Latitude-dependent implications of lighting regimes on lettuce physiology and resource utilisation in decoupled aquaponics systems

Abstract

Aquaponics, a circular agri-aquaculture system, offers the potential to enhance food production resilience across diverse environmental contexts. Plant physiological processes that regulate water and nutrient fluxes in decoupled aquaponics are responsive to environmental dynamics such as stomatal behaviour. In greenhouses, these dynamics are largely driven by changes in natural solar radiation. This research investigates plant physiological dynamics of lettuce traits to various natural light conditions in a fully climate-controlled environment mimicking geographic latitude-based light variations and lighting application modes. We explored the physiological and resource utilisation effects of these regimes as basis for a geographic-adjusted planning of climate-resilient aquaponic systems. For that, four lighting scenarios were applied in a climate chamber over a period of 21 days in decoupled aquaponic setups, involving two daily light integrals (DLIs) and two daily light dynamics (DLDs) for lighting application modes: North (LAT 59° 54' 41.37'' N) natural sunlight dynamics, North static, South (LAT 40° 25' 0.39'' N) natural sunlight dynamics (Sn), and South static (Ss). DLIs and natural sunlight dynamics were derived from Northern (Oslo, Norway) and Southern (Madrid, Spain) Europe in March 2022. Observed plant physiological variables were plant growth, chlorophyll and carotenoid contents, stomatal conductance and morphology, and net photosynthesis (Pn). Resource-use variables at leaf level, including CO2, light, water, and nutrient utilisation, were also estimated. Latitude-dependent DLIs, in general, significantly affected lettuce growth, quality, and physiological responses; with lower latitudes (Sn, Ss) improving Pn by 68% compared to North-DLI treatments. Resource utilisation was also positively impacted in South-DLI treatments, e.g., light use efficiency was in average 2.2 times higher in South-DLI (0.75 g [CO2] mol−1 [PPFD]) than in North-DLI (1.62 g [CO2] mol−1 [PPFD]) treatments. Lighting modes had limited effects, and interactions between DLIs and DLDs were largely absent. These findings indicate the significance of geographic differences in natural solar radiation dynamics on designing climate-resilient aquaponics facilities, and highlight the influence of geography on crop productivity and resource efficiency.