Today is a festival you would never expect!

How many festivals can you name that are named after plants? Thinking carefully, it seems that I can't remember many such festivals. September 19th is designated as Poplar Day in China, which is also one of the few festivals named after plants.

There are four trees behind my yard, one is a poplar, one is a poplar, one is a poplar, and the other is also a poplar. This is not to imitate the style of the great writer Lu Xun, but the real scene in the China Poplar Museum.

Interior view of China Poplar Museum. Image source: People's Daily Overseas Edition

Anyone who has been to the China Poplar Museum will surely remember the four poplar trees over half a century old growing at the back of the courtyard. They were the first batch of Italian poplars that moved from Italy to Siyang in 1976. They have witnessed the history of Italian poplar planting across the country and the development of China's energy supply from being in ruins to being "clean and diversified". It is also because of them that poplars have their own festival - Poplar Festival (September 19) .

Historical mission, "passing on the flame" of hope

In the early days of the founding of the People's Republic of China in the 20th century, my country's economy, industry, science and technology were in a state of disrepair. National construction required wood, and people's daily lives also required firewood. For a time, the shortage of wood became an important problem facing the country.

Historical photos of Chengdu timber yard in the early days of the People's Republic of China. Image source: Qingbaijiang International Timber Trading Center official website

In order to solve this problem, it is urgent to find economical wood that can be grown in a short time. Although my country has a vast territory and abundant resources, with a wide variety of tree species, the research level of forest tree breeding is still far behind that of European countries.

Therefore, in the autumn of 1972, Liang Changwu, then Vice Minister of the State Forestry Department, and his delegation went to Argentina to attend the Seventh World Forestry Conference. At the request of Premier Zhou Enlai, they detoured to Italy on their way back to China and brought back 61 European and American black poplar cuttings from the Monferrato Poplar Science Institute.

These 61 little guys curled up in plastic bags for many days, traveled across the ocean to China, carrying the hope of the people of the country, and were sent to the Chinese Academy of Forestry, Hubei Institute of Forestry, and Nanjing Forestry College (renamed Nanjing Forestry University in 1985) for breeding experiments.

After two years of trial planting, the young seedlings of American and European black poplars bred by Nanjing Forestry University have grown as expected. Because the seed strips were introduced from Italy, they were named "Italian Poplars".

The crown and trunk of Populus nigra. Image source: China Plant Image Library

Black poplar leaves and flowers. Image source: China Plant Image Library

Crossing the ocean and taking root

Perhaps you may wonder, poplar seeds are only the size of sesame seeds and are easy to carry, so why didn’t Minister Liang and his team bring seeds back?

The first reason is of course the poplar seeds themselves. There are a large number of ovules in the ovary of the female flower of the poplar, which slowly mature in the cup-shaped flower disk at the base of the female flower. After maturity, they float away under the protection of the poplar fluff, looking for fertile soil to take root.

Poplar seeds have a big disadvantage, which is that the seed coat is too thin, they lose water very easily and are difficult to preserve . Once they leave the mother body, they easily lose vitality. Therefore, it is not realistic to bring them back to China from faraway Italy.

Female flowers of poplar and their internal structure (partial) Image source: BioArt Plants

Poplar branches and seeds. Image credit: author

Secondly, it is due to the omnipotence of plant cells . As long as a plant cell has a complete membrane system and a nucleus, it has a set of genetic foundations to develop into a complete plant. As long as the conditions are appropriate, it can divide and differentiate to regenerate a complete plant that is exactly the same as the mother.

It is like every worker in a factory has the skills that everyone in the factory has, and every worker can go out and set up an identical factory.

Most of us have used cuttings in our lives. For example, when you visit a friend's house and take a fancy to the flowers he grows, you will cut a branch, take it home and put it in your own flowerpot, and soon you will have exactly the same flower.

Image source: Unsplash

The most important thing is that if we want to quickly solve the problem of lack of firewood and wood, we must plant and grow timber quickly.

The growth of seeds requires a lot of time and environment, and it takes a long time to wait for them to mature. Cuttings are different. They can be done at any time in spring, autumn, or even winter in the south. As long as the growth environment is suitable, the cuttings can quickly take root and grow into usable materials.

The Chosen One, Fast Business

The reason for choosing Yiyang is its speed.

Italian Poplar is a new variety bred from the hybrid of Populus nigra and Populus deltoides based on industry demand. It combines the complementary excellent traits of its parents and has obvious hybrid advantages.

Italian poplar is a large deciduous tree. From a distance, you can see its slender oval crown and straight trunk. It inherits the "skin color" of its father and mother, and its bark is gray-brown.

Looking closer, you can see that the entire leaf of the Italian poplar is triangular in shape, with a rounded heart-shaped base and feels thick.

