| The Pinus densata forests in Nyingchi,Tibet,were used as research objects.Field survey and laboratory experiment were conducted to study the species composition,quantitative characteristics,species diversity and species similarity between the ground vegetation and the soil seed bank were studied systematically.And the spatial distribution pattern of P.densata soil seed bank was also studied.In order to understand the status of soil seed bank in local P.densata forests and provide scientific basis for the protection and rational management of P.densata forests.Main results were as follows:1.Spatial distribution pattern of P.densata soil seed bank:The seed density in P.densata soil seed bank was not significantly different in the horizontal direction of east,south,west and north(P>0.05),but the seed density gradually became smaller as the horizontal distance from the parent tree increased.The trend of the distribution of near-mother trees was obvious.As the depth of soil increases,the number of seeds gradually decreases.The litter layer and 0～2 cm soil layer were the key areas of soil seed bank,and more than 90%of the total seeds were distributed.And in the research plot,the seed density of P.densata gradually increases with elevation.The number of worm seeds in the soil seed bank was the highest,which accounting for 43.90%of the total seeds,the number of viable seeds was very small,accounting for only 1.43%,and 73.38%of the viable seeds were stored in the litter.Therefore,timely disturbance of surface litter plays an important role in the natural regeneration of P.densata populations.2.Species composition and life style of P.densata community:There were115 species of higher plants in the ground vegetation of P.densata community,including 8 species of trees,39 species of shrubs and 68 species of herbaceous,and the genus of Compositae,Rosaceae,Leguminosae and Gramineae dominates.The life style of ground vegetation was mostly perennial herb and deciduous shrub,and the proportion of evergreen trees,deciduous trees,evergreen shrubs and annual herbs was low.From the perspective of the family composition of vegetation,the genus of the ground vegetation of P.densata forest was relatively concentrated.From the vegetation level,the tree layer was relatively single,and the shrub layer and the herb layer were more developed.In general,the species composition of P.densata community was rich in the study area.3.Species diversity of ground vegetation in P.densata forests:At different vegetation levels,Shannonn-Wiener diversity index,Pielou evenness index and Margalef richness index were all:herbaceous layer>shrub layer>arbor layer,while Simpson dominance index was:tree layer>shrub layer>herb layer,which indicated that the number of species and the number of species in the grass layer was the most,and the distribution was the most uniform,followed by shrubs.The number of species and the number of species in the tree layer were the least,and the distribution was the most uneven.In the same way,the Shannonn-Wiener diversity index,Pielou evenness index and Margalef richness index were both:LZ plot>DJ plot>BR plot,and Simpson dominance index was:BR plot>DJ plot>LZ plot,which indicated that in LZ plot the number of species and species were the largest,and the species distribution was the most uniform.On the contrary,the number of species and the number of species in the BR plot was the least,and the species distribution was the most uneven.Through comparative analysis,it was found that the topography and disturbance will also affect the species diversity of P.densata community in a different degree.4.Species composition and seed density of soil seed bank in P.densata forest:The seed density of DJ plot,LZ plot and BR plot was 2062.6 grains/m~2,1901.2 grains/m~2,971.5 grains/m~2,respectively.The average density was 1645.1grains/m~2,of which herbaceous plants occupy the most advantages,followed by shrubs,and only one species of tree.A total of 46 species of 1596 plants,1species of arbor,10 species of shrubs and 35 species of herbaceous plants were planted in the soil seed bank,among which Asteraceae(8 species),Rosaceae(5species),Labiatae(3 species)and Gramineae(3 species)dominated.The life forms of the species in the soil seed bank were mostly perennial herbs.In addition,there were 14 species of occasional species(multiple degrees≤3)in the soil seed bank,and 11 species in the three plots.Interference and the thickness of the surface litter will have a greater impact on the species distribution and seed density of the soil seed bank.5.Species diversity analysis of soil seed bank in P.densata forest:Shannonn-Wiener diversity index,Pielou evenness index and Margalef richness index were all:herb layer>shrub layer>tree layer,and Simpson dominance index was:tree layer>shrub layer>herb layer,which indicated that the herbaceous layer was the most abundant species,with the largest number of germination and the most uniform distribution.At the shrub level,the tree layer has the least number of species and the most uneven distribution.Simpson dominance index and Pielou evenness index of DJ plot,LZ plot and BR plot soil seed bank had little change,and the species distribution was relatively uniform.Shannonn-Wiener diversity index and Margalef richness index of DJ plot were the largest.Obviously,the species richness and the number of species in the soil seed bank are also the most.6.Species similarity between soil seed bank and ground vegetation in P.densata forest:The number of common species between soil seed bank and ground vegetation in P.densata forest is small(32 species),and the similarity was low(C_j=0.25,C_m=0.006,C_s=0.40),the similarity between soil seed bank and ground vegetation in P.densata forest plots was also low(C_jwas 0.18～0.29,C_mwas 0.006～0.009,C_swas 0.31～0.46).And the proportion of species in the soil seed bank is higher(69.57%),the proportion of seeds in the total seed seed bank is also higher(88.22%).Although the similarity between soil seed bank and ground vegetation was small,the ground vegetation contributes a lot to the soil seed bank. |
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