| Nitrification has been thought to be carried out in two steps for a hundred years,and it is completed by two kinds of microorganisms.Firstly,ammonia is transformed into nitrite by ammonia oxidizing microorganisms,and then NO2-is transformed into nitrate(NO3-)by nitrite oxidizing bacteria.In December 2015,scientists found the complete ammonia oxidizer microorganism(comammox),which can directly oxidize NH3 to NO3-in one step independently,providing a new idea for the study of nitrification.Currently,they are found in only a few ecosystems.In order to understand the distribution and community structure of comammox bacteria in different ecosystems more comprehensively,and combined with environmental factors to explore the key factors affecting the distribution of comammox bacteria.In this paper,0-30cm or 0-40cm vertical depth soil of Bangda dryland/wetland,Dangxiong dryland/wetland,Gulu dryland,Naqu dryland and Yangbajing dryland in the region with relatively independent evolution and less human impact in the natural environment is selected.The determination of soil background physical and chemical factors including ammonia nitrogen concentration,nitrate nitrogen concentration,nitrite nitrogen concentration,p H,water content and organic matter content,as well as PCR,q RT-PCR and high-throughput sequencing of functional genes were used to study the ecosystem.The following conclusions are drawn:1)The soil p H is 6.37-8.55,water content is 10.29-35.90%,organic matter content is20.96-129.98 g kg-1,ammonia nitrogen concentration is 0.52-5.36 mg kg-1,nitrate nitrogen concentration is 0.36-27.50 mg kg-1,nitrite nitrogen concentration is 0.017-0.10 mg kg-1.2)The abundance of comammox bacteria was detected in all soil samples,the range of which was from 1.62×105 to 1.30×107 copies g-1,AOA from 2.44×106 to 2.58×108 copies g-1,AOB from 1.92×105 to 1.83×107 copies g-1.The abundance of comammox bacteria was lower than that of AOA in all samples,and lower than that of AOB in most samples.3)There was a significant positive correlation(p<0.05)between the bacterial abundance of comammox and the concentration of substrate NH4+-N,which indicated that the concentration of substrate NH4+-N had a positive feedback regulation effect on the bacterial abundance of comammox when the concentration of substrate NH4+-N was low in the whole region.This result is different from the negative correlation between the bacterial abundance of comammox and the concentration of NH4+-N reported in literature.4)At present,there are three species of comammox bacteria isolated and cultured.Only two species,Candidaus Nitrospira nitrificans and Candidaus Nitrospira nitrosa,have been detected in this area,but no Candidaus Nitrospira inopinata has been detected.Candidaus Nitrospira nitrificans is the dominant species.This study explored the whole process of ammoxidation in the ecosystem of high altitude area of Qinghai Tibet Plateau,analyzed the distribution and community structure characteristics of comammox bacteria in this area,and explored the key factors affecting the distribution and community structure of comammox bacteria.The results further deepen the understanding of the distribution of comammox bacteria in the environment with relatively independent evolution and small human input,which has important environmental benefits and potential application value. |
PDF Full Text Request