CO2Effects on Phasic Development, Leaf Number and Rate of Leaf Appearance in Wheat

Abstract

It has been predicted that the concentration of CO 2 in the air could double during the 21st century. Though it is recognized that CO 2 -doubling could increase yield through its effects on plant photosynthesis and stomatal behaviour, it is unclear whether CO 2 -doubling will change phasic development in wheat. A phytotron study was conducted with two contrasting cultivars of wheat, Condor (spring) and Cappelle Desprez (winter), to determine whether development is affected by a season-long exposure to 360 and 720 ppmv CO 2 . Plants were vernalized for 50 d (8/4 °C, 8 h photoperiod) before their exposure to the CO 2 treatments. There were significant differences between cultivars in the duration of different phenophases as well as in the final number of leaves. However, CO 2 concentration had no effect in either cultivar on the duration of the early developmental phase to terminal spikelet initiation, or on the final number of leaves, though CO 2 -doubling did slightly increase the later phase from terminal spikelet initiation to heading in Cappelle Desprez. Condor and Cappelle Desprez also differed markedly in the dynamics of leaf appearance. While the former had a constant rate of leaf appearance throughout development, the latter had a fast rate initially (between leaves 1 and 7), similar to that of Condor, which was followed by a slower rate after the appearance of leaf 7. Overall, CO 2 -doubling did not significantly affect the rates of leaf appearance nor the shape of the relationship. Phyllochron for the first seven leaves was the same for both CO 2 concentrations. However, the change in phyllochron associated with CO 2 -doubling for leaves 7–12 in Cappelle Desprez, although quite small (4%), accounts for part of the slightly increased duration of the phase from terminal spikelet initiation to heading under high CO 2 concentration in that cultivar. We conclude that CO 2 concentration does not influence development in wheat to a degree relevant to agronomy.