16 Jan 2018
 | 16 Jan 2018
Status: this preprint was under review for the journal BG but the revision was not accepted.

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

Yong Zhang, Feixue Fu, David A. Hutchins, and Kunshan Gao

Abstract. 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.

Yong Zhang et al.

Yong Zhang et al.

Yong Zhang et al.


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Short summary
To investigate responses of the calcifying E. huxleyi to multiple environmental factors, we investigated its growth, POC and PIC quotas and photosynthesis parameter at different levels of CO2, light, dissolved inorganic nitrogen and phosphate concentrations. High CO2 (HC) and low nitrogen (LN) synergistically decreased growth rates, high light compensated for inhibition of low phosphate (LP) on growth rates at LC, but exacerbated inhibition of LP at HC. LN or LP increased PIC quotas and ETRmax.