Effect of Rising Temperature and Carbon Dioxide on the Growth, Photophysiology, and Elemental Ratios of Marine Synechococcus: A Multistressor Approach

Marine picocyanobacteria belonging to the genus Synechococcus are one of the most abundant photosynthetic organisms on Earth. They are often exposed to large fluctuations in temperature and CO2 concentrations in the ocean, which are expected to further change in the coming decades due to ocean acidification and warming resulting from rising atmospheric CO2 levels. To decipher the effect of changing temperature and CO2 levels on Synechococcus, six Synechococcus strains previously isolated from various coastal and open ocean sites were exposed to a matrix of three different temperatures (22 degrees C, 24 degrees C and 26 degrees C) and CO2 levels (400 ppm, 600 ppm and 800 ppm). Thereafter, the specific growth rates, photophysiological parameters (sigma(PSII) and F-v/F-m), C/N (mol/mol) ratios and the nitrogen stable isotopic composition (delta N-15 (parts per thousand)) of the strains were measured. Temperature was found to be a stronger driver of the changes in specific growth rates and photophysiology in the Synechococcus strains. Carbon-concentrating mechanisms (CCM) operational in these strains that shield the photosynthetic machinery from directly sensing ambient changes in CO2 possibly played a major role in causing minimal changes in the specific growth rates under the varying CO2 levels.

Automated summary

This study investigated the response of marine picocyanobacteria Synechococcus strains to changes in temperature and CO2 concentrations. The results showed that temperature was the main factor influencing the specific growth rates and photophysiology of the Synechococcus strains, while the carbon-concentrating mechanisms had minimal impact on the growth rates under different CO2 levels.