Monitoring five reactive nitrogen gases across a full wetting–drying cycle, the team identified duckweed’s dual role as both an effective NOx mitigation tool and a source of significant environmental trade-offs.
Rice paddies are among the largest global anthropogenic sources of reactive nitrogen gases, including NH₃, N₂O, HONO, and NOₓ. These emissions stem from tightly coupled microbial processes such as ammonification, nitrification, and denitrification, all of which respond rapidly to shifts in soil oxygen status, pH, and nitrogen availability. While nitrogen fertilizers have long been central to boosting rice yields, their low utilization efficiency contributes to substantial atmospheric losses—exacerbating eutrophication, air pollution, and climate forcing. Although duckweed has gained attention for its nitrogen uptake capacity and phytoremediation benefits, past studies largely focused only on its ability to suppress NH₃ volatilization. Its influence on the broader suite of Nr gases has remained unknown, creating an urgent need to evaluate whether duckweed can truly serve as a holistic nitrogen management tool in rice–aquatic systems.
A study (DOI:10.48130/nc-0025-0008) published in Nitrogen Cycling on 28 October 2025 by Qingnan Chu’s & Zhimin Sha’s team, Shanghai Jiao Tong University, demonstrates that duckweed can significantly curb NOy emissions but may inadvertently elevate N₂O and NH₃, underscoring the need for balanced, integrated approaches to nitrogen mitigation in paddy soils.
Using a dynamic chamber system to continuously monitor reactive nitrogen (Nr) gas fluxes, this study quantified how duckweed incorporation influences emissions of HONO, NO, NO₂, N₂O, and NH₃ from paddy soils throughout a full wetting–drying cycle, while simultaneously tracking changes in soil physicochemical properties and nitrogen-cycling functional genes. This controlled design enabled direct comparison among unfertilized soil, nitrogen-fertilized soil, and fertilized soil covered with duckweed, with peak emissions analyzed in relation to microbial gene expression and soil variables through PCA, stepwise regression, and PLS-PM. The results showed that duckweed substantially reduced NOy emissions, lowering cumulative HONO and NOₓ fluxes by 72.4% and 52.9%, respectively. Although both NO and NO₂ decreased, an elevated NO/NO₂ ratio indicated restricted oxygen diffusion and inhibited NO oxidation. HONO and NOₓ peaks appeared simultaneously across treatments, yet duckweed consistently dampened their magnitudes through increased soil pH and electrical conductivity, greater microbial biomass carbon, and enhanced expression of denitrification genes such as nirK, nirS, and nosZ. In contrast, the same monitoring framework revealed that duckweed sharply amplified N₂O and NH₃ emissions, raising them 2.6-fold and 143-fold relative to fertilized soil without duckweed. These increases were associated with elevated soil NO₂⁻, enhanced nitrification potential reflected by amoA upregulation, and stimulated denitrification driven by labile carbon released from duckweed decomposition. Rapid biomass breakdown under drying conditions also contributed directly to high NH₃ volatilization. Soil measurements showed reduced NH₄⁺ but extreme NH₃ peaks in duckweed-amended soils, indicating volatilization from decomposing duckweed tissue rather than soil nitrogen pools. Overall, the integrated analyses demonstrated that duckweed effectively suppresses HONO and NOₓ emissions but intensifies N₂O and NH₃ losses through coupled shifts in soil chemistry, oxygen availability, and microbial nitrogen-transformation pathways.
The finding that duckweed sharply reduces HONO and NOₓ emissions suggests substantial benefits for controlling atmospheric nitrogen pollution, mitigating ecosystem acidification, and reducing harmful nitrogen deposition. From an agronomic perspective, duckweed also improves nitrogen retention and may enhance nitrogen-use efficiency. Yet these advantages are countered by increases in N₂O—a greenhouse gas nearly 300 times more potent than CO₂—and NH₃, a major driver of secondary particulate pollution. These results highlight that unregulated duckweed use may inadvertently shift nitrogen losses from one harmful pathway to another.
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References
DOI
10.48130/nc-0025-0008
Original Source URL
https://doi.org/10.48130/nc-0025-0008
Funding information
This work was supported by the Agricultural Research System of Shanghai, China (Grant No. 202203) and 2025 Shanghai Municipal Grassroots Science Popularization Action Plan Project (JCKP2025-29), Shanghai Qingpu Regenerative Agriculture Science and Technology Field Station.
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