PHYSIOLOGY AND GROWTH OF WHEAT ACROSS A SUBAMBIENT CARBON-DIOXIDE GRADIENT

Two cultivars of wheat (Triticum aestwum L.), ‘Yaqui 54’ and ‘Seri M82’, were grown along a gradient of daytime carbon dioxide concentrations ([C02]) from near 350-200 //mol C02mol-1air in a 38 m long controlled environment chamber. Carbon dioxide fluxes and evapotranspiration were measured for stands (plants and soil) in five consecutive 7'6-m lengths of the chamber to determine potential effects of the glacial/interglacial increase in atmospheric [COJon C3plants. Growth rates and leaf areas of individual plants and net assimilation per unit leaf area and daily (24- h) net C02 accumulation of wheat stands rose with increasing [C02]. Daytime net assimilation (PD, mmol C02m-2 soil surface area) and water use efficiency of wheat stands increased and the daily total of photosynthetic photon flux density required by stands for positive C02accumulation (light compensation point) declined at higher [C02].Nighttime respiration (PN, mmol C02m-2soil surface) of wheat, measured at 369-397 //mol mol-1 C02, apparently was not altered by growth at different daytime [C02], but R1,/PD of stands declined linearly as daytime [C02] and PD increased. The responses of wheat to [C02], if representative of other C3species, suggest that the 75-100% increase in [COJsince glaciation and the 30% increase since 1800 reduced the minimum light and water requirements for growth and increased the productivity of C3plants. © 1993 Annals of Botany Company.