Plant growth-promoting diazotrophic bacteria enhance nitrogen acquisition in sugarcane during early establishment under ammonium nitrate fertilization

Abstract

Abstract Nitrogen (N) fertilizer recovery by sugarcane is generally low, resulting in substantial environmental N losses. Plant growth-promoting diazotrophic bacteria (PGPDB) have been proposed as a strategy to improve N acquisition under fertilized conditions. However, it remains unclear whether the beneficial effects of PGPDB under N fertilization are primarily associated with enhanced N acquisition or improved N utilization. Therefore, this study investigated whether bacterial inoculation could improve N acquisition and plant performance under N-fertilized conditions in sugarcane. Sugarcane plants (cv. RB966928) were grown under controlled conditions and assigned to three treatments: (i) an unfertilized and noninoculated control, (ii) N fertilization (NF), and (iii) N fertilization combined with inoculation (NF+PGPDB) via a consortium of five diazotrophic bacterial strains. Biomass production, nitrogen uptake efficiency (NUpE), nitrogen utilization efficiency (NUtE), nitrogen use efficiency (NUE), and N-related compounds were evaluated. Inoculation under N fertilization increased NUpE by 14.8% and shoot N accumulation by 17.7% compared with those under NF alone, whereas NUtE and NUE remained unchanged. Compared with NF alone, NF+PGPDB increased the root dry biomass by 25.1% and the total plant dry biomass by 8.3%. In addition, ammonium accumulation increased by 63.8% in the shoots and 65.5% in the roots, whereas the root amino acid content increased by 44.4%. Overall, bacterial inoculation enhanced N acquisition and altered N-related metabolite accumulation during early sugarcane establishment under ammonium nitrate fertilization. These findings indicate that the primary effect of inoculation was associated with improved N uptake and root-associated metabolic responses rather than with greater N utilization efficiency.