Abstract: With Carex brevicuspis as the competitor species, we set four sedimentation depths (0, 3, 6, and 12 cm) and four competition treatments (no competition, full competition, aboveground competition, and belowground competition) to assess the growth and stoichiometric traits of Polygonum hydropiper, a representative wetland plant in Dongting Lake. The results showed that both sedimentation and competition significantly affected the total biomass of P. hydropiper. Moderate sedimentation (3-6 cm) facilitated biomass accumulation, whereas excessive sedimentation (12 cm) suppressed growth. P. hydropiper had the lowest total biomass under full competition. Under 6 cm sedimentation without competition, P. hydropiper exhibited the highest individual biomass (10.89 g). Under all competition treatments, the intensity of competition experienced by P. hydropiper increased initially and then decreased as sedimentation depth increased. Under sedimentation condition, competition led to a decrease in the root-to-shoot ratio and an increase in specific leaf area of P. hydropiper, indicating a shift in resource allocation toward aboveground part under competition pressure. Under no sedimentation, competition significantly suppressed plant height, suggesting that P. hydropiper would reduce vertical growth investment under resource-limited condition, indicating a conservative growth strategy. Under the competition condition, sedimentation significantly increased nitrogen content in aboveground part and carbon content in belowground part. Across sedimentation treatments, competition increased phosphorus content and C/N in both aboveground and belowground, while significantly reduced N/P and C/P. Total biomass was positively correlated with nitrogen in aboveground tissues but negatively correlated with nitrogen, phosphorus, and N/P in belowground part. Specific leaf area and plant height were positively associated with aboveground phosphorus. In conclusion, P. hydropiper effectively responded to the combined stress of varying sedimentation depths and competition through reducing root-to-shoot ratio, increasing specific leaf area, elevating the C/N, and lowering the C/P and N/P.

Key words: wetland plant, sediment deposition, interspecific competition, ecological stoichiometry