Arbuscular mycorrhizal fungi and glomalin mediate the effects of microplastics on soil carbon storage

Microplastics are increasingly recognized as critical drivers of perturbations in biogeochemical cycles, particularly in modulating the storage and release of soil organic carbon (SOC). However, the mechanisms by which microplastics influence microbial-derived carbon remain poorly understood. In this study, we conducted a controlled pot experiment to investigate the effects of nondegradable and biodegradable microplastics on glomalin-related soil protein (GRSP), microbial necromass carbon (MNC), and the arbuscular mycorrhizal fungi (AMF) community. Biodegradable microplastics increased SOC by an average of 33.09 %, while nondegradable microplastics increased it by 19.45 %. Microplastics altered the structure of bacterial and AMF communities, enhanced the stability of their co-occurrence networks, and highlighted the central roles of Proteobacteria, Glomus, and Paraglomus, which thereby influenced MNC and GRSP dynamics. A random forest model indicated that microplastics primarily affected SOC sequestration through GRSP, rather than through MNC. These findings provide novel insights into the mechanisms of microplastic-mediated microbial carbon cycling and underscore the critical role of AMF-derived GRSP in maintaining soil carbon stability. Our study advances the understanding of microbial contributions to soil carbon dynamics under microplastic stress and offers valuable perspectives for assessing the ecological risks of soil microplastic pollution.