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.

The combination of surface densification and superheated steam treatment is an effective method to improve the mechanical properties and dimensional stability of low-density wood. The objective of the current work is to evaluate the effects of superheated steam treatment on the micromechanical behavior of surface densified wood. The microstructure, chemical composition, cellulose crystalline structure, and micromechanical behavior of surface densified wood under different superheated steam pressures were investigated. Results indicated that both 0.1 MPa and 0.3 MPa superheated steam treatments increased the elastic modulus and hardness of fiber cell walls in surface densified wood. However, the average creep ratio and maximum creep compliance J(50) of surface densified wood under 0.3 MPa decreased by 41.59% and 6.76%, respectively, compared with untreated wood. The improvement of elastic modulus, hardness and creep resistance of surface densified wood treated with superheated steam was associated with the increase of relative crystallinity (CrI) and crystalline size. In addition, 0.3 MPa superheated steam treatment displayed a better effect on the enhancement of the elastic modulus, hardness, and creep resistance of the fiber cell wall than 0.1 MPa superheated steam treatment.

In recent years, bamboo has been widely used in a broad range of applications, a thorough understanding of the structural characteristics of bamboo nodes is essential for better processing and manufacturing of biomimetic materials. This study investigated the complex anatomical structure for the nodes of two bamboo species, Indocalamus latifolius (Keng) McClure and Shibataea chinensis Nakai, using a high-resolution X-ray microtomography (μCT). The results show that the vascular bundle system in the nodal region of I. latifolius and S. chinensis is a net-like structure composed of horizontal and axial vascular bundles. Furthermore, the fiber sheath surrounding metaxylem vessels tended to be shorter in the tangential direction. This structure of bamboo nodes facilitates the tangential and axial transport of moisture and nutrients. The anatomical structure of I. latifolius and S. chinensis nodes has obvious differences, especially in the arrangement of vascular bundles. Vascular bundle frequency was significantly higher in S. chinensis nodes than in I. latifolius nodes. These findings indicate that μCT is a nondestructive three-dimensional imaging method that can used to examine the anatomical structure of bamboo nodes.

The mechanical performance of bamboo is highly dependent on its structural arrangement and the properties of biomacromolecules within the cell wall. The relationship between carbohydrates topochemistry and gradient micromechanics of multilayered fiber along the diametric direction was visualized by combined microscopic techniques. Along the radius of bamboo culms, the concentration of xylan within the fiber sheath increased, while that of cellulose and lignin decreased gradually. At cellular level, although the consecutive broad layer (Bl) of fiber revealed a relatively uniform cellulose orientation and concentration, the outer Bl with higher lignification level has higher elastic modulus (19.59–20.31 GPa) than that of the inner Bl close to the lumen area (17.07–19.99 GPa). Comparatively, the cell corner displayed the highest lignification level, while its hardness and modulus were lower than that of fiber Bl, indicating the cellulose skeleton is the prerequisite of cell wall mechanics. The obtained cytological information is helpful to understand the origin of the anisotropic mechanical properties of bamboo.