Root Transporters Shape Rhizosphere Microbiomes to Enhance Nitrogen Acquisition Efficiency in Plants

Root nitrogen acquisition is a central belowground process that determines how efficiently plants capture nitrogen from the rhizosphere and influences fertilizer demand and environmental nitrogen losses. Root N transporters, including nitrate, ammonium, amino acid, and peptide transporters, provide the molecular basis for inorganic and organic N uptake. However, root N acquisition is not determined solely by plant transport systems but is also shaped by rhizosphere microbial communities that regulate N mobilization, transformation, and availability. In addition to bacteria and archaea, saprotrophic fungi and mycorrhizal associations contribute to organic matter decomposition, N mineralization, and symbiotic N transfer. Mechanistically, transporter activity may alter rhizosphere N gradients and substrate availability, while root exudates and microbial metabolites can influence microbial recruitment, root physiology, and transporter expression. Evidence from rice NRT1.1B and OsLHT1 suggests that specific N transporter genes can influence rhizosphere microbiome assembly, although direct genetic evidence remains limited to a small number of transporter systems and crop contexts. This review synthesizes current knowledge on root N transporter diversity, rhizosphere microbial N cycling, organic N availability, and transporter–microbiome feedbacks in root-level N acquisition. By integrating plant physiology, soil microbiology, and rhizosphere ecology, this review proposes a conceptual framework in which root N transporters and microbial communities act as interconnected components of belowground N acquisition. Future integration of transporter-informed breeding, microbiome management, and fertilization strategies may improve root N capture while reducing reliance on synthetic N inputs.