High levels of solar radiation offset impacts of ocean acidification on calcifying and non-calcifying strains of Emiliania huxleyi

Abstract

Coccolithophores, a globally distributed group of marine phytoplankton, showed diverse responses to ocean acidification (OA) and to combinations of OA with other environmental factors. While their growth can be enhanced and calcification be hindered by OA under constant indoor light, fluctuation of solar radiation with ultraviolet irradiances might offset such effects. In this study, when a calcifying and a non-calcifying strain of Emiliania huxleyi were grown at 2 CO 2 concentrations (low CO 2 [LC]: 395 µatm; high CO 2 [HC]: 1000 µatm) under different levels of incident solar radiation in the presence of ultraviolet radiation (UVR), HC and increased levels of solar radiation acted synergistically to enhance the growth in the calcifying strain but not in the noncalcifying strain. HC enhanced the particulate organic carbon (POC) and nitrogen (PON) productions in both strains, and this effect was more obvious at high levels of solar radiation. While HC decreased calcification at low solar radiation levels, it did not cause a significant effect at high levels of solar radiation, implying that a sufficient supply of light energy can offset the impact of OA on the calcifying strain. Our data suggest that increased light exposure, which is predicted to happen with shoaling of the upper mixing layer due to progressive warming, could counteract the impact of OA on coccolithophores distributed within this layer.

Effects of Ocean Acidification on Marine Photosynthetic Organisms Under the Concurrent Influences of Warming, UV Radiation, and Deoxygenation

“…For instance, when three diatom species were grown under different levels of sunlight, lowered pH with elevated CO 2 stimulated growth under low to moderate levels of light, but inhibited it under high levels (Gao et al, 2012a; Figure 3). However, such a reversed response to OA with increasing light levels was not found in coccolithophores, which showed enhanced growth rates (with reduced calcification) under the elevated pCO 2 under all tested PAR levels (Jin et al, 2017; FIGURE 3 | A schematic representation of the differing relationship between sunlight intensity and the growth rates of diatoms (A) and coccolithophores (B) grown at low (390 µatm, blue lines) and high (1,000 µatm, red lines) CO 2 concentrations, respectively. Note that elevated CO 2 stimulates growth in diatoms at low light but inhibits them at high light levels.…”

Physiological and biochemical responses of <i>Emiliania huxleyi</i> to ocean acidification and warming are modulated by UV radiation

“…Phytoplankton use several mechanisms to repair UVinduced damage, many of which involve nitrogen-requiring enzymes and/or protein cofactors (Litchman et al, 2002). Korbee et al (2010) reported that UVA could stimulate algae nitrogen metabolism (nitrate transport and reductase activity). In contrast, UVB was found to damage cell membranes and negatively affect nitrogen incorporation mechanisms, leading to an increase in the C / N ratio (Sobrino et al, 2004).…”

Adaptive evolution in the coccolithophore Gephyrocapsa oceanica following 1,000 generations of selection under elevated CO2

“…Increased light supply to E. huxleyi has recently shown to decrease the inhibitory effects of OA on its calcification (Jin et al. ).…”