title: Two Southern Ocean diatoms are more sensitive to ocean acidification and changes in irradiance than the prymnesiophyte Phaeocystis antarctica.
abstract: To better understand the impact of ocean acidification (OA) and changes in light availability on Southern Ocean phytoplankton physiology, we investigated the effects of pCO2(380 and 800 µatm) in combination with low and high irradiance (20 or 50 and 200 µmol photons m-2s-1) on growth, particulate organic carbon (POC) fixation and photophysiology in the three ecologically relevant species Chaetoceros debilis, Fragilariopsis kerguelensis and Phaeocystis antarctica. Irrespective of the light scenario, neither growth nor POC per cell was stimulated by OA in any of the tested species and the two diatoms even displayed negative responses in growth (e.g. C. debilis) or POC content (e.g. F. kerguelensis) under OA in conjunction with high light. For both diatoms, also maximum quantum yields of photosystem II (Fv/Fm) were decreased under these conditions, indicating lowered photochemical efficiencies. To counteract the negative effects by OA and high light, the two diatoms showed diverging photoacclimation strategies. While cellular chlorophyll a (Chl a) and fucoxanthin contents were enhanced in C. debilis to potentially maximize light absorption, F. kerguelensis exhibited reduced Chl a per cell, increased disconnection of antennae from photosystem II reaction centers and strongly lowered absolute electron transport rates (ETR). The decline in ETRs in F. kerguelensis might be explained in terms of different species-specific strategies for tuning the available flux of adenosine triphosphate and nicotinamide adenine dinucleotide phosphate. Overall, our results revealed that P. antarctica was more tolerant to OA and changes in irradiance than the two diatoms, which may have important implications for biogeochemical cycling.
authors.affiliation: Department of Biogeosciences, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, 27515, Germany.|Marine Botany, University of Bremen, Bremen, Germany.
authors.forename: Scarlett
authors.initials: S
authors.lastname: Trimborn
authors.affiliation: Department of Biogeosciences, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, 27515, Germany.
authors.forename: Silke
authors.initials: S
authors.lastname: Thoms
authors.affiliation: Department of Biogeosciences, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, 27515, Germany.
authors.forename: Tina
authors.initials: T
authors.lastname: Brenneis
authors.affiliation: Department of Biogeosciences, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, 27515, Germany.|Marine Botany, University of Bremen, Bremen, Germany.
authors.forename: Jasmin P
authors.initials: JP
authors.lastname: Heiden
authors.affiliation: Department of Biogeosciences, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, 27515, Germany.
authors.forename: Sara
authors.initials: S
authors.lastname: Beszteri
authors.affiliation: Marine Botany, University of Bremen, Bremen, Germany.
authors.forename: Kai
authors.initials: K
authors.lastname: Bischof
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002244:Carbon / Q000378:metabolism*; D002734:Chlorophyll / Q000031:analogs & derivatives / Q000378:metabolism; D017377:Diatoms / Q000378:metabolism*; D004579:Electron Transport / Q000502:physiology; D009249:NADP / Q000378:metabolism; D009792:Oceans and Seas; D010839:Phytoplankton / Q000378:metabolism; D024341:Xanthophylls / Q000378:metabolism
chemical_list: D024341:Xanthophylls; C025164:fucoxanthin; D002734:Chlorophyll; C085815:chlorophyll a'; D009249:NADP; D002244:Carbon; D000255:Adenosine Triphosphate