PARIS • Scientists say that they have created a rice variety with starchier grains that emits less methane, a step towards the twin goals of feeding more people and curbing global warming.
The cultivation of rice, a staple starch for billions of people, is also mankind's major emitter of methane, a potent climate-altering gas.
Methane lives for a shorter time in the atmosphere than carbon dioxide, the most abundant greenhouse gas, but traps far more heat radiated from earth's surface.
Every year, rice paddies pump out 25 million to 100 million tonnes of methane. This means a high risk for the planet as rice cultivation expands to feed a growing population, said the paper, published in the journal Nature.
"There is an urgent need to establish sustainable technologies for increasing rice production while reducing methane fluxes from rice paddies," wrote the team from the Swedish University of Agricultural Sciences. In 2002, scientists reported that the more grain carried by rice plants, the less methane they emitted. The leaves and stems of rice plants take up carbon dioxide, which is transformed through photosynthesis into sugars used to produce starch.
Carbon released from dead plants or directly into the soil via the roots is transformed by micro-organisms into methane, which can escape into the atmosphere. Starchier rice grains mean there is less carbon transferred to the soil to be turned into methane.
But attempts to reduce emissions from paddies have focused on changes in farming practices, which can be onerous and expensive. Tackling the problem differently, a team from China, the US and Sweden added a barley gene to a conventional rice cultivar to create a variety dubbed Susiba2. "Three-year field trials in China demonstrated that the cultivation of Susiba2 rice was associated with a significant reduction in methane emissions," said the study. It said the rice offers a sustainable means of providing increased starch content for food production.
Dr Paul Bodelier of the Netherlands Institute of Ecology called the research "groundbreaking", but cautioned it also raised several "biological and ethics concerns".
"In addition to the general questions surrounding the use of genetically modified crops for human consumption and how access to seed for such crops is controlled, we do not yet have a clear picture of how this modification affects rice plants' survival and general function," said Dr Bodelier.
Long-term measurements of methane emissions would be needed to calculate the crop's potential overall impact on greenhouse gas reduction efforts, he wrote.
Also, the reduction of carbon in soil may have unknown consequences for other types of micro-organisms that could aid or harm the plants.