Tropospheric O3: A cause of concern for terrestrial plants

Abstract

Tropospheric ozone (O3) is a phytotoxic pollutant causing risk to food production, pasture, and forest communities. In the present scenario, unsustainable resource utilization has turned this secondary pollutant into a major component of global climate change. The background levels of O3 are very high, and IPCC projections have shown that it will increase by 20-25% in 2050 and 40-60% in 2100, causing severe consequence on global food security. Ozone enters plants through stomata, where it can be dissolved in the apoplastic fluid. Ozone has several potential effects on plants: direct reaction with cell membranes, generation of ROS and H2O2 (which alter cellular function by causing cell death), induction of premature senescence, negative impact on photosynthetic machinery and up- or downregulation of antioxidants, defense reactions, and variations in metabolic pathways. Tropospheric O3 causes changes in tree diameter, wood quality, herbivory pattern, forage quality, and crop yield and quality. In this chapter, we make an attempt to present an overview of O3 concentrations throughout the globe and its impact on agricultural crops, forest, and grassland ecosystems. We summarized the information available on plant responses to O3 at physiological, cellular, and biochemical levels; crop yield; and forest and grassland communities at present concentrations and also under projected future concentrations.