Age-dependent dynamics of carbon density in Phyllostachys edulis culms

The underlying age-dependent carbon accumulation in bamboo remains poorly understood. Here, Phyllostachys edulis (moso bamboo) aged 1-10 years were investigated to reveal how carbon-related traits vary with maturity. Eight year old represents the critical age for maximum volumetric carbon related performance. The mass-based carbon content stayed stable (45.69-46.73 %) across all ages, while basic density rose from 0.51 to 0.67 g/cm 3 for 1 to 8 year old culms, raising volumetric carbon density by 34.78%. Volumetric carbon density peaked at 8 years and correlated closely with basic density. Anatomical lignocellulosic maturation (higher fiber fraction, secondary wall thickening, rising lignin/cellulose crystallinity and falling hemicellulose) drove tissue densification; Raman imaging confirmed progressive lignin deposition into secondary walls. Volumetric energy density followed the same trend as volumetric carbon density. Results demonstrate that improved volumetric carbon storage originates from cell wall densification instead of elevated mass-based intrinsic carbon concentration. This work offers mechanistic understanding for age oriented management to balance carbon sequestration and biomass valorization.