Diffusion and Active Transport of Inorganic Carbon Species in Freshwater and Marine Macroalgae

Abstract

Some macroalgae from both freshwater and marine habitats are known (by a number of criteria of varying degress of rigour) to be able to use exogenous HCO3 - in photosynthesis, while other can only use CO2 (1--5). Furthermore, while some of the macroalgae have photosynthetic physiology characteristic of C3 plants, others are ``C4-like'', although the dominant carboxylase active in illuminated tissue is RUBSICO (ribulose bisphosphate carboxylase-oxygenase) carboxylase (1--5) . The extent to which the use of HCO3 - and the C4-like physiology are invariably correlated is not clear. The aim of this paper is to outline the inorganic carbon acquisition processes of two taxonomically and ecologically contrasting macroalgae (Table 1) and to suggest some possible ecological significance of the attributes discussed.