Metagenomic insight into the ecological effects of the plastisphere in coastal salt marshes

Abstract

Microplastics (MPs) introduce a unique ecological niche for microorganisms, termed the "plastisphere". Coastal salt marshes are critical blue‑carbon systems and MP sinks. However, the impacts of the plastisphere on major elemental cycling in coastal salt marshes remain poorly understood. To answer this important question, we conducted a 1-year field experiment in both the intertidal (Spartina alterniflora, SA) and supratidal (Phragmites australis, PA) zones of Yancheng salt marshes in China and investigated the dynamics using metagenomics. Results show pronounced heterogeneity in the ecological effects of the plastisphere in intertidal and supratidal zones. At the SA site, plastisphere communities showed increased gene abundance for nitrogen fixation, assimilatory nitrate reduction to ammonium, and thiosulfate oxidation (by sulfur oxidation complex). In contrast, at the PA site, plastisphere communities exhibited elevated gene abundance for carbon degradation, dissimilatory nitrate reduction to ammonium, and sulfite oxidation. Antibiotic resistance genes (ARGs) and pathogens were enriched in the plastisphere, with different compositions at SA and PA sites and some taxa exclusively present in the plastisphere despite low abundance. These findings highlight the plastisphere's potential to modulate biogeochemical processes and antibiotic resistance in salt marshes, providing a foundation for assessing MPs' ecological roles in these critical habitats.