Abstract
We have hypothesized that seasonal changes of light quality in daylight influence photomorphogenesis of plants. Further, we also have speculated that the patterns of its changes differ from place to place, and this difference has been useful in the formation of a vegetation at each place. In the present study, photon flux (PF) in the spectral regions of 300-400 nm (UV), 400-500 nm (B), 500-600 nm (G), 600-700 nm (R), 700-800 nm (Fr) were simultaneously observed at noon at Sapporo (Aug. 2000-Mar. 2002), Gifu (Jan. 2000-Dec. 2002) and Naha (Jan. 2001-Sep. 2002) in order to determine the differences in the seasonal changes of light quality in daylight for different places. There was a similar trend in the changes in spectral ratio of B, G and R/photosynthetic photon flux (PPF) on fine days among the three cities. The G/PPF ratio was almost constant during the observation, and there was a negative correlation between variations of B and R/PPF ratios. These changing patterns were in agreement with the one in the previous paper (Ishii and Yamazaki, Environ. Control in Biol. (2002) 40: 207-213) . On the other hand, it was found that the daylight in Naha abundantly comprised the spectral region of B. Further, the spectral composition of B in Naha was entirely different from those in the other two cities. In Naha, the ratios of 410-419, 420-429 and 430-439 nm regions to B were high and the ratios of 450-459, 460-469, 470-479, 480-489 and 490-499 nm regions to B were low as compared with Sapporo and Gifu. These results suggest that the seasonal changes in spectral photon flux of daylight in each city are mainly influenced by solar altitude.
