Contrasting Lignocellulose Degradation and Humification Responses to Biochar, Manganese Dioxide, and Penicillium oxalicum during Donkey Manure Composting

Efficient valorization of lignocellulose-rich livestock manure requires not only the decomposition of recalcitrant biomass but also the stabilization of organic carbon during composting. Here, biochar, manganese dioxide (MnO2), and a five-strain Penicillium oxalicum inoculum were compared in the same donkey manure composting system to determine whether preferential degradation of individual lignocellulosic fractions was accompanied by a proportional humification response. Biochar produced the greatest humification response, increasing final humic acid content by 191.2% relative to the control while increasing cellulose degradation by 6.11 percentage points. MnO2 resulted in the highest lignin degradation rate (31.14%), together with greater laccase activity and relatively high abundances of auxiliary activity family 2 and manganese peroxidase genes. P. oxalicum inoculation produced the highest hemicellulose degradation rate (80.42%) and higher acetylxylan esterase activity. Fluorescence analyses revealed distinct dissolved organic matter transformation patterns, while bacterial community analyses and structural equation modeling showed different relationships between lignocellulosic components and humification among treatments. Greater degradation of an individual lignocellulosic fraction was therefore not accompanied by a proportional increase in humification. These findings indicate that amendment selection for lignocellulose-rich manure should consider organic carbon stabilization together with substrate degradation, providing a basis for the resource utilization of livestock manure.