Abstract
The actual effects of light fluctuations within plant canopies have not still been clarified. In this study, field and indoor experiments were conducted for the purpose of obtaining the characteristics of fluctuating light within six plant canopies.
(1) Light fluctuations under natural light within field-type plant canopies were investigated under various conditions and the following results were obtained. That is, (1) The difference between bright and dark lights in light fluctuations showed a daily change almost proportional to the intensity of solar radiation. (2) Light fluctuations were not obvious at various measured points in a citrus crown. (3) Light fluctuations developed markedly as planting density increased. (4) The difference was confirmed between the waveforms of fluctuating lights according to the kinds of plant canopies and considered to be caused by the kinetic energy of wind in plant canopies and the physical characteristics of the plant canopies.
(2) As a result of the wind tunnel experiment related to light fluctuations, the frequency bringing the spectral density of the fluctuating light within each plant canopy (height: about 20 cm) to a definite level or more were about 15 Hz in eggplants, sweet peppers, asparagus and garland chrysanthemums on the case of a wind velocity of 1.7 ms-1. Also, it was about 11 Hz in the turnip canopy, and 6 Hz in welsh onion, of which the waveform showed a line spectrum. With respect to six plant canopies, there was no great difference in peak frequency between weak wind (1.7 ms-1) and strong wind (2.5 ms-1), and the peak frequencies of both cases were within a range of 1.5 Hz N 5.0 Hz. The peak value of power spectra became large in proportion to an increase in wind velocity and this relation was also confirmed within the observed frequency range (Fig. 7) .
