Effect of shade on the growth, leaf morphology, and photosynthetic capacity of an American sycamore clone [Platanus occidentalis]

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 20dm2under a RI of 45, while leaf thickness was greatest (254 μm) in full sunlight, and lowest (192 μm) 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.