Rising atmospheric carbon dioxide and seed yield of soybean genotypes

If intraspecific variation to rising atmospheric CO2 exists in soybean [Gly cine max (L.) Merr.], such variation could be used to select for optimal, h igh-yielding cultivars. To quantify the range and determine the basis for v ariation in seed-yield with increasing CO2, eight ancestral and one modern soybean cultivar differing in determinacy, maturity group, and morphology w ere grown to reproductive maturity at two CO2 partial pressures, 40 Pa (amb ient) and 71 Pa (elevated). Experiments were replicated three times in temp erature controlled glasshouses during 1998 and 1999. Although all cultivars showed a significant increase in seed yield with elevated CO2,(similar to 40%) Mandarin, an ancestral indeterminate cultivar, showed a greater relati ve response of seed yield to increased CO2 than did all other cultivars (si milar to 80%). The observed variation in seed yield response to CO2 was not correlated with any vegetative parameter. At maturity, significant correla tions in the relative response of seed yield to CO2 were observed for both pod weight per plant and seed weight from branches. The later observation s uggests that the sensitivity of seed yield response to CO2 was associated w ith plasticity in the ability to form new seed in axillary branches in a hi gh CO2 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 resp onse to increasing atmospheric CO2.