The Role of Soil Microorganisms in Microplastic Biodegradation: Mechanisms, Carbon Preferences, and Ecological Impacts

Microplastics (MPs) impact soil microorganisms by altering habitats and community structures. However, generalising these effects across polluted environments is challenging, particularly concerning soil carbon's role in biodegradation. This review aims to address crucial knowledge gaps regarding the relationship between soil carbon availability and microbial preferences for MP-derived polymers. It highlights that, despite being carbon-based, the unique structures of MPs prevent them from functioning like natural organic matter in the soil. This limitation affects both the degradation process and the ability of soil microorganisms to utilise MPs effectively as a carbon source. Notably, even polymers that are not directly assimilated after MP biodegradation can be transformed by other soil microorganisms into more readily exploitable forms through vital microbial interactions within the soil food web, which play a key role in carbon cycling. Moreover, this review emphasises attention on understanding how the microbial preferences for substrates derived from MPs are influenced by more readily available organic carbon in the soil. Evaluating carbon use efficiency among these communities reveals intricate responses of soil microorganisms to various carbon sources, including those from MPs. Overall, this review underscores the complex interplay between soil microorganisms, carbon sources, and MP pollution.