Improving Soybean Yields in Elevated [CO2] and Elevated [O3].

In the last 250 years, atmospheric [CO₂] has risen from 280 parts per million (ppm) to over 400 ppm. Over that same period ground-level ozone concentrations ([O₃]) have more than doubled. Over this century, atmospheric [CO₂] is projected to rise to at least 550 ppm by 2050 and 700-1000 ppm by 2100. These two greenhouse gases have opposing effects on crops, with increased atmospheric [CO₂] typically stimulating photosynthesis, growth and yield of C3 crops, while rising [O₃] has the opposite effect. Research at the Soybean Free Air Concentration Enrichment (SoyFACE) facility has been investigating the effects of rising [CO₂] and [O₃] on soybean for the past 15 years. Experiments have examined the productivity, physiology and genetics of soybean responses to rising [CO₂] and [O₃], and there is significant genetic variation in response of soybean to both atmospheric changes. Eighteen soybean genotypes were grown at elevated [CO₂] for multiple years, and on average elevated [CO₂] stimulated total aboveground 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. Two genotypes (HS93-4118 and Loda) showed similar yields in ambient [CO₂], but HS93-4118 showed no yield gain at elevated [CO₂] while Loda showed a 25% increase in yield. These genotypes are being further investigated for the physiological basis for this difference in response. A recombinant population of soybean (Pana x Dwight) was grown for 3 years at elevated [O₃] and ongoing work is identifying QTLs associated with O₃ tolerance. Experiments at SoyFACE aim to improve the productivity and resiliency of soybean in a future elevated [CO₂] and elevated [O₃] environment.