Dynamic Changes Of Bacterial Diversity On The Surface Of Alfalfa And Duckweed And Its Correlation With Environmental Factors

A large number of bacteria,fungi and other microorganisms are attached to the surface of the forages.These attached microorganisms participate in the physiological metabolism of the pasture by interacting with the forage host.Pasture-attached microorganisms play an important role in the global carbon and nitrogen cycle.They not only have a very complicated relationship with plant hosts,but also fix nitrogen,promote pasture growth,enhance pasture resistance,change pasture surface characteristics,and degrade pasture surface pesticide residues.At the same time,in terms of silage preparation,we can select suitable silage additives according to the microorganisms attached to the surface of the silage raw materials to prepare highquality silage.However,factors such as climate,season,and pasture types will affect the structure and distribution of microbial communities.Therefore,this study took alfalfa and orchardgrass grown in Guizhou as the research object,and adopted the 16 S r RNA gene-based Mi Seq high-throughput sequencing technology to analyze alfalfa and orchardgrass surface bacteria,explore the differences in the surface bacterial community structure of alfalfa in different regions of Guizhou,explore the differences in the structure and distribution of the surface bacterial communities of alfalfa and orchardgrass in different seasons,and explore the differences between alfalfa and orchardgrass in the composition of the bacterial community on the surface,and the correlation analysis with environmental factors,to reveal the factors that affect the difference in the composition of the bacterial community on the surface of the two types of forages.The main findings are as follows:(1)The composition of the microbial community on the surface of alfalfa under different growth environments is quite different.The abundance of bacteria on the surface of the Huaxi group is relatively high,and the diversity of the flora varies is different with the varieties of alfalfa.In the M01 sample,the diversity of the bacteria in the Shiqian group is higher;in the M02 sample,the Huaxi group is high.The composition of the community structure indicated that the Proteobacteria was the dominant flora on the surface of alfalfa in the 2 regions.At the genus level,in the M01 sample,the dominant flora of the Shiqian group is Izhakiella(9.56%),the dominant flora of the Huaxi group is Sphingomonas(30.14%);in M02 sample,the dominant bacteria of Huaxi group is Buchnera(26.06%),and the dominant flora of the Shiqian group is Sphingomonas(39.18%).Correlation analysis showed that Sphingomonas and Methylobacterium were extremely significantly negative correlated with altitude,rainfall,moonlight hours and relative humidity(P<0.01),and extremely significantly positive correlated with temperature(P<0.01);Pantoea was significantly negative correlated with altitude,rainfall,sunshine hours and relative humidity(P<0.05),and was significantly positive correlated with temperature(P<0.05).(2)Comparison of the Alpha diversity index of alfalfa in different seasons: the Chao I index of the surface bacterial community of M01 sample in the Huaxi group is Winter > Summer > Autumn,Shannon index is Winter > Autumn > Summer;the Chao I index of the surface bacterial community of the M02 sample is Autumn > Winter >Summer,Shannon Index is Autumn > Summer >Winter.The Chao I index of the bacterial community on the surface of the M01 sample from Shiqian group is Summer >Autumn > Winter,and the Shannon index is Autumn > Winter > Summer;the Chao I and Shannon indices of the bacterial community on the surface of the M02 sample are both Autumn > Summer > Winter.At the level of phylum classification,Proteobacterial and Cyanobacteria are the dominant flora in the three seasons of alfalfa.At the level of genus classification,the dominant flora of the M01 sample in the Huaxi group is lzhakiell(9.57%)in Summer,Citrobacter(1.56%)in autumn,and Methylobacterium(14.37%)in Winter,the dominant flora of the M02 sample is Buchnerella(26.06%)in Summer,Sphingomonas(7.06%)in Autumn,Methylobacterium(3.38%)and Lactobacillus(3.10%)in Winter;In the Shiqian group,the dominant flora of the two alfalfa varieties are Sphingomonas in Summer,Methylobacterium in Autumn,and Bacillus in Winter.Correlation analysis showed that Sphingomonas,Pseudomonas and Pantoea in Shiqian group are extremely significantly positive by temperature,rainfall and moonlight hours(P<0.01),and are significantly negative by relative humidity(P<0.05);Methylobacterium showed a very significant positive by relative humidity(P<0.01).The genus Pantoea in the Huaxi group has a very significant positive correlation with temperature,rainfall and moonlight hours(P<0.01),and a very significant negative correlation with relative humidity(P<0.01);Pseudomonas is related to temperature and moonlight hours showed a significant positive correlation,and a significant negative correlation with the relative humidity(P<0.05).(3)The composition of the microbial community on the surface of orchardgrass at different seasons is quite different.The composition of the community structure indicated that the Proteobacteria was the dominant flora on the surface of Orchardgrass,and the relative abundance was Summer > Winter > Autumn.The dominant flora of orchardgrass in summer is Methylobacterium(15.06%),Streptococcus(3.94%)and Lactobacillus(3.59%)in Autumn,and Methylobacterium(8.75%)in Winter.Correlation analysis showed that the difference between the surface flora of orchardgrass and environmental factors was not significant(P>0.05).(4)Comparing the composition of the surface microbial communities of alfalfa and orchardgrass found that the two types of pastures are composed of their own surface bacterial flora.Streptococcus,Citrobacter,Nocardioides and Ellin6055 are unique flora of orchardgrass,lzhakiell,Massilia,Hymenobacter,Buchnera is a unique flora of alfalfa.