This study investigated consolidation trends in the rhizosphere community of crops grown in an aquaponics system.. Aquaponics Rhizosphere

Terrestrial plant roots mediate a complex network of prokaryotes and eukaryotes collectively referred to as the rhizobiome. The ability to promote beneficial plant symbionts contributes to increased crop productivity. Despite recognition of the microbial underpinnings, plant cultivation strategies remain primarily focused on plant physiology to determine crop health. The success of plant cultivation in hydroponics indicates that fundamental rhizosphere activity is preserved regardless of the surrounding milieu vis à vis nutrient uptake, abiotic and biotic stress resistance. What has not been explored is how the rhizobiome adapts to soil-less hydroponic or aquaponic cultivation. Microbial dynamics in aquaponic systems are more complex than their hydroponic equivalents insomuch as additional communities are incorporated via the inflow water to plant units from the fish rearing tank, thus influenced by the microbiome of the intake water and fish GI tract, and influenced as well by the biofilter community of the recirculating aquaculture system (RAS) (soluble-waste treatment loop). This study presents results from a series of experiments aimed at analyzing the development of the rhizobiome during cultivation of Batavian lettuce (Lactuca sativa) in hydroponic or aquaponic systems coupled to RAS with common carp (Cyprinus carpio) or Nile tilapia (Oreochromis niloticus). In the first set of experiments, we employed standard water purification techniques (UV, ozone, H2O2) to impede microbial proliferation in hydroponic beds to test the effects of sterilization on microbial diversity and plant growth rates. A second experiment assessed the capacity of the rhizosphere to resist colonization from foreign microbial communities (upstream RAS microbiome, soil rhizosphere community, probiotic supplementation). These were compared to treatments supplied with sterilized nutrient solution. The similarity of taxonomic profiles across all treatments indicated that the plant roots strongly dictate the rhizobiome regardless of other environmental pressures or microbial influences. Surprisingly, microorganisms corresponding to specific metabolic profiles (e.g. nitrification) were not reflected in the rhizobiome – indicating that nitrifying organisms from the biofilter do not carry over to the rhizosphere but rather are functionally replaced by rhizosphere-specific nitrifiers. Nonindigenous communities in proximity to plants are not capable of displacing the autochthonous rhizobiome in hydroponic nor aquaponic systems.