Nanoparticle-rhizosphere crosstalk: Insights into transformation, microbial interaction, plant uptake and...

For soil-applied engineered nanomaterials, the rhizosphere is the critical frontline zone where they encounter crop roots, microbes, and soil, determining their agronomic potential and environmental risks. Within this dynamic interface, nanoparticles (NPs), depending on their surface chemistry, particle size, properties, and composition, undergo physicochemical and biological transformations that govern their stability, dissolution, mobility, availability, and ecotoxicological outcomes. This review synthesizes current mechanistic evidence linking root exudation patterns, microbial activity, and soil physico-chemical conditions to NPs aggregation, dissolution, redox conversions, and eco-/bio-corona formation. Microbial extracellular polymeric substances, low-molecular-weight metabolites, siderophores, and biofilms further reshape particle speciation, modulating ion release, immobilization, nutrient availability, and potential toxicity to soil biota and crops. Once inside roots, nanoparticles follow multiple uptake routes, including apoplastic diffusion, endocytosis, plasmodesmata-mediated transport, and vascular translocation, while undergoing in-planta transformations into ionic or ligand-bound forms with distinct physiological and agronomical consequences. These processes are strongly context-dependent, shaped by plant species, development stage, NPs concentration, and soil-climate conditions, and mediated by a tripartite molecular dialogue among NPs, microbes, and plant signalling pathways that regulate root system architecture, rhizosphere microbial recruitment, and nutrient acquisition efficiency. Advances in high-resolution and multi-omics tools-such as synchrotron-based spectroscopy, single-particle ICP-MS, NanoSIMS, stable-isotopic tracers, and metagenomics are offering new insights into these interactions under realistic agricultural scenarios. We propose an integrated agroecological framework linking rhizospheric NPs transformations to plant uptake and responses, emphasizing the need for standardized exposure metrics, realistic concentrations, and long-term field trials for safe and sustainable nanotechnology use in agriculture.