Microplastic-Induced Alterations in Soil Aggregate-Associated Carbon Stabilization Pathways: Evidence from δ13C Signature Analysis

Microplastics (MPs) are known to affect soil carbon stability in a numerous ways. However, the mechanisms by which they alter the carbon stability within soil aggregates remain unclear . Herein, a one-year field experiment was conducted in an arid agricultural region employing stable isotope techniques to evaluate the soil organic carbon flow in the presence of both persistent (PE, PVC) and biodegradable (PLA, PHA) MPs. PE and PVC reduced the stability of soil aggregates, while PLA and PHA maintained it. Additionally, organic carbon content increased in microaggregates but decreased in small macroaggregates for PE and PVC treatments. By contrast, treatment with PLA and PHA enhanced organic carbon content across aggregates. The δ 13 C values of PE- and PVC-treated aggregates ranged from −25.34 to −20.85‰, while those of PLA and PHA ranged from −16.29 to −9.26‰. Notably, MPs altered the direction of carbon flow between aggregates, reduced carbon flux, and accelerated carbon emissions. RFP and PLS–PM analyses revealed that persistent MPs affected carbon flow primarily via abiotic factors, whereas biodegradable MPs influenced it via biotic factors. These findings provide insights into the mechanisms by which MPs impact aggregate-associated carbon, highlighting their effects on soil ecosystem services.