AUTHOR=Qin Jiahui , Jia Minjuan , Sun Jun 

TITLE=Examining the effects of elevated CO2 on the growth kinetics of two microalgae, Skeletonema dohrnii (Bacillariophyceae) and Heterosigma akashiwo (Raphidophyceae)

JOURNAL=Frontiers in Marine Science

VOLUME=11

YEAR=2024

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2024.1347029

DOI=10.3389/fmars.2024.1347029

ISSN=2296-7745

ABSTRACT=<p>Carbon dioxide (CO<sub>2</sub>) serves as the primary substrate for the photosynthesis of phytoplankton, forming the foundation of marine food webs and mediating the biogeochemical cycling of C and N. We studied the effects of CO<sub>2</sub> variation on the Michaelis-Menten equations and elemental composition of <italic>Skeletonema dohrnii</italic> and <italic>Heterosigma akashiwo</italic>. CO<sub>2</sub> functional response curves were conducted from 100 to 2000 ppm. The growth of both phytoplankton was significantly affected by CO<sub>2</sub>, but in different trends. The growth rate of <italic>S. dohrnii</italic> increased as CO<sub>2</sub> levels rose up to 400 ppm before reaching saturation. In contrast to <italic>S. dohrnii</italic>, the growth rate of <italic>H. akashiwo</italic> increased with CO<sub>2</sub> increasing up to 1000 ppm, and then CO<sub>2</sub> saturated. In addition, <italic>H. akashiwo</italic> showed a slower growth rate than <italic>S. dohrnii</italic> for all CO<sub>2</sub> concentrations, aside from 1000 ppm, and the Michaelis-Menten equations revealed that the half-saturation constant of <italic>H. akashiwo</italic> was higher than <italic>S. dohrnii</italic>. An increase in CO<sub>2</sub> concentration was seen to significantly affected the POC: Chl-<italic>a</italic> of both <italic>S. dohrnii</italic> and <italic>H. akashiwo</italic>, however, the effects on their elemental composition were minimal. Overall, our findings indicate that <italic>H. akashiwo</italic> had a more positive reaction to elevated CO<sub>2</sub> than <italic>S. dohrnii</italic>, and with higher nutrient utilization efficiency, while <italic>S. dohrnii</italic> exhibited higher carbon fixation efficiency, which is in line with their respective carbon concentrating mechanisms. Consequently, elevated CO<sub>2</sub>, either alone or in combination with other limiting factors, may significantly alter the relative relationships between these two harmful algal blooms (HAB) species over the next century.</p>