Nano/microplastics induce distinct reed growth defense tradeoff via hormone signal transduction and carbohydrate metabolism

The widespread presence of nano/microplastics (N/MPs) and the various consequences on aquatic macrophytes have raised growing concerns. However, how the growth-defense tradeoff strategy of aquatic macrophytes responds to N/MP stress remains unclear. Here, we investigated the effects of polystyrene N/MPs at different exposure levels on Phragmites australis (P. australis), a widespread aquatic macrophyte. Under NP exposure, root biomass was significantly reduced by 26.4 % at 10 mg/L, 19.3 % at 50 mg/L, and 17.2 % at 100 mg/L. Similarly, leaf biomass was reduced by 20.3 % at 10 mg/L, 19.1 % at 50 mg/L, and 25.2 % at 100 mg/L. Conversely, root and leaf biomass were significantly increased by 11.87 % and 23.47 % at 100 mg/L MP exposure, while no significant effects at lower levels. NPs suppressed photoprotection and root hair development and induced oxidative damage, whereas MPs had the opposite effects. Transcriptomic analysis revealed that signal transduction pathways were enriched in P. australis exposed to N/MPs, resulting in tissue-specific responses. Network analysis of gene expression modules indicated that P. australis increased ion transport and energy mobilization in defense against NPs while reducing stress responses and cellular damage to maintain growth under MP stress. Furthermore, P. australis shifted from growth to defense under NP stress by prioritizing jasmonic acid- and abscisic acid-mediated defenses and reducing the levels of growth-regulating hormones. MPs promoted plant growth by upregulating indole-3-acetic acid, gibberellin, and carbohydrate metabolism. These findings elucidate the molecular mechanism of the reed growth-defense tradeoff strategy induced by N/MPs, providing new insights into the toxicological effects of N/MPs on aquatic macrophytes.