The Adaptability to Light Intensity of Seedlings of Quercus Petraea (Matt.) Liebl.

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Abstract
The response of Quercus petraea to light of different intensities was investigated in garden experiments with artificial shade, in laboratory measurements of photosynthesis, and in a semi-natural oakwood in different conditions of shade, vegetation and root competition. Shading resulted in increased height, leaf area, specific leaf avea, leaf area ratio, and chlorophyll content; and in decreased root weight, root/stem ratio, net assimilation rate and relative growth rate. For an entire growing season, growth saturation was not reached at full daylight. Seedlings with only one whorl of leaves reached maximum net assimilation rate and relative growth rate at 56% daylight values in Aug.; values in full daylight were less. The compensation point was estimated to be not more than 2% daylight. A more significant value of 5.9% was obtained by excluding the weight of leaves lost at leaf fall. At low light intensity other factors such as mildew raised the compensation point to above 8% daylight. The capacity of the photochemical process and the rate of photosynthesis at light saturation were greater in shade-grown than in sun-grown leaves. Photosynthesis per unit of chlorophyll was greater in sun-grown leaves. Exposure to light of high intensity reduced subsequent photosynthesis at low light intensities more in shade than in sun-grown leaves. During exposure to bright light the rate of photosynthesis by sun and shade-grown leaves decreased by 4.2 and 7.8% per hour, respectively. In a semi-natural oak wood, light intensity at normal tree spacing and in clearings was sufficient for oak regeneration provided that Pteridium aquilinum was not present. At low light intensities, root competition from older trees and other species had a greater effect on seedling growth than light intensity. Concepts of shade adaptation are discussed. It was concluded that oak seedlings possess a degree of adaptability to shade similar to that of other shade plants.