RESUMO
To optimize crop production/quality in space, we studied various "light recipes" that could be used in the Advanced Plant Habitat currently aboard the International Space Station (ISS). Lettuce (Lactuca sativa cv. 'Outredgeous') plants were grown for 28 days under seven treatments of white (W) LEDs (control), red (635â¯nm) and blue (460â¯nm) (RB) LEDs, Wâ¯+â¯blue (B) LEDs, Wâ¯+â¯green (520â¯nm) (G) LEDs, Wâ¯+â¯red (R) LEDs, Wâ¯+â¯far red (745â¯nm) (FR) LEDs, and RGBâ¯+â¯FR LEDs with ratios similar to natural sunlight. Total PAR was maintained near 180⯵molâ¯m-2â¯s-1 with an 18â¯h photoperiod. Lettuce grown under RGBâ¯+â¯FR produced the greatest leaf expansion and overall shoot biomass, while leaves from WB and RB showed the highest levels of pigmentation, secondary metabolites, and elemental nutrients. All other supplemental treatments had varying impacts on morphology that were dependent on crop age. The WG treatment increased fresh mass early in the cycle, while WR increased biomass later in the cycle. The plants grown under WFR exhibited elongation of petioles, lower nutrient content, and similar shoot biomass to the W control. The findings suggest that supplementing a broad spectrum, white light background with discrete wavelengths can be used to manipulate total yield, morphology, and levels of phytonutrients in lettuce at various times during the crop cycle.