Light-emitting diodes and exogenous amino acids application improve growth and yield of strawberry plants cultivated in recycled hydroponics

Strawberry plants in recycled hydroponics exhibit growth and yield reduction due to autotoxicity. Strawberry plants were grown under light-emitting diodes (LED) and sprayed with amino acids to investigate their influence on the growth and yield under autotoxicity. In the first study, plants were grown under three LED light conditions [Red : Blue (R : B) = 8:2, 5:5, and 2:8 adjusted to similar light intensity of 106-117, 107-125, and 105-121 μmol m−2 s−1, respectively] and under white light provided by fluorescent lamps [104-129 μmol m−2 s−1] and also treated with two amino acids [hydroxyproline (Hyp) and glutamic acid (Glu)] and water (control). This study was conducted under relatively high temperature (30/25 °C; day/night) in order to enhance the occurrence of autotoxicity. Further, the nutrient solution was recycled for the duration of the crop cycle to allow the accumulation of autotoxic compounds. Greater growth and fruit yield, higher ascorbic acid content in fruits and also higher calcium and iron content in leaves, crowns and roots of strawberry plants were observed due to R : B = 8:2 LED lighting and Glu spray. In the second study, the selected LED (R : B = 8:2) from the first study was used with three different intensities (i.e., 149, 269, and 567 μmol m−2 s−1) and either with or without Glu spray under controlled environment condition (25/20 °C; day/night). Results showed that plants exposed to 567 μmol m−2 s−1 of R : B = 8:2 LED showed greater performances on growth and minerals content in leaves, crown and roots of strawberry plant supplied either with or without Glu whereas higher number of fruits per plant and fruit yield were observed with Glu spray. Therefore, we propose that combining Glu spray with exposure to R : B = 8:2 LED light of 567 μmol m−2 s−1 may improve the growth, yield and quality of strawberry cultivated in a hydroponic system with a recycled nutrient solution.