Effects Of Soil Salinity Rate On Morphological Characteristics Of Phragmites Australis, And Its Potential Applications In Constructed Wetlands

In recent years, as the development and use of the wetland, it suffered serious pollution and destruction, and the area of wetland had decreased, so, to protect and restore wetland became hot issue. In restorating those damaged wetlands or in constructing wetlands, Phragmites australis is an important tool plant for its ability of stain resistance, decontamination and etc. Phragmites australis (common reed) has a wide ecological amplitude, which enables it to tolerate many types of habitat. The interacting influences of different environmental selective forces, such as water depth, salinity, nutrients and climate, lead to differentiation and variation among reed clones or populations, and form various ecological types which differ in morphology, physiology or genetics. In this research we selected two zones, Taihu lake and Yancheng beach, and chose 12 Phragmites australis populations in the two zones, investigated the relationship between the morphological variation and soil salinity rate; In Yancheng beach, we selected three Phragmites australi population which grow in three different degrees of soil salinity rate in order to learn the effects of salinity on photosynthesis. So we can use Phragmites australi to protect and restore the wetlands in correct ways. Based on the analysis on the comparison of gas exchange and chlorophyll fluorescence of Phragmites australis and Typha orientalis, the optimum tool species would be chosen in constructed wetlands. The results showed:(1) The morphological characters of Phragmites australis have significant differences between Taihu lake and Yancheng beach, and the coefficient of variation of the same characters changed greatly among different populations.(2) The morphological characters of Phragmites australis have significant differences among different populations in the same zone, but those populations could be classified to several clusters based on morphological characters.(3) The soil salinity rate of the sample plots in this research is 0.255%,0.176% and 0.162%. Reed, grow in the habitat that soil salinity rate is below 0.255%, will increase water absorption, Gs, Tr and the stability and function of cell membrane (thylakoid membrane et al.) in order to enhances Pn. Then the Phragmites australis could promote its physiological and biochemical metabolism such as photosynthesis. The biomass accumulation of seedlings would increase and the salt tolerance of Phragmites australis would be improved. Phragmites australis is able to normal growth and complete the whole growth and development process in moderate saline habitats, so it has strong salt tolerance. According to Zhao KF's division standard, Phragmites australis is a kind of moderately salt-tolerant plants.(4) The net photosynthetic rate of Phragmites australis decrease at midday may be due to stomatal closure. Compared with Typha orientalis, Phragmites australis has higher net photosynthetic rate and chlorophyll content which are benefit to the accumulation of biomass and the absorption of more nutrients in constructed wetlands. Excessively strong light lead to the reduction of net photosynthetic rate of Typha orientalis and Phragmites australis, while Phragmites australis will dissipate more light energy with thermal energy in order to protect the PSII system of the reed leaves better. Therefore, compared to Typha orientalis, Phragmites australis is more suitable for treating water pollution as a tool plant in the condition of strong light and high temperature.