| Paddy soil developed from different parent materials after flooding and rice cultivation. Under long-term of man-made cultivation and oxidation-reduction alternate action, paddy soil had the particular physic-chemical and biological characteristics. Soil microorganisms are the important composition of soil ecosystem and there have been many reports about soil microorganism involving in the global biogeochemical cycles. Soil microbial diversity has been the hot-spot of microbial ecology research in recent years. As an independent and very important soil type in China, it is necessary and significant to work on biogeochemistry of paddy soils, the succession and impact factors of functional microbial populations in paddy soils.In this study, two paddy soil profiles with different parent materials were selected to study the microbial diversity in different soil layers, which was ranging from 0 cm to 85 cm of depth. The relations between soil parameters and microbial diversity were analyzed. The community structures of mineral-weathering bacteria in the two paddy soil profiles were explored by traditional plate culture technology and modern BIOLOG ECO plate system was used to studying the carbon-source-utilization by microbial populations during the two paddy soil profiles.Denaturing gradient gel electrophoresis (DGGE) technology was used to study the bacterial community structures in the two paddy soil profiles. The results showed that there were 7 bacterial communities in TaiLake paddy soil profile and the predominant communities were α-, β-, γ-, δ-Proteobacteria and Firmicutes. While there were 11 bacterial communities in Sichuan purplish paddy soil profile and the major bacterial communities were Actinobacteria、β-, γ-, δ-Proteobacteria and Firmicutes. The common predominant bacterial communities in the two paddy soil profiles were α-,β-, γ-,δ-Proteobacteria and Firmicutes. Some predominant bacterial community structures changed with vertical depths in the two paddy soil profiles as a whole.Canonical analysis of the soil parameters and the microbial species information obtained by quantification of DGGE fingerprints showed that the bacterial community structures were influenced by soil parameters. In the TaiLake paddy soil profile, the contents of Si, Fe, OM and pH significantly affected the bacterial community structures. P-Proteobacteria was significantly correlated with Si (R=0.886, P<0.01) and pH (R=0.889, P<0.01), and y-Proteobacteria also showed significantly correlations with Si (R=0.836, P<0.01) and pH (R=0.746, P<0.01). Differently, the major impacts on bacterial community structures in the Sichuan purplish paddy soil profile were Cu and Al. γ-Proteobacteria and Firmicutes showed significantly negative correlations to these two parameters. The coefficient between y-Proteobacteria and Cu, Al was-0.6 (P< 0.01) and-0.544 (P<0.05), respectively. And the coefficient between Firmicutes and Cu, Al was-0.635 (P<0.01) and -0.55 (P<0.05), respectively.BIOLOG ECO plate was used to analyze the functional diversity microbial communities. The results indicated that the indices of Shannon’s diversity, Mclntosh and carbon-source utilization in TaiLake paddy soil profile were higher than that in Sichuan purplish paddy soil profile, but the microbial evenness index was lower than that in purplish paddy soil profile. In both paddy soil profiles, all the indices decreased as the increasing of soil depth and showed significant correlation with Fe and Ca. Maybe the two parameters had great effect on the microbial metabolism in the soil profiles. The microbes in each soil profile had their own preferential carbon source.Total 975 strains were isolated from different soil depths of the two soil profiles by traditional isolation and culture methods. The weathering of silicate mineral-biotite by isolated strains was studied. The results indicated that there were plenty of mineral-weathering bacteria, which could release Fe, Si, Al, and K from biotite, in the two paddy soil profiles.16S rDNA sequences analysis and phylogenetic analysis revealed that 267 strains with mineral-weathering ability from TaiLake paddy soil profile belonged to 13 genera affiliated to 4 phyla including Actinobacteria, Proteobacteria, Firmicutes and Bacteroidetes. The predominant mineral-weathering bacteria were Arthrobacter, Pseudomonas and Bacillus. The 381 strains with mineral-weathering ability isolated from Sichuan purplish paddy soil profile were grouped to 27 genera which was more abundant than TaiLake paddy soil. And the predominant mineral-weathering bacteria in purplish paddy soil profile were Bacillus, Pseudomonas and Pantoea. In both paddy soil profiles, the strains from surface layer had greater mineral-weathering ability than that isolated from subsoil.The statistical and comparative analysis of bacterial mineral-weathering ability of the strains from two paddy soil profiles showed that isolates from TaiLake paddy soil had greater Si-releasing ability. On the other hand, the mineral-weathering abilities of strains isolated from TaiLake paddy soil profile belonging to genera Arthrobacter and Bacillus increased with soil depth.Strain 1007 had the highest similarities with Sphingomonas spp., and showed 97.05%-97.32%sequences similarities with the closest type strains. The major fatty acids of strain 1007 are summed feature 8 (comprising C18：1ω7c or C18:1 ω6c) (60.44%), C16:0(15.8%) and 2-OH-C14:0 (3.94%). No 3-OH fatty acids are detected. Strain 1007T contains the special lipid of sphingoglycolipid (SGL). The major isoprenoid Quinone is ubiquinone Q-10. The DNA G+C content of strain 1007 is 71.09 mol%. DNA-DNA reassociation values between strain 1007 and the four type strains (Sphingomonas pruni IFO15498T, Sphingomonas mali IFO15500T, Sphingomonas japonica KC7T, and Sphingomonas koreensis JSS-26 T) were 28.1,45.1,20.1 and 22.5, respectively. These results indicated that strain 1007T represents a novel species of the genus Sphingomonas, for which the name Sphingomonas yantingensis sp.nov. is proposed. |
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