Acclimation of key photosynthetic traits drives edible biomass increases in crop species grown in aquaponics

Abstract

Sustainable agriculture practices may contribute to increasing food demand while alleviating issues with fertilizer over-use and water availability in traditional agriculture. Aquaponics systems provide plants with a constant supply of nutrient dense water from fish efflux. Root uptake filters the fish efflux and water is recycled back to fish tanks, reducing the water needed to produce both plants and fish. Plants acclimate their physiology and anatomy to changing environments, yet, the degree of acclimation in aquaponics is unknown. We tested if acclimation of leaf physiology and anatomy to constant water and nutrient supply in aquaponics affected edible yield. We measured acclimation of leaf gas exchange (A_sat, g_sw), photosynthetic capacity (J_max,Vc_max), stomatal density and chlorophyll production by comparing plants grown in aquaponics or soil for three species: Lactuca sativa (Romaine lettuce), Triticum aestivum (Winter Wheat), and Ocimum basilicum (Basil). We hypothesized that non-limiting nitrogen supply in aquaponics would drive increased production of chlorophyll, increasing electron transport rate (J_max) and carboxylation rate (Vc_max). Additionally, constant water supply in aquaponics would remove limitations driving stomatal closure, leading to higher photosynthesis rates. We found aquaponics plants produced more chlorophyll, driving increased photosynthetic capacity through higher J_max and Vc_max. Additionally, aquaponics plants increased photosynthesis rates (A_sat) via higher stomatal conductance (g_sw) of fewer stomata. Acclimation of key photosynthetic traits in aquaponics plants resulted in more edible biomass compared to soil grown plants, often with reduced investment in root production. Overall, aquaponics appears well suited to producing higher yields of certain crop species, while also reducing environmental impacts.