Effects of red-blue light spectrum on growth, yield, and photo-synthetic efficiency of lettuce in a uniformly illumination environment

This study comprehensively investigates the impact of varying red-to-blue light ratios on the growth of Spanish lettuce. The research considers various factors such as growth morphology, photosynthetic parameters, and chlorophyll fluorescence. Lettuce was cultivated in an environment with a photosynthetic photon flux density (PPFD) of 200 ± 20 μmol/m2/s and a photoperiod of 16 h per day. The experiment incorporated eight distinct light treatment methodologies, with the red-to-blue light ratios ranging from 2:8 (R2B8) to 9:1 (R9B1). The data implies that during the initial 20 days of growth, groups exposed to a higher proportion of red light demonstrated superior growth. In particular, the R9B1 group exhibited the highest increase in plant height. The photosynthetic performance of leaves (net photosynthetic rate, stomatal conductance, and transpiration rate) showed a tendency to rise with a decreasing red-to-blue ratio within a particular range, peaking at R3B7. However, both the dry matter content and fresh weight were relatively lower under the R3B7 light quality ratio. The results indicate that cultivating lettuce under the R8B2 ratio led to optimal outcomes. This group significantly outperformed the other test groups in terms of weight and exhibited higher photosynthetic rates. Despite exhibiting lower stomatal conductance, this group reduced energy consumption and ultimately achieved the highest overall weight.