title: Ocean acidification alters the photosynthetic responses of a coccolithophorid to fluctuating ultraviolet and visible radiation.
abstract: Mixing of seawater subjects phytoplankton to fluctuations in photosynthetically active radiation (400-700 nm) and ultraviolet radiation (UVR; 280-400 nm). These irradiance fluctuations are now superimposed upon ocean acidification and thinning of the upper mixing layer through stratification, which alters mixing regimes. Therefore, we examined the photosynthetic carbon fixation and photochemical performance of a coccolithophore, Gephyrocapsa oceanica, grown under high, future (1,000 μatm) and low, current (390 μatm) CO₂ levels, under regimes of fluctuating irradiances with or without UVR. Under both CO₂ levels, fluctuating irradiances, as compared with constant irradiance, led to lower nonphotochemical quenching and less UVR-induced inhibition of carbon fixation and photosystem II electron transport. The cells grown under high CO₂ showed a lower photosynthetic carbon fixation rate but lower nonphotochemical quenching and less ultraviolet B (280-315 nm)-induced inhibition. Ultraviolet A (315-400 nm) led to less enhancement of the photosynthetic carbon fixation in the high-CO₂-grown cells under fluctuating irradiance. Our data suggest that ocean acidification and fast mixing or fluctuation of solar radiation will act synergistically to lower carbon fixation by G. oceanica, although ocean acidification may decrease ultraviolet B-related photochemical inhibition.
authors.affiliation: State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Jin
authors.forename: Kunshan
authors.initials: K
authors.lastname: Gao
authors.forename: Virginia E
authors.initials: VE
authors.lastname: Villafañe
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Campbell
authors.forename: E Walter
authors.initials: EW
authors.lastname: Helbling
mesh_terms: D000042:Absorption; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D058087:Haptophyta / Q000502:physiology*; D008027:Light; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010839:Phytoplankton / Q000502:physiology; D012623:Seawater / Q000737:chemistry; D014466:Ultraviolet Rays
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D002245:Carbon Dioxide; D002244:Carbon; D000077194:Chlorophyll A