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 Therefore, we compiled 46 journal articles and unpublished datasets that reported leaf photosynthetic and biochemical traits, plant biomass, and yield in five C(3) crops (chickpea, rice, snap bean, soybean, and wheat)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.