Exogenous Phytohormones: Effects on Lettuce Photosynthesis, Antioxidant Response and Growth

Constantly changing environments often negatively affect yield potential. Phytohormone-based biostimulants are known for their ability to control plant development and reduce the influences of negative environmental impacts and facilitate more efficient usage of resources. The aim of this study was to evaluate the effect of phytohormone-based biostimulants on lettuce (Lactuca sativa L.) antioxidant and photosynthetic responses and biomass formation. Lettuce was grown in a greenhouse with supplemental lighting; a 16 h photoperiod was maintained. Ten combinations of kinetin, indole-3-acetic acid, gibberellic acid, abscisic acid and salicylic acid were applied at 12–13 BBCH. The results thereof have shown that combining growth and stress phytohormones resulted in higher biomass formation; additionally, combining two growth or two stress hormones led to antagonistic effects and reduced photosynthetic rates. Furthermore, the application of gibberellic and salicylic acid had the most positive effect on lettuce productivity. The perspective offered by this work has shown that with the manipulation of hormone concentrations, photosynthetic and antioxidant systems can be controlled, thus enabling control of yield and quality.