Abstract
We investigated effects of dim light irradiation (about 11 μmol m−2 s−1 photon flux density) of the root zone on the growth and development of leaf lettuce (Lactuca sativa ‘Okayama saradana’) plants under nutrient film technique (NFT) hydroponics with monochromatic light emitting diodes (LEDs) of five types with respective peak wavelengths (and colors) of 405 nm (violet), 465 nm (blue), 525 nm (green), 660 nm (red), and 735 nm (far-red). Shoot fresh weight and specific root length in the treatments of dim light irradiation of the root zone with violet, blue, and far-red LEDs were significantly lower than in the control (no irradiation of the root zone). Roots in these treatments developed thickly, probably because of suppressed lateral root initiation because sparsely distributed roots were observed in these treatments. Dim light irradiation of the root zone of leaf lettuce plants did not affect mass production, but it did affect root morphology.
