研究により、水田における窒素ガス損失の主な原因は肥料ではなく土壌であることが明らかになった(Study Reveals Soil, Not Fertilizer, Is Primary Source of Nitrogen Gas Loss in Rice Paddies)

2026-04-27 中国科学院（CAS）

A microbial nitrogen pump driving distinct sources of soil gaseous nitrogen losses from flooded rice systems. (Image by YAN Xiaoyuan’s team)

＜関連情報＞

• https://english.cas.cn/newsroom/research-news/202604/t20260423_1157878.shtml
• https://www.pnas.org/doi/10.1073/pnas.2603983123

湛水稲作システムにおける窒素損失は、肥料ではなく土壌有機窒素によって引き起こされる Soil organic nitrogen rather than fertilizer drives dinitrogen losses in flooded rice systems

Yuanyuan Lei, Zhijun Wei, Kaiye Ye, +16 , and Longlong Xia
Proceedings of the National Academy Sciences  Published:April 22, 2026
DOI:https://doi.org/10.1073/pnas.2603983123

Significance

Flooded rice fields lose large amounts of nitrogen as dinitrogen (N₂), yet the sources of this loss remain unclear. Using a cutting-edge in situ isotopic technique, we show that most N₂ emissions arise not from fertilizer, as widely assumed, but from soil organic nitrogen mineralized by fertilization-stimulated microbial processes, termed as a microbial nitrogen pump. This hidden pathway highlights a previously overlooked source of soil-derived nitrogen loss, causing conventional methods to overestimate fertilizer-derived losses. Our findings revise nitrogen budgets for rice systems and highlight the need to manage soil–plant–microbe interaction to sustain rice yields while reducing N₂ losses. Hybrid rice cultivars markedly lower yield-scaled gaseous nitrogen losses by enhancing plant and microbial nitrogen use efficiency while maintaining high productivity.

Abstract

Rice production underpins food security but relies heavily on nitrogen (N) fertilization, much of which is lost as gaseous emissions. Dinitrogen (N₂) represents the largest N loss, yet its sources remain poorly constrained because biological dinitrogen (N₂) fluxes are difficult to quantify against the atmospheric background. Here, we apply an in situ ¹⁵N tracing–membrane inlet mass spectrometry (¹⁵N–MIMS) technique to simultaneously measure N₂, ammonia (NH₃), and nitrous oxide (N₂O) emissions and partition their soil- versus fertilizer-derived origins across the growing season in conventional japonica rice and hybrid rice. We find that soil organic N (SON) accounts for most N₂ emissions (72 to 75%), overturning the prevailing assumption that fertilizer dominates this loss pathway, which is independently confirmed by a 14-y fertilization experiment. In contrast, NH₃ originates mainly from fertilizer (71 to 77%) and N₂O derives from both sources in near-equal proportions. We identify a previously unrecognized “microbial N pump”, in which rapid microbial assimilation of fertilizer-derived ammonium (NH₄⁺) induces stoichiometric imbalance and stimulates SON mineralization, mobilizing soil-derived NH₄⁺ that ultimately fuels N₂ emissions, with depleted SON partially replenished through microbial N turnover. Neglecting SON contributions causes systematic overestimation of fertilizer-derived N₂ and NH₃ losses by ~35%. Hybrid rice increases yield by 59% and reduces yield-scaled gaseous N losses by 43% through enhanced fertilizer uptake and microbial N use efficiency. Together, these findings reveal an underappreciated pathway of fertilization-driven soil N losses, revise N budgets for flooded rice systems, and demonstrate that cultivar-informed management can simultaneously enhance rice productivity and environmental sustainability.