Abstract
Lettuce seedlings of cv. “Okayama” were water cultured in a growth chamber for 24 hours of 12 hours day and night in order to study the effect of light quality on the absorption of water and minerals. Artificial lighting was done by lamps of white, red, yellow, green and blue colors. Light intensities were controlled to three levels of 250, 125 and 62.5μmol·m-2·s-1 in PPFD for each color and the amount of water and minerals absorbed by plants were measured at the end of 24 hours of treatments. The effect of light quality on the content of minerals in saps and dried leaves were also studied after 15 days of cultivation under artificial lighting of 250μmol·m-2·s-1
1) Larger amounts of water and minerals were absorbed by plants under high light intensity compared with middle or low light intensity. Ca absorption was most strongly affected by the light intensity. Absorption of P, however, was less affected. Effects of light intensity on the absorption of water and minerals were rather clear under white and green lights compared with under yellow and red.
2) Effects of light quality on the absorption of water and minerals were generally clear under high light intensity. The amount of absorbed water was larger under white and blue light and decreased as following order, green, red, yellow color. The amount of water absorbed under yellow light was lowest and 70% of that under white. Minerals absorption generally showed the same tendency as that of water absorption generally showed the same tendency as that of water absorption and was higher under white and blue lights but lower under yellow light.
3) Sap nitrate concentration was most strongly affected with light quality and was higher under white and blue lights and lower under yellow light. On the contrary, sap K concentration was little affected with light quality. Calcium and magnesium concentration in the sap extracted from mid-rib showed similar tendency to the absorption of water and minerals, and were higher under white and blue but lower under yellow color. However, those elements extracted from leaf lamina of inner or outer leaves was higher under red light. Sap P concentration was significantly higher under blue light.
