Rising Atmospheric Carbon Dioxide and Seed Yield of Soybean Genotypes

Abstract

If intraspecific variation to rising atmospheric CO 2 exists in soybean [ Glycine max (L.) Merr.], such variation could be used to select for optimal, high‐yielding cultivars. To quantify the range and determine the basis for variation in seed‐yield with increasing CO 2 , eight ancestral and one modern soybean cultivar differing in determinacy, maturity group, and morphology were grown to reproductive maturity at two CO 2 partial pressures, 40 Pa (ambient) and 71 Pa (elevated). Experiments were replicated three times in temperature controlled glasshouses during 1998 and 1999. Although all cultivars showed a significant increase in seed yield with elevated CO 2 ,(∼40%) Mandarin, an ancestral indeterminate cultivar, showed a greater relative response of seed yield to increased CO 2 than did all other cultivars (∼80%). The observed variation in seed yield response to CO 2 was not correlated with any vegetative parameter. At maturity, significant correlations in the relative response of seed yield to CO 2 were observed for both pod weight per plant and seed weight from branches. The later observation suggests that the sensitivity of seed yield response to CO 2 was associated with plasticity in the ability to form new seed in axillary branches in a high CO 2 environment. Genotypic differences in the seed yield response among existing ancestral soybeans suggests that sufficient germplasm is available for breeders to begin selecting lines which maximize soybean yield in response to increasing atmospheric CO 2