From Waste to Wealth: Elucidating the Depolymerization Pathways of Lignocellulose in Coniferous Forest Residues during Weathering and Brown-Rot Decay Processes

Coniferous forest residues, recognized as sustainable biomass feedstocks, undergo progressive degradation through weathering and brown-rot decay processes in outdoor natural environments. This biochemical transformation results in the depolymerization of lignocellulose components into diverse chemical derivatives. However, the compositional profiles and potential applications of these degradation products have yet to be systematically characterized or effectively utilized within current biorefinery frameworks. In this study, the degradation pathways of lignocellulosic components during weathering and brown-rot nonenzymatic decay, which was simulated by the Fenton reaction, were elucidated. Specifically, the investigation focused on alterations in the degree of polymerization, chemical functional groups, monosaccharide content, oxidation process, chemical bonding, and structural units of lignocellulose. The results indicated that weathering facilitated the cleavage of glycosidic bonds and the ring-opening of monosaccharide units in cellulose and hemicellulose, leading to the formation of uronic acids. Unstable polysaccharide structures were found to be more susceptible to depolymerization into monosaccharides and organic acids during subsequent nonenzymatic degradation. The molecular weight (Mw) of cellulose decreased by 79% after 30 days of weathering and nonenzymatic degradation. The predepolymerization (photodegradation-induced chain scission during weathering) of cellulose and hemicellulose generated shorter polymer chains, which potentially enhanced saccharification efficiency for biofuel production. Conversely, carbonyl compounds derived from the photodegradation of lignin exhibited a heightened susceptibility to oxidative degradation in subsequent nonenzymatic processes, leading to an 86% reduction in the Mw. The degradation of lignin-yielded derivatives such as quinones and apocynin, which indicated potential high-value applications as free radical scavengers, UV absorbers, and antifungal agents.