The beauty of bamboo both inside and outside

 Green and green bamboo, upright and strong, without gorgeous posture, but with the appearance of danqing, without the attitude of fat and powder, but with the will of the clouds, has become a symbol of many beautiful things in the aesthetic habits of our people, and occupies an important place in people's hearts. However, from the perspective of a bamboo researcher, the many fine qualities of bamboo are closely related to the unique internal structure of bamboo, which is still very beautiful. The beauty of bamboo can be described as distinctive, both inside and out.

Bamboo is versatile because of its various excellent qualities. It is strong, flexible, stable and less dense, so it is used in the construction and furniture manufacturing industries. It is rich in fiber components, so it is used in the paper industry. It is verdant and evergreen, so it is used in green landscape and garden construction. It grows rapidly and has important applications in environmental protection and ecological restoration. It is popular for its delicious taste and rich nutrition. These qualities are related to the microstructural decisions of bamboo, determined by the type, size, shape, and arrangement of the cells, as well as the structure and composition of the cell walls.

Not a long history of research

In contrast to the thousands of years of bamboo cultivation and use, the internal structure of bamboo has been studied in depth for less than 50 years. Microscopic anatomical studies of bamboo are within the scope of wood anatomy. In order to make better use of wood, it is necessary to do various microanatomical studies on wood. Only by understanding the microstructure of various woods more carefully can we turn the experience gained from practice alone into quantifiable scientific indicators. Currently, some of the world's largest wood processing yards have their own wood microanatomy research facilities. As with wood utilization, various anatomical studies on bamboo microscopy are necessary to better utilize bamboo. In the field of bamboo anatomy research, the most important contributors are Prof. Zhengli Li of Peking University and Prof. W. Liese of the University of Hamburg, Germany, former President of the IUF.

In the early 1960s, Prof. Li developed the steam sectioning method in order to better study the properties of various bamboo materials. It involves boiling the harvested bamboo samples for a period of time and then slicing them while blowing steam against them in order to soften the bamboo material. This method overcame the difficulty that the bamboo material was hard and not easy to produce, and laid the foundation for future microscopic studies of bamboo material. Prof. Li studied the anatomical structure of 25 species of bamboo in China and prepared the first subspecies search list for taxonomic identification based on anatomical features. Later, Prof. W. Liese et al. studied the unique vascular bundle structure in 14 genera and 52 species of bamboo in Asia in the 1970s and 1980s to do the analysis, comparing the differences of this structure in different heights in the same bamboo and among different individuals of the same species, and observed the ultrastructure of the bamboo fiber cell wall using scanning electron microscopy and transmission electron microscopy, and proposed a model of the bamboo fiber cell wall structure.

Why does bamboo grow fast?

There is an interesting phenomenon in the growth of bamboo, that is, the number of nodes of bamboo shoots growing out of the ground is the number of nodes of the grown bamboo; how thick the bamboo shoots are, and how thick the grown bamboo is. This peculiar phenomenon is determined by the unique microscopic structure of bamboo.

Bamboo shoots develop from the buds of underground bamboo stems, which are wrapped layer by layer in a shell called a culm sheath. The topmost part of the internal structure of the shoot is called the apical meristem, and at the point where the culm sheath leaves occur, the cells of the apical meristem divide and differentiate to form the nodal compartment, which is the node of the bamboo after it grows into a bamboo. The nodal compartment separates the meristem into several segments from the bottom up, each segment being an internode. When the internode grows, it is the section of the bamboo that we see. In young bamboo shoots, the internodes are extremely short and the entire internode is a type of cell that we call interstitial meristem. The interstitial meristem plays a decisive role in the growth of the bamboo.

After the bamboo shoot grows out of the ground, the cells that formed the internodes stop dividing and differentiating, so no new internodes appear, so the bamboo shoot has as many nodes as it grows into. From this point on, the growth of bamboo is the result of the activity of the "interstitial meristem". The cells of this tissue have the characteristic that they can only divide in the direction of the long axis of the bamboo stem, and the expansion and elongation of the cells also take place in the direction of the long axis of the bamboo stem, and cannot increase the number and width of the cells in the horizontal direction, and therefore cannot increase the thickness of the bamboo stem. In the same bamboo shoot, the "interstitial meristem" of each node is growing at the same time, so on a macroscopic level, it shows the rapid growth of the bamboo shoot. Most types of bamboo shoots grow an average of 8-15 cm tall in a day, with some growing as fast as 1 meter in a day and night.

