Soybean growth and yield response to elevated carbon dioxide

Abstract Soybeans ( Glycine max L. Merr. ‘Bragg’) were grown in seeded rows in open-top field chambers and exposed continuously to a range of elevated CO 2 concentrations through-out the 1982 and 1983 growing seasons. During 1983, a water stress treatment was also imposed. Comparison of vegetative growth with a similarly conducted pot experiment showed an increased ration of leaf area to total top dry weight in the seeded row plants, but generally similar qualitative effects of elevated CO 2 . Careful recording of mainstem leaf emergence rates and reproduction stages showed no consistent effect of CO 2 under well watered conditions, but in 1983 there was a distinct modification by high CO 2 of the water stress-induced hastening of the time to physiological maturity. In 1982, and for the well watered plants in 1983, standing biomass at maturity was increased significantly by elevated CO 2 , but harvest index decreased and yield was (statistically) unaffected by the treatment. The yield responses calculated for a doubling of the current CO 2 concentrations for these well watered treatments were 1.07 and 0.93, respectively. In the water stress treatment in 1983, however, harvest index did not decrease in the presence of elevated CO 2 , and a highly significant yield response occurred (1.41 at 700 μll −1 ).