To investigate the effects of light treatments on the growth morphology and chemical constituents of Mesembryanthemum crystallinum L. plants, red (R), blue (B), far red (Fr), and white (W) light-emitting diodes (LEDs) were configured to provide different combinations of light spectra and photosynthetic photon flux densities (PPFDs). In Expt. 1, five light spectra of red/white (RW), red/white/far red (RWFr), red/white/high-intensity far red (RWFrD), red/blue (RB), and red/blue/far red (RBFr) were set up in two 3-layered racks with circulating hydroponic systems. In each light spectrum treatment, the distance between the LED lamps and the transplanting board was regulated to provide low PPFD and high PPFD treatments. In Expt. 2, the effect of Fr was further investigated in plants in the early and late growth stages. RWFr light was modified by covering the Fr lamps to become red/white without far red (RW−Fr) light during the early growth stage, and then removing the covers to provide the Fr spectrum red/white with far red (RW+Fr) during the later growth stage. This study suggested that high PPFD was not beneficial for promoting plant growth in any light spectrum treatment. Among light spectrum treatments at a PPFD of 215 ± 15 μmol·m−2·s−1, RW light produced higher vegetative growth. In the late growth stage, RW and RB combined with Fr light promoted reproductive growth, antioxidant activities, and secondary compounds, such as phenolic compounds, pinitol accumulation, and betacyanins. Therefore, RW (227 μmol·m−2·s−1), RW−Fr (162 μmol·m−2·s−1), and RB (162 μmol·m−2·s−1) are suggested for the early growth stage to promote vegetative growth. Then additional Fr light can be applied in addition to RW for secondary metabolite induction in the late growth stage.
Enhancing Water use Efficiency of Maize under Deficit Irrigation: the Case of Moisture Deficit Areas of Tigray, Ethiopia