Ozone Exposure Response for U.S. Soybean Cultivars: Linear Reductions in Photosynthetic Potential, Biomass, and Yield

Abstract

Abstract Current background ozone (O3) concentrations over the northern hemisphere’s midlatitudes are high enough to damage crops and are projected to increase. Soybean (Glycine max) is particularly sensitive to O3; therefore, establishing an O3 exposure threshold for damage is critical to understanding the current and future impact of this pollutant. This study aims to determine the exposure response of soybean to elevated tropospheric O3 by measuring the agronomic, biochemical, and physiological responses of seven soybean genotypes to nine O3 concentrations (38–120 nL L−1) within a fully open-air agricultural field location across 2 years. All genotypes responded similarly, with season-long exposure to O3 causing a linear increase in antioxidant capacity while reducing leaf area, light absorption, specific leaf mass, primary metabolites, seed yield, and harvest index. Across two seasons with different temperature and rainfall patterns, there was a robust linear yield decrease of 37 to 39 kg ha−1 per nL L−1 cumulative O3 exposure over 40 nL L−1. The existence of immediate effects of O3 on photosynthesis, stomatal conductance, and photosynthetic transcript abundance before and after the initiation and termination of O3 fumigation were concurrently assessed, and there was no evidence to support an instantaneous photosynthetic response. The ability of the soybean canopy to intercept radiation, the efficiency of photosynthesis, and the harvest index were all negatively impacted by O3, suggesting that there are multiple targets for improving soybean responses to this damaging air pollutant.