"I'll Trade Two Phosphorus for Three Carbs"

March 10, 2012 06:17 AM

It’s a complex world out there under your crop stubble, and research shows it is also a vast underground trading market during the growing season. Plants and some types of fungi in the soil have an arrangement whereby the plants supply food in the form of carbohydrates to the fungi and the fungi supply phosphorus (P) to the plants—but only if both parties feel they’re getting a fair deal.

"Phosphorus is required for the elongation and division of plant cells and for the transfer of starches and especially sugars," says Farm Journal Field Agronomist Ken Ferrie. "If a corn plant can’t transfer sugars, which are produced in the upper part of the plant, to other areas, the plant stops growing and turns purple."

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Some soilborne fungi allow plants to recycle phosphate without directly getting it from the soil.

To understand more about P uptake by plants, an international team of researchers observed interactions between three types of soilborne fungus and a legume related to alfalfa. They used radioactive tags to track the carbon produced by the plant and the plant-friendly, inorganic form of P that is produced by the fungi’s metabolic process.

Observing the relationship between the fungi and the legume, they found more carbon was given to a fungus if it was being "cooperative" by giving more P to the plant.

"This is one of the first recorded examples of a biological market in which both partners reward fair trading rather than one partner having the advantage," says Stuart West of Oxford University’s Department of Zoology.

"We think that this sort of biological market, reminiscent of a market economy, has arisen because there are so many individuals either partner could trade with," West says. "Rather like with human traders, if they are given a chance, both plants and fungi will go elsewhere to get a better deal."

While Ferrie says the biggest source of P is dead microbes, which include fungi, understanding the plant-microbe relationship is critical when looking at microbe activity and residue management, which determines fertilizer timing and amount.

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