Distinct lignocellulose degradation strategies of white- and brown-rot fungi in thermally modified Scots pine wood

Thermal modification (TM) improves wood decay resistance. However, it remains unclear whether thermally modified wood (TMW) limits brown- and white-rot decay through a universal pathway or distinct functional bottlenecks, and whether fungal transcriptional responses translate into effective extracellular degradation. This study aimed to determine how TM alters the degradation systems of the brown-rot fungus Gloeophyllum trabeum (Gt) and the white-rot fungus Trametes versicolor (Tv) to identify the stages at which decay becomes constrained. Here, thermally modified Scots pine was exposed to both fungi, linking decay outcomes and wood chemical changes to extracellular enzyme activities, hydroxyl radical generation, organic acid production, and fungal transcriptional responses. In Gt, redox-related genes were induced, whereas hydroxyl-radical production and hydrolytic enzyme activities decreased. This uncoupling between transcriptional activation and functional oxidative activity indicates that TM disrupted the oxidative initiation required for subsequent polysaccharide depolymerization. In Tv, TM stimulated laccase- and lignin-peroxidase-related responses together with antioxidant and detoxification pathways, while suppressing functions related to carbohydrate degradation and fungal growth. Thus, TM did not impose a uniform inhibition of fungal decay; instead, it generated fungus-specific functional bottlenecks, characterized by constrained oxidative initiation in Gt and a shift toward ligninolytic and stress-management functions in Tv. These findings suggest that the decay resistance of TMW emerges from distinct biochemical constraints imposed on different fungal decay systems, rather than from a common suppression of fungal activity. This study advances the mechanistic understanding of fungal degradation of TMW and provides a basis for improving the durability of bio-based materials.