Characteristics And Influencing Factors Of The Phylogenetic Structure Of Herbaceous Plant Communities In The Middle-eastern Qilian Mountains

In the process of ecological research,the maintenance mechanism of species coexistence and diversity has always been a hot field,but the study of community phylogenetic structure provides a more effective method to reveal the ecological mechanisms that affect species coexistence in a community.The study of community phylogenetic structure mainly emphasizes the phylogenetic distances between species in the community,and judges the main ecological process in the process of community construction by analyzing whether it is different from the phylogenetic distances under the random zero model.The relationship between phylogeny,expression traits and ecological niche of different coexisting species in the community was emphasized to infer the historical reasons for the community formation.Pedigree diversity is used to determine the size of the evolutionary potential of the community,and to predict whether the community is more capable of resisting the risks brought about by changes in the environment.The Qilian Mountains are located at the intersection of the Qinghai-Tibet Plateau,Mongolian Plateau and Loess Plateau.The huge geographic differences create different vegetation and landscape features.It is a natural barrier to maintain the ecological balance of the Qinghai-Tibet Plateau,maintain the stability of the Hexi Corridor oasis,and ensure the ecological safety of northern my country.It is also a priority area for biodiversity conservation in my country.However,due to increased human disturbance and the impact of climate change,ecological problems such as grassland degradation in the region have become prominent,and the local ecological environment has been severely damaged.Therefore,it is of great theoretical and practical significance to investigate the status quo of herbaceous plants in the Qilian Mountains,reveal the main ecological processes in the construction of herbaceous plant communities,and explore the main factors affecting the construction of herbaceous plant communities,which can provide theoretical support for the protection and sustainable utilization of herbaceous plant resources in the Qilian Mountains.This study took 6 different herbaceous plant communities in the middle and eastern part of Qilian Mountains as the research object,and improves the distribution characteristics of herbaceous plants in the central and eastern Qilian Mountains,and clarify the diversity of herbaceous plant communities,Using Net Relationship Index(NRI)and Pedigree Diversity Index(PD)as the main indicators to study the phylogenetic structure of herbaceous plant communities in the central and eastern Qilian Mountains,to analyze the relationship between phylogenetic structure and species diversity,and explore the effects of biological and abiotic factors on community phylogenetic structure,The main conclusions are as follows:(1)Through the investigation of 189 plots in 63 plots in the study area,a total of235 species of herbaceous plants belonging to 37 families and 126 genera were recorded.Among them,the dominant families are Asteraceae and Poaceae,and the dominant genera are Saussurea and Potentilla.From the perspective of altitude distribution characteristics: the families distributed throughout the region include Fabaceae,Poaceae,Asteraceae,Rosaceae,Cyperaceae,and Brassicaceae;For the 6families with a whole region distribution,except for the Brassicaceae,which does not have a whole region distribution of genera,all the other families have a whole region distribution of genera.(2)Among 6 different herbaceous communities in the middle and eastern Qilian Mountains,The Shannon-Wiener index and Simpson index of the alpine meadow community were the highest,the Pielou index of the warm steppe community was the highest,and the three indices of the understory herbage community were the lowest.The three indices of herb community under shrub were higher than those of warm desert herb community and lower than those of other herb communities without woody plants.Shannon-Weiner index and Simpson index were significantly positively correlated with altitude.but there is no significant correlation between Pielou index and altitude.(3)The phylogenetic structure of different herb communities in the study area is over-dispersed(NRI<0),indicating that interspecies interaction(similarity limitation)was the main driving factor for community construction.The performance of PD index from large to small is: herbaceous plant community under shrub> herbaceous plant community without arbor and shrub> herbaceous plant community under arbor and shrub.Among the four herbaceous plant communities without arbor and shrubs,the PD index was the highest in the alpine meadow community and the lowest in the warm desert steppe community.There was no significant regression correlation between NRI index and altitude and species diversity,and there was a significant positive regression correlation between PD index and altitude and species diversity.(4)The physical and chemical properties of soil are significantly different under different herb communities,and show different changes with the increase of soil depth.there was a very significant negative correlation between Soil organic carbon,Total Phosphorus and Bulk density.there is a very significant negative correlation between Sand and Field water holding capacity,Porosity,Silt,and Clay,and there was a very significant positive correlation between Soil organic carbon,Total Nitrogen,Ammonium Nitrogen,and Available Phosphorus.(5)Abiotic factors(soil)explained NRI index and PD index of herbaceous plant community more strongly than biological factors(the presence of arbor and shrub).Available Phosphorus and Sand content significantly affected NRI index.Total Nitrogen,Available Phosphorus and Sand content significantly affected PD index.it is found that the existence of life forms(trees and shrubs)has a negative impact on the diversity of herb community lineages to a certain extent,with a relative contribution rate of 7.63%,but the results are not significant.Through the comparison of soils at different depths,it is found that soil physical and chemical properties at a depth of0-10 cm have the greatest impact on the NRI index,while soil physical and chemical properties at a depth of 10-20 cm have the greatest impact on the community PD index.The results of this study show that in the central and eastern Qilian Mountains,the main ecological process in the construction of herbaceous plant communities is the interaction between species(similarity limitation).the influence of abiotic factors(soil)on herb communities is stronger than that of biological factors(woody plants).The growth and development of herbaceous plants are more dependent on soil than on trees and shrubs.The same factor that affects the phylogenetic structure and phylogenetic diversity is the phosphorus content and sand content in the soil.the results can provide theoretical support for the maintenance of herbaceous plant diversity in the central and eastern part of Qilian Mountains.