Studies On Microbial Community Structure And Functional Groups In Alpine Steppe Soils Of The Qilian Mountains

The Qilian Mountain is the joint of the loess plateau, Qinghai-Tibet Plateau and thedesert in the Inner Mongolia and Xinjiang, as well as the transition zone of Arid and semi aridareas in Northwest China. The unique geographical environment creates its special ecologicalenvironment. It is the important biological resource and the gene pool in China. Grassland isthe largest terrestrial ecosystem in China. As the climate change and the human interfere,grassland desertification become to be one of the main environmental problems facing theworld. There is a closely link between the soil microorganism and aboveground plants by thetransmission of plant roots. The aboveground plants have a direct influence on the balance ofthe global ecosystem. Alpine meadow is one of the most important ecosystems in the QilianMountain. It is important to research on soil microbial community structure and functionalgroups in the area of alpine grassland ecosystem. Furthermore, we can obtain the informationof unique microorganism gene resource in this area, which also had a significant meaning inthe development of microbial resources in alpine grassland ecosystem. In this study, weselected12soil samples along the different altitude in the Qilian Mountain to reveal themicrobial community structure using the culturable microbe, real-time PCR and Biologmethods. Besides, we investigate the distribution and the structure characteristics of thenitrogen cycle key genes, nifH and amoA, in the area using the clone library method. Our aimis to understand comprehensively the microbial ecology features in the region. The results areas follows:1. The most important features of the soil physicochemical property in this area was thatpH value was greater than8in all the soil samples, which belonged to the typical alkaline soil.There was a tendency that the pH value was became higher with the deepness of soil deepen.Taking all the factors together, the soil fertility was low in low altitude sample.2. The quantity relations of the functional microorganisms are that: Ammoniationbacteria> Aerobic nitrogen-fixing bacteria> Nitrifying bacteria> Phosphate-Solubilizingbacteria> Aerobic denitrifying bacteria. On the whole, there was a decrease tendency with theincrease of soil deepen. The influence of altitude on the quantity of microorganism was notobvious in this study. The pH value had a most significantly negative influence on aerobicdenitrifying bacteria, nitrifying bacteria and phosphate-solubilizing bacteria. The growth ofnitrifying bacteria had a significantly positive effect on other soil microorganism, whichillustrated that nitrification was one of the most important roles in the nitrogen cycle. It wasbecause that ammoxidation was the rate-limiting reaction in the nitrogen circle, whichinfluenced the growth of other nitrogen circle function microorganisms. 3. The quantity relations of the microorganism gene copy number were: Bacteria>Archaea> nitrogen-fixing bacteria> Ammonia oxidizing archaea>Fungi> Ammonia oxidizingbacteria. The gene copy number of bacteria ranged from1.19×10~9to4.79×10~9. The genecopy number of archaea ranged from5.14×10~6to6.28×10~7. The gene copy number ofnitrogen-fixing bacteria ranged from2.19×10~6to3.45×10~7. The gene copy number ofammonia oxidizing archaea ranged from6.83×10~4to1.34×10~7. The gene copy number ofammonia oxidizing bacterial ranged from1.03×10~3to1.87×10~5. The gene copy numbers ofnitrogen-fixing bacteria, ammonia oxidizing bacteria and ammonia oxidizing archaea were theleast at the lowest altitude. The gene copy number of ammonia oxidizing archaea was greaterthan ammonia oxidizing bacterial in this area, which indicated that ammoxidation was mostlycompleted by ammonia oxidizing archaea in the area.4. The priority of the carbon source utilized by soil microorganisms was: saccharides>lipid> amino acids. The ability of carbon source utilization was decreased with the increasedof soil deepen.The same was true with the decrease of altitude. With the increase of incubation time,the total amount of carbon resource utilization was increase. There was no obvious differencebetween the Shannon diversity indexes, which illustrated that the microorganism diversitywas almost same among different soil samples along the altitude. But the Mcintosh index wasbigger at high altitude than low altitude, indicated that average degree of microorganism wasbetter at high altitude than low altitude, the degree of carbon resource utilization was greattoo.5. Gene sequenceing showed that in a community structure of nifH genes the percentageof Cyanobacteria genes was41%, Firmicutes genes was14%, Proteobacteria genes was8%,and unknown bacterium genes was37%. We found a new nifH gene sequence in the soilsample AQ1, which was assigned as AQ1-12(KC41210~9). Besides, we found three new nifHgenes in soli sample AQ4, which were assigned as AQ4-3(KC412133), AQ4-4(KC412134)and AQ4-5(KC412135). These results indicate that there were unique nitrogen-fixingmicroorganisms resources in the alpine grassland of the Qilian Mountain.We found that the contribution of ammonia oxidizing bacteria to ammoxidation was lessimportant through the real-time PCR and clone library preliminary experiment, so we onlybuilt the clone library of ammonia oxidizing archaea gene. The uncultured Crenarchaeote wasthe dominate gene in ammonia oxidizing archaea gene. Others were the unculturedThaumarchaeote, while other studys about this gene only found uncultured Crenarchaeote inmany soil samples, which indicated that there was much ammonia oxidizing archaea genes inthe alpine grassland of the Qilian Mountain.