Diversity Of Bacteria And Its Relationship With Soil Physicochemical Properties In The Glacier Forefield

Most alpine glaciers have been retreating since the end of the Little Ice Age around 1850. This retreat exposed large areas to colonization by microorganisms, plants, and animals. These glacier forefields provide unique opportunities to study biological succession, biogeochemical weathering processes, and the conversion of glacial till into fertile soils along the chronosequence (from the glacier to the valley).Soil samples at different distances were collected from the forefield of Zhadang glacier and Tianshan No.1 glacier. Cultivation-dependent and cultivation-independent approaches, denaturing gradient gel electrophoresis(DGGE), were used to reveal the microbial community structure and diversity. Physicochemical analyses (pH, water content, total C and N content)were also performed on the samples. The results obtained here were summarized as follows:1. Soil Physicochemical PropertiesShifts in the total C,N contant and water content were correlated to different distances in the samples from the forefield of Zhadang glacier. Total C,N contant increased signficantly in the 20-year ice-free forefield, and pH also decreased to 6.69. It is showed that microorganisms need a long time to transform the deglaciated soil.Soil physicochemical properties were different in the forefields of different receding glaciers, but the total soil C and total N contents were very low. There was not a certain regularity of the transformation process. It is a long process.2. The Culturable Cell NumberThe amount of culturable bacteria ranged from 104 to 105 CFU g-1 in Zhadang glacier forefield. With increasing time of soil exposed, the number was increased.The amount of culturable bacteria ranged from 104 to 106 CFU g-1 in east Tianshan No.1 Glacier forefield, from 103 to 105 CFU g-1 in west Tianshan No.1 Glacier forefield.The number was correlated to different distances in Tianshan No.1 Glacier forefield(from the 0 to 90m soils).3. The Diversity of Culturable BacteriaAnalysis based on 16S rDNA indicated that there wereα-Proteobacteria,β-Proteobacteria,γ-Proteobacteria,CFB and Actinobacteria, which can be cultured from the forefield of Zhadang glacier. The number of Actinobacteria increased with forefield distance, but the number of CFB andβ-Proteobacteria decreased.Isolates from Tianshan No.1 Glacier forefield samples affiliated with 6 phylogenetic groups:α-Proteobacteria,β-Proteobacteria,γ-Proteobacteria,CFB,Actinobacteria,Firmicutes. As the climate and nutrient cycling in ecosystems were different, the types and quantities of microbes there were regional differences.Microorganisms were survive on glacier forefield. Because there was cell circulation among soil, ice, and atmosphere, with wind and water being the agents of transport.4. Analysis of Bacteriun Community Using DGGEAnalysis of bacteriun community structure diversity (shannon index) showed that shannon index:Zhadang glacier forefield< west Tianshan No.l Glacier forefield< east Tianshan No.1 Glacier forefield. This may be subject to geographical location and man-made factors.DGGE analysis of bacteria showed that the18 representative bacterial bands at Zhadang glacier forefield belong to following groups:α-proteobacteria,β-proteobacteria,γ-proteobacteria,CFB,Firmicutes,Cyanobacteria,Acidobacteria. Phylogenetic diversity and the number of phylotypes ofβ-proteobacteria were highest.Twenty-three presentative bacterial bands were selected for sequeneing and phylogenetic analysis from east Tianshan No.1 Glacier forefield. The phylogenetic trees placed these clones into 7 major groups:α-proteobacteria,β-proteobacteria,γ-proteobacteria,δ-proteobacteria,CFB,Firmicutes,Chlorobi,Acidobacteria. Thirteen presentative bacterial bands were selected for sequeneing and phylogenetic analysis from west Tianshan No.1 Glacier forefield. The phylogenetic trees placed these clones into 5 major groups:α-proteobacteria,β-proteobacteria,CFB,Nitrospira,Acidobacteria.Above all, these studies have shown that the number of bacteria, composition and distribution in glacier forefield were very different with forefield distances. Bacteria can transform glacier forefield soils. They can provide scientific reference to the effects of bacteria in primary plant succession.