Selective enrichment of nitrogen-metabolizing species in agricultural small water bodies: the potential regulation of additives from microplastics color

The influence of microplastics (MPs) color on nitrogen-metabolizing microorganisms and the nitrogen cycle in agricultural small water bodies has been largely overlooked, particularly concerning the role of additives from colored MPs. The total content of 25 additives (16 organic compounds and 9 heavy metals) in bulk colored polyethylene (PE) was quantified, along with the leaching behavior of the heavy metal additives. Results revealed that light absorption and additives co-regulated the aging of colored PE. The color significantly influenced plastisphere microbial communities, with Proteobacteria (a phylum exhibiting functional diversity in nitrogen metabolism) dominating at 38.97-61.40%. Selective enrichment of nitrogen-metabolizing genera (Nitrospira, unclassified_Comamonadaceae, Methylophilus) and the denitrifying gene nirS in the plastisphere varied with PE color, showing maximal effects in blue PE. Notably, nirS abundance and key nitrogen-metabolizing species correlated positively with Cu leaching from additives. These findings demonstrated that PE aging and additive leaching collectively regulate microbial selection, highlighting the significant role of MPs color and offering a novel perspective for assessing the impacts of MPs pollution on biogeochemical cycles.