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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-4
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-4
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 15 Feb 2019

Submitted as: research article | 15 Feb 2019

Review status
This discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The revised manuscript was not accepted.

Hyposalinity tolerance inthecoccolithophorid Emiliania huxleyi under the influence of ocean acidification involves enhanced photosynthetic performance

Jiekai Xu1, John Beardall2, and Kunshan Gao1,3 Jiekai Xu et al.
  • 1State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China
  • 2School of Biological Sciences, Monash University, Clayton, VIC. 3800, Australia
  • 3Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China

Abstract. While seawater acidification induced by elevated CO2 is known to impact coccolithophores, the effects in combination with decreased salinity caused by sea ice melting and/or hydrological events have not been documented. Here we show the combined effects of seawater acidification and reduced salinity on growth, photosynthesis and calcification of Emiliania huxleyi grown at 2 CO2 concentrations (low CO2 LC: 400 μatm; high CO2 HC: 1000 μatm) and 3 levels of salinity (25, 30 and 35 ‰). A decrease of salinity from 35 to 25‰ increased growth rate, cell size and effective photochemical efficiency under both LC or HC. Calcification rates were relatively insensitive to combined effects of salinity and OA treatment but were highest under 3 5‰ and HC conditions, with higher ratios of calcification to photosynthesis (C : P) in the cells grown under 35 ‰ compared with those grown at 25 ‰. In addition, elevated dissolved inorganic carbon (DIC) concentration at the salinity of 35 ‰ stimulated its calcification. In contrast, photosynthetic carbon fixation increased almost linearly with decreasing salinity, regardless of the pCO2 treatments. When subjected to short-term exposure to high light, the low-salinity-grown cells showed the highest photochemical effective quantum yield with the highest repair rate, though HC treatment enhanced PSII damage rate. Our results suggest Emiliania huxleyi can tolerate low salinity plus acidification conditions by up-regulating its photosynthetic performance together with a relatively insensitive calcification response, which may help it better adapt to future ocean global environmental changes, especially in the coastal areas of high latitudes.

Jiekai Xu et al.
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AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Jiekai Xu et al.
Jiekai Xu et al.
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Short summary
A lot of papers studying Ocean acidification (OA) have been published while no related reports can be found on the combined effects of OA with decreased salinity on coccolithophores yet.Thus, we investigated the physiological responses of an Emiliania huxleyi strain grown at 2CO2 concentrations and 3 levels of salinity and found cells could tolerate reduced salinity under OA as its increased light capturing capability, which suggests a potential niche extension of coccolithophores in the future.
A lot of papers studying Ocean acidification (OA) have been published while no related reports...
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