Impacts of non-steroidal anti-inflammatory drugs on Phragmites australis root exudation throughout plant life cycle: Defense responses and phytoremediation potential.

Non-steroidal anti-inflammatory drugs (NSAIDs) are emerging contaminants of high-priority risks in surface waters, imposing pseudo-persistent stress on aquatic plants. Understanding these plants' root exudation responses and regulatory mechanisms is crucial for preserving their ecological functions and advancing phytoremediation strategies. This study investigated the root exudate profiles of Phragmites australis across its life cycle under exposure to an environmental-level mixture of NSAIDs (diclofenac, ibuprofen, indomethacin, ketoprofen, and naproxen; 100 ng/L each). NSAID accumulation, oxidative stress, and antioxidant activity in plants were also analyzed to elucidate defense-related exudation mechanisms. The results revealed that NSAID stress significantly suppressed amino acid secretion in root exudates, particularly during the seedling to heading stages (30 % to 90 % of control levels), while markedly stimulating organic acid release, with pronounced increases (1.2- to 2.6-fold relative to controls) at the bolting, heading, and mature stages. NSAID accumulation in roots, stems, and leaves rose with plant development (up to 148, 65, and 34 ng/g dw, respectively), impairing photosynthesis and intensifying oxidative stress, which triggered stronger antioxidant defenses. The decline in root-exudated amino acids, such as glutamate, glutamine, proline, γ-aminobutyric acid, serine, threonine, valine, glycine, and isoleucine, suggests their increased utilization within plants to counteract NSAIDs-induced oxidative stress. Conversely, the enhanced secretion of organic acids, including quinate, tartrate, citrate, propanoate, malonate, malate, and oxalate, likely reduces root uptake of NSAIDs by increasing root-pollutant repulsion mediated by these compounds and recruiting bacteria capable of NSAID degradation via quinate co-metabolism.