Spearmint enhances lettuce biomass and provides microbes to co-cultured lettuce in a decoupled aquaponic system

Abstract

Aquaponics, where recirculating aquaculture systems (RAS) and hydroponics are combined to grow fish and plants, is a promising farming technique for sustainable food production. We investigated whether lettuce yield in aquaponics can be enhanced by companion plants and the role of companion plant-derived microbes. Lettuce and companion plants (spearmint, rucola, wormwood) were grown for 30 days in hydroponic units in RAS effluents in three time replicates. The growth of lettuce increased when grown with spearmint and rucola. Companion plants also influenced the bacterial community composition in lettuce. In particular, lettuce grown with spearmint or wormwood contained bacteria that potentially originated from the companion plant. A specific subset of bacterial taxa from spearmint were also associated with increased lettuce growth. On the other hand, the microbial community in mature lettuce did not develop markedly from the RAS effluents. However, the factor with the largest effect on plant growth and bacterial community composition was time replicate. In conclusion, the companion plants particularly spearmint enhanced the growth of lettuce through facilitation and potentially by providing lettuce with bacteria associated with increased growth. Our results emphasize the importance of the bacterial components and temporal fluctuations in optimizing aquaponics productivity.