Data from: Degradable versus inert microplastics: Effects on soil organic carbon persistence via microbial drivers in an agroecosystem

Microplastics (MPs) are widespread in terrestrial ecosystems, raising global concerns that they may disrupt soil organic carbon (SOC) cycling and undermine agroecosystem contributions to climate mitigation. Yet it remains unclear how degradable versus inert MPs affect microbially mediated SOC stabilization. We conducted a field experiment in a dryland agroecosystem using polyethylene (PE; inert) and polylactic acid (PLA; degradable) MPs at three residue levels, integrating metagenomics with SOC fractionation, microbial necromass quantification, and extracellular enzyme stoichiometry to resolve microbial pathways underpinning SOC persistence. PE and PLA-MPs exerted contrasting effects on SOC stabilization. PE-MPs intensified microbial C limitation, enriched Actinobacteria, and increased the abundance of carbohydrate-degrading CAZy families, thereby accelerating decomposition and reducing particulate organic C by 10.5-16.7%; concomitantly, PE-MPs constrained microbial necromass formation and depleted SOC. In contrast, PLA-MPs increased labile C availability, stimulated C and N metabolic pathways and amino sugar metabolism. These responses enhanced microbial necromass formation by 3.6-6.9% and increased exopolysaccharide synthesis, ultimately promoting mineral-associated organic C accumulation. Collectively, these polymer-specific microbial responses demonstrate how plastic residues can either weaken or reinforce soil C persistence, with implications for forecasting agroecosystem C sinks and guiding plastic substitution and residue management under climate relevant land stewardship.