| Wetland is a treasure house of resources on which human beings rely for survival and development.It has irreplaceable important functions in maintaining regional balance of nature,and protecting global biodiversity and rare species resources.However,the global natural wetland area has been gone through a long-term downward trend towards constantly deteriorating in wetland ecosystems and weakening,in their ecological service functions.resulting in a critical situation.The restoration and reconstruction of wetland vegetation are crucial in the restoration process of degraded wetlands.It is thus of high significance both in theory and practice to carry out a study on wetland ecological restoration with focus on investigation and analysis of the vegetation composition of the wetland ecosystems,their characteristics of soil seed bank and relevant correlations among them.In this dissertation,the lake-shore of the Ximaoli Lake was chosen as the experimental area,along which five transects were set up based on the distance away from the water and the nature of the vegetation types.The,five transects were denoted,respectively,as T1(seasonal flooded),T2(near the water),T3(middle distance to the water),T4(far from the water)and T5(naturally recovered wetland,distance to the water similar to T3).Based on the results obtained from the field investigation,sampling,indoor cultivation and germination of seed banks,statistical analyses were performed to determine the composition and biodiversity of the vegetation,the characteristics,of soil seed bank,soil organic carbon,and relevant factors affecting the wetland ecosystems in the lake-shore zone of the Ximaoli Lake.The main findings are summarized as follows:(1)According to the statistical results of vegetation background survey,there are 201plant species in the lake-shore zone,belonging to 59 families and 134 genera,respectively.Compared with arbor,shrub and liana,herb species dominated absolutely in the lake-shore.(2)Research on vegetation community diversity showed significant difference in sampling time(i.e.,season)for the Margalef,Shannon-Wiener,Simpson and Pielou indices(P<0.001).In addition to the Pielou index,the other three indices decreased significantly with increase in sampling month;the diversity was significantly greater in spring than in summer;and the plant richness in late autumn and early winter was the lowest.There were significant differences among transects for both Margalef and Shannon Wiener,but not for Simpson and Pielou.The Margalef and Shannon-Wiener indices increased apparently from lake water region towards land area.The species diversity of the artificial restoration transect was lower than that of the natural restoration transect.(3)The results of Detrended Correspondence Analysis(DCA)ordination and Two-way indicator species analysis(TWINSPAN)also showed significant differences in community composition among both sampling transects and sampling time.The vegetation in the Ximaoli lake can be classified into four vegetation groups(namely,hygrophyte type,meadow type,swamp type and hydrophyte type)including 40 formations.Water level and soil nutrient conditions(mainly,soil organic matter,total nitrogen and total potassium)were the main factors controlling the vegetation composition and distribution of wetland community.(4)The research results of soil seed bank background characteristics showed that there were 110 species of plants sprouting,belonging to 34 families and 85 genera.The number of germinated plants had a very significant difference among different zones(P<0.001).The number of germinated plants had an obvious increasing trend towards the shore land direction.The average density of the seed bank was 51641 seed/m~2(T4),and the minimum density was 10990 seed/m~2(T1).The analysis of variance showed that the density of the seed bank had a gradual change in the vertical distribution,and the density value decreased with the increase in soil depth(P<0.01);The density of the seed bank changed significantly in different seasons(P<0.05).The highest density of soil seeds was found in spring,followed by winter and summer.In terms of species richness,the Margalef and Simpson indexes of the seed bank were lower in summer than in spring and winter.(5)The analysis of similarity between soil seed bank and vegetation species showed that the similarity coefficients were in the range between 0.10-0.413,and the radiation along the lakeside land direction was decreasing.This supported the view that the similarity between seed bank capasity and plant species composition exhibits a decreasing trend with the increase in succession series level.From the perspective of inter-annual change,the similarity coefficient between the seed bank and the above-ground species composition after one year of restoration was between 0.24～0.42,which had increased to a certain extent compared with that before restoration,indicating the presence of a significant correlation between the density of the soil seed bank and the characteristics of above-ground vegetation.The seed bank had made a great contribution to vegetation restoration.(6)The research results of soil organic carbon showed that the soil organic carbon(SOC)decreased with the increase in soil depth.With the increase in months,SOC increases continuously.The values of SOC were significantly different among different transects(i.e.,land use types)(P<0.05),suggesting that land use types affected SOC in the lake-shore.The results gave the support to the conclusion that a project for restoring wetland is often regarded as an important measure to increase SOC,which thus provided a meaningful case study for an increase in SOC with the advancement of succession.(7)The correlation analysis between soil organic carbon and soil physicochemical properties indicated that most factors were closely related to SOC(P<0.01).Total nitrogen accounted for 81%of SOC variation,suggesting that total nitrogen was the dominant factor affecting SOC.An“S-shaped”curve was determined for the relationship between SOC and the total nitrogen,suggesting that the application of nitrogen fertilizer should have a greater contribution to SOC at lower nitrogen content than at higher one.The present study adopted the research approach of replacing time with space,and set up different water level gradient transects along the lakeside land direction,simulating different stages of succession sequence.By comparing the differences of vegetation composition and seed bank characteristics in different transects and seasons,the study revealed the dynamic changes of species diversity and the function of soil seed bank in succession sequence,added values to relevant theories of ecosystem succession,and provided thus a theoretical basis with valuable data for promoting the restoration of wetland ecosystems in the lake-shore area. |
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