CO2 EFFECTS ON PHASIC DEVELOPMENT, LEAF NUMBER AND RATE OF LEAF APPEARANCE IN WHEAT

It has been predicted that the concentration of CO2 in the air could d ouble during the 21st century. Though it is recognized that CO2-doubli ng could increase yield through its effects on plant photosynthesis an d stomatal behaviour, it is unclear whether CO2-doubling will change p hasic development in wheat. A phytotron study was conducted with two c ontrasting cultivars of wheat, Condor (spring) and Cappelle Desprez (w inter), to determine whether development is affected by a season-long exposure to 360 and 720 ppmv CO2. Plants were vernalized for 50 d (8/4 degrees C, s h photoperiod) before their exposure to the CO2 treatmen ts. There were significant differences between cultivars in the durati on of different phenophases as well as in the final number of leaves. However, CO2 concentration had no effect in either cultivar on the dur ation of the early developmental phase to terminal spikelet initiation , or on the final number of leaves, though CO2-doubling did slightly i ncrease the later phase from terminal spikelet initiation to heading i n Cappelle Desprez. Condor and Cappelle Desprez also differed markedly in the dynamics of leaf appearance. While the former had a constant r ate of leaf appearance throughout development, the latter had a fast r ate initially (between leaves 1 and 7), similar to that of Condor, whi ch was followed by a slower rate after the appearance of leaf 7. Overa ll, CO2-doubling did not significantly affect the rates of leaf appear ance nor the shape of the relationship. Phyllochron for the first seve n leaves was the same for both CO2 concentrations. However, the change in phyllochron associated with CO2-doubling for leaves 7-12 in Cappel le Desprez, although quite small (4%), accounts for part of the slight ly increased duration of the phase from terminal spikelet initiation t o heading under high CO2 concentration in that cultivar. We conclude t hat CO2 concentration does not influence development in wheat to a deg ree relevant to agronomy. (C) 1997 Annals of Botany Company