Forest Fungi May be Taking Advantage of Trees: Symbiotic Relationship Theory Questioned

The long-held theory that there exists a symbiotic relationship between trees and the fungi that grow on their roots may not be as mutually beneficial as once believed. Scientists have discovered that the fungi may be taking more than they're giving back.

Fungi, or micorrhizae, can be found on tree roots the world over. Previously, scientists believed that the fungi worked with the trees in a relationship that was beneficial for both parties, providing needed nutrients to both fungi and trees. These fungi include edible mushrooms and are particularly common in boreal forests with scarce nutrients.

Yet recent experiments reveal that the relationship may not quite be as beneficial toward the trees. Scientists have found that rather than alleviating nutrient limitations in soil, the root fungi maintain that limitation by transferring less nitrogen to the trees when nutrients are scarce than when they are abundant in the soil.

"The new theory pictures a more business-like relationship among multiple buyers and sellers connected in a network," said Oskar Franklin, one of the researchers, in a news release. "Having multiple symbiotic trading-partners generates competition among both the fungi and the plants, where each individual trades carbon for nutrients or vice versa to maximize profits, not unlike a capitalistic market economy. Although doing business with fungi is a good deal from each tree's own point of view, it traps the whole forest in nutrient limitation."

The findings reveal a little bit more about boreal forest nutrient cycles. This, in particular, is important for modeling climate change; it influences how much carbon dioxide these regions can absorb, as well as how they are influenced by the increasing concentrations of greenhouse gases in the atmosphere.

The findings are published in the journal New Phytologist.