Responses of Panax notoginseng (Burk.) F.H. Chen to cadmium stress: hormetic effects on growth, antioxidant systems, and rhizosphere microbial dynamics

Moderate Cd exposure (∼30 mg kg^-1) enhanced plant growth and antioxidant enzyme activities, whereas high Cd ( ≥ 80 mg kg^-1) caused physiological inhibition, consistent with a hormetic response. Microbial alpha diversity also peaked under moderate Cd but declined sharply at high Cd levels. Beta diversity differentiation was primarily driven by shifts in relative abundance rather than taxonomic turnover. Severe Cd stress reduced co-occurrence network connectivity and increased negative correlations, although several persistent core taxa (e.g., <i>Granulicella</i>) were maintained. Functional predictions indicated substantial functional redundancy, with key nutrient-cycling pathways largely retained despite pronounced network simplification.