Temporal And Spatial Variation Of Vegetation And Soil Seed Bank In The Water Level Fluctuation Zone Of The Three Gorges Reservoir,China

After the operation of the Three Gorges Reservoir,reservoir falls area bad evolve from the original terrestrial ecosystem succession to the amphibious alternate wetland degraded ecosystems succession.A longstanding anti-seasonal water logging had some bad influences on vegetation degradatiin such as poor stability of ecological structure and a reduction of species diversity and so on.In this case,what influences do different vegetation restoration mode and falling zone type of vegetation succession make on the succession of surface vegetation?How about the response of soil seed banks?This is the main scientific problem which this article intends to solve.Therefore,based on a test on mainstream and tributaries,natural and artificial restoration of falling zone and a project demonstration base which are built by a team in the Three Gorges Reservoir,this article carried out exploratory research on the damage to the wetland vegetation and soil seed bank of space-time dynamic by adopting the method of random sample of typical vegetation,For three consecutive year(2013-2015),spring(March),summer(July),autumn(September),winter(The following January).Four seasons and four continuous elevation 185-175m(control area),175-165 m,175-155m and 155-145 m elevation sectio.The results show that(1)The Surface vegetation:In natural restoration area,the total species number of annual biomass in both mainstream and tributaries in 2013 was significantly lower than that of 2014 and 2015,and annual variation of perennial species was not obvioius.The total species number in mainstream:for the number of annual biomass species,the number in spring is more than it in summer combining with the number in autumn is more than it in spring.For the perennial species,the differences in number among spring,summer and autumn are not obvious and species number in any one of spring,summer and autumn is more than it in winter.The total species number in tributaries:for both annual biomass species and perennial species,the differences in number among spring,summer and autumn are not obvious and species number in any one of spring,summer and autumn is more than it in winter.The total species number and the perennial species number decrease with altitude reducing.For all years,all seasons and all altitudes,Setaria viridi,Xanthium sibiricum,Echinochlo acrusgalli,Polygonum hydropiper,Cynodon dactylon and Alternanthera phildoxeroides are the commom dominant species.In artificial repair area,the annual variation of the species number of all the annual species,perennial species and the total species is not obvious,while both the number of total species and perennial species decrease with altitude reducing.For annual species,Setaria viridi is the dominant species in 175-165m altitudes,Xanthium sibiricum is the dominant species in 155-145m altitudes.But in 165-155m altitudes,there is no dominant species.For perennial species,Cynodon dactylon is the donminant species in all altitudes.(2)Soil seeds bank:the trends of species number and dominant species composition in mainstream and tributaries,natural repaired area and artificial repaired area are common.the annual and seasonal variation of the species number of all the annual species,perennial species and the total species is not obvious,while the number of total species decreases with altitude reducing.Youngia japonica,Gnaphalium affine and Oxalis corniculata are the dominant species in 175-165m altitudes.In 165-155m altitudes,Youngia japonica,Ranunculus japonicus and Artemisia argyi are dominant,while in 155-145m altitudes,Ranunculus japonicus is the only dominant species.(3)Similarity between soil seed bank and surface vegetation:Inthe year of2013-2015,the Similarity coefficient in all seasons and all altitudes is lower than 0.39,and the coefficient is always the highest in autumn and the lowest in spring.(4)Biodiversity Index:all Shannon-Wiener index,Simpson index,Evenness index,and Margalef index increased year by year,and all above indexes decreased with altitude reducing.Evenness index in artificial repaired area is smaller than it in natural repaired area.Besides all Shannon-Wiener index,Simpson index,Evenness index,and Margalef index in soil seeds bank increased year by year.(5)The impacts on biodiversity of environmental factors:Altitude has been the most significant environmental factor in affecting biodiversity.With the succession,seasonal variation had significant effects on species diversity and evenness.Meanwhile,the restoration types play a more and more important role in the species richness and species diversity.At this stage,restoration types has the most significant effects on the species richness and species diversity.The above results have certain scientific significance for the ecological restoration and management of vegetation in the Three Gorges Reservoir area,and some of the results which have been preliminarily or are being transformed have good application prospects.(6)On the duration for seed germination of soil seed bank in the water level fluctuating zone of Three Gorges reservoir,it is suggested that the soil samples were collected in summer 240-270d,the soil samples were collected in autumn and 200-210d,the soil samples were collected in winter and 210-240d,and the soil samples were collected in spring 150-180d.