From carrier to reactor: How microplastic as a mobile source of dissolved organic matter reshapes soil carbon cycling and microbial communities.

Soil microplastic (MP) pollution is a growing global concern, with MPs ubiquitously detected across ecosystems. This review systematically examines the multifaceted interactions between MPs and soil dissolved organic matter (DOM), focusing on three core mechanisms: physical adsorption, chemical reactions, and microbial mediation. We highlight how MPs transition from passive carriers to active reactors of DOM, influencing DOM molecular diversity, stability, and environmental persistence. Key findings include the role of MP aging in generating reactive oxygen species that accelerate DOM mineralization, and the formation of MPs-DOM complexes that act as mobile vectors for co-transporting contaminants. Notably, microbial colonization forms the "plastisphere" biofilm, which becomes a key interface for DOM transformation and significantly influences carbon cycling. Furthermore, biodegradable MPs induce a strong priming effect, accelerating the loss of native soil organic carbon. This synthesis bridges critical knowledge gaps and provides a scientific basis for risk assessment and policy-making in soil pollution control.