The symbiosis of plants and fungi is based on the laws of economics, and the exchange of valuable substances between them takes place at a "floating rate".
It's no secret that most sushi plants live in close, often symbiotic relationships with mushrooms. This union is more than 400 million years old. Their roots and mycelium are closely intertwined and even penetrate each other. By supplying partners with organic substances of their own production, plants receive valuable and often quite scarce minerals in the soil, such as phosphorus, from fungi.
This exchange is not nearly as simple as it might seem at first glance. The authors of a new article, published in the journal Current Biology, showed that fungi can transport minerals in areas where they are especially lacking in order to "bargain" from a partner plant more favorable terms of exchange. Scientists have discussed the existence of "biological markets" before, in which the movement of resources occurs largely according to the laws of economics. However, now it was possible to observe their work in dynamics.
Scientists from the Free University of Amsterdam investigated the movement of phosphorus in arbuscular mycorrhiza, the fungi of which penetrate deep into the intercellular space of a partner plant, and even inside its cells. This structure is formed by the fungi Rhizophagus irregularis in the roots of carrots - their relationship was examined in the laboratory. To do this, the Petri dish with soil was divided into three parts, allowing the mushroom to stretch from the central part with the plant to both adjacent ones containing phosphorus with labels of different colors.
The authors varied the phosphorus content in different compartments and tracked how this would affect the "behavior" of the fungus. It was found that if you divide a mineral into highly unequal parts and place 90 percent of its mass in one compartment and only 10 percent in another, then the mushroom not only transfers it from a “rich” site to a “scarce” one, but also controls this transport. Noticing a lack of a valuable mineral, the plant enhances the return of organic matter, stimulating the fungus to grow more actively and filter out phosphorus.
This is what his “trading partner” uses: by precisely controlling the deficit, he makes the roots pay the maximum. According to the authors, the mushroom achieves a very favorable "exchange rate" and in scarce conditions can receive for the same amount of phosphorus in 3, 8 times more organic matter than in conditions of mineral abundance.