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How plants compensate symbiotic microbes

Picture of plant roots and dirt.

Plants and microbes exchange resources in symbiotic relationships – but Stanford ecologists suggest that plants don’t quite compensate all their microbes equally.

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Jul 9 2021

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Research, Faculty

Combining economics, psychology and studies of fertilizer application, researchers find that plants nearly follow an “equal pay for equal work” rule when giving resources to partner microbes – except when those microbes underperform.

In a new study, published July 6 in the journal American Naturalist, the researchers investigated this question by analyzing data from several studies that detail how different plants “pay” their symbionts with carbon relative to the “work” those symbionts perform for the plants – in the form of supplying nutrients, like phosphorus and nitrogen. What they found was that plants don’t quite achieve “equal pay” because they tend not to penalize low-performing microbes as much as would be expected in a truly equal system. The researchers were able to come up with a simple mathematical equation to represent most of the plant-microbe exchanges they observed.

“It’s a square root relationship,” said Kabir Peay, who is an associate professor of biology in the School of Humanities and Sciences. “Meaning, if microbe B does one-quarter as much work as microbe A, it still gets 50 percent as many resources – the square root of one-quarter.”