Background/Objectives: Microbial inoculants effectively alleviate inhibitory factors during plant cultivation; however, the effects and underlying mechanisms of arbuscular mycorrhizal fungi (AMF) and Chaetomium globosum on the growth, metabolism, and bioactive compound production of A. membranaceus are still poorly understood. Methods: In this experiment, different concentrations of C. globosum (104, 106, 108 spores/mL) (Q1, Q2, Q3), AMF, and their combined treatments (AQ1, AQ2, AQ3) were applied to A. membranaceus seedlings via root irrigation, with an equal amount of sterile water as a control (CK). Results: The results showed that: (1) Under single inoculation with C. globosum, root colonization rate increased with higher inoculation concentrations, reaching its peak at Q3. Additionally, AQ3 significantly enhanced AMF colonization in A. membranaceus, and the presence of C. globosum promoted AMF root colonization and expansion. (2) AQ3 significantly enhanced the growth and photosynthesis of A. membranaceus, while also demonstrating excellent efficacy in alleviating lipid peroxidation-induced damage. (3) AQ3 treatment led to increased accumulation of major bioactive compounds in A. membranaceus, including calycosin-7-glucoside, cycloastragenol, and astragalosides I–III. (4) AQ3 treatment significantly upregulated multiple key structural genes involved in phenylalanine metabolism and flavonoid biosynthesis pathways, including PAL, 4CL, FLS, and CYP75B1. Conclusions: This upregulation enhanced the metabolic flux allocation from L-phenylalanine toward downstream flavonoid metabolites, thereby promoting the accumulation of major flavonoid constituents of A. membranaceus, such as galangin and luteolin, in both roots and leaves.
Gong et al. (Sun,) studied this question.