Microplastics, defined as plastic particles ≤ 5 mm in size, have emerged as a global environmental concern due to their widespread distribution and potential toxicity to ecosystems and human health. While research on microplastics has traditionally focused on marine environments, growing evidence suggests that terrestrial ecosystems—particularly island soils—may serve as important yet underrecognized reservoirs of microplastic pollution.

Building on previous investigations into the distribution characteristics of microplastics in soils under different vegetation types in the Xisha Islands, researchers observed substantial amounts of microplastics in the soils of shrub and tree communities. This presence is closely linked to marine floating debris and human activities.

As carbon-based materials, microplastics and their degradation products have the potential to directly interfere with soil carbon cycling. Soil microorganisms and their byproducts play a central role in regulating soil organic carbon (SOC) storage. However, the mechanisms by which microplastics influence microbially mediated soil carbon processes remain largely unclear.

To address this knowledge gap, a research team from the South China Botanical Garden of the Chinese Academy of Scienceshas conducted controlled pot experiments in a greenhouse. They planted Scaevola taccada—the most dominant shrub species on coral islands in the South China Sea—in coral sand amended with varying amounts of conventional and biodegradable microplastics, respectively. The study aimed to evaluate the effects of conventional and biodegradable microplastics on soil microbial necromass carbon (MNC), glomalin-related soil protein (GRSP), and the community structures of arbuscular mycorrhizal fungi (AMF) and bacteria.

The results revealed that microplastics significantly enhanced SOC accumulation, with biodegradable microplastics exerting a more pronounced effect than conventional ones. Microplastic exposure reshaped bacterial and AMF community structures, strengthened the stability of symbiotic networks, and highlighted the pivotal roles of key taxa—such as Proteobacteria, Glomus, and Paraglomus—in regulating MNC and GRSP dynamics. Notably, GRSP emerged as a dominant mediator of SOC stabilization under microplastic stress.

These findings provide mechanistic evidence for how microplastic pollution reshapes belowground carbon processes, offering new insights for refining global change models and optimizing soil management strategies.

The researchers also found that biodegradable microplastics inhibited the growth of Scaevola taccada. This result underscores the need for caution when promoting biodegradable plastics as alternatives to conventional plastics, particularly in sensitive island ecosystems. Comprehensive assessments of their potential impacts on plant growth and ecosystem functioning are essential prior to large-scale adoption.

The research findings were recently published in the Journal of Hazardous Materials. This work was supported by the National Key Research and Development Program of China and other relevant funding sources.