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Biodegradable polylactic acid microplastics affect nutrient cycling during the entire crop growth cycle: Implications for soil ecosystem multifunctionality
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"Biodegradable" plastics, often marketed as an eco-friendly alternative, still disrupt soil health when they break down into microplastics in farm fields, according to new research. Scientists found these particles threw off the balance of soil bacteria and nutrients over an entire corn growing season—boosting carbon but reducing nitrogen and phosphorus, key nutrients crops need to grow. Since soil health directly affects crop quality and the food we eat, this suggests "biodegradable" plastics used in farming (like mulch films) may not be as harmless as assumed and deserve more scrutiny before widespread use.
While microplastics (MPs) have been extensively studied for their effects on soil nutrient cycling, their influence on ecosystem multifunctionality (EMF) across the entire crop growth cycle remains poorly understood. This study systematically investigated the impacts of a model biodegradable MP, polylactic acid (PLA), on soil microbiomes and EMF across different maize incubation periods. Results of 16S rRNA amplicon sequencing and metagenomic analysis revealed that PLA-MPs decreased bacterial community α-diversity, co-occurrence network complexity, and stability throughout the 120-day incubation period. Particularly, PLA-MPs exerted more pronounced effects at early incubation stages (30 and 60 days), and these effects were intensified with increasing PLA-MP concentrations. PLA-MPs suppressed anaerobic carbon fixation (porA, porB, frda) and pyruvate metabolism (ppdk), while promoting fermentation (L-lactate dehydrogenase), nitrogen fixation (nifD, nifH, nifK, anfG), and microbial phosphorus (P) acquisition (phoD, phn cluster). Over the entire incubation period, PLA-MP-induced shifts in nutrient cycling enhanced soil carbon (C) function by 37.6-569%, while decreasing nitrogen (N) and P functions by 8.40-22.4% and 16.8-56.2%, respectively. Path analysis revealed that PLA-MPs altered soil properties and bacterial community diversity, which in turn regulated functional genes and these individual soil functions, thereby reducing EMF by 2.05-27.0% (R = 0.923), with bacterial community diversity as the primary driver of EMF (standardized path coefficient of 0.978). These findings underscore the impacts of PLA-MPs on EMF in the soil-crop system throughout the entire maize growth cycle, advancing the understanding of the agroecological safety of biodegradable MPs.
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Effect of polylactic acid microplastics on soil properties, soil microbials and plant growth
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Researchers tested whether microplastics from biodegradable polylactic acid plastic, often proposed as an eco-friendly alternative to conventional plastic, affect soil health and plant growth. High concentrations of these biodegradable microplastics reduced soil pH, altered the ratio of carbon to nitrogen, decreased plant growth, and shifted soil microbial communities. The study suggests that even biodegradable plastics can negatively affect agricultural ecosystems when they break down into microplastic-sized particles.
Polyethylene and Polylactic Acid Microplastics Reshape Soil Phosphorus Cycling by Modulating Microbial Function and Aggregate Stability in Maize‐Growing Soil
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Tiny plastic particles from farm plastics and packaging waste—both regular plastic (polyethylene) and "biodegradable" plastic (PLA)—are building up in soil and messing with how crops get phosphorus, an essential nutrient plants need to grow. In this study, both types of microplastics reduced available phosphorus in soil and stunted corn growth, even though the plastics also changed soil structure and shifted which microbes were present. This matters because it suggests that even "eco-friendly" plastics aren't necessarily harmless to farmland, and disruptions to soil health could eventually affect crop yields and food production
Biodegradable microplastics decreased plant-derived and increased microbial-derived carbon formation in soil: a two-year field trial
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A two-year field experiment compared the effects of conventional (polypropylene) and biodegradable (polylactic acid, PLA) microplastics on soil carbon cycling in agricultural soil. Researchers found that while neither plastic type changed total soil carbon levels, PLA microplastics significantly reduced plant-derived carbon (lignin) by 32% while boosting microbial-derived carbon, suggesting that "biodegradable" plastics still meaningfully alter soil biology and chemistry. This matters because it challenges the assumption that biodegradable plastics are environmentally benign once they break down in farmland.
Chlorpyrifos degradation and its impacts on phosphorus bioavailability in microplastic-contaminated soil
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This study found that microplastics made from polylactic acid (a biodegradable plastic) in soil changed how the pesticide chlorpyrifos breaks down and altered the availability of phosphorus, a key nutrient for crops. The microplastics slowed pesticide degradation and affected soil enzyme activity, which could impact both food safety and crop nutrition. The findings show that even biodegradable microplastics can disrupt important soil processes that affect the food supply.
Conventional and Biodegradable Microplastics Both Impair Soil Phosphorus Cycling and Availability via Microbial Suppression
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Researchers conducted a 150-day experiment comparing the effects of conventional polyethylene and biodegradable polylactic acid microplastics on soil phosphorus cycling. Both types of microplastics reduced available phosphorus by approximately 15% and suppressed key phosphorus-cycling bacteria and enzyme activity. The findings challenge the assumption that biodegradable plastics are environmentally benign, showing they disrupt soil nutrient cycles similarly to conventional plastics.
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