Leaf reflectance and transmittance were measured with an integrating sphere (Optronic IS-1000) following the procedures by Optronic Laboratories, Inc. (1997). The integrating sphere, powered by a constant power-output supply (OL 65 Programmable Current Source, Optronic, FL), was used in combination with an irradiance standard (Optronic OL Series 752-10) and a high accuracy UV/Visible spectroradiometer (OL 754) connected to a computer. Spectral scanning was performed from 250 nm - 800 nm at 5 nm intervals to produce a spectral distribution of the reflectance and transmittance on a whole-leaf basis for each species. Leaf adaxial/upper side was illuminated using a 200-W tungsten coiled-coil filament lamp with a 1.3 cm x 7 cm quartz envelope. The spectral irradiance values were provided within the wavelength ranging from 250 nm to 800 nm and were based on the National Institute of Standard and Technology (NIST) 1973 scale of spectral irradiance (Saunders and Shumaker, 1977). Measurements of both spectral transmittance and reflectance were based on the procedure of direct substitution
(Optronic Laboratory, 1997). The spectral absorbance, Ai, of a leaf sample, was computed from the knowledge of its spectral transmittance, TÄ, and spectral reflectance, RÀ, as follows:
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