High Light Intensity from Blue-Red LEDs Enhance Photosynthetic Performance, Plant Growth, and Optical Properties of Red Lettuce in Controlled Environment

Abstract

Plant factories using artificial light to produce vegetables have high energy costs due to the high demand for electricity for lighting. Compared to conventional light sources, light-emitting diodes (LEDs) offer the possibility of tailoring the light spectrum and regulating light intensity and are more energy-efficient in terms of energy conversion regardless of the levels of lighting intensity. Optimal light intensity and daily light integral (DLI) requirements are key factors for plant growth; however, their values vary among species and varieties. Our experiment aimed to identify the best light intensity to produce lettuce plants in controlled environment. Lettuce plants of the type Batavia cv ‘Blackhawk’ were grown in plastic pots filled with perlite and peat (20:80 v/v) for 33 days in a growth chamber under blue (B, 20%) and red (R, 80%) LED light at a photosynthetic flux density of 130 µmol m−2 s−1 (BR 130, DLI 7.49 mol m−2 d−1), 259 µmol m−2 s−1 (BR 259, DLI 14.92 mol m−2 d−1), and 389 µmol m−2 s−1 (BR 389, DLI 22.41 mol m−2 d−1). Our results showed that increasing light intensity and DLI promotes net photosynthesis, sustains the electron transport rate (ETR), and stimulates the synthesis of anthocyanins and carotenoids, with positive results for plant photoprotection. Furthermore, the decreases in vegetation indexes (photochemical reflectance index (PRI), greenness, and modified chlorophyll absorption in reflectance index (MCARI1)) also indicate changes in photosynthetic pigment content in response to plant acclimation to different DLIs. Among the three light intensities, 389 µmol m−2 s−1 (DLI 22.41 mol m−2 d−1) gave the best results for growing Batavia red lettuce cv ‘Blackhawk’, since it enhances both production and qualitative traits. These results highlight the importance of a proper light intensity to promote plant growth and qualitative traits and to reach high production targets. Hence, preliminary screening of plant performance under different light treatments is recommended to optimise plant response to artificial lighting.

Modulations in Chlorophyll a Fluorescence Based on Intensity and Spectral Variations of Light

“…On exposure to green light, Pyropia haitanensis maintained the photochemical quenching and quantum yields of PSII but failed to maintain the electron transport efficiency as compared to the control. Moreover, exposure to blue-green light increased the photosynthetic pigments of different unicellular marine algae, and the changes in the quality of light significantly altered the composition of pigments in this organism [ 108 ]. A study conducted on Lactuca sativa showed the importance of green light intensity in plant photosynthetic performance [ 109 ].…”

Determination of optimal daily light integral (DLI) for indoor cultivation of iceberg lettuce in an indigenous vertical hydroponic system

“…Cui et al 29 recommended a DLI of 6.35 mol m –2 day –1 for cucumber plug seedlings that could be achieved by using PPFD of 110–125 µmol m −2 s −1 and a photoperiod of 14–16 h. For indoor cultivation of red-leaf lettuce plants, a minimum DLI of 6.5 to 9.7 was suggested 35 . DLI requirement for lettuce ranges between 12 and 16 mol m –2 day –1 , however their value varies among species and cultivars 17 , 22 , 26 , 36 .…”

Hydroponic and Aquaponic Floating Raft Systems Elicit Differential Growth and Quality Responses to Consecutive Cuts of Basil Crop

“…The chlorophyll content decreased between the first and second cuts only in hydroponics, in which we observed as a response an increase in carotenoid content to cope with possible photodamage and nutrient imbalances, such as in iron or manganese [ 37 , 38 ]. It is well known that light and other environmental variables directly affect gas exchanges and plants’ capacity to absorb light [ 39 , 40 ]. In our experiment, the leading cause of reductions in gas exchange in both systems has to be ascribed to the different environment and the particular light scenario since the first cut occurred in July and the second in September, with a large difference in light intensity and daylight integrals being reduced in September.…”