Effect Of Long-term Fertilization On Bacterial Diversity In A Red Paddy Soil

The quantity of adding chemical fertilizer to soil is increasing with the development of agricultural production in China.Substantial inputs of fertilizers have become one of the main limiting factors which impact on the security of food.Different fertilization treatments can change microbial species,quantity and activity,thus affecting soil fertility.Of the microorganism in soil,bacteria dominate in both species and quantity. Study on diversity of soil bacteria can reveal the effect of application of fertilizers on soil microbial ecology and will deepen the understanding and cognition of the correlation between bacteria and the soil environment.The field experiment was established at the Taoyuan Agro-ecosystem Research Station in Hunan Province.The long-term fertilization experiment was started in 1990 with double cropping rice system.Soil samples were collected from the following four treatment plots:1)CK(no fertilizer),2)N,3)NPK,4)NPKOM(NPK plus Astragalus sinicus L.and rice straw produced in the plot).16S rDNA clone library technology was applied to extract soil microbial DNA.Biodiversity were analyzed by DNA sequencing and phylogenetic analysis.Phylogenetic analysis revealed that 427 16S rDNA OTUs were mainly grouped into the following 11 phyla(Fig 1) which were Proteobacteria(α,β,γ,δ-Proteobacteria), Acidobacteria,Verrucomicrobia,Firmicutes,Chloroflexi,Bacteroidetes, Gemmatimonadetes,Nitrospira,Actinobacteria,Planctomycetes,and Chlorobi(49.8%, 19.3%,9.8%,7.0%,3.8%,1.6%,1.3%,1.3%,1.2%,0.8%,0.7%of the total clones, respectively).Besides,10 OTUs were clustered into an unclassified group. Shannon-Wiener Index was applied to reflect bacterial diversity while Pielou Evenness Index denotes distribution of bacteria.Shannon Index indicated that bacterial diversity was affected by fertilizer application as follows:NPK＞N＞NPKOM＞CK.The CK treatment possessed the lowest value of Shannon Index and Pielou Evenness.Fertilizer inputs caused an obvious increase in both bacterial diversity and evenness while NPK achieved the highest divergence followed by N treatment.However,application of organic matter induced lower bacterial diversity when compared to the NPK treatment. LIBSHUFF statistics indicated that the sequence library compositions of CK,N,NPK and NPKOM were significantly different between each other,indicating that all three fertilization treatments caused obvious changes in bacterial composition.Furthermore,long-term fertilizer inputs caused obvious variations of the community structure of bacterial phyla.Nitrogen treatment not only induced more phylotypes ofα-Proteobacteria,γ-Proteobacteria,Chloroflexi and Acidobacteria,but also caused less phylotypes ofδ-Proteobacteria,Nitrospira and Firmicutes than the other treatments. Application of NPK and NPKOM increased the number of phylotypes ofδ-Proteobacteria,Firmicutes and Phanctomycetes in comparison with CK.Compared to NPK the NPKOM treatment caused more phylotypes ofα-Proteobacteria and Nitrospira, but less ofβ-Proteobactia,Chloroflexi and Verrucomicrobia bacteria.Therefore, fertilizer inputs caused clear variation in paddy soil microbial communities.