Artificial roots cut methane emissions from rice paddies in half

The Methane Problem in Rice Farming

Rice paddies, which provide a staple food for billions, are a substantial source of atmospheric methane, a greenhouse gas over 80 times more potent than carbon dioxide over a 20-year period. The flooded, oxygen-poor conditions of these fields create a perfect environment for methanogens—microbes that produce methane as they break down organic matter. While methods like alternate wetting and drying can reduce emissions, they often come with drawbacks such as increased weed growth. A new study presents a durable and effective solution to this agricultural and environmental challenge.

A System Inspired by Nature

Researchers led by Xianjin Tang and Zhao-Feng Yuan at the Institute of Soil and Water Resources and Environmental Science at Zhejiang University have developed a technology that mimics the natural oxygen-transporting tissues in rice plants. The system, called man-made aerenchymatous tissues or MAT, uses a network of O₂-permeable silicone tubes placed in the soil. By pumping air through these tubes, the MAT system continuously releases oxygen directly into the oxygen-depleted soil layers where methane is produced.

Altering the Soil Environment

The constant supply of oxygen from the MAT system fundamentally changes the soil’s chemistry. In both laboratory and field tests, the researchers observed a substantial increase in the soil's redox potential, a measure of its tendency to acquire electrons and be oxidized. The soil environment shifted from a strongly reducing state, ideal for methanogens, to a milder one that suppresses their activity. This chemical alteration is the first step in a multi-pronged approach to stopping methane at its source.

A Triple-Action Effect on Methane Production

The MAT system reduces methane emissions through three distinct mechanisms. First, the higher oxygen levels directly inhibit the activity and abundance of methane-producing microbes. Second, the released oxygen promotes the oxidation of iron in the soil, forming iron oxides. These compounds act like a sponge for dissolved organic matter, locking away the food source that methanogens would otherwise consume. Third, the presence of iron oxides encourages the growth of different microbes, known as iron-reducers, which outcompete methanogens for any remaining organic substrates.

Proven Success from Lab to Field

The effectiveness of the MAT approach was confirmed in both controlled mesocosm experiments and real-world paddy field trials. The research team, including collaborators Zheng Chen from Xi’an Jiaotong-Liverpool University and Andreas Kappler from the University of Tübingen, found that the system consistently reduced methane emissions by approximately 50 percent. This reduction rate is among the highest reported for sustainable methane mitigation strategies in agriculture.

A Flexible and Sustainable Future

A key advantage of the MAT system is its adjustability and sustainability. The research team showed that the amount of oxygen released can be easily controlled by adjusting the air pressure inside the tubes. In one test, increasing the pressure to 200 kPa boosted methane reduction to 74.2 percent. Unlike chemical additives that are quickly consumed, the MAT system provides a continuous, long-term supply of oxygen with minimal energy input, which can be supplied by solar panels. The authors suggest that deploying the MAT network could be integrated with existing rice transplanting machinery, making it a feasible and cost-effective tool for farmers worldwide to combat climate change.

Corresponding Author:

Xianjin Tang

Original Source:

https://doi.org/10.1007/s44246-023-00049-1

Contributions:

X.T. and Z.Y. designed the research; Z.Y. performed the research; Z.Y., X.T., Y.Z., Z.C., Y.W., A.K., and J.X. wrote the paper. The authors read and approved the final manuscript.