Faculty Opinions recommendation of Evolutionary temperature compensation of carbon fixation in marine phytoplankton.

Previous studies have shown that reduced levels of solar UV radiation (280–400 nm) can enhance photosynthetic carbon fixation of marine phytoplankton, but the mechanisms are not known. The supply of CO2 for photosynthesis is facilitated by extracellular (periplasmic) carbonic anhydrase (CAe) in most marine phytoplankton species. The present study showed that the CAe activity of Skeletonema costatum (Greville) Cleve was stimulated when treated with UV-A (320–395 nm) or UV-A + UV-B (295–320 nm) in addition to visible radiation. The presence of UV-A and UV-B enhanced the activity by 28% and 24%, respectively, at a low irradiance (PAR 161, UV-A 28, UV-B 0.9 W m−2) and by 21% and 19%, respectively, at a high irradiance (PAR 328, UV-A 58, UV-B 1.9 W m−2) level after exposure for 1 h. Ultraviolet radiation stimulated CAe activity contributed up to 6% of the photosynthetic carbon fixation as a result of the enhanced supply of CO2, as revealed using the CAe inhibitor (acetazolamide). As a result, there was less inhibition of photosynthetic carbon fixation compared with the apparent quantum yield of PSII. The UV radiation stimulated CAe activity coincided with the enhanced redox activity at the plasma membrane in the presence of UV-A and/or UV-B. The present study showed that UV radiation can enhance CAe activity, which plays an important role in counteracting UV inhibition of photosynthesis.

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Nitrate uptake in marine phytoplankton: Energy sources and the interaction with carbon fixation

Marine Biology ◽

10.1007/bf00395161 ◽

1975 ◽

Vol 32 (1) ◽

pp. 77-84 ◽

Cited By ~ 92

Author(s):

P. G. Falkowski ◽

D. P. Stone

Keyword(s):

Nitrate Uptake ◽

Carbon Fixation ◽

Marine Phytoplankton ◽

Energy Sources

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Physiological and biochemical responses of <i>Emiliania huxleyi</i> to ocean acidification and warming are modulated by UV radiation

10.5194/bg-2017-269 ◽

2017 ◽

Cited By ~ 1

Author(s):

Shanying Tong ◽

David A. Hutchins ◽

Kunshan Gao

Keyword(s):

Ocean Acidification ◽

Uv Radiation ◽

Carbon Fixation ◽

Co2 Concentration ◽

Emiliania Huxleyi ◽

Marine Phytoplankton ◽

Negative Effects ◽

Photosynthetic Carbon Fixation ◽

Photosynthetic Carbon ◽

Increasing Temperature

Abstract. Marine phytoplankton such as bloom-forming, calcite-producing coccolithophores, are naturally exposed to solar UV radiation (UVR, 280–400 nm) in the ocean's upper mixed layers. Nevertheless, effects of increasing CO2-induced ocean acidification and warming have rarely been investigated in the presence of UVR. We examined calcification and photosynthetic carbon fixation performance in the most cosmopolitan coccolithophorid, Emiliania huxleyi, grown under high (1000 μatm, HC; pHT: 7.70) and low (400 μatm, LC; pHT: 8.02) CO2 levels, at 15 °C (LT), 20 °C (MT) and 24 °C (HT) with or without UVR. The HC treatment didn't affect photosynthetic carbon fixation at 15 °C, but significantly enhanced it with increasing temperature. Exposure to UVR inhibited photosynthesis, with higher inhibition by UVA (320–395 nm) than UVB (295–320 nm), except in the HC and 24 °C-grown cells, in which UVB caused more inhibition than UVA. Reduced thickness of the coccolith layer in the HC-grown cells appeared to be responsible for the UV-induced inhibition, and an increased repair rate of UVA-derived damage in the HCHT-grown cells could be responsible for lowered UVA-induced inhibition. While calcification was reduced with the elevated CO2 concentration, exposure to UVB or UVA affected it differentially, with the former inhibiting and the latter enhancing it. UVA-induced stimulation of calcification was higher in the HC-grown cells at 15 and 20 °C, whereas at 24 °C, observed enhancement was not significant. The calcification to photosynthesis ratio (Cal / Pho ratio) was lower in the HC treatment, and increasing temperature also lowered the value. However, at 20 and 24 °C, exposures to UVR significantly increased the Cal / Pho ratio, especially in HC-grown cells, by up to 100 %. This implies that UVR can counteract the negative effects of the greenhouse treatment on the Cal / Pho ratio, and so may be a key stressor when considering the impacts of future greenhouse conditions on E. huxleyi.

