Synthetic microbial communities derived from nanoplastic-reshaped root endophytes alleviate phytotoxicity in Populus × euramericana cv. '74/76'

To address nanoplastic phytotoxicity that limits phytoremediation efficiency, we assembled synthetic microbial communities (SynComs) from polystyrene nanoplastic (PS-NP)-enriched root endophytes of Populus × euramericana cv. '74/76' (Poplar 107) and demonstrated their protective mechanisms through multi-omics analysis. PS-NP exposure profoundly altered endophytic diversity and composition, selectively enriching taxa with stress tolerance and putative plastic-degrading capacity. Six consistently upregulated species (bacteria: Chryseobacterium taeanense, Pseudomonas psychrotolerans, and Rhizobium cellulosilyticum; fungi: Rhodotorula toruloides, Trichosporon asahii, and Fusarium oxysporum) were assembled into bacterial (SynComB), fungal (SynComF), and cross-kingdom (SynComBF) communities. Under severe PS-NP stress (800 mg/L), SynCom inoculation significantly improved plant growth and photosynthesis, reduced PS-NP accumulation, and alleviated oxidative damage compared to the mock control. Each SynCom employed distinct yet complementary strategies: SynComB promoted detoxification and organic acid production. SynComF enhanced energy storage and polysaccharide metabolism. SynComBF synergized these mechanisms for comprehensive protection. Integrated transcriptomic and metabolomic analyses revealed tissue-specific metabolic reprogramming with enhanced flavonoids biosynthesis in shoots for antioxidant defense, enhanced fatty acids biosynthesis in roots for membrane protection, and enhanced TCA cycle activity in both tissues for energy compensation. Our work provides a mechanistic understanding of plant-microbe interactions in response to PS-NP exposure and presents an eco-friendly framework for boosting phytoremediation in plastic-contaminated environments.