Studies On Soil Bacterial Diversity In The Foreland Of The Tianshan Mountain Glacier No.1

Over the past100years, the average global temperature has increased by0.74℃. The increase of the temperature is resulting in glaciers deglaciation in many mountainous areas of the world. As glaciers retreat, the newly exposed land is a new habitat for microorganisms. Microbial communities may be key determinants of glacier forefield ecosystem stability and function because of their important roles in soil development, biogeochemical cycles and heterotrophic activities. Most of previous studies are focus on Polar and Europe mountain areas but rarely on the high Asia area, so studies on the bacteria community structure variation along the chronosequences in high Asia area including in Tianshan Mountains are still needed.Samples were taken at the east branch of Tianshan Mountain Glacier No.1foreland along the chronosequence in the front of retreating glacier. We studied the number of culturable bacteria, bacterial diversity and bacterial succession rules using the methods of the oligotrophic nutrients of cultivation, the restriction fragment length polymorphism (RFLP), and the metagenome sequencing. We also analyzed the relationship between the soil physicochemical and the numbers of cultureable bacterial. The results are as follows:1. Soil physicochemical propertiesThe total N and total C contents were very low at glacier foreland. The N content was in the range0.048%-0.388%, C content varied form0.393%to4.930%and increased along the chronosequence. The pH values decreased along the chronosequence. The polyphenol oxidase, urease, dehydrogenase and sucrase activities showed an increasing trends along the chronosequence.2. The number and the diversity of culture bacteriaThe numbers of cultureable bacteria ranged from1.39×105to1.14×106CFU·g-1at4℃and ranged from1.84×105to3.31×106CFU·g-1at25℃癈incubation. The numbers of cultureable bacteria increased along the chronosequence both at4℃and25℃. Cultivation-dependent approaches showed that the35strains were isolated. The16S rDNA sequencing results of the35bacteria showed that the culturable bacteria belong to following groups, i.e. a-Proteobacteria, β-Proteobacteria, y-Proteobacteria, Actinobacteria, Bacteroides, Deinococcus-Thermus. Among these groups, Actinobacteria, Bacteroides, a-Proteobacteria were the predominant genus.3. The relationships between number of culturable bacteria and soil physicochemical parametersThe results of correlation analysis showed that the numbers of culturable bacteria significantly positively correlated with contents of total N (r=0.9873,p<0.01), total C (r=0.992, p<0.01), and urease activity (r=0.995,p<0.01). The numbers of culturable bacteria positively correlated with dehydrogenase activity (r=0.813, p<0.05) and invertase activity (r=0.813, p<0.05), and have not significant correlation with pH values, proteases activity, polyphenol oxidase activity, and catalase activity.4. The bacterial diversity from metagenome sequencingThe operation taxa unit (OTU) ranged from1,892/g to5,159/g soils. The Shannon-Wiener index significantly increased in the early age, decreased in the intermediate age and reached a peak in the oldest age soils. The Simpson index showed a decreasing trend and reflected an increase of the ecosystem heterogeneous along the chronosequence. The most striking finding from this study was the extraordinarily high species turnover (beta diversity). The turnover rate is high at early times along the chronosequence (19%per year), and then, at later times, the turnover rate decreased to0.9%per year. All of the sequences fell into31phyla and a small proportion of unclassified sequences. Acidobacteria, Actinobacteria, Proteobacteria, and Bacteroidetes were the predominant phyla in all the samples. The proportions of Bacteroidetes and Proteobacteria had decreasing trends along the chronosequence, while the proportion of Acidobacteria had an increasing trend approximately.5. The bacteria diversity and variation of metagenome sequencingSome known functional bacterial genera are also found in our study, including nitrifying bacteria, nitrogen-fixing bacteria, methane-oxidizing bacteria, and sulfur-and sulfate-reducing bacteria. Some functional bacteria groups always existed in the soils of all the ages from the glacier retreat, some existed in the early age soils and disappeared in the older age soils, some did not existed in the early age soils and appeared in the later age soils, and some did not existed in the earliest and oldest age soils but only appeared in the intermediate age soils. This reflects that functional groups of bacteria undergo a succession process along the chronosequence. The reason for this change requires further study.