A new study suggests that cadmium contamination, despite its well-known environmental toxicity, may enhance the ability of biochar to retain carbon in soil. The findings reveal an unexpected interaction between heavy metal pollution and soil carbon cycling, with implications for the use of biochar in contaminated agricultural soils.
"Our results show that cadmium can strengthen biochar-based carbon sequestration through both chemical stabilization and microbial inhibition," said the study authors. "This interaction suggests that biochar may provide simultaneous benefits for heavy metal remediation and carbon retention in contaminated soils."
The researchers conducted a 60-day soil incubation experiment using carbon isotope tracing to distinguish carbon dioxide released from native soil organic carbon from that derived from biochar. Soils were exposed to different cadmium concentrations, with or without biochar amendment.
The results showed that increasing cadmium concentrations reduced the mineralization of both native soil carbon and biochar. At medium and high cadmium levels, mineralization of native soil organic carbon in biochar-amended soils decreased by 37.3% and 43.4%, respectively. Biochar mineralization also declined by 5.8% to 30.0% as cadmium concentrations increased.
The researchers identified two main mechanisms behind this effect. First, cadmium ions acted as cation bridges, linking biochar with dissolved organic carbon and increasing carbon adsorption. Molecular calculations supported the formation of Cd-mediated bonds between oxygen-containing groups on biochar and organic matter. Cadmium also promoted the formation of larger soil aggregates, which can physically protect organic carbon from decomposition.
Second, cadmium accumulated on biochar surfaces and suppressed microorganisms living directly on the biochar particles. Microbial biomass carbon on biochar decreased from 211.6 to 137.0 mg kg⁻¹ as cadmium exposure increased, accompanied by declines in several microbial groups associated with the decomposition of resistant organic matter.
Together, these processes shifted biochar's effect on soil carbon from positive toward negative priming, reducing overall carbon mineralization.
The findings reveal a potential win-win interaction in which biochar helps immobilize cadmium while cadmium, in turn, increases biochar-associated carbon retention. The authors caution, however, that the study was conducted under controlled laboratory conditions for 60 days. Longer-term field studies will be needed to determine whether these mechanisms persist in real agricultural environments.
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Journal reference: Nie H, Shen C, Han X, Lai Z, Chen M, et al. 2026. Cadmium enhances biochar-based carbon sequestration in soils via cation bridging and microbial toxicity. Biochar X 2: e019 doi: 10.48130/bchax-0026-0016
https://www.maxapress.com/article/doi/10.48130/bchax-0026-0016
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About the Journal:
Biochar X (e-ISSN: 3070-1686) is an open access, online-only journal aims to transcend traditional disciplinary boundaries by providing a multidisciplinary platform for the exchange of cutting-edge research in both fundamental and applied aspects of biochar. The journal is dedicated to supporting the global biochar research community by offering an innovative, efficient, and professional outlet for sharing new findings and perspectives. Its core focus lies in the discovery of novel insights and the development of emerging applications in the rapidly growing field of biochar science.
