Microplastics undermine biochar's climate hero status: A new study reveals

Biochar, hailed as a climate change mitigation tool for its ability to reduce greenhouse gas emissions, may not be as effective as once thought when microplastics are in the picture. A new study investigates how polyethylene microplastics interact with aged biochar to affect carbon and nitrogen stability in Fluvic Cambisol soil, offering surprising results.

The research found that while aged biochar and polyethylene microplastics individually can reduce CO₂ emissions by 49% and 18% respectively over a 91-day period, their combined presence has a counterproductive effect. The coexistence of polyethylene actually diminishes the efficacy of biochar in mitigating CO₂ emissions by 44-82% and destabilizes microbial necromass carbon (MNC) by 18-23%.

This occurs because the interaction between polyethylene and biochar promotes the formation of macroaggregates and the accumulation of dissolved organic matter (DOM), while decreasing DOM aromaticity. This change boosts microbial biomass and chitinase activity, which are key in the decomposition of soil organic matter (SOM).

Furthermore, the study shows that aged biochar significantly reduces N₂O emissions by 54%, attributed to a decrease in nirK but an increase in nifH genes. Conversely, polyethylene increases N₂O emissions by 5% and 25% in biochar-free and aged biochar soil, respectively, likely by upregulating nirS and nirK but downregulating nifH gene expression.

This study serves as a wake-up call, indicating that polyethylene microplastics may undermine the climate change mitigation benefits of biochar. It underscores the critical need to consider microplastics as a global change factor and to integrate their role in elemental cycling alongside their global transport.

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Citation: Chen, Y., Wang, Z., Zhang, A. et al. Polyethylene microplastics hamper aged biochar’s potential in mitigating greenhouse gas emissions. Carbon Res. 4, 5 (2025). https://doi.org/10.1007/s44246-024-00170-9 

Title: Polyethylene microplastics hamper aged biochar’s potential in mitigating greenhouse gas emissions

Keywords: Microplastics; Aged biochar; Amino sugars; Dissolved organic matter; Greenhouse gas emission

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The journal Carbon Research is an international multidisciplinary platform for communicating advances in fundamental and applied research on natural and engineered carbonaceous materials that are associated with ecological and environmental functions, energy generation, and global change. It is a fully Open Access (OA) journal and the Article Publishing Charges (APC) are waived until Dec 31, 2025. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon functions around the world to deliver findings from this rapidly expanding field of science. The journal is currently indexed by Scopus and Ei Compendex, and as of June 2025, the dynamic CiteScore value is 15.4.