The Influence Of Nitrogen Deposition And Increased Precipitation On Soil Microbial Composition And Diversity Dynamic In A Stipa Baicalensis Meadow Steppe

As the crucial part of solid ecosystem,bacterial communities play a vital role in material cycle of the ecosystem and the energy flow.Global change have a profound effect on the structures of grassland plant communities and plant diversity,as well as the composition and diversity of bacterial communities in grassland soil.Currently,researches about the respond mechanism of composition and diversity of bacterial communities in meadow steppe of our country are insufficient,and reports about the dynamic of bacterial community are especially scarce.This research based on the sample of Stipa baicalensis meadow steppe which located in eastern area of Inner Mongolia.Randomized grouping design was used to simulate global climate changes with three treatment methods: nitrogen deposition,increased precipitation,and their interactive treatment,regard the natural state-controlled as the block design.Soil sample collection and plant community investigation were conduct at four period of 2014(fifth year after the treatment biginning): Turning Green Period(15th May),Growing Period(1st July),Biomass Peak Period(15th August),End of the Growing Season Period(10th September).16 S rRNA gene was served as the target,soil bacterial composition,community structure and diversity information were acquired by applying High-throughput sequencing method;and qPCR technology is used to analysis bacterial relative abundance and B/F ratio.Plan to answer follow science problems:(1)What impact do the simulation of nitrogen deposition and precipitation treatment have on the composition and diversity of soil bacterial communities?(2)What is the relationship between the composition and diversity of soil bacterial communities and the feature of soil and vegetation? The results show that:(1)By contrasting High-Throughput Sequencing results,there are 34 phylums,77 classes and 298 families of bacterial are discovered.Among these advantage,list ranked in phylum level is: Actinobacteria,Proetobacteria,Acidobacteria and Chloroflexi;ranked in class level is: Actinomycete,Acidobacteria,Alphaproteobacteria,Acidimicrobidae,Deltaproteobacteria.(2)The pattern of bacteria abundance variation alone with seasons shows a unimodal curve,and peaked in August: The average gene copy reached 2.7 million copy/ng,and is triple that of May.Dynamic growth of relative abundance and B/F ratio share a same trend;diversity index stay changeless.(3)During the same period,nitrogen deposition,precipitation and their interactive treatment have no remarkable effect on the total bacterial abundance.However,when confine the data within one treatment,bacterial abundance changes remarkable alone with the seasons(P<0.05).Similar to bacterial abundance,the 16 advantage bacterial classes present no remarkable difference to the same treatment process.Different process to bacterial class have different responds.And on seasonal changes,there are 10 classes of advantage communities(Acidimicrobiia,Alphaproteobacteria,Acidobacteria,Bacilli,Deltaproteobacteria,Gemmatimonadetes,Planctomycetacia,Thermomicrobia,Cytophagia,Chloroflexia)reached extremely significant level.And there are 6 advantage communities(Alphaproteobacteria,Acidobacteria,Chloroflexia,Deltaproteobacteria,Thermomicrobia,Bacilli)reached an extremely significant level(P<0.01).(4)By correlation analysis,it is discovered that diversity indices which indicate soil bacterial communities(OTUs,Ace,Chao,Shannon and Simpson index)and physicochemical parameters(pH,TOC,TN,AN,TOC/TN,SM)are not explicitly related.But bacterial gene copies number and B/F ratio are positively related with PR and CC(P<0.05).Those affected by above-ground plants greatly are: Acidobacteria,Acidimicrobiia,Deltaproteobacteria,Planctomycetacia,Thermomicrobia,Bacilli,Chloroflexia.In summary,nitrogen deposition,precipitation and their interactive processing for five consecutive years just have little effect on the composition and diversity of soil bacterial.But seasonal variation of soil bacterial communities is remarkable,that is to say seasonal effect exceed experimental treatment.Stipa baicalensis meadow steppe soil microbial communities maybe directly affected by seasonal dynamic.This research shows that the effect of nitrogen deposition and precipitation pattern variation to soil bacterial is a tardiness and complex process,the simulation of global variation detection could be a long term process.