Physiology and Growth of Wheat Across a Subambient Carbon Dioxide Gradient

Abstract

Two cultivars of wheat (Triticum aestivum L.), 'Yaqui 54' and 'Seri M82', were grown along a gradient of daytime carbon dioxide concentrations ([CO2]) from near 350-200 μmol CO2 mol-1 air 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 determined potential effects of the glacial/interglacial increase in atmospheric [CO2] on C3 plants. Growth rates and leaf areas of individual plants and net assimilation per unit leaf area and daily (24-h) net CO2 accumulation of wheat stands rose with increasing [CO2]. Daytime net assimilation (PD, mmol CO2 m-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 CO2 accumulation (light compensation point) declined at higher [CO2]. Nighttime respiration (RN, mmol CO2 m-2 soil surface) of wheat, measured at 369-397 μmol mol-1 CO2, apparently was not altered by growth at different daytime [CO2], but RN /PD of stands declined linearly as daytime [CO2] and PD increased. The responses of wheat to [CO2], if representative of other C3 species, suggest that the 75-100% increase in [CO2] since glaciation and the 30% increase since 1800 reduced the minimum light and water requirements for growth and increased the productivity of C3 plants.