Arbuscular Mycorrhizal Fungi Inoculation Promotes Growth and Alleviates Fusarium tricinctum-Induced Growth Inhibition in Quercus variabilis Seedlings

Quercus variabilis is a key species for reforestation in East Asia, yet the mechanisms by which arbuscular mycorrhizal fungi (AMF) influence seedling growth and responses to soil-borne fungal challenge remain incompletely understood. This study combined physiological and metagenomic approaches to address this gap. Among seven rhizosphere fungal isolates, Fusarium tricinctum (F15) exerted the strongest growth-inhibitory effect on Q. variabilis seedlings and was therefore selected for subsequent experiments. Inoculation with the AMF Rhizophagus intraradices significantly promoted seedling growth (p < 0.05), increasing root length by 4.94% relative to the uninoculated control and increasing ground diameter and aboveground fresh weight by 28.57% and 117.07%, respectively, relative to F15-treated seedlings. AMF inoculation also significantly altered substrate nutrient status (p < 0.05), particularly nitrogen, phosphorus, and potassium, and enhanced the activity of antioxidant enzymes, including peroxidase and catalase (p < 0.05). Metagenomic analysis revealed that AMF significantly reshaped rhizosphere microbial community composition and bacterial α-diversity (p < 0.05), enriching beneficial taxa such as Mesorhizobium. Functional profiling showed differences in predicted microbial functional profiles between AMF-inoculated and F15-treated groups. Together, these results indicate that AMF enhances seedling growth and mitigates the negative effects associated with F15 challenge, potentially through altered substrate nutrient dynamics, enhanced antioxidant capacity, and modulation of the rhizosphere microbial community.