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Small-sized biodegradable PLA microplastics inhibit plant nitrogen uptake by reshaping soil microbial communities and stimulating microbial metabolism
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"Biodegradable" plastics are often marketed as the eco-friendly alternative, but this study found that tiny fragments of PLA (a common compostable plastic) can actually make it harder for plants to get nitrogen from soil. This happens because soil microbes gobble up the broken-down plastic as food, then hoard the soil's nitrogen for themselves, leaving less for crops. Since nitrogen is essential for plant growth and food production, this suggests biodegradable plastic pollution in farmland could quietly undermine soil health and crop yields, an important consideration as these plastics become more common in agriculture.
The effects of microplastics (MPs) varying in polymer type and size on soil microbial community composition, metabolic functions, and nutrient cycling remain insufficiently understood. Here, we conducted a pot experiment using MPs differing in polymer type (non-biodegradable polyethylene [PE], and biodegradable polylactic acid [PLA]) and four particle sizes (1200-1400, 600-700, 120-150, and 25-38 μm), with amplicon sequencing, shotgun metagenomics, and nitrogen-15 (N) tracing model. Our results showed that small-sized PLA-MPs (25-38 μm) reduced bacterial diversity, destabilized microbial networks, and shifted community assembly toward deterministic processes, whereas PE-MPs and larger-sized PLA-MPs exerted minimal effects. This shift was associated with enhanced depolymerization-related enzymatic potential, accompanied by greater dissolved organic carbon (DOC) availability. The resulting increase in C availability stimulated central C metabolism, promoting microbial resource acquisition and biomass synthesis. To maintain microbial C:N homeostasis, microbial N assimilation was stimulated through ammonium (NH) assimilation mediated by the glutamate dehydrogenase (GDH) and glutamine synthetase-glutamate synthase (GS-GOGAT) pathways and nitrate (NO⁻) assimilation via assimilatory nitrate reduction to ammonium (ANRA). Consistently, the N tracing model revealed that microbial assimilation rates of NH-N and NO⁻-N increased by 10.5-fold and 12.7-fold, respectively, exceeding gross N mineralization rates, thereby depleting soil inorganic N pools and suppressing plant N uptake. Overall, our findings provide mechanistic insights into how PLA-MPs reshape soil functioning by reprogramming microbial communities and metabolism, thereby altering plant-microbe competition for N. These results highlight the potential risks of increasing biodegradable plastic inputs for cropland nutrient cycling and plant N acquisition.
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Biodegradable and conventional microplastics affect soil-plant systems through altering microbial community assembly and functions
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"Biodegradable" plastics are often marketed as the eco-friendly choice, but this study found that when they break down into microplastics in soil, they actually harm plant growth and soil health more than regular plastics like polyethylene do, by disrupting the soil bacteria that plants depend on for nutrients. This matters because these microplastics could end up in the crops we eat, and it suggests that switching to "biodegradable" plastics isn't automatically a safer bet for our food supply without more research into how they actually break down in real farm soil.
Microplastic induces microbial nitrogen limitation further alters microbial nitrogentransformation: Insights from metagenomic analysis
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Researchers studied how both conventional and biodegradable microplastics affect nitrogen cycling in soil over 120 days. They found that biodegradable microplastics significantly disrupted microbial nitrogen processes by acting as a carbon source that shifted bacterial communities toward nitrogen-fixing species. The findings suggest that even biodegradable plastics in soil can alter nutrient availability in ways that may affect soil fertility and plant growth.
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
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Scientists found that biodegradable plastic particles (PLA, often used in "eco-friendly" packaging) can actually cause peas to absorb more cadmium—a toxic heavy metal—from contaminated soil, with smaller plastic particles making the problem worse. This matters because as microplastics and industrial pollutants increasingly mix in farm soils, this research suggests "biodegradable" plastics aren't automatically safer and could inadvertently increase toxic metal contamination in the food we eat.
Biodegradable microplastics impact on soil: how poly-3-hydroxybutyrate alters microbial diversity and nitrogen mineralization processes
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Researchers found that biodegradable plastic made from poly-3-hydroxybutyrate (P3HB), when present as microplastics in soil, disrupts the microbial communities that cycle nitrogen — reducing the availability of nitrate that plants need to grow, which contributed to stunted maize growth in pot experiments. The findings suggest that even biodegradable plastics can harm soil health when they break down into microplastic particles.
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