Growth and photosynthesis characteristics of lettuce cultivars in response to supplementary LED lights and replacement methods of the nutrient solution

Growing global warming and a projected rise in the world's population have made it imperative to produce food and agricultural products with a limited supply of water and energy sources. Conversely, there is a need to employ modern technologies, such as LED artificial lights, to ensure that plants receive adequate light energy. Therefore, this research was aimed at increasing the efficiency of supplementary LED lights, with three lettuce cultivars namely Red Sail, Edox and Summer Bibb, for four light spectrums (white, a combination of red and blue, monochromatic red and monochromatic blue) and three replacement methods of the nutrient solution for the aeroponic system such as complete replacement of the nutrient solution, based on electrical conductivity (EC) and based on plant needs. The results depicted that white light significantly affected the fresh shoot and root weight in Red Sails variety under the complete replacement method of the nutrient solution. Similarly, the highest photosynthetic pigments concentrations were observed under the combination of red and blue and for monochromatic red light. Moreover, the significant Pn, E, gs, Ci and spad were observed under white light and in all three replacement methods of nutrient solutions whereas the most positive effect was recorded in the replacement method based on plant needs. Therefore, the simultaneous use of supplemental lights and replacement methods of nutrient solution, particularly replacement based on the plant needs increases the production of agricultural products like lettuce in addition to lowering the consumption of electricity, water, and nutrients for agricultural production.