Adjustments in leaf physiological and metabolic processes in Coffea arabica exposed to ozone

Although current ozone (O₃) concentrations significantly reduce crop yields globally, their potential effects on Coffea arabica plantations remain largely unexplored. This study addresses that gap by testing the hypothesis that C. arabica plants may tolerate O₃-induced oxidative stress by adjusting leaf physiological and metabolic processes. An experimental study was conducted using a FACE (free air-controlled exposure) facility to assess gas-exchange parameters, phenolics, lignin and carbohydrate contents, cell-damage indicators, antioxidant responses, and metabolic profiling in coffee plants (cv. Geisha) exposed to three O₃ levels: 1[O3]AA (ambient), 1.5 × [O3]AA and 2.0 × [O3]AA, corresponding to 47.0, 68.2, 94.3 ppb as mean hourly concentrations, respectively. Geisha plants responded by adjusting their leaf physiological and metabolic processes, showing reduced photosynthetic activity and activating compensatory mechanisms, such as increased antioxidants, accumulation of amino acids, and elevated fatty acids, to support redox balance, energy metabolism, and membrane repair. These responses partially reduced oxidative damage and highlighted the complex metabolic changes involved in O3 tolerance. However, these adjustments did not prevent leaf injury, indicating that the original hypothesis was not supported. Chronic ozone exposure caused significant physiological and metabolic disruptions, including reduced photosynthesis, lower leaf biomass, and impaired redox balance. These effects likely weaken cell walls by reducing lignin, cellulose, and pectin, thereby compromising leaf structure. Our findings emphasize the importance of understanding plant-specific metabolic responses to develop strategies that enhance resilience and productivity in agroecosystems facing rising O3 pollution.