The coexistence between trees and fungi is supposed to be very peaceful. Fungi grow on the roots of a plant, providing nitrogen to it in exchange for carbon, in a nearly perfect symbiotic exchange. Each individual fungus, traditional wisdom holds, works in tune with the root it grows in tandem with. But a new study presents a different model: The supposed buddies are actually acting like buyers and sellers in a capitalist market.
Led by IIASA Ecosystems Services and Management researcher Oskar Franklin, the Swedish study (paywall) started with a surprising observation. Root fungi were actually working to maintain nitrogen scarcity in the forest. When less nitrogen was available in the soil, fungi gave up less nitrogen to the trees. But when nitrogen was abundant, they built up their stores like speculators cornering the market in a commodity, effectively forcing the trees to get their nitrogen from the fungi no matter what.
“The new theory pictures a more business-like relationship among multiple buyers and sellers connected in a network,” Franklin said in a press release. Instead of being a cooperative trade of carbon and nitrogen between organisms, trees are forced to export large amounts of carbon in order to unlock nitrogen stores from the fungi.
What’s more, fungi can play clients off against one another. When different plants get their nitrogen from one fungal partner, the study states, the allocation of nitrogen to each of those plants isn’t dictated by need or fairness. Instead, the fungus seeks the best possible return on investment. “Having multiple symbiotic trading-partners generates competition among both the fungi and the plants,” Franklin said, “where each individual trades carbon for nutrients or vice versa to maximize profits, not unlike a capitalistic market economy.”
This gives trees an incentive to offer up more carbon than their neighbors. The trade isn’t always beneficial for both parties. In fact, plants and fungi could get locked-in to a mutual trade agreement that isn’t optimal for either party. The authors compare this to carbon lock-in, where industries are stuck in a fossil fuel-based system, even when other energy options are superior.
And while trees may thrive from this exchange, the fact that the fungi hoard nitrogen ”traps the whole forest in nutrient limitation,” Franklin said. In general, the authors stated, how fungi collect and distribute resources is largely unexplored. But this should change. If we don’t understand the market structure of the fungi and trees, Franklin said, won’t really know how forests will react to the changes in carbon availability that climate change could bring about.