Agriculture and Evolution – Wheat Absorbs Phosphorus From Desert Dust Science & Technology

W.WARMTH WAS was one of the first domesticated plants and is now the most widespread culture in the world. It therefore sounds unlikely that much remains to be learned about what will make it thrive. But around 12,000 years after human-wheat relationships began, a wheat plant was caught that did something unexpected. It used a dose of much-needed phosphorus when its leaves were coated with desert dust.

The plant (or rather plants) in question was in the care of Avner Gross of Ben Gurion University in the Negev in Israel. As Dr. Gross told this year’s American Geophysical Union meeting, held online in the first half of December, his study was stimulated by hiking near Neve Shalom, his home village in the Judean Hills. He often noticed plant leaves on them that were completely covered with dust and had been carried there by sandstorms from the Sahara.

It occurred to him that this dust might not be the light-blocking nuisance he had at first sight. On the contrary, it could be beneficial because of the growth-promoting elements like phosphorus it contained. Until then, botanists had assumed that phosphorus in dust that lands on a plant was of little value because it was trapped in an insoluble mineral called apatite. This makes it unavailable for absorption. Dr. Gross argued, however, that plants that developed near deserts, the source of almost all naturally occurring dust in the atmosphere, may have found a way to use it.

He and two colleagues, Sudeep Tiwari, also at Ben Gurion, and Ran Erel from the Gilat Research Center, therefore experimented with two species, wheat and chickpeas (the 17th most commonly planted crop in the world), both of which originally came from the Middle East . As a control, they also grew corn, a plant native to America that developed in a far less dusty environment.

After establishing themselves as seedlings, they initially starved for phosphorus until signs of deficiency such as yellow leaves appeared. They then scattered desert dust on the leaves of half of the specimens of each species while taking steps to prevent any of it from reaching the ground. After that, the wheat and chickpea plants recovered, although the dust-dosed corn continued to suffer from a lack of phosphorus, and grew more than twice the size of their undamped laboratory mates. In addition, these species were clearly ready for the dust to arrive. As soon as a phosphorous deficiency was announced, two things happened. Their leaves became hairier and could therefore better collect dust. And these leaves also began to secrete acidic fluids that could dissolve any incoming apatite and aid the absorption of phosphorus.

The fact that plants can absorb phosphorus through their leaves is nothing new for farmers – as this was discovered in the 1950s. So far, however, the practical consequence of this knowledge has been that plants are sprayed with liquid fertilizer, which in turn comes from apatite-containing rocks that have been treated with acid. Pollination of leaves could, according to Dr. Big, be an alternative and more efficient way to provide desert-derived plant species with the phosphorus they need. And maybe not just this. His next plan is to study avocado and cocoa trees, which have developed in tropical regions of America and regularly receive a helpful transatlantic dose of Saharan dust carried west by the trade winds. It will be interesting to see if they grew the same tricks as wheat and chickpeas.

This article appeared in the Science & Technology section of the print edition under the heading “Good Catch”.

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