Interactions between carbon dioxide and oxygen in the photosynthesis of three species of marine red macroalgae

Abstract

Summary Red algae have the highest known selectivity factor (Srel) for CO2 over O2 of ribulose bisphosphate carboxylase-oxygenase (RUBISCO). This allows the prediction that a red alga relying on diffusive supply of CO2 to RUBISCO from air-equilibrated solution should have less O2 inhibition of photosynthesis than would an otherwise similar non-red alga with a lower Srel of RUBISCO. Furthermore, RUBISCO shows an increased Srel values at low temperatures. The prediction that O 2inhibition of photosynthesis should be small for marine red algae relying on diffusive CO2 entry growing in the North Sea with an annual temperature range of 4–16°C was tested in O2 electrode experiments at 12°C. Phycodrys rubens and Plocamium cartilagineum, which rely on diffusive CO2 entry showed, as predicted, only a small inhibition at lower inorganic C concentrations. Palmaria palmata, which has a CO2 concentrating mechanism, had the expected negligible O 2 inhibition of photosynthesis at any inorganic C concentration except (non-significantly) for saturating inorganic C.