Soil Microbial Diversity In Rhizosphere Of Three Stipa Species With Substituted Distribution In Central And Eastern Steppe Of Inner Mongolia

Stipa baicalensis,Stipa grandis and Stipa krylovii steppes are unique zonal steppe groups in central Asia.The populations of S.baicalensis,S.grandis and S.krylovii present a horizontal substituted distribution with the precipitation and temperature gradients gradually decreased from east to west in Hulunbuir and Xilingol of Inner Mongolia steppes.In this study,plant diversity,soil physicochemical properties,soil enzymes,and soil microorganisms?AM fungi?diversity were studied using high-throughput sequencing in two transects from Hulunbuir to Xilingol?including six plots of three Stipa species?were selected,and the diversity and evolution of soil microorganisms?AM fungi?under the substituted distribution of Stipa communities were explored.The main research results are as follows:?1?A total of 23 families,48 genera and 73 species of angiosperms were found in the plant community of Stipa steppe.The majority of the families were Gramineae,Liliaceae,Compositae,Leguminosae and Cyperacea.The shannon indices were1.40-2.27,the simpson indices were 0.61-0.86,and evenness indices were 0.58-0.83,the diversity of plant communities is not significant.The heights of Stipa were17-59.3 cm,the biomasses of Stipa were 30.5-180.2 g,the relative abundances of Stipa were 5.92-40.86%,the relative coverages of Stipa were 30.04-66.84%,the relative frequencies of Stipa were 6.25-12.5%,the importance values of Stipa were16.84-38.74%,The heights of Stipa,the biomasses of Stipa and importance values are significantly different among plots.The plant community of Stipa steppe changed significantly from S.baicalensis to S.krylovii.The types and number of plants decreased,and non-drought tolerant and non-saline tolerant plants were gradually replaced by drought-tolerant and saline-tolerant plants.?2?Based on the results of high-throughput sequencing,the number of OTUs for AM fungi in the endosphere and rhizosphere soil were 137 and 159,respectively.A total of 42 species belonging to 6 genera in the endosphere and 45 species belonging to 6 genera in the rhizosphere soil were annotated,belong to Glomus,Diversispora,Paraglomus,unclassified_cGlomeromycetes,Scutellospora,Ambispora,respectively.Glomus was the dominant genus.The AM fungal community changed significantly from S.baicalensis to S.krylovii,and the species and quantity decreased.The AM fungal community structure of the same Stipa species in different areas is stable.The richness indices of AM fungi in the endosphere were 9.52-102.95 and 15.52-31.17,respectively,diversity indices were 1.57-1.97,The richness indices of AM fungi in rhizosphere soil were 22.58-48.06 and 19.83-28.33,diversity indices were 1.42-2.35.The richness index and diversity index of AM fungi varied greatly among the various Stipa species.?3?Based on the results of high-throughput sequencing,the number of OTUs for bacteria in rhizosphere soil was 2029,belonging to 24 phyla,57 classes,117 orders,231 families,408 genera,including Actinobacteria?31.73-44.73%?,Proteobacteria?15.79-23.85%?,Acidobacteria?9.42-15.14%?,and Chloroflexi?4.90-13.60%?,the rest belong to other phyla.The bacterial community structure of the same species of Stipa in different areas is stable.The richness indices of bacteria in rhizosphere soil were 306.91-333.85 and 306.65-340.57,diversity indices were 4.02-4.49,the changes in the richness index and diversity index of bacteria in each Stipa are relatively small.The number of OTUs for fungi in rhizosphere soil were 2326,belonging to 6phyla,31 classes,92 orders,186 families,397genera,including Ascomycota?16.93-82.12%?,Basidiomycota?2.44-81.28%?,and Zygomycota?0.40-18.92%?,the rest belong to other phyla.The community structure of S.grandis is stable in different areas.The richness indices of fungi in rhizosphere soil were 131.01-227.95 and134.23-226.26,respectively,diversity indices were 0.93-3.27,the richness index and diversity index of fungi vary greatly among various Stipa species.?4?A total of 34 species of AM fungi belonging to 5 families and 8 genera were isolated from the soil of six plots.The genera included Acaulospora,Claroideoglomus,Diversispora,Funneliformis,Glomus,Rhizophagus,Septoglomus,Scutellospora,and Glomus was the dominant genus.The main dominant species were A.sp1,A.sp3,A.sp4,A.sp6,G.brohultii,G.deserticola,G.versiforme,Sept.constrictum.The spore densities were 43-442 from 20 g soil samples;the species richness included 7-18 species from 20 g soil samples,from S.baicalensis to S.krylovii,the spore density and species richness of AM fungi decreased.The shannon indices were 1.33-2.53,and the simpson indices were 0.73-0.91,the evenness indices were 0.72-0.92,The difference in diversity index is not obvious.?5?The number of culturable microorganisms in the soils were as follows:The numbers of bacteria were 0.135-1.195 10⁷ CFU/g,the numbers of fungi were0.015-3.875 10⁴ CFU/g,the numbers of actinomycetes were 0.037-1.515 10⁶ CFU/g.The number of fungi and actinomycetes decreased with the soil layer decreased.From S.baicalensis to S.krylovii,the number of fungi and actinomycetes showed a downward trend.?6?The physicochemical properties of the soil were as follows:soil moisture was1.35-33.43%,pH value was 6.21-8.69,ammonium nitrogen was 3.2-16 mg/kg,available phosphorus was 3.4-13.6 mg/kg,available potassium was 1.67-306.33mg/kg,total carbon was 3.37-51.43 g/kg,total nitrogen was 0.26-4.68 g/kg,total phosphorus was 0.11-0.77 g/kg.The pH value have increased with the decrease of the soil layer,and other indicators have decreased with the decrease of the soil layer basically.The soil moisture,pH value,total carbon,total nitrogen,and total phosphorus of all plots were significantly different on the same soil layer?P<0.05?.Whereas,ammonium nitrogen,available phosphorus,and available potassium were partially different on the same soil layer?P<0.05?.From S.baicalensis to S.krylovii,the pH value have increased,and the soil moisture,ammonium nitrogen,total carbon,and total nitrogen have decreased.?7?Soil enzyme activities in the research area were as follows:sucrase was glucose 0.03-0.24 g/d/g,urease was NH₃-N 0.42-0.89 mg/d/g,acid phosphatase was4.25-28.25 phenol?mol/d/g,neutral phosphatase was phenol 1.18-29.96?mol/d/g,alkaline phosphatase phosphatase was 8.02-31.17 phenol?mol/d/g.Soil enzyme activity have decreased with the soil layer decreases.From S.baicalensis to S.krylovii,the urease and neutral phosphatase activities have increased,and the acid phosphatase activity have decreased.?8?The genetic diversity of AM fungi showed a significant positive correlation with importance value of Stipa,soil moisture,ammonium nitrogen,total carbon,total nitrogen,total phosphorus,sucrase,phosphatase,and simpson index of plant communities?P<0.05?,and a significant negative correlation with pH,available phosphorus.This study provide a theoretical basis for health evaluation and protection of steppe ecosystem by exploring the diversity and distribution characteristics of plant communities and microorganisms?AM fungi?communities under the substituted distribution of Stipa populations in the central and eastern steppes of Inner Mongolia.