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

Although primordium initiation in wheat (Triticum aestivum L,) has been extensively researched, a complete description of the growth dynamics of the apex at elevated CO2 concentrations is lacking. This study determined the rates of main stem and tiller apical elongation and widening in plants grown under two levels of CO2 concentration. Spring wheat was grown at the University of Arizona's Maricopa Agricultural Center at elevated (550 mu mol mol(-1)) or ambient (370 mu mol mol(-1)) CO2 concentrations. Individual plant samples were collected at different developmental stages and dissected. After dissection, the Lengths and widths of the spires of the main stem (MS), coleoptile tiller (T0), primary tillers (T1, T2, and T3), and secondary tillers (T00, T01, T02, T10, T11, and T12) were measured with a stage micrometer. Apex dimensions were fitted to an exponential model, Elevated CO2 increased 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 T2 at double ridge stage, and of T2, T3, T10, and T11 at the flag leaf appearance stage. Combining these results with a parallel study, the longer apices did not have more spikelet primordia, but wider apices had more floret primordia, Elevated CO2 changed apex elongation or widening patterns within a plant by enhancing elongation or widening rates of the MS, and later formed tillers. Earlier-formed tillers were less responsive to elevated CO2 levels. This information will be used in modeling wheat apical development and grain production in the elevated atmospheric CO2 environments of the future.