Typical Wetland Vegetation Characteristics And Environmental Interpretation Of Their Distribution In Dongting Lake

The distribution of wetland plants usually show a belt distribution patterns along the environmental gradient. However, the formation mechanism of plant zonation is far from clear. A large number of facts showed that the formation mechanism of wetland vegetation patterns is very complicated, mainly determined by the natural environment of wetlands and biological characteristics of wetland plants as well as human disturbance. The distribution of wetland plants showed a zonation distribution patterns along with the gradient of water level in the Dongting Lake with the following sequence:submerged plants community→Phalaris arundinacea community→Polygonum hydropiper+Carex. sp community→Carex.sp community→Miscanthus sacchariflorus or Phragmites communis communty→Populus nigraor or Salix purpurea community from the bottom of the lake to land. In this paper, the community characteristics and soil physiochemical properties, as well as the relationship between community distribution, biomass, special diversity and abiotic environment of P. arundinacea community, P. hydropiper community, Carex. sp community and M. sacchariflorus community were studied in order to investigating the most important environment factors that determinning plant zonation distribution. It can provide theory basis for the protection of wetland resources and the restoration of the degradation wetlands. The results are as followed:1. Community characteristics of typical vegetation in the Dongting LakeA total of 55 species, mostly annual or perennial herbs, belonging to 21 families 51 genera, were found in the investigation plots. The plants belongs to Gramineae and Compositae families distribute widely in this wetland. There were significant difference with the biomass and Shannon-Weiner diversity index between these four vegetation community. The order of biomass was M. sacchariflorus community (5.9 kg·m-2)>P. arundinacea community (2.8 kg·m-2)>P hydropiper community (2.5 kg·m-2)> Carex.sp community (1.6 kg·m-2) and the order of species diversity was M. sacchariflorus community(0.55)>P. arundinacea community (0.47)>P. hydropiper community (0.40)>Carex.sp community (0.19). Biomass and species diversity index had significant relationships with the layers of community and species characteristics.2. Abiotic environmental characteristics of 4 typical vegetation in the Dongting Lake WetlandsThere were significant differences among P. arundinacea community, P. hydropiper community, Carex. sp community and M. sacchariflorus community in the average groundwater depths and the values are 31cm,59cm,80cm,176cm, respectively. The content of Soil nutrient in the four vegetation communities have the same performance which was highest in the soil surface, but there was signficant difference between different soil layers of these four vegetation communities. No significant difference was found in the soil total phosphorus and potassium between different vegetation community, which might be determined by the sediment deposition in the Dongting Lake. There were significant differences between these four vegetation communities in the soil ammonia nitrogen, nitrate nitrogen, available phosphorus and available potassium, moreover, significant differences were also found with different regions.Due to the impact of groundwater depths, soil physical properties, such as water content, redox potential and conductivity changed greatly in these four vegetation communities. Soil water content, soil bulk density and electrical conductivity increased significantly with the enhancement of groundwater depths, but redox potential decreased serioulsy. Soil bulk density changed with the range of 0.88-1.40 g·cm-3.Correlation analysis showed that groundwater depths had a significant relationship with soil physiochemical properties. Changes in groundwater depths will inevitably lead to soil wetting and drying by turns, which then influencing the soil physical and chemical properties. Therefore, changes in groundwater depths play a important role in regulating the change of soil physical and chemical properties.3. Environmental interpretation of typical vegetation distribution in the Dongting Lake WetlandsDCCA showed that eigenvalues of the first and second axis were 0.562 and 0.189, respectively. Cumulative percentage variance of species-environment relation of the first axis was 52.6% and this of the fromer two axis was 77.1%. The first axis reflect the waterlevel and soil physical properties environmental gradients of diffrent communities, but the waterlevel gradient was the most crucial. The second axis basically showed the changes of soil organic matter and nitrogen of plant communities. Therefore, groundwater depths, reflected by the changes of groundwater levels and altitude, is the key environmental factor determinning the distributions of plant communities.