Growth and Appearance Quality of Four Microgreen Species under Light-emitting Diode Lights with Different Spectral Combinations

Abstract

To investigate plant growth and quality responses to different light spectral combinations, cabbage ( Brassica oleracea L. var. capitata f. rubra ), kale ( Brassica napus L. ‘Red Russian’), arugula ( Eruca sativa L.), and mustard ( Brassica juncea L. ‘Ruby steak’) microgreens were grown in a controlled environment using sole-source light with six different spectra: 1) FL: cool white fluorescent light; 2) BR: 15% blue and 85% red light-emitting diode (LED); 3) BRFR L : 15% blue, 85% red, and 15.5 µmol·m −2 ·s −1 far-red (FR) LED; 4) BRFR H : 15% blue, 85% red, and 155 µmol·m −2 ·s −1 FR LED; 5) BG L R: 9% blue, 6% green, and 85% red LED; and 6) BG H R: 5% blue, 10% green, and 85% red LED. For all the light treatments, the total photosynthetic photon flux density ( PPFD ) was set at ≈330 µmol·m −2 ·s −1 under a 17-hour photoperiod, and the air temperature was ≈21 °C with 73% relative humidity (RH). At harvest, BR vs. FL increased plant height for all the tested species except arugula, and enlarged cotyledon area for kale and arugula. Adding high-intensity FR light to blue and red light (i.e., BRFR H ) further increased plant height for all species, and cotyledon area for mustard, but it did not affect the fresh or dry biomass for any species. Also, BRFR H vs. BR increased cotyledon greenness for green-leafed species (i.e., arugula, cabbage, and kale), and reduced cotyledon redness for red-leafed mustard. However, BG L R, BG H R, and BRFR L , compared with BR, did not affect plant height, cotyledon area, or fresh or dry biomass. These results suggest that the combination of 15% blue and 85% red LED light can potentially replace FL as the sole light source for indoor production of the tested microgreen species. Combining high-intensity FR light, rather than low-level (≤10%) green light, with blue and red light could be taken into consideration for the optimization of LED light spectral quality in microgreen production under environmental conditions similar to this experiment.

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