Beneath the charming fields and productive farmland, where roots entwine and microbial life thrives, an unseen drama is reshaping the very foundation of soil health. A groundbreaking two-year field trial has revealed that biodegradable microplastics—once hailed as the sustainable alternatives to conventional plastics—are exerting profound and unexpected effects on soil organic carbon dynamics. Published on August 22, 2025, in the open-access journal Carbon Research, this international collaboration between scientists at Nanjing Agricultural University, China, and Bangor University, UK, uncovers a paradox in the soil’s response to these emerging pollutants.
The study focuses on two widely used plastic types: polypropylene (PP), a conventional plastic staple in agriculture, and polylactic acid (PLA), a biodegradable polymer derived from renewable resources. Both were introduced into agricultural topsoil at realistic concentrations and observed over two agricultural cycles. While neither plastic type altered the total soil organic carbon (SOC) content, the intricate balance of the carbon’s origin and stabilization pathways shifted dramatically, illuminating complex microbial interactions hitherto unappreciated.
Contrary to common assumptions, the biodegradable plastic PLA exhibited the most pronounced impact on the soil carbon composition. By reducing plant-derived lignin—a resistant polymer derived from roots and crop residues—by a striking 32%, PLA interrupted one of soil carbon sequestration’s most stable components. This shift was attributed to the proliferation of specialized microbes known as K-strategists, organisms adept at metabolizing complex carbon structures but slow-growing and efficient in resource use. These microbes treat PLA as a carbon-rich resource buffet, enhancing enzymatic activity that inadvertently accelerates the breakdown of recalcitrant lignin, thereby potentially destabilizing long-term carbon storage.
Yet this microbial feast is not without compensations. The PLA-enriched soils showed a remarkable 35% increase in microbial necromass, the dead microbial biomass critical for forming stable soil organic matter. The boost in microbial diversity (a 5.3% rise) and the emergence of more complex microbial networks (up by 11%) point to a more dynamic and resilient soil ecosystem under PLA influence. Intriguingly, fungal necromass emerged as the dominant contributor to SOC, composing nearly a quarter of the total soil carbon, compared to a mere 11% under PP treatment. Fungi, as it turns out, flourish on PLA substrates and assist in generating stable soil macroaggregates that physically shield carbon from microbial decomposition.
However, this microbial paradise carries a hidden cost linked with nutrient stoichiometry: the PLA, abundant in carbon yet deficient in nitrogen, induces microbial nitrogen limitation. This imbalance forces soil microbes to cannibalize their own biomass, as demonstrated by a 19% decline in bacterial necromass and a worrying negative correlation between bacterial remains and nitrogen-scavenging enzyme activity. Such nitrogen starvation reflects microbes’ desperate survival strategy but raises questions about soil fertility, microbial community resilience, and the stability of microbial-derived carbon pools over extended times.
In stark contrast, polypropylene (PP) imposed a different form of soil toxicity. Rather than fueling microbial metabolism, PP suppressed microbial growth by limiting accessible carbon sources and leaching toxic additives. This led to a significant decrease in microbial necromass synthesis, thereby undermining one of soil’s natural carbon stabilization pathways. The metaphor of PP acting as a “blanketing layer over a garden” aptly captures its suppressive effect on soil microbial growth and soil vitality, effectively starving the ecosystem beneath.
Soil’s role as Earth’s second-largest carbon reservoir makes these findings especially significant. The origin and form of soil organic carbon—whether from sturdy plant residues or microbial biomass—determines its resistance to decomposition and therefore its capacity to serve as a long-term carbon sink mitigating climate change. This research warns against simplistic assumptions that biodegradable plastics inherently safeguard soil carbon sequestration. Instead, it exposes a nuanced reality: biodegradable plastics may rewire soil microbial pathways, shifting carbon pools with ambiguous consequences for climate resilience.
The study exemplifies the power of international scientific collaboration, weaving together expertise in soil biogeochemistry and microbial ecology to illuminate the subterranean impact of agricultural plastics. At the College of Agriculture within Nanjing Agricultural University, cutting-edge approaches to sustainable farming are being paired with Bangor University’s leadership in ecosystem science to address one of today’s most urgent environmental challenges. The joined perspectives of Dr. Jie Zhou and Dr. Davey L. Jones have produced one of the most thorough field-based assessments of microplastic effects on soil carbon dynamics, marking a leap forward in both soil science and environmental stewardship.
Agricultural plastics, from mulching films to irrigation components, permeate modern farming, boosting productivity but accumulating pollution risks. While the drive to biodegradable plastics aims to curtail environmental damage, this study becomes a pivotal reality check, emphasizing the need for deeper material design considerations. Biodegradability alone is insufficient; plastics must degrade in manners that harmonize with soil microbial communities and uphold soil health rather than disrupt it.
The implications extend beyond soil chemistry into broader agroecological and planetary health. If biodegradable plastics reconfigure soil carbon and microbial networks in unforeseen ways, there could be cascading effects on crop productivity, nutrient cycling, and greenhouse gas emissions. Designing future plastics demands integrating soil biological knowledge, fostering materials that support mutualistic microbial functions while minimizing adverse biochemical feedback.
This trial’s findings prompt urgent questions about current agricultural practices, regulatory frameworks, and innovation trajectories. Can biodegradable plastics be engineered to balance carbon and nitrogen to prevent microbial starvation? How might soil microbial community monitoring become a standard component of evaluating agricultural inputs? The answers will shape the next generation of sustainable farming and climate mitigation strategies.
Ultimately, this pioneering research underscores a vital truth: the concept of “biodegradable” masks layers of ecological complexity beneath the soil surface. As Dr. Zhou cautions, the decomposition of plastics within living soil systems influences processes far beyond mere breakdown rates. Understanding these intricate interactions is essential to align technological innovations with the resilience of the Earth’s foundational ecosystems. Thanks to this impactful collaboration and commitment to field-based evidence, we are now closer to unearthing the full story of plastics in our soils.
Subject of Research: Not applicable
Article Title: Biodegradable microplastics decreased plant-derived and increased microbial-derived carbon formation in soil: a two-year field trial
News Publication Date: 22-Aug-2025
Web References: http://dx.doi.org/10.1007/s44246-025-00231-7
References: Guo, X., Zhang, W., Lu, Y. et al. Biodegradable microplastics decreased plant-derived and increased microbial-derived carbon formation in soil: a two-year field trial. Carbon Res. 4, 61 (2025).
Image Credits: Xinhu Guo, Wentao Zhang, Yingxin Lu, Haishui Yang, Lingling Shi, Feng-Min Li, Jie Zhou & Davey L. Jones
Keywords: Microplastic; Soil organic carbon; Plant lignin; Microbial necromass; Microbial life strategy
