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Addition of inorganic nitrogen significantly increases the real and apparent priming effects of polyethylene and PHBV microplastics in soil
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Researchers compared the effects of conventional polyethylene and biodegradable PHBV microplastics on soil organic matter turnover through priming effect experiments. Both MP types altered priming effects on native soil carbon and microbial biomass, with PHBV causing greater stimulation of microbial activity due to providing additional organic carbon.
Plastic mulch films (PMFs) enhance crop productivity but degrade into microplastics, raising concerns about their effects on soil health. This study compared the effect of conventional polyethylene (PE) and biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) microplastics on soil organic matter (SOM) turnover through real (native SOM) and apparent (microbial biomass) priming effects. Using 14C-labelled assays, we assessed three microplastic loading rates (10, 100, 1000 kg ha-1) with addition of nitrogen (N) (80 kg N ha-1), and without. Comparing responses to inert sand and organic residues (clover, straw). Nitrogen addition significantly enhanced real priming in all treatments. PHBV caused dose-dependent (although non-significant) positive priming, greater than equivalent straw or clover loading. Generally, apparent priming was negative without N but positive with N, suggesting microbial responses depend on substrate stoichiometry and accessibility. Microbial (16S rRNA and ITS2) sequencing showed that N addition mainly drove bacterial community changes, while PHBV uniquely altered fungal communities, increasing Ascomycota dominance in a dose-dependent manner. PE behaved similarly to inert sand, indicating minimal impact on SOM turnover. While biodegradable plastics reduce conventional microplastic accumulation, PHBV may enhance SOM loss via priming (with no direct analogue found in this study), with potential long-term consequences for soil carbon stocks. These findings emphasise the importance of evaluating biodegradable plastics within broader soil nutrient and carbon cycling frameworks.
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Organic carbon loss from agricultural soil is accelerated by biodegradable microplastics and mitigated by mineral nitrogen addition
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A 193-day lab experiment found that biodegradable microplastics — especially a PLA-PHA blend — can accelerate the loss of native soil carbon through a 'priming effect,' essentially stimulating soil microbes to break down stored organic matter faster than they otherwise would. Adding nitrogen to soil partially offset this carbon loss, suggesting that fertilization practices may influence how biodegradable agricultural films affect soil health.
Nitrogen Availability Governs Priming Effect Induced by Biodegradable Microplastics Through Microbial Life‐Strategies
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This meta-analysis and isotope labeling study examined how biodegradable microplastics alter soil organic matter decomposition (the priming effect) under varying nitrogen availability, finding that nitrogen addition shifted microbial strategies toward the degradation of added carbon rather than native soil organic matter.
Microplastic contamination accelerates soil carbon loss through positive priming
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Researchers studied how polyethylene and biodegradable PHBV microplastics affect the decomposition of soil organic matter through a process called the priming effect. They found that both types of microplastics accelerated soil carbon loss when fresh carbon was added, with biodegradable PHBV causing 72% more carbon release than polyethylene. The study suggests that microplastic contamination in soils could worsen carbon loss from terrestrial ecosystems, with biodegradable plastics potentially having a greater impact than conventional ones.
Effect of different polymers of microplastics on soil organic carbon and nitrogen – A mesocosm experiment
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Researchers found that adding polyethylene and biodegradable microplastics to agricultural soil altered carbon and nitrogen dynamics, with biodegradable microplastics having stronger effects on soil organic carbon decomposition and nutrient cycling than conventional plastics.
Incorporation of microbial strategies for carbon-utilization in interpreting soil priming effects induced by microplastics
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Researchers investigated how microplastics in soil influence the way microbes break down carbon, finding that plastics alter microbial strategies for using carbon sources and disrupt the natural 'priming effect' — the process by which fresh organic matter stimulates decomposition of older soil carbon. These changes could affect carbon cycling and long-term soil fertility in microplastic-contaminated environments.
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