Actavia 0 VITALE, L. VITALE, E. GUERCIA, G. TURANO, M. ARENA, C. 2020 2020-9-4 932-943 In this work, the effects of light quality and beneficial microbes (biofertilizer) supply on structural and ecophysiological traits of spinach were investigated. Plants were grown under four light quality regimens: white light (WL), red-blue (RB), red-green (RG), and red (R) light, with or without the addition of biofertilizer. RG and R plants without biofertilizer showed morphological traits typical of shaded plants as wide leaf lamina and high photosynthetic pigment content. These plants also exhibited a higher photosynthetic capacity compared to WL and RB plants. The improved photosynthesis in RG plants was due to both morphological and physiological adjustments allowing a better utilisation of light energy, whereas in R plants it has been attributed to a reduced photorespiration rate. Biofertilizer application under WL improved plant performance enhancing photosynthesis. The high carbon gain compensates the costs of symbiosis. Biofertilizer application under R light favouring too much the microbial root colonisation, removed the benefits of symbiosis. The interaction of light quality and biofertilization significantly affects the root-microbe relationship. 4 58