CO2 succumb sooner. The underlying mechanism for collapse appears to be a system failure resulting from “loss of relational resilience,” that is, inability to adopt physiological states matched to N-availability and phase of the diurnal cycle. Importantly, under elevated CO2 conditions diatoms sustain relational resilience over a longer timeframe, demonstrating increased resilience to future acidified ocean conditions. This stress test framework can be extended to evaluate and predict how various climate change associated stressors may impact microbial community resilience.

Continue reading ‘Ocean acidification conditions increase resilience of marine diatoms’

Ocean acidification stimulates particulate organic carbon accumulation in two Antarctic diatom species under moderate and high natural solar radiation

Impacts of rising atmospheric CO2 concentrations and increased daily irradiances from enhanced surface water stratification on phytoplankton physiology in the coastal Southern Ocean remain still unclear. Therefore, in the two Antarctic diatoms Fragilariopsis curta and Odontella weissflogii the effects of moderate and high natural solar radiation combined with either ambient or future pCO2 on cellular particulate organic carbon (POC) contents and photophysiology were investigated. Results showed that increasing CO2 concentrations had greater impacts on diatom physiology than exposure to increasing solar radiation. Irrespective of the applied solar radiation regime, cellular POC quotas increased with future pCO2 in both diatoms. Lowered maximum quantum yields of photochemistry in PSII (Fv/Fm) indicated a higher photosensitivity under these conditions, being counteracted by increased cellular concentrations of functional photosynthetic reaction centers. Overall, our results suggest that both bloom‐forming Antarctic coastal diatoms might increase carbon contents under future pCO2 conditions despite reduced physiological fitness. This indicates a higher potential for primary productivity by the two diatom species with important implications for the CO2 sequestration potential of diatom communities in the future coastal Southern Ocean.

Continue reading ‘Ocean acidification stimulates particulate organic carbon accumulation in two Antarctic diatom species under moderate and high natural solar radiation’

Combined effects of ocean acidification and warming on physiological response of the diatom Thalassiosira pseudonana to light challenges

Highlights

• Photoinactivation was induced by multiple environmental changes.
• Higher pCO2 alleviates the negative effect of temperature rise on PSII.
• Ocean acidification stimulates much faster PsbA removal.
• NPQ and SOD induction showed different response to temperature.

Abstract

Diatoms are one of the most important groups of phytoplankton in terms of abundance and ecological functionality in the ocean. They usually dominate the phytoplankton communities in coastal waters and experience frequent and large fluctuations in light. In order to evaluate the combined effects of ocean warming and acidification on the diatom’s exploitation of variable light environments, we grew a globally abundant diatom Thalassiosira pseudonana under two levels of temperature (18, 24 °C) and pCO2 (400, 1000 μatm) to examine its physiological performance after light challenge. It showed that the higher temperature increased the photoinactivation rate in T. pseudonana at 400 μatm pCO2, while the higher pCO2 alleviated the negative effect of the higher temperature on PSII photoinactivation. Higher pCO2 stimulated much faster PsbA removal, but it still lagged behind the photoinactivation of PSII under high light. Although the sustained phase of nonphotochemical quenching (NPQs) and activity of superoxide dismutase (SOD) were provoked during the high light exposure in T. pseudonana under the combined pCO2 and temperature conditions, it could not offset the damage caused by these multiple environmental changes, leading to decreased maximum photochemical yield.

Continue reading ‘Combined effects of ocean acidification and warming on physiological response of the diatom Thalassiosira pseudonana to light challenges’

Calcification moderates the increased susceptibility to UV radiation of the coccolithophorid Gephryocapsa oceanica grown under elevated CO2 concentration: evidence based on calcified and non‐calcified cells

The physiological performance of calcified and non‐calcified cells of Gephyrocapsa oceanica (NIES‐1318) and their short‐term responses to UV radiation were compared for cultures grown under present‐day (LC, 400 μatm) and high pCO2 (HC, 1000 μatm) conditions. Similar growth rates and Fv / Fm values were observed in both types of cell under LC conditions, indicating that the loss of calcification in the non‐calcified cell did not lead to a competitive disadvantage under such conditions. Detrimental effects of elevated pCO2 were observed in both cell types, with the growth rate of non‐calcified cells decreasing more markedly, which might reflect a negative impact of higher cytoplasmic H+. When exposed to short‐term UV radiation, similar trends in effective quantum yield were observed in both cell types acclimated to LC conditions. Elevated pCO2 and associated seawater chemical changes strongly reduced effective quantum yield in non‐calcified cells but no significant influence was observed in calcified cells. Based on these findings and comparisons with previous studies, we suggest that the negative impact of elevated cytoplasmic H+ would exacerbate the detrimental effects of UV radiation while the possession of calcification attenuated this influence.

Continue reading ‘Calcification moderates the increased susceptibility to UV radiation of the coccolithophorid Gephryocapsa oceanica grown under elevated CO2 concentration: evidence based on calcified and non‐calcified cells’


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Ocean acidification in the IPCC AR5 WG II

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