Abstract

Spartina alterniflora，originating in North America, has been introduced to China and has now invaded many inter-tidal zones of gulfs and estuaries in China. With its spread, Scirpus mariqueter,a native grass species, has experienced a concurrent decrease in area. Based on field investigation at Chongming Dongtan Wetland and potted plant competition experiments at Fudan University, we compared growth characteristics and relative competitive ability between the two species. The results indicated that in terms of height, coverage, above-ground biomass, below-ground biomass, and mean seed number per spike, values for Spartina alterniflora were all significantly higher than those of Scirpus mariqueter.However, the density and number of flowering tillers per square meter for Spartina alterniflora were significantly lower than those of Scirpus mariqueter.In terms of seed output per square meter and seed germination rate, there were no significant differences between the mature populations of the two species. Both interspecific and intraspecific competition between Spartina alterniflora and Scirpus mariqueter remarkably reduced the number of ramets, the proportion of fruiting ramets, the above-ground biomass and the number of corms (only Scirpus mariqueter has corms). The interspecific relative competitive ability (measured as relative neighbour effect index, RNE) of Spartina alterniflora was significantly greater than that of Scirpus mariqueter. The obvious growing advantage of Spartina alterniflora compared with Scirpus mariqueter might explain its greater interspecific competitive ability, which might explain its successful invasiveness into the native Scirpus mariqueter community in the Yangtze River estuary.