Diversity And Community Assembly Mechanisms Of Plant And Soil Microbial In Qilian Mountain National Park

Qilian Mountain National Park is located at the northern end of the eastern margin of the Qinghai-Tibet Plateau,spanning Gansu and Qinghai provinces.It is a key ecological functional area and priority biodiversity conservation region and one of the top ten national parks in China.Through field investigations and literature reviews,the characteristics of the seed plant flora in this region were elucidated.Forests are the main body of terrestrial ecosystems,and a complete and stable ecosystem includes two parts: aboveground plants and underground soil microorganisms.Exploring the assembly mechanisms of forest plant communities and soil microbial communities in Qilian Mountain National Park can provide a deeper understanding of the diversity and function of forest ecosystems and better predict the response of communities to environmental factors.Juniperus przewalskii forests are mainly distributed on sunny slopes,while Picea crassifolia forests are mainly distributed on shady slopes.These two types of forests are the most widely distributed typical forest types with significant differences in slope distribution in the region and play important roles in water and soil conservation and maintaining ecological balance.This study focused on these two typical forests to analyze the differences in plant species composition,species and phylogenetic structure.The potential mechanisms and driving factors of plant diversity formation were explored by combining environmental factors data.The differences in the composition and diversity of rhizosphere microbial communities were analyzed.The co-occurrence patterns,assembly mechanisms and driving factors of rhizosphere microbial communities were explored.The impact of aboveground plant communities on underground soil microbial communities was revealed.The main results are as follows:(1)There are a total of 1358 species of seed plants in Qilian Mountain National Park,belonging to 77 families and 369 genera,indicating a rich species diversity.The families with more than 100 species are Asteraceae and Poaceae 2 family,and the genera with more than 30 species are Artemisia,Saussurea,Carex,and Pedicularis 4 genera,indicating diverse composition at the family and genus levels.Ranunculaceae,Rosaceae,Gentianaceae,and Caryophyllaceae 4 families are both dominant and characteristic families;Artemisia,Saussurea,Potentilla,Elymus,and Caragana 5 genera are both dominant and characteristic genera,indicating the dominant phenomenon was obvious,and the characteristic taxa were prominent.The geographical element of the seed plant genera flora is complex,with temperate components genera accounting for 89.03% of the total genera in this region,indicating significant temperate properties,with the northern temperate distribution types being dominant.Floristic geographical elements are young.(2)A total of 127 species from 81 genera and 35 families were found in J.przewalskii forests,while 94 species from 62 genera and 30 families were found in P.crassifolia forests,with significant differences in species and phylogenetic structure.The Margalef richness index,Shannon-Wiener diversity index,Simpson dominant index,Pielou evenness index,and phylogenetic diversity index(PD)of J.przewalskii were significantly higher than those of P.crassifolia forests.The stability of J.przewalskii forests is stronger than that of P.crassifolia forests.In the J.przewalskii and P.crassifolia communities plots,59% and 75% of the Net relatedness index(NRI)and Netnearest taxa index(NTI)values were greater than 0,indicating that the majority of community phylogenetic structures are clustered,with most species being closely genetic relationship,and community assembly is more affected by habitat filtering.The correlation between species and phylogenetic dissimilarity of plant communities,environmental distance and geographic distance,and relative contribution of environmental differences and geographic distance for accounting for community assembly were tested,using the Mantel test method and multiple regression models(MRM)based on dissimilarity matrices.The results showed that environmental filtering and dispersal limitation jointly influenced the assembly process of plant communities,and environmental filtering had stronger effects.Annual mean temperature and annual precipitation were found to be the main influencing factors for plant community assembly mechanisms of J.przewalskii forests;annual mean temperature,total nitrogen,soil organic carbon,total potassium,and available nitrogen were found to be the main influencing factors for plant community assembly mechanisms of P.crassifolia forests.(3)Analysis of the relative abundance differences of dominant bacterial and fungal groups at the phylum,class and genus levels showed similarities in dominant groups between the two forests,mainly composed of Proteobacteria,Actinobacteria,Acidobacteria,Basidiomycota and Ascomycota.The relative abundance of Actinobacteria,Acidobacteria,and Ascomycota in J.przewalskii forests is significantly higher than that in P.crassifolia forests,while the relative abundance of Proteobacteria and Basidiomycota is significantly lower than that in P.crassifolia forests.There were significant differences in the diversity of rhizosphere soil microorganisms between the two typical forests,with higher diversity in J.przewalskii forests than in P.crassifolia forests.Soil p H is a key factor affecting J.przewalskii bacterial diversity;annual precipitation is a key factor affecting P.crassifolia bacterial diversity;The content of soil total nitrogen,organic carbon,and available nitrogen affects J.przewalskii fungal diversity.(4)The strong positive correlation between bacterial and fungal co-occurrence networks indicates that microorganisms adapt to similar niches through active cooperation.Analysis of3 unique node topological features(degree centrality,betweenness centrality,and closeness centrality)showed significant differences in the network co-occurrence patterns between the two forests,with higher values of node number topological features observed in J.przewalskii bacterial communities and in P.crassifolia fungal communities.Using the normalized stochasticity ratio(NST)and neutral community model,the roles of deterministic and stochastic processes in the assembly of microbial communities in the two typical forests were analyzed.The results showed that bacterial community assembly was mainly governed by stochastic processes(NST > 0.5),while fungal community assembly was mainly governed by deterministic processes(NST < 0.5).(5)This study employed correlation,linear regression,and PLS-PM structural equation modeling to analyze the correlation between aboveground plant diversity and belowground microbial diversity.The correlation between soil bacterial diversity index and plant diversity index is strong,while the correlation between fungal diversity index and plant diversity index is poor.Redundancy analysis results showed that the composition of soil bacterial communities was influenced by the Margalef richness index and mean annual temperature,while the composition of soil fungal communities was controlled by annual precipitation.Random forest models analysis demonstrated that plant diversity index,mean annual temperature,annual precipitation,soil total phosphorus,total potassium,and soil p H were key factors controlling the assembly of microbial communities.