GAS-EXCHANGE AND CARBON FIXATION PROPERTIES OF THE MAT-FORMING CYANOPHYTE LYNGBYA-BIRGEI SMITH,G.M.

The macroscopic cyanophyte Lyngbya birgei G.M. Smith showed low, O2-insentive rates of CO2 release into CO2-free media, as well as low CO2 compensation points and O2-insensitive photosynthetic rates. These gas exchange traits indicate that this organism can suppress photorespiration. The ability to thus optimize photosynthetic rates is based on HCO3- use as well as limited C4-like metabolism; both systems could elevate internal CO2 levels and thereby reduce the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase. It was further found that while the low photorespiration state did not change in Lyngbya grown at various inorganic carbon levels, the enzymatic potential for C4 metabolism varied with external HCO3- levels. It is suggested that Lyngbya has adapted its photosynthetic systems to be efficient, so as to ensure optimal production in a variety of inorganic carbon and O2 environments, and that this ability is of competitive advantage under conditions where it becomes an aquatic weed. © 1990.