Duckweed offers promise and caution as nature-based solution for rice paddy pollution

A new study has revealed both the promise and the complexity of using duckweed as a biological tool for managing nitrogen pollution in rice agriculture. While this tiny floating plant can sharply curb certain harmful nitrogen oxide emissions, it may also unintentionally boost releases of ammonia and a potent greenhouse gas, nitrous oxide. These findings highlight the importance of smart, integrated strategies for sustainable farming and environmental protection.

Nitrogen: Friend to Farmers, Challenge to Planet

Rice feeds nearly half the world’s population, and nitrogen fertilizers are vital for high yields. Yet much of this nitrogen escapes from paddy fields as reactive nitrogen gases, contributing to air and water pollution, soil acidification, and climate change. International research teams have long sought alternatives that can boost yield while reducing environmental damage.

Duckweed’s Surprising Dual Impact

The study, published in Nitrogen Cycling, explored the impact of duckweed (Lemna minor L.) on the release of five types of reactive nitrogen gases from flooded paddy soils. Using high-precision chambers, scientists closely monitored gases under different conditions: with only soil, with nitrogen-fertilized soil, and with both fertilizer and duckweed.

Results showed that introducing duckweed reduced cumulative emissions of harmful nitrogen oxides, specifically HONO and NOx—by over 70 percent and 50 percent, respectively, when compared to fertilized soil without duckweed. The key lies in duckweed’s ability to alter soil chemistry and encourage beneficial microbial communities that suppress nitrogen oxide production. By covering flooded soil, duckweed changes the redox conditions, raises pH, and influences how nitrogen is processed—a win for efforts to curb acid rain and lower harmful air pollution.

But this success comes with a catch. The same conditions that reduce nitrogen oxides can lead to a dramatic increase in emissions of ammonia (NH3) and nitrous oxide (N2O). In the study, duckweed tripled N2O emissions and caused a 140-fold increase in ammonia release. This is largely due to the breakdown of duckweed biomass, which adds loosely-bound carbon and nitrogen to the soil. Microbial activity then transforms these nutrients into gases that escape quickly to the atmosphere.

The Science Behind the Trade-Off

Researchers used molecular tools to pinpoint how duckweed alters gene activity in soil microbes. They found spikes in genes responsible for denitrification and ammonia production, providing a clear mechanism for the shift in gas emissions. Advanced modeling techniques showed that duckweed’s impact on each gas is the result of many direct and indirect factors, including changes in soil moisture, pH, available nutrients, and microbial gene expression.

The message is clear: nature-based interventions like duckweed can play a powerful role in pollution control, but their application must be carefully managed to avoid swapping one environmental problem for another.

Towards Smarter, Sustainable Solutions

The authors suggest combining duckweed with additional measures, such as timely harvesting and soil amendments, to capture its benefits while limiting unintended emissions. Removing duckweed biomass before it decomposes can prevent secondary pollution, and using materials like biochar or nitrification inhibitors can help manage excess nitrogen.

“Duckweed should be viewed as part of a toolkit for sustainable rice farming, not a single fix,” says Dr. Zhimin Sha, senior author of the study. “Our findings point to the need for integrated management strategies that balance multiple environmental goals.”

While conducted under controlled laboratory conditions, the research provides a crucial step toward field-ready solutions for cleaner, more efficient rice production. The team calls for long-term field studies and system-level evaluations to fully capture the real-world impact of duckweed interventions.

This work underscores the importance of looking at the whole environmental picture when designing new agricultural practices. Sometimes, the tiniest plants can have the biggest, and most nuanced, effects.

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Journal Reference: Lan Y, Xu S, Liu X, Li D, Chu Q, et al. 2025. Mechanistic evaluation of duckweed intervention on reactive nitrogen gas fluxes from paddy soils. Nitrogen Cycling 1: e008    

https://www.maxapress.com/article/doi/10.48130/nc-0025-0008

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About Nitrogen Cycling:
Nitrogen Cycling is a multidisciplinary platform for communicating advances in fundamental and applied research on the nitrogen cycle. It is dedicated to serving as an innovative, efficient, and professional platform for researchers in the field of nitrogen cycling worldwide to deliver findings from this rapidly expanding field of science.

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