Experts: Decline in Rice Yields Linked to Global Warming

By Art Chimes
Shaobing Peng of the International Rice Research Institute and his colleagues analyzed 25 years worth of weather and production data at the institute's farm in the Philippines. Over that period, there was an average temperature increase of about three-quarters of a degree , but most of the increase was at night. In other words, it wasn't getting as cool after sundown.
According to Kenneth Cassman, an American researcher on the team, the higher nighttime temperatures force the rice plants to, in effect, work harder.
"And what happens then is that diverting energy to maintain important metabolic functions that keep the plant alive during the nighttime diverts energy away from producing biomass and grain yield," he explained.
The effect is quite dramatic. The researchers concluded that rice yield declined by 10 percent for each one-degree increase in minimum nighttime temperature.
"The elevated temperature, we believe, increases what we call the 'maintenance respiration costs' of the plant at night. That is, the amount of energy the plant needs to use to keep itself alive during the nighttime," said Mr. Cassman.
Professor Cassman says that the rice was under controlled conditions where best growing practices were in place.
"So that the yields aren't limited by weeds or insects or diseases or nutrient deficiencies or water - too much water, too little water - so that year in and year out, the only thing that determines the yield of that crop is the amount of solar radiation and the temperature," he said.
Previous studies, using computer simulations or hothouse experiments, also predicted declining yields with higher temperatures. But the University of Nebraska researcher says the real world data used in this study indicates the effect of higher temperatures is even greater than predicted by earlier experiments.
"Our study shows that the magnitude of the yield decrease due to increasing night temperatures that we measured from the field studies was double the rate of decrease predicted by computer simulation models," Mr. Cassman went on to say.
Rice, along with wheat and maize, is one of the top three food crops on planet Earth. And Professor Kenneth Cassman points out that feeding an increasing population when warmer climates could cut production presents a critical challenge for the world's farmers in the years ahead.
The study of rice yields was published in the Proceedings of the National Academy of Sciences.
I am Art Chimes in Washington.

注释：
International Rice Research Institute 国际水稻研究所
Philippines 菲律宾
biomass（单位面积内）生物的数量
grain 谷类
yield 产量
nutrient 有营养的
deficiency 缺乏
solar 日光的
radiation 辐射
previous 先前的
simulation 模拟
hothouse 温室
Proceedings of the National Academy of Sciences 《国家科学院学报》