Abstract
Ozone (O3) is a phytotoxic air pollutant that limits crop productivity. Breeding efforts to improve yield under elevated O3 conditions will benefit from understanding the mechanisms that contribute to O3 tolerance. In this study, leaf gas exchange and antioxidant metabolites were compared in soybean genotypes (Glycine max (L.) Merr) differing in ozone sensitivity. Mandarin (Ottawa) (O3-sensitive) and Fiskeby III (O3-tolerant) plants grown under charcoal-filtered (CF) air conditions for three weeks were exposed for five days to either CF conditions or 70 ppb O3 in continuously stirred tank reactors (CSTRs) in a greenhouse. In the CF controls, stomatal conductance was approximately 36% lower for Fiskeby III relative to Mandarin (Ottawa) while the two genotypes exhibited similar levels of photosynthesis. Ozone exposure induced significant foliar injury on leaves of Mandarin (Ottawa) associated with declines in both stomatal conductance (by 77%) and photosynthesis (by 38%). In contrast, O3 exposure resulted in minimal foliar injury on leaves of Fiskeby III with only a small decline in photosynthesis (by 5%), and a further decline in stomatal conductance (by 30%). There was a general trend towards higher ascorbic acid content in leaves of Fiskeby III than in Mandarin (Ottawa) regardless of treatment. The results confirm Fiskeby III to be an O3-tolerant genotype and suggest that reduced stomatal conductance contributes to the observed O3 tolerance through limiting O3 uptake by the plant. Reduced stomatal conductance was associated with enhanced water-use efficiency, providing a potential link between O3 tolerance and drought tolerance.
Highlights
Ozone (O3 ) is a problematic greenhouse gas and air pollutant when present at high levels in the troposphere of the Earth’s atmosphere [1,2,3]
Reduced stomatal conductance was associated with enhanced water-use efficiency, providing a potential link between O3 tolerance and drought tolerance
Genetic variation in O3 response in soybean can be seen in the varying levels of decreased biomass production, seed yield, stomatal conductance, and carbon assimilation, as well as increased foliar injury [6,9,11,12,13,14,15]
Summary
Ozone (O3 ) is a problematic greenhouse gas and air pollutant when present at high levels in the troposphere of the Earth’s atmosphere [1,2,3]. Current levels of O3 have significant effects on the growth and yield of many plants, including agricultural crops [2,4,5]. The susceptibility to O3 damage varies greatly among plant species and genotypes within species [8,9,10]. Genetic variation in O3 response in soybean can be seen in the varying levels of decreased biomass production, seed yield, stomatal conductance, and carbon assimilation, as well as increased foliar injury [6,9,11,12,13,14,15]. The variation in soybean genotype O3 response provides a useful research opportunity to understand O3 tolerance mechanisms
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