Salicylic acid acts upstream of nitric oxide in elevated carbon dioxide-induced flavonoid biosynthesis in tea plant (Camellia sinensis L.)

•Elevated CO2 increased the concentrations of flavonoid, SA and NO dose-dependently.•Suppression of endogenous SA and NO levels reduced flavonoid level under elevated CO2.•Scavenging of NO did not alter endogenous SA level but SA deficiency reduced NO level.•Exogenous NO could reverse SA deficiency effect on flavonoid level and PAL activity.•SA acts upstream of NO in elevated CO2-induced flavonoid biosynthesis in tea leaves.