Foliar Application of Bacillus thuringiensis Regulates Soil Physicochemical Properties and Microbial Ecological...

Bacillus thuringiensis (Bt) is widely employed as a biological control agent against pests in tea plantations, yet its impacts on soil health and microbial ecology remain insufficiently understood. This study investigated the effects of two Bt application regimes, namely moderate-frequency conventional Bt application (Bt1, 3 sprays over 21 days) and high-frequency intensive Bt application (Bt2, 6 sprays over 42 days), on soil physicochemical properties, enzyme activities, and microbial community structure and function in tea soils. The moderate-frequency conventional Bt1 significantly improved soil nutrient status by increasing organic matter, available nitrogen, and potassium, and boosted acid protease, sucrase, and cellulase activities, while Bt2 achieved the maximum urease and polyphenol oxidase activities but failed to promote soil available nutrients and organic matter as effectively as Bt1. Although neither Bt treatment induced notable shifts in overall microbial alpha-diversity indices, community composition differed distinctly between the two treatments. Bt1 enriched beneficial taxa related to nitrogen fixation and organic matter degradation including Pseudomonas, Bradyrhizobium, and Sphingomonas, and sharply suppressed pathogenic fungi such as Aspergillus and Curvularia, whereas Bt2 caused an 18.29% reduction in Sphingomonas abundance with limited enrichment of beneficial bacteria. Functional predictions indicated that Bt1 amplified microbial carbon degradation and nitrogen cycling, enriched saprotrophic and symbiotic fungi and reduced plant pathogens by 85.78%, while both Bt treatments elevated saprotrophic fungi yet Bt2 only reduced pathogens by 11.84%. Co-occurrence network analyses revealed enhanced microbial interactions and community stability under Bt1, while excessive high-frequency Bt2 reduced network connectivity and stability compared with CK and Bt1. These results suggest that moderate-frequency conventional Bt application can positively modulate soil microbial communities and ecosystem functions, providing valuable insights for sustainable pest management and soil health maintenance in tea agroecosystems.