Dose-dependent effects of manganese dioxide-modified biochar on lignocellulose degradation and humification in donkey manure composting: Insights into microenvironment-driven biotic-abiotic regulation.

The low degradation efficiency of lignocellulose during donkey manure composting restricts its humification. Manganese dioxide-modified biochar (MBC) can strengthen this process, whereas its dose effect remains unclear. This study investigated the effects and regulatory mechanisms of MBC levels (5% MBC1, 10% MBC2 and 15% MBC3) on lignocellulose degradation and humification during donkey manure composting. The results showed humus content followed the order: MBC1/MBC2 > CK > MBC3 (p<0.05), implying that an appropriate dosage of MBC promoted humification, while an excessively high dosage inhibited it. All MBC groups markedly enhanced lignocellulose degradation rate. MBC1 yielded the highest cellulose degradation rate (45.20%), whereas MBC3 attained maximum hemicellulose and lignin degradation rates (52.30% and 43.25%), attributable to varied lignocellulase activities under different MBC dosages. Two-dimensional correlation spectroscopy revealed that with increasing MBC addition rate, the variation order of fluorescence peaks of dissolved organic matter was: C1/210 nm>C1/255 nm>C2/200 nm>C2/290 nm; and C1/210 nm>C3/260 nm>C3/325 nm>C2/290 nm. Core microbial community analysis demonstrated that MBC1 and MBC2 significantly enhanced the diversity, relative abundance and functional diversity of core bacteria related to lignocellulose degradation and humus synthesis. Mantel test and partial least squares structural equation model confirmed that MBC coordinately regulated humification through biotic and abiotic pathways by modifying composting microenvironment. Considering economic cost and comprehensive efficiency, MBC1 was identified as the optimal dosage. This study provides theoretical basis and technical parameter guidance for MBC application in the composting of lignocellulose-rich materials.