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Improper disposal of abandoned plant materials and wastewaters with a low C/N ratio in natural environments often bring about a series of environmental issues. Therefore, it is imperative to identify effective solutions to concurrently address these pollution problems. The research investigations have shown that the utilization of plant materials as external carbon sources for denitrification in constructed wetlands (CWs) could be a potential solution to recovery of plant resources and the promotion of nitrogen-containing wastewater treatment. In this research, three typical deciduous leaves (phoenix tree leaf, lotus leaf, and reed leaf) were systematically investigated for their viability in releasing carbon and the enhanced performance as external carbon sources for nitrogen removal in CWs. EEM-PARAFAC, SUVA 254 and high-throughput sequencing were applied to unravel mechanisms of enhancing wastewater nitrogen removal with plant carbon sources. The results demonstrated that plant materials exhibited efficacy in releasing organic carbon obviously, with a cumulative amount of carbon release ranging from 119.78 to 172.84 mg·g-1. The dissolved organic matters (DOMs) released by abandoned plant materials were primarily composed of humic acid and fulvic acid. SUVA 254 values indicated that the DOMs emanating from the decomposition of plant materials could be hydrophilic substances. The CWs with received plant carbon sources exhibited a remarkable TN removal of 49.62%− 61.3%, accompanied by a promotion of nitrogen removal bacteria reproduction, with relative abundance increased by 16.33%− 21.97%, but it resulted in a slight increase in N 2 O emissions unavoidably. These findings indicated that utilizing abandoned plant materials as external carbon sources in CWs for treating low C/N ratio sewage have tremendous application potential and can enhance nitrogen removal efficiency obviously. [Display omitted] [ABSTRACT FROM AUTHOR]