By tracing the exact microbial pathways responsible for N₂O production, the scientists reveal why the same soil amendment produces opposite climate outcomes under different land uses.
Nitrous oxide is a potent greenhouse gas with a global warming potential 265 times that of carbon dioxide over 100 years and is now the leading ozone-depleting substance in the 21st century. Agricultural nitrogen fertilization is its dominant source, particularly in acidic soils common in humid subtropical regions. Biochar has been widely promoted as a solution: it can raise soil pH, alter microbial processes, and in many cases reduce N₂O emissions. However, previous studies have reported inconsistent results, especially in strongly acidic soils and under different water regimes. A key unresolved question has been whether biochar’s mitigation effect arises simply from pH changes—similar to liming—or from deeper microbial mechanisms that vary across land-use types.
A study (DOI: 10.48130/nc-0025-00 21 ) published in Nitrogen Cycling on 22 January 2026 by Jinbo Zhang’s team, Hainan University, highlights the need for land-use-specific mitigation strategies and offers a mechanistic roadmap for designing smarter, climate-resilient soil management practices.
Using a controlled short-term incubation experiment combined with natural-abundance isotopic tracing and high-resolution molecular analyses, the researchers quantified N₂O fluxes and partitioned their microbial sources in acidic upland and flooded paddy soils amended with graded biochar or CaO. N₂O emissions were monitored over 96 hours following urea addition, and isotopic signatures (δ¹⁵N_bulk, δ¹⁵N_SP, and δ¹⁸O) were integrated into a Bayesian FRAME model to apportion contributions from bacterial denitrification (bD), fungal denitrification (fD), nitrifier denitrification (nD), autotrophic nitrification (Ni), and heterotrophic nitrification (hN). Parallel measurements of soil physicochemical properties, nitrogen species, and functional gene abundances (including amoA, nirS, nirK, and nosZII) were conducted using qPCR and high-throughput sequencing. The results revealed sharply contrasting responses between land-use types. In upland soil, biochar significantly reduced cumulative N₂O emissions relative to the control and CaO treatments, with isotopic modeling showing marked declines in bD- and fD-derived N₂O. This reduction corresponded with decreased abundance of high N₂O-producing fungi such as Chaetomium and a substantial increase in the nosZII/(N₂O-producing genes) ratio, indicating enhanced microbial reduction of N₂O to N₂. Biochar also lowered residual N₂O fractions and increased total N₂ production, confirming more complete denitrification. In contrast, in flooded paddy soil, biochar dramatically increased cumulative N₂O emissions—by more than five- to fourteen-fold at higher application rates. All five microbial pathways contributed nearly equally, and their absolute N₂O production rates were amplified following biochar addition. Gene abundances linked to nitrification and denitrification increased, and high soil organic carbon and nitrogen availability appeared to stimulate multiple N₂O-producing processes simultaneously. Collectively, the pathway-based isotope and molecular evidence demonstrates that biochar suppresses denitrification-driven N₂O in upland soil but enhances multi-pathway N₂O production in flooded paddy soil.
Overall, the study reveals that biochar’s climate benefits are not universal but depend critically on land-use type and underlying microbial ecology. By combining isotopic pathway partitioning with molecular analyses, the research demonstrates that upland mitigation arises from targeted suppression of N₂O-producing fungi and enhanced N₂O reduction, whereas in flooded systems, biochar can stimulate multiple production routes simultaneously. These findings underscore the importance of mechanistic, pathway-level assessments before scaling up biochar applications and point toward precision soil manageme.
###
References
DOI
Original Souce URL
https://doi.org/10.48130/nc-0025-0021
Funding information
This work was supported by the Hainan Provincial Natural Science Foundation of China (Grant No. 425CXTD606), the National Natural Science Foundation for Excellent Youth Science Foundation of China (Grant No. RZ2400002277), and College initial funding (Grant No. 1677772342Y).
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.
Experimental study
Not applicable
Biochar's contrasting effects on N2O emissions in acidic upland and flooded paddy soils
22-Jan-2026
The authors declare that they have no competing interests.