( )Titanium dioxide nanoparticles (TiO2 NPs) have been widely used in industrial and commercial products, resulting in potential environmental risks. However, the impacts of these nanoparticles on wastewater treatment in ecological systems are less known. In this study, short- and long-term effects of TiO2 NPs on contaminant removal in constructed wetlands (CWs) were investigated. The results showed that short-term exposure to TiO2 NPs (1 and 50 mg/L) induced marginal adverse effects on treatment performance (COD, TN, NH4+-N, and TP) of CWs, while N removal evidently declined under prolonged exposure to TiO2 NPs. Furthermore, metagenomics and enzyme activities analyses suggested that the reduced N removal efficiency could possibly be due to the decrease in the relative abundance of nitrifiers (Nitrospira and Nitrosomonas) and inhibition of ammonia monooxygenase activity. In contrast, long-term exposure to TiO2 NPs promoted net photosynthesis rate, stomatal conductance, transpiration rate and root activity of Phragmites australis, indicating a positive impact of TiO2 NPs on plant physiology. Overall, the findings of this study suggested that long-term exposure to TiO2 NPs at an environmentally relevant concentration (1 mg/L) significantly altered the functionalities of microorganisms and plants, which in turn impaired the wastewater treatment performance of CWs.