Biodegradable Plastics May Be Worse for the Climate Than Conventional Ones, Soil Study Finds

Biodegradable plastics have long been marketed as the environmentally responsible alternative to conventional polymers, a way to keep agriculture productive without saddling the planet with centuries of persistent plastic waste. But a new laboratory study from China’s Loess Plateau suggests that the story is far more complicated, and potentially far more troubling, than the label implies. Researchers at Northwest A&F University, working with colleagues in Spain, have found that when biodegradable polylactic acid, or PLA, microplastics are mixed into orchard soil, the soil dramatically ramps up its emissions of two potent greenhouse gases, carbon dioxide and nitrous oxide. Conventional plastics such as polyethylene and polyethylene terephthalate, the workhorses of mulch films and packaging, actually suppressed those same emissions in the same experiment. The findings, published in the journal Plant and Soil, expose an uncomfortable trade-off at the heart of the bioplastics revolution: what is good for the soil’s long-term plastic burden may be bad for the climate in the short term.

The Loess Plateau is China’s apple heartland, a vast semi-arid region where intensive fruit production depends heavily on agricultural plastics, from mulch films that conserve precious soil moisture to bags, nets, and tubing used throughout the growing season. Decades of this practice have left orchard soils laced with microplastic fragments, tiny particles that break off from larger plastic items as they weather in the sun and are tilled into the ground. Previous surveys have documented substantial microplastic accumulation across the region’s agricultural land, yet the consequences for soil ecology, and in particular for the fluxes of greenhouse gases that soils exhale, remained poorly understood. Because soils are simultaneously one of the planet’s largest carbon reservoirs and a major source of nitrous oxide, a greenhouse gas nearly 300 times more powerful than carbon dioxide at trapping heat over a century, any pollutant that alters soil microbial metabolism has the potential to shift the climate equation.

To probe that question, the research team carried out a 60-day laboratory incubation experiment using soil collected from Loess Plateau orchards. They amended the soil with microplastics of three chemically distinct types, biodegradable PLA alongside conventional polyethylene, known as PE, and polyethylene terephthalate, known as PET, each added at a concentration of 0.5 percent by weight, a level designed to reflect heavily contaminated agricultural soils. Over the two-month incubation, the researchers tracked the cumulative release of carbon dioxide and nitrous oxide from each treatment, then sequenced the soil’s microbial communities and measured a suite of soil physicochemical properties to piece together the mechanisms behind the observed gas fluxes.

The results were strikingly asymmetric. Soils treated with PLA emitted 190.7 percent more cumulative carbon dioxide than the untreated control, nearly tripling the soil’s respiratory output, and 12.3 percent more nitrous oxide. The conventional plastics moved in the opposite direction. Polyethylene reduced cumulative carbon dioxide emissions by 12.4 percent and nitrous oxide emissions by 49.1 percent, while PET cut carbon dioxide by 15.8 percent and nitrous oxide by 36.5 percent. In other words, the plastic that microbes can digest supercharged the soil’s greenhouse gas output, while the plastics they cannot digest appeared to dampen it. For anyone who has assumed that switching to biodegradable mulch is an unambiguous climate win, the numbers are a sobering corrective.

The explanation lies in what the microbes did. PLA is a polymer built from lactic acid units, an organic molecule that soil microorganisms can metabolize as a carbon and energy source. When PLA particles entered the soil, bacterial diversity measurably declined and the overall community structure shifted, with the relative abundances of Actinobacteria and Proteobacteria, two bacterial phyla rich in polymer-degrading specialists, increasing significantly, along with the fungal phylum Ascomycota. These organisms effectively treated the plastic as food, oxidizing its carbon into carbon dioxide and, in the process, altering the nitrogen transformations that produce nitrous oxide. The conventional plastics, by contrast, are chemically inert on these timescales, and their addition left the microbial community largely untouched, with minimal impact on diversity or composition.

