title: Dissecting the impact of CO2 and pH on the mechanisms of photosynthesis and calcification in the coccolithophore Emiliania huxleyi.
abstract: Coccolithophores are important calcifying phytoplankton predicted to be impacted by changes in ocean carbonate chemistry caused by the absorption of anthropogenic CO2 . However, it is difficult to disentangle the effects of the simultaneously changing carbonate system parameters (CO2 , bicarbonate, carbonate and protons) on the physiological responses to elevated CO2 . Here, we adopted a multifactorial approach at constant pH or CO2 whilst varying dissolved inorganic carbon (DIC) to determine physiological and transcriptional responses to individual carbonate system parameters. We show that Emiliania huxleyi is sensitive to low CO2 (growth and photosynthesis) and low bicarbonate (calcification) as well as low pH beyond a limited tolerance range, but is much less sensitive to elevated CO2 and bicarbonate. Multiple up-regulated genes at low DIC bear the hallmarks of a carbon-concentrating mechanism (CCM) that is responsive to CO2 and bicarbonate but not to pH. Emiliania huxleyi appears to have evolved mechanisms to respond to limiting rather than elevated CO2 . Calcification does not function as a CCM, but is inhibited at low DIC to allow the redistribution of DIC from calcification to photosynthesis. The presented data provides a significant step in understanding how E. huxleyi will respond to changing carbonate chemistry at a cellular level.
authors.affiliation: Helmholtz-Zentrum für Ozeanforschung Kiel (GEOMAR), D-24105, Kiel, Germany.
authors.forename: Lennart T
authors.initials: LT
authors.lastname: Bach
authors.affiliation: Helmholtz-Zentrum für Ozeanforschung Kiel (GEOMAR), D-24105, Kiel, Germany.|Marine Biological Association of the UK, The Laboratory, Citadel Hill, Plymouth, PL1 2PB, UK.
authors.forename: Luke C M
authors.initials: LCM
authors.lastname: Mackinder
authors.affiliation: Helmholtz-Zentrum für Ozeanforschung Kiel (GEOMAR), D-24105, Kiel, Germany.
authors.forename: Kai G
authors.initials: KG
authors.lastname: Schulz
authors.affiliation: Marine Biological Association of the UK, The Laboratory, Citadel Hill, Plymouth, PL1 2PB, UK.|Plymouth Marine Laboratory, Prospect Place, Plymouth, PL1 3DH, UK.
authors.forename: Glen
authors.initials: G
authors.lastname: Wheeler
authors.affiliation: Marine Biological Association of the UK, The Laboratory, Citadel Hill, Plymouth, PL1 2PB, UK.
authors.forename: Declan C
authors.initials: DC
authors.lastname: Schroeder
authors.affiliation: Marine Biological Association of the UK, The Laboratory, Citadel Hill, Plymouth, PL1 2PB, UK.
authors.forename: Colin
authors.initials: C
authors.lastname: Brownlee
authors.affiliation: Helmholtz-Zentrum für Ozeanforschung Kiel (GEOMAR), D-24105, Kiel, Germany.
authors.forename: Ulf
authors.initials: U
authors.lastname: Riebesell
mesh_terms: D001639:Bicarbonates / Q000378:metabolism; D002113:Calcification, Physiologic; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide; D005786:Gene Expression Regulation; D058087:Haptophyta / Q000254:growth & development / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D009792:Oceans and Seas; D010788:Photosynthesis; D010839:Phytoplankton / Q000502:physiology; D012623:Seawater
chemical_list: D001639:Bicarbonates; D002245:Carbon Dioxide; D002244:Carbon