Growth and Biochemical Responses of Ice Plant Irradiated by Various Visible Light Spectra in Plant Factories

Abstract

The goal of this study was to determine the effects of various visible light spectra on the growth and bioactive compounds of ice plant (Mesembryanthemum crystallinum L.) in a plant factory with artificial light. Three-week-old seedlings were transplanted into subirrigation systems in a plant factory (average of 23 degrees C air temperature, 60% relative humidity, 170 mu mol.m(-2).s(-1) photosynthetic photon flux density, 12 h photoperiod, and 1,000 mu mol.mol(-1) CO2) equipped with fluorescent lamps (FL, control); monochromatic red (R, 654 nm), green (G, 518 nm), and blue (B, 455 nm) light-emitting diodes (LEDs); and various combinations of R and B (R:B = 6:4, 7:3, 8:2, 9:1), or RB with G (R:G:B = 5:1:4, 6:1:3, 7:1:2, 8:1:1, 9:1:0) LEDs. Shoot fresh weight was higher in the R8B2, R7B3, and R8G1B1 treatments, but did not significantly differ from that in the control. Root fresh weight was highest in the R8G1B1 treatment among all treatments. Leaf area showed a similar trend to shoot fresh weight. The specific leaf weight increased as the ratio of B LEDs increased under the RB and RGB treatments, except in the R8G1B1 treatment. Plants in the RGB treatments with 5 - 6% G light had a higher photosynthetic rate when compared with the RB treatments. The total phenolic content based on unit grams in plants irradiated with RB and RGB LEDs did not show a significant difference except in the R9G1B0 treatment. Antioxidant capacity per unit dry weight tended to increase as the ratio of B LEDs increased in the RB treatments. Regarding total phenolic content and antioxidant capacity per plant, the highest values were recorded in treatments R8B2, R7B3, and R8G1B1, which was similar to the shoot growth results. These results indicate that LEDs with R8B2, R7B3, and R8G1B1 ratios, as well as FL, are suitable visible lighting sources for producing high-value ice plants in plant factories.