Spectral composition of LED light differentially affects biomass, photosynthesis, nutrient profile, and foliar nitrate accumulation of lettuce grown under various replacement methods of nutrient solution.

To enhance crop yield and quality, plant cultivation in controlled-growing systems is an alternative to traditional open-field farming. The use of light-emitting diode (LED) as an adjustable light source represents a promising approach to improve plant growth, metabolism, and function. The objective of this study was to assess the impact of different light spectra (red, red/blue (3:1), blue, and white) with an emission peak of around 656, 656, 450, and 449 nm, respectively, under various replacement methods of nutrient solution (complete replacement (CR), EC-based replacement (ECBR), and replacing based on plant needs (RBPN)), on biomass, physiological traits, and macro- and micronutrient contents of two best-known lettuce varieties, Lollo Rossa (LR) and Lollo Bionda (LB), in the nutrient film technique (NFT) hydroponic system. The results indicated that mix of red and blue LED spectra under RBPN method is the most effective treatment to enhance fresh and dry weights of lettuce plants. In addition, red LED spectrum under RBPN, and red and blue light under ECBR nutrient solution significantly increased leaf stomatal conductance, net photosynthesis and transpiration rate, and intercellular CO2 concentration of LR variety. Phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mn) content in LR variety, and iron (Fe), zinc (Zn), copper (Cu), and manganese (Mn) content in both varieties increased upon exposure to blue and red LED light spectrum with RBPN method. Our results suggest that exposure to combination of red and blue light along with feeding plants using RBPN and ECBR methods can increase absorption of macro- and micronutrient elements and improve photosynthetic properties, and eventually increase lettuce yield with lower nitrate accumulation.

The plant growth, water and electricity consumption, and nutrients uptake are influenced by different light spectra and nutrition of lettuce.

The aim of this study was to investigate the effect of different replacement methods of nutrient solution (complete replacement, electrical conductivity (EC)- based replacement, and replacing based on the plant needs) and different LED light spectra (monochromic white, red, blue, and a combination of red/blue) on the uptake of mineral nutrients, water and electricity consumption and biomass production of two varieties of lettuce (Lollo Rossa and Lollo Bionda; Lactuca sativa var. crispa) in the hydroponic systems. The results showed that replacement methods based on the plant needs and based on EC increased shoot fresh mass and yield index in the NFT system. Also, results showed that the combination of red/blue light increased shoot fresh mass and yield index in the NFT system and in the plant factory under treatment by replacement method based on plant needs. Increasing the concentrations of N, K, and Zn and loss of Fe in nutrient solution were observed in all three replacement methods of nutrient solution in the NFT system. Water consumption was decreased under plant nutrition based on plant needs and based on EC. In the plant factory, the application of LED light spectrum also decreased electricity consumption and cost against fluorescent lamps. In general, it is concluded that nutrient solution replacement based on the plant needs and based on EC and the use of different LED light spectra (especially the combination of red and blue light) can be used to reduce the consumption of water and nutrients in the hydroponic cultivation of lettuce.

Manipulation of light spectrum is an effective tool to regulate biochemical traits and gene expression in lettuce under different replacement methods of nutrient solution.

The use of light-emitting diode (LED) technology represents a promising approach to improve plant growth and metabolic activities. The aim of this study was to investigate the effect of different light spectra: red (656 nm), blue (450 nm), red/blue (3:1), and white (peak at 449 nm) on biochemical properties, photosynthesis and gene expression in two lettuce cultivars (Lollo Rossa and Lollo Bionda) grown under different methods of nutrient solution replacement in hydroponics. Complete replacement and EC-based replacement of nutrient solution increased content of proline and soluble sugars and activity of antioxidant enzymes (CAT, GPX and SOD) under the red/blue LED and red LED light treatments in both cultivars. In addition, the red/blue and the monochromatic red light increased the soluble protein content and the antioxidant activity in the Lollo Rosa cultivar under the replacement method according to the needs of the plant. An increase in flavonoid content in the EC-based method in the Lollo Rosa variety treated with a combination of red and blue light was also observed. The red/blue light had the greatest induction effect on anthocyanin content, expression of the UFGT, CHS, and Rubisco small subunit genes, and the net photosynthetic rate. Data presented here will directly contribute to the development of nutrient solution and LED spectrum management strategies to significantly improve plant growth and metabolism, while avoiding water and nutrient waste, and environmental pollution.