A Study On Soil Seed Banks In Evergreen And Deciduous Broad-leaved Mixed Forest At Jinzi Mountain In Hubei Province

The evergreen and deciduous broad-leaved mixed forest is a transitional vegetation type between subtropical evergreen broad-leaved forests and warm-temperate deciduous broad-leaved forests.It constitutes the main type of mountain forest in the northern subtropical region or at high altitudes in China,boasting high biodiversity and ecological value,albeit being sensitive to climate fluctuations.As seasons change,ecological factors such as light and temperature in the understory of the evergreen and deciduous broad-leaved mixed forest are significantly influenced by the ratio of individual numbers between evergreen and deciduous tree species(Evergreen/Deciduous,E/D),which,in turn,impacts the soil seed bank.Understanding the characteristics of the soil seed bank in the evergreen and deciduous broad-leaved mixed forest and its relationship with the E/D ratio is critical for forest management and ecological protection.However,such studies are scarce.To address this knowledge gap,this study selected the secondary subtropical evergreen and broad-leaved mixed forest in Jinzi Mountain State Forest Farm,Lichuan,Hubei Province,as the research object.We selected thirty 20 m×20 m plots based on the proportion of needle-leaved and broad-leaved tree species aboveground and used the five-point sampling method to set five 20 cm×20 cm soil seed bank sampling points in each plot.Soil samples were collected from four layers and cultured in a greenhouse to identify plant species in each soil sample layer and count the number of seeds for each plant species.Finally,based on the ratio of evergreen and deciduous tree species aboveground,we conducted a comprehensive analysis of the characteristics of the soil seed bank and aboveground vegetation.The results of this study showed that:1.The E/D ratio has a significant impact on the species diversity of the aboveground vegetation.As the E/D ratio increases,the richness of families,genera,and species decreases.When the E/D ratio is within the range of 0 to 0.4,there are the most species in the sample plot,with 83 species belonging to 43 families and 70genera.When the E/D ratio is greater than 1,there are the fewest species in the sample plot,with only 59 species belonging to 33 families and 52 genera.Rosaceae plants are the most adaptable,appearing in all five E/D ratio-level sample plots.The dominant species in different E/D ratio communities are different.When the E/D ratio is within the range of 0 to 0.4,the dominant species is Castanea henryi;when the E/D ratio is within the range of 0.4 to 0.6,the dominant species is Cunninghamia lanceolata;when the E/D ratio is within the range of 0.6 to 0.8,the dominant species is Castanea mollissima;when the E/D ratio is within the range of 0.8 to 1,the dominant species is Cornus macrophylla;and when the E/D ratio is greater than 1,the dominant species is C.henryi.2.The ratio of E/D has a significant impact on the species diversity of the soil seed bank.As the E/D ratio increases,the density of the soil seed bank shows a"rise-fall-rise"trend.When the E/D ratio is between 0.4 and 0.6,the density of the soil seed bank reaches its maximum,at(3167±1150)seeds/m~2.Herbaceous plant seeds generally make up the majority of the soil seed bank,but as the E/D ratio increases,the density of herbaceous plant seeds decreases,while the density of woody plant seeds increases.The seed density of shrubs is also much higher than that of trees.Among the species composition of the soil seed bank,Idesia polycarpa has the highest seed density for trees,while Viburnum betulifolium,Spiraea japonica,and Hydrangea aspera have the highest seed density for shrubs.The seed density of perennial herbaceous plants is highest for Schoenoplectiella juncoides,and the seed density of annual and biennial herbaceous plants is highest for Stellaria media and Cyperus microiria.Overall,the data suggests that the soil seed bank is strongly influenced by the ratio of E/D,and the composition of the seed bank varies with changes in this ratio.3.The similarity in species composition between the soil seed bank and the aboveground vegetation is low.Only 20 species are common to both the soil seed bank and the aboveground vegetation,while 42 species appear exclusively in the soil seed bank and 132 species appear exclusively in the aboveground vegetation.Although the species composition of the aboveground vegetation is more strongly influenced by the E/D ratio than that of the soil seed bank,the similarity in species composition between the two is not significantly affected by the E/D ratio.Notably,the woody plant C.macrophylla,Betula luminifera,and V.betulifolium are present in both the aboveground vegetation and the soil seed bank across different E/D ratios.This suggests that their seedlings have a wide ecological range and high stability and regeneration potential within the evergreen and deciduous broad-leaved mixed forest ecosystem.These species may be a key focus of future conservation efforts in this mixed forest ecosystem.