The interaction of water, vegetation and soil in Zhalong wetland, China

We examined the effects of water level gradient and soil solutes on the characteristics of Phragmites australis (Cav.) community in the Zhalong wetland at monthly intervals over a period of 3 growing season (2008, 2010 and 2011). Eleven plots were selected according to water gradient. Results indicate that the stem height, density and overall biomass of P. australis changed greatly along the water level gradient. In Zhalong wetland, the height and density of P. australis apparently correlated to the presence or absence of surface water. The total above-ground biomass had a similar pattern. The maximum biomass in 22.54 cm water gradient was 5093.18 g/m(2), about 360 times of zero water levels in the same period. The importance value of P. australis was significantly positively correlated with the water level gradient, and the correlation coefficient was about 0.726 (p<0.01). Meanwhile, the ratio of soil ions varied with water level gradient suggesting P. australis could decrease the salt-alkali mixed stress by regulating the soil ions. We saw that artificial replenishment of water not only increased the total above-ground biomass of P. australis but also enhanced the stability of Zhalong wetland, and that 10 cm of water level increase was optimum for P. australis growth.