Spectral Properties of Sunlight and Phytochrome Photoequilibrium as Influenced by Leaf Number in Chrysanthemum

摘要

As the incident sunlight passes through plant leaves, the amount of light is reduced due to the absorption and reflection by leaves. There are also qualitative changes in transmitted light. The present work examined light intensity, spectral quality transmitted, and phytochrome photoequilibrium as influenced by the number of leaf in chrysanthemum (Dendranthema grandiflorum). The photon flux of incident sunlight increased rapidly from 300 to 500 nm and remained relatively constant above these wavelengths and had approximately equal photon flux of red and far-red lights. As the number of leaf increased, photon flux in 300-800 nm range decreased rapidly but photosynthetically active radiation in 400-700 nm range attenuated more rapidly from 3.0 to <0.1%. There were also changes in light composition. Most of sunlight in the red and blue regions decreased more rapidly than green and UV regions. The rapid attenuation of blue and red lights was attributed to the absorption by chlorophylls, because red andblue regions are absorbed more effectively than other lights. The light transmitted by leaves was predominantly far-red light and as a result, the red/far-red ratio decreased. Such results led to changes in the phytochrome photoequilibrium. Phytochromephotoequilibrium of incident sunlight was 0.72, but it decreased to 0.26, 0.12, and 0.09 with the increasing leaf number. These results show that light environment and phytochrome photoequilibrium change as leaf number changes, and these changes may control photosynthetic and morphological characteristics in a plant or plant populations of chrysanthemum.