Elevated tropospheric ozone and crop production: potential negative effects and plant defense mechanisms

Ozone (O 3 ) levels on Earth are increasing because of anthropogenic activities and natural processes. Ozone enters plants through the leaves, leading to the overgeneration of reactive oxygen species (ROS) in the mesophyll and guard cell walls. ROS can damage chloroplast ultrastructure and block photosynthetic electron transport. Ozone can lead to stomatal closure and alter stomatal conductance, thereby hindering carbon dioxide (CO 2 ) fixation. Ozone-induced leaf chlorosis is common. All of these factors lead to a reduction in photosynthesis under O 3 stress. Long-term exposure to high concentrations of O 3 disrupts plant physiological processes, including water and nutrient uptake, respiration, and translocation of assimilates and metabolites. As a result, plant growth and reproductive performance are negatively affected.…