Effects Of Nitrogen And Water Additions On Soil Bacterial Diversity In Stipa Baicalensis Steppes, Inner Mongolia Of North China

Atmospheric nitrogen deposition and precipitation as an important phenomenon of global climatechange have a great impact on grassland ecosystems. In our study, we set the control experiment ofnitrogen and water additions to simulate the increased N deposition and precipitation in Stipabaicalensis steppes, the responses of soil physico-chemical properties, soil enzyme activity and soilbacterial diversity to N application and water addition were researched by field survey and laboratoryanalysis, theory and methods of modern ecology, and modern biotechnology BIOLOG andPCR-DGGE. The main conclusions were as follows:1. The nitrogen and water additions changed soil physico-chemical factors significantly. The content ofsoil organic carbon, total nitrogen, nitrate nitrogen and ammonium nitrogen were significantly changedunder two water additions. There is no significant difference between total P, available P and N0treatment. The soil pH values have decreasing trend under nitrogen addition treatments.2. The soil enzyme activities have different response to the addition of nitrogen and water. Appropriateapplication of nitrogen can enhanced the activity of urease, the activity of urease under N100treatmentwas significantly higher than that of N0treatment. The application of higher nitrogen increased theactivity of catalase and phosphatase but decreased the activity of polyphenol oxidase.The significantlypositive correlation existed between total N, organic C, nitrate N and catalase, significantly negativecorrelation between nitrate N, ammonium N, total N and polyphenol oxidase, there was no significantcorrelation between soil nutrient and the activity of urease and phosphatase.3. Nitrogen and water additions have significant effect on soil microbial biomass C and N. The values ofmicrobial biomass C ranged from497.04to694.79mg/kg under water addition and334.50to552.22mg/kg under no-water addition. Higher level of N significantly reduced microbial biomass C. Thevalues of microbial biomass N ranged from58.12to74.64mg/kg under water addition and36.69to52.05mg/kg under no-water addition. The microbial biomass N was on the rise with the application rateof nitrogen. The addition of water increased the microbial biomass C and N.4. Nitrogen and water additions changed the utilization ability of carbon source. Compared withno-water addition treatments, water enhanced the soil microbial metabolic activity and the utilizationability of carbon source. The interaction of water and N15level of N fertilizer significantly increasedthe utilization ability of carbon source and functional diversity of the soil microorganism. Highernitrogen significantly reduced the richness and evenness index of microorganism, but increased thedominance index. The principal component analysis (PCA) showed that there was a very significantdifference in the carbon source utilization mode of the microbial communities between the lower Ntreatments and higher N treatments. Carbohydrates, amino acids, intermediate metabolites, andsecondary metabolites were the main carbon source utilized by the microbial communities. In addition,pH, total N, available N in soil had a closed relationship to the microbial biomass and microbialfunctional diversity. 5. Nitrogen and water additions changed the community structure of AOB and AOA. Higer values ofAOB diversity exist in N15and N30treatments, and there was a significantly decreased diversity in theAOB community in higher N application, but an obvious increase in the AOA community,demonstrating the active growth of AOA in higher N soils. Phylogenetic analysis showed that AOBcommunities were dominated by Nitrosospira clusters3,4and Nitrososmonas clusters6under wateraddition and Nitrosospira culsters1,3and4and under no-water addition, while AOA communitieswere grouped into Crenarchaeote clusters1,2and water linge under water addition and Crenarchaeoteclusters1,2and5under no-water addition. In contrast to the AOA, the diversity of AOB and AOA wassignificantly correlated with pH, organic carbon, total N, total P, NH+4-N and NO-3-N.