Microbial Effects on the Production of Aquaponically Grown Lettuce

In the study of aquaponics, questions have risen concerning the role of microbiota upon plant growth. This experiment compared unaltered aquaponic nutrient solution at pH 7.0 (treatment A7) with sterilized aquaponic nutrient solution at pH 7.0 (treatment SA7) to quantify effects that live microorganisms had on the growth of lettuce (Lactuca sativa). Baseline comparisons were made to conventional hydroponic conditions using inorganic nutrients at pH 5.8 (treatment H5) or pH 7.0 (treatment H7), which showed a 51% reduction in lettuce fresh weight (FW) growth, indicating a strong negative effect of the higher pH nutrient solution; a similar large difference (38%) occurred for dry weight (DW) comparisons between these two treatments. No difference occurred between the sterilized aquaponic treatment (SA7) and H5 in FW or DW. H5 produced more FW and DW than the non-sterile aquaponic treatment (A7). Responses were not different in FW and DW between the two aquaponic conditions. Reduced FW and DW of A7 compared to H5 may be related to the 50 times higher microbial community living in the A7 treatment water than in H5 at the beginning of each trial. Given that the sterile aquaponic solution SA7 and the H5 hydroponic condition were not different in performance, we concluded that the beneficial effects of the microbial community in the fish recirculating aquaculture system (RAS) occurred before the water was sterilized. An interesting implication of our findings is that an RAS can be decoupled from the hydroponic growing system, since its benefits are not dependent upon continuous recirculation between the plant and fish system and its living biotic community