| The growth and distribution of species are not only related to their genetic and physiological characteristics,but also related to their biological and abiotic environments.The northern section of the Qinghai-Tibet Railway is located on the Qinghai-Tibet Plateau,where there is a great difference in altitude along the line,and the ecological environment is quite heterogeneous.Along the line,there are a variety of vegetation types,such as desert,desert steppe,alpine steppe and alpine meadow,and the terrain composition of species is relatively complex The vulnerability of ecological environment,vegetation in the region once destroyed,more difficult to recover,and the ecological species group was divided by number of vegetation classification,explore the vegetation distribution pattern and the relationship between environmental factors and to determine the changes in vegetation,species and the potential distribution of plant communities and strategy is of great significance to the protection of plant diversity.Based on the field investigation,the vegetation of the primary and secondary communities along the northern section of Qinghai Tibet railway was classified by two-way indicator species analysis and DCA ordination,and the species composition of each community was described;the relationship between the overall species and individual community species of the primary and secondary communities and environmental factors was analyzed by DCCA ordination,and the results were compared Partial DCCA ranking method was used to evaluate the relative importance of environmental factors to species composition;GLM model and gam model were used to fit the response between species richness of primary and secondary vegetation communities and environmental factors,respectively(1)Along the northern section of Qinghai Tibet railway,139 species of plants belonging to 74 genera and 28 families were found in the primary vegetation,including 8 shrubs and 16 annual plants;the dominant species were Leontopodium pusillum(IV = 0.1174),accounting for the absolute dominance;121 species of plants belonging to 72 genera and 23 families were found in the secondary vegetation,including 7 shrubs and 16 annual plants;the dominant species of secondary vegetation were Potentilla bifurca(IV = 0.1069),Kobresia pygmaea(IV = 0.0742)and Leontopodium pusillum(0.0703).The species composition of secondary vegetation community was mainly drought tolerant and barren tolerant species.(2)Based on Two-way indicator species analysis and DCA ordination,the primary vegetation and secondary vegetation along the northern section of the Qinghai Tibet railway were both divided into seven community types,and each of the seven communities was zonal along the altitude.There was a cross between the communities in the altitude range,and there was community overlap in the central elevation region(about 4225-4757 m).In the same community of primary vegetation and secondary vegetation,the similarity index was 0.31,which indicated that the species composition of community was different.(3)Different environmental factors affect the species composition and distribution pattern of primary and secondary vegetation.Topography and climate and soil in the three kinds of environmental factors,native vegetation terrain factor,the net effect is 13.24,significantly explain along qinghai-tibet railway section of native vegetation community distribution pattern and species composition(P<0.05),secondary community soil factor,the net effect is 40.74,significantly explain secondary vegetation community distribution pattern and species composition(P<0.05)of native vegetation and secondary vegetation environment factors explain ability of soil factor > terrain factor > climate factor of all the environmental factors,elevation of the average annual temperature Significantly explained the annual average precipitation of native vegetation species(P<0.05),the secondary vegetation only elevation and average annual precipitation of two environmental factors explain the species significantly(P<0.05)of native vegetation and secondary vegetation can significantly explain environmental factors and their relative importance of different species,native vegetation,altitude explain ability strongest(gross effect is 10.48,net effect is 3.54).The second is annual mean precipitation(gross effect is 10.36,net effect is 3.52)and annual mean temperature(gross effect is 9.62,net effect is 2.97).For secondary vegetation,the explanatory power of altitude(total effect is 10.58,net effect is 5.82)and annual mean precipitation(total effect is 10.01,net effect is 5.82)was the same.(4)There are certain differences in the environmental factors that can significantly affect the species richness of primary and secondary vegetation along the northern section of Qinghai-Tibet Railway,and there are also certain differences in the response curves of species richness to environmental factors.Native vegetation,the species richness and the annual average precipitation,altitude,total nitrogen content and organic matter content was significantly increases monotonously relations,and the annual average temperature,soil pH,total phosphorus content was significantly monotone decline and microbial carbon content and the decline of ammonium nitrogen content had significant linear relationship,and microbial nitrogen rise by linear relationship;and total phosphorus content is a complex "S" curve relationship;in the secondary vegetation community,the species richness of the secondary vegetation increased monotonically with the annual mean precipitation,slope,altitude,total nitrogen content,organic matter content,available phosphorus content,microbial carbon content and microbial nitrogen content.And soil pH and ammonium nitrogen content showed a monotonous decrease relationship.The relationship between species richness and soil nitrate nitrogen increased linearly.It showed a linear decrease relationship with slope direction and total phosphorus content,and a multi-peak distribution pattern with annual mean temperature. |
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