[The influence of low and high oxygen concentrations on oxygen and carbon dioxide gas exchange of Amaranthus and Phaseolus leaves during illumination].

Carbon dioxide and oxygen gas exchange of illuminated Amaranthus and Phaseolus leaves was measured from 0-600 ppm of CO2 in an open system.At low oxygen concentration (2% O2) the ratio of CO2 uptake to O2 evolution came close to 1.At high oxygen partial pressure (42% O2) the O2 compensation point of an Amaranthus leaf was increased and oxygen evolution was depressed. Accordingly the CO2/O2 quotients were variable; the lowest value of 1,9 differed significantly from 1,0.The oxygen and carbon dioxide compensation points of a Phaseolus leaf were increased at high oxygen concentration (42% O2) and oxygen evolution as well as carbon dioxide uptake were reduced. Therefore the ratios CO2 over O2 varied and differed greatly from 1,0.It was concluded that the nature of photosynthates is regulated by the gas composition around the leaves.