Atmospheric CO₂ levels have been increasing from about 280 ppm in the pre-industrial era to 379 ppm in 2005. Higher CO₂ concentrations might stimulate photosynthesis in C3 plants such as wheat, but large variations have been reported in the literature in the response to elevated CO₂. The objective of the current study is to determine the response to elevated CO₂ of 20 genotypes which differ in tillering, water soluble carbohydrate (WSC) accumulation, transpiration efficiency and early vigour. Our hypothesis is that genetic variability in the response to elevated CO₂ does exist in wheat, and that the traits mentioned above are partially responsible for this variability. In addition, as these traits are of considerable interest to current breeding programs interested in drought tolerance, it is important to determine if these traits are still useful in a high CO₂ environment. 

Experiments were performed in control environment chambers and in a glasshouse with CO₂ levels controlled at 420 ppm (ambient) and 700 ppm (elevated). An effort was made to select lines with similar height and time to flowering, as well as lines with similar genetic backgrounds for contrasting trait expression. Measurements included characterisation of leaf appearance, crop and tiller development, non-destructive measurements of early leaf widths and lengths, destructive measurements for leaf area and biomass at anthesis, WSC and nitrogen content, gas exchange measurements and yield and yield components. Preliminary data indicates that all four adaptive traits are expressed in a consistent manner in ambient and elevated CO₂ environments. For example, low tillering lines remain low tillering under elevated CO₂, although the total number of tillers is higher. This implies that breeders may expect consistent rankings of traits in the future, although drought and high temperature are expected to create interactions with these traits.