Response Of Soil Actinomycete Community Structure And Genetic Diversity To The Simulated Nitrogen Deposition And Increased Precipitation In A Stipa Baicalensis Meadow Steppe

Changes in the nitrogen (N) level and precipitation regime are likely to alter soil microbial community structure and genetic diversity. Based on the climate models, which predict that both of annual precipitation and N deposition rate will increased in this century in the semi-arid steppe on northeastern China. We used the phosphor lipid fatty acid (PLFA) and denaturing gradient gel electrophoresis (DGGE) methods to evaluate the response of the Actinomycetic community structure and genetic diversity to N addition and an increase in precipitation on a Stipa baicalensis meadow steppe in Inner Mongolia. The experiment was employed in a complete randomized block factorial experimental design with the N addition (NO:0kg/ha2, N1:50kg/ha2, N2:100kg/ha2) and water addition (WO:natural precipitation, W1:increase by a proportion of1/7the natural precipitation, W2:increase by a proportion of2/7the natural precipitation) as fixed factors since2010. There were three levels for each factor, namely, nine treatments (WON0, W0N1, W0N2, W1N0, W1N1, W1N2, W2N0, W2N1and W2N2), with four replicates for each treatment. A total of thirty-six plots (2m×2m) were arranged in four randomized blocks. This study aimed to assess variations in the Actinomycetic community structure and genetic diversity under N addition and increased precipitation on a Stipa baicalensis meadow steppe. The scientific questions are that1) the Actinomycetic community composition and the dominant Actinomycetic groups on Stipa baicalensis meadow steppe,2) N and water additions would have interactive effects on the Actinomycetic community structure and genetic diversity,3) the primary factors influence on the Actinomycetic community structure and genetic diversity.(1) Based on the sequences from the cloning of DGGE bands, the BLAST results showed that all the sequences were belonged to Actinobacteria, including2orders,15familes,22genus and most of them were rare actinomycetes。The unclassified groups might belong to new actinomycete groups. The dominant Actinomycetic groups were Micromonosporaceae (10.45%), Pseudonocardiacea (4.32%), Streptomycetaceae (3.64%), Promicromonosp-raceae (2.50%).(2) Sequencing analysis showed that there were9families in W0N1and W1N2, its more richness than other treatments, especially in W1N0and W2N2, there were only3families. In addition, there were9genus in W1N2, however, we only obtained1genus (Luedemannella) in W2N2. (3) N addition significantly decreased the Pielou index (P<0.05) and Shannon-Wiener index Hi (P<0.05) of actinomycete community; Increased precipitation decreased the Shannon-Wiener index Hi (P<0.05), Pielou index (P<0.05) and species richness (P<0.05). The nitrogen addition made the actinomycetes biomass decreased first, then increased; so do the precipitation increased; N and water additions had significantly interactive effects on the genetic diversity of soil Actinomycetic community (P<0.05). Moreover, the genetic diversity of actinomycetic community decreased in W2N2.(4) Increased precipitation reduced the actinomycetic PLFAs (P<0.05).There were significantly interannual variations in the soil Actinomycetic community (P<0.01).(5) The genetic diversity of Actinomycetic community had significantly positive correlation with soil temperature(P<0.05) and plant community density(P<0.05). In addition, the species richness of Actinomycete had positive correlation with soil temperature(P<0.05), whereas had negative correlation with soil water content(P<0.05) and real dielectric constant.(P<0.05) However, there were non-significant relationships among soil properties, vegetation characteristics and other data of Actinomycetic community.