Microplastics Type and Size Influence Soil Respiration by Mediating Root Biomass in Cultivated Agricultural Ecosystem, <scp>N</scp> orth <scp>C</scp> hina

ABSTRACT Microplastics persisting in soil can modify soil structure and nutrient status and alter biological activity, thereby influencing soil respiration. However, the mechanisms by which microplastics regulate soil respiration remain poorly understood. In this study, a field experiment was conducted in a winter wheat farmland to examine the effects of microplastic type (polypropylene and polyethylene) and particle size (13 and 500 μm) on soil respiration and to identify the associated driving factors. Soil respiration was significantly increased by microplastics, with a greater impact observed for 13 μm than for 500 μm microplastics. Microplastics increased root biomass and microbial biomass carbon, whereas they reduced aboveground biomass and soil available nitrogen content. Structural equation modeling indicated that the microplastic‐induced increment in soil respiration was primarily driven by root biomass. Microplastics stimulated root growth by changing soil physical structure, such as reducing bulk density, increasing soil porosity, and altering aggregate stability, thereby promoting soil respiration. Overall, this study highlights that microplastics can substantially alter belowground carbon dynamics by reshaping plant–soil–microbe interactions, and provides a scientific basis for evaluating the ecological consequences of microplastic pollution in agricultural soils.