title: Ocean acidification decreases the light-use efficiency in an Antarctic diatom under dynamic but not constant light.
abstract: There is increasing evidence that different light intensities strongly modulate the effects of ocean acidification (OA) on marine phytoplankton. The aim of the present study was to investigate interactive effects of OA and dynamic light, mimicking natural mixing regimes. The Antarctic diatom Chaetoceros debilis was grown under two pCO2 (390 and 1000 μatm) and light conditions (constant and dynamic), the latter yielding the same integrated irradiance over the day. To characterize interactive effects between treatments, growth, elemental composition, primary production and photophysiology were investigated. Dynamic light reduced growth and strongly altered the effects of OA on primary production, being unaffected by elevated pCO2 under constant light, yet significantly reduced under dynamic light. Interactive effects between OA and light were also observed for Chl production and particulate organic carbon quotas. Response patterns can be explained by changes in the cellular energetic balance. While the energy transfer efficiency from photochemistry to biomass production (Φe,C ) was not affected by OA under constant light, it was drastically reduced under dynamic light. Contrasting responses under different light conditions need to be considered when making predictions regarding a more stratified and acidified future ocean.
authors.affiliation: Alfred Wegener Institute - Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, Bremerhaven, 27570, Germany.
authors.forename: Clara J M
authors.initials: CJM
authors.lastname: Hoppe
authors.affiliation: Alfred Wegener Institute - Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, Bremerhaven, 27570, Germany.
authors.forename: Lena-Maria
authors.initials: LM
authors.lastname: Holtz
authors.affiliation: Alfred Wegener Institute - Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, Bremerhaven, 27570, Germany.|University Bremen, Leobener Straße NW2-A, Bremen, 28359, Germany.
authors.forename: Scarlett
authors.initials: S
authors.lastname: Trimborn
authors.affiliation: Alfred Wegener Institute - Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, Bremerhaven, 27570, Germany.
authors.forename: Björn
authors.initials: B
authors.lastname: Rost
mesh_terms: D000143:Acids / Q000378:metabolism*; D000864:Antarctic Regions; D002734:Chlorophyll / Q000378:metabolism; D017377:Diatoms / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects*; D004579:Electron Transport / Q000528:radiation effects; D004602:Elements; D005453:Fluorescence; D008027:Light; D009792:Oceans and Seas; D012623:Seawater / Q000737:chemistry
chemical_list: D000143:Acids; D004602:Elements; D002734:Chlorophyll
keywords: CO
  2; Chaetoceros debilis; Southern Ocean; multiple stressors; photophysiology; phytoplankton; primary production