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Federal Research Center 
"Krasnoyarsk Science Center of the Siberian
Branch of the Russian Academy of Sciences"

 Федеральный исследовательский центр «Красноярский научный центр Сибирского отделения Российской академии наук»

Federal Research Center 
"Krasnoyarsk Science Center of the Siberian
Branch of the Russian Academy of Sciences"

Scientists have created a global map of the tree/microbial/fungal network

3 June 2019 г.

Ученые составили всемирную карту древесно-микробно-грибной сети
An international team of ecologists and biologists has constructed a map revealing the symbiotic relationships of trees with soil microbes and fungi inhabiting 70 countries of the world. In total, the map includes information about more than a million trees. During the work, the scientists found that the spread of symbiosis of different types depends mainly on climate.

Under each forest there is  a kind of internet - a complex underground network of interconnected roots, fungi and bacteria. These organisms are often associated with each other through symbiosis — for example, fungi and bacteria help plants absorb useful organic and inorganic substances from the soil, and also bind carbon dioxide and nitrogen from the atmosphere.

Symbionts can be of several different types. Some of them, such as arbuscular mycorrhizal fungi, can penetrate the filaments of the mycelium, between plant cells or even into the cells themselves. At the same time, the plant roots hardly change, and only using a microscope can such symbionts be detected. Others, such as ectomycorrhiza, wrap the root with a dense net of their threads and can penetrate into the interface space rather than into the cells. There are also those which come into symbiosis with plants of a single family. Finally, still another type of symbionts, nitrogen-fixing bacteria, can capture nitrogen from the atmosphere and enrich the soil with it.

"There are many different symbiotic types, and we have shown that they follow strict rules. Our models predict significant changes in the symbiotic state of the world's forests - changes which may affect the climate in which your grandchildren will live," says the co-author of the article, Nadezhda Chebakova, Doctor of Biological Sciences, senior research associate at the V.N. Sukachev Institute of Forest SB RAS.

Previously, scientists already tried to suggest why one or another type of symbiosis predominates in a particular area. However, due to the lack of geographic data and without climatic factors being considered, their results are incomplete. The authors of the new study took all this into account.

In this regard, the team of scientists used the database of the project “Global Forest Observations”, which is involved in forest monitoring. It contains information on more than a million families of trees (more than 1,100,000 specimens, 28,000 species) from more than 70 countries of the world. Using a machine learning algorithm, scientists determined how different factors related to climate, soil chemistry, vegetation, and topography affect the number of each type of symbiont of each tree. In addition, the researchers also took into account the rate of decomposition of organic residues, depending on temperature and precipitation.

Scientists have mapped all these calculations, having obtained a picture of the global distribution of different types of symbiosis. Thus, scientists have visualized the global tree/microbial/fungal network.

The scientists revealed that trees that enter into symbiosis with ectomycorrhiza constitute only 2% of plant species, but, in numbers, it is 60% of all trees on the Earth. Ectomycorrhizal symbiosis is most often found in forests, wh ere the seasonally cold and dry climate interferes with decomposition. In addition, this type of symbiosis is predominant in high latitudes and in the areas.

On the contrary, arbuscular-mycorrhizal symbiosis is more widely spread in warm seasonal tropical forests. The boundary between this and the ectomycorrhizal type is sufficiently sharp; it depends on climatic zones, which also affect the types of decomposition.

The third type of symbionts, whose spreading was investigated by scientists, includes nitrogen-fixing bacteria. Unlike mycorrhizal fungi, they are not very sensitive to climate. These bacteria are most commonly found in arid regions with alkaline soil and high maximum annual temperatures.

The model obtained by scientists can now be used to analyze changes in global ecosystems. With its help, scientists will be able to understand how biogeochemical processes and climate interact.