Intraspecific variation in seed yield of soybean (Glycine max) in response to increased atmospheric carbon dioxide

The growth characteristics of six and the reproductive development of five soybean [Glycine max (L.) Merr.] cultivars were examined at 39 Pa (ambient) and 70 Pa (elevated) CO2 partial pressures in temperature-controlled glasshouses. Significant intraspecific variation for both growth and seed yield in response to elevated CO2 was observed among the cultivars. At elevated CO2, total biomass increased an average of 42% at the end of the vegetative stage, while average seed yield increased by only 28%. No changes in % protein or % oil were observed for any cultivar at elevated CO2, relative to ambient CO2. The relative enhancement of either vegetative or reproductive growth at elevated CO2 was not correlated with changes in the absolute or relative increase in single leaf photosynthetic rate among cultivars at elevated CO2. For soybean, the greatest response of seed yield to elevated CO2 was associated with increased production of lateral branches, increased pod production or increased seed weight, suggesting different strategies of carbon partitioning in a high CO2 environment. Data from this experiment indicates that differences in carbon partitioning among soybean cultivars may influence reproductive capacity and fecundity as atmospheric CO2 increases, with subsequent consequences for future agricultural breeding strategies.