the roles of light in a plant factory: photosynthesis efficiency and gas exchange parameters of lettuce as a function of light spectra

Artificial light source is one of the most important factors for high quality and quantity vegetable production in a plant factory. aiming to investigate the role of light spectra on growth, chlorophyll fluorescence, photosynthesis and stomata parameters in lettuce plants grown in a plant factory, a factorial experiment was conducted based on a completely randomized design with two lettuce cultivars (lollo rossa and lollo bionda) and four spectra led illumination red (656 nm), red/blue (3:1) (656 nm), blue (450 nm) and white (449 nm). the results showed that the combination of red and blue led light had the greatest effect on stomatal conductance (gs), number of stomata, length and width of stomata in both lettuce cultivars. also the maximum substomatal co2 concentration (ci) was observed in both lettuce cultivars when they were treated with red led light. the results also showed that the maximum co2 assimilation rate (pn) was observed in rossa variety under white led and in bionda cultivar under blue led light. contrary to the results related to some of photosynthetic parameters, the highest values of vegetative traits (plant height, dry and fresh mass of shoots and roots, leaf number and leaf area) of plants were observed in the treatment of red and blue light combination. it is concluded that plant growth, chlorophyll fluorescence characteristics, photosynthetic and stomatal properties can be affected by different spectra and cultivars of lettuce, so that the choice of proper lighting is a fundamental requirement for the cultivation of this plant