Microplastic Diversity as a Potential Driver of Soil Denitrification Shifts

Microplastics (MPs) are raising significant global concerns due to their environmental impacts. While most studies have focused on the effects of individual MP types, MPs in natural environments typically coexist as multiple types, and their combined effects remain poorly understood. In this study, we conducted a microcosm experiment with four levels of MP diversity (0, 1, 3, and 5 types) to investigate the effects of MP diversity on soil ecosystem functions using metagenomic sequencing. Our results revealed that increasing MP diversity significantly raised soil pH and organic carbon content while reducing available nitrogen. Notably, bacterial alpha diversity (Shannon and Invsimpson indices) increased significantly with higher MP diversity. Moreover, increasing MP diversity markedly shifted bacterial life-history strategies to adapt to the altered environment. Importantly, the abundance of nitrogen-related functional genes also increased with MP diversity. In particular, the abundance of denitrifying genes, predominantly driven by Rhodocyclaceae, was notably enhanced, resulting in a reduction of soil available nitrogen. Collectively, these findings offer valuable insights into the impact of MP diversity on soil function─especially within the nitrogen cycle─and have important implications for soil management strategies under MP stress.