Rising atmospheric [CO2] is a uniform, global change that increases C-3 photosynthesis and could offset some of the negative effects of global climate change on crop yields. Genetic variation in yield responsiveness to rising [CO2] would provide an opportunity to breed more responsive crop genotypes. A multi-year study of 18 soybean (Glycine maxMerr.) genotypes was carried out to identify variation in responsiveness to season-long elevated [CO2] (550ppm) under fully open-air replicated field conditions. On average across 18 genotypes, elevated [CO2] stimulated total above-ground biomass by 22%, but seed yield by only 9%, in part because most genotypes showed a reduction in partitioning of energy to seeds. Over four years of study, there was consistency from year to year in the genotypes that were most and least responsive to elevated [CO2], suggesting heritability of CO2 response. Further analysis of six genotypes did not reveal a photosynthetic basis for the variation in yield response. Although partitioning to seed was decreased, cultivars with the highest partitioning coefficient in current [CO2] also had the highest partitioning coefficient in elevated [CO2]. The results show the existence of genetic variation in soybean response to elevated [CO2], which is needed to breed soybean to the future atmospheric environment.

This study investigated the response of 18 soybean varieties to elevated carbon dioxide concentrations ([CO2]) in the field. There was variation in the response of seed yield in the genotypes, ranging from no stimulation to a 22% increase in yield, and consistency from year to year in the varieties that were the most and least responsive to elevated [CO2]. Results support the potential to breed crops for enhanced CO2 response.