Biodegradable microplastics, often promoted as eco-friendly alternatives to traditional plastics, are now revealing an unexpected side. A groundbreaking study published on August 22, 2025, in Carbon Research shows that these “green” plastics can significantly reshape how carbon is stored and cycled in agricultural soils.
The research was co-led by Dr. Jie Zhou from the College of Agriculture at Nanjing Agricultural University, China, and Dr. Davey L. Jones from the School of Environmental and Natural Sciences at Bangor University, UK. Their collaboration bridges expertise in soil science, microbiology, and climate resilience, marking a milestone in international environmental research.
The Study: Testing Biodegradable vs. Conventional Plastics
The team examined how polylactic acid (PLA) is a widely used biodegradable plastic. They also looked at polypropylene (PP), which is a common conventional plastic. These plastics influence soil organic carbon (SOC) in real-world farming conditions.
Both materials were added to topsoil at realistic concentrations (0.2% w/w), while a control plot remained unamended. Interestingly, while neither plastic changed the overall carbon content in the soil, their effects on carbon composition and microbial activity were strikingly different.
The Biodegradable Paradox: When “Eco” Plastics Complicate Soil Health
PLA, the supposed environmentally friendly option, had the strongest and most complex impact on soil carbon chemistry. It reduced plant-derived lignin in the soil by 32%, suggesting that fewer stable carbon compounds from plant residues were preserved.
The reason lies in microbial behavior. PLA attracts K-strategist microbes, slow-growing organisms that excel at breaking down tough, carbon-rich materials like lignin. “These microbes see PLA as a feast,” explained Dr. Zhou. “But in doing so, they increase production of enzymes. These enzymes degrade other resistant carbon compounds, including those vital for long-term carbon storage.”
Despite reducing plant carbon, PLA increased microbial necromass, the remains of dead microbes, by 35%. This shift came with a rise in microbial diversity (+5.3%) and network complexity (+11%), resulting in a more resilient microbial community.
Fungi benefited the most. Under PLA, fungal necromass accounted for 24% of total soil carbon, compared to only 11% under PP. Fungi use PLA as a food source and help stabilize soil aggregates, which physically protect carbon from decomposition.
The Nitrogen Trap: Microbes Starved by Biodegradable Plastics
However, the study also found a critical downside. PLA contains plenty of carbon but very little nitrogen, creating an imbalance that triggers microbial nitrogen limitation. To adapt, microbes began breaking down their own biomass, specifically bacterial necromass, which fell by 19%.
“There’s clear evidence that microbes start cannibalizing their own kind to survive,” said Dr. Jones. “It’s a short-term strategy, but it could undermine long-term soil fertility and the stability of stored carbon.”
This nitrogen trap could have cascading effects on soil health, reducing nutrient availability and weakening the capacity of agricultural soils to store carbon sustainably.
Conventional Plastic: Starving the Soil Instead of Feeding It
Polypropylene (PP), on the other hand, told a different story. Rather than stimulating microbial activity, PP suppressed it. The material’s chemical additives leached into the soil, reducing microbial growth and lowering necromass production, a key pathway for carbon sequestration.
“PP doesn’t feed the soil—it starves it,” noted Dr. Jones. “It’s like putting a plastic blanket over a garden; nothing thrives underneath.”
This stagnation limits soil’s ability to generate and stabilize organic matter, gradually weakening its fertility and carbon storage potential.
Why Soil Carbon Balance Matters for Climate
Soil is the second-largest carbon sink on the planet, storing more carbon than all of Earth’s vegetation combined. How that carbon is stored—whether as stable plant compounds or as microbial remains—determines how long it stays locked away instead of returning to the atmosphere as CO₂.
This study highlights that even biodegradable plastics can alter that delicate balance, shifting carbon storage from plant-based to microbe-based forms. The long-term consequences of this shift are uncertain but could affect both soil health and global climate regulation.
“We can’t assume that biodegradable means harmless,” warned Dr. Zhou. “These materials interact with soil ecosystems in ways we’re only beginning to understand.”
A Global Collaboration for Soil Science
The partnership between Nanjing Agricultural University and Bangor University underscores the importance of international cooperation in environmental research.
Dr. Zhou’s expertise in soil biogeochemistry and Dr. Jones’s background in microbial ecology made this one of the most comprehensive field studies yet on the impact of microplastics on soil carbon dynamics. Both institutions are recognized leaders in sustainability and environmental science, pushing forward research that connects agriculture, climate, and ecology.
Rethinking the Future of Agricultural Plastics
From mulching films to seed coatings and irrigation systems, plastics are deeply integrated into modern farming. As global agriculture transitions toward biodegradable materials to reduce plastic pollution, this study serves as a critical warning.
“Biodegradable plastics aren’t a silver bullet,” said Dr. Zhou. “We need to design them not only to decompose but to decompose in ways that support soil ecosystems rather than disrupt them.”
The researchers call for smarter material design, improved regulations, and deeper study of soil–plastic interactions. Understanding how these materials behave in complex soil environments will be vital for sustainable agriculture and climate mitigation.
The Takeaway: Beneath the Surface, the Story Is Complicated
This study reveals that the term “biodegradable” doesn’t always mean “benign.” Even as these plastics break down, they trigger subtle yet profound shifts in soil chemistry and microbial ecology.
As Dr. Jones summarized, “We’re learning that in soil, the truth is buried deeper than the plastic itself.” Thanks to the work of Dr. Zhou, Dr. Jones, and their team, the world is one step closer to understanding how to protect the planet’s most vital carbon sink—its soil.
