Effect of Atmospheric Carbon Dioxide Enrichment at Different Developmental Stages on Growth and Yield Components of Soybeans¹

Abstract

Vegetative and reproductive parameters were measured at maturity on field‐grown soybean plants [ Glycine max (L.) Merr., var. Hark] given CO 2 enrichment to 1,200 (±150) ppm for 5‐week periods corresponding to vegetative, flowering, and pod‐filling stages of development. CO 2 enrichment during the vegetative stage had no effects on the measured parameters at maturity. CO 2 enrichment during flowering caused increased node numbers, leaf and stem dry weights, and pod numbers. Seed size decreased and need yield was not affected. CO 2 enrichment during pod filling had no effects on vegetative parameters, but caused a slight increase in pod number, and a marked increase in pod weight and seed yield at maturity. These results are discussed in terms of source‐sink relationships and the limitations imposed by the availability of photosynthate.