Unraveling Polycyclic Aromatic Hydrocarbon-Triggered Reactive Oxygen Species' Generation in Maize Rhizosphere:...

Reactive oxygen species (ROS) are critical drivers of redox-associated biogeochemical processes within the rhizosphere, yet the mechanisms of their generation under contaminant stress remain poorly understood. A 24-day pot cultivation experiment with four treatments (control, naphthalene, phenanthrene, and anthracene) was conducted to investigate how polycyclic aromatic hydrocarbons (PAHs) alter the production of three kinds of ROS (e.g., O₂^•-, H₂O₂, and ^•OH) in the maize rhizosphere. PAHs promoted the production of rhizosphere ROS, and the promotion effects were compound-dependent, following the order of anthracene > phenanthrene ~ naphthalene. The increases in O₂^•- content were 55.6%, 14.3%, and 17.9% under anthracene, phenanthrene, and naphthalene treatments. The H₂O₂ content was enhanced by 58.6% under anthracene treatment, 10.4% under phenanthrene treatment, and 15.4% under naphthalene treatment. The ^•OH concentrations increased by 62.5%, 21.1%, and 0.5% under anthracene, phenanthrene, and naphthalene exposure, respectively. Importantly, the variations in rhizosphere ROS' content simultaneously fluctuated with stem length, photosynthetic rates, root exudates, dissolved organic carbon (DOC), water-soluble phenols, and enzymes activities induced by PAHs stress. Statistical analysis suggested PAH stress enhanced maize biomass (particularly stem growth), thereby improving photosynthetic efficiency and thus stimulating root exudate release. Root exudates could promote water-soluble phenol and DOC release and enhance microorganism reproduction, thereby mediating abiotic ROS' production via electron transfer and biotic ROS' production via extracellular release. These findings clarify the response of rhizosphere ROS to PAHs stress, providing valuable insights for rhizosphere-ROS-mediated remediation of soil pollutants.