REPERCUSSIONS OF INCREASED ATMOSPHERIC CO2 ON MAIZE MORPHOGENESIS ANDGROWTH FOR VARIOUS TEMPERATURE AND RADIATION-LEVELS

The effect of atmospheric CO2 enhancement on maize production was stud ied through four crops in two glasshouse compartments, with and withou t CO2 enrichment. Development (number of organs, duration of phenologi cal phases) was measured during cultivation and growth (dry matter pro duction) was measured at flowering and at final harvest. The main resu lts were as follows: The number of initiated organs (florets and leave s) was not affected by the CO2 enrichment. According to the runs, aeri al and whole plant production were significantly or not increased in t he enriched compartment. The production increase was significantly dif ferent bem een treatments under poor radiation or high plant demand co nditions. The balance between supply and demand enabled or not the eff ect of CO2 enhancement to be expressed. Among the four crops, the ligh t conversion efficiency was significantly modified by CO2 enrichment o nly in one run. The dry matter increase was not equally partitioned be tween the organs. It was higher in stem, husks and cob than in leaves and grains. These organs have a morphogenetically limited size (throug h the number of grains). This controlled the expression of the effect of CO2 enhancement in these runs and explained why the conversion effi ciency only increased in one run, which was not morphogenetically limi ted. These crops proved the interactions between CO2 concentration and the other main climatic factors (temperature and radiation) and the n eed to know the morphogenesis in order to be able to estimate the effe cts of CO2 enrichment correctly.