Effect of alternating red and blue irradiation on the growth of leaf lettuce

Alternating red (R) and blue (B) irradiation has been paid attention to as a new light environment promoting the growth of leaf lettuce. The promoting effect of leaf lettuce growth by alternating RB irradiation was investigated and the reason for growth promotion was confirmed. First, the optimum irradiation time ratio of alternate irradiation was confirmed by experiments. As a result, the shoot fresh weight reached the maximum in R21B3 treatment (21 h of R irradiation and 3 h of B irradiation in alternating pattern without a dark period). Then, the cause of growth promotion centering on this light condition was investigated. Using three treatments (RB24 (24 h of R and B simultaneous irradiation without a dark period), R21B3, R12B12), data on photosynthetic ability and morphology were obtained and discussed. The photosynthetic ability (PAW (photosynthetic rate per area at the approximately same fresh weight)) was higher in the alternate irradiation sections (R21B3, R12B12) than in the simultaneous irradiation section. This means that the lettuce cultivated under the alternate irradiation treatment has high photosynthetic ability at the approximately same growth stage. Furthermore, it was shown that PA/LA, which is the morphological indicator correlated with leaf overlap, is also highly possible in the alternate irradiation treatment. From these facts, the growth promotion of plants by alternating RB irradiation seems to be the effect of both high PAW and morphological superiority.