In Xinjiang, I saw the legend of "a thousand years of standing"

On the shore of Lop Nur Lake in Xinjiang Uygur Autonomous Region, my country, there is a site of ruins of the Kingdom of Loulan buried by sand. As an important point on the Silk Road, it once flourished in the barren desert.

In the ruins, archaeologists found a lot of wood used as building materials, which were taken from Populus euphratica. Hearing the name of Populus euphratica, we seem to be able to feel the sandstorms of the desert Gobi and its tenacity to take root and grow in the desert. People at that time used Populus euphratica to build a prosperous ancient desert country.

Image source: Pixabay

#1 Species Profile

Populus euphratica is a representative tree species in Xinjiang, my country, and its number accounts for 91.1% of the world's total. However, the distribution range of Populus euphratica is also wide, from Central Asia to Egypt, as far as Spain and Monaco, you can see them. Populus euphratica lives in dry continental climate areas. They like sunshine and hot environments, are resistant to drought and salt, and are a tree species that is highly adapted to desert environments.

Populus euphratica is usually 10 to 18 meters tall, with a maximum height of more than 20 meters, and a trunk diameter of more than 1 meter. It blooms from late April to May and bears fruit from late June to late August. The most interesting morphological feature of Populus euphratica is its leaves. The leaves of Populus euphratica have very significant diversity within the species, lanceolate or linear-lanceolate, ovate, and flat ovate. The leaf morphology of different individuals of the same species varies greatly. Based on this feature of Populus euphratica, its scientific name is sometimes written as Populus diversifolia (meaning diverse leaves).

#2 The legendary "Thousand Years of Standing"

It is said that the poplar tree "lives for a thousand years, stands for a thousand years after death, and does not rot for a thousand years after falling." Is this true? In fact, the life span of the poplar tree is about 150 years. A poplar tree with a trunk diameter of 101.5 cm found in the Tarim River Basin holds the record for the longest life span of the poplar tree - 233 years.

After the death of the poplar, due to the dry climate in the desert, it will be dried in a short time. The dried trunk lacks water and is not easy to rot. In addition, the strong root system that the poplar grew in order to find underground water sources during its lifetime can prevent it from falling over for a period of time after its death. Although it is not a thousand years old, the poplar does have a longer lifespan than other tree species, and it will maintain its original posture for a long time after death.

#3 The mystery of salt resistance

Although moist, low-salinity soil is most suitable for poplars to survive, they have strong salt resistance. Studies have shown that poplars can survive even in conditions of 2% to 5% salinity. Plants belonging to the genus Populus, like poplars, generally have a certain degree of salt resistance. However, even with a close relationship, not all poplar plants have the same strong salt resistance as poplars. The strong salt resistance of poplars may be a characteristic that has evolved to adapt to the environment and is different from their "relatives."

Image source: Pixabay

Generally speaking, poplar plants maintain a suitable ratio of sodium and potassium ions, store substances that can adjust osmotic pressure, and activate antioxidant enzymes and antioxidant substances to reduce the harm caused by high-salt environments, making them salt-resistant. Because poplars have strong salt resistance, they are selected as greening tree species and widely planted in some desert areas in my country that suffer from salt damage.

#4Are trees also divided into male and female?

Populus euphratica is a dioecious plant, with female and male flowers belonging to different individuals, and each individual has only one sex. Dioecious plants only account for about 6% of angiosperms. For example, ginkgo and willow species are dioecious.

The male plants of Populus euphratica bloom slightly earlier than the female plants, and the pollen produced by the male plants is spread to the female plants by wind. This method of pollination is called "wind pollination". Compared with asexual reproduction, species populations of sexual reproduction usually have higher genetic diversity. These genetic diversities are the driving force for the evolution of organisms to adapt to various environments. The reproductive strategy adopted by dioecious plants such as Populus euphratica is to complete cross-pollination and successfully carry out sexual reproduction, thereby obtaining higher genetic diversity. Some common bisexual flowers, in which both pistils and stamens exist in one flower, sometimes self-pollination occurs, thereby losing genetic diversity. Although plants use various reproductive strategies to avoid self-pollination, male and female plants on different individuals like Populus euphratica can carry out cross-pollination more directly and simply. Perhaps it is precisely because of the harsh desert environment that Populus euphratica has evolved this reproductive method.

#5 “Three Heroes of the Desert”

Tamarix tenuissima and Elaeagnus angustifolia are known as the "Three Heroes of the Desert" along with Populus euphratica. Tamarix tenuissima is a plant native to China. Its leaves look like those of conifers, and its flower diameter is only about 1 mm, which is very inconspicuous. But like Populus euphratica, it is very drought-resistant and salt-resistant. Even in the dry desert, Tamarix tenuissima can grow roots deep underground to absorb water.

Elaeagnus angustifolia also has lanceolate leaves and blooms fragrant silvery-white flowers in summer. Similarly, due to its drought resistance, Elaeagnus angustifolia is also used for soil and water conservation, sand control and forest protection.

Tamarix, Elaeagnus angustifolia and Populus euphratica belong to completely different orders in biological taxonomy, but they have evolved similar traits in adapting to the desert environment. This phenomenon of completely different organisms evolving similar traits because they have been in the same ecological niche for a long time is called convergent evolution in biology. In addition to Tamarix, Elaeagnus angustifolia and Populus euphratica, if you are willing to go into nature and carefully observe various organisms, you will find more phenomena of convergent evolution.

Source: Chongqing Science and Technology Museum

Author: Remineon, PhD student at the Center for Ecological Research, Kyoto University.

Review experts: Huang He, Li Chunli, Chen Tao, Xu Xiaoping

Disclaimer: Except for original content and special instructions, some pictures are from the Internet, non-commercial use, only as popular science materials, copyright belongs to the original author, if there is any infringement, please contact to delete. Author: Remineon, PhD student at the Ecological Research Center of Kyoto University.