Elevated Ozone Reduces the Quality of Tea Leaves but May Improve the Resistance of Tea Plants.

Tropospheric ozone (O) pollution can affect plant nutritional quality and secondary metabolites by altering plant biochemistry and physiology, which may lead to unpredictable effects on crop quality and resistance to pests and diseases. Here, we investigated the effects of O (ambient air, Am; ambient air +80 ppb of O, EO) on the quality compounds and chemical defenses of a widely cultivated tea variety in China ( 'Baiye 1 Hao') using open-top chamber (OTC). We found that elevated O increased the ratio of total polyphenols to free amino acids while decreasing the value of the catechin quality index, indicating a reduction in leaf quality for green tea. Specifically, elevated O reduced concentrations of amino acids and caffeine but shows no impact on the concentrations of total polyphenols in tea leaves. Within individual catechins, elevated O increased the concentrations of ester catechins but not non-ester catechins, resulting in a slight increase in total catechins. Moreover, elevated O increased the emission of biogenic volatile organic compounds involved in plant defense against herbivores and parasites, including green leaf volatiles, aromatics, and terpenes. Additionally, concentrations of main chemical defenses, represented as condensed tannins and lignin, in tea leaves also increased in response to elevated O. In conclusion, our results suggest that elevated ground-level O may reduce the quality of tea leaves but could potentially enhance the resistance of tea plants to biotic stresses.