Effect of Temperature Variation and Blue and Red LEDs on the Elongation of Arugula and Mustard Microgreens

Abstract

Recent studies using LED lighting at low to modest intensity have indicated that compared with red light, blue light can promote plant elongation in many crops as a shade avoidance response despite varying sensitivity with light environments, plant species, and growth stages. Currently, there is limited understanding of how temperature affects the blue light-mediated plant response. To clarify this point, two microgreen species (arugula and mustard) were grown indoors under two light quality × two temperature treatments: red LED light (peak at 670 nm) and blue LED light (peak at 450 nm) at 18 °C or 28 °C. A photosynthetic photon flux density of 110 µmol m−2 s−1 and a photoperiod of 12 h d−1 were used for all treatments. After 6 to 8 days of treatment, at both temperatures, blue vs. red light promoted plant elongation, as demonstrated by a greater plant elongation rate, final plant height, and hypocotyl length, in arugula but not in mustard. Blue vs. red light also promoted some shade-avoidance responses such as decreased cotyledon size in both species and increased petiole length and dry mass partitioning to hypocotyls in arugula only. The elongation promotion in arugula by blue light was greater at 18 °C than at 28 °C, showing interactions between light and temperature on most plant traits. For mustard, plant elongation was promoted at 28 °C compared to 18 °C independent of light treatment, showing no interactions between light and temperature on most plant traits. These results suggest that the blue light-mediated elongation as a shade-avoidance response is not reversed by high temperature, despite the varying sensitivity with temperatures and species.