Influence Of Ammonium Nitrogen And Nitrifaction Inhibitors On Complete Ammonia-oxidizing Bacteria In The Agricultural Soil

Nitrogen fertilizer is widely applied in agricultural production,and as nitrification inhibitors(NIs),3,4-dimethylpyrazole phosphate(DMPP)and dicyandiamide(DCD)are often used to reduce the loss of nitrogen fertilizer in soil.Ammonia-oxidation,as an important step of nitrogen cycle in soil,is the key process of controlling the application and improving the efficient utilization of nitrogen fertilizer in agricultrural soil.However,whether the available ammonium concentration has a differential impact on the growth of the newly discovered complete ammonia-oxidizing bacteria(CAOB)as well as canonical ammonia-oxidizing bacteria(AOB)and archaea(AOA)in agricultural soil still remains unclear.In this study,the growth of ammonia-oxidizing microorganisms under ammonium concentrations of 0,5,50,200,and 500 ?g NH4+-N g-1 soil was investigated by incubating the soil microecosystem.It was suggested that AOB grew in response to the two highest ammonium concentrations,whereas CAOB only grew significantly at 0 and 5 ?g NH4+-N g-1 soil through quantitative PCR analysis,demonstrating CAOB favored oligotrophic environments,owned an AOA-like niche specialization but were tolerant to a broader ammonium concentration than AOA.Phylogenetic and Pearson correlation analysis indicated that clade B cluster of CAOB contributed more than clade A cluster to the nitrification process.Moreover,the influence of DMPP and DCD on the abundance and community diversity of ammonia-oxidizing microorganisms,and their inhibitory effect on nitrification process in agricultural soil were investigated by microcosmic culture with the application of urea(300 ?g g-1 soil)and different concentraions of DMPP(0,1.5,3.0,7.5,15 ?g g-1 soil)or DCD(0,4,10,20,40 ?g g-1 soil).When DCD applied at 20 ?g g-1 soil,NI showed the most effective inhibitory effect on nitrification.In addition,the use of DMPP or DCD significantly impaired the growth of AOB and CAOB,while no treatment affected on the abundance of AOA.Furthermore,phylogenetic analysis demonstrated that the community structures of CAOB were obvious influenced by addition with 7.5 ?g g-1 soil DMPP or 40 ?g g-1 soil DCD for incubation.This study revealed an important role of the ammonium concentration in affecting the ecological niche differentiation of ammonia-oxidizing microorganisms,and exhibited different response of CAOB to NIs,which provided a theoretical and practical significance for improving the utilization of nitrogen in agricultural soil.