CO2 Compensation Concentration in Maize (Zea mays L.) Genotypes

Heichel and Musgrave (4, 5) reported photosynthetic rates of maize genotypes ranging from 21 to 85 mg CO2 dmhr-' which were inversely associated with similar large differences in CO2 compensation concentration of from 9 to 25 plll. Since genotypic differences of the magnitude reported by Heichel and Musgrave would be of great value in breeding for increased photosynthetic efficiency, we conducted similar experiments in an attempt to confirm their results. There is also much literature citing the fact that maize plants possess low CO. compensation points of around 0 pl/1 (7, 10, 11), while their maximum photosynthetic rates are normally around 40 to 60 mg CO, dm-' hr-' (6, 9). The fact that the results of Heichel and Musgrave were contrary to these observations and to our own experiences further prompted us to investigate the topic.