Study On The Changes Of Seed Banks With Different Water Depth Gradients In Longgan Lake

At present,wetlands are one of the most threatened habitats in China and even the world.With the deepening understanding of the importance of wetland protection,more and more attention has been paid to wetlands.How to restore and rebuild the ecosystem of damaged waters has become a hot topic for many scholars at home and abroad.As an important part of wetland research,seed bank research is an important content to deeply understand the structure and function of wetland vegetation.The role of seed banks in damaged wetland soils in vegetation restoration is attracting increasing attention.Longgan Lake is located in the border area between Huangmei County in Hubei Province and Susong County in Anhui Province.Its wetland types are diverse and it is one of the important wetland reserves in the middle and lower reaches of the Yangtze River.In recent years,under the interference of natural and human factors,longgan Lake wetland has been seriously degraded.Therefore,it is of great significance for the restoration and reconstruction of Longgan Lake wetland to strengthen the dynamic change study of the seed bank of Longgan Lake wetland and explore the succession rule of its wetland vegetation,and provide basic reference for the natural restoration study of wetlands in the middle and lower reaches of the Yangtze River.This study takes Longgan Lake as the object of study.Through germination experiment of soil seed bank,investigation of aboveground vegetation and analysis and comparison of physical and chemical properties of soil and water,the results are as follows:(1)The seed germination test results showed that 40 species,belonging to 22 families and 35 genera,were germinated in the seed bank of Longgan lake,among which the species of Graminae were the most,followed by Cyperaceae,Hydrocharitaceae and Polygonaceae.The seed bank was dominated by perennial species,and the density of soil seed bank was 5796±155.75 seeds/m~2.The dominant species are:Ceratopteris pteridoides,Gratiola japonica Miq.,Callitriche palustris and Zizania latifolia.The density of soil seed banks was 12169±171.74 seeds/m~2 in shallow water,4309±83.76seeds/m~2 in middle water and 911±7.68 seeds/m~2in deep water,respectively.The dominant species in shallow,middle and deep water were Ceratopteris pteridoides,Gratiola japonica Miq.,and Vallisneria natans,respectively.The number of seed banks decreases with the increase of water depth gradient.(2)Survey of aboveground vegetation showed that there were 17 species of aboveground vegetation in Longgan Lake,belonging to 11 families and 15 genera,among which Gramineae and Polygonaceae had the most species and number.Aboveground vegetation ecotype was dominated by hygrophytes,while perennial herbs were the majority of life forms.The dominant species are perennial herbs,mainly Zizania latifolia and Eichhornia crassipes,which are the absolute dominant species of terrestrial vegetation.(3)The number of soil seed banks under all water depth gradients was higher than that of aboveground vegetation,and the similarity between soil seed banks and aboveground vegetation was low.(4)The water bodies of Longgan Lake reached eutrophication state in spring and summer,and the degree of eutrophication in summer was higher than that in spring.The total phosphorus had the most significant effect on the number of seed bank species,and the total nitrogen also had a significant effect on it,and the total nitrogen content was positively correlated with the seed bank density(P<0.05).(5)Compared with 2004,the number and species of seed bank species decreased significantly in 2019,and the species and quantity of aboveground vegetation also deteriorated seriously.The degradation of vegetation is particularly serious in deep water areas,with only two species remaining(Trapa natans and Nelumbo nucifera),In the shallow water area,the dominant species of aboveground vegetation were still Zizania latifolia and Polygonum maackianum.In the middle water area,the dominant species of aboveground vegetation were Alternanthera philoxeroides,which was replaced by Eichhornia crassipes.The original zonal distribution of the plant community has become sporadic and fragmented distribution.