Mechanism of Arbuscular Mycorrhizal Fungi in Enhancing Lead Stress Resistance in Poplar Trees

This study investigates the role of arbuscular mycorrhizal (AM) fungi, particularly Rhizophagus irregularis, in enhancing the lead (Pb) stress tolerance of poplar trees (Populus simonii x P. nigra '1307'). Under Pb stress conditions (0, 250, and 750 mg/kg), AM fungi significantly improved poplar growth, evidenced by increases in plant height (25.4%-31.2%), shoot biomass (21.6%-37.8%), and root biomass (28.9%-41.7%). Photosynthetic parameters, including net photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr), were substantially enhanced by AM inoculation. For instance, at 750 mg/kg Pb, Pn increased by 46.8% compared to non-inoculated controls. AM fungi facilitated Pb sequestration primarily in the roots, leading to 53.7% lower Pb concentrations in leaves and 47.3% lower concentrations in stems under 750 mg/kg Pb stress. This was attributed to root barrier effects and reduced Pb translocation. AM fungi also mitigated oxidative stress by increasing antioxidant enzyme activities, including superoxide dismutase (SOD, +45.6%), catalase (CAT, +38.2%), and peroxidase (POD, +32.5%). Concurrently, hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels decreased significantly, indicating enhanced membrane stability. These findings reveal that AM fungi improve Pb stress resistance in poplar by promoting Pb immobilization in roots, enhancing photosynthetic performance, and fortifying antioxidant defense systems. This study provides both theoretical insights and practical implications for utilizing AM fungi in phytoremediation of Pb-contaminated soils.