Science | ‘Wood wide web’—the underground network of microbes that connects trees—mapped for first time
Trees, from the mighty redwoods to slender dogwoods, would be nothing without their microbial sidekicks. Millions of species of fungi and bacteria swap nutrients between soil and the roots of trees, forming a vast, interconnected web of organisms throughout the woods. Now, for the first time, scientists have mapped this “wood wide web” on a global scale, using a database of more than 28,000 tree species living in more than 70 countries.
“I haven’t seen anybody do anything like that before,” says Kathleen Treseder, an ecologist at the University of California, Irvine. “I wish I had thought of it.”
Before scientists could map the forest’s underground ecosystem, they needed to know something more basic: where trees live. Ecologist Thomas Crowther, now at ETH Zurich in Switzerland, gathered vast amounts of data on this starting in 2012, from government agencies and individual scientists who had identified trees and measured their sizes around the world. In 2015, he mapped trees’ global distribution and reported that Earth has about 3 trillion trees.
Inspired by that paper, Kabir Peay, a biologist at Stanford University in Palo Alto, California, emailed Crowther and suggested doing the same for the web of underground organisms that connects forest trees. Each tree in Crowther’s database is closely associated with certain types of microbes. For example, oak and pine tree roots are surrounded by ectomycorrhizal (EM) fungi that can build vast underground networks in their search for nutrients. Maple and cedar trees, by contrast, prefer arbuscular mycorrhizae (AM), which burrow directly into trees’ root cells but form smaller soil webs. Still other trees, mainly in the legume family (related to crop plants such as soybeans and peanuts), associate with bacteria that turn nitrogen from the atmosphere into usable plant food, a process known as “fixing” nitrogen.
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