| Qilian Mountains has a unique geological history and natural conditions and rich biological community types, and it plays a huge role in maintaining biodiversity in the area. In recent years, due to the impact of human activities and environmental changes, grassland degradation and desertification in Qilian gradually have increased and the vulnerability of ecosystems have been more obvious, which have made a major impact to sustainable social and economic development. So far, the research in the region has mainly been focused on vegetation, but relatively few reports on microbess and microbial resources of the region. This study selected a total of 10 soil samples of five different elevations, two different depths, by plate count, Biolog trace analysis, high-throughput sequencing technology, combined with the analysis of soil physical and chemical properties in the middle of southern Qilian Mountains. The microbial distribution law and diversity were studied, and the results and conclusions were shown as following:1. The soil pH of entire area was neutral, up to 7.24, the lowest was 6.81. The highest of soil conductivity was 89.6 mS/cm, the minimum was 16.3 mS/cm.The study results shown that each sample’s pH and conductivity were increase trend with the soil depth increase. Soil pH and conductivity indicated the degree of soil salinity, study results showed that soil salinity was higher in the deep than in the surface. Available P, available K, SOC and total nitrogen were a decreasing trend with increasing altitude and soil depth, and these indicators represent soil fertility. So, all the indicators together showed that the soil tends to be poor and salinization with the increasing altitude and soil depth in the Qilian Mountains.2. Study results of the soil culturable microbesof three groups showed that culturable bacteria varied from 51 × 107 ~ 4.8 × 107 CFU / g, actinomycetes from 5.59 × 106 ~ 4.19 × 106 CFU / g, fungi from 5.98 × 105 ~ 1.92 × 105 CFU / g. The quantitative characteristics of culturable microbes in Qilian Mountains soil was bacteria> actinomycetes> fungi. Among them, the number of bacteria in the majority may decide the distribution of the number of microorganisms. The general trend of three types of microbial quantities in different soil depths was same. With the increase of altitude and soil depth, the number of three types of microorganisms showed the decreasing trend.3. The soil microbial overall activity variation trend in study area was: low activity within 24 h, then gradually increased with the extension of incubation time after 24 h. The soil microbial diversity index H at 0-10 cm layer of soil change range was not very large, but the diversity index U was obviously decreased with the increasing altitude. The correlation analysis found that the microbial diversity index H of the 0-10 cm layer soil and conductivity was significantly positively related and the diversity index U with altitude and pH into a significant negative correlation, but it had significantly positively related with urease content and organic carbon(10-20 cm layer were similar). It means that the richness of the soil microorganisms with little changed in elevation, mainly affected by the conductivity. But uniformity was mainly affected by altitude, pH, organic carbon and urease. The microbial richness of the study area at different altitudes was unconspicuous, however, the evenness was large changes. The main carbon source of microbes using at 5 samples of 0-10 cm layer soil were esters, amino acids and the lowest one was sugar(except sample 1). The correlation analysis between the utilization of microbes to carbon sources and environment factors shown that microbes using six types of carbon source was significant or extremely negative correlation with pH, but significantly positive correlation with electrical conductivity, organic carbon, total nitrogen and urease content. The main carbon source of microbes using at 10-20 cm layer soil were esters, amino acids and the lowest one was sugar.4. MiSeq metagenomics sequencing: Chao/Ace index, Shannon index, Simpson index and OTU cluster analysis showed that the differences of microbial species richness and evenness in different altitude and different soil depth were significant and they were shown a trend of increases at first and then decreased with the elevation. Microbial community richness and evenness of the surface soil were higher than deep soil. The dominant species at 10 samples included: Protebateria, Actinobacteria, Bacteroidetes, Verrucomicrobia, Planctomycetes, Nitrospirae, Chloroflex, Gemmatimonadetes, Acidobacteria, WS3, TM7, OD1, Chlorobi, Firmicutes, Chlamydiae, Armatimonadetes, Fibrobacteres and other. Advantage bacterium group in the 10 samples were Protebateria, Actinobacteria, Verrucomicrobia and Acidobacteria. Number of four advantage bacterium group in different soil depths were significantly different. The amount of Protebateria and Acidobacteria in the surface soil were more than in the deep layer soil. On the contrary, the number of Actinobacteria in the surface soil was more than in the deep layer. The number of Verrucomicrobia did not change significantly with soil depth. Correlation analysis between the physical and chemical factors and the microbial abundance found that the microbial abundance of 10 samples had significant correlation with organic matter, organic carbon, total nitrogen, urease, sucrase and catalase.This study systematically expounded soil microbial community structure and influening factors in the middle southern Qilian Mountain. It reveals the soil microbial diversity in the region at different altitudes and different depths. The study results provide a scientific support for the environmental conservation and restoration of Qilian Mountain region, and provide a scientific basis and germplasm resource for the application of microbial technology in the environmental management in the Qilian Mountains region. |
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