Global Responses of Soil Extracellular Enzyme Activities to Biodegradable and Nonbiodegradable Microplastics: A Meta-Analysis of Laboratory Studies

Microplastics (MPs) are pervasive environmental pollutants that disrupt soil ecosystem functions by influencing extracellular enzyme activities (EEAs). Although the effects of MPs on soil EEAs have garnered increasing attention, the generalizable patterns and mechanisms underlying these effects remain unclear. To bridge this knowledge gap, we conducted a meta-analysis of 453 paired observations from 72 peer-reviewed publications evaluating MP-induced changes in soil EEAs with a focus on the roles of MP biodegradability, experimental additions, and the presence or absence of plants in mediating these effects. Our findings demonstrated that MPs increased soil N-acquiring (4%), P-acquiring (14%), and oxidative (8%) enzyme activities and decreased soil C-acquiring enzyme activities (2%). Notably, biodegradable MPs exhibited a more pronounced promotion of soil EEAs than did nonbiodegradable MPs. Experimental additions substantially mediated the effects of MPs on soil EEAs, where toxic substances promoted positive effects. However, the presence of plants attenuated these effects compared with plant-free conditions. Furthermore, critical mediators included MPs' size (C-acquiring and N-acquiring enzyme activities), initial SOC content (P-acquiring enzyme activities), and experimental duration (oxidative enzyme activities). These findings highlight the potential effects of MPs on soil biochemical processes, providing insights into developing targeted management strategies to mitigate MP-induced threats in terrestrial ecosystems.