Impact of microplastic concentration on soil nematode communities on the Qinghai-Tibet Plateau: Evidence from a field-based microcosms experiment

Microplastics are an emerging pollutant that poses a threat to local ecosystems. Recent studies have revealed that microplastics have penetrated the Qinghai-Tibetan Plateau. While previous studies have investigated the migration and distribution of microplastics and their effects on soil properties, their effects on soil fauna communities remain underexplored. Here, we conducted a 1-year microplastic addition experiment to evaluate the responses of soil nematode communities and employed piecewise structural equation modeling to disentangle the direct and indirect effects of microplastics on these communities. We found that: (1) nematode abundance, diversity, and metabolic footprints exhibited a hump-shaped response to microplastic treatments, peaking at the 0.1 % treatment; (2) nematode biomass was significantly affected by microplastics, with the lowest biomass observed at the 10 % treatment; (3) the direct effects of microplastics on nematode abundance outweighed indirect effects, particularly influencing fungivores and omnivorous nematodes; (4) although microplastics did not significantly alter energy flow within nematode communities, the relationship between the energy flow of fungivores and omnivorous was stronger than those among other trophic groups. Our study offers insights on microplastics' impact on nematode communities and their varied responses to microplastic concentrations, crucial for understanding ecological effects on soil ecosystems.