Screening, Identification and Biological Activity of Rhizosphere Functional Microorganisms in Alpine Aconitum carmichaelii

Purpose To explore beneficial rhizosphere microorganisms of alpine Aconitum carmichaelii, evaluate their biological activities, and investigate their plant growth-promoting (PGP) effects on maize seedlings, laying a theoretical foundation for the development of microbial inoculants.

Methods Rhizosphere microorganisms were isolated from four dominant A. carmichaelii cultivars cultivated in Shangri-La and Lijiang, Yunnan Province, followed by functional microbial screening and biological activity evaluation. Strains were identified through sequencing of conserved genes (16S rRNA and gyrB). A pot experiment with maize was conducted to analyze the PGP effects of root irrigation with selected strains and their impacts on soil pH and available nutrient content.

Results Four strains (C77, E1, A1, and Y83) with superior nitrogen fixation, phosphate solubilization, potassium release, siderophore production, and indole-3-acetic acid (IAA) production were isolated. Strains A1 and Y83 demonstrated strong nitrogen-fixing capacity, with soluble indices of nitrogen-fixing zones at 2.09 and 1.91, respectively. Strain A1 exhibited enhanced organic phosphorus mineralization and inorganic phosphorus solubilization, increasing phosphorus release by 111.01% and 342.46% compared to the control, respectively. Strain E1 showed high inorganic phosphorus solubilization (increased by 332.64%), potassium release (increased by 72.17%), IAA production (99.14 mg/L), and soluble index was 2.06 in CAS medium. Strains C77 and E1 displayed strong antagonistic activity against Fusarium solani, F. oxysporum, F. graminearum, and Thielaviopsis basicola, with inhibition rates exceeding 60%. The pot experiment revealed that root irrigation with these strains significantly promoted maize seedling growth, decreased soil pH, increased the contents of available phosphorus and alkali-hydrolyzable nitrogen, while declined the content of available potassium.

Conclusion The four PGP strains isolated from A. carmichaelii rhizosphere demonstrate potential in nitrogen fixation, phosphorus solubilization, potassium release, siderophore and IAA production, and antagonism F. solani, F. oxysporum, F. graminearum, and T. basicola. They also enhance maize seedling growth and improve soil physicochemical properties. This study provides a theoretical foundation for developing microbial inoculants and applying functional PGP microorganisms in integrated crop-medicinal plant systems, while offering valuable references for related research.