We can't find the internet
Attempting to reconnect
Something went wrong!
Hang in there while we get back on track
Microplastics and co-occurring nitrogen synergistically accelerate blue carbon loss
Summary
Scientists found that "biodegradable" plastic (PLA), when combined with nitrogen fertilizer runoff, dramatically speeds up the breakdown of carbon stored in coastal ecosystems like seagrass meadows—nearly tripling CO2 release compared to untreated soil. This matters because these coastal habitats act as major carbon sinks that help buffer climate change, and the combo of plastic pollution and fertilizer runoff could be quietly undermining that protective function, meaning the "eco-friendly" label on some biodegradable plastics may be misleading when it comes to environmental impact.
Blue carbon ecosystems (BCEs)-including seagrass meadows, mangroves, and salt marshes-store vast amounts of organic carbon, yet their carbon sink function is increasingly threatened by hazardous microplastics and co-occurring nitrogen pollution. Here, we used a controlled microcosm experiment and multi-omics analysis (16S rRNA amplicon sequencing, Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, and Ultra-Performance Liquid Chromatography-Mass Spectrometry) to investigate how two common microplastics-polyethylene terephthalate (PET) and polylactic acid (PLA)-interact with nitrogen fertiliser (N-dominated fertiliser with co-delivered nutrients) to influence seagrass soil biogeochemistry. We showed that PLA combined with N-fertiliser increased CO₂ emissions from seagrass soil by 106% relative to nitrogen alone and by 195% compared to controls (p < 0.01), while PET addition had negligible effects. PLA degradation released carboxylic acid and derivatives, supporting putative sulphate-reducing and fermentative bacteria, and increasing the formation of organic-oxygen compounds (e.g., disaccharides, o-glycosyl compounds). N-fertiliser addition further enriched putative organic matter-degrading microbial taxa, particularly Clostridia and Bacteroidia, and elevated microbial metabolic potential across pathways. Combined PLA and nitrogen treatments resulted in the lowest (-37% vs control) residual dissolved organic carbon concentrations, indicating accelerated carbon loss. These findings suggest that microplastics, especially PLA biopolymer, and nitrogen act as hazardous co-contaminants that enhance microbial mineralisation of soil organic matter, potentially weakening blue carbon storage. Plastic waste and fertiliser inputs should therefore be considered together in future risk assessments of coastal carbon stocks and in the development of strategies to safeguard BCEs.