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Ningxia University (2018)

Community Assembly Mechanisms of Local Stipa Breviflora Community in Desert

王兴;

Titre : Community Assembly Mechanisms of Local Stipa Breviflora Community in Desert

Auteur : 王兴;

Grade : Doctoral Dissertation 2018

Université : Ningxia University

Résumé
In the 21st century,China has transformed from an ecologically degraded nation to a marvel of ecological restoration.A variety of ecological engineering techniques have made this restoration possible in the desert steppe.After the restoration efforts,vegetation coverage and biomass increased significantly over the landscape.A few lessons can be carried forth from this restoration in future efforts to maintain and develop the desert grassland ecosystem.The first is that long-term grazing exclusion ought to be utilized to serve an ecological function,and the second is that moderate grazing can promote both ecological functions and productivity.How to develop particular desert grassland depends on the development of vegetation and environment in tandem.Vegetation assembly is key because the maintenance of grassland ecosystem productivity and stability depends greatly on the biodiversity of grassland communities.Uncovering the mechanisms behind vegetation assembly will advance knowledge used in sustaining and restoring diversity,especially in the degraded grasslands of the desert steppe.Soil habitat condition,or the degree of desertification,is a key factor in determining community composition in the desert steppe.Widening the scope one step further,grazing disturbance is the key driving force for soil desertification.In this study,we selected local Stipa breviflora communities to undergo one of three treatments ;long-term grazing exclusion,moderate utilization and heavy utilization.The scalar characteristics of spatial organization in the actual communities can be described as follows:Many mini-patches(about 0.5m2)exist in plant communities affected by long-term grazing exclusion and moderate grassland utilization.However,S.breviflora communities exist in heavily-utilized grasslands in the form of larger patches(100-400m2).We aimed to study assembly mechanisms of local S.breviflora communities by considering scalar characteristics of spatial organization,as well as the differences in soil habitat types.In the above study,the principal coordinates of neighbor matrices(PCNM),variability decomposition,null-model simulation,community ordination,and multivariate regression tree analyses were performed based on species composition,the plant functional traits,functional diversity,and phylogenetic community structure,respectively.The main results from the study are outlined below.1、S.breviflora communities were competitively structured and regulated by environmental filtering and limiting similarity in the long-term grazing exclusion treatment.(1)S.breviflora was dominant,with Lespedeza potaninii and Convolvulus ammannii as the main accessory species.The average values of species richness and biomass per community were 10.73 and 106.1 g/m2,respectively.(2)The soil clay content explained 80%of the total variation in community composition.(3)Environmental processes mainly regulated the leaf dry matter content and leaf specific area,while limiting similarity mainly regulated stoichiometric lability for traits in an individual.However,the functional structure was negative for traits in aggregate.(4)Multiple trait-based assembly processes operate simultaneously in species composition and differ in degree depending on the type of mini-patch in community.2、S.breviflorra communities were non-competitively structured and mainly regulated by environmental filtering in the moderate utilization treatment.(1)S.breviflora was dominant,with L.potaninii and Cleistogenes squarrosa as the main accessory species.The average values of species richness and biomass per community were 13.73 and 124.44 g/m2,respectively.(2)The coarse sand soil content explained 63.6%of the total variation of in community composition.(3)The environmental processes mirrored those of the community undergoing the long-term grazing exclusion treatment,but the functional structure was positive for traits in aggregate.3、5.breviflora communities were non-competitively structured and regulated partially by limiting similarity and dispersal limitation,but mostly by environmental filtering in the heavy utilization treatment.(1)The average values of species richness and biomass were 7.5 and 82.96 g/m2,respectively.

Mots clés : Desert steppe; Environmental filtering; Dispersal limitation; Limiting similarity; Functional diversity; Phylogenetic community structure;

Présentation (CNKI)

Page publiée le 12 avril 2019