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Carbon fixation and carbon availability in marine phytoplankton

Photosynthesis Research ◽

10.1007/bf00014587 ◽

1994 ◽

Vol 39 (3) ◽

pp. 259-273 ◽

Cited By ~ 29

Author(s):

John A. Raven

Keyword(s):

Carbon Fixation ◽

Marine Phytoplankton ◽

Carbon Availability

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Diurnal regulation of photosynthetic light absorption, electron transport and carbon fixation in two contrasting oceanic environments

Biogeosciences ◽

10.5194/bg-16-1381-2019 ◽

2019 ◽

Vol 16 (7) ◽

pp. 1381-1399 ◽

Cited By ~ 8

Author(s):

Nina Schuback ◽

Philippe D. Tortell

Keyword(s):

Electron Transport ◽

Light Absorption ◽

Carbon Fixation ◽

Spatial Scales ◽

Marine Phytoplankton ◽

Optical Data ◽

Reaction Centre ◽

Phytoplankton Productivity ◽

Ne Pacific ◽

Insight Into

Abstract. Understanding the dynamics of marine phytoplankton productivity requires mechanistic insight into the non-linear coupling of light absorption, photosynthetic electron transport and carbon fixation in response to environmental variability. In the present study, we examined the variability of phytoplankton light absorption characteristics, light-dependent electron transport and 14C-uptake rates over a 48 h period in the coastal subarctic north-east (NE) Pacific. We observed an intricately coordinated response of the different components of the photosynthetic process to diurnal irradiance cycles, which acted to maximize carbon fixation, while simultaneously preventing damage by excess absorbed light energy. In particular, we found diurnal adjustments in pigment ratios, excitation energy transfer to reaction centre II (RCII), the capacity for non-photochemical quenching (NPQ), and the light efficiency (α) and maximum rates (Pmax) of RCII electron transport (ETRRCII) and 14C uptake. Comparison of these results from coastal waters to previous observations in offshore waters of the subarctic NE Pacific provides insight into the effects of iron limitation on the optimization of photosynthesis. Under iron-limited, low-biomass conditions, there was a significant reduction of iron-rich photosynthetic units per chlorophyll a, which was partly offset by higher light absorption and electron transport per photosystem II (PSII). Iron deficiency limited the capacity of phytoplankton to utilize peak midday irradiance for carbon fixation and caused an upregulation of photoprotective mechanisms, including NPQ, and the decoupling of light absorption, electron transport and carbon fixation. Such decoupling resulted in an increased electron requirement (Φe,C) and decreased quantum efficiency (ΦC) of carbon fixation at the iron-limited station. In both coastal and offshore waters, Φe,C and ΦC correlated strongly to NPQ, albeit with a significantly different slope. We discuss the implications of our results for the interpretation of bio-optical data and the parameterization of numerical productivity models, both of which are vital tools in monitoring marine photosynthesis over large temporal and spatial scales.

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Physiological and biochemical responses of <i>Emiliania huxleyi</i> to ocean acidification and warming are modulated by UV radiation

Biogeosciences ◽

10.5194/bg-16-561-2019 ◽

2019 ◽

Vol 16 (2) ◽

pp. 561-572 ◽

Cited By ~ 5

Author(s):

Shanying Tong ◽

David A. Hutchins ◽

Kunshan Gao

Keyword(s):

Ocean Acidification ◽

Carbon Fixation ◽

Co2 Concentration ◽

Emiliania Huxleyi ◽

Marine Phytoplankton ◽

Negative Effects ◽

Solar Ultraviolet Radiation ◽

Photosynthetic Carbon Fixation ◽

Photosynthetic Carbon ◽

Increasing Temperature

Abstract. Marine phytoplankton such as bloom-forming, calcite-producing coccolithophores, are naturally exposed to solar ultraviolet radiation (UVR, 280–400 nm) in the ocean's upper mixed layers. Nevertheless, the effects of increasing carbon dioxide (CO2)-induced ocean acidification and warming have rarely been investigated in the presence of UVR. We examined calcification and photosynthetic carbon fixation performance in the most cosmopolitan coccolithophorid, Emiliania huxleyi, grown under high (1000 µatm, HC; pHT: 7.70) and low (400 µatm, LC; pHT: 8.02) CO2 levels, at 15 ∘C, 20 ∘C and 24 ∘C with or without UVR. The HC treatment did not affect photosynthetic carbon fixation at 15 ∘C, but significantly enhanced it with increasing temperature. Exposure to UVR inhibited photosynthesis, with higher inhibition by UVA (320–395 nm) than UVB (295–320 nm), except in the HC and 24 ∘C-grown cells, in which UVB caused more inhibition than UVA. A reduced thickness of the coccolith layer in the HC-grown cells appeared to be responsible for the UV-induced inhibition, and an increased repair rate of UVA-derived damage in the HC–high-temperature grown cells could be responsible for lowered UVA-induced inhibition. While calcification was reduced with elevated CO2 concentration, exposure to UVB or UVA affected the process differentially, with the former inhibiting it and the latter enhancing it. UVA-induced stimulation of calcification was higher in the HC-grown cells at 15 and 20 ∘C, whereas at 24 ∘C observed enhancement was not significant. The calcification to photosynthesis ratio (Cal ∕ Pho ratio) was lower in the HC treatment, and increasing temperature also lowered the value. However, at 20 and 24 ∘C, exposure to UVR significantly increased the Cal ∕ Pho ratio, especially in HC-grown cells, by up to 100 %. This implies that UVR can counteract the negative effects of the “greenhouse” treatment on the Cal ∕ Pho ratio; hence, UVR may be a key stressor when considering the impacts of future greenhouse conditions on E. huxleyi.

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Significant organic carbon acquisition by Prochlorococcus in the oceans

10.1101/2022.01.14.476346 ◽

2022 ◽

Author(s):

Zhen Wu ◽

Dikla Aharonovich ◽

Dalit Roth-Rosenberg ◽

Osnat Weissberg ◽

Tal Luzzatto-Knaan ◽

...

Keyword(s):

Organic Carbon ◽

Growth Rates ◽

Carbon Fixation ◽

Eastern Mediterranean ◽

Large Fraction ◽

Carbon Sources ◽

Marine Phytoplankton ◽

Relative Contribution ◽

The Pacific ◽

Ecological Success

Marine phytoplankton are responsible for about half of the photosynthesis on Earth. Many are mixotrophs, combining photosynthesis with heterotrophic assimilation of organic carbon but the relative contribution of these two carbon sources is not well quantified. Here, single-cell measurements reveal that Prochlorococcus at the base of the photic zone in the Eastern Mediterranean Sea are obtaining only ~20% of carbon required for growth by photosynthesis. Consistently, laboratory-calibrated evaluations of Prochlorococcus photosynthesis indicate that carbon fixation is systematically too low to support published in situ growth rates in the deep photic layer of the Pacific Ocean. Furthermore, agent-based model simulations show that mixotrophic cells maintain realistic growth rates and populations 10s of meters deeper than obligate photo-autotrophs, deepening the nutricline and Deep Chlorophyll Maximum by ~20 m. Time-series of Prochlorococcus ecotype-abundance from the subtropical North Atlantic and North Pacific suggest that up to 30% of the Prochlorococcus cells live where light intensity is not enough to sustain obligate photo-autotrophic populations during warm, stratified periods. Together, these data and models suggest that mixotrophy underpins the ecological success of a large fraction of the global Prochlorococcus population and its collective genetic diversity.

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