Elevated CO1 Increases Wheat CER\ Leaf and Tiller Development\ and Shoot and Root Growth

Whole!plant responses to elevated CO1 throughout the life cycle are needed to understand future impacts of elevated atmospheric CO1[ In this study\ Triticum aes! tivum L[ leaf carbon exchange rates "CER# and carbo! hydrates\ growth\ and development were examined at the tillering\ booting\ and grain!_lling stages in growth chambers with CO1 concentrations of 249 "ambient# or 699 "high# mmol mol[ Single!leaf CER values measured on plants grown at high CO1 were 49) greater than those measured on plants grown at ambient CO1 for all growth stages\ with no photosynthetic acclimation observed at high CO1[ Leaves grown in high CO1 had more starch and simple sugars at tillering and booting\ and more starch at grain!_lling\ than those grown in ambient CO1[ CER and carbohydrate levels were positively correlated with leaf appearance rates and tillering "especially third!\ fourth! and _fth!order tillers#[ Elevated CO1 slightly delayed tiller appearance\ but accelerated tiller devel! opment after appearance[ Although high CO1 increased leaf appearance rates\ _nal leaf number:culm was not e}ected because growth stages were reached slightly sooner[ Greater plant biomass was related to greater till! ering[ Doubling CO1 signi_cantly increased both shoot and root dry weight\ but decreased the shoot to root ratio[ High CO1 plants had more spikes plant and spike! lets spike\ but a similar number of fertile spikelets spike[ Elevated CO1 resulted in greater shoot\ root and spike production and quicker canopy development by increas! ing leaf and tiller appearance rates and phenology[ Key words] carbohydrates * CO1 * develop! ment * phenology * photosynthesis * wheat Abbreviations] CER\ carbon exchange rate * GDD\ growing degree!days * PPFD\ photosynthetic pho! ton ~ux density