Abstract: We investigated the quantitative characteristics of Phragmites australis populations and their responses to soil factors in different communities in Zhalong wetland, and analyzed the changes of plant population during community succession. Depending on species composition, three plots of P. australis community, P. australis+Leymus chinensis community and L. chinensis+P. australis community were selected. The density and biomass of P. australis population in different communities were compared by unit area sampling, while the correlation between soil factors and density and biomass of P. australis population was analyzed. The results showed that the density of P. australis population in P. australis community, P. australis+L. chinensis community and L. chinensis+P. australis community was 309-570, 176-375, and 79-191 tillers·m^-2, and its biomass was 130-4395, 97-2453, and 32-1041 g·m^-2, respectively. The density and biomass of P. australis population were the highest in P. australis community, intermediate in P. australis+L. chinensis community, the lowest in L. chinensis+P. australis community, with the highest being 3.2-5.4 times of the lowest. The density and biomass showed a unimodal growth dynamic in the form of logarithmic function, with the peak values  all in September. The soil environment of different communities was heterogeneous. The quantitative characteristics of P. australis populations were influenced by various soil factors, being positively correlated with moisture, organic matter, available nitrogen, available phosphorus and available potassium, but negatively correlated with pH and soluble salts. Different dominant species had different adaptability to soil factors. P. australis population could expand niche and improve competition ability by adjusting density and biomass, with consequences on community structure and composition. Together, those results indicate Zhalong wetland is under a progressive succession.

Key words: Zhalong wetland, community, Phragmites australis population, population density, population biomass.