Unveiling the impact of microplastics with distinct polymer types and concentrations on tidal sediment microbiome and nitrogen cycling.

ABSTRACT

Microplastics (MPs) are distributed widely in the ocean surface waters and sediments. Increasing MPs contamination in intertidal zone profoundly impacts microbial ecosystem services and biogeochemical process. Little is known about the response of tidal sediment microbiome to MPs. We conducted a 30-day laboratory microcosm study using five polymers (PE, PBS, PC, PLA and PET) at three concentrations (1 %, 2 % and 5 %, w/w). High throughput sequencing of 16 S rRNA, qPCR and enzyme activity test were applied to demonstrate the response of microbial community and nitrogen cycling functional genes to MPs. MPs reduced the microbial alpha diversity and the microbial dissimilarity while the effects of PLA-MPs were concentration dependent. LEfSe analysis indicated that the Proteobacteria predominated for all MP treatments. Mantel's test, RDA and correlation analysis implied that pH may be the key environmental factor for causing microbial alterations. MPs enhanced nitrogen fixation in tidal sediment. PLA levels of 1 % but not 5 % produced the most significant effects in nitrogen cycling functional microbiota and genes. PLS-PM revealed that impacts of MPs on tidal sediment microbial communities and nitrogen cycling were dominated by indirect effects. Our study deepened understanding and filled the knowledge gap of MP contaminants affecting tidal sediment microbial nitrogen cycling.