Research On The Diversity And Abundance Of Ammonia Oxidizers In Agricultural Corn Soil In Heilongjiang, China

Ammonia oxidation is the rate-limiting step of nitrification and crucial in soil nitrogen cycle. Ammonia oxidizing bacteria (AOB) with amoA gene, the key enzyme responsible for ammonia oxidation, was once recognized as the only ammonia-oxidizing organisms to accomplish this conversion. However, this perception has been overturned since the first AOA (ammonia oxidizing archaea) Nitrosopumilus maritimus was isolated from a marine aquarium tank. More and more researches indicated that the abundance of AOA amoA genes is greater than AOB and AOA were dominant in many soil environments. Anammox (anearobic ammonia oxidizing) can directly oxidize ammonium into dinitrogen gas under anaerobic or anoxic condition, which also played an important role in soil environemtnal nitrogen cycle. Thus, in this research, the diversity and abundance of AOA^AOB and anammox bacteria were studied by molecular biology techniques. Moreover, statistical methods were used to explore the relationship between environmental factors and the microorganisms.The samples studied in this research were collected from several experimental fertilized corn fields of Heilongjiang Academy of Agricultural Science. The different nitrogen input may affect the growth of AOA> AOB or anammox bacteria as NH4+-N and N02--N were the substrates of nitrification and anammox reaction. Therefore, seven different fertilization (0-250%of optimization of N application) experimental fields in three different periods (May、July and Octoer) were chosen as the research targets in this study. Real time fluorescent quantitative Polymerase Chain Reaction (RT-PCR) analysis was used to quantify the amounts of AOA, AOB and anammox bacteria in Heilongjiang fertilized agricultural soil by amoA genes and16S rRNA genes. The peak value of archaea amoA gene copy number in seven experimental fields during the three periods was1.38×108copies/g wet soil, while the minimum was1.36×109copies/g wet soil. The difference was not significant in the experimental fields during different periods. However, the abundance of AOB amoA genes changed significantly. The amoA gene copy numbers were between2.93×105copies/g wet soil and9.07×10copies/g wet soil in May and between8.70×106copies/g wet soil and9.01×107copies/g wet soil in July, while the abundance of AOB was under the limit of detection in samples collected in October. It can be indicated from the above results that the season variation has great influence on the abundance of AOB. In general, AOA amoA genes outnumbered AOB obviously and were the dominant ammonia oxidizing organism in the studied soils. Anammox bacteria were detected in all collected samples while its abundance was between1.70×105copies/g wet soil and6.66×106copies/g wet soil with few differences among different samples It was concluded that there are different major factors influencing on the numbers of AOA amoA genes and AOB amoA genes through Redundancy analysis (RDA). It illustrated that the abundance of AOA and AOB amoA genes were affected by many environmental factors. This study showed the abundant characterisitics of AOA and AOB in different periods. Moreover, the distributions of AOA and AOB have affected by many environmental factors not a single factor.The diversity analysis of AOA and AOB suggested that archaea amoA gene was detected in all the samples during three periods while bacteria amoA gene only existed in May and July. Therefore, ammonia oxidizing organisms distributed widely in Heilongjiang fertilized soils while most detected AOB belonged to Nitrosospira. Furthermore, the different nitrogen input and different periods barely have impact on the diversity of AOA or AOB.