To collect data the team planted 500 species of grass taken from six continents. A majority of seeds were provided by the United States Department of Agriculture, while 52 species were collected from the Konza Prairie in the Flint Hills of Kansas. Grasses were grown on campus in a walk-in growth chamber with high intensity lighting that simulated sunny weather. After six weeks, researchers stopped watering the grass samples and observed at what point each grass stopped being able to take up water.
"In the end they all succumbed to drought," Craine said. "But that was our goal: to stress them all enough to know at what point they give in. What we saw was that some of grass species were about as tough as lettuce, meaning that after a day or two without water they would start to wilt and curl up. Others, however, were able to go for a week or two without water."
When comparing the drought resistance across the sampled species, the team found that drought-resistant grasses are well distributed across the world. As a result, grasslands are more likely to tolerate the increased periods and intensity of drought that are predicted with climate change in the future, Craine said.
"If we still have grasslands that are diverse, the grasslands are going to continue to function relatively well and not change too much," Craine said. "But when we replace our prairies with ones that just have a few species in it, then it's less likely that grasslands will be able to function normally in the future. That affects the animals and other things that depend on grasslands, making it more likely that the whole ecosystem collapses."
Additionally, researchers developed a drought index for the tested species based on the data. The index details each species' tolerance to drought and can help ecologists understand why grasslands around the world are composed of their species. More than 11,000 species of grass exist on Earth.