Light use in the plant factory: changes in chlorphyll fluorescence and gas exchange parameters of two lettuce cultivars at LED spectra in floating hydroponics

Abstract

Artificial light source is one of the most important factors for high quality and quantity vegetable production in plant factory. With the aim of investigating the role of light spectra on chlorophyll fluorescence, photosynthesis, and stomata parameters in lettuce plants grown in plant factory, a factorial experiment was conducted based on a completely randomized design with two lettuce cultivars (Rossa and 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 blue and white LED light had the most significant effect on chlorophyll fluorescence parameters Fo, Fm, Fv, Area and PIabs in both lettuce cultivars compared to the other light treatments. The results also showed that the combination of red and blue LED light had the highest effect on stomatal conductance (gs), number of stomata, length and width of stomata in both lettuce cultivars. On the other hand, the maximum substomatal CO2 concentration (Ci) was observed in both lettuce cultivars when treated with red LED light. Also, transpiration rate (E) increased with the combination of red and blue LED in Rossa cultivar and red LED in Bionda cultivar. The results also showed that the maximum CO2 assimilation rate (A) was observed in Rossa cultivar under white LED and in Bionda cultivar under blue LED light. It is concluded that chlorophyll fluorescence characteristics and photosynthetic and stomatal properties can be affected by different spectra and cultivars of lettuce.