Korean flowering cherry (Prunus × yedoensis Matsum.) response to elevated ozone: physiological traits and biogenic volatile organic compounds emission

Ozone (O₃) absorption through leaf stomata disrupts plant physiological processes, prompting various defense mechanisms to mitigate O₃-induced harm. This study measured parameters including cell structure, gas exchange, carbon assimilation, lipid peroxidation, and biogenic volatile organic compounds (BVOCs) emissions to evaluate the physiological impact of Prunus × yedoensis under elevated ozone (E-O₃) exposure. The seedlings exhibited a slight stimulatory effect during the early phases of E–O₃ exposure; however, E–O₃ beyond a specific threshold significantly and negatively affected photosynthetic parameters, pigment content, and potential antioxidant capacity, and E–O₃ was significantly correlated with the BVOCs emission rate. After three weeks of E–O₃ exposure, no significant differences were observed in leaf stomatal appearance in the field emission scanning electron microscopy results, but according to the results of leaf mesophyll cell ultrastructure, grana degradation, membrane decomposition, cell wall thickening, wart–like protrusion formation, and increased plastoglobulus density within the chloroplasts were observed. Chlorophyll content significantly decreased by 38.71%, and solute leakage increased by 20.57% in the E–O₃ group. The net photosynthetic rate was almost two times lower with E–O₃. In contrast, there were no significant differences in stomatal conductance. In conclusion, E–O₃ can induce a hormetic stimulatory effect during the early exposure phase. However, when the critical threshold is exceeded, O₃ adversely affects the physiology of P. × yedoensis seedlings. Therefore, E–O₃ is a harmful air pollutant that hinders the growth of woody plants, and urban trees require the continuous management of O₃ phytotoxicity.