Differential impacts of microplastics on carbon and nitrogen cycling in plant-soil systems: A meta-analysis

Microplastics (MPs) are widely present in terrestrial ecosystems. However, how MPs impact carbon (C) and nitrogen (N) cycling within plant-soil system is still poorly understood. Here, we conducted a meta-analysis utilizing 3338 paired observations from 180 publications to estimate the effects of MPs on plant growth (biomass, nitrogen content, nitrogen uptake and nitrogen use efficiency), change in soil C content (total carbon (TC), soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC)), C losses (carbon dioxide (CO₂) and methane), soil N content (total nitrogen, dissolved organic nitrogen, microbial biomass nitrogen, total dissolve nitrogen, ammonium, nitrate (NO₃^--N) and nitrite) and nitrogen losses (nitrous oxide, ammonia (NH₃) volatilization and N leaching) comprehensively. Results showed that although MPs significantly increased CO₂ emissions by 25.7 %, they also increased TC, SOC, MBC, DOC and CO₂ by 53.3 %, 25.4 %, 19.6 % and 24.7 %, respectively, and thus increased soil carbon sink capacity. However, MPs significantly decreased NO₃^--N and NH₃ volatilization by 14.7 % and 43.3 %, respectively. Meanwhile, MPs significantly decreased plant aboveground biomass, whereas no significant changes were detected in plant belowground biomass and plant N content. The impacts of MPs on soil C, N and plant growth varied depending on MP types, sizes, concentrations, and experimental durations, in part influenced by initial soil properties. Overall, although MPs enhanced soil carbon sink capacity, they may pose a significant threat to future agricultural productivity.