Performance of Three Species of Salad-type Plants Grown under Narrow-spectrum Light-emitting Diodes (LEDs) in a Controlled Environment

Abstract

Light-emitting diodes (LEDs) are a promising light source for growing crop plants in spaceflight systems because of their superior safety, durability, small mass and volume, wavelength specificity, and long life. To address the usefulness of LEDs as a plant lighting source, radish (Raphanus sativus L. cv. Cherriette), lettuce (Lactuca sativa L. cv. Waldmann's Green), and spinach (Spinacea oleracea L. cv. Nordic IV) were grown using nutrient film technique hydroponics under cool-white fluorescent (CWF) lamps, red LEDs (peak emission 660 nm), and red LEDs + 30 μmol·m–2·s–1 supplemental blue fluorescent (BF) light (400–500 nm). Each lighting treatment was maintained in a separate controlled-environment chamber with total photosynthetic photon flux (PPF) maintained near 300 μmol·m–2·s–1 and a photoperiod of 18-h light/06-h dark. Results showed significant reductions in total dry mass (TDM) accumulation for radish plants grown under red LEDs + 30 μmol·m–2·s–1 BF or red LEDs only as compared to CWF-grown plants. Although TDM tended to decrease with decreasing BF for lettuce, treatment differences were not significant. TDM for spinach plants was significantly less under red LEDs compared to CWF or red LEDs + 30 μmol·m–2·s–1 BF. Interestingly, single-leaf photosynthesis and leaf conductance were not significantly different for any treatment, regardless of species. The data suggest a species-specific response for the amount of blue necessary for normal plant growth.