Paddy soils are a major opportunity for climate change mitigation, but not all organic amendments help soil store carbon in the same way. A new study published in Biochar shows that rice straw and straw-derived biochar take very different routes once they enter the soil, largely because they favor different microbial "life strategies."
The research team conducted a 65-day incubation experiment using 13C-labeled rice straw and straw-derived biochar, allowing them to trace where added carbon went and how it affected existing soil organic carbon. The study focused on two key soil carbon pools: particulate organic carbon, a relatively active form derived largely from decomposing plant residues, and mineral-associated organic carbon, a more stable form that can persist longer through interactions with soil minerals and microbial residues.
"Our results show that biochar is not simply a more persistent form of straw," said corresponding author Yuxue Liu. "It changes the microbial pathway of carbon storage. By favoring slow-growing microbial groups and reducing carbon losses from native soil organic matter, biochar can help paddy soils retain carbon much more efficiently."
Both straw and biochar increased soil organic carbon compared with the control treatment. However, the difference in carbon retention was striking. By day 65, straw increased soil organic carbon by 38.7%, while biochar increased it by 103%. The study also found that straw produced a positive priming effect, meaning it stimulated microbes to decompose not only the added straw but also existing native soil carbon. In contrast, biochar produced a negative priming effect, reducing the loss of native soil carbon.
This difference translated into sharply different carbon sequestration efficiencies. At the end of the incubation, straw achieved a carbon sequestration efficiency of 22.8%, while biochar reached 99.7%.
The microbial explanation lies in the contrast between fast and slow life-history strategies. Straw provides easily available carbon and nutrients, stimulating fast-growing r-strategist microbes such as Mortierellomycota and Firmicutes. These microbes accelerate decomposition and help build both particulate and mineral-associated carbon, but they also drive higher carbon dioxide emissions and native soil carbon mineralization.
Biochar, by comparison, is more chemically resistant and contains less easily available energy. It shifted microbial activity toward slow-growing K-strategist microbes, including Actinobacteriota and Chloroflexi. These microbes were linked with greater formation of stable mineral-associated organic carbon, partly through bacterial necromass, or the remains of microbial cells that can bind with soil minerals and contribute to long-term carbon storage.
The study also found that straw strongly stimulated several soil enzymes involved in carbon, nitrogen, and phosphorus cycling, while biochar had a more selective effect. This suggests that straw drives rapid microbial activity and short-term carbon turnover, whereas biochar promotes a slower but more stable carbon pathway.
These findings offer practical guidance for rice-growing regions seeking to improve soil health and support climate-smart agriculture. Returning straw to fields can boost active soil carbon and nutrient cycling, but converting part of that straw into biochar may better support long-term carbon sequestration.
"Understanding how microbes respond to different carbon inputs helps us design better soil management strategies," Liu said. "For paddy agroecosystems, biochar amendment may be a powerful tool for increasing stable soil carbon while reducing unnecessary carbon loss."
The authors conclude that substrate quality is a key factor shaping microbial communities and determining whether added carbon is rapidly cycled or efficiently stabilized. By revealing the microbial mechanisms behind straw and biochar effects, the study provides a clearer foundation for optimizing organic amendments in agricultural soils.
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Journal Reference: Na, L., Liu, Y., Nan, Q. et al. Microbial life-history strategies mediate differential effects of straw and biochar amendments on soil POC/MAOC dynamics and SOC sequestration. Biochar 8, 118 (2026).
https://doi.org/10.1007/s42773-026-00630-y
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
