Impact of Tropospheric Ozone on Crop Plants

Tropospheric ozone (O-3) is the most important regional atmospheric pollutant causing risk to food production across the globe due to its phytotoxicity and prevalence over agricultural areas. Peak O-3 concentrations have declined in Europe and North America due to reductions in precursors during the last decades, however, emissions of O-3 precursors have increased in Asia. The current critical level of ozone is determined by the threshold for yield loss which is based on the seasonal sum of the external concentration above 40 ppb. In the present article, the impact of tropospheric O-3 on crop photosynthesis, defense mechanism, growth, reproductive processes and yield of crop plants have been documented. O-3 upon its entry into the leaf intercellular spaces rapidly forms reactive oxygen species and reacts with components of the leaf apoplast to initiate a complex set of responses that constitute variable countermeasures by antioxidative enzymes. Ozone affects photosynthetic process by influencing photosynthetic pigments, chlorophyll fluorescence kinetics and electron transport as well as carbon fixation in terms of decreased Rubisco activity and quantity. Translocation and allocation pattern of photosynthate also get influenced under O-3, which affect reproductive processes and yield of crops. Plant species and cultivars exhibit a range of sensitivity to O-3, which is identifiable in terms of biochemical, physiological, molecular and yield responses. Hence, understanding of cultivar sensitivity in context to O-3 would be helpful in development of potential O-3 biomarkers and O-3 tolerant variables.