Is there potential to adapt soybean (Glycine max Merr.) to future [CO₂]? An analysis of the yield response of 18 genotypes in free-air CO₂ enrichment

Rising atmospheric [CO₂] is a uniform, global change that increases C₃ 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.