Use of bicarbonate ions as a source of carbon in photosynthesis by Callitriche hermaphroditica

Previous studies on four amphibious species of Callitriche have shown photosynthesis to be restricted to CO2 as an external carbon source. In contrast. we found that C. hermaphroditica, an obligately submerged species, is able to use bicarbonate ions in addition to CO2 as an external source of inorganic carbon for photosynthesis. In pH-drift experiments, the final concentration of CO2 was driven below 1 mumol CO2 l(-1) (0.01-0.08 mumol l(-1) for at range of alkalinities) and rates of carbon uptake were around 400 mumol carbon g(-1) DW h(-1) at an essentially zero CO2 concentration at high alkalinity. Rates of photosynthesis, as oxygen evolution, increased with the concentration of bicarbonate and exceeded the CO2-dependent rate by up to 2.2- to 2.8-fold. In addition to underwater-pollination and obligate submersion. the physiological feature of bicarbonate use is another indication of the greater reliance of this species to life in water and may be a further character that separates the section Pseudocallitriche from the Eucallitriche. (C) 2002 Elsevier Science B.V. All rights reserved.