Microplastics effects on soil biota are dependent on their properties: A meta-analysis

Microplastics (MPs) pollution is identified as an important new global change factor potentially influencing ecosystem functions and services. MPs have been shown to strongly affect soil biota. However, whether soil biota respond differently to biodegradable and conventional MPs, and the generalizable pattern of responses of soil biota to MPs size, dose and the time of exposure to MPs remain poorly understood. Here we conducted a global-scale meta-analysis of 781 observations from 92 publications to investigate the effects of MPs on soil biota (i.e., microbiota and fauna). We also explored how soil biota respond to different experimental conditions (e.g., MPs properties and experimental duration). Results showed that MPs significantly increased soil microbial biomass, while decreased the growth and reproduction of soil fauna (nematodes, springtails and earthworms). However, MPs significantly decreased soil bacterial diversity (Shannon index) and shifted microbial community structure, and the effect of MPs on soil bacteria was more intense than that on soil fungi. The responses of soil biota were dependent on MPs types, sizes, concentrations and experimental duration. For example, biodegradable MPs had stronger impacts on soil microbial community, while had weaker negative impacts on soil fauna than conventional MPs. Likewise, smaller size of MPs appeared to have more adverse impacts on soil bacterial diversity, and the growth and reproduction of nematodes, but this trend was opposite in the reproduction of earthworms. Furthermore, the response of soil microbial community and fauna significantly correlated with the MPs concentration and experimental duration, suggesting that soil biota exposed to MPs for high concentrations and long periods were more vulnerable. Regardless of specific experimental conditions, these results highlight that prolonged MPs pollution may have considerable negative effects on the structure and function of soil biota and consequently affect the ability of soil ecosystems to provide ecosystem services and sustain human societies.