FREE-AIR CO2 ENRICHMENT EFFECTS ON RATE AND DURATION OF APICAL DEVELOPMENT OF SPRING WHEAT

Rates and durations of individual phases of wheat (Triticum aestivum L .) apical development are among the most important factors that determ ine yield components. Because atmospheric CO2 has been increasing stea dily, it is important to evaluate the effects of elevated CO2 on wheat development. This study was conducted to determine rates and duration s of leaf, spikelet, and floret primordium initiation in a Free-Air Ca rbon Dioxide Enrichment (FACE) system. Spring wheat (cv. Yecora Roja) was planted at the University of Arizona Maricopa Agricultural Center. The two CO2 concentrations were 550 (elevated) and 370 (ambient) mu m ol mol(-1) CO2. Individual plant samples were collected every 3 to 4 d . We dissected the main stem (MS), coleoptile tiller (T0), primary til lers (T1, T2, and T3) and secondary tillers (T00, T01, T02, T10, T11, and T12) and counted primordia. Apex primordium data were fitted to a four-piece linear-spline segmented regression model with the SAS proc NLIN. No influence of elevated CO2 (550 mu mol mol(-1)) on leaf primor dium initiation of MS was detected. Nevertheless, CO2 enrichment signi ficantly increased rates of spikelet primordium initiation of MS, T1, T2, T10, and T11, and diminished the durations of spikelet development phase of MS, T1, T2, T3, T10, and T11. Within the floret phase, CO2 e nrichment significantly increased rates of floret primordium initiatio n of MS, T0, T1, T2, and T3, and diminished the time to the completion of floret primordium initiation of MS, T0, T1, T3, and T11. The infor mation from this study will be utilized to predict wheat apical develo pment and grain production in the elevated atmospheric CO2 environment s of the future.