Capturing the physiological and growth dynamics of cucumber cultivated in coupled and decoupled aquaponic systems

Decoupled aquaponics, an emerging area of research, has garnered interest due to its potential in overcoming the constraints identified in coupled (one-loop) aquaponics systems, thereby enhancing crop productivity. The present study employs a physiological approach to elucidate the mechanisms underlying the growth responses of cucumber in both coupled (CAP) and decoupled (DCAP) aquaponics systems, in comparison to conventional hydroponics (HP). A 90-day experiment was conducted in a pilot-scale aquaponics greenhouse, where detailed and regular measurements of various physiological and growth parameters were taken to capture their dynamics. Additionally, fruit quality parameters were assessed to complete the evaluation of the tested cropping systems. CAP plants exhibited stunted growth in terms of aerial biomass accumulation and leaf area, while anatomical features such as leaf thickness and leaf specific mass were significantly higher than those observed in HP and DCAP plants. However, the photosynthetic performance, the light use efficiency, and the photosynthetic pigments concentration were comparable among treatments. The leaf elemental analysis revealed that adequate N and Fe concentrations supported high photosynthetic rates, however, the reduced K, P and Zn levels influenced the growth profile of CAP plants. DCAP demonstrated comparable performance to HP in almost all the evaluated characteristics. Collectively, the results indicate that DCAP addressed limitations associated with coupled systems, indicating its significant potential to support the transition of conventional hydroponics towards a more sustainable cropping system.