Ammonia Oxidation Microbial Abundance And Population Diversity In Brown Soil With Different Fertilization Treatments

Ammonia oxidation process is a key step in soil nitrification,which plays an important role in the nitrogen cycle of soil ecosystem.It is mainly drived by ammonia-oxidizing bacteria(AOB)and ammonia-oxidizing archaea(AOA).Long-term single application of chemical fertilizer is easy to make the soil pH drop,plowing soil compaction,thus affecting the growth of crop roots.The application of organic manure and chemical fertilizers can increase soil organic matter by affecting the soil microbial population and quantity,which may affect the quality of cultivated land and the safety of ecological environment.In this paper,long-term fertilization of brown soil as the research object,mainly using real-time quantitative PCR(Real-time PCR)and PCR products based on denaturing gradient gel electrophoresis(PCR-DGGE)technology to detect different fertilization soil nitrogen,soil nitrification intensity,AOA and AOB amoA gene abundance,community structure and diversity and other indicators of the temporal and spatial changes,and analyze the correlation between soil microbial community and soil nitrogen,pH and soil nitrification intensity.It is expected to evaluate the role of soil ammonia microbial population in brown soil ecosystem,and to provide an important theoretical basis for soil quality improvement and productivity improvement.The results are as follows:(1)The soil physical and chemical factors were different for different fertilization treatments:Fertilizer treatment increased NH4+-N content in soil,and NH4+-N content in soil showed N4>M2N2>N2>CK;Different growth period,the content of NH4+-N in CK,N2 and M2N2 treatments was the highest in April,while N4 fertilization was the highest in July;The content of NH4+-N in soil was 0-20 cm>20-40 cm>40-60cm in different soil depth.The accumulation of nitrate nitrogen in the treated soil was between 1.15 and 45.27 mg,and CK was significantly lower than that of all fertilization treatments.The content of nitrate nitrogen in all the tested soils was higher in July,and the content of nitrate nitrogen in M2N2 was lower than that of N2 and N4 under the same soil depth.There was no significant change in the content of nitrite nitrogen between different soils.All tested soil pH was less than 7,between 4.38-6.52;The change of pH in each treated soil was CK>M2N2>N2>N4;The soil pH at different depths is 0-20 cm<20-40 cm<40-60 cm.The change of nitrification intensity in each treated soil was between 0.51-64.39 mg(Kg d)-1,except that M2N2 was the highest in 0-20 cm in November,and the other treatments were the highest in April,among them,CK,N4 and N2 in the 20-40 cm and 0-20 cm depth of the highest nitrification strength.(2)The abundance of ammonia-oxidizing microorganisms(AOM)in different fertilization treatments are as follows:The amoA gene abundance of AOA and AOB in different fertilization treatments was significantly different.The copies of AOA and AOB amoA genes in each fresh soil were 1.55×106-5.96×107 and 9.39×103-4.18×106,under the same treatment,AOB amoA gene abundance was significantly lower than AOA.Soil AOA abundance showed that fertilization significantly reduced AOA abundance;The abundance of AOA amoA gene was the highest in November and lowest in July under different growth stages;Under different soil depth,the AOA abundance of soil fertilization and control treatments was 20-40 cm and 0-20 cm,respectively.Soil AOB abundance showed that different fertilization treatments could increase or decrease the abundance of AOB in soil;Under different growth stages,the abundance of soil AOB was the highest in April;Different soil depth,fertilization and control treatment soil,AOB abundance in 0-20 cm and 20-40 cm soil layers were the highest.(3)The soil AOM community structure of different fertilization treatments show:The population structure of AOA amoA gene in soil showed that the minimum value of community diversity index(H)and simpson index(D)appeared in the soil of M2N2 fertilization in 20-40 cm soil in April,the evevness index(J)minimum appears in April M2N2 fertilization treatment 0-20 cm soil;The maximum of AOA amoA gene comunity diversity index(H)and simpson index(D)appeared in the control of 20-40 cm soil in November,the maximum of evenness index(J)appears in April N2 treatment in 40-60 cm soil.The comunity structure of AOB amoA gene in soil showed that the diversity index(H)and simpson index(D)were the highest in CK 40-60 cm soil in April,the maximum value of the evenness index(J)appears in April N4 fertilization treatment for 20-40 cm soil.The minimum value of the diversity index(H),evenness index(J)and the simpson index(D)were found in the control of CK 40-60 cm soil in November.(4)Correlation between AOM and soil physical and chemical factors:There was a significant negative correlation between AOA abundance and soil nitrate content,and positively correlated with soil pH.The AOB abundance was positively correlated with the content of NH4+-N and nitrite nitrogen in soil,and negatively correlated with soil pH.AOB comunity diversity index(H),evenness index(J),Simpson index(D)and soil pH were significantly negatively correlated.There was no significant correlation between AOA and AOB abundance and diversity index and nitrification intensity.[Conclusion]Fertilization treatment resulted in the accumulation of ammonium and nitrate in soil,and the soil pH was acidic.Fertilization treatment significantly can reduce soil AOA abundance,but to a certain extent,increase soil AOB abundance;Fertilization treatment can affect the diversity index of AOA and AOB in different degree.The abundance of AOA amoA gene and the content of nitrate nitrogen were negatively correlated with soil pH.The AOA diversity index was negatively correlated with the content of NO2--N.AOB amoA gene abundance was positively correlated with nitrite nitrogen in soil,and negatively correlated with nitrification intensity.AOB diversity,index,simpson index and nitrate content were significantly negatively correlated,diversity index,simpson index and pH were significantly positively correlated.The effect of long-term fertilization on the ammonia-oxidizing microorganisms in the soil is an extremely complicated process,fertilization patterns,soil types,crop types and fertilizers are likely to have an impact.By understanding the response of ammonia-oxidizing microorganisms to different fertilization patterns in brown soil,we provide a theoretical basis for the development of reasonable fertilization system.