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Absorption of Radiant Energy by Leaves

Walter E. Loomis
Ecology
Vol. 46, No. 1/2 (Jan., 1965), pp. 14-17
Published by: Wiley
DOI: 10.2307/1935253
Stable URL: http://www.jstor.org/stable/1935253
Page Count: 4
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Absorption of Radiant Energy by Leaves
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Abstract

Leaves of common plants absorb 80-95% of the blue (400-500 m(mu)), 60-80% of the green (500-600 m(mu), and 80-90% of the red (600-700 m(mu)). Absorption in the infrared is about 5% at 800 to 1,200 m(mu) and increases to near 100% beyond, 3,000 m(mu) or 3 @(mu). Absorption at 550 m(mu) by equal quantities of leaf pigments was two to six times greater for intact leaves than for methanol solutions. Shifts of the absorption bands toward shorter wavelengths, which are characteristic of chlorophyll solutions, were not observed in isolated whole or sonically disintegrated chloroplasts. Leaves in sunlight are heated from a few degrees above air temperature for thin leaves to 30 degrees C or more for very thick leaves before reaching a steady temperature. The heating and cooling curves shown by wilted leaves were not significantly different from those of transpiring leaves. Dried leaves heated less and cooled faster than normal, transpiring leaves. Leaves in sunshine were cooled quickly toward air temperature by wind at 5 mph. It is concluded that leaves tend to assume the temperature of the surrounding air; that they are heated rapidly by radiant energy, and cooled primarily by conduction of energy to the air.

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