Size- and Time-Dependent Effects of Polyethylene Microplastics on Soil Nematode Communities: A 360-Day Field Experiment

Soil ecosystems are seriously contaminated by microplastics of varying particle sizes, yet the ecological consequences across a broader size spectrum remain poorly understood. We conducted a 360-day field experiment to examine the effects of seven microplastic size fractions (ranging from 6.5 μm to 1000 μm) on the composition, trophic structure, temporal dynamics, complexity, and stability of soil nematode communities. Results showed that microplastics altered nematode community composition and structure, with impacts clearly dependent on both particle size and exposure time. Microplastics generally reduced the abundance, complexity, and stability of nematode communities, except for the 25 μm and 500 μm particles. Temporal analysis revealed an initial increase in nematode abundance, followed by a long-term decline across most treatments. Structural equation modeling indicated that microplastics regulated nematode diversity and stability through pathways that varied with particle size. We recommend that the environmental risk assessments for soil microplastics incorporate testing across a broad size spectrum and over extended timescales to capture their complex and dynamic impacts.