Suppression mechanism of soilborne diseases by biochar: Immobilization and deactivation of pathogenic enzymes and toxic metabolites

Greenhouse vegetable production aggravates soilborne diseases. Biochar has been recently considered as soil amendment to effectively prevent soilborne diseases. This study evaluates the immobilization and deactivation of pathogen-produced cell wall degrading enzymes (CWDEs) and toxic metabolites (TMs) by biochar to understand the mechanism involved in tomato Fusarium wilt, with activated carbon as the control. The results reveal that cellulase takes shorter time to reach the adsorption equilibrium than pectinase does. The adsorption isotherm of pectinase follows the Langmuir model, and the adsorption isotherm of cellulase follows the Freundlich model. The adsorption capacity of pectinase is greater than that of cellulase on biochar (on activated carbon). The adsorbed enzymes are completely immobilized and observably deactivated. The activity of immobilized pectinase decreases as 43.01 % of the original activity on biochar and 44.91 % on activated carbon. But the activity of immobilized cellulase decreases only as 1.88 % on biochar and 3.89 % on activated carbon. The tomato seedling bioassay analysis demonstrates that the adsorption of CWDEs and TMs is conducive to the reduction of disease severity. However, these established models (or laboratory simulation) cannot explain the enzyme adsorption process of biochar in the real soil, which requires the further exploration in the future.