A piece of ginkgo leaf you picked up may come from billions of years ago

As the temperature gradually drops, the ginkgo begins its most gorgeous chapter of the year, changing from emerald green to golden yellow, playing the changing of festivals in full dress. Many people know that ginkgo is ancient and precious, but they don't take it seriously because it can be seen everywhere. This unique tree species has witnessed the ancient history, and hundreds of millions of years of vicissitudes are imprinted in every fallen leaf you pick up.

01 From flourishing for a time to becoming independent, what has the lonely ginkgo tree experienced?

Ginkgo first appeared 270 million years ago and is widely distributed in every corner of the world. Fossil evidence has also found many of its relatives, which can be said to be the "dominant species" on Earth at that time. In the Jurassic period of the Mesozoic Era 170 million years ago, dinosaurs dominated the world and ginkgo plants also reached their peak.

Jurassic Ginkgo fossil. (Image source: Wikipedia)

About 140 million years ago, in the late Cretaceous period, the Earth's climate became dry and cold, and angiosperms appeared and began to devour the living space of gymnosperms, becoming the new favorite of nature. They also invented the "annual" life history, which was almost a cheating life history - only blooming and bearing fruit in the warm summer, and then spending the cold winter in the form of seeds. After that, it experienced several ice ages, and the glacial movement brought about drastic climate and geological changes. Ginkgo and other gymnosperms declined rapidly and suffered a crisis of almost extinction. The drop in temperature caused ginkgo to migrate south continuously, and in the last ice age, it was compressed to the southwest of today's China.

Why is China the only country in the world that may have natural ginkgo trees? This is mainly due to its special geographical environment. Compared with other continents, China's mountains and rivers are all east-west oriented, which is perpendicular to the direction of glacier movement from the north (the poles) to the south (the equator), which brings geographical obstacles to the promotion of glaciers. In addition, the Hengduan Mountains in the southwest are late, forming many folds. These mountains and rivers form a natural barrier that hinders glaciers, allowing many plants to hide in these valleys and folds and survive.

On a cliff at an altitude of about 1,040 meters in Zhejiang Tianmu Mountain National Nature Reserve, a thousand-year-old ginkgo tree is swaying its huge crown in the autumn wind.

Image source: Xinhua News Agency

At present, the wild ginkgo population is only distributed in Jinfo Mountain in Chongqing, Wuchuan in Guizhou, and Xing'an and Nanxiong in Guangxi. There are 254 ginkgo trees in the Tianmu Mountain Nature Reserve in Zhejiang. There has been controversy in the academic community as to whether they are wild populations. After research, scholars from Zhejiang University believe that the trees in Tianmu Mountain are most likely cultivated artificially.

02 After 200 million years of changes, it has its own powerful genetic code

As a rare tree species left over from the Mesozoic Era, the living ginkgo is the only surviving member of the ancient ginkgo family, and has faithfully preserved the appearance of its ancestors hundreds of millions of years ago. Finding wild ginkgo populations and deciphering the secret of their "longevity" has become a research direction that scientists have spared no effort to study.

In 2016, Chinese scientists decoded the genome of Ginkgo biloba and found that it had undergone two doubling events, which allowed it to increase its defense mechanisms and create opportunities for evolution. Gene doubling is common in organisms. It is like playing poker. When two decks of cards are put together, the probability of forming a "tractor" (or "straight flush") is much greater, and three decks are even easier. Doubling allows more and richer combinations of genes, and provides a material basis for genetic diversity (genetic diversity). This is reflected in individuals and populations, that is, more mutations and a higher probability of survival. If there is reproductive isolation or geographical isolation, more species can be formed.

In front of the Confucius Temple in Shou County, Anhui Province, a thousand-year-old ancient city, two towering ginkgo trees are falling, creating an intoxicating scene.

Image source: Xinhuanet

In addition, there are a lot of disease and pest resistance genes in the ginkgo genome. Most of these genes are repeated, which enables ginkgo to have the ability to defend against various diseases and pests.

In autumn, you may see dazzling golden ginkgo trees in parks, on both sides of roads, or even downstairs of your community. When you pick up a fan-shaped, slightly concave ginkgo leaf and count its lines and veins, you will find that it has hardly changed in shape compared with the ginkgo leaf fossils from hundreds of millions of years ago.

03 Protecting wild populations of species is a long and arduous task

We marvel at Ginkgo's powerful adaptability and resistance to adversity, which allow it to increase its defense mechanisms and create opportunities for evolution, spanning hundreds of millions of years to come to humans - but the only thing humans can do now is to "copy" their only bloodline through means such as introduction and cultivation.

At present, many ginkgo trees around the world, including those in China, are descendants or clones of the ginkgo trees in Tianmu Mountain, Zhejiang Province. This means that the ginkgo trees you see on the streets may all be sisters from the same mother. "Inbreeding" has led to a very narrow genetic diversity, which to a certain extent poses considerable risks. If they encounter pests or other diseases, they may be wiped out. Another worrying situation is that scientists have found in field monitoring that many wild ginkgo populations have not had seedlings or renewal for decades.

On October 20, photography enthusiasts took photos of ancient ginkgo trees in Tianhe Village, Jialing Town, Hui County, Longnan City, Gansu Province.

Image source: Xinhua News Agency

This is also the key factor that determines the "endangered" status of ginkgo - because of its small population, monotonous genetic diversity, and the fault phenomenon, it is understandable that wild ginkgo is listed as a national first-class protected tree species and is classified as an endangered species in the wild by the World Conservation Union (IUCN).

Today, most wild ginkgo populations are still not in nature reserves. The scope of human activities is constantly expanding and the frequency of human activities is increasing, which to a certain extent also threatens the living environment of ginkgo. Only by protecting the natural ginkgo resources can we truly protect this ancient species. I hope these "Gongsun trees" that have grown for thousands of years can have a longer future.

Planning: Yan Dong

Review expert: Director of the National Botanical Gardens Science Museum, Dr. Wang Kang

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.