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A mushroom known as Dermocybe is part of the vast underground network of wood that sews the forests of California.
Kabir Gabriel Peay
By Gabriel Popkin
Trees, from redwoods to thin dogwoods, would be nothing without their microbial mites. Millions of species of fungi and bacteria exchange nutrients between the soil and tree roots, thus forming an extensive network of interconnected organisms in the woods. Today, for the first time, scientists have mapped this "vast wooded network" on a global scale, using a database of more than 28,000 species. Trees living in more than 70 countries.
"I had never seen anyone do that," says Kathleen Treseder, an ecologist at the University of California at Irvine. "I would have liked to think about it."
Before scientists could map the underground ecosystem of the forest, they needed to know something more fundamental: the place of residence of trees. Ecologist Thomas Crowther, today at ETH Zurich in Switzerland, collected a lot of data on this from 2012 from government agencies and scientists who had identified trees. and measured their size in the world. In 2015, he mapped the global distribution of trees and reported that the Earth had about 3 trillion trees.
Inspired by this paper, Kabir Peay, a biologist at Stanford University in Palo Alto, Calif., Sent an email to Crowther to suggest he do the same for the network of underground organisms that connect the trees. of the forest. Each tree in Crowther's database is closely associated with certain types of microbes. For example, the roots of oaks and pines are surrounded by ectomycorrhizal (EM) fungi capable of forming vast underground networks in their search for nutrients. Maple and cedar, on the other hand, prefer arbuscular mycorrhizae (AM), which burrow directly into tree root cells but form smaller soil systems. Other trees, mainly from the legume family (related to crop plants such as soybean and peanut), associate with bacteria that transform the nitrogen of the plant. atmosphere into a useable plant food, a process called "nitrogen fixation".
Researchers have written a computer algorithm to look for correlations between trees associated with the EM fixer, AM and nitrogen fixator in the Crowther database, and local environmental factors such as temperature, precipitation, soil chemistry, and topography. They then used the correlations found by the algorithm to fill the global map and predict which types of fungi would live in places where they did not have data, including Africa and Asia.
The local climate paves the way for wood, announced the team today at Nature. In cool temperate forests and boreal forests, where wood and organic matter decompose slowly, EM fungi establishing a network reign in a network. According to the authors, about four trees in these five regions are associated with these fungi, suggesting that the networks found in local studies actually permeate the soils of North America, Europe, and Asia. .
On the other hand, in the warmer tropical regions where wood and organic matter decompose rapidly, AM mushrooms dominate. These fungi form smaller networks and perform less inter-tree permutation, which means that the large tropical timber network is probably more localized. About 90% of all tree species are associated with AM fungi; the vast majority is grouped in the tropics hyperdiverses. Nitrogen fixers were more abundant in hot, dry places such as the desert in the southwestern United States.
Charlie Koven, Earth System Scientist at the Lawrence Berkeley National Laboratory in California, applauds what he says is the first global map of forest microbes. But he wonders if the authors have forgotten some important factors that are also shaping the underworld. Hard-to-measure processes, such as the loss of nutrients and soil gases, could affect areas where different microbes live; if so, the study's predictions may be less accurate, he says.
Despite these uncertainties, having the first precise figures for which tree-associated microbes live will be very useful, says Treseder. The results could, for example, help researchers develop better computer models to predict the amount of carbon forests that escape and the amount of forests released into the atmosphere when the climate warms, she says.
Crowther, however, is ready to make a prediction now. His results suggest that as the planet warms up, about 10% of the trees associated with the SE could be replaced by trees associated with AD. In AM-dominated forests, microbes filter carbon-containing organic matter faster, allowing them to release a lot of carbon dioxide that traps heat, potentially accelerating the climate change process that is already occurring. at a frightening pace.
This argument is "a bit weaker" for Treseder. She added that scientists still do not know how different soil fungi interact with carbon. But, she adds, "I am ready to be convinced".
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