They grow fast, several times faster than trees such as Masson pine and fir in southern China. They can be cut down in rotation every 10 to 15 years to provide timber resources, and have a high yield rate. Therefore, they are the best choice for fast-growing renewable fuels.

Is there any secret why Yi Yang grows so fast?

Italian poplar leaves. Image source: China Plant Image Library

The growth of trees depends on primary growth and secondary growth . Primary growth is the growth of plant organs caused by the division, differentiation and growth of cells in the apical meristem of roots and stems. It is mainly manifested as an increase in the length of the plant body, so it is also called elongation growth.

Secondary growth is also called thickening growth, which is mainly manifested as the thickening of the roots and stems of the plant.

The structure of the woody stem of a tree is bark (including epidermis and phloem), cambium, xylem and pith from outside to inside. The thin cambium is the growth part of the trunk, which splits inward to supply xylem and splits outward to supply phloem, making the trunk thicker and stronger.

After the arrival of spring and summer, the temperature rises and the rainfall increases, and the cambium wakes up from hibernation. At this time, the cambium cells are active, with many differentiated vessel molecules, large diameters, and thin walls, producing "early wood" (spring wood) with loose texture.

In autumn, the temperature begins to gradually cool down, the activity of the cambium cells gradually weakens, the differentiated vessel molecules are fewer, the diameter is smaller, and the wall is thickened, forming the "late wood" or "autumn wood" with more fibers and a tight texture.

The early wood and late wood in the same year together are the annual rings, so the annual rings can reflect both the age of trees and their growth rate.

Tree rings. Image source: Unsplash

With the same body structure and growth principles, Italian poplar grows fast partly due to its "hard work".

Under natural conditions, the growth rate of plants will change regularly with day and night or seasons. This phenomenon is called the periodicity of forest growth . The changes caused by the alternation of day and night are called diurnal periodicity , and the changes caused by the alternation of seasons are called seasonal periodicity .

Due to the differences in day and night, temperature, light, water and other factors in the four seasons, different trees have different adaptability to the environment. The early growth type of trees with a "slow" character have a short high growth period in a year. They "work" for a period of time, grow for a while, and rest when they are almost done.

However, precisely because these plants grow extremely slowly, they can grow hard wood to support the body. The body's nutrient transport problems will not become apparent quickly, and the lifespan will be longer.

In comparison, fast-growing trees are more "curly". They have a very long period of high growth in a year, which can last throughout the entire growing season (3 to 6 months in the north and 6 to 8 months in the south) . They will never rot or lie flat, but their rapid growth rate will also cause the wood to be relatively loose. Under physical attacks such as thunderstorms and strong winds, their defense characteristics are relatively weak.

Compared with my country's iron birch (the hardest tree in the world), fast-growing trees are like putting teething biscuits and crispy egg rolls together. The trees are less hard and more easily damaged, so their lifespan is relatively shorter.

If you bloom, the breeze will come

The abundant poplar resources have transformed the former saline-alkali beach into a nationally famous plain forest, creating a huge "natural oxygen bar" for Siyang, bringing invaluable ecological effects, and making green Siyang famous all over the world.

Italian poplar has not only made itself successful, but also made Siyang a veritable "hometown of Italian poplar". It is the well-deserved "King of Italian Poplars in China".

References

[1] Chen Xuesen, Wang Nan, Zhang Zongying, et al. Understanding and thinking on several issues of fruit tree germplasm resources and genetic breeding[J]. Chinese Agricultural Science, 2022, 55(17): 3395-3410.

[2] Chen Yongmi. Populus spp. settled in China[J]. Botanical Journal, 1983(02):29-30.

[3] Peng Yuanhang, Feng Jiayi, Long Fengling, et al. Response of growth rhythm of three garden plant seedlings to municipal sewage sludge [J/OL]. Journal of Ecology: 1-11 [2023-09-16].

[4] Chao Nan, Chen Weiqi, Cao Xu, et al. Plant hormones coordinate the lignin biosynthesis pathway in poplar to adapt to seasonal changes [C] // Chinese Society of Botany. Abstracts of the First Frontier Academic Conference on Plant Science (II). Abstracts of the First Frontier Academic Conference on Plant Science (II), 2022: 23. DOI: 10.26914/c.cnkihy.2022.021279. [5] Zhang Zhenjue, Lin Jinyi, Chen Zhongren, et al. Activity cycle of cambium and seasonal changes of secondary phloem in four tannin plants [J]. Yunnan Plant Research, 1997(03): 57-60.

Planning and production

Produced by | Science Popularization China

Producer｜China Science Expo

Author: Li Tong, Institute of Botany, Chinese Academy of Sciences

Review丨Wang Bochen Institute of Botany, Chinese Academy of Sciences

Editor: Yang Yaping