Effects Of Long-term Fertilization On The Content Of Soil Molybdenum And Flora Of Nitrogen-fixing Microbes

Biological nitrogen fixation is the main resource of soil nitrogenand is mainly dependent on nitrogen-fixing microbes in soil,which can convert di-nitrogen(N2)to biologically available ammonium.However,human activities like fertilization and irrigation may influence the communities and function of soil nitrogen-fixing microorganisms.In this study,four fertilization treatments in the Qiyang and Urumqi long term fertilization experiment station were selected,i.e.,no fertilizer(CK),chemical fertilizer(NPK),pig manure(M),chemical fertilizer plus pig manure(NPKM).The effects of fertilization treatments on total molybdenum(Mo),available Mo,chemical properties and communities of nitrogen-fixing microorganisms were studied.In addition,two-dimensional(2D)FTIR correlation spectroscopy was used to explore the binding of Mo(VI)with soil dissolved organic matter(DOM).The main results are summurized as follows.1.Compared with CK,the contents of toal Mo,total nitrogen and soil organic matter in the other three treatments in the Qiyang and Urumqi increased and reached asignificant level in the M and NPKM treatments.The available Mo contents in the M and NPKM treatments from Qiyang significantly improved while NPK signinficantly reduced.In addition,soil available Mo improved in all fertilization treatments of Urumqi.Soil pH was significantly improved in the M and NPKM treatments from Qiyang,while significantly reduced in the NPK treatment.However,soil pH did not change significantly in all fertilization treatments from Urumqi.2.The peaks in one-dimensional FTIR spectra strongly overlapped,while 2D FTIR spectra improved their resolution and distinguished them very well.The contents of soil DOM in the NPK and M treatments were almost the same,which was mainly composed by cellulose,polysaccharide,aliphatic compound and mineral particles.The Si-O stretching of silicate was only detected in the M treatment.Therefore,it is reasonable to surmise that the non-crystalline minerals such as allophone[Al2O31.22SiO22.5H2O]or imogolite[(OH)3Al2O3SiOH]were formed in the M treatment,which couldsequestrate Mo and prevent Mo mobility.3.Real-time PCR analysis indicated that nifH gene abundances were the highest in the M treatment,followed by NPKM,CK,NPK.Moreover,nifH gene abundances in the M treatmentwas significantly higher than that of the NPK treatment.4.The results of MiSeq sequencing showed that the NPK treatment had the greatest influence on soil nifH gene community structure,followed by M and NPKM.Meanwhile,the nifH gene community in the M and NPKM treatments were very closed;NPK may significantly reduce the abundance and diversity of nifH gene.