August 10, 2010
Source: SciDev.Net
by Cecilia Rosen
Hotter nights arising from climate change will put a brake on the rise in rice production in Asia over the coming decades, with the effect worsening as the century progresses, scientists said yesterday (9 August).
The first study to use 'real-world' data from farmer-managed rice farms has shown that, while hotter days may boost productivity, hotter nights more than compensate by reducing it.
"There is very little doubt that higher night temperature is harmful to rice and that further increases will continue to harm production unless there are technological changes in the way is produced," lead author of the study Jarrod Welch, from the University of California in San Diego, told SciDev.Net.
The researchers analysed six years of data collected by the International Rice Research Institute (IRRI) in the Philippines from nearly 230 farmer-managed irrigated farms across six major rice-growing countries in Asia.
The international team wanted to disentangle the effects on rice productivity of three factors: daytime temperature, night temperature and sunshine.
The scientists confirmed what previous, experimental trials have suggested: that warmer temperatures lead to a net decline in production.
The reason for the fall in productivity at night may lie in a key stage in the rice plant's cycle: grain filling. It is thought that, at night, energy needed for grain-filling goes instead to power the increased respiration a plant requires in hotter weather.
The scientists' long-term prognosis is even worse because, once day time temperatures reach a certain height they, too, will start to restrict the rice growth cycle, leading to an additional loss in production.
The phenomenon is set against a background of increased rice productivity, achieved through improvements in technology such as better seeds, use of fertiliser and mechanisation. The net effect will be a slowing down of the rate of growth of rice yield.
Reiner Wassmann, coordinator of the Rice and Climate Change Consortium at IRRI, said that plant-breeding using rice varieties that have evolved traits to adapt to very hot environments could provide a way forward.
Hilton Pinto, director of the Center for Meteorology and Climate Research Applied to Agriculture at the Brazilian university Unicamp, told SciDev.Net that adaptation of agriculture to climate has to begin immediately.
"If we want to obtain a new variety of plant more resistant to high temperatures we need to start now. This takes ten years of work with an estimated cost of one million dollars per year in research. Let's start now."
In Asia, where 60 per cent of the world's population lives, each hectare of land used for rice provides food for 27 people. By 2050, IRRI estimates the same land will have to feed 43 people.
Link to paper abstract in Proceedings of the National Academy of Sciences
夜间变暖威胁亚洲的稻米产量
科学家昨天（8月9日）说，气候变暖导致的更热的夜间将在未来的几十年阻碍亚洲稻米产量的增加。
这项首次使用来自农民管理的农场的“现实世界” 数据的研究表明，尽管更热的白天可能增加产量，更热的夜间通过减少产量而不仅仅是抵消了前者。
“几乎没有人怀疑更高的夜间温度对于水稻有害，而且进一步的增加将继续危害产量，除非出现什么技术革新。”该研究的第一作者、加州大学圣地亚哥分校的Jarrod Welch告诉本网站说。
这组科学家分析了设在菲律宾的国际水稻研究所（IRRI）从亚洲6个水稻生产大国的将近230个农民管理的灌溉农场收集的6年的数据。
这个国际研究组希望弄清3个因素对水稻产量的影响，包括日间温度、夜间温度和阳光。
这组科学家证实了此前的实验性测试所提示的，即更高的温度导致产量的净下降。
夜间产量下降的原因可能在于水稻周期的一个关键阶段：灌浆期。人们认为，在夜间，灌浆所需的能量被转而用于植株在更热的天气下增加呼吸。
这组科学家的长期预测结果甚至更严重，因为一旦日间温度达到了某一点，它们也将开始限制水稻的生长，导致产量的额外损失。
这种现象所处的背景是技术改良（诸如更好的种子、使用化肥和机械化）带来的水稻产量增加。变暖的净效应将是水稻产量增长率变缓。
IRRI的水稻与气候协作体协调员Reiner Wassmann说，利用进化出了适应非常炎热的环境的水稻品种的植物育种项目可能提供一个解决方法。
巴西坎皮纳斯州立大学的气象与气候研究农业应用中心主任Hilton Pinto告诉本网站说，让农业适应气候的行动需要立即开始。
“如果我们希望获得一种更耐高温的新的植物品种，我们需要从现在就动手。这需要10年时间，估计每年的研究成本是100万美元。让我们现在开始。”
在生活着全世界60%人口的亚洲，每公顷稻田为27个人提供粮食。IRRI估计，到2050年，同样的土地将需要养活43人。
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