Physiological changes in marine picocyanobacterial Synechococcus strains exposed to elevated CO₂ partial pressure

Abstract

Unicellular marine cyanobacteria are abundant in both coastal and oligotrophic environments, where they contribute substantially to primary production. The physiological effect of future increases in atmospheric CO₂ concentrations on the marine picocyanobacteria is still poorly known. We studied the physiological changes in marine phycocyanin (PC)-rich and phycoerythrin (PE)-rich Synechococcus strains under different CO₂ partial pressures (350, 600 and 800 ppm). The PE strain showed no significant change in growth rate over the experimental CO₂ range. A significant increase (25.4%) in carbohydrate was observed at 800 ppm CO₂, but no significant change in protein and RNA/DNA ratio was observed in any CO₂ treatment. The PC strain showed a significant increase (36.7%) in growth rate at 800 ppm CO₂, but no significant change in carbohydrate or protein content was observed over the entire CO₂ range. The RNA/DNA ratio increased with increasing CO₂ concentration and was positively correlated with growth rate. Cellular red fluorescence and orange fluorescence of the PE strain tended to decline in all CO₂ treatments. However, no such decline was observed at higher CO₂ treatments in the PC strain. Our results suggest that the PC strain would probably benefit more than the PE strain from future increases in atmospheric CO₂ concentrations.

Keywords:

• CO₂
• physiological change
• phycocyanin
• phycoerythrin
• Synechococcus

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgments

We are very grateful to Dr Peng Zaiqing and Zhai Weidong (State Key Laboratory of Marine Environmental Science, Xiamen University) for their contributions to flow cytometer and dissolved inorganic carbon analysis, respectively. This work was supported by the MOST Projects No. G2000078500, 2003AA635160, 2003DF000040 and the NFSC Projects No. 40232021, 40176037, 30170189. Professor John Hodgkiss is thanked for his assistance in preparing the manuscript.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark