Tomato plants rather than fertilizers drive microbial community structure in horticultural growing media

Synthetic fertilizer production is associated with a high environmental footprint, as compounds typically dissolve rapidly leaching emissions to the atmosphere or surface waters. We tested two recovered nutrients with slower release patterns, as promising alternatives for synthetic fertilizers: struvite and a commercially available organic fertilizer. Using these fertilizers as nitrogen source, we conducted a rhizotron experiment to test their efect on plant performance and nutrient recovery in juvenile tomato plants. Plant performance was signifcantly improved when organic fertilizer was provided, promoting higher shoot biomass. Since the microbial community infuences plant nitrogen availability, we characterized the root-associated microbial community structure and functionality. Analyses revealed distinct root microbial community structure when diferent fertilizers were supplied. However, plant presence signifcantly increased the similarity of the microbial community over time, regardless of fertilization. Additionally, the presence of the plant signifcantly reduced the potential ammonia oxidation rates, implying a possible role of the rhizosheath microbiome or nitrifcation inhibition by the plant. Our results indicate that nitrifying community members are impacted by the type of fertilizer used, while tomato plants infuenced the potential ammonia-oxidizing activity of nitrogen-related rhizospheric microbial communities. These novel insights on interactions between recovered fertilizers, plant and associated microbes can contribute to develop sustainable crop production systems.