Functional enzyme addition facilitated multi-precursor co-humification via cleavage of β-O-4 bond during straw...

The recalcitrance of lignocellulose is a major cause of the slow straw composting process. Although inoculating functional microbial agents can enhance the degradation rate of lignocellulose, their efficacy is often limited by nutrient scarcity and competition with indigenous microorganisms during composting. To address this, we added a fungal enzyme solution to intensify lignocellulose hydrolysis. The results indicated that the addition of functional enzyme solution disrupted the network structure of lignocellulose, enhanced its bioavailability, and thereby promoted the degradation of lignocellulose, the loss rates of cellulose, hemicellulose, and lignin in the treatment with functional enzyme solution addition were 86.81%, 87.47%, and 81.08%, respectively. ¹H-¹³C 2D-HSQC-NMR analysis revealed that the addition of functional enzyme solution accelerated the cleavage of β-O-4 bonds in lignin and facilitated the oxidative transformation of aromatic units. On this basis, the supplementation of functional enzyme solution induced more oxidized lignin fragments, as well as protein and carbohydrate derivatives, to participate in the formation of humic acid, thereby enhancing the structural complexity and degree of polymerization of humic acid. The proportion of the complex humic acid fraction (HA-C3) in the functional enzyme solution addition treatment was the highest (47.13%) among all treatments, and its fluorescence emission peak showed a 10 nm red shift compared with the control group. Overall, this study effectively overcame the structural barrier of lignocellulose via the addition of functional enzyme solution, thereby accelerating its degradation and humification processes. It provides strategies and new insights into the mechanisms underlying compost humification.