Growth, Leaf Gas Exchange and Leaf Anatomy of three Ornamental Shrubs Grown under different Light Intensities

The aim of this work was to determine the long-term response of growth, leaf morphology and gas exchange of three widely grown shrubs to the level of irradiance. To this purpose, one-year-old uniform rooted cuttings of Camellia x williamsii W.W.Sm. 'Debbie', Photinia x fraseri Dress 'Red Robin' and Viburnum tinus L. 'Eve Price' grown in containers were placed for 2 years under different woven polypropylene fabrics that reduced light intensity by 60 % and 30 % and, as a control, plants were also grown in full sun. Plant dry weight, LAI, LAR, NAR, RGR, mean leaf area, number, ultrastructure and gas exchange were measured during the experiment. The species reacted in different ways to shading, indicating a strong genetic influence, even if some parameters as transpiration, leaf thickness, leaf size and stomatal frequency responded similarly to irradiance. Camellia showed a great adaptability to light conditions. Shading photinia greatly reduced root biomass but did not alter leaf gas exchange, thus is not a recommendable practice for this species. Viburnum increased leaves and stems biomass and increased net photosynthesis and water use efficiency under shaded conditions. In conclusion, effects of shading can positively affect plant growth and physiology, but response to shading is species-specific