Biochar’s climate benefits may depend on microplastics in soil, study finds
image: Biochar-microplastics interaction modulates soil nitrous oxide emissions and microbial communities
Credit: Ziheng Zou, Qidong Yu, Runyu Chen, Jinyang Wang & Xueyan Liu
Microplastics are increasingly found in agricultural soils worldwide, raising new questions about how they interact with widely promoted climate solutions such as biochar. A study reveals that these tiny plastic particles can significantly alter how biochar affects soil health, greenhouse gas emissions, and microbial life.
Biochar, a carbon rich material produced from biomass, has been widely studied for its ability to improve soil fertility and reduce emissions of nitrous oxide, a potent greenhouse gas. However, the new research shows that its effectiveness is not universal and may depend strongly on the type of microplastics present in the soil.
“Biochar is often seen as a reliable tool for improving soil and mitigating climate change, but our results show that its performance can be modified by plastic pollution in ways we did not fully anticipate,” said the study’s corresponding author.
In a controlled greenhouse experiment, researchers grew coriander plants in soil treated with biochar and two common types of microplastics: conventional polyethylene and biodegradable polylactic acid. They then monitored plant growth, soil nitrogen cycling, microbial communities, and nitrous oxide emissions over time.
The results showed that biochar consistently boosted plant growth by increasing the availability of nitrogen in the form of ammonium. This positive effect occurred regardless of whether microplastics were present.
However, the impact on greenhouse gas emissions was more complex. Biochar alone reduced nitrous oxide emissions by about 16 percent. When microplastics were introduced, this reduction became less consistent and depended on the plastic type.
Polylactic acid, a biodegradable plastic often promoted as a sustainable alternative, reduced nitrous oxide emissions regardless of biochar addition. It did so by suppressing microbial processes responsible for nitrogen transformation in soil.
In contrast, polyethylene showed a very different pattern. Without biochar, it reduced emissions by inhibiting key microbial genes involved in nitrogen cycling. But when combined with biochar, this effect reversed. The interaction stimulated microbial activity linked to nitrogen transformation, leading to increased nitrous oxide emissions.
“These findings highlight that not all microplastics behave the same way in soil,” the authors explained. “Their chemical properties can shape microbial processes and ultimately determine whether biochar reduces or enhances emissions.”
The study also found that while overall microbial diversity remained stable, the composition of soil microbial communities shifted significantly under different treatments. These shifts were closely linked to changes in nitrogen cycling processes, which are critical for both plant nutrition and greenhouse gas production.
Microplastics are now recognized as a widespread contaminant in agricultural systems, largely due to plastic mulching, irrigation, and organic amendments. As these particles accumulate, they can alter soil structure, nutrient dynamics, and microbial habitats.
The findings suggest that plastic pollution may complicate efforts to use biochar as a climate mitigation strategy. In some cases, the presence of certain microplastics could weaken or even reverse the intended environmental benefits.
“Our work underscores the importance of considering real world soil conditions when evaluating sustainable agricultural practices,” the authors said. “Future strategies should account for the growing presence of microplastics in soil systems.”
As agriculture faces the dual challenge of increasing food production while reducing environmental impacts, understanding these complex interactions will be critical. The study provides new evidence that managing plastic pollution may be essential for maximizing the benefits of emerging climate solutions like biochar.
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Journal Reference: Zou, Z., Yu, Q., Chen, R. et al. Biochar-microplastics interaction modulates soil nitrous oxide emissions and microbial communities. Biochar 7, 15 (2025).
https://doi.org/10.1007/s42773-024-00413-3
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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.