Rice farming contributes approximately 12% of the world’s methane emissions, and these levels are projected to rise due to climate change and population growth. Recently, researchers have discovered specific chemical compounds released by rice roots that influence methane production. They announce that this insight has led to the development of a new rice variety that can produce up to 70% less methane.
Rice farming contributes approximately 12% of the world’s methane emissions, and these emissions are anticipated to rise due to climate change and population growth. Researchers have now pinpointed chemical compounds released by rice roots that affect how much methane these plants emit. On February 3, in the Cell Press journal Molecular Plant, they reveal that this knowledge has allowed them to create a new rice variety that emits as much as 70% less methane.
“This study demonstrates that it is possible to achieve low methane emissions while maintaining high rice yields,” says lead author Anna Schnürer, a microbiologist at the Swedish University of Agricultural Sciences. “Additionally, it can be done using traditional breeding techniques, without resorting to genetic modification, if you know what you’re aiming for.”
The methane produced in rice paddies originates from microbes that decompose organic compounds released by rice plant roots. These roots exude substances known as “root exudates” to nourish soil microbes, which in turn enhance plant growth by providing essential nutrients. While it has long been recognized that soil microbes and root exudates play a role in methane emissions, the specific compounds in root exudates responsible for this process were previously unclear.
To pinpoint which root exudate compounds contribute to methane production, the researchers studied exudates from two distinct rice varieties: SUSIBA2, a low-methane GMO variety, and Nipponbare, a non-GMO type with average methane emissions. They discovered that SUSIBA2 roots yielded far less fumarate and noticed a connection between the quantity of fumarate released and the number of methane-producing archaea, or “methanogens,” present in the soil.
To verify the impact of fumarate, the team introduced fumarate into the soil of container-grown rice plants, which resulted in heightened methane emissions. They also found that applying oxantel, a compound that prevents the breakdown of fumarate, effectively reduced methane emissions. However, since the SUSIBA2 plants emitted less methane than the Nipponbare plants, the researchers concluded that fumarate was not the sole factor influencing emissions.
“It felt like solving a riddle,” Schnürer recalls. “We discovered that the soil itself seemed to contain something that mitigated methane emissions, leading us to believe there must be an inhibitor responsible for the differences between the rice varieties.”
Upon re-evaluating the root exudates, the researchers realized that the SUSIBA2 plants also produced significantly higher amounts of ethanol. When ethanol was added to the soil around rice plants, methane emissions were reduced.
Next, the team explored traditional breeding techniques to create a rice variety that emits low levels of methane but still achieves high yields. They crossbred a high-yield, or “elite,” rice variety with the low-methane emitting Heijing cultivar, which is characterized by low fumarate and high ethanol in its root exudates.
The resulting rice plants from this crossbreeding consistently demonstrated root exudate profiles that were low in fumarate and high in ethanol (LFHE). When these LFHE rice varieties were grown at different sites throughout China, they exhibited an average reduction of 70% in methane emissions compared to the elite variety. Additionally, the LFHE crops yielded a relatively high average of 8.96 tons per hectare, far exceeding the 2024 global average of 4.71 tons per hectare.
The scientists also tested whether ethanol and oxantel could effectively reduce methane emissions on a wider scale. In a two-year trial conducted at two separate locations in China, this approach led to roughly a 60% reduction in methane emissions while maintaining crop yield.
The researchers are now pursuing the registration of the LFHE rice variety with the Chinese government and other regulatory bodies, which could allow it to be offered to farmers in the future. They are also collaborating with fertilizer companies to explore the possibility of adding oxantel to commercial fertilizers.
“To facilitate these changes, we’ll need support from governments to encourage and assist farmers in adopting these low-methane rice varieties,” Schnürer emphasizes. “It’s one thing to develop eco-friendly rice strains, but it’s crucial to bring them to market and ensure farmer acceptance.”
Support for this research came from Mr. Zheng Fang, Beijing Xianhe Transportation Technology Co. Ltd., Trees and Crops for the Future, the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, NSFC Projects of International Cooperation and Exchanges, and the China Scholarship Council.
