Missouri soybean growers know the drill. One day it’s too wet to plant, and the next it’s too hot for pods to set. But what if soybeans had a built-in way to beat the heat? University of Missouri researchers say they do — and this natural cooling trick could help farmers protect yields in a changing climate.
Ron Mittler, Curators’ Distinguished Professor of Plant Science and Technology with the University of Missouri’s College of Agriculture, Food and Natural Resources, has spent years studying how plants handle stress. His latest discovery: soybeans use differential transpiration, a process where the plant keeps cooling pores (stomata) open on flowers and pods but closes them on the leaves.
“It’s like sweating, but smarter,” Mittler says. “If the plant opened all its stomata, it would lose too much water. So instead, it closes the ones on the leaves and keeps the ones on the flowers and pods open. That lets it cool the parts that really matter — the parts that make seeds.”
The result? A water-saving strategy that helps soybeans survive during those critical reproductive stages, flowering and pod fill, even when water is limited.
What Farmers Can Do Now
Mittler says differential transpiration doesn’t work without at least a little water.
“Soybeans are tough plants,” he says. “If they have enough water, they can handle heat. But if they face drought or flooding, especially during reproduction or seed fill, and there’s a big heat wave, it becomes a real issue.”
That’s why he urges farmers to consider water management as part of their strategy.
“What they really need to care about is the water availability of soybean plants during really big heat waves,” he says. “If the plant cannot cool the reproductive tissues, even with a little bit of water, then we start seeing problems.”
Planting date matters too — although it’s not always predictable.
“Timing is key,” Mittler says. “Can I manage when I plant to counter the heat waves? That’s the question. It’s not always ideal, but it helps.”
New Varieties on the Horizon
Right now, the team is testing different soybean lines to see if some are naturally better at differential transpiration.
“We found that already two genotypes do this, but they’re not elite cultivars,” Mittler says. “Our next challenge is to identify lines that do it better and come up with recommendations.”
And yes, Missouri farmers are part of the plan.
“We’ll look at Missouri-adapted varieties,” he says. “They change every year, but we can still follow up and test under real field conditions.”
Even better, this trait could eventually be bred into commercial varieties — or added through gene editing.
“If a big company takes it on and adds differential transpiration to their screening platforms, it could move pretty fast,” Mittler says. “I hope within five years, we’ll have something useful.”
Real-World Science, Real-World Impact
Mittler doesn’t farm, but he understands the stakes.
“It feels really good to have discovered something that matters,” he says. “When I spoke at crop conferences and people told me this was exciting — that’s when I knew this could make a real difference.”
And when it comes to explaining the science? He keeps it relatable.
“The best comparison is sweating,” he says. “If you don’t have enough water, you can’t sweat. Same with soybeans — they need at least a little water to use this cooling strategy.”
As Missouri faces hotter, drier summers, this research offers hope that soybeans — and the farmers who grow them — can stay one step ahead.
Did you know?
A soybean plant can save up to 95% of its water during extreme stress by shutting down cooling in its leaves and focusing only on its reproductive tissues. That’s like your body sweating only through your forehead to save fluids — and still beating the heat.
It’s not magic — it’s plant physiology.
Soybeans cool themselves by releasing water through tiny pores called stomata. But when water is scarce, they don’t treat all tissues equally. Instead, they close the stomata on their leaves and keep them open on their flowers and pods — protecting reproduction while saving water. Researchers call this strategy differential transpiration, and it could be a game-changer for drought and heat resilience.