Bamboo shoots are good tasting and nutritious because the cell walls of all types of bamboo shoots are not yet lignified, and the cell walls are rich in cellulose, hemicellulose and pectin. By the time the bamboo shoot grows into a new bamboo and the cell wall lignification is complete, the bamboo becomes hard and pliable and is no longer edible.

For bamboo, the period when bamboo shoots are just becoming new bamboo is the most dangerous period of their lives. Since the bamboo has grown very tall at this time, but the mechanical tissues in the body are not yet fully developed, especially at the nodes, where the interstitial meristem ceases to be active at the latest, it is easily broken in case of external damage (wind, human or animal aggression, etc.). Moreover, this is also the period when bamboo is very sensitive to pests and diseases as well as adverse environmental conditions, so bamboo farmers will take more care of their bamboo plantations.
When is the bamboo hardest?

Most species of bamboo stop growing rapidly after one year of growth, their height no longer increases, and their internal structure is basically fully developed. By looking through a polarized light microscope you can see that the cell walls of the basic tissue cells have thickened and the process of lignification is basically complete.

Although the internal structure of three-year-old and seven-year-old bamboos is basically the same as that of annual bamboos, scientists have found that the cell walls of bamboos continue to thicken and show a multilayer structure as the age of the bamboos increases through careful observation of the microstructure, and studies by Prof. W. Liese et al. have shown that even after 12 years of growth, the thickness, number of layers, and degree of lignification of the bamboo cell walls continue to increase.

The thickness, number of layers and degree of lignification of bamboo cell walls directly affect the quality of bamboo timber. Therefore, there is a close relationship between the age of bamboo and the mechanical strength of bamboo timber. Generally speaking, the mechanical strength of bamboo increases with the age of bamboo, but when bamboo ages, especially after flowering, the strength decreases rapidly and the material starts to become brittle and break easily.

In southern China, bamboo farmers often mark the year of birth on each bamboo plant with their homemade markers, and then cut down the 4-6 year old bamboo. Although the age of the bamboo can be roughly estimated based on its color, texture, and other characteristics, accurately recording the age of each culm and harvesting it accurately and on time ensures the quality of the bamboo material. Although the cell walls will thicken and lignification will continue, the mechanical strength of the bamboo will have basically reached a stable value, and the increase in strength will be very limited thereafter, so it would be uneconomical for bamboo farmers to wait a few more years for this.

Why is bamboo both hard and flexible?

Among all plants, bamboo is one of the best raw materials used as structural materials, it is light and firm, thick hollow skin, strong bending and tensile strength, fully demonstrating the mechanical beauty of nature. In terms of strength and stiffness, it is a step above wood and even ordinary steel, and can be widely used in construction projects. For example, bamboo scaffolding is more resistant to hurricane than steel scaffolding. The mechanical properties of bamboo are determined by its microstructure, which determines macroscopic properties.

Bamboo is mainly composed of vascular bundles that carry the load and a basic tissue cell matrix that connects and transmits the load. The shape, size, and density of the vascular bundles in bamboo poles vary in the same cross-section of the bamboo wall, showing an obvious regularity, from outside to inside, the volume of the vascular bundles from small to large, to near the yellow (the innermost wall of the bamboo) surface and slightly change. The density of the vascular bundles changes from dense to sparse and then becomes slightly denser near the yellow side of the bamboo. The very hard surface system of the bamboo pole (bamboo green), which consists of the epidermis and subcutaneous layer, and the pith ring (bamboo yellow), which consists of multiple layers of stone cells, form the inner and outer sandwich walls of the bamboo pole, holding the vascular bundles and basic tissues tightly in the middle, which plays a good stabilizing role in the nature of the bamboo material. This is the reason why bamboo is so hard.

The cell wall of bamboo fiber is distinctive in that it has multiple layers of unevenly thickened secondary walls, forming a multilayer structure with alternating widths and narrows. This laminar structure is important for the flexural strength of bamboo. In addition, the structure of the vascular bundle density and the gradual increase of fiber density from inside to outside in bamboo poles is also its best adaptation to bending loads subjected to wind. This is the secret of bamboo's flexibility.

However, bamboo also has its disadvantages, such as bamboo in starch, reducing sugar, protein and other cellular after-containing substances than wood, so that bamboo and its products in the storage, processing and use process, prone to mildew, affecting its quality, reduce or even completely lose its use value. In order to prevent mildew, fungal rot and insect infestation, it is necessary to carry out the necessary physical methods such as steaming, drying and chemical reagent treatment after harvesting and during the processing of bamboo.

Green bamboo with its strong and upright external appearance