A 50 percent boost in rice, with methane dropping by 90 percent.
When it comes to major anthropogenic sources of methane (an important greenhouse gas), livestock and leaky natural gas wells and pipelines might come to mind. However, rice cultivation is also among the largest sources. Microbes in wetlands, where water saturation leads to low-oxygen conditions, produce most of the world’s methane, and rice paddies are essentially human-controlled wetlands.
Photo: Feng Wang
Down in the warm muck of a rice paddy, the roots of the rice plant release some organic compounds, and they eventually die off and decay themselves, providing the food that microbes turn into methane. Researchers are working on ways to limit that methane production, but this will always be a secondary concern for farmers. Yields rule the day, especially as demand is growing. But a 2002 study hinted at a win-win: increase above-ground growth at the expense of below-ground growth, and yield goes up while methane production goes down.
A great idea, but how to make it happen? A group of researchers led by Swedish University of Agricultural Sciences researchers Jun Su, Changquan Hu, and Xia Yan have used a gene from barley to create a genetically modified rice plant that does just that.
The barley gene causes the plant to put more energy into above-ground growth, including the seeds. Having inserted the gene into a couple rice cultivars, the researchers planted trials in several areas of China with varying climates to see the results. Compared to a common cultivar grown as a baseline, the genetically modified plants produced substantially less methane—90 to 99 percent less, depending on the growth stage.
To see what was happening, the researchers tracked the growth of the rice, as well as the activity of genes in various parts of the plants. The genetically modified plants had stronger flower clusters that produced more seeds, meaning a greater yield of rice per plant—close to 50 more percent by weight. And the starch content of those grains of rice was about 10 percent higher. In total, above-ground weight increased by about 30 percent, while below-ground weight decreased by 35 percent.
Meanwhile, the abundance of methane-producing microbes living on the plants’ roots decreased by half or more, apparently starved of food.
Measurements of gene expression confirmed that the barley gene was busy in the seeds and stems of the modified plants. The gene boosted the conversion of sugars to starch, maintaining a greedy demand for sugars in those parts that left less for the roots.
In an article accompanying the paper in Nature, Netherlands Institute of Microbial Ecology researcher Paul Bodelier celebrated the study but cautioned that further trials will be necessary to make sure this crop would be ready for long-term, widespread use. Since the microbial community around the plant’s roots changes, there could potentially be knock-on effects that reduce the plant’s disease resistance or require greater fertilizer use, for example.
Barring major trade-offs, a variety of rice that produces more food while releasing less methane into the atmosphere would obviously be a boon.
by Scott K. Johnson - Jul 28, 2015 5:33pm CEST