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Reportedly, methane is more than 28 times as potent as carbon dioxide as a greenhouse gas. However, "As of recent data, the atmospheric methane concentration is around 1,900 parts per billion (ppb), which is equivalent to roughly 1.9 parts per million (ppm)." (Google AI). Methane is much less of a trace gas than CO2 (about 400 ppm).
"Rice farming is an underrated [underreported] driver of climate change, responsible for roughly one tenth of global methane emissions. The problem is not the rice plants themselves, but the methane-emitting microbes (methanogens) that thrive in their flooded paddies.
A team of researchers in China has found a promising solution.
First, they identified two compounds with a significant impact on these microbes; fumarate and ethanol. The former enhanced methanogen abundance, and the latter inhibited it.
By breeding hybrid rice varieties low in fumarate and high in ethanol, they were able to reduce methane emissions by 70 percent in field trials while achieving high yields."
From the abstract:
"Methane in rice paddies is mainly produced by methanogenic communities feeding on carbon from root exudates and debris.
However, the dominant root secretion governing methane emissions is not yet identified after decades of studies, even though secreted carbohydrates and organic acids have been shown to contribute to methane emissions.
In this study, we discovered that fumarate and ethanol are two major rice-orchestrated secretions and play a key role in regulating methane emissions. Fumarate released in the rhizosphere is metabolized by microorganisms, supporting the growth of methanogenic archaea that produce methane as an end carbon product, while ethanol mitigates methane emissions through inhibition of methanogenic activity and growth as well as reducing fumarate synthesis in the rice root.
Furthermore, we elucidated the route of fumarate metabolism in the anoxic rhizospheric zone. We found that fumarate in the rice root is produced from acetate via propionate and succinate, and when released into soil directly is oxidized to propionate before conversion via acetate into methane as the end product.
The knowledge on fumarate and ethanol metabolism in rice was then used for hybrid breeding of new rice varieties with the property of low methane emission. Cultivation of these novel rice lines or employing our findings for rice cultivation managements showed up to 70% reductions in methane production from seven paddy field sites during 3 years of cultivation trials. Taken together, these findings offer great possibilities for effective mitigation of the global climatic impact of rice cultivation."
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