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Light intensity plays a critical regulatory role in determining plant yield and quality, and energy consumption in plant factory with artificial light (PFAL). The effects of different light intensities (200, 300, 400, 500, and 600 µmol·m−2·s−1) of light-emitting diodes (LED) red and blue light with ratio 4:1 on growth, quality, nitrogen and amino acid metabolisms of ryegrass were investigated. The results showed the tiller number and shoot fresh weight in ryegrass were increased, while plant height and stem diameter remained stable with the improvement of light intensity. The highest levels of soluble protein, free amino acid, and DPPH free radical clearance rate in photon flux density (PPFD) at 500 µmol·m−2·s−1, and then significantly decreased with light intensity increased. The highest soluble sugar content was found at PPFD of 600 µmol·m−2·s−1, while malondialdehyde (MDA) content remained stable in all treatments. As the light intensity increased, nitrate content decreased, while nitrate reductase (NR) activity and the ammonium content increased. As light intensity was increased from 200 to 600 µmol·m−2·s−1, nitrite reductase (NiR) activity first decreased and then increased. Moreover, glutamate and cysteine contents increased first and then decreased, while glutamate synthase (GOGAT), glutamine synthase (GS), glutamate dehydrogenase (GDH), and cysteine synthases (CS) activities increased continuously with light intensity. Light intensity was significantly correlated with the parameters of growth, quality, nitrogen and amino acid metabolisms in ryegrass. It was recommended that PPFD at 400–500 µmol·m−2·s−1, photoperiod of 16 h/d was suitable for ryegrass high-efficient production in PFAL with relatively low energy cost. [ABSTRACT FROM AUTHOR]

Background: In countries characterized by limited per capita arable land and grassland, agricultural development is hindered by insufficient forage productivity. The plant factory with artificial light (PFAL) system has emerged as a highly efficient approach to address this challenge by cultivating forage on finite land resources. In the PFAL framework, the regulation of light intensity plays a critical role in determining both the yield and quality of cultivated plants. Aims: This study seeks to delve into the optimal range of light intensity for achieving high efficiency and quality in the production of alfalfa in the PFAL. Additionally, it seeks to explore the effects of light intensity on nitrogen metabolism, as well as the accumulation and metabolism of amino acid in alfalfa. Methods: To achieve these objectives, alfalfa was sown and subjected to five treatments involving red and blue LED light in a 4:1 ratio. The light intensities used were 200, 300, 400, 500, and 600 µmol m–2 s−1, respectively. The alfalfa plants were then harvested at intervals of 15, 20, 25, 30, and 35 days. The quality and nitrogen metabolisms of alfalfa during this period were assessed by evaluating the plant's growth performance and determining the optimal cutting time. Conclusion: In summary, high‐light intensity (400–600 µmol m−2 s−1) improved alfalfa yield and quality, while also promoting nitrogen and amino acid metabolism. Photon flux density at 400–500 µmol m−2 s−1 light intensity for a duration of 30 days was identified as the optimal condition for PFAL alfalfa production. [ABSTRACT FROM AUTHOR]

A glasshouse experiment was conducted to investigate the effects of five days’ treatment before harvest with various light intensities and seven hydroponic solutions on nitrate reduction in lettuce. The results showed that SPAD of new and expanded leaves were elevated by most of the hydroponic solutions under shading compared with the full nutrient solution, while no effect was demonstrated under non-shading. Additionally, lettuces under non-shading presented slightly higher leaf SPAD than those under shading. Nitrate concentrations of lettuce new leaves, expanded leaves and petiole were lowered significantly by all hydroponic solutions under shading and non-shading conditions compared with the full nutrient solution. Under non-shading, the efficiencies of seven hydroponic solutions varied largely, but no efficiency differences were showed under shading. N-free solution, 0.75 mM potassium sulphate solution and 5×10−5 mM ammonium molybdate solution functioned more efficiently in reducing nitrate concentration both in expanded leaves and petiole of lettuce before harvest. In conclusion, proper light intensity is a key important factor that determines the efficiencies of nitrogen-free hydroponic solution treatments in lowering nitrate concentrations in leaf blades and petioles of lettuce before harvest. [ABSTRACT FROM PUBLISHER]

