Strong shift from HCO3 − to CO2 uptake in Emiliania huxleyi with acidification: new approach unravels acclimation versus short-term pH effects

Abstract

Effects of ocean acidification on Emiliania huxleyi strain RCC 1216 (calcifying, diploid life-cycle stage) and RCC 1217 (non-calcifying, haploid life-cycle stage) were investigated by measuring growth, elemental composition, and production rates under different pCO2 levels (380 and 950 μatm). In these differently acclimated cells, the photosynthetic carbon source was assessed by a 14C disequilibrium assay, conducted over a range of ecologically relevant pH values (7.9–8.7). In agreement with previous studies, we observed decreased calcification and stimulated biomass production in diploid cells under high pCO2, but no CO2-dependent changes in biomass production for haploid cells. In both life-cycle stages, the relative contributions of CO2 and HCO3− uptake depended strongly on the assay pH. At pH values ≤ 8.1, cells preferentially used CO2 (≥ 90 % CO2), whereas at pH values ≥ 8.3, cells progressively increased the fraction of HCO3− uptake (~45 % CO2 at pH 8.7 in diploid cells; ~55 % CO2 at pH 8.5 in haploid cells). In contrast to the short-term effect of the assay pH, the pCO2 acclimation history had no significant effect on the carbon uptake behavior. A numerical sensitivity study confirmed that the pH-modification in the 14C disequilibrium method yields reliable results, provided that model parameters (e.g., pH, temperature) are kept within typical measurement uncertainties. Our results demonstrate a high plasticity of E. huxleyi to rapidly adjust carbon acquisition to the external carbon supply and/or pH, and provide an explanation for the paradoxical observation of high CO2 sensitivity despite the apparently high HCO3− usage seen in previous studies.Electronic supplementary materialThe online version of this article (doi:10.1007/s11120-014-9984-9) contains supplementary material, which is available to authorized users.

Vanishing coccolith vital effects with alleviated carbon limitation

“…Cell division rates at pre-industrial DIC levels (∼ 2 mmol kg −1 ) are similar to those found in the published literature (Langer et al, 2006(Langer et al, , 2009Rickaby et al, 2010;Bach et al, 2013;Candelier et al, 2013;Hermoso et al, 2014;Kottmeier et al, 2014;Sett et al, 2014). Emiliania huxleyi is the fastest grower for the smaller cell size, achieving about one division per day (µ ∼ 0.7 day −1 ) ( Fig.…”

Decline in Coccolithophore Diversity and Impact on Coccolith Morphogenesis Along a Natural CO2 Gradient

“…Coccolith malformation and dissolution occurs when pH is lowered in culture experiments (Bach et al, 2012;Kottmeier et al, 2014), and our results are the first evidence of this effect in natural coccolithophore assemblages. The fall in coccolithophore diversity and cell concentration pattern as CO 2 levels increased is not explained by dissolution of the assemblage at the seep.…”

Ocean acidification has different effects on the production of dimethylsulfide and dimethylsulfoniopropionate measured in cultures of Emiliania huxleyi and a mesocosm study: a comparison of laboratory monocultures and community interactions

“…A previous mesocosm experiment identified decreased net specific growth rate from 0.5 to 0.43 day À1 in the highest pCO 2 mesocosms, [72] and the reduced haptophyte equivalent Chl-a concentrations and calcified E. huxleyi abundance values seen in our medium and high pCO 2 mesocosms support this. However, in the laboratory, varying responses have been identified for different E. huxleyi strains where growth rates either increased, [9,70,73] remained unchanged as in this study [65,69,74] or decreased. [66,75,76] Specific growth rates during the E. huxleyi RCC1229 experiment were lower (0.48 day À1 for the 900 matm pCO 2 treatment and 0.47 day À1 for the ambient CO 2 control) than found previously for that strain under near-identical growth conditions at the same …”