Microplastics and Soil Greenhouse Gas Emissions: A Critical Reflection on Meta-Analyses

Microplastics (MPs) are widespread in agricultural soils and may influence emissions of greenhouse gases (GHGs), though their specific impacts remain uncertain. This study utilized conventional and network meta-analysis to evaluate the effects of long-term exposure to environmentally relevant MP concentrations. Results showed that, compared with uncontaminated soil, polypropylene increased CH₄ emissions by 2.01 times, while polyethylene terephthalate reduced them to 0.47 times. Polybutylene adipate terephthalate (PBAT) and polylactic acid/PBAT increased CO₂ emissions by 3.13 and 2.70 times, respectively; polyethylene raised N₂O emissions by 1.52 times. Other MPs had no significant impact. Most types of MPs increased GHG emissions, with conventional MPs contributing more to N₂O emissions and biodegradable MPs contributing more to CO₂ emissions. Biodegradable plastics were not necessarily more environmentally friendly in terms of global warming potential. Moreover, the study summarized issues in current meta-analyses targeting MPs, emphasizing the need to prioritize MP types, account for correlations and interactions among moderators, ensure effect size independence, and address potential "P-hacking" during the discretization of continuous variables. This deepens our comprehension of the environmental impacts of MPs and provides valuable guidance for future meta-analyses to accurately assess effects of MPs.