Effect of UV-B radiation on photosynthesis based flavonoid synthesis in daylily leaves

In order to assess the impact of UV-B radiation on flavonoid compound levels in 'Stella de Oro' daylily leaves, three distinct treatment groups were established: a control group (CK) devoid of UV-B exposure, a low-dose UV-B group (L, 10 μw/cm²), and a high-dose UV-B group (H, 20 μw/cm²). Throughout the UV-B exposure period, parameters including leaf gas exchange, dry weight ratio, and flavonoid compound content were monitored. Following the UV-B treatment, there was a notable increase in the net photosynthesis rate (Pn) by 72 %, stomatal conductance (Gs) by 46 %, transpiration rate (Tr) by 42 %, and water use efficiency (WUE) by 21 %. Moreover, there was a notable increase in the total content of rutin, myricetin, and quercetin in the leaves by 110 %, 55 %, and 47 % respectively. The observed changes in leaf dry weight ratio under UV-B exposure in group H were consistent with the alterations in flavonoid compound levels in the leaves. Based on the results, PCA analysis indicated a significant correlation between WUE and flavonoids content, possibly related with the combined effect of Pn and Tr.