Nutrient accumulation, growth and quality of leafy vegetables in aquaponics system are modulated by supplemental LED lighting

Aquaponics is a highly efficient production system that relies on the food introduced for fish as the only nutrients input for growing both fishes and vegetables. However, plant ability to absorb nutrients in an aquaponics system may be reduced in the winter months characterised by low evaporative demand (low temperature and radiation) which in turn could cause accumulation of nitrate, nitrite, and ammonia in the water. These by-products are harmful for fishes, forcing growers to renew the water more often. The aim of the study was to evaluate growth, physiological response, nutrient accumulation, and quality of lettuce and curly endive, grown in floating raft recirculating aquaponic system (RAS) combined with tilapia, under natural light (NL) or NL integrated with 16 h of supplemental white LED lighting (IL, PPFD: 173 µmol m‑2 s‑1, daily light integral (DLI), 10 mol m‑2 d‑1). Results show a species-specific response to the lighting regimes. Compared to NL, IL promoted plant growth and nutrient accumulation in both species. Particularly in endive it increased leaf area and induced new leaf formation. Supplemental lighting increased whole plant assimilation capacity by increasing the specific leaf area with no effect on pigments content and photochemical efficiency. However, supplemental lighting decreased the maximal photochemical efficiency (Fv/Fm) in lettuce. The different lighting regimes affected nutrient accumulation and translocation in both leaves and roots. To summarize, curly endive performs better than lettuce in aquaponics. Supplemental lighting can guarantee a stable filtration capacity during the winter season, improving overall system performances and plant qualitative attributes of the tested crops.