Fluctuations of Light in Some Plant Canopies

Abstract

Although the actual effects of light fluctuations within plant canopies have not still been clarified, some applied examples of fluctuating light to cultivation exist due to the conversion control of continuously irradiated artificial light to intermittently irradiated fluctuating light. In this study, indoor experiments were conducted for the purpose of obtaining the characteristics of fluctuating light within some plant canopies.
(1) As a result of the wind tunnel experiment relating to light fluctuations, the frequency bringing the spectral density of the fluctuating light within each plant canopy (height: about 20cm) to a definite level or more was in the order of paddy (28Hz)>corn (22Hz)>burdock (17Hz)>carrot (13Hz)/broad bean (11Hz)/soybean (10Hz) in the case of wind velocity of 1.7ms^-1. With respect to six plant canopies, differences were small in the peak frequency between a weak wind (1.7ms^-1) and strong wind (2.5ms^-1), and the peak frequencies of both cases were within a range of 1.5-3.5Hz. The peak value of power spectra became large in proportion to the increase in wind velocity and this relation was also confirmed within the observed frequency range (Fig. 4).
(2) The observed frequency range of fluctuation of light was proportional to the wind velocity at different plant heights of broad bean and corn. All were formed as regression equation. In corn regression lines were arranged according to plant height, whereas in broad bean those were not arranged.