Fungi involved in lignin degradation and humic substances formation during composting of Chinese medicinal herbal residues

Abstract

This study aimed to investigate the fungal taxa responsible for lignin degradation and humic substances (HS) formation, as two distinct but related key processes during the composting of Chinese medicinal herbal residues (CMHRs). Fungal strains with favorable lignin-degrading potential were isolated using the activities of three key ligninolytic enzymes (laccase, lignin peroxidase, and manganese peroxidase) as indicators. The variations of lignin-degrading enzyme activities, content of HS fractions, and fungal communities throughout the composting process, along with their interrelationships, were explored. The results showed that strain CM-d10–2, identified as Pleosporales sp., exhibited the highest lignin-degrading enzyme activity. The total activity of ligninolytic enzymes in compost attained its highest level during the thermophilic phase. The HS content accumulated continuously during the composting process and reached 110.02 g·kg⁻¹ at the maturation stage. Redundancy analysis (RDA) indicated that Kodamaea and Melanocarpus were positively correlated with the content of HS. These findings revealed key microbial groups that were associated with lignin degradation and HS formation, providing new insights for accelerating composting and improving compost quality.