Comparative Effects of Trichoderma guizhouense NJAU4742 and Bacillus velezensis SQR9 on Growth and Pb Accumulation in Salix suchowensis

Soil lead (Pb) contamination poses a severe threat to agricultural sustainability and food security. Phytoremediation offers a green alternative for remediation, yet its efficiency is limited by poor plant tolerance and restricted metal uptake. In this study we investigated the functional roles of the microbial inoculants <i>Trichoderma guizhouense</i> NJAU4742 and <i>Bacillus velezensis</i> SQR9 in enhancing the performance of <i>Salix suchowensis</i> P1024 grown in Pb-contaminated soil. NJAU4742 significantly increased plant biomass by 34% (<i>p</i> < 0.05), accompanied by increased soil microbial biomass and higher activities of urease, acid phosphatase, and sucrase. In contrast, SQR9 strongly enhanced Pb accumulation by 19% (<i>p</i> < 0.05), which was accompanied by upregulated antioxidant enzymes, reduced lipid peroxidation, and elevated cysteine levels. Random forest and correlation analyses demonstrated that soil nutrient cycling indices (urease, MBC, sucrase) were key predictors of biomass, whereas antioxidant defenses (POD, CAT) primarily explained Pb accumulation. These findings provide new insights into the distinct contributions of NJAU4742 and SQR9 to willow growth and Pb remediation, and provide a basis for developing more effective microbe-assisted phytoremediation strategies.