UV-A and UV-B combined with PAR intensity change in plant growth, total phenol, flavonoid, antioxidative and essential oil composition of Pelargonium graveolens

Abstract Background Different wavelengths of solar radiation incident on earth [herein: Photosynthetically Active Radiation )PAR(,Ultra Violet-A )UV-A( and Ultra Violet-B (UV-B)] and their spectral balance not only have an impact on plants′ growth, morphology and physiology, but also have been shown to be important for the quality and quantity of secondary metabolites produced by plants. Material and Methods In this outdoor study we addressed the effects of PAR intensity and UV on the growth, yield, antioxidative, phenolic, flavonoids and essential oil production of Pelargonium graveolens L’Hér. The experiment was performed as split plots in a randomized complete block design with three replications. During the growth, two PAR intensities (ambient PAR and reduced PAR) and four UV treatments (ambient UV, enhanced UV-A, enhanced UV-B and enhanced UVA + B) were applied. Results High PAR intensity declined the length and width of leaf, the height of plant and fresh weight of aerial part, but increased dry weight of aerial part. Enhanced UV-B irradiation was associated with reduced plant height, leaf expansion and fresh and dry weight of aerial part. Interestingly, negative influence of enhanced UV-B radiation on morphology and growth of plant was largely alleviated by high PAR intensity. The amount of total phenols and flavonoids, antioxidant activity and essential oil production of P. graveolens strongly increased with both enhanced UV-B irradiation and high PAR. On the contrary, UV-A radiation did not significantly influence total phenols, flavonoids, antioxidant activity and essential oil. Moreover, the combination of high PAR intensity and enhanced UV-B led to further increases in total flavonoid content and the antioxidant capacity. Both high PAR intensity and enhanced UV-B increased the percentage of geraniol in essential oil, leading to a slight reduction of C/G ratio. Conclusions Considering that the lower C/G ratio is the most important indicator of the high economic value of rose geranium essential oil, reducing C/G ratio under enhanced UV-B radiation and/or high PAR is likely to be favorable. Overall, we conclude that PAR and UV-B irradiation, as two important environmental factors, have positive effects on the quality and quantity of rose geranium secondary metabolites.