Fungi and plants have been thriving for hundreds of millions of years through cooperation, each providing the other with nutrients they are better at acquiring. Botanists have been astonished to discover how sophisticated these arrangements can be, with fungi moving their most precious element to where demand is greatest – and they can therefore attract the highest price.
Many people in history have become rich through realizing some item was abundant in one place but scarce in another. By moving quantities to where the demand was greatest, often in the face of considerable dangers, they attracted a price they could not have won back home. No one realized, however, that brainless fungi hit on the same idea long before us.
Certain fungi are much better at extracting phosphorus from the soil than plants. As one of the five elements almost all life depends on, this puts them in a powerful position, one they exploit by demanding carbon in return. However, phosphorus isn't evenly distributed. Professor Toby Kiers of Vrije Universiteit, the Netherlands, wanted to see how the fungi responded to large variations in supply.
Kiers and co-authors created fluorescent nanoparticles of varying colors, allowing them to track phosphorus atoms' movement through networks of mycorrhizal fungi distributed among the roots of carrots. They manipulated phosphorus concentrations within their test area, creating areas of abundance and scarcity. Their observations are described in Current Biology.
“The fungus physically moves resources to the poor patches where demand for the resources from plant partners is highest,” said Kiers in an emailed statement. This probably plays a big part in maximizing the Earth's productivity – without it, some places would have more phosphorus than they can use, while others might struggle to support much life at all.
However, the fungi are not motivated by a sense of altruism. Plants give them carbon in return for the phosphorus they provide, and while Kiers ran into trouble measuring this, she concluded that the fungus received a better “exchange rate” of carbon for each phosphorus atom provided to places where the resource was scarce.
Fungi will sometimes store phosphorus, rather than use it themselves or exchange it with plants immediately. Those exposed to more even distributions of resources hoarded more phosphorus, even though the total supply was the same, than those encountering greater inequality. Presumably, this is because prices were moderate, with a high chance patches of local depletion would subsequently raise them.
These sorts of mycorrhizal networks can stretch for meters, and encounter similar natural differences in resource availability to the ones artificially created in the study.
Puzzlingly, even while most phosphorus was moved from rich to poor areas, some went the other way, a fungal equivalent of taking coals to Newcastle.