Effect of Shade on the Growth, Leaf Morphology, and Photosynthetic Capacity of an American Sycamore Clone

Cuttings from a single American sycamore clone were rooted and grown under four levels of artificial shade: 27, 45, 72 and 100 percent of full sunlight to learn more about the ecological role of this species in deciduous forests of the Southern Appalachians. After 132 days, leaf angle, leaf area, leaf thickness, stomatal frequency and size, and dry matter production of the leaves, stem, and roots were determined. Leaf angle was significantly higher under a relative illumination (RI) of 27 percent than for the other treatments, including full sunlight. Leaf area reached a maximum of 20 dm2 under a RI of 45, while leaf thickness was greatest (254 Mm) in full sunlight, and lowest (192 Mm) under a RI of 27. Shade appeared to affect stomatal frequency and size only on the upper surfaces of leaves. Net photosynthesis rates were studied from light intensities ranging from 2,000 to 10,000 foot-candles for determination of light saturation intensities. Although photosynthetic light saturation occurred near the same intensity for all shade levels, plants grown in full sunlight had higher rates of net photosynthesis. American sycamore (Platanus occidentalis L.) is one of the largest trees of the eastern deciduous forest biome. It occurs in forest communities that are pioneer, transitional, subclimax, and climax in nature (Fowells 1965). It is also of interest to foresters where close spacing and application of nitrogen fertilizers in plantations has led to increased growth (Wood et al. 1976). Few studies of a physiological nature have been conducted on sycamore which would help ecologists and foresters to assess *The investigation reported in this paper (No. 78-8-15) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director. The research was supported in part by the McIntire-Stennis Cooperative Forestry Research Program.