Microplastics Disrupt Soil Aggregate Stability and Associated Nutrient Dynamics in Mulched Salt-Affected Agricultural Soils

Soil aggregates (SAGs) are fundamental to soil quality, influencing nutrient storage, cycling, and overall soil functionality. However, the accumulation and aging of microplastics (MPs) in soils pose emerging challenges to SAG stability and nutrient dynamics, particularly in salt-affected soils. This study provides a novel investigation into the relationship between MP characteristics and SAG dynamics, with a specific focus on salt-affected soils in northeastern China. Our findings demonstrate that high MP abundance significantly disrupts SAG structure, reducing the proportion of large aggregates (p = 0.032) and increasing microaggregates (<0.25 mm), with microaggregates serving as hotspots for MP accumulation (p < 0.05). MP type and size emerged as dominant factors of SAG structural instability, leading to pronounced imbalances in aggregate-associated nutrients (AANs) across aggregate fractions. The inherent characteristics of salt-affected soils─such as elevated salinity, alkalinity, and low organic matter─further amplified these destabilizing effects. This study elucidates the complex interplay between MPs and soil properties, demonstrating their contribution to the deterioration of soil structure and the reduced availability of SAG and AAN. These findings emphasize the need for targeted strategies to mitigate MP contamination in salt-affected agricultural soils, particularly under the intensifying use of plastic mulch in modern agriculture.