Study On The Composition And Structure Of Rhizosphere Soil Microorganisms In Poplar Plantation

Populus spp.is one of the most important industrial timber species in China.The healthy operation and the maintenance of long-term productivity of poplar plantation are important subjects of forestry and ecology research.Based on the close relationship between fine roots and forests productivity,fine roots of poplar plantations need to strengthen research.The root system of trees is the key organ of material exchange and energy transport between tree and soil environment.The interaction between forest root and soil environment is an important influence on the nutrient cycling of both sides and rhizosphere environment.Rhizosphere soil microbes play a crucial role as the regulator of material transformation in interactions between forest and soil.Therefore,it is important to study rhizosphere soil microbes to understand and improve the microbial community structure and to regulate rhizosphere soil nutrient cycling.Based on this,the Populus × eurameicana 'Neva' was used to study the colonization of rhizosphere and non-rhizosphere bacteria and the rhizosphere soil bacterial and fungal community structure of different orders of root by high-throughput sequencing,and the stoichiometric characteristics of soil carbon nitrogen and phosphorus in rhizosphere soils of gifferent root orders and their correlation with rhizosphere soil microbial community were studied,and the soil nitrogen cycling related bacteria were also screened in order to explore the rhizosphere soil nutrient cycling process and root-soil interaction to provide a more scientific theoretical basis.From this research,we can find that:(1)Comparison of bacteria community structure in rhizosphere and non-rhizosphere showed that rhizosphere soil contained 145 bacterial genera and bulk soil contained 141 bacterial genera,with 8 common genera shared by both at a relative abundance of more than 4%.The relative abundance of the same bacterial community was significantly different between rhizosphere and bulk soil environments.Alpha diversity analysis showed that the bacterial community diversity of rhizosphere soil was higher than that of bulk soil,but the difference was not significant.The results of bacterial communities sorting could reflect the variation of soil bacterial communities from the rhizosphere to the bulk and the spatial variation among different sampling points,indicating a contribution of about 21.2% variance of bacterial communities by the effect of rhizosphere.Beta diversity analysis showed great differences between rhizosphere and bulk soil samples in bacterial community composition.There were 15 genera specific to rhizosphere soil and 11 to soil of bulk.The abundance of 23 genera,mainly cellulose degrading bacteria and nitrogen-fixing bacteria,changed significantly.Selectivity of root to rhizosphere microorganisms is an important mechanism leading to significant differences in the rhizosphere microbial community composition and structure,which may significantly impact on the carbon and nitrogen cycles of the root-soil interface.(2)Comparison of soil bacterial and fungal community structure in different orders showed that root order 1-2,root order 3 and root order 4 rhizosphere soil containing respectively 607,593 and 604 bacterial genera,128.124 and 130 Fungi genus,with 12 common bacterial genera shared by both at relative abundance of more than 1%,in which the highest abundance genus in root order 1-2 is Burkholderia,followed by Bacteroides genus;and Bacteroides genus in root order 3 and 4 rhizosphere soil is the most abundant species,with 7 common fungi genera shared by both at a relative abundance of more than 1%,in which the highest abundance genus in root order 1-2 rhizosphere soil is Trichosporon,followed by Trichoderma genus;the relative abundance of the Trichosporon genus is the highest at root order 3;the relative abundance of Aspergillus genus is the highest at root order 4.Alpha diversity analysis showed that rhizosphere soil bacterial community richness and diversity are significantly reduced from lower to higher order roots,richness and diversity of soil fungi did not change significantly.Principal component analysis of soil samples showed that there is a big difference in poplar different orders of root rhizosphere soil bacterial and fungi community structure.Beta diversity analysis showed the similarities and differences of poplar plantation soil bacteria and fungi community composition at different orders of root were negatively correlation.In addition,as the orders of root increased,the relative abundance of acid resistance of bacteria and reduction of nitrate significantly increased,the relative abundance of azotobacter and biodegradable bacteria significantly downregulated.The shift of microorganism communities in rhizophere soils surrounding different orders of roots provides insights into plant-microbes interaction,and a new model for studying the mechanism of priming effect in rhizosphere soils.(3)Characteristics of carbon nitrogen and phosphorus in rhizosphere Soil and their correlation with rhizosphere were microbial diversity.The results showed significant differences in C,N and P contents between the rhizosphere soils and bulk soils.However,the contents of available nitrogen and phosphorus,NH4+ and NO3-ratio did not show the significant difference(P > 0.05).The C content in rhizosphere soil decreased significantly along with root orders,while the N content increased gradually.The P content in the rhizosphere soil of 1-2 order roots was significantly higher than that of 4-5 order roots(P < 0.05).C/N in rhizosphere soil decreased significantly along with root orders,while the decreased C/P did not show significant differences among root orders(P > 0.05).The non-parametric estimators based on bacterial OTUs showed that there were significant differences in bacterial community diversity between rhizosphere soils and bulk soils.Both the C and N contents in soils and the stoichiometric characteristics of C,N and P were significantly correlated with bacterial community richness(Chao index and ACE index),while the correlation between P content and bacterial community diversity was not significant(P < 0.05).It was concluded that the ecological cycling of C,N and P in poplar rhizosphere soil depended on root orders and root orders might play an important role in the building of bacterial community in rhizosphere soils.(4)Two strains of nitrite bacteria W31 and W42 were screened in rhizosphere soil by enrichment culture and isolation and purification.The molecular identification was Burkholderia cenocepacia strain AU1054 and Burkholderia terrae strain KMY02,respectively.It were the optimum fermentation conditions when the concentration of ammonia nitrogen was 200 mg / L and 300-500 mg / L,the pH was 7.5 and 8.5,respectively.