Similar photosynthetic but different yield responses of C₃ and C₄ crops to elevated O₃

The deleterious effects of ozone (O₃) pollution on crop physiology, yield, and productivity are widely acknowledged. It has also been assumed that C₄ crops with a carbon concentrating mechanism and greater water use efficiency are less sensitive to O₃ pollution than C₃ crops. This assumption has not been widely tested. Therefore, we compiled 46 journal articles and unpublished datasets that reported leaf photosynthetic and biochemical traits, plant biomass, and yield in five C₃ crops (chickpea, rice, snap bean, soybean, and wheat) and four C₄ crops (sorghum, maize, Miscanthus × giganteus, and switchgrass) grown under ambient and elevated O₃ concentration ([O₃]) in the field at free-air O₃ concentration enrichment (O₃-FACE) facilities over the past 20 y. When normalized by O₃ exposure, C₃ and C₄ crops showed a similar response of leaf photosynthesis, but the reduction in chlorophyll content, fluorescence, and yield was greater in C₃ crops compared with C₄ crops. Additionally, inbred and hybrid lines of rice and maize showed different sensitivities to O₃ exposure. This study quantitatively demonstrates that C₄ crops respond less to elevated [O₃] than C₃ crops. This understanding could help maintain cropland productivity in an increasingly polluted atmosphere.