Emission Characteristics Of N₂O And Mechanism Of Microorganisms Under Different Fertilization Treatments In Three Typical Dryland Soils

Nitrous oxide（N₂O）is a very important greenhouse gas in the atmosphere.N₂ O can not only cause the greenhouse effect but also destroy the ozone layer of the stratosphere,so it is of great concern in global environmental change.Farmland soil is an important source of N₂ O to the atmosphere.In our study,three kinds of dryland soils were collected from Taoyuan（Hunan Province）,Xuchang（Henan Province）and Gongzhuling（Jilin Province）.Three soils were set to four treatments,CK（not nitrogen fertilizer）,N（nitrogen）,NI（nitrogen and nitrification inhibitor mixed）and NS（nitrogen and straw mixed）,respectively.There were four replicates for each treatment.We conducted the pot experiment in 2015 and the field experiment in 2016,and we studied the characteristic of N₂ O emission and microorganism（the nirK and nosZ genes of denitrification process were investigated in this study）across different fertilization treatments and soils.The main results of the research were described as follows:1.In this study,N₂O emission was observed by static box method.Nitrogen treatment promoted the N₂ O emission in the pot experiment in 2015 compared to CK,especially NS treatment,which might be well explained that the application of nitrogen and straw would provide sufficient substrate for the microbial activity in the soil,and promote the nitrification process and the occurrence of denitrification process.Compared to N and NS treatments,NI significantly reduced N₂ O emissions from soil,suggesting that nitrification inhibitors inhibited N₂ O emissions under controlled conditions.The field experiment in 2016,NI treatment did not show significant inhabiting effects on N₂ O emissions in the three soils,indicating that nitrification inhibitors did not inhibit soil N₂ O emissions in the field.2.We studied microbial community composition based on the molecular biology of polymerase chain reaction（PCR）,real-time fluorescence quantitative PCR and T-RFLP.The results of quantitative PCR showed that the abundance of nirK and nosZ genes did not significantly changed due to the soils types or fertilization treatments.The abundance of nirK and nosZ genes did not significantly varied with the culture days.The results of T-RFLP of nirK and nosZ genes showed that there were 91 bp and 56 bp new fragment of nirK in 15,60 and 120 d compared to 0 d,and the 456 bp nosZ gene fragment appear in 15,60 and 120 d in red soil.There were no significant differences on nirK and nosZ microbial populations under different fertilization treatments in fluvo-aquic soil.In black soil,467 bp nir K fragment appeared,which was not found in CK.There were newly 191 bp nosZ fragment in N and NI treated black soil,in addition,191 bp,202 bp and 451 bp nosZ fragments were not detected in NI.The results of RDA analysis showed that the change of microbial community affected by interaction between soil physical and chemical properties including pH,NH4+-N,NO3--N,soluble organic carbon（DOC）and soil moisture.In general,fertilization significantly increased N₂ O emissions,but the denitrifying microorganisms（nirK and nosZ）in red soil and fluvo-aquic were insensitive to different fertilization treatments.Both nirK and nosZ were sensitive to the different fertilization treatments in black soil.