Nitrous Oxide Emissions from Paddies: Understanding the Role of Rice Plants

: Paddies are a potential source of anthropogenic nitrous oxide (N₂O) emission. In paddies, both the soil and the rice plants emit N₂O into the atmosphere. The rice plant in the paddy is considered to act as a channel between the soil and the atmosphere for N₂O emission. However, recent studies suggest that plants can also produce N₂O, while the mechanism of N₂O formation in plants is unknown. Consequently, the rice plant is only regarded as a channel for N₂O produced by soil microorganisms. The emission of N₂O by aseptically grown plants and the distinct dual isotopocule fingerprint of plant-emitted N₂O, as reported by various studies, support the production of N₂O in plants. Herein, we propose a potential pathway of N₂O formation in the rice plant. In rice plants, N₂O might be formed in the mitochondria via the nitrate-nitrite-nitric oxide (NO₃-NO₂-NO) pathway when the cells experience hypoxic or anoxic stress. The pathway is catalyzed by various enzymes, which have been described. So, N₂O emitted from paddies might have two origins, namely soil microorganisms and rice plants. So, regarding rice plants only as a medium to transport the microorganism-produced N₂O might be misleading in understanding the role of rice plants in the paddy. As rice cultivation is a major agricultural activity worldwide, not understanding the pathway of N₂O formation in rice plants would create more uncertainties in the N₂O budget.