Plant Growth-Promoting Bacteria Modulate Amino Acid-Derived Nitrogen Utilization and Plant Growth in Sugarcane in a Genotype-Dependent Manner

Amino acids represent an important source of nitrogen (N) in the rhizosphere; however, how plant growth-promoting bacteria (PGPB) modulate plant use of amino acid-derived N remains poorly understood. This study investigated whether inoculation with PGPB enhances sugarcane growth, N metabolite profiles, and N use efficiency under amino acid-based N nutrition in a cultivar-dependent manner. Two sugarcane cultivars (RB966928 and RB867515) were grown under greenhouse conditions and supplied with either inorganic N (ammonium nitrate), organic N provided as a mixture of five amino acids (alanine, asparagine, glutamine, arginine, and glycine), or organic N combined with PGPB inoculation. The inoculant consortium included Gluconacetobacter diazotrophicus, Herbaspirillum seropedicae, Herbaspirillum rubrisubalbicans, Paraburkholderia tropica, and Nitrospirillum viridazoti. The biomass accumulation, N metabolite profiles, N accumulation, and N use efficiency were evaluated. PGPB inoculation significantly enhanced plant growth, root and total biomass, N accumulation, and N use efficiency in cultivar RB966928, reaching levels comparable to those obtained under inorganic N supply. In contrast, RB867515 showed limited responsiveness to inoculation. PGPB also altered N metabolite profiles, particularly by increasing ammonium concentrations in the shoots of RB966928. PGPB enhanced sugarcane performance under amino acid-based N nutrition in a cultivar-dependent manner, highlighting the functional contribution of plant-associated bacteria to organic N assimilation and N use efficiency.