Abstract

Copper is essential yet phytotoxic when excessive, and polypropylene microplastics (PP-MPs) are increasingly co-occurring with Cu in soils, but their mechanistic impact on woody ornamentals remains unclear. Jasminum sambac in Cu spiked soil across a PP-MPs gradient and found a dose-dependent, non-monotonic modulation of Cu toxicity. PP-MPs accumulated on root surfaces, shifting Cu partitioning along the soil-root-shoot axis: an intermediate load reduced shoot Cu and translocation, lowered membrane lipid peroxidation, and was accompanied by coordinated adjustment of glutathione redox metabolism ( GSR, G6PD, PGD ) and GSH turnover ( GGT, GGCT ). Transcriptomics indicated that moderate PP-MPs partially restored genes for chlorophyll biosynthesis ( CHLI/CHLH/CHLM ) and light-harvesting ( Lhcb1/2 ), aligning with improved photosynthesis and chlorophyll a/b balance. However, high dose PP-MPs weakened this protection: root Cu rebounded, antioxidant enzymes (SOD/POD) dropped below control levels, PetC expression remained low, and chlorophyll a/b imbalance reoccurred. At a higher load, protection weakened root Cu rebounded, SOD and POD fell below control levels, PetC associated electron transport remained constrained, and Chl a/b imbalance re-emerged. The data suggest that PP-MPs act as both an interfacial sorptive buffer and a regulator of redox photosynthetic networks, informing risk assessment of metal-microplastic co‑contamination in soils.