Performance and mechanism of immobilized laccase biochar for phenolic acid degradation in capsicum monoculture systems

The accumulation of phenolic acid autotoxins is a key factor contributing to the challenges of continuous chili cropping, but efficient and stable remediation methods are currently lacking. This study innovatively employs K₂CO₃ alkali etching to prepare engineered biochar as a laccase carrier, achieving high-efficiency immobilization via glutaraldehyde cross-linking (maximum loading capacity: 177.3 U/g). Compared to free laccase, the immobilized system exhibits significant advantages: broader pH and temperature adaptability, enhanced long-term storage stability, and improved reusability. Experimental results demonstrate that 2 U/mL of immobilized laccase can completely degrade 20 mg/L phthalic acid within 10 h and is effective against multiple chili autotoxic phenolic acids (ferulic acid, cinnamic acid, coumaric acid, and p-hydroxybenzoic acid). After phthalic acid degradation, the solution no longer inhibits chili seed germination, and soil experiments confirm a degradation rate of 51.07% after 11 days. Mechanistic studies reveal that the degradation process relies on synergistic radical and non-radical pathways, with electron transfer playing a dominant role. LC–MS analysis confirms the transformation of phenolic acids into low-toxicity small molecules. This study is the first to propose a biochar-immobilized laccase synergistic degradation strategy, which offers high efficiency, environmental safety, sustainability, and broad applicability compared to existing methods.