Microplastic diversity boosts greenhouse-gas-producing soil microbes

Soils with a variety of microplastics may allow microbes that perform denitrification processes to thrive; this could cause soils to lose nitrogen while the microbes produce nitrous oxide, a greenhouse gas nearly 300 times as potent as carbon dioxide (Environ. Sci. Technol. 2025, DOI: 10.1021/acs.est.5c04981).

Microplastics have been heavily investigated for potential effects on organisms or ecosystems, but most studies have focused on one type of microplastic at a time. In real-world environments, microplastics seldom occur in isolation, observed Yi-Fei Wang and Dong Zhu of the Institute of Urban Environment at the Chinese Academy of Sciences. For example, the use of agricultural plastics, fertilizer packaging, or biosolids sludge introduces a wide variety of microplastics to croplands: one survey of microplastics in soils collected from orchards and vegetable and paddy fields in southern China found 32 types of plastics.

To investigate the effects that microplastics might exert in combination, Wang, Zhu, and their colleagues cultivated microorganisms in soils containing low concentrations of microplastics. The soil mixtures contained zero, one, three, or five different types of microplastics.

After 40 days, the researchers measured higher soil pH, higher soil organic carbon, and lower available nitrogen in the soils that contained five types of microplastics compared with the soils that had one or three. Analysis of DNA extracted from the soils revealed that genes involved in nitrogen cycling processes—such as the reduction of nitrate and nitric oxide—became more abundant in the microbial communities exposed to more microplastic types. The researchers also found that with increasing microplastic diversity, communities shifted in favor of microbes known to perform denitrification—in particular, the Rhodocyclaceae family of bacteria.

The researchers have not yet measured greenhouse gas emissions from the soils. They plan to do so in further experiments to better link microplastic diversity to denitrification and nitrous oxide production. “If microbial denitrification is accelerated, the consequences are twofold,” Zhu said in an email. As soil loses nitrogen more quickly, fertilizer becomes less efficient; an increase in production of nitrous oxide could also exacerbate climate change, he explained.

The researchers also plan to perform longer-term experiments to observe any other effects that have yet to become apparent from soil bacteria’s exposure to microplastics.