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

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 Therefore, we compiled 46 journal articles and unpublished datasets that reported leaf photosynthetic and biochemical traits, plant biomass, and yield in five C crops (chickpea, rice, snap bean, soybean, and wheat) and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