Optimizing the Light Environment for the Cultivation of Ornamental Tree Species: the Influence of LED Spectra on the Photosynthetic Apparatus and Secondary Metabolism

Abstract

In urban environments, green areas often lack sunlight during the day and rely on artificial illumination at night, which reduces their ecological services. Application of LED illumination with specific spectral characteristics in green areas of megacities could enhance their aesthetic value and safety and optimize the health of urban vegetation. The effects of monochrome red, blue, and mixed red-blue LED lighting on photosynthetic pigments, flavonoids, anthocyanins, and tannin accumulation in the leaves of the shaded seedlings of ornamental woods Pinus sylvestris L., Rhododendron catawbiense Michx., Magnolia × soulangeana Soul.-Bod., Magnolia Kobus DC., and Ginkgo biloba L. were studied in pot experiments. The species specificity of physiological responses to LED illumination with a specific spectral composition was established. The contents of photosynthetic pigments and tannins in the leaves of the heliophytes M. × soulangeana, M. kobus, G. biloba, and P. sylvestris were the most effectively stimulated by monochrome red LED lighting. While the accumulation of flavonoids in the leaves of the mentioned test-plants was the highest at red-blue or monochrome blue LED lighting. In the shade-tolerant Rh. catawbiense the different tendency was observed: the highest levels of photosynthetic pigments in the leaves were observed in the plants treated with red-blue LED lighting, the highest content of flavonoids was observed in plants treated with monochrome red. The monochrome blue LED lighting had the highest promoting effect on anthocianin synthesis in all test-plants. Thus, using five ornamental tree species with different light requirements, it was demonstrated that supplemental red and blue LED lighting could effectively optimize photosynthesis and secondary metabolism in urban woody vegetation exposed to light deficiency.