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For Rice, Warmer Earth Brings Uncertain Future, UF Research Shows

Aaron Hoover

Hartwell Allen, (352) 392-8194
Kenneth Boote, 392-1811, ext. 231

GAINESVILLE, Fla.—Temperature increases anticipated as part of global warming appear to significantly reduce rice yields, a finding that has worrisome implications for the third of the world’s population that relies on rice as a primary staple.

University of Florida researchers have found above-average temperatures interfere with the life cycle and pollination process in rice plants. Modest temperature increases predicted by some climate change scenarios would reduce rice yields by 20 to 40 percent by 2100, while the most severe predicted temperature increases could force yields to zero.

The findings are among the latest to come out of the Carbon Dioxide and Climate Change Project at UF’s Institute of Food and Agricultural Sciences. Researchers involved in the project, managed in cooperation with the U.S. Department of Agriculture and funded by UF and several federal agencies, have discovered that warmer temperatures also lead to declines in yields of peanuts, soybeans and dry beans such as kidney beans.

“I think we’ve demonstrated clearly that seed producing plants are much more at risk from rising temperatures than are vegetative plants such as forage plants,” said Hartwell Allen, a USDA and UF crop and climate research scientist.

The latest experiment tested a variety of rice commonly grown in the Philippines, a tropical climate, and a variety grown in California, a temperate climate.

Researchers planted the rice in chambers that were maintained at different temperature cycles simulating day and nighttime fluctuations. They found the plants steadily produced less rice as temperature diurnal cycles exceeded 73-91 degrees Fahrenheit for the tropical variety and 68-86 degrees for the temperate one. Those optimum cycles already fall a bit below current temperatures where the rice is cultivated, said Kenneth Boote, a UF agronomy professor involved in the project.

“We’re on the downhill side for rice and soybeans now, so if there’s any temperature increase the yield will slide down,” Boote said.

Although the plants continued to flourish, they produced nearly no rice at the highest temperature cycle of 86 to 104 degrees, the study found.

“We were hoping to find some evidence that the tropical cultivar could sustain reproductive ability at the highest temperature, but it didn’t, which is bad news,” said Alison Snyder, a UF graduate student who worked on the study for her masters thesis.

Indeed, the temperature cycles used in the experiment closely track scientists’ more modest predictions for global warming. An average global increase of 5.4 degrees by 2100, considered probable by many scientists, would produce temperatures in the experiment’s higher range, Snyder said. And that prediction is about half the 10 degree increase viewed as the most dire possibility.

Rice comprises 40 percent of the daily calories of 2 billion people, many of whom live in Third World tropical regions, Snyder said. If rice production ceased or moved into more northern regions, it would have a severe impact on these already poor areas, she said.

“The Third World regions have the potential to be hit hard,” she said.

The findings track earlier UF research on soybeans, peanuts and dry beans, although rice and dry beans appear the most sensitive to temperature change, Allen said.

The news, however, is not necessarily all bad. Snyder and Allen said plant scientists likely can develop more heat-tolerant varieties of rice and other grains. Still, selective breeding has a limit. “If this happens with so many different species, then I don’t see a lot of potential for selecting genetically within a species for a solution to it,” Boote said.

Another possibility is that other grains will become tomorrow’s staples. UF scientists have recently experimented with a grain called the pigeon pea, which is more tolerant of hot, dry climates because it grows slowly and flowers late in the summer, Allen said.

Snyder, Boote and Allen plan to submit a paper about the rice research, funded by the International Rice Research Institute, to a scientific journal for publication. Since launching their efforts in 1981, researchers with the Carbon Dioxide and Climate Change Project have published about 100 papers in peer-reviewed journals and book chapters, Allen said.