Unraveling microbial networks mediating the synergistic effects of nitrogen fertilization and microbial inoculants in Mombasa grass rhizosphere

• Grant number: 25/14275-9
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• Start date: July 20, 2026
• End date: January 19, 2027
• Field of knowledge: Agronomical Sciences - Agronomy
• Principal Investigator: José Lavres Junior
• Grantee: Cássio Carlette Thiengo
• Supervisor: Francisco Dini Andreote
• Host Institution: Centro de Energia Nuclear na Agricultura (CENA). Universidade de São Paulo (USP). Piracicaba , SP, Brazil
• Institution abroad: Pennsylvania State University, United States
• Associated to the scholarship: 23/02584-1 - Investigating the interactive effect of rhizobacterial inoculation associated with nitrogen fertilization on Mombasa Grass: isotopic approaches (15N), antioxidant profile, N metabolism, hormone quantification and ultra-morphological changes in the root, BP.DR

Abstract

Low nitrogen (N) use efficiency is a global problem that threatens human well-being and raises significant environmental and economic concerns. Rhizosphere microbial activity plays a central role in nitrogen cycling and its availability to plants; however, intensive fertilization practices can compromise the structure and diversity of these communities, impairing their functionality. Plant growth-promoting rhizobacteria (PGPR) are promising alternatives to reduce the use of synthetic fertilizers, while potentially improving the functional soil microbiome. However, this potential is underexplored in tropical forage systems, particularly under varying nitrogen inputs, and the synergy between N fertilizer and PGPR is still partially misunderstood. In this context, the response of Mombasa grass (Megathyrsus maximum cv. Mombasa) to inoculation with PGPR, in association with different levels of N fertilization, was evaluated under controlled conditions. Treatments consisted of a control (uninoculated), individual inoculations with Azospirillum brasilense (Azo), Pseudomonas fluorescens (Pf), Bacillus subtilis (Bs), as well as Azo+Pf and Azo+Bs coinoculations, combined with four N levels: 0, 50, 150, and 300 mg N kg¿¹ soil. Evaluations included physiological parameters (chlorophyll, gas exchange, and chlorophyll fluorescence), morphophysiological characteristics (tillering, leaf area, dry biomass, and root-to-shoot ratio), root length and surface area, and the relative contribution of N from biological fixation, fertilizer, and soil (15N isotope dilution technique). At physiological maturity, rhizosphere soil samples were collected for molecular analyses, including 16S rRNA gene sequencing and qPCR quantification of N cycle genes (nifH, amoA, nirS, nirK, nosZ). The overseas internship will focus on advanced bioinformatics training to to evaluate the effects of the different treatments on bacterial community composition, diversity, and functional profiles, and to link these changes to agronomic performance. The results are expected to provide new insights for sustainable nitrogen management in tropical forages by aligning fertilizer rates with the functional enhancement of rhizosphere bacterial communities through PGPR co-inoculation. (AU)