Abstract
The photon flux density (PFD) and spectrum regulate the growth, quality attributes, and postharvest physiology of leafy vegetables grown indoors. However, limited information is available on how a photon spectrum enriched with a broad range of different wavebands regulates these factors. To determine this, we grew baby-leaf lettuce ‘Rouxai’ under a PFD of 200 µmol m−2 s−1 provided by warm-white (WW; control) light-emitting diodes (LEDs) supplemented with either 30 µmol m−2 s−1 of ultraviolet-A (+UV30) or 50 µmol m−2 s−1 of blue (+B50), green (+G50), red (+R50), or WW (+WW50) light. We then quantified growth attributes and accumulated secondary metabolites at harvest and during storage in darkness at 5 °C. Additional +G50 light increased shoot fresh and dry weight by 53% and 59% compared to the control. Relative chlorophyll concentration increased under +UV30, +G50, and especially +B50. At harvest, +B50 increased total phenolic content (TPC) by 25% and anthocyanin content (TAC) by 2.0-fold. Additionally, +G50 increased antiradical activity (DPPH) by 29%. After each day of storage, TPC decreased by 2.9 to 7.1% and DPPH by 3.0 to 6.2%, while TAC degradation was less pronounced. Principal component analysis indicated a distinct effect of +G50 on the lettuce at harvest. However, concentrations of metabolites before and during storage were usually greatest under the +B50 and +R50 treatments.
Highlights
There was no significant effect on shoot fresh weight (FW) when plants were grown under the +UV30, +WW50, +B50, and +R50 treatments (200 μmol m−2 s−1 of WW supplemented with 30 μmol m−2 s−1 of UV-A, or with 50 μmol m−2 s−1 of WW, blue (B), and red (R) light, respectively)
Plants grown under the +G50 treatment had increased shoot dry weight (DW) by 59%, and there were no significant differences between other lighting treatments on shoot DW compared to the control (Figure 1B)
The addition of G light led to the greatest plant growth and leaf width as well as chlorophyll content in lettuce leaves
Summary
Controlled-environment agriculture (CEA) enables growers to control environmental and cultural factors, extending the growing season and achieving a more uniform crop. CEA encompasses semi- or fully-closed growing structures such as greenhouses or indoor farms (i.e., plant factories) [1]. The typical features of indoor farms are the efficient use of water and fertilizer, automatic air temperature and humidity control, and electric lighting, which enable year-round crop production on a demand basis [2]. The photon flux density (PFD) and spectrum are two of the main environmental factors that influence plant productivity and quality when crops are produced indoors. The need to deliver an efficient PFD and spectrum that balances crop development, growth, and quality attributes, while considering energy consumption, necessitates further research on photomorphogenesis and LED technology [5]
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