Biochar is widely promoted as a tool for improving soil health and storing carbon. Yet its effects on soil carbon are not always consistent. New research published in Biochar shows that part of the explanation may lie in highly reactive molecules produced by persistent free radicals within biochar.
"Our findings show that biochar does more than simply add stable carbon to soil. Its reactive chemistry can influence the enzymes that control how quickly native soil carbon is decomposed," said corresponding author Shuping Qin. "Importantly, this protective effect varies substantially among different soils."
The researchers tested wheat-straw biochar in three contrasting Chinese soils: Fluvo-aquic soil, Black soil, and Red soil. They compared untreated biochar with biochar whose persistent free radicals had been chemically quenched. They also directly removed hydroxyl radicals from soil to determine their role in carbon cycling.
In Black and Red soils, untreated biochar reduced carbon dioxide emissions by 6.8% and 12.9%, respectively. When the biochar radicals were quenched, carbon dioxide emissions and the activities of key carbon-degrading enzymes increased. Directly removing hydroxyl radicals produced a similar response, increasing dissolved organic carbon, enzyme activity, and soil respiration while reducing soil organic carbon.
The results indicate that biochar-derived hydroxyl radicals can damage or suppress extracellular enzymes that microorganisms use to break down organic matter. This slows carbon mineralization and helps retain soil carbon in acidic, mineral-rich soils.
However, the pattern differed in Fluvo-aquic soil. There, biochar increased carbon dioxide emissions because the stimulation of microbial activity and decomposition outweighed enzyme suppression.
The findings highlight that biochar should not be managed as a one-size-fits-all soil amendment. Soil acidity, mineral composition, biochar feedstock, and production conditions may all determine whether biochar protects existing soil carbon or stimulates its loss.
The study provides a new chemical explanation for biochar's variable effects and supports the development of soil-specific biochar strategies for climate mitigation and sustainable agriculture.
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Journal Reference: Wu, P., Fu, Y., Wang, H. et al. Soil-specific protection of organic carbon by biochar-derived hydroxyl radicals associated with enzyme suppression. Biochar 8, 126 (2026).
https://doi.org/10.1007/s42773-026-00641-9
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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.
