Fe-modified biochar-driven ROS generation in the rhizosphere and their role in microplastic transformation

Reactive oxygen species (ROS) are critical mediators of soil biogeochemical processes. While the production of ROS with biochar (BC) in the rhizosphere has not been explored. We demonstrate that BC and Fe-modified biochar (FeBC), prepared at 400°C and 600°C, influence ROS generation in paddy soil containing biodegradable (polybutylene succinate: PBS) and conventional (polystyrene) microplastics (MPs). FeBC, particularly FeBC prepared at 600°C, enhance ROS (O₂^•-, H₂O₂, ^•OH) production in paddy soil. The results of rhizosphere-focused pot experiment simulating field-like flooded conditions highlight that FeBC significantly increased O₂^•-, H₂O₂, ^•OH concentrations, especially with PBS (25.63, 27.69, 35.82 µM/kg, respectively) surpassing control by 3.1-3.6-folds. Iron plaque formation, water-soluble phenols, and microbial activity further influenced ROS dynamics and accelerated MP degradation via oxidative fragmentation (SEM surface fissures), dissolved organic carbon release (484 mg/kg), and SUVA₂₅₄ decline (4.6 folds). Microbial shifts toward Actinobacteria (37-43 %) and Firmicutes (25-28 %) correlated with ROS dynamics, linking biotic-abiotic degradation pathways. This work reveals the novel role of FeBC in rhizosphere ROS generation and the environmental behavior of MPs in BC-treated agricultural systems.