Effects of CO2 and O2 on the Photosynthetic O2 Evolution of Spirodela polyrrhiza Turions

Net photosynthetic rates of Spirodela polyrrhiza turions, at low O(2) levels, were 6.2 and 38.8 micromoles O(2) per gram fresh weight per hour at 1 millimolar HCO(3) (-) and CO(2) saturation, respectively, and much lower in a regular low-pH growth solution. Air equilibration O(2) concentrations decreased rates considerably, except at CO(2) saturation. The surfacing rate of turions in various inorganic carbon surroundings correlated positively with their photosynthetic rates, but were the same at high and low O(2) levels. The relevance of these findings in relation to environmental conditions conductive to germination of autotrophically growing turions is discussed.