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

Abstract

<h4>Background</h4>Cadmium (Cd) contamination poses a major threat to <i>Panax notoginseng</i> (Burk.) F.H. Chen cultivation, yet the dose-dependent thresholds separating adaptive responses from toxicity remain poorly understood, particularly at the level of rhizosphere microbial processes.<h4>Methods</h4>A 75-day pot experiment was conducted using eight soil Cd concentrations (0-100 mg kg^-1). Plant growth traits and antioxidant enzyme activities (SOD, POD, CAT) were measured. Rhizosphere microbial communities were characterized in terms of alpha and beta diversity, co-occurrence network structure, and predicted functional potential using PICRUSt2 and FAPROTAX.<h4>Results</h4>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.