Variable Responses to CO₂ of the Duration of Vegetative Growth and Yield within a Maturity Group in Soybeans

Prior experiments in indoor chambers and in the field using free-air carbon dioxide enrichment (FACE) systems indicated variation among soybean cultivars in whether and how much elevated CO2 prolonged vegetative development. However, the cultivars tested differed in maturity group, and it is not known whether variation exists in CO2 effects on the duration of vegetative growth within a maturity group. In these experiments, a total of five soybean cultivars of maturity group IV were grown at ambient and elevated CO2 in the field in Maryland, USA using FACE systems, over three years. The time of first flowering, the time of the first open flowers at the apex of the main stem, the total number of main stem nodes at maturity, and seed yield were recorded. In each year of the study, there were cultivars in which elevated CO2 did not affect the duration of vegetative growth or the main stem node number, and other cultivars in which elevated CO2 prolonged vegetative growth and increased the number of main stem nodes and seed yield at maturity. The stimulation in yield by elevated CO2 was highly correlated with the increase in the number of main stem nodes, indicating that CO2 effects on the duration of vegetative growth may be important in adapting soybean to higher atmospheric CO2.