Characteristics Of Reproduction Bank Of Typical Plant Communities In Dongting Lake Wetland And Its Response Mechanism To Water Level Changes

Dongting Lake is an important wetland in the world.The vegetation of the wetland is mainly of grass type and distributed in a belt shape in spatial pattern,which plays an important role in maintaining wetland habitats in the lake region.Propagule banks is a potential plant community,including seed banks and bud banks,which is the internal driving force of wetland vegetation evolution.The current research on wetland vegetation succession focuses on the role of abiotic environment such as hydrology and soil,while ignoring the role of propagule banks role in succession process.Taking typical plant communities in Dongting Lake wetland as the research object,the density,composition and seasonal dynamics of propagule banks(seed banks and bud banks)were studied through field investigation and laboratory culture experiment;The characteristics of species composition and density of dominant plant communities under different water levels were studied by setting water level control experiments.This study is of guiding significance to enrich and perfect the theory of wetland propagule banks and to the restoration and reconstruction of wetland vegetation.The main results are as follows:(1)The seasonal variation of seed bank density in the C.brevicuspis communities and M.sacchariflorus communities was significant,and the change rules were relatively consistent.The overall change trend was:May(before the flood)>March(at flowering)>November(after the flood)and>January(in winter).Soil seed banks at different levels(0-5cm,5-10cm,10-20cm)were analyzed,and it was found that seed banks of C.brevicuspis and M.sacchariflorus communities were mainly concentrated in0-5cm,which reached the maximum in May,accounting for 87.6%and 94.5%of the total density,this indicated that the seed banks mainly came from the 0-5cm soil layer on the surface.The similarity coefficient between seed banks and surface vegetation indicated that the similarity coefficient of C.brevicuspis communities(0-0.04)and the and M.sacchariflorus communities similarity coefficient(0.06-0.19)between is low.The germination experiment of seed banks showed that annual plants accounted for more than 60%in the germination of the two communities,and perennial plants dominated the ground vegetation survey(56%),which was the reason for the low similarity coefficient of the two communities.(2)The bud banks density of C.brevicuspis communities and M.sacchariflorus communities was seasonal.The two communities were the lowest in May and the highest in January before the flood,and the C.brevicuspis communities(41-980 buds/m~2)was significantly higher than that of M.sacchariflorus communities(52-261 buds/m~2).The buds of the two communities were analyzed,and it was found that the C.brevicuspis communities were mainly short rhizome buds(0-838 buds/m~2),while the majority of the M.sacchariflorus communities was rhizome axillary buds(97-170 buds/m~2).Through investigation,it was found that the C.brevicuspis communities was composed of only the Carex,while the M.sacchariflorus communities was composed of the Carex,amur silvergrass and the reed.The similarity coefficient between the buds bank and the surface vegetation indicated that,the C.brevicuspis communities(0.21-0.93)was significantly higher than that M.sacchariflorus communities(0-0.46),since the surface plants of the C.brevicuspis communities were mainly Carex(accounting for 90%),and the lodging of C.brevicuspis itself was not conducive to the germination of other species on the surface,which was also the reason for the high similarity coefficient between the C.brevicuspis communities and surface plants.(3)There was a significant correlation between the propagule banks density and season(P<0.001),and the change trend was consistent.The maximum value was reached in May(C.brevicuspis communities:15331.20±4671.082 strains/m~2;M.sacchariflorus communities:17363.20±2486.679 strains/m~2),and the minimum value was reached in January(C.brevicuspis communities:1403.73±211.266 strains/m~2;M.sacchariflorus communities:745.87±96.400 strains/m~2).In January of winter,the bud banks density of the two communities accounted for 69.8%(C.brevicuspis communities)and 35%(M.sacchariflorus communities).In May,the seed banks density of the two communities accounted for 99.8%of the propagule banks density,indicating that the bud banks and the seed banks were both indispensable parts of the propagule banks.Vegetation similarity coefficient showed that the reproduction and the earth's surface,C.brevicuspis communities similarity coefficient between 0.25 to 0.93,the M.sacchariflorus communities similarity coefficient between 0.17 to 0.55,in May,the bud banks similarity coefficient accounted for 100%(C.brevicuspis communities)and70.9%(M.sacchariflorus communities)of the reproduction bank similarity coefficient.It could be seen that the bud banks contributed a large proportion to the propagule banks,and the bud banks was not negligible in the propagule banks.(4)The water level experiment on the communities of C.brevicuspis,M.sacchariflorus and poplar communities showed that the water level was significantly correlated with plant density,species richness and Simpson diversity index(P<0.05).The water level tended to decrease with the increase of water level,indicating that water level played an important role in plant growth and flooding was an important factor restricting the species composition of the plant communities.-20cm is the optimal water level for plant density,species richness and Simpson diversity index.In the early stage of water level treatment,plant density,species richness,Simpson diversity index and important value IV were significantly higher than in the later stage,indicating that water level stress over a long period was unfavorable to plant communities development.(5)According to the characteristics of wetland plant propagule banks density and seasonal changes,seed banks should be used as the foothold in the early stage to promote the rapid establishment of surface vegetation,and bud banks should be used as the foothold in the later stage to achieve the purpose of stable plant communities in the future wetland restoration work.