Changes Of Culturable Microbial Communities With Altitude In The Rhizosphere Of Alpine Meadow In Gannan,China

The rhizosphere is the place where plant roots and rhizosphere microorganisms interact.It is the basis of soil formation,carbon cycle and the final productivity of the terrestrial ecosystem of the earth.Rhizosphere microorganisms provide nutrients to plants by decomposing litter and activating minerals in the soil,and plants also provide a good shelter for microbial growth.In this paper,the rhizosphere soil microorganisms of Potentilla fruticosa,a typical shrub plant in Gannan alpine meadow,and Koeleria cristata,a dominant Gramineae plant,were studied.The changes of rhizosphere soil microbes and soil physical and chemical properties at different altitude(3000 m,3250m,3500 m,3750 m,4000 m)gradients were investigated by using the dilution plate method and the Most Probable Number(MPN)method,and the correlation between different rhizosphere soil microbes,plant communities and environmental factors as well as their changes with altitude were analyzed.The purpose of this paper is to study the internal relationship between soil microorganisms and environmental factors in the rhizosphere of different plants in alpine meadows,and to better understand the relationship between rhizosphere microorganisms and plant growth.The purpose of this study is to provide a theoretical basis for exploring the interaction between plants and microorganisms at the community level and their response mechanism to environmental changes.The main results of the study are as follows:(1)With the increase of altitude,soil water content,soil available phosphorus,soil urease and soil catalase in the rhizosphere of Potentilla fruticosa population showed a“V-shaped”change,while soil organic carbon and soil available nitrogen gradually increased,soil temperature and soil electrical conductivity gradually decreased,soil total phosphorus and soil p H decreasing first and then increasing,soil total nitrogen fluctuation increased,soil bulk density change was not significant.The rhizosphere soil of Koeleria Cristata,soil bulk density showed fluctuation decreased,soil available nitrogen,soil organic carbon and soil catalase showed fluctuation increased.Soil total phosphorus and soil p H showed a trend of decreasing first and then increasing.Soil water content,soil total nitrogen,soil available phosphorus,soil electrical conductivity and soil urease showed an“inverted V-shaped”change,and soil temperature gradually decreased.(2)The microbial community in rhizosphere soil was dominated by bacteria.With the increase of altitude,the total amount of microorganisms in rhizosphere soil Potentilla fruticosa showed a fluctuating decreasing trend.The total amount of microorganisms was the most at 3000 m,reaching 26.2×10~6cfu/g,and only 10~6cfu/g at3250 m.The total amount of microorganisms in rhizosphere soil was only 9.92×10~6cfu/g at 3250 m.The total amount of soil microorganisms in the rhizosphere of Koeleria Cristata population decreased with the increase of altitude,and the amount was the lowest at 4000m,which was 13.31×10~6cfu/g.The change trend of microbial functional groups was the same between the two populations,which showed an“inverted V shaped”with the increase of altitude,and the total amount of rhizosphere soil functional groups reached 30.4×10~6cfu/g and 21.34×10~6cfu/g respectively when the altitude reached3500m.There were significant differences in the number of rhizosphere soil microorganisms and functional groups among different plant populations on different elevation gradients(p(27)0.05).With the increase of altitude,the rhizosphere soil bacteria of Potentilla fruticosa population showed a change of decreased initially,followed by an increase,but then again decreased,the amount of actinomycetes gradually decreased,and the fungi showed a“V-shaped”change.The microbial bacteria and actinomycetes in the rhizosphere soil of Koeleria Cristata population decreased with the increase of altitude,while the amount of fungi decreased first then increased.Among the microbial functional groups,azotobacter,ammonifier and nitrifier all changed in“inverted V shaped”with the increase of altitude,and the amount was the highest at 3500 m.(3)Path analysis can be obtained that:In the rhizosphere soil of Potentilla fruticosa population,the main environmental limiting factor of bacteria is soil organic carbon.With the increase of altitude,soil bulk density gradually becomes the main environmental factor restricting the growth of bacteria.The decision coefficient of soil bulk density reached-4.482 at 4000 m above sea level.The main environmental limiting factor of actinomycetes is soil bulk density,and when the altitude is above 3750m,soil temperature becomes the main environmental factor restricting the growth of actinomycetes.At 3000 m and 3250 m,the main environmental limiting factor of azotobacter,ammonifier and nitrifier was soil urease,and when the altitude increased,soil total nitrogen became the main environmental factor limiting their growth.In the rhizosphere soil of Koeleria Cristata population,the main environmental limiting factor of bacteria changed from soil temperature to soil organic carbon.Except for 3000 m,the main environmental limiting factor of actinomycetes was soil bulk density,while at3000 m,actinomycetes were mainly affected by soil temperature.The main environmental limiting factors of the three microbial functional groups were soil total nitrogen,which did not change with the increase of altitude.The environmental limiting factor of fungi is soil organic carbon and there is no change between the two plants populations.In addition,soil water content is the main environmental determinant affecting the amount of soil microbial groups and microbial functional groups,and the decision coefficient increases with the increase of altitude.