Black carbon from wheat straw burning shown to curb antibiotic resistance spread in farmlands with plastic mulch residues

A new study published in New Contaminants reveals that black carbon formed during wheat straw burning can significantly reduce the spread of antibiotic resistance genes in soil and soybean crops, offering a promising strategy for safer and more sustainable farming in regions burdened by plastic mulch debris.

Every year, millions of hectares of farmland accumulate fragments of polyethylene and biodegradable mulch films. These residues gradually break down into microplastics that reshape soil chemistry, disrupt microbial communities, and accelerate the proliferation and movement of antibiotic resistance genes. This process increases the risk that crop plants will carry antibiotic resistant bacteria onto dinner plates.

In many farming regions, particularly remote areas of China, straw burning remains a common practice due to narrow planting windows and limited agricultural infrastructure. Burning produces black carbon rich ash that mixes with surface soil. Although typically linked with air pollution concerns, black carbon may play an overlooked role in soil health. Until now, however, its influence on antibiotic resistance in fields contaminated with plastic mulch had never been clarified.

To address this knowledge gap, researchers led by Manman Cao and Shuai Ma investigated how two types of plastic mulch residues, polyethylene and a biodegradable film, interact with black carbon produced either through direct straw burning or added as an external material. The team tracked antibiotic resistance genes across soil, roots, leaves, and soybean seeds from early growth through maturity. They also examined how bacterial communities responded to these combined stressors.

The findings were striking. While mulch film residues alone increased soil antibiotic resistance gene abundance by up to 38 percent within only fifteen days, the presence of black carbon reversed these effects. In soils containing polyethylene or biodegradable film residues, black carbon treatments lowered antibiotic resistance gene levels by 30 to nearly 50 percent during early incubation. As soybeans matured, black carbon continued to suppress antibiotic resistance in non rhizosphere soil, rhizosphere soil, root surfaces, leaves, and even seeds. In some cases, reductions reached more than 90 percent in plant tissues.

“Black carbon created by straw burning is often viewed only as a source of environmental risk, but our study shows that it can also provide important benefits,” said Fei Wang, corresponding author of the study. “By changing soil chemistry, reshaping microbial communities, and altering the surface properties of mulch film fragments, black carbon slows the movement of antibiotic resistance genes from soil into crops. This offers a practical pathway to reduce agricultural antibiotic resistance in regions where mulch film pollution is common.”

Importantly, the team found that although straw burning initially disturbed soil microbes, the microbial communities recovered fully within three months and did not experience long term harm. At the same time, black carbon altered nutrient availability and modified the physical and chemical aging of mulch films, which contributed to reduced gene transfer.

These findings suggest that black carbon has potential as a natural and scalable tool for agricultural management. As the global threat of antibiotic resistance grows, strategies that suppress its spread through soil and food systems are urgently needed.

“Given the vast areas of farmland where straw burning and mulch film residues coexist, understanding their interactions is essential,” Wang added. “Our results provide a scientific basis for using black carbon more thoughtfully to protect soil health, crop safety, and public health.”

The authors note that future studies should evaluate long term crop rotation systems and environmental conditions to optimize black carbon applications across diverse agricultural landscapes.

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Journal reference: Cao M, Ma S, Wang F, Yuan X, Bashir S, et al. 2025. Black carbon derived from wheat straw burning mitigates antibiotic resistance gene dissemination in soil-crop systems under polyethylene and biodegradable plastic mulch film residues. New Contaminants 1: e013  

https://www.maxapress.com/article/doi/10.48130/newcontam-0025-0013  

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About the Journal:

New Contaminants is an open-access journal focusing on research related to emerging pollutants and their remediation.

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