title: Acclimation conditions modify physiological response of the diatom Thalassiosira pseudonana to elevated CO2 concentrations in a nitrate-limited chemostat.
abstract: Diatoms are responsible for a large proportion of global carbon fixation, with the possibility that they may fix more carbon under future levels of high CO2 . To determine how increased CO2 concentrations impact the physiology of the diatom Thalassiosira pseudonana Hasle et Heimdal, nitrate-limited chemostats were used to acclimate cells to a recent past (333 ± 6 μatm) and two projected future concentrations (476 ± 18 μatm, 816 ± 35 μatm) of CO2 . Samples were harvested under steady-state growth conditions after either an abrupt (15-16 generations) or a longer acclimation process (33-57 generations) to increased CO2 concentrations. The use of un-bubbled chemostat cultures allowed us to calculate the uptake ratio of dissolved inorganic carbon relative to dissolved inorganic nitrogen (DIC:DIN), which was strongly correlated with fCO2 in the shorter acclimations but not in the longer acclimations. Both CO2 treatment and acclimation time significantly affected the DIC:DIN uptake ratio. Chlorophyll a per cell decreased under elevated CO2 and the rates of photosynthesis and respiration decreased significantly under higher levels of CO2 . These results suggest that T. pseudonana shifts carbon and energy fluxes in response to high CO2 and that acclimation time has a strong effect on the physiological response.
authors.affiliation: University of Washington - School of Oceanography, Seattle, Washington, 98105, USA.
authors.forename: Gwenn M M
authors.initials: GM
authors.lastname: Hennon
authors.affiliation: University of Washington - School of Oceanography, Seattle, Washington, 98105, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Quay
authors.affiliation: University of Washington - School of Oceanography, Seattle, Washington, 98105, USA.
authors.forename: Rhonda L
authors.initials: RL
authors.lastname: Morales
authors.affiliation: University of Washington - School of Oceanography, Seattle, Washington, 98105, USA.
authors.forename: Lyndsey M
authors.initials: LM
authors.lastname: Swanson
authors.affiliation: University of Washington - School of Oceanography, Seattle, Washington, 98105, USA.
authors.forename: E
authors.initials: E
authors.lastname: Virginia Armbrust
keywords: Thalassiosira pseudonana; acclimation; carbon dioxide; chemostat; diatom; ocean acidification; oxygen isotopes