Effects of the pH/<i>p</i>CO<sub>2</sub> control method on medium chemistry and phytoplankton growth

Abstract

Abstract. The control of key chemical parameters in phytoplankton cultures, such as pCO 2 , pH and (the saturation state of calcium carbonate), is made difficult by the interdependence of these parameters and by the changes resulting from the growth of the organisms, such as CO 2 fixation, nutrient uptake and, for coccolithophores, calcite precipitation. Even in cultures where pCO 2 or pH is maintained constant, other chemical parameters change substantially at high cell densities. Experimentally we observed that various methods of adjustment of pCO 2 /pH -acid or base addition, use of buffers or pH-stats, or bubbling of CO 2 -enriched air -can be used, the choice of one or the other depending on the goals of the experiments. At seawater pH, we measured the same growth rates in cultures of the diatom Thalassiosira weissflogii where the pCO 2 /pH was controlled by these different methods. The pH/pCO 2 control method also did not affect the rates of growth or calcification of the coccolithophore Emiliania huxleyi at seawater pH. At lower pH/higher pCO 2 , in the E. huxleyi strain PLY M219, we observed increases in rates of carbon fixation and calcification per cell, along with a slight increase in growth rate, except in bubbled cultures. In our hands, the bubbling of cultures seemed to induce more variable results than other methods of pCO 2 /pH control. While highly convenient, the addition of pH buffers to the medium apparently induces changes in trace metal availability and cannot be used under trace metal-limiting conditions.

Effects of elevated CO<sub>2</sub> and temperature on phytoplankton community biomass, species composition and photosynthesis during an experimentally induced autumn bloom in the western English Channel

“…CO 2 -enriched seawater was added to the high-CO 2 treatment replicates every 24 h, acclimating the natural phytoplankton population to increments of elevated pCO 2 from ambient to ∼ 800 µatm over 8 days followed by maintenance at ∼ 800 µatm as per the method described by Schulz et al (2009). Adding CO 2 -enriched seawater is the preferred protocol, since some phytoplankton species are inhibited by the mechanical effects of direct bubbling (Riebesell et al, 2010;Shi et al, 2009), which causes a reduction in growth rates and the formation of aggregates (Love et al, 2016). pH was monitored daily to adjust the pCO 2 of the experimental media (+/−) prior to dilutions to maintain target pCO 2 levels in the incubation bottles.…”

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

“…Estimates of CO 2 tolerance under laboratory conditions may also be influenced by experimental acclimation periods (Trimborn et al, 2014;Hennon et al, 2015;Torstensson et al, 2015;Li et al, 2017a), differences in experimental conditions (e.g. nutrients, light climate) (Hoppe et al, 2015;Hong et al, 2017;Li et al, 2017b), methods of CO 2 manipulation (Shi et al, 2009;Gattuso et al, 2010), and region-specific environmental adaptations (Schaum et al, 2012). Thus, investigations on natural communities are essential in order to better understand the outcome of these complex interactions.…”

Ocean Acidification Alters the Photosynthetic Responses of a Coccolithophorid to Fluctuating Ultraviolet and Visible Radiation

“…Ocean acidification generally decreases calcification by coccolithophores (Riebesell et al, 2000;Zondervan et al, 2002;Delille et al, 2005;Beaufort et al, 2011) and other calcifying algae (Gao and Zheng, 2010;Sinutok et al, 2011), with responses differing across species or different environmental conditions (Langer et al, 2006(Langer et al, , 2009Iglesias-Rodriguez et al, 2008;Doney et al, 2009;Shi et al, 2009). Algal calcification, in turn, influences the impacts of solar ultraviolet radiation (UVR; 280-400 nm) on the algae's photophysiology Gao and Zheng, 2010;Guan and Gao, 2010).…”