To untangle cause from correlation, the team applied a partial least squares structural equation model, a statistical framework that can quantify direct and indirect pathways of influence. The analysis showed that microplastics shaped the greenhouse gas fluxes both directly and indirectly, with the indirect route operating through changes in soil physicochemical properties that in turn restructured the microbial community. Complementary Mantel tests and redundancy analysis, two methods for linking community data to environmental variables, converged on a single conclusion: microbial activity is the primary regulator of both carbon dioxide and nitrous oxide emissions in these soils. The gases are, in essence, a metabolic fingerprint of the microbial assemblage that the plastic particles cultivate or suppress.

The study fits into a growing body of evidence that biodegradable and conventional microplastics are not interchangeable in their ecological effects. Recent work on lake sediments has found that biodegradable plastics aggravate greenhouse gas emissions more severely than conventional ones, and field experiments in barley systems have documented divergent responses of nitrous oxide fluxes and microbial communities to the two plastic classes. Researchers have also described the so-called microplastisphere, the distinctive microbial biofilm that forms on plastic surfaces in soil, which for degradable polymers becomes an active zone of enzymatic breakdown. At the same time, other studies have reported that biodegradable mulch films can degrade more slowly than expected in the field, complicating simple narratives in either direction. The new orchard soil results add a semi-arid, fruit-production context to this emerging picture.

The authors are careful to frame the trade-off honestly. PLA’s biodegradability is genuinely advantageous in one crucial respect: it does not persist in soil for centuries the way polyethylene does, and it therefore reduces the burden of long-term plastic contamination. But the same degradability means the polymer’s carbon enters the active biological cycle almost immediately, fueling microbial respiration and nitrogen transformations that vent greenhouse gases to the atmosphere. Conventional microplastics, by contrast, contribute to long-term soil contamination while leaving the soil’s carbon and nitrogen metabolism comparatively undisturbed, at least over the timescales examined here. Neither outcome is desirable, and the study does not suggest that conventional plastics are environmentally benign. It instead highlights that the environmental profile of a plastic depends on which harm you weigh most heavily: persistence in the ground or emissions into the air.

There are important caveats to keep in mind. The experiment was conducted in the laboratory over 60 days at a single microplastic concentration, and real orchard soils experience fluctuating temperatures, wetting and drying cycles, plant roots, and management interventions that can amplify or mute microbial responses. The 0.5 percent dosing rate represents a heavily contaminated scenario rather than a typical field average, although such concentrations are plausible in long-term mulched orchards. Whether the PLA-driven emission surge persists as the polymer fully degrades, or whether it is a transient pulse confined to the early stages of breakdown, remains an open question that longer-term and field-scale studies will need to answer.

Even with those limitations, the findings arrive at a consequential moment. Global plastic production continues to climb, agriculture remains one of the largest direct users of plastic film, and governments and retailers are increasingly mandating or encouraging a shift toward biodegradable alternatives. If those alternatives systematically raise soil greenhouse gas emissions in the regions where they are deployed, the net climate benefit of the transition could be far smaller than assumed, or in the worst case negative. The Loess Plateau study suggests that the next generation of bioplastic policy will need to look beyond the persistence question and ask a harder one: what does the material do once the microbes get hold of it? For the apple orchards of semi-arid China, and perhaps for farmland everywhere, the answer may determine whether biodegradable plastics are a climate solution or an overlooked source of warming.

Subject of Research: Effects of biodegradable and conventional microplastics on greenhouse gas emissions and microbial communities in Loess Plateau orchard soils

Article Title: Comparative effects of conventional and biodegradable microplastics on greenhouse gas emissions from Loess Plateau orchard soils

Article References: Tong, X., Meng, X., Wang, W., Zhang, L., Zhang, Q., Peñuelas, J., Zhu, Y., & Zhang, M. (2026). Comparative effects of conventional and biodegradable microplastics on greenhouse gas emissions from Loess Plateau orchard soils. Plant and Soil. https://doi.org/10.1007/s11104-026-09110-5

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09110-5

Keywords: microplastics, biodegradable plastics, PLA, polyethylene, greenhouse gas emissions, nitrous oxide, carbon dioxide, soil microbiome, Loess Plateau, orchard soil, agriculture, Plant and Soil