| Soybean is a crop with high molybdenum（Mo）requirement,the lack of Mo will seriously affect its yield and quality.Previous studies have proved that Mo O3 NPs is better than conventional Mo fertilizer in promoting soybean nodulation and yield,but the mechanism is still unclear.Based on the synthesis and characterization of Mo O3NPs,the form transformation of Mo O3 NPs in rhizosphere soil and its effect on the diversity of azotobacter were studied.The main results obtained are as follows:1.Sheet-like Mo O3 NPs was synthesized and its physicochemical properties were characterized.Using micron-sized Mo powder as the precursor,hydrogen peroxide and glacial acetic acid as the oxidant,the sheet-like Mo O3 NPs particles were synthesized by oxidative etching method.XRD,FTIR,XPS