Lignin photodegradation governs the stage-dependent anti-mold performance of bamboo scrimber through fungal metabolic reprogramming.

Bamboo scrimber (BS) faces significant challenges from the interplay between weathering and microbial colonization in outdoor applications. This study elucidated the stage-dependent evolution of BS mildew resistance during accelerated UV weathering (0-960 h) and uncovered the underlying molecular mechanisms using GC-MS, SEM, and RNA-Seq. The results revealed a non-monotonic response. While initial and long-term weathering facilitated mold growth, a transient peak in antifungal resistance emerged at 480 h. GC-MS identified this peak as coinciding with the maximum release of lignin-derived aromatic stressors (e.g., 2,4-di-tert-butylphenol). Transcriptomic profiling of Aspergillus niger demonstrated that these chemicals triggered a "triple paralysis" mechanism: inhibiting extracellular hydrolases to block carbon source acquisition, disrupting chitin biosynthesis to compromise cell wall integrity, and arresting central carbon metabolism to exhaust energy supply. Conversely, prolonged weathering (960 h) led to catastrophic structural failure, creating sheltered, nutrient-rich niches that overshadowed residual chemical inhibition and resulted in pervasive colonization. These findings provided mechanistic insights into the stage-dependent regulation of fungal colonization by weathering-induced chemical changes and offered theoretical guidance for exploring potential green modification concepts for enhancing the durability of bamboo composites.