CREVE COEUR — One billion hectares of land, an area about the size of the U.S., are affected by salty soil, according to the Food and Agricultural Organization of the United Nations. The majority of crops are sensitive to salt, resulting in production declines that cost at least $27 billion each year, says a study published by the United Nations.
“And it’s continually getting worse,” said David Goad, a doctoral candidate at Washington University.
As agricultural fields are irrigated, water evaporates but salt doesn’t, producing saltier soils each year. These issues are particularly problematic in dry, hot climates, including the western U.S.
In Arizona, irrigation practices caused high levels of salt to build up in the soil, leading to declines in corn production.
“The soil became concrete and corn stalks were the size of pencils. They just didn’t grow,” said William Gene Stevens, a professor of plant sciences at the University of Missouri.
Hard-packed soil prevents water and plant roots from penetrating the ground, reducing crop yields, Stevens said. At the same time, crop production must increase by 70% between 2005 and 2050 to feed a growing human population, according to the Economics of Land Degradation Initiative.
Although salty soil is less problematic for Missouri farmers, researchers at Washington University and the Donald Danforth Plant Science Center in Creve Coeur are addressing global declines in crop production by figuring out how to increase salt tolerance in plants.
Tolerant turf grass
Plants deal with salty environments in several ways. Some species refuse to let salt into their tissues, some excrete it, and others “just put up with it,” said Elizabeth Kellogg, distinguished professor at the Danforth Center.
“These interesting processes are under genetic control,” said Pengyin Chen, professor and soybean breeder at the University of Missouri. Identifying genes that allow plants to deal with high levels of salt can give breeders a better idea of what to target when trying to improve tolerance in crops, he said.
A type of grass, seashore paspalum, is particularly good at putting up with salty conditions. It grows along the coast of the southern U.S. and is a relative of important crops, including corn, rice and wheat.
It’s also used on golf courses because it grows quickly, permits short cuts and performs well in dune and coastal environments. Because of this, Goad, Kellogg and their collaborators received funding from the United States Golf Association for their research.
A salty experiment
To determine how seashore paspalum tolerates salt, the scientists set up an experiment in which they exposed plants to different levels of salt and characterized changes in plant genes, growth and appearance.
Using a growth room at the Danforth Center, the researchers manipulated salt exposure while controlling for temperature, humidity and other factors that affect plant performance.
Three salt treatments were used in the experiment: no salt, a little bit of salt each week, or a lot of salt at once. These treatments reflect different scenarios that plants may be exposed to in agricultural fields, golf courses and natural environments.
In the growth room, a conveyor belt moved potted plants to watering spouts that regulate water and salt exposure. It also moved plants through a photo booth that took color and infrared pictures every day of every plant.
About a week into the experiment, the researchers received an emergency alert. The grass had grown down into the conveyor belt and jammed the system.
“We were panicking,” Goad said.
Goad ended up sitting in the room for weeks, waiting for plants to emerge from the photo booth and then using bent paper clips to tie up the plant tissue.
With nearly 1,200 plants in the experiment, Goad said he went through thousands of paper clips.
“There’s a reason they call it an experiment,” said Kellogg.
Now that the experiment is over, the scientists have thousands of pictures to process.
They will use these pictures to characterize changes in plant biomass and color under the different salt treatments. Biomass estimates plant yield, whereas red or yellow-colored plants show signs of stress. The researchers also extracted DNA to identify genes that respond to salt exposure.
Although they don’t have any conclusive results yet, they did notice an immense diversity in salt tolerance among their plants.
“Some of them croak and some of them grow really well. A lot actually do better in saltwater than they do in freshwater,” Kellogg said.
Identifying which plants are highly salt tolerant and the genes underlying this trait is critical for informing breeding efforts, which “could save millions of people from starving,” Goad said.