Diversity And Abundance Of Ammonia-oxidizing Archaea Communities Under Different Fertilization Practices In Dry Highland Soil Of Loess Plateau

Ammonia-oxidizing bacteria (AOB) have been considered the main driver of ammonia oxidation process. With the development of molecular biology techniques, studies based on deepening of nitrogen cycling have revealed that ammonia-oxidizing archaea (AOA) may have a potential capacity for ammonia oxidation. A large number of AOA not only proved a greater role in soil, but also provided a theoretical basis for understanding the global Nitrogen cycle. The community structure diversity and abundance of AOA were studied in the long-term fertilizer treatments in order to improve the efficiency of Nitrogen utilization and explicate the function of ammonia-oxidizing archaea under changes of soil quality in the Loess Plateau.In this study, the soil samples were collected from Changwu long-term fertilization experimental stations. The fertilization experiment included nine treatments: LD (bare land), CK (control, cultivation without fertilization), N (nitrogen), P (phosphorus), and M (organic manure), and combined with nitrogen, phosphorus and organic manure: NP, NM, PM, NPM. N, P and M treatments were applied in the form of urea (120 kg N ha-1 per year), super phosphate (60 kg P ha-1 per year) and dairy manure (7500 kg ha-1 per year). The community diversity and abundance of AOA were analyzed with restriction fragment length polymorphism (PCR-RFLP) and real-time polymerase chain reaction (PCR), to investigate the responses of AOA under long-term different fertilization treatments. The main results were as follows:(1) From the clone libraries of the nine different fertilization treatments, there were 21(LD), 25(CK), 18(N), 25(P), 18(M), 13(NP), 29(NM), 20(PM) and 30(NPM) restriction endonuclease types respectively. The coverage (C value) of the clone libraries were above 90.00%. Dominant ammonia-oxidizing archaea existed in different fertilization treatments, and with the increase in diversity, the evenness of dominant AOA was gradually increased. There were not many the same OTUs between different fertilization treatments, because the different fertilization treatments maybe resulted in population shift of AOA.(2) Theαdiversity indices indicated that there was a pronounced difference among the different fertilization treatments. Four diversity indices were highest in NPM treatment; however, the Shannon-Wiener indexes and Simpson indexes were lowest in N treatment. In addition, the Margalef indexes and Species Evenness indexes were lowest in NP and CK treatments, respectively. Shannon-Wiener indexes and Simpson indexes were the same trends and represented an identical order NPM>NM>P>CK>M>LD>PM>NP>N and NPM>NM>P> CK>M>NP>PM>LD>N, there were pronounced difference between Margalef and Species Evenness indices. The rescaled distance matrix tree indicated that the different fertilization had the largest convergence coefficient of AOA community types with the NP treatment soil, but there was a high community similarity in NM and NPM treatments.(3) All preponderant sequences of AOA amoA gene fell within unculture Crenarchaeota. Phylogenetic analysis showed the most dominant AOA sequences fell within cluster S (soil origin) and very few sequences fell within cluster M (marine and sediment origin). These results suggested that long-term fertilization application impact was minimal on AOA in the alkaline soil.(4) Quantitative data showed that the trends of AOA abundance changed significantly than AOB in different fertilization treatments, while little change was detected in the copy numbers of the AOB in the different treatments, except LD treatment. The NM and CK treatments had the highest amoA gene copy numbers of AOB among the treatments, and the copy numbers was 1.90×10~6 per g dry soil, which was 5.17 times higher than LD treatment. There was a pronounced difference of AOA amoA gene copy numbers among the different fertilization treatments. The NPM treatment had the highest amoA gene copy numbers of AOA among the treatments, whereas the lowest copy numbers were recorded in the fertilizer treatments that received N fertilizer, AOA amoA gene copy numbers, ranging from 9.16×10~4-4.83×10~6 per g dry soil. The amoA gene copy numbers of AOB were more abundant than AOA in some treatments, except NPM, M and NP treatments. Those results suggested that long-term fertilization had a significant impact on AOB and AOA abundance.These results demonstrated that long-term fertilization resulted in changes of AOA community diversity and abundance.