Effect of CO_2 enrichment on phytoplankton photosynthesis in the North Atlantic sub-tropical gyre

摘要

Highlights•3 CO2enrichment experiments were conducted in the North Atlantic sub-tropical gyre.•Dinoflagellates dominated the biomass but there was no significant difference between high & low CO2.•There were significantly higher photosynthetic rates at high CO2.•These were due to the connection of reversible photosystem antennae at elevated CO2.AbstractThe effects of changes in CO2concentration in seawater on phytoplankton community structure and photosynthesis were studied in the North Atlantic sub-tropical gyre. Three shipboard incubations were conducted for 48h at ∼760ppm CO2and control (360ppm CO2) from 49°N to 7°N during October and November 2010. Elevated CO2caused a decrease in pH to ∼7.94 compared to ∼8.27 in the control. During one experiment, the biomass of nano- and picoeukaryotes increased under CO2enrichment, but primary production decreased relative to the control. In two of the experiments the biomass was dominated by dinoflagellates, and there was a significant increase in the maximum photosynthetic rate (PmB) and light-limited slope of photosynthesis (αB) at CO2concentrations of 760ppm relative to the controls. 77K emission spectroscopy showed that the higher photosynthetic rates measured under CO2enrichment increased the connection of reversible photosystem antennae, which resulted in an increase in light harvesting efficiency and carbon fixation.