This study investigated the effects of bamboo age, bamboo parts, and pyrolysis temperatures on the physiochemical properties of bamboo char throughout a series of pyrolysis processes spanning from 150 °C to 1000 °C. The results indicated that as the pyrolysis temperature increased from 150 °C to 500 °C, the yield of bamboo char experienced a rapid decline, settling at a maximum of 69%, with no significant impact from bamboo age and parts. Subsequently, as the pyrolysis temperature continued to rise from 500 °C to 1000 °C, the yield stabilized at 25.74–32.64%. Besides, fixed carbon (FC), volatile matter (VM), and ash content were temperature-dependent, while the H/C, O/C, (N + O)/C, and aromatic index kept constant after reaching 500 °C. Notably, 800 °C was confirmed to be a crucial turning point for physiochemical properties, at which the graphitic structural changes occurred, pore collapsed, and potassium salts released. Bamboo age was proved to enhance the stability. Pearson correlation coefficient (PCC) analysis revealed that the pyrolysis temperature was positively correlated (p < 0.01) with ash (0.76), FC (0.97), AI (0.81), R₅₀ (0.77), and C–C/C = C/C–H (0.87). Conversely, negative correlations (p < 0.01) were observed with VM (−0.91), O/C (0.88), H/C (−0.95), (N + O)/C (−0.87), C loss (−0.79), and labile organic-C (−0.78). Additionally, bamboo age was negatively correlated (p < 0.01) with C loss (−0.40), volatile organic-C (−0.63), labile organic-C (−0.45), and recalcitrant organic-C (−0.40), but positively associated with R₅₀ (0.54), refractory organic-C (0.42), and inorganic-C (0.52). Bamboo parts did not exhibit significant correlations with char properties. Graphical Abstract

The vascular bundle is an important structural unit that determines the growth and properties of bamboo. A high-resolution X-ray microtomography (μCT) was used to observe and reconstruct a three-dimensional (3D) morphometry model of the vascular bundle of the Qiongzhuea tumidinoda node due to its advantages of quick, nondestructive, and accurate testing of plant internal structure. The results showed that the morphology of vascular bundles varied significantly in the axial direction. In the cross-section, the number of axial vascular bundles reached a maximum at the lower end of the sheath scar, and the minimum of it was at the middle of the diaphragm. The frequency of axial vascular bundles decreased from the lower end of the node to the nodal ridge, and subsequently increased until the upper end of the bamboo node. The proportion of parenchyma, fibers, and conducting tissue was 65.7%, 30.5%, and 3.8%, respectively. The conducting tissues were intertwined to form a complex 3D network structure, with a connectivity of 94.77%. The conducting tissue with the largest volume accounted for 60.26% of the total volume of the conducting tissue. The 3D-distribution pattern of the conducting tissue of the node and that of the fibers were similar, but their thickness changed in the opposite pattern. This study revealed the 3D morphometry of the conducting tissue and fibers of the bamboo node, the reconstruction of the skeleton made the morphology more intuitive. Quantitative indicators such as the 3D volume, proportion, and connectivity of each type of tissue was obtained, the bamboo node was enlarged mainly caused by the particularly developed fibers. This work laid the foundation for a better understanding of the mechanical properties and water transportation of bamboo and revealed the mystery of bamboo node shedding of Q. tumidinoda.