title: Influence of light history on the photosynthetic and motility responses of Gymnodinium chlorophorum exposed to UVR and different temperatures.
abstract: In the wake of global climate change, phytoplankton productivity and species composition is expected to change due to altered external conditions such as temperature, nutrient accessibility, pH and exposure to solar visible (PAR) and ultraviolet radiation (UVR). The previous light history is also of importance for the performance of phytoplankton cells. In order to assess the combined impacts of UVR and temperature on the dinoflagellate Gymnodinium chlorophorum we analyzed the effective photochemical quantum yield (Y), relative electron transport rate vs. irradiance curves (rETR vs. I), percentage of motile cells and swimming velocity. Cells were grown at three different temperatures (15, 20 and 25 °C) and two PAR intensities: low light (LL, 100 μmol photons m(-2) s(-1)) and high light (HL, 250 μmol photons m(-2) s(-1)). Pre-acclimated cells were then exposed to either PAR only (P), PAR+UV-A (PA) or PAR+UV-A+UV-B (PAB) radiation at two different irradiances, followed by a recovery period in darkness. The Y decreased during exposure, being least inhibited in P and most in PAB treatments. Inhibition was higher and recovery slower in LL-grown cells than in HL-grown cells at 15° and 20 °C, but the opposite occurred at 25 °C, when exposed to high irradiances. Maximal values of rETR were determined at t0 as compared to the different (before and after exposure) radiation treatments. The effects of temperature and UVR on rETR were antagonistic in LL-grown cells (i.e., less UVR inhibition at higher temperature), while it was synergistic in HL cells. Swimming velocity and percentage of motile cells were not affected at all tested temperatures and exposure regimes, independent of the light history. Our results indicate that, depending on the previous light history, increased temperature and UVR as predicted under climate change conditions, can have different interactions thus conditioning the photosynthetic response of G. chlorophorum.
authors.affiliation: Neue Str. 9, 91096 Möhrendorf, Germany. Electronic address: donat@dphaeder.de.
authors.forename: Donat-P
authors.initials: DP
authors.lastname: Häder
authors.affiliation: Friedrich-Alexander Universität, Department Biologie, Lehrstuhl für Zellbiologie, AG für Gravitationsbiologie, Staudtstr. 5, 90158 Erlangen, Germany. Electronic address: Peter.richter@fau.de.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Richter
authors.affiliation: ESTACIÓN de Fotobiología Playa Unión, Casilla de Correo 15, U9103ZAA Rawson, Chubut, Argentina. Electronic address: efpu@efpu.org.ar.
authors.forename: Virginia E
authors.initials: VE
authors.lastname: Villafañe
authors.affiliation: ESTACIÓN de Fotobiología Playa Unión, Casilla de Correo 15, U9103ZAA Rawson, Chubut, Argentina. Electronic address: whelbling@efpu.org.ar.
authors.forename: E Walter
authors.initials: EW
authors.lastname: Helbling
mesh_terms: D057231:Climate Change; D004141:Dinoflagellida / Q000502:physiology*; D004579:Electron Transport; D009043:Motor Activity / Q000528:radiation effects*; D010788:Photosynthesis / Q000528:radiation effects*; D011789:Quantum Theory; D013696:Temperature; D014466:Ultraviolet Rays
keywords: Effective photochemical quantum yield; Electron transport vs. irradiance; Global change; Gymnodinium chlorophorum; Temperature; UVR