Photosynthesis by aquatic plants: effects of unstirred layers in relation to assimilation of co2 and hco3−and to carbon isotopic discrimination

TLDR: Experimental evidence indicates that the unstirred layers of solution bathing aquatic plant cells or organs represent a major factor limiting their rate of photosynthesis under natural conditions and may also limit membrane transport of HCO3− where this occurs.

Abstract: Summary We review and reassess experimental evidence which indicates that the unstirred layers of solution bathing aquatic plant cells or organs represent a major factor limiting their rate of photosynthesis under natural conditions. Unstirred layers may also limit membrane transport of HCO3− where this occurs. Some authors have suggested that aquatic plants carry out C4photosynthesis and cite in support measurements of discrimination between 13C and 12C. We propose that this discrimination can also be a manifestation of the presence of unstirred layers or membrane transport or both.