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Population Structure and Niche Dynamics Characteristics of Plants Communities in the Sandy Succession of Maqu Alpine Meadow in First Meander of Yellow River

QI Deng-chen1,CHEN Wen-ye1,LIU Zhen-heng2,GONG Xiao-lan2,JIN Ba3, MIN Xiao-ping2,XU Xiao-wei2,LIU Ming-qing2(1 Gansu Forestry Science and Technology Research Academy,Lanzhou 730020,China;2 Gansu General Grassland Station of Maqu County,Maqu,Gansu 747300,China;3 West Creek Farm of Maqu County,Maqu,Gansu 747300,China)  
With the application of space instead of time-series sequence method,the desertification of alpine meadow succession of different stages of plant community structure and niche of main population characteristics were studied in Maqu.The results showed that:(1)With the succession of the desertification,species composition showed a single peak-type curve number variation.In the mild stages of desertification,there are the largest number of species,43 species.The important value and niche breadth of grasses and leguminous species showed the law of diminishing,the dominance gradually weakened.In extreme desertification stages,grasses and leguminous species(except Elymus nutans) almost completely disappeared,the important value and niche breadth of sedges and forbs class showed the law of increasing,the dominance gradually increased.In severe or extreme desertification stage,sedges and forbs class became the dominant species,sub-dominant species or important associated species.With the deepening of sandy succession,some species such as dandelion,euphorbia and white Hong Qing and other species are unstable and finally disappeared,which resulted in desertification process of succession,the quality of alpine meadow decreased;(2)In adjacent sandy succession stages,the similarity index of species composition in plant community is higher,while far away from the sandy stage,the similarity index of species composition in plant community is smaller.In the two extremes of sandy succession series,the similarity index of species composition in plant community minimum;(3)In the entire sandy succession process,the important value and niche breadth of Elymus nutans were gradually reduced,but the values are still large;(4)Niche accounted for the total width of the top five species were:Elymus nutans,Potentilla fragarioides,Kobresia humilis,Thalictrum alpinum and Carex kansuensis,and their total width of the niche were 1.653,1.438,1.387,1.295 and 1.204,respectively;(5)The average niche overlap coefficient between populations showed a single peak-type curve variation during the desertification process.In mild stages of desertification,there is a higher niche overlap(0.824) between populations.
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