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.

Ocean acidification of a coastal Antarctic marine microbial community reveals a critical threshold for CO<sub>2</sub> tolerance in phytoplankton productivity

“…5). Acclimation to increased CO 2 has been reported in a number of studies, resulting in shifts in carbon and energy utilisation (Sobrino et al, 2008;Hopkinson et al, 2010;Hennon et al, 2014;Trimborn et al, 2014;Zheng et al, 2015). Numerous photophysiological investigations on individual phytoplankton species also report species-specific tolerances to increased CO 2 (Gao et al, 2012a;Gao and Campbell, 2014;Trimborn et al, 2013Trimborn et al, , 2014, and a general trend toward smaller-celled communities with increased CO 2 has been reported in ocean acidification studies globally .…”

“…Thus far, respiration rates are commonly reported as either unaffected or lower under increasing CO 2 (Hennon et al, 2014;Trimborn et al, 2014;Spilling et al, 2016). This effect is generally attributed to declines in cellular energy requirements via processes such as the down-regulation of CCMs, which can result in observed increased rates of production (Spilling et al, 2016).…”

Interactive effects of ocean acidification and nitrogen limitation on two bloom-forming dinoflagellate species

“…While the combined effects of elevated pCO 2 and N limitation have been assessed in diatoms (Li et al 2012, Hennon et al 2014) and coccolithophores (Sciandra et al 2003, Rouco et al 2013, dinoflagellates have so far been largely overlooked. Yet, they are expected to be highly sensitive to changes in CO 2 availability due to their type II ribulose 1, 5-bisphosphate carboxylase/oxygenase (RuBisCO), which features low affinities for its substrate CO 2 (Morse et al 1995, Badger et al 1998.…”

Interactions of anthropogenic stress factors on marine phytoplankton

“…However, such interaction was not observed in the coccolithophore Emiliania huxleyi (Jin, Gao et al unpublished data). Ocean acidification may increase (Wu et al, 2010;Yang and Gao, 2012) or decrease (Hennon et al, 2014) mitochondrial respiration, increase photorespiration (Gao et al, 2012b;Xu and Gao, 2012) and influence the photophysiology of phytoplankton (Gao and Campbell, 2014). In the South China Sea, surface phytoplankton assemblages were found to assimilate less carbon either based on chl a or based on per volume of seawater under elevated CO 2 levels of 800 or 1000 µatm, with their nonphotochemical (Figure 2) (Gao et al, 2012b), after acclimation to the CO 2 -induced acidification for about a week.…”