Similar photosynthetic but different yield responses of C 3 and C 4 crops to elevated O 3 .

The deleterious effects of ozone (O ₃ ) pollution on crop physiology, yield, and productivity are widely acknowledged. It has also been assumed that C ₄ crops with a carbon concentrating mechanism and greater water use efficiency are less sensitive to O ₃ pollution than C ₃ 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 Therefore, we compiled 46 journal articles and unpublished datasets that reported leaf photosynthetic and biochemical traits, plant biomass, and yield in five C ₃ crops (chickpea, rice, snap bean, soybean, and wheat) and four C ₄ crops (sorghum, maize, Miscanthus × giganteus , and switchgrass) grown under ambient and elevated O ₃ concentration ([O ₃ ]) in the field at free-air O ₃ concentration enrichment (O ₃ -FACE) facilities over the past 20 y. When normalized by O ₃ exposure, C ₃ and C ₄ crops showed a similar response of leaf photosynthesis, but the reduction in chlorophyll content, fluorescence, and yield was greater in C ₃ crops compared with C ₄ crops. Additionally, inbred and hybrid lines of rice and maize showed different sensitivities to O ₃ exposure. This study quantitatively demonstrates that C ₄ crops respond less to elevated [O ₃ ] than C ₃ crops. This understanding could help maintain cropland productivity in an increasingly polluted atmosphere.