Uptake and evolution of carbon dioxide during photosynthesis : a survey of plant divisions.

The exchange of CO2 in light was studied in plants of six divisions. The rates of CO2 uptake in light, of CO2 evolution in darkness, and the concentration of CO2 at C02 compensation point were measured in a closed system with an infrared gas analyser. The CO2 evolution rate in light was then calculated from these measurements. Rates of C02 exchange and CO2 compensation points were similarly measured at several concentrations of oxygen between 2% and 100%. The CO concentration at CO compensation point was a linear function of O2 concentration in eleven of the twelve species studied. The CO2 compensation point of corn was not affected by O2 . At 60% O2, the inhibition of rates of CO2 uptake was of the same magnitude in all species studied. The minimum rate of CO2 evolution in light was found to be at least twice the rate of CO2 evolution in the dark in ten of eleven species.