Effect of Light Intensity and UV Radiation on Morpho-physiological Charactrestics and Biomass of Rose-Scented Geranium (Pelargonium graveolens L'Heritier)

Rose-scented geranium (Pelargonium graveolens Lchr('39')Heritier) is an important ornamental plant that is cultivated worldwide due to its valuable medicinal properties. The present research was conducted to evaluate the effect of light intensity and UV radiation on the morphological and physiological characteristics of rose-scented geranium in 2020. The experiment was performed as split plots in a completely randomized design. Light intensity was considered as the first factor at two levels (low light intensity and high light intensity) and ultraviolet radiation at four levels (environmental UV, UV-A, UV-B and UVA+B) as the second factor. The results showed that high light intensity reduced petiole length, leaf length and width and plant height of P. graveolens; in contrast, the number of lateral branches and stem diameter were increased by rising light intensity. UV-B and UVA+B reduced plant height, petiole length and leaf length and width; but, the number of lateral branches and stem diameter were increased by UVB treatments and UVA+B treatments. While, plant produced leaves and branches with elongated shapes when traeted by UVA and environmental UV. In terms of physiological traits, results showed that increasing the light intensity reduced the relative water content of leaf, intercellular CO2 and stomata conductivity. In contrast, chlorophyll a, chlorophyll b, total chlorophyll, transpiration, electrolyte leakage, catalase activity and photosynthesis rate were increased by increasing light intensity. Also, UVB and UVA+B treatments led to reduce chlorophyll a, chlorophyll b, total chlorophyll and photosynthesis rate. Under high light intensity, UVB and UVA+B reduced the stomata conductivity. The amount of electrolyte leakage, malondialdehyde, intercellular CO2 and the activity of catalase and peroxidase enzymes were increased by UVB and UVA+B radiations. Althogh, the rate of increase of these traits by UVB and UVA+B was more severe in low light intensity.