Objective The study aimed to investigate the effects of different intensities of nighttime supplemental UV-A on the growth, physiology,and flavonoid metabolism of Ginkgo biloba,and select optimal nighttime supplemental light quality and techniques to enhance its medicinal and economic value. Method One-year-old half-sibling potted seedlings of golden-leaf G.biloba and green-leaf G.biloba were used as materials.The seedlings were divided into control and experimental groups.After normal daytime light exposure,the experimental groups were exposed to supplemental nighttime 390 nm UV-A radiation at three different intensities:15,30,and 45 μmol/(m2·s).During different growth stages,measurements were taken of biomass, mineral elements,primary metabolites,antioxidant-related enzymes,phenylpropanoid biosynthesis-related enzymes,and total flavonoids.The effects of nighttime supplemental UV-A at different intensities on the growth and metabolism of G.biloba were analyzed. Result ①When supplemented with nighttime UV-A irradiation at an intensity of 30 μmol/(m2·s),the aboveground biomass of green-leaf G.biloba significantly increased by 55.57% during the rapid growth period compared with the control group.At the terminal bud set stage,the root-to-shoot ratio was at its lowest,64% of that in the control group,indicating the optimal growth conditions.The biomass showed significant postive correlation with the mineral elements content.②Under supplemental nighttime UV-A treatments of 30 μmol/(m2·s),the soluble protein content in the leaves of golden- and green-leaf G.biloba at the terminal bud set stage significantly increased,reaching 2.02-fold and 1.90-fold that of the control,respectively.At this stage,golden-leaf G.biloba exhibited the highest POD activity under the 30 μmol/(m²·s) treatment,while green-leaf G.biloba showed the highest activity under the 45 μmol/(m²·s) treatment,with increases of 19.8% and 18.4% compared with the control,respectively.Both values were significantly higher than those of the control.③During the terminal bud set stage,the phenylpropanoid biosynthesis enzyme activity and total flavonoid content in the leaves of green-leaf G.biloba reached their highest levels under supplemental nighttime UV-A radiation of 30 μmol/(m2·s),with the total flavonoid content being 2.07 times that of the control.④A comprehensive evaluation using the fuzzy membership function method revealed that the mean membership degrees of G.biloba plants were relatively high under supplemental nighttime UV-A treatments of 30 and 45 μmol/(m2·s),indicating that these treatments yielded the optimal medicinal value of leaf flavonoids. Conclusion Under normal daytime irradiation conditions,supplemental nighttime UV-A radiation at 30,45 μmol/(m2·s) is most conducive to the growth of G.biloba seedlings and the accumulation of flavonoids in their leaves,thereby enhancing their medicinal value.
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