Effects of plastic pollution on soil carbon dynamics in arable soils across three distinct river valleys

Plasticulture has become an integral component of intensive crop production, yet its long-term implications for soil carbon dynamics and agronomic quality remain insufficiently understood. Microplastics alter microbial community structure and activity — sometimes reducing overall respiration, shifting the balance of microbes that mediate carbon transformations. This study evaluated the effects of microplastic (MP; <5 mm) contamination on soil properties, with particular emphasis on soil carbon mineralization, across plastic greenhouse and adjacent open-field systems in three river valleys of Serbia (Sava, Danube, and South Morava). Microplastic contents were significantly higher in greenhouse soils than in open fields. Potentially mineralizable carbon was generally lower in greenhouse soils, especially at the Danube site, where labile carbon was reduced by 34.4% relative to open-field soil, while mineralization rate constants were higher under plasticulture, indicating accelerated decomposition of limited carbon pools. Correlation analyses revealed predominantly negative relationships between MP abundance and key soil fertility indicators whereas soil porosity and specific mass showed positive associations with MP content. Network analysis further demonstrated that MPs exerted weak influence in open-field soils but played a more prominent role in greenhouse systems, primarily by altering soil structure and adsorption capacity. Overall, the findings indicate that chronic MP accumulation in plasticulture soils disrupts soil structure, accelerates carbon mineralization, and diminishes nutrient retention, thereby reducing agronomic soil quality. These results underscore the need for long-term monitoring of microplastic thresholds, their interactions with soil organic matter, and their implications for soil health, carbon sequestration, and sustainable agricultural management.