LED red (R) and blue (B) continuous light (CL) is a potential efficient way to increase plant productivity of plant factory with artificial light (PFAL), but limited information was explored about their effects on plant mineral nutrition. In an environmentally controlled plant factory with artificial light (PFAL), the effects of CL of different intensities and spectral qualities, emitted by R and B LEDs on growth and nutrient element content and accumulation of lettuce (Lactuca sativa L.), were conducted in three hydroponic experiments. Two treatments, normal light (12 h/12 h) and CL (24 h/0 h) in experiment 1, three CL intensities (100, 200 and 300 μmol·m−2·s−1) in experiment 2, and three CL light qualities (1R:3B, 1R:1B and 3R:1B) in experiment 3 were designed. The results showed that CL significantly increased the fresh and dry lettuce shoot biomass compared with normal light, and shoot fresh and dry biomass increased with the intensity increment of CL. In experiment 3, shoot fresh biomass was great under high R light proportion CL treatment, while dry shoot biomass remained unchanged. Both CL and CL with increased intensities promoted shoot C content and accumulation in lettuce. CL reduced N, P, K, Ca, Mg, Cu and Zn contents in lettuce shoot, while Fe and Mn contents did not change compared to NL. Moreover, CL increased Ca, Fe and Mn accumulation. 100–200 μmol·m−2·s−1 CL facilitated N, P, Ca, Mg, Fe, Mn, Cu and Zn contents in shoot, but K content was not influenced compared with 300 μmol·m−2·s−1. The data showed that high B light ratio (75%) facilitated C content comparison with low B ratios (50% and 25%). However, lettuce grown under 3R1B treatment had the higher C accumulation. Shoot N, P, K, Ca, Mg, Fe, Mn and Zn contents were higher under 1R1B treatment, and Cu content did not affected by light quality. Moreover, accumulation of N, P, K, Ca, Mg, Fe, Mn, Zn and Cu in shoot was higher under 1R1B treatment, while P, Ca, Mg, Mn accumulation under 3R1B treatment was the lowest. In conclusion, CL tends to reduce shoot mineral element contents due to dilution effect as shoot dry weight increases compared to NL. However, long-term (12 days) CL composed of 1R1B, 100–200 μmol·m−2·s−1 tends to obtain relative higher K, Ca, Fe and Zn contents in the greater dry lettuce shoot. [ABSTRACT FROM AUTHOR]

• EOP high light irradiation increased the ascorbate content of lettuce. • EOP high light intensity regulated the expression of genes and the activity of enzymes involved in ascorbate synthesis and cycling. • EOP high light intensity induced the production of ROS, and the content of ascorbate, as an important antioxidant, increased accordingly. • EOP high light intensity increased the carbohydrate content of lettuce. Increasing the L-ascorbate (AsA) content of vegetables is very important for improving plant quality in greenhouses and plant factories because AsA is an antioxidant that is essential for the proper function of plants and the human body. End-of-production (EOP) high light irradiation is an economical preharvest practice for improving product quality. Here, we studied the dynamic responses of the AsA pool and AsA metabolism in lettuce exposed to EOP high light irradiation (300, 400, and 500 μmol m−2·s−1) from red and blue LEDs over a 16-h time course. Compared to the control (200 μmol m−2·s−1), the content of AsA and total AsA (T-AsA) in lettuce leaves significantly increased after 8 h of high light irradiation, and the contents of AsA and T-AsA increased by 42.4 % and 36.9 %, respectively, under 500 μmol m−2·s−1 irradiation. Transcript levels of the AsA metabolism-related genes GME , GGP , GPP , GLDH , APX , MDHAR1 , MDHAR2 , DHAR1 , DHAR2 , and GR were upregulated under higher light. Likewise, the activities of AsA-related enzymes (GLDH, APX, DHAR, and GR) increased under 500 μmol m−2·s−1. The expression of genes (GGP , GPP , GLDH , MDHAR1 , MDHAR2 , DHAR1 , DHAR2 , and GR) was more sensitive to high light irradiation in AsA metabolism. Both high light intensity and long irradiation time increased the soluble sugar content. Moreover, high light intensity (500 μmol m−2·s−1) increased the content of H 2 O 2 , O 2 *−, and MDA in lettuce leaves, especially at 16 h. In conclusion, EOP high light increased AsA levels by upregulating the expression of genes and the activity of enzymes in AsA metabolism. The increase in soluble sugar availability and the signaling of reactive oxygen species also contributed to AsA accumulation. We therefore recommend 8 h of high light (500 μmol m−2·s−1) irradiation before harvest to increase the AsA content of lettuce. [ABSTRACT FROM AUTHOR]