As the climate warms, rice farmers may face a difficult balance. Higher temperatures can make nitrogen more available to crops, but they can also increase nitrogen losses to the atmosphere. A new study shows that flooded rice soils may partly compensate by redirecting nitrogen into more stable forms protected within soil aggregates and mineral particles.
"Our findings suggest that warming does not simply cause nitrogen to disappear from rice soils. Instead, it changes where nitrogen goes and how securely it is stored," said corresponding author Pil Joo Kim of Gyeongsang National University. "Understanding these pathways could help us develop more climate-resilient nitrogen management strategies for rice production."
Nitrogen is essential for crop growth and is a major component of agricultural fertilizers. However, scientists still have a limited understanding of how rising temperatures and atmospheric carbon dioxide concentrations will affect nitrogen cycling in flooded rice paddies.
To investigate these changes, the researchers conducted a three-year field experiment in South Korea using open-top chambers. The chambers simulated three atmospheric conditions: current climate conditions, a temperature increase of 2 °C, and a combined increase of 2 °C with an additional 200 parts per million of carbon dioxide.
The team measured nitrogen uptake by rice plants, nitrous oxide emissions, soil nitrogen fractions, nitrogen isotope signatures, root inputs, and the abundance of microbial genes associated with biological nitrogen fixation.
Warming increased nitrogen uptake by rice and raised nitrous oxide emissions, indicating faster nitrogen turnover and greater nitrogen availability during the growing season. Nitrous oxide is a powerful greenhouse gas and also represents a loss of valuable nitrogen from agricultural soils.
Despite these increased nitrogen outputs, total soil nitrogen was maintained or increased under the future climate treatments. The researchers found that warming changed the distribution of nitrogen among different soil pools.
The amount of nitrogen trapped within soil aggregates increased substantially under both warming treatments. These protected pools can restrict microbial and enzymatic access to organic matter, helping nitrogen remain in the soil for longer periods. Nitrogen associated with silt and clay particles also showed isotope patterns consistent with intensified microbial processing.
The results suggest that warming simultaneously accelerates nitrogen loss and promotes the stabilization of microbially processed nitrogen in protected soil fractions.
The researchers also detected a significant increase in the abundance of the nifH gene, a widely used marker for microorganisms capable of fixing atmospheric nitrogen. The ratio of nifH genes to bacterial 16S rRNA genes also increased, suggesting that nitrogen-fixing microorganisms became more prominent within the soil bacterial community.
However, the researchers emphasize that gene abundance does not directly measure actual nitrogen fixation rates. Additional experiments using nitrogen isotope tracers will be needed to confirm whether biological nitrogen fixation provides a meaningful new nitrogen input under warming.
Elevated carbon dioxide did not consistently strengthen the effects of warming. In some cases, the combined treatment reduced plant nitrogen uptake compared with warming alone. The researchers propose that reduced stomatal opening under elevated carbon dioxide may limit evaporative cooling, increasing heat stress in rice canopies and offsetting some potential benefits of higher carbon dioxide concentrations.
The findings point to possible strategies for protecting soil fertility, including maintaining moderate organic carbon inputs, optimizing flooding practices, supporting nitrogen-fixing microorganisms, and avoiding management practices that disrupt soil aggregates.
The study highlights that future nitrogen management must consider not only how much nitrogen enters or leaves rice fields, but also how climate change redistributes nitrogen among plant-available, vulnerable, and protected soil pools.
The authors note that the experiment included only two field plots per treatment. The findings should therefore be considered indicative and should be tested across additional soil types, rice-growing regions, and climate conditions.
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Journal Reference: Song HJ, Seo YH, Shin HJ, Lee JJ, Ampode SJG, et al. 2026. Warming reshapes nitrogen partitioning and stabilization pathways in flooded rice soils. Nitrogen Cycling 2: e023 doi: 10.48130/nc-0026-0010
https://www.maxapress.com/article/doi/10.48130/nc-0026-0010
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Nitrogen Cycling (e-ISSN 3069-8111) 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.
