Root nodule symbiosis between rhizobia and legumes can fix atmospheric nitrogen, but it is also known to release N₂O during the late growth stages of legumes. In this project, we will establish symbiosis systems in which N₂O-reducing rhizobia preferentially infect the host leguminous plants, by (i) searching for rhizobia with higher activities of N₂O reduction and establishing new technology to improve their N₂O-reducing activities, and (ii) optimizing host plants that preferentially accommodate N₂O-reducing rhizobia.

To establish the N₂O detoxifying/recycling/absorbing upland and paddy field technology, (i) isolation and characterization of N₂O detoxifying/recycling microorganisms and (ii) functional analysis of N₂O-transforming soil microbial community will be performed.



Ⅱ-2: Detoxification of N₂O by rhizospheric/endohytic microorganisms
Since the Industrial Revolution, atmospheric CO₂ level has raised to 410 ppm, which has induced approximately 1.09 ℃ increasing in the global surface temperature. An environmental-friendly agronomy using the combination of cover crop and no-tillage managements results in a massive CO₂ capture and storage into the soil carbon pools, therefore, it has been expected to mitigate the global warming and climate change. However, the increased soil organic carbon enhances the N₂O emission from soil. Our study is aimed to 1) unveil the microbial process involved in the nitrogen cycle in the field soil managed with the long-term cover crop and no-tillage treatments; 2) obtain high-affinity N₂O-reducing microbes and develop their application in the sustainable crop cultivation.
Endophytic bacteria are derived from diverse soil bacteria, but which are limited to specific bacteria by strong effects of plant such as supply of specific substances from plant and protective responses of plant. Therefore, it is expected that endophytic bacteria with high N₂O detoxification ability can be used sustainably and effectively to N₂O detoxification in crops. In this study, we are searching for endophytic bacteria with high N₂O detoxification ability from the forage crop.



Ⅱ-3: N₂O recycling by N₂O fixing bacteria and iron-reducing bacteria
Recently, we isolated the iron-reducing bacteria from paddy soil, which harbors the potential not only to reduce N₂O but also to convert into organic nitrogen, i.e., to fix N₂O. In this project, we verify the N₂O fixation activity of iron-reducing bacteria and develop basic technology to enhance their N₂O activity in soils. In addition, we work on researches to elucidate the dynamics of N₂O-fixing iron-reducing bacteria in soils based on microcosmic experiments and global trends for diversity of N₂O-fixing microbiome in soils by analyzing soil metagenomic data around the world.