Free-air CO2 enrichment effects on apex dimensional growth of spring wheat

Although primordium initiation in wheat (Triticum aestivum L,) has been ext ensively researched, a complete description of the growth dynamics of the a pex at elevated CO2 concentrations is lacking. This study determined the ra tes of main stem and tiller apical elongation and widening in plants grown under two levels of CO2 concentration. Spring wheat was grown at the Univer sity of Arizona's Maricopa Agricultural Center at elevated (550 mu mol mol( -1)) or ambient (370 mu mol mol(-1)) CO2 concentrations. Individual plant s amples were collected at different developmental stages and dissected. Afte r dissection, the Lengths and widths of the spires of the main stem (MS), c oleoptile tiller (T0), primary tillers (T1, T2, and T3), and secondary till ers (T00, T01, T02, T10, T11, and T12) were measured with a stage micromete r. Apex dimensions were fitted to an exponential model, Elevated CO2 increa sed the apex lengths of T2 at the double ridge stage, and of T3 and T10 at the double ridge and the terminal spikelet stages, and the apex widths of T 2 at double ridge stage, and of T2, T3, T10, and T11 at the flag leaf appea rance stage. Combining these results with a parallel study, the longer apic es did not have more spikelet primordia, but wider apices had more floret p rimordia, Elevated CO2 changed apex elongation or widening patterns within a plant by enhancing elongation or widening rates of the MS, and later form ed tillers. Earlier-formed tillers were less responsive to elevated CO2 lev els. This information will be used in modeling wheat apical development and grain production in the elevated atmospheric CO2 environments of the futur e.