Evolutionary and ecological perspectives on carbon acquisition in phytoplankton

Abstract

Statistically significant differences exist among the major algal and cyanobacterial taxa in the catalytic efficiency of Ribulose-1,5 bisphosphate carboxylase/oxygenase (RubisCO)the rate limiting carboxylase in C-fixation. With the notable exception of the red algae, a comparison of the kinetic properties of RubisCO among phytoplankton of different geological ages suggests that the enzyme has evolved towards higher CO2 affinity in response to decreasing atmospheric CO2/O2 ratios over geological time. Taxonomic differences in the kinetic properties of RubisCO influence the mechanisms of C acquisition among phytoplankton groups. A significant negative correlation exists between the CO2 specificity factor of RubisCO and the capacity of cells to concentrate inorganic C through active uptake mechanisms. Differential resource requirements associated with C acquisition could affect the relative fitness of phytoplankton groups and thus their ecological interactions. I argue that inorganic C may play a more important role in phytoplankton productivity and community ecology than has been previously recognized and highlight some outstanding questions for future research.