Microplastics reduce soil microbial network complexity and ecological deterministic selection

Microplastics have been proposed as emerging threats for terrestrial systems as they may potentially alter the physicochemical/biophysical soil environments. Due to the variety of properties of microplastics and soils, the microplastic-induced effects in soil ecosystems are greatly manifold. Here, we studied effects of three polymer microplastics (polyamide-6, polyethylene, and polyethylene terephthalate) on soil properties with four different soil types. The success patterns, interaction relationships, and assembly processes of soil bacterial communities were also studied. Microplastics have the potential to promote CO2 emissions and enhance the soil humification. Even though microplastics did not significantly alter the diversity and composition of the soil microbial community, the application of microplastics decreased the network complexity and stability, including network size, connectivity, and the number of module and keystone species. The bacterial community assembly was governed by deterministic selection (77.3%-90.9%) in all treatments, while microplastics increased the contribution of stochastic processes from 9.1% in control to 13.6%-22.7%. The neutral model results also indicated most of the bacterial taxa were present in the predicted neutral region (approximately 98%), suggesting the importance of stochastic processes. These findings provided a fundamental insight in understanding the effects of microplastics on soil ecosystems.