Growth and Bioactive Compounds of Lettuce as Affected by Light Intensity and Photoperiod in a Plant Factory Using External Electrode Fluorescent Lamps

Abstract

External electrode fluorescent lamps (EEFLs) are a new, efficient light source that can be used in plant factories. We examined the effects of light intensity and photoperiod combinations on growth, total phenolic content, antioxidant capacity, and light use efficiency of lettuce (Lactuca sativa 'Cheongchima') in a plant factory employing EEFLs. Two-week-old seedlings were grown for 3 weeks at a photosynthetic photon flux density of 150 (150P) or 200 (200P) μmol•m -2 •s-1 under 12, 16, 20, or 24 h photoperiods. The air temperature was maintained at 20 ± 2°C and Yamazaki nutrient solution was supplied using a deep flow technique. Fresh shoot and root weights increased as photoperiod was extended, becoming greatest under the 150P/24 h condition. The shoot/root ratio was lowest at the 24 h photoperiod under 150P and 200P conditions. Leaf length decreased at longer photoperiods, but leaf width and number was increased; therefore, leaf shape became broader under longer photoperiods. Leaf area increased at the 150P/20 h condition but decreased at the 200P/24 h condition. Specific leaf weight (thickness) increased significantly as photoperiod was extended irrespective of light intensity and became greater under 200P than 150P. Total phenolic content and antioxidant capacity increased continuously with increasing photoperiods under 150P; however, in the 200P treatment, both increased up to 20 h, then decreased under the 24 h photoperiod. Light use efficiency was generally higher under 150P, but became similar at either light intensity under the 24 h period. Considering the growth rate, leaf size, antioxidant capacity, and cropping cycle, the 150P/20 h condition was deemed to be the most efficient and economical for growth of 'Cheongchima' lettuce in a plant factory system.

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

“…The decrease in phenolic content at DLI of 14.4 mol m −2 day −1 might be due to the achievement of light saturation point. This result was in accordance with Cho et al 69 , where they have used external electrode fluorescent lamps to study the impact of various combinations of photoperiod and PPFD on leaf lettuce. Carvalho et al 70 , observed that the total phenolic content in leaves of sweet potato was higher at 16 h photoperiod compared to 8 h photoperiod with PPFD of 150 µmol m −2 day −1 .…”

“…Ali et al 73 observed that the levels of antioxidant activity in swiss chard, red beet, green amaranth, red amaranth and red spinach were found to be higher at a photoperiod of 12 h. Antioxidant capacity of lettuce was found to be highest under a combination of 12 h photoperiod and half strength of nutrient solution 74 . Cho et al 69 , demonstrated that the antioxidant capacity of green leaf lettuce increased up to 20 h and then decreased at 24 h. In our study, we observed that the antioxidant capacity was increased up to A DLI of 11.5 mol m −2 day −1 and then decreased at 14.4 mol m −2 day −1 . Antioxidant activity has been demonstrated by about 70% of the phenolic substances found in lettuce 75 , suggesting that the trends in total phenolic content and antioxidant level in this study may be similar to each other.…”

“…Similar results were obtained by Refs. 62 , 68 , 69 . However, Palmer and van lersel 63 found that different photoperiods (10, 12, 14, 16, 18, and 20 h) at constant DLI of 16 mol m −2 day −1 had no influence on leaf area of lettuce and mizuna.…”

Seasonal Variations in Bioactive Compounds and Antioxidant Activity in the Leaves of Sasa quelpaertensis

“…TPC was estimated according to a previously described method using Folin-Ciocalteu's reagent (Blainski et al, 2013;Cho et al, 2020;Lee et al, 2021a;Lee et al, 2022b). Each sample reacted with 200 µL of 2% sodium carbonate and 10 µL of Folin-Ciocalteu's reagent for 30 min at RT.…”

The Immune-Stimulating and Anti-Diabetic Effects of Allium hookeri Leaves Grown in a Plant Factory with Artificial Lights in Immunosuppressed Obese C57BL/6 Mice

“…An orange or green LED increases phenolic compounds, α-carotene, and anthocyanin in baby leaf lettuce, and a blue, red, or green LED increases its total flavonoid content [ 21 ]. The light intensity and photoperiod changed the growth condition, the leaf size and shape, the total phenolic content, and the antioxidant level of the ‘Cheongchima’ lettuce [ 22 ].…”