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Abstract: Differential responses of growth and vegetative reproduction among coexisting species to water-level fluctuation might explain their distribution patterns in wetlands. In the present study, we investigated the effect of water-level, ranging from dry to flooded conditions, on the vegetative reproduction of 2 coexisting rhizomatous species, Carex brevicuspis C. B. Clarke and Polygonum hydropiper Linnaeus, at Dongting Lake wetlands, China. Carex brevicuspis exhibited optimal growth and vegetative reproduction when the aboveground parts were not submerged (at -40 cm to 0 cm water level), but remained quiescent under flooded conditions (at 20cm and 40cm water level). In comparison, P. hydropiper was sensitive to changes in water level, with an almost linear decline in biomass and rhizome production as the water level increased from - 40cm to 40cm. In general, there was less change in biomass production, biomass allocation, and vegetative reproduction for C. brevicuspis compared to P. hydropiper at different water levels. This result indicates that C. brevicuspis is more tolerant of water stress than P. hydropiper; therefore, C. brevicuspis is likely to have a wider distribution in wetlands, with the latter species embedding in the stands of the former species.