Abstract: To investigate the regulatory effects and mechanisms of biological synergistic improvement on continuous cropping obstacles of under-forest Codonopsis pilosula, two-year continuously cropped Codonopsis pilosula under pear forest in Pingshun County, Shanxi Province was used as the test material, and five treatments including a water control, single biological amendments and compound biological amendments were set up. Plant growth, physiological resistance, active ingredient content, soil physicochemical properties, rhizosphere microorganisms, and the occurrence of root rot were measured. The results showed that the treatment of 1 235.5 kg/hm² biological organic fertilizer + 24.71 kg/hm² biological soil amendment had the best effect. Compared with the control, this treatment significantly increased plant height, stem diameter, and main root length by 34.4%, 41.2%, and 28.4%, respectively, and increased fresh weight per root and dry weight per root by 52.3% and 55.6%, respectively. Leaf peroxidase (POD) activity increased by 141.2%, malondialdehyde(MDA) content decreased by 42.08%, and soluble protein content increased by 96.62%. The contents of lobetyolin and polysaccharide in laternal roots increased by 61.33% and 27.35%, respectively. Soil pH was adjusted to 6.5, organic matter content increased by 135.29%, the number of rhizosphere bacteria increased significantly, while the numbers of fungi and Fusarium decreased significantly. The incidence of root rot decreased to 6.67%, with a control effect of 84.3%. Biological synergistic improvement could effectively alleviate continuous cropping obstacles of under-forest Codonopsis pilosula by optimizing the soil microecology, enhancing plant physiological resistance, and promoting the accumulation of active ingredients.

Key words: Codonopsis pilosula, biological synergistic improvement, continuous cropping obstacle, physiological resistance