Invasion of Microplastic-Derived DOM Disturbs Soil-Microbe-Plant System through Component-Driven Effects

Microplastic-derived dissolved organic matter poses an emerging threat to terrestrial ecosystems. Here, we investigated the effects of PP-DOM and PS-DOM (at concentrations of 0.1, 1, and 10 mg/L) on Chinese cabbage (Brassica rapa), planted soils, and soil microbial communities. PP-DOM at 1 mg/L increased soil TOC, TN, and phosphorus, enriched opportunistic pathogens (Scedosporium), and affected iron outer membrane receptor proteins, while 1 mg/L PS-DOM enhanced available nitrogen and nitrogen-transforming bacteria (Rhodobacter, Luteimonas, and Nitrosospira). Both of them increased the abundance of three carbon metabolism-related genes (galR, atoB, fabG). PP-DOM stimulated plant growth at 0.1 mg/L but inhibited growth at higher concentrations; PS-DOM exhibited the opposite trend. PP-DOM at higher concentrations reduced chlorophyll and suppressed CAT/superoxide dismutase activities, while high-level PS-DOM increased chlorophyll and carotenoids with weaker oxidative damage. Transcriptomic analysis revealed that MP-DOM modulated the plant photosynthetic and amino acid metabolism pathways. Collectively, MP-DOM chemical composition critically shapes soil-microbe-plant ecological outcomes.