Dynamics of Functional Traits and Molecular Regulation in the Vascular Cambium Across Different Ages of Styphnolobium japonicum

Understanding whether long-term vascular cambium vitality in ancient trees reflects progressive decline or adaptive reprogramming is central to grasping woody plant longevity. We performed an integrative analysis of functional traits, transcriptome profiles, and metabolomic landscapes of cambial zone enriched from 80-, 500-, and 1000-year-old Styphnolobium japonicum trees. With increasing tree age, the vascular cambium showed fewer cell layers, reduced thickness, and lower auxin, gibberellin, and IAA/ABA ratios, whereas bark thickness, malondialdehyde, abscisic acid, jasmonic acid, and salicylic acid contents increased. Transcriptomic and metabolomic analyses revealed that differentially expressed genes and metabolites were primarily enriched in the cell cycle, phytohormone signaling, and phenylpropanoid biosynthesis pathways. Specifically, genes associated with cell division were down-regulated in millennial trees, whereas phenolic acids, flavonoids, and lignin-related metabolites significantly accumulated. Piecewise structural equation modeling suggested associations among tree age, transcription factors, structural genes, metabolites, and cambial functional traits. These results indicate that cambial senescence is not a simple linear decay but a highly coordinated remodeling process, providing crucial evidence for delayed senescence in long-lived woody species.