Effect of varying calcium concentrations and light intensities on calcification and photosynthesis in Emiliania huxleyi

Abstract

Various protective and metabolic functions for coccolithophore calcification have been proposed such as providing a means to supply CO 2 for photosynthesis. It has also been speculated that calcification helps to dissipate excess energy under high irradiance, thereby circumventing photoinhibition. To address these questions, cells of a calcifying strain of Emiliania huxleyi were grown at three irradiances (30, 300, and 800 mmol photons m 22 s 21 ) in combination with four calcium (Ca) concentrations (0.1, 1, 2.5, and 10 mmol L 21 ) leading to different degrees of calcification in the same strain. Growth rates (m), particulate organic carbon (POC), and inorganic carbon (PIC) production as well as carbon isotope fractionation (e p ) were determined. Photosynthetic O 2 evolution and CO 2 and HCO { 3 uptake rates were measured by membrane inlet mass spectrometry (MIMS). The application of this multimethod approach provides new information on the role of calcification in E. huxleyi. Noncalcifying cells showed POC production rates as high as calcifying ones. No differences in e p were observed under different Ca concentrations. MIMS measurements indicate that noncalcifying cells can photosynthesize as efficiently as, or even more efficiently than, calcifying ones and that both use HCO { 3 as the main carbon source. The ratio of photosynthetic HCO { 3 uptake relative to net fixation did not differ among cells acclimated to 10 mmol L 21 or to 0.1 mmol L 21 Ca. These results indicate that (1) calcification is not involved in photosynthetic carbon acquisition, and (2) calcification does not provide a means of energy dissipation under high irradiances.

Photosynthetic responses of <i>Emiliania huxleyi</i> to UV radiation and elevated temperature: roles of calcified coccoliths

“…Emiliania huxleyi depends on Ca 2+ to form carbonate crystals that build up the coccolith shell that shelters the cells. Ca 2+ availability is also associated to other process, as seen in other studies (Trimborn et al, 2007;Leonardos et al, 2009) that demonstrated that cells grown under low (0.1 mM Ca 2+ ) or without Ca 2+ decreased their growth rates as compared to those cultured under higher Ca 2+ concentrations (e.g., 1-10 mM). Similarly, in our study we determined a significant decrease in the growth rates of E. huxleyi cells after being transferred from 10 mM Ca 2+ to 0.1 mM Ca 2+ , but only during the initial 12 generations in 9 days (data not shown).…”

“…Similarly, in our study we determined a significant decrease in the growth rates of E. huxleyi cells after being transferred from 10 mM Ca 2+ to 0.1 mM Ca 2+ , but only during the initial 12 generations in 9 days (data not shown). After 100 days (148 generations), there were no significant differences in growth rates between the two Ca 2+ concentrations (Table 2), clearly suggesting that acclimation to the lowered Ca 2+ level took longer time than expected (Herfort et al, 2002(Herfort et al, , 2004Trimborn et al, 2007;Leonardos et al, 2009). Nevertheless, significant differences between the two Ca 2+ concentrations were observed in the amount of pigments -chl-a and carotenoids per cell ( Table 2).…”

“…Other studies (Herfort et al, 2002(Herfort et al, , 2004Trimborn et al, 2007;Leonardos et al, 2009) however, found that low Ca 2+ concentrations did not affect the POC production, photosynthetic carbon fixation or photosynthetic oxygen evolution. In addition, Trimborn et al (2007) using SEM analysis found naked cells but not coccoliths or even residues, and they concluded that cells did not calcify at 0.1 mM Ca 2+ concentrations. In general, it can be considered that calcite dissolution occurs when the calcite saturation state ( ) is <1 (Trimborn et al, 2007).…”

“…In addition, Trimborn et al (2007) using SEM analysis found naked cells but not coccoliths or even residues, and they concluded that cells did not calcify at 0.1 mM Ca 2+ concentrations. In general, it can be considered that calcite dissolution occurs when the calcite saturation state ( ) is <1 (Trimborn et al, 2007). In our study, and although some part of the coccolith layer dissolved under the calcium carbonate undersaturated conditions ( <0.1), our SEM analysis of the LCa-grown cells showed that they did not lose the capacity to produce coccoliths (Fig.…”

“…While still is under debate, calcification in coccolithophores appears to be strongly linked to photosynthesis by favoring supply of CO 2 (Anning et al, 1996;Sikes et al, 1980;Sikes and Wilbur, 1982); moreover, Nimer et al (1996) found reduced photosynthetic rates when removing external calcium. Other studies (Herfort et al, 2002(Herfort et al, , 2004Trimborn et al, 2007;Leonardos et al, 2009) however, showed that changes in calcification under altered Ca 2+ concentrations did not bring about concomitant changes in photosynthesis.…”