Quantitative and qualitative evaluation of selected wheat varieties released since 1903 to increasing atmospheric carbon dioxide: can yield sensitivity to carbon dioxide be a factor in wheat performance?

The sensitivity of yield and quality parameters to carbon dioxide concentration [CO2] was determined for individual lines of hard-red spring wheat released in 1903, 1921, 1965 and 1996. All cultivars were evaluated with respect to growth and vegetative characteristics, grain yield and nutritional quality in response to [CO2] increases that corresponded roughly to the CO2 concentrations at the beginning of the 20th century, the current [CO2], and the future projected [CO2] for the end of the 21st century, respectively. Leaf area ratio (cm^2 g^-1) declined and net assimilation rate (g m^2 day^-1) increased in response to increasing [CO2] for all cultivars during early vegetative growth. By maturity, vegetative growth of all cultivars significantly increased with the increase in [CO2]. Seed yield increased significantly as [CO2] increased, with yield sensitivity to rising [CO2] inversely proportional to the year of cultivar release. Greater [CO2] yield sensitivity in older cultivars was associated with whole-plant characteristics such as increased tillering and panicle formation. Grain and flour protein, however, declined significantly with increasing [CO2] and with year of release for all cultivars, although absolute values were higher for the older cultivars. Overall, these data indicate that yield response at the whole-plant level to recent and projected increases in [CO2] has declined with the release of newer cultivars, as has protein content of grain and flour. However, if agronomic practice can be adapted to maximize individual plant performance, [CO2] responsive characteristics of older cultivars could, potentially, be incorporated as factors in future wheat selection.