Species Diversity And Community Structure Characteristics Of Seed Plants In The Yalong River Basin

Biodiversity is an important material foundation for human survival and development,related to human well-being and long-term sustainable development.Due to the rapid growth of the Earth’s population,excessive utilization of the Earth’s biological resources,and unreasonable development and utilization of natural resources,biodiversity is facing serious threats.The main area of Yalong River Basin is located in Yalong National Scenic Area,which is an important birthplace of ancient Tibetan civilization and has an important status in Tibetan region.This paper takes the Yalong River basin as the study area,and studies the seed plant composition,plant community characteristics,the relationship between plant diversity and environmental factors as well as the ecological niche and interspecific association characteristics of dominant species in this basin,aiming to provide basic information and reference data for biodiversity conservation,sustainable development of ecosystem,resource development and utilization in this basin.According to vegetation types and topographic conditions,19 sampling points were set up in the study area,and each sampling point was randomly set with 5 samples,totaling 95 samples,recording the abundance,height,coverage and total coverage of plants in the samples.A soil sample of about 1kg was collected near the sample,and the contents of water,total nitrogen,total phosphorus,hydrolyzed nitrogen,available phosphorus,available potassium,soil organic carbon and their p H values were measured.Record the geographic position information of the sample.Ward minimum variance cluster analysis was used to classify the plant communities.The ordination of plant community was carried out by Detrended Correspondence Analysis(DCA)and Canonical Correspondence Analysis(CCA).Regression analysis of the Shannon-wiener diversity index,species richness and environmental factors of the plant community was performed using curve fitting.The niche breadth and overlap of dominant species were analyzed by Shannon-Wiener niche breadth index and Pianka niche overlap index.The variance ratio(VR),interspecific association coefficient(AC),χ2 test,and Ochiai index(OI)were used to analyze the interspecific association of dominant specie.The results are as follows:(1)A total of 263 species of seed plants belonging to 142 genera and 52 families were recorded in the Yalong River Basin.The families were mainly small families and single families,and the genera were mainly small genera and single genera.The floristic elements of families were divided into 6 distribution types and 5 subtypes,including 13 tropical families and 11 temperate families.The R/T value of families was1.182,showing weak tropical nature.The floristic composition of the genera was divided into 12 distribution types and 9 subtypes,including 11 tropical genera and 108 temperate genera,with R/T value of 0.102,showing strong temperate nature.The life form of seed plants in this basin was mainly herbaceous.Among herbaceous plants,perennial herbs were the main body,and no trees were recorded.A total of 113 species of resource plants were recorded,among which medicinal plants,protein and amino acid resources plants and fiber resources plants were the most abundant.(2)According to cluster analysis,95 samples were divided into 7plant associations,namely:Tripogon bromoides+ Artemisia stechmanniana(ASS),Stipa bungeana+ Sophora moorcroftiana(ASS),Kobresia pygmaea +Potentilla saundersiana(ASS),Carex alatauensis + Kobresia pygmaea(ASS),Artemisia stechmanniana+Leptodermis pilosa(ASS),Blysmus sinocompressus+Potentilla anserina(ASS)and Pennisetum flaccidum+ Carex alatauensis(ASS).The DCA ordination divides 95 samples into 5 community types,namely: alpine steppe community,swamp wetland community,alpine meadow community,desert steppe community and shrub grassland community.The CCA ordination showed that the plant community distribution pattern in the Yalong River basin was mainly influenced by the environmental factors of altitude,latitude,soil organic carbon,and soil water content.(3)Shannon-wiener diversity index of plant community in Yalong River Basin and altitude,latitude,soil water content,soil total nitrogen,soil available phosphorus,soil available potassium,soil hydrolyzable nitrogen and soil organic carbon showed a single peak change pattern of increase at first and then decrease;With longitude and slope aspect,it showed a U-shaped change pattern of first decreasing and then rising;It showed a linear increasing pattern with soil total phosphorus.Species richness and soil water content,soil total nitrogen,soil hydrolyzable nitrogen and soil organic carbon showed a linear increasing pattern;It was approximately linearly increasing with altitude and soil total phosphorus;With latitude,soil available potassium and soil available phosphorus,it showed a single peak change pattern of increase at first and then decrease;With longitude and slope aspect,it showed a U-shaped change pattern of first decreasing and then rising.Geographical factors and soil factors were important factors affecting the distribution pattern of plant communities,and geographical factors were the dominant factors.(4)The niche width of dominant species in Yalong River Basin ranged from 1.548 to 3.676,and the Carex alatauensis,Pennisetum flaccidum,Potentilla saundersiana,Kobresia pygmaea and Astragalus strictus was the largest,while that of Polygonum macrophyllum,Potentilla anserina,Blysmus sinocompressus and Kobresia tibetica was the smallest.The niche overlap values of dominant species ranged from 0 to 0.87,with 9 pairs having an niche overlap value equal to 0 and 8 pairs having an niche overlap value greater than or equal to 0.50.The results of the overall correlation and interspecific association coefficients(AC),χ2 test test and Ochiai index(OI)analysis of the dominant species in the basin indicated that the plant community structure of the basin was relatively stable and in a relatively stable successional stage.