| Mountainous cities provide good conditions for the preservation of natural forests in cities.However,due to the continuous acceleration of urbanization,urban natural forests are seriously damaged.The use of soil seed banks to restore and rebuild urban forests is particularly important in landscape projects.Taken the soil seed bank and regeneration seedlings of natural forest in Chongqing urban mountain park as samples,this paper studies the composition characteristics,seedling regeneration characteristics,influencing factors and relationship with plant community of soil seed bank under natural forest.Through field community investigation and indoor germination experiments,it provides a scientific basis for the use of soil seed banks for vegetation restoration,reconstruction and ecological garden construction.The main findings are as follows:(1)Species structure,spatiotemporal distribution and germination characteristics of soil seed bank: there are 113 species of plants in 55 families,106 genera in the soil seed bank,dominated by Compositae and Gramineae.The life form composition shows that perennial herbs are the main plant,and trees,small trees and shrubs are in the minority.Biodiversity of herb is higher than that of woody plants.in winter,the soil seed bank density is significantly higher than that in spring.Plants seeds like Broussonetia papyrifera,Ficus virens,Melia azedarach are the highest in density.Herb seeds such as Solanum nigrum,Oplismenus undulatifolius,Sinosenecio oldhamianus,Youngia japonica,Acalypha australis,Gnaphalium affine,Mazus pumilus is the highest in density.Seeds have obvious vertical distribution in soil,and the density of soil seed bank in 0-5cm soil layer is significantly higher than that in5-10 cm soil layer.There are certain differences in the composition of soil seed banks among these three plots.The soil seed bank of Zhaomushan Forest Park is the most abundant in species composition,biodiversity and seed density,followed by Hong’en Temple Forest Park,while Pingdingshan forest park is the lowest.The seed germination rate is the highest in the first three weeks of seed germination test,and the seed germination rate in spring is significantly higher than that in summer.(2)Association of soil seed banks with regeneration seedling species structure:the survey results of field regeneration seedlings shows that there are 47 kinds of trees in the plot,but only 25 kinds of trees were observed to have regeneration seedlings,while it is difficult for the other 22 kinds of trees to regenerate.Deciduous broad-leaved trees such as Broussonetia papyrifera,Koelreuteria paniculata,Melia azedarach,and evergreen broad-leaved trees such as Cinnamomum japonicum and C.camphora are better regenerated.These plants have large seed yield,strong spreading ability,drought resistance and barren resistance,and could adapt to the urban environment of Chongqing better.By calculating the transformation rates among seedlings and young trees at different height levels,the result showes that the transformation rates among seedling heights and among seedlings and young trees are higher,and the transformation rates among young trees are lower,this may be an important reason affecting the natural regeneration of forests.(3)Association of soil seed banks,regeneration seedlings,and plant communities :The results of Sorensen similarity analysis showed that soil seed bank share low similarity with plant community and high similarity with regeneration seedlings.The percentage of woody plant seeds in the soil seed bank is significantly lower than that in the plant community.The common dominant species of soil seed bank and plant community are Broussonetia papyrifera,Ficus virens and Oplismenus undulatifolius.The average Sorensen similarity index between soil seed bank and plant community in winter is 0.32,and in spring it is 0.24.The distribution characteristics of soil seed density are significantly correlated with the distribution characteristics of the number of natural young seedlings(P<0.05).The average Sorensen similarity index of each plot is 0.58,indicating that the soil seed bank is closely related to regeneration seedlings.In terms of species composition,there are 12 common species in total among the regeneration seedlings and arbor seeds in the soil seed bank.In terms of density,Broussonetia papyrifera,Cinnamomum japonicum,Koelreuteria paniculate,Melia azedarach,Cinnamomum camphora are the highest in density of regeneration seedlings,while Broussonetia papyrifera,Ficus virens,Melia azedarach,Vitex negundo,and Triadica sebifera seeds are the highest in density in soil seed bank.(4)Responses of soil seed banks and regeneration seedlings to ecological factors:after analyzing the effects of 13 impact factors on soil seed bank density and regeneration seedling density,the results shows that: soil seed bank density is significantly negatively correlated with herb cover,slope,p H,organic matter,and available phosphorus(P<0.05),and is significantly positively correlated with available nitrogen and bulk density(P<0.05).As the altitude increases,the density of soil seed bank first increases and then decreases(P<0.05).The density of soil seed bank and regeneration seedlings on sunny slopes is significantly lower than that on shady slopes(P<0.05).Regeneration seedling density is significantly positively correlated with slope and bulk density(P<0.05),and significantly negatively correlated with soil organic matter and available nitrogen(P<0.05).With the increase of herb cover,it first increases(P<0.05),and then decreases(P<0.05).The Canonical Correlation Analysis(CCA)results of soil seed bank species and regeneration seedling species abundance and 13 ecological factors shows that: soil p H,canopy and slope position have the biggest impact on the distribution of soil seed bank species,followed by shrub cover and slope aspect.shrub cover,available nitrogen,available potassium,organic matter and soil p H have the biggest impact on the distribution of regeneration seedling species,followed by available phosphorus and bulk density. |
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