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Microplastics promote N2O emissions by enhancing nitrification via ammonia-oxidizing bacteria in estuarine and coastal sediments
Summary
Incubation experiments with sediments from China's Yangtze River estuary found that polyethylene, polypropylene, and PET microplastics all significantly increased nitrous oxide (N2O) emissions — a potent greenhouse gas — by stimulating ammonia-oxidizing bacteria (AOB) rather than the archaea that normally dominate nitrogen cycling. Genomic analysis revealed that these bacteria carry enzymes capable of degrading plastic, possibly explaining why they thrive in plastic-contaminated sediments. This links microplastic pollution to climate change through an overlooked pathway: disrupting coastal nitrogen cycling and increasing greenhouse gas emissions.
Estuarine and coastal ecosystems are critical interfaces between land and ocean, serving as sinks for anthropogenic pollutants such as ammonium and microplastics. However, the impact of microplastic pollution on nitrification processes in these environments remains largely unexplored. This study investigates the coastal region of the Yangtze River to examine how different microplastic types (polyethylene terephthalate, polypropylene, and polyethylene) affect nitrous oxide (NO) emissions and the dynamics of nitrifiers, including ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), complete ammonia-oxidizing (comammox) Nitrospira, and nitrite-oxidizing Nitrospira. Results from incubation experiments show that all microplastic types significantly increase NO emissions across sediment samples. The reconstructed representative metagenome-assembled genomes revealed that AOA belong to group I.1a, while AOB are classified within the Nitrosomonas genus. Microplastics were found to have a stronger stimulatory effect on AOB, which are linked to higher NO production, than on AOA, which are associated with low NO production, thereby enhancing NO emissions during nitrification. Furthermore, AOB genomes encode a range of putative plastic-degrading enzymes, which may partially explain their enrichment in microplastic-contaminated environments, although other factors such as differential tolerance to ammonium or oxidative stress cannot be ruled out.