Upland Red Soil Bacterial Community Structure Under Long-term Different Fertilizations And The Driving Factor

Red soil is a ferralosols according to the World Reference Base for Soil Resources(WRB).In recent decades,agricultural activities with high inputs and outputs fluxes havestrongly effected on microorganism communities.Unbalanced fertilizations may induce soilacidification or soil fertility decline,especially in red soil.Microbes are the foundation ofthe earth's biosphere,and play unique roles in ecosystem functions.In farmland ecosystems,soil microorganisms are playing important roles in element cycling,soil structurestabilizing and pollutants eliminating and are indispensable maintainers of soil productivity.Using 454 pyrosequencing and GeoChip-based technologies,we characterized thebulk soil bacterial communities of ten main fertilizer management strategies and fivequicklime improvement soils in agricultural upland red soil of Southern China.In addition,we also set up a preliminary study to determine the driving factors of the soil bacterialcommunity reconstruction.The following results are obtained:1.Twenty-two years different fertilization changed the soil in different ways,nocultivation(Fallow)and cultivation without fertilization(CK)maintained the original pH(5.0?5.6)of this red soil as 22 years ago,all the nitrogen-containing chemicalfertilizations(N,NP,NK,NPK and NPKS)acidified the soil(pH<4.3),but long-termorganic fertilizations(M and NPKM)increased soil pH significantly(pH>6.0).It isobvious that long-term nitrogen-containing chemical fertilizations decrease soil nutrient andorganic matter contant and had significantly lower soil microbial biomass C,enzymaticactivity and bacterial diversity compared with other treatments.These results suggestingthat long-term nitrogen-containing chemical fertilization will induce soil chemical andbiological fertility decline.2.Low pH with NPK and significantly increased pH with NPKCa and NPKR wasobserved,indicating that both lime and manure alleviates soil acidification effectively.Thesoil characterization data demonstrated that short-term lime treatment had little effect on nutrient contents.Lime application only affected the solution and adsorption of different ions but did not introduce additional nutrients.In contrast,manure treatment increased soil enzymatic activity,followed by an increase in available nutrients without substantial effects on total nutrients.Our results revealed that the bacterial community composition was significantly altered by lime and manure application.The frequency of oligotrophs was higher with NPK,whereas copiotrophs occurred more frequently with NPKM and NPKR and less with NPKCa and NPK.The correlations between the relative abundances of dominant phyla and soil properties also indicated that the presence of oligotrophs is negatively correlated with nutrient contents,whereas the presence of copiotrophs is positively correlated with nutrient contents.Therefore the relative abundances of oligotrophs and copiotrophs can be used to characterize the status of soil fertility.Overall,both the lime and manure applications improved the acidified soil(NPK)in different manners.Thus,we suggest that for acidified soils,lime should be the first choice to increase soil pH in the short term,whereas manure should be applied in the long term to maintain the improvements with lime and further contribute to bacterial richness and activity.3.RMT-based network method was performed for each soil group.For HPP and Ac,only 8.67%(32)of the nodes(OTUs)were shared and network parameters(e.g.the average clustering coefficient,average path distance and modularity etc.)were significantly different,whereas for Ac and Qlime,27.04%(83)of the nodes were shared and network parameters were significantly different.Though three networks showed differences on nodes and links,the sizes were nearly the same and nodes belonging to Proteobacteria dominated in all three networks,followed by Acidobacteria,Actinobacteria,Bacteroidetes,Chloroflexi and Gemmatimonadetes etc.More positive interactions(links)in HPP than Ac indicating that HPP has more cooperators while Ac more defectors.In this case,the HPP network could be appeared as a better organized(operational)network than Ac.Besides,P/N ratio from Qlime has deviated from 1,indicating that more cooperators occurred after quick lime improvement.In this respect,quick lime demonstrates a positive effect on bacterial community of acidified soil.The topological roles of individual nodes reflect the potential importance of OTUs in community.More generalists in HPP mean more stable communities in HPP.Interestingly,among three types of generalists,we observed that all of the module hubs have significantly relationships with soil properties while the connectors not.According to the differences of generalists between HPP and Ac,it is reasonable to give hypotheses.In agricultural upland red soil bacterial communities,connectors always appeared whether in high-fertility soils or in low-fertility soils;module hubs would be the most important members to differentiate high-fertility soils and low-fertility soils;the module hubs usually be restricted by soil properties significantly while the connectors not.So,the connectors and module hubs can be used as important indicators of soil fertility.4.To determine the driving factors in bacterial community reconstruction.Two soil samples of the same origin but differed in fertilization over the past decade were used.Their microbial communities were swap inoculated and the composition of the reconstructed bacterial communities was determined by barcode pyrosequencing of the 16S rRNA gene.Soil physicochemical properties,microbial biomass,enzymatic activity and functional gene abundances were also assessed.Total phosphorus,and potassium levels along with the overall organic matter content of the non-sterilized soil were all equal to those of the same soil that had been sterilized and self/swap inoculated Additionally,the microbial biomass carbon value was not affected by the specific inoculum and varied only by soil type.The activity of catalase,invertase,urease,protease,acid phosphatase and phytase was lower in the sterilized soils that had been inoculated with organisms from chemical fertilizer amended soil(NPK)when compared to sterilized soil inoculated with organisms from manure and chemical fertilizer amended soil(NPKM)and non-sterilized soil samples.Bacterial 16S rRNA examined by 454-pyrosequencing revealed that the composition of bacterial community reconstructed by immigrant microbial seed bank in the soil was mainly influenced by its physicochemical properties,although the microbial seed bank contains different abundances of bacterial taxa.For example,the pH of the soil was the dominant factor in reconstructing a new bacterial community.Taken together,these results contribute to our understanding of how soil microbial communities are generated and maintained and help us to explore the biological functions of soil.Soil bacterial community and functional gene composition of ong-term different fertilizations and soil bacterial community response to improvement strategies indicating that the relative abundance of oligotroph and copiotroph can be used as one of the microbial indicators of soil fertility.Soil physicochemical properties are the driving factors in bacterial community reconstruction.So it is possible to artificially regulate a high yield and high efficiency microbial community by reasonable fertilization.