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

Abstract

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.