6PPD and 6PPD-Q driven phytotoxicity in Eichhornia crassipes: From molecular damages to ecological potential implications.

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its derivative 6PPD-quinone (6PPD-Q) are emerging concerns due to their widespread occurrence and poorly understood ecological effects. This study reveals the multifaceted toxicity mechanisms of these compounds in water hyacinth (Eichhornia crassipes) through an integrated physiological-multi-omics approach. We demonstrate that 6PPD-Q triggers severe oxidative stress and photosynthetic impairment, reducing the maximum quantum efficiency of PSII (Fv/Fm) by 22.58 % at 20 μg/L. While plants activated defense responses through phytohormone reprogramming (notably 19.62 %-20.98 % jasmonic acid elevation) and recruited stress-mitigating microorganisms through altered root exudates. The enhanced plant-microbe interactions failed to prevent a 21.62 %-24.62 % reduction in chemical oxygen demand (COD) removal capacity, revealing a critical trade-off between stress adaptation and ecosystem function. Our findings provide mechanistic insights into contaminant-induced phytotoxicity and highlight the hidden risks of 6PPD and 6PPD-Q to aquatic phytoremediation systems.