Sdtudies On The Characters Of The Vegetation And The Soil Seed Bank During Wetland Restoration In Nansi Lake

Wetland which locates in the transitional zone between the aquatic and terrestrial ecosystems is one of the ecosystems with richest biodiversity, highest productivity and numerous irreplaceable ecological functions. Its importance has been recognized widely. Many wetlands had been destroyed seriously due to its internal frangibility and human disturbance in the past century. So the studies on wetland restoration and protection become the hot topic of ecology research. Agricultural utilization is one of the two main causes of wetland degradation. To prevent the degrading trend of wetland, some countries have carried out various programs, such as wetlands compensation and restoration of wetland converted from farmland. In China, the project of converting farmland to wetland is carried out in most of the lake regions. Vegetation restoration of these wetlands lacks the scientific guidance and is in urgent need of the research of ecological restoration on the theories and techniques aiming at the characters of wetlands converted from farmland.The vegetation restoration is one important and antecedent step for wetland ecosystem restoration. The technique of vegetation restoration includes the selection of restoration mode, the selection and combination of species, etc. Soil seed bank is a stock of regeneration potential of wetland vegetation and it is the basement of natural restoration for degraded wetland. Thus the compositive ecological research on the stand vegetation and the soil seed bank will offer the theoretical basement and technique support.In this paper, the characters of wetland vegetation in Nansi Lake was studied by comparing the history and the status of wetland vegetation and the functional characters of typical wetland communities restored by different ways, analyzing the characters of the flora and the life-form spectrum of native plants and the key influencing factors. Then, the characters and the main affecting factors of soil seed banks of wetland converting by farmland were studied:the seasonal dynamics of soil seed bank of typical communities from different wetlands were detected by seedling emergence method; a simulation experiment was conducted in lab which simulated three flooding conditions to understand the response of wetland soil seed bank to different hydrological regimes, the prediction of vegetation pattern after Nansi Lake was impounded as a reservoir for China’s South-to-North Water Transfer Project was made accordingly; then, a seed bank germination experiment controlling the water level and light conditions was conducted to reveal the ecological mechanism of effect of flooding on the seed germination. On the base of the research of vegetation and soil seed bank, the restoration pattern was suggested for wetland converted from farmland in lakeshore of Nansi Lake. At last, suggestions on vegetation restoration of wetland converted from farmland in lakeshore of Nansi Lake and the future study were proposed.Results of vegetation study showed that, in Nansi Lake area, the vegetation had been affected seriously by the human disturbances and water-level fluctuation in the past decades, so that it has the trend of area shrinking, habitat broken, and biodiversity declining, at the same time, it is under the threats of vegetation fragmentation and exotic species invasion. Accordingly, wetlands in Nansi Lake are in urgent need of restoration and protection. The flora and the life-form spectrum of native species implied that the local environment was wet and changed frequently; the communities in natural secondary wetland had higher plant biodiversity, while constructed wetland could restore the most wetland ecological functions in a shorter time in term of its coverage and biomass; water level and human disturbances were the key factors influencing the community characters.Studies on soil seed bank of wetland converted by farmland found that there were43vascular species detected in the soil seed banks of wetland converted from farmland in lakeshore of Nansi Lake and the mean germinable seed density was2822seed/m2(0～12499seed/m2); community type and restoration mode presented significant effects on the germinable seed density and there are significant interaction effects between the two factors, season and restoration mode present significant effect on the germinable species abundance and there were significant interaction effect between them, which were demonstrated in the following aspects:in natural restoration wetland converted from farmland, soil seed banks of Populus nigra Plantation Community in all one year and Phragmites australis community in winter had higher seed density than soil seed banks in constructed wetlands; in the two type wetlands, species abundance of the winter soil seed banks of P. australis community and the summer and winter soil seed banks of P. tomentosa Plantation Community showed the same rule; in a word, restoration mode has stronger impact on the winter soil seed banks of P. australis community and P. tomentosa plantation community.Results of water controlled germination experiment showed that the seedling number was the least under submerged30cm treatment in all the ten months, but the data in the second month is higher significantly than the other two treatments which indicate that the flooding might delay and suppress the seed germination. From the species perspective, the difference response of distrinct species seeds to flooding could be explained by the species-specific flooding tolerance; from the community perspective, the P. tomentosa plantation and the P. australis community are more sensitive to flooding than the other types; from restoration mode angle, the natural restoration wetland converted from farmland is more sensitive than the man-made restoration one which might be caused by the relatively high proportion of terrestrial plants in the natural restoration wetland in our research. Accordingly, the P. tomentosa plantation and the P. australis community in the natural restoration wetlands will be affected more easily by flooding. Thus, a prediction of vegetation pattern after Nansi Lake was impounded as a reservoir for China’s South-to-North Water Transfer Project was made:the pattern of the emergent aquatic vegetation and the wetland forest will change greatly, some aquatic species existing in the soil seed bank might build natural restoring populations; the species with high flooding tolerance will dominate in the future communities. Addtionally, the temporal dynamic of seed ermergence implied the prolonged experiment time could help to decrease the test error.Results of the water and light controlled germination experiment showed that under substrate-saturated with strong light treatment, the seedling density and species abundance both were higher significantly than those under the other two treatments indicating that light promoted the seed germination of soil seed bank from P. tomentosa plantation and the P. australis community; the seedlings from the P. tomentosa plantation seed bank under flooding30cm with strong light treatment was notable less than those under substrate-saturated with weak light treatment indicating the more sensitivity of species in the P. tomentosa plantation seed bank. In view of the above results, the effect extent of light is different with the species-specific characters of seed bank, the same to flooding. In the studies on the vegetation restoration pattern, an evaluation index system was established for selecting species to restore wetland vegetation, the important species in lakeshore of Nansi Lake wetland communities were evaluated, selected and combined by their interspecific relationship and their regeneration potential in soil seed banks. Accordingly, the primary species configuration pattern was built and the management measures for wetland vegetation were put up which could be used in the practice of "converting farmland to wetland" project.To sum up, by the studies on vegetation and soil seed banks, their characters were revealed, the influncing mechanisms of restoration mode, water depth and light to soil seed bank were discussed, so the main conclusions were made that the wetland converting from farmland is suitable to be restored by additional artificial help, the ermergent plant communities and the wetland forest could be affect heavily by flooding in lakeshore wetlands of Nansi Lake. Also the wetland vegetation restoration mode in Nansi Lake was suggested based on the study.