Effect of Light Intensity and Temperature on Yield of Salad Crops for Space Exploration

The candidate crops that have been considered by NASA for providing moderate quantities of supplemental food for crew's consumption during near term or long duration missions include minimally processed “salad” species. Lettuce (cv. Flandria), radish (cv. Cherry Bomb II) and green onion (cv. Kinka) plants were grown under cool-white fluorescent (CWF) lamps with light intensities of 8.6, 17.2, or 25.8 mol m⁻² d⁻¹, at air temperatures of 25 and 28 °C, 50% relative humidity, and 1200 µmol mol⁻¹ CO₂. Following 35 days growth, final edible mass yields were recorded. All three species grown at 25 °C showed an increase in edible fresh mass and growth rates as light intensity increased. When grown at 28 °C however, the edible fresh mass and crop growth rate of radish, lettuce and onion was significantly reduced at all light intensities when compared to yields at 25 °C. Overall, results indicated that all three crops were sensitive to changes in light intensity and temperature. Therefore understanding the interactions of these environmental factors on crop performance is crucial to the success of future missions which incorporate plant-based life support technologies.