Anaerobic digestion for degrading saponins from Panax notoginseng root and applying biogas slurry to promote degradation of autotoxic saponins in continuous cropping soil

Anaerobic digestion degrades complex organic matter and biogas slurry can control soilborne pathogens. However, the potential and efficiency of anaerobic digestion and biogas slurry in degrading autotoxins need further investigation. In this study, we investigated the efficiency of saponin degradation in anaerobic digestion systems (with increasing amounts of Panax notoginseng root powder in groups G1, G4, and G8), and analyzed changes in microbial communities after fermentation. We also determined the degradation efficiency of autotoxic saponins in continuous cropping soil treated with biogas slurry. The degradation rate of saponins (R1, Rg1, and Rb1) in the three anaerobic digestion systems exceeded 80%, and the biogas slurry from these anaerobic digestion systems enhanced autotoxic saponin degradation in continuous cropping soil to over 95%. Microbiome diversity decreased and its structure and composition were altered in anaerobic digestion groups G4 and G8. The predominant methanogenesis pathway in G4 was the acetoclastic pathway of Methanothrix, while that in G8 was the hydrogenotrophic pathway of Methanosarcina. Both G4 and G8 enriched potentially saponin-degrading taxa and shared 33 taxa. In conclusion, anaerobic digestion can enrich specific microbial taxa that degrade saponins, and biogas slurry can promote the degradation of autotoxic saponins in continuous cropping soil.