Trees, from the mighty deciduous trees to the narrow dogwoods, would be nothing but their microbial side peaks. Millions of fungal species and bacteria change nutrients between soil and tree roots, forming a large, interconnected tissue of organisms throughout the forest. For the first time, researchers have mapped this "wood wide web" on a global level, with a database of over 28,000 species of trees that live in more than 70 countries.
"I haven't seen anyone doing anything like it before," says Kathleen Treseder, an ecologist at the University of California, Irvine. "I wish I had thought about it."
Before Scientists Could Identify Forest's Underground Ecosystems , they needed to know something more basic: where trees live Ecologist Thomas Crowther, now at ETH Zurich in Switzerland, collected large amounts of data on this from 2012, from authorities and individual researchers who had identified trees and measured their sizes around In 2015, he mapped the tree's global distribution and reported that the Earth has about 3 trillion trees.
Inspired by this paper, Kabir Peay, a biologist at Stanford University in Palo Alto, California, emailed Crowther and suggested that he do the same for Webb of subterranean organisms connecting forest trees.Each tree in Crowther's database is closely associated with certain types of microbes, eg oak and pine reds surrounded by ectomycorrhizal (EM) fungi that can build large underground nets in their nutrient search. Maple and cedar trees, on the other hand, prefer arbuscular mycorrhizae (AM), which are housed directly in the root cells of the trees but form smaller soil pathways. Still other trees, mainly in the bone family (related to crops such as soybeans and peanuts), associate with bacteria that turn nitrogen from the atmosphere into useful plant food, a process called "fixation" nitrogen.
The researchers wrote a computer algorithm to search for correlations between EM, AM and nitrogen fixer related trees in Crowther's database and local environmental factors such as temperature, precipitation, soil chemistry and topography. They then used the correlations found by the algorithm to fill out the global map and predict the types of fungi that would live in places where they did not have data, which included much of Africa and Asia.
Local climate sets the stage for the wooden board, reports the team today in Nature . In cool temperate and boreal forests, where wood and organic matter break down slowly, network-building regulates EM fungi. About four in five trees in these areas associate with these fungi, the authors found, suggesting that the webs found in local studies really penetrate the lands of North America, Europe and Asia.
However, in the warmer tropics where wood and organic matter decay rapidly, AM fungi dominate. These fungi form smaller paths and make less intertree bytes, which means that the tropical wood width is probably more localized. About 90% of all tree species associate with AM fungi; the vast majority are clusters in the hyperdiverse tropics. Nitrogen fixers were most abundant in hot, dry places such as the US southwestern east.
Charlie Koven, a Earth Systems scientist at the Lawrence Berkeley National Laboratory in California, welcomes what he says is the first global forest microbook. But he wonders if the authors missed some important factors that also shape the underground world. Difficult processes such as nutrient and gas loss from the soil can affect where different microbes live. If so, the study's predictions may be less accurate, he says.
Despite such uncertainties, Treseder says having the first hard numbers that tree-related microbes live there will be "very useful". The result can, for example, help researchers build better computer models to predict how much coal forests will squirrel away and how much they will vomit into the atmosphere as the climate warms, she says.
However, Crowther is ready to make a prediction now. His results indicate that about 10% of EM-associated trees can be replaced by AM-associated trees as the soil grows. Microbes in forests dominated by AM fungi faster through carbon-containing organic matter faster, allowing them to rapidly release highly heat-generating carbon dioxide, potentially accelerating a climate change process that is already happening at a frightening pace.
This argument is "A bit more modest" to Treseder. She says researchers still perceive how different soil fungi interact with coal. But she adds, "I'm willing to be convinced."