Redesigning Roots to Help Crop Plants Survive Hard Times

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Among the likely effects of climate change, perhaps the one with the most potential to devastate human and natural communities is drought—not just a dry season or two, but a prolonged lack of rainfall over vast areas, lasting years or even decades.

Drought is already making itself felt in Europe, Australia, and the United States. Much of the American West and Southwest is several years into a deep drought, and by 2060 the Midwest is expected to experience conditions that rival the Dust Bowl. But it is developing countries that are suffering the most, with drought so severe that it has disrupted societies, spawned or worsened civil strife, and led to the forced migration of millions of people no longer able to find water or grow food in their homelands.

Penn State crop scientist Jonathan Lynch has spent his career exploring how to make crop plants better able to grow in dry, low-nutrient soils, as a way to fight the chronic food shortages that plague much of the world. He has never considered himself a climate-change scientist, but in recent years his work has taken on new urgency due to the global changes we’re seeing.

“If you’re a small farmer in Rwanda and you only have half an acre of land to feed your family, and your crops are only yielding ten percent of what they should because of drought and poor soil, that’s a serious problem,” says Lynch. “Right now there are about 850 million chronically hungry people on Earth. 850 million! Chronic malnutrition is the leading cause of childhood deaths in the Third World. It’s already a massive problem, and climate change has barely begun to sink its teeth into these agricultural systems yet.

“An important way to address this challenge is to develop plants that can tolerate these stresses.”

Where the good things are

Plant breeders worldwide have been trying to do that by improving the efficiency of physiological processes such as photosynthesis.

Those are good improvements for plants that are well-watered and in nutrient-rich soil, says plant biologist Kathleen Brown, but in poor soils or drought conditions, having souped-up physiology won’t help. What willhelp is enabling the roots to reach more sources of water and nutrients in soils that have little of either.

So Brown, Lynch, and their students at the Roots Lab at Penn State study how root structure can improve the ability of key crop plants—primarily corn (Zea mays) and the common bean (Phaseolus vulgaris)— to produce good yields under stressful conditions.

That may sound simple, but it gets complicated in a hurry. For one thing, most of the root features known to enhance resilience to poor conditions are not controlled by a single gene and therefore are hard to select for. A plant may have to have a whole suite of genetic variations to produce the kinds of roots that will enable it to grow deep enough to access water deep below the surface.

“If Nature could improve drought tolerance in plants by changing one gene, that would have been figured out, like, 300 million years ago,” says Lynch. “It’s more complex than that.”

Another challenge is that not everything the plant needs can be found with the same root characteristics. Fertilizers and natural decomposition of the previous year’s crop residue deliver nitrogen and phosphorus to the soil surface. Nitrogen almost immediately moves down, riding along with water as it seeps deep into the soil. Phosphorus, though, stays near the surface.

“It stays stuck to the soil particles, so it can’t move freely,” says Brown. “If the root isn’t extremely close, microscopically close, to phosphorus, it doesn’t get it. If the plant has used up all the phosphorus around it, it has to keep growing and exploring new soil to keep getting phosphorus.”

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