The Effects Of Fertilization And Straw Residue Incorporation On Bacterial Communities In Lime Concretion Black Soil

Soil bacteria are important drivers for nearly all biogeochemical cycles in terrestrial ecosystems and participate in most nutrient transformations in soil.Farmland ecosystem is one of the largest terrestrial ecosystem carbon pools which have a great potential for sequestrating atmospheric carbon dioxide?CO₂?,and CO₂ assimilation by autotrophic bacteria is an important process in the soil carbon cycle with major environmental implications.In this paper,the composition and abundance of soil bacteria and CO₂-assimilating bacteria in lime concretion black soil were investigated using high-throughput sequencing technique,cloning and sequencing,terminal restriction fragment length polymorphism?T-RFLP?technique and quantitative PCR.Soil samples were collected from lime concretion black soil in Mengcheng,Anhui province,China with four treatments: CK?control,no fertilizer?,CK-F?mineral NPK fertilizers alone?,W-NF?wheat straw residue incorporation,no mineral NPK fertilizers?,W-F?mineral NPK fertilizers combined with wheat straw residue?.The main results showed as bellow:?1?The soil SOC,total N,available N,P,K in W-F treatment were increased by 23.9%,31.3%,35.1%,339.8% and 37.4%,respectively,comparing to the CK treatment.Compared with CK,the soil nutrients in CK-F treatment were increased to a certain degree,but increasing extent was less than W-F treatment;while the nutrients had no significant difference between CK and W-NF treatment.These results indicated that fertilization significantly increased the content of soil total N,organic carbon and available nutrition,while straw residue incorporation had no significantly influence on soil nutrients.Fertilization and straw residue incorporation can both decreased the soil pH,and W-F treatment had the lowest pH?5.27?.?2?The abundance of the soil bacteria varied among samples from the different fertilization treatments,ranging from 1.39×109to 2.04×109copies/g soil,generally,fertilization and straw incorporation both increased the abundance of the soil bacteria,and the highest 16 s r RNA copy number was found in W-NF treatment.There were 228,603high-quality reads in all samples and 4964?CK?,4291?CK-F?,5618?W-NF?,4600?W-F?operational taxonomic units?OTUs?were generated at 3% cutoff level,respectively.The bacterial OTUs were assigned into 19 different known phyla,41 classes,286 genera.Proteobacteria,Acidobacteria,Actinobacteria,Bacteroidetes Gemmatimonadetes and Chloroflexi were the dominant phyla?relative abundance>5%?in lime concretion blacksoil;Alphaproteobacteria,Betaproteobacteria,Actinobacteria,Gammaproteobacteria,Deltaproteobacteria,Acidobacteria,Sphingobacteriia,Gemmatimonadetes and Thermoleophilia were the dominant classes?relative abundance>5%?;the total number of the known dominant genera?relative abundance>1%?in all four treatments were 42,including Sphingomonas,Gemmatimonas,Flavisolibacter,Ramlibacter,Haliangium,Mucilaginibacter,Massilia,Rhizomicrobium,Flavobacterium,Bryobacter,Granulicella,et al;and the shared number of known genera were 12,the largest number?36?of dominant genera was found in the treatment of W-F.The largest relative abundance of dominant at phylum,class and genus level was Proteobacteria?38.7%⁴3.1%?,Alphaproteobacteria?14.5%²0.4%?and Sphingomonas?4.6%⁷.7%?in all four treatments.Fertilization had a greater effect on the composition,relative abundance of the dominant bacterial group and bacterial structure in soils than straw residue incorporation;fertilization resulted in the decrease of soil bacterial richness,straw residue incorporation increased soil bacterial diversity,fertilization combined with straw residue incorporation increased the soil bacterial predominance.A linear relationship was observed between the relative abundance of some phylum or classes and the content of soil nutrients.?3?Among all of the treatments,the carbon fixation microorganisms were mainly distributed in 13 bacteria genera,mainly including Nitrosomonas,Mesorhizobium,and Bradyrhizobium et al.In the treatments of CK and W-NF,the cbbL-containing bacterial communities were dominated by obligate autotrophic bacteria.In contrast,the dominated cbbL-containing bacterial communities were both of obligate and facultative autotrophic bacteria in the treatments of CK-F and W-F.Fertilizing or straw returning increased bacterial cbbL abundance?1.32×107³.29×107 copies/g soil?with the highest cbbL copy number?3.29×107 copies/g soil?in W-F treated soil.Among the measured soil parameters,total nitrogen,soil organic carbon and pH were the most significant factors influencing the abundance of the cbbL-containing bacteria.These results suggest that fertilization regimes have a strong impact on the structure,diversity and abundance of cbbL-containing bacterial community in lime concretion black soil,especially when straw returning is combined with fertilizing.