Temperature and Light Spectrum Differently Affect Growth, Morphology, and Leaf Mineral Content of Two Indoor-Grown Leafy Vegetables

Abstract

This study was carried out to determine the effect of three commercial LEDs of different spectra with or without far red (FR) photons on the growth, morphology, and mineral content of two leafy vegetables under two temperatures (30 °C and 21 °C). The two leafy greens were ‘Cegolaine’ lettuce (Lactuca sativa) and ‘Petite Star’ pak choy (Brassica rapa subsp. Chinensis). In each temperature, there were three light spectra: red and blue LED, and white LED with or without FR. All spectra of lights were adjusted to a total photon flux density of 250 μmol m−2 s−1 at the top of the plant canopy. Results indicated that temperature treatment had a significant influence on most measured parameters. When temperature increased from 21 to 30 °C, lettuce shoot fresh and dry weights increased by 30% and 53%, respectively, while those of pak choy increased by approximately 22%. For both species, plants at high temperature had a larger leaf area but lower mineral content compared to those at low temperature. The spectrum treatment had a minor or no effect on the measured traits. In conclusion, the 5% FR did not impact the yield or biomass of either crop and the plant responses to spectra varied with temperature and species. The two temperatures resulted in significant differences in growth, morphology, and leaf mineral content in both species.