Estuarine plastisphere as an overlooked source of N 2 O production.

"Plastisphere", microbial communities colonizing plastic debris, has sparked global concern for marine ecosystems. Microbiome inhabiting this novel human-made niche has been increasingly characterized; however, whether the plastisphere holds crucial roles in biogeochemical cycling remains largely unknown. Here we evaluate the potential of plastisphere in biotic and abiotic denitrification and nitrous oxide (N 2 O) production in estuaries. Biofilm formation provides anoxic conditions favoring denitrifiers. Comparing with surrounding bulk water, plastisphere exhibits a higher denitrifying activity and N 2 O production, suggesting an overlooked N 2 O source. Regardless of plastisphere and bulk water, bacterial and fungal denitrifications are the main regulators for N 2 O production instead of chemodenitrification. However, the contributions of bacteria and fungi in the plastisphere are different from those in bulk water, indicating a distinct N 2 O production pattern in the plastisphere. These findings pinpoint plastisphere as a N 2 O source, and provide insights into roles of the new biotope in biogeochemical cycling in the Anthropocene.