Abstract: The Yilong Lake, one of the nine major plateau lakes in Yunnan Province, is currently facing severe threats from water eutrophication. To investigate the adaptive mechanisms of dominant riparian wetland plants under eutrophic conditions, this study focused on reeds (Phragmites australis) and cattails (Typha orientalis) along the lakeshore of the Yilong Lake. We analyzed the characteristics of leaf nitrogen (N) and phosphorus (P) resorption in response to different chemical oxygen demand (COD) gradients: high (45.23-51.47 mg/L), medium (23.04-31.76 mg/L), and low (3.10-18.50 mg/L). Plant and surface water samples were collected synchronously during the peak growing season. The N and P concentrations in both mature and senescing leaves were measured to calculate resorption efficiency. The results showed that the N and P contents in reed leaves declined over the seasons. Leaf N decreased from 24.64 mg/g in spring to 12.25 mg/g in winter, with a reduction of 50.28%, while leaf P peaked in spring (2.70 mg/g), decreased in summer (1.72 mg/g), and reached its lowest in winter (0.61 mg/g). In contrast, cattail leaf N and P initially increased and then decreased with seasonal changes. Leaf N and P were relatively low in spring (20.93 mg/g and 1.84 mg/g), increased in summer (33.56 mg/g and 2.01 mg/g), began to decline in autumn (26.35 mg/g and 1.96 mg/g), and reached the lowest values in winter. The mean N and P resorption efficiencies of reed leaves were 41.93% and 57.85%, respectively, while those of cattail leaves were 42.87% and 63.53%. Across different COD concentrations, the N and P resorption efficiencies were highest under low COD, followed by medium and then high COD. N resorption efficiency differed significantly among COD levels, whereas P resorption efficiency showed no significant variation. Nutrient contents in mature leaves were significantly positively correlated with those in senescent leaves, indicating coordinated nutrient dynamics between the two stages. Moreover, leaf N resorption was significantly negatively correlated with COD concentration, suggesting that higher environmental COD levels reduce leaf N resorption efficiency. Both N and P resorption efficiencies were significantly negatively correlated with nutrient contents in senescent leaves; the greater the nutrient transfer from senescent to young tissues, the longer nutrients are retained within the plant, thereby reducing nutrient leaching during litter decomposition and slowing nutrient loss from the system. This study elucidates the ecological adaptation mechanisms by which wetland plants respond to eutrophication stress through nutrient resorption strategies, providing a theoretical basis for wetland restoration and eutrophication control in the Yilong Lake.