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Aquatic Microbial Ecology

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AME 79:137-147 (2017)  -  DOI:

Elevated CO2 and associated seawater chemistry do not benefit a model diatom grown with increased availability of light

Nana Liu1, John Beardall1,2, Kunshan Gao1,*

1State Key Laboratory of Marine Environmental Science/College of Ocean and Earth Sciences, Xiamen University, Xiang-An campus, Xiamen 361005, PR China
2School of Biological Sciences, Monash University, Clayton 3800, Victoria, Australia
*Corresponding author:

ABSTRACT: Elevated CO2 is leading to a decrease in pH in marine environments (ocean acidification [OA]), altering marine carbonate chemistry. OA can influence the metabolism of many marine organisms; however, no consensus has been reached on its effects on algal photosynthetic carbon fixation and primary production. Here, we found that when the diatom Phaeodactylum tricornutum was grown under different pCO2 levels, it showed different responses to elevated pCO2 levels under growth-limiting (20 µmol photons m-2 s-1, LL) compared with growth-saturating (200 µmol photons m-2 s-1, HL) light levels. With pCO2 increased up to 950 µatm, growth rates and primary productivity increased, but in the HL cells, these parameters decreased significantly at higher concentrations up to 5000 µatm, while no difference in growth was observed with pCO2 for the LL cells. Elevated CO2 concentrations reduced the size of the intracellular dissolved inorganic carbon (DIC) pool by 81% and 60% under the LL and HL levels, respectively, with the corresponding photosynthetic affinity for DIC decreasing by 48% and 55%. Little photoinhibition was observed across all treatments. These results suggest that the decreased growth rates under higher CO2 levels in the HL cells were most likely due to acid stress. Low energy demand of growth and energy saving from the down-regulation of the CO2 concentrating mechanisms (CCM) minimized the effects of acid stress on the growth of the LL cells. These findings imply that OA treatment, except for down-regulating CCM, caused stress on the diatom, reflected in diminished C assimilation and growth rates.

KEY WORDS: Ocean acidification · Intracellular DIC · Photosynthesis

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Cite this article as: Liu N, Beardall J, Gao K (2017) Elevated CO2 and associated seawater chemistry do not benefit a model diatom grown with increased availability of light. Aquat Microb Ecol 79:137-147.

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