Growth of red pak choi under red and blue, supplemented white, and artificial sunlight provided by LEDs

Abstract

To explore lighting strategies for crop production in space, we investigated the impacts of light spectrum on morphology, biomass, and phytonutrients of red pak choi (Brassica rapa var. chinensis, ‘Rubi F1’) over a 28-day cycle. Light treatments were white light-emitting diodes (WLEDs) as a control, W + red (WR), W + green switched to red at 21 days (WG–R), W + far-red (WFR), red and blue (RB), and an LED-based artificial sunlight research module (ASRM). The photosynthetic photon flux density (PPFD) was maintained near 180 μmol m−2·s-1 for all light treatments. Our results indicated that red pak choi grown under a narrow spectrum of RB light was most suitable for leaf expansion, biomass yield, and relative anthocyanin accumulation. The various broad-spectrum WLED treatments reduced yield, leaf area, and anthocyanin content. Supplemental G and FR augmented the reduction of growth and phytonutrients, however chlorophyll and anthocyanin levels recovered to levels comparable to the control within 7 days of switching WG to WR. The ASRM was used to assess direct sunlight as an alternative lighting option for plant growth in space. ASRM increased overall yield and specific leaf weight compared to WLED and supplemental treatments, and was similar to plants grown under RB in terms of fresh/dry weight, but lower in phytonutrients. Our results suggest both narrow and broad-band light sources can be used to manipulate morphology, phytonutrients, and partitioning of biomass in red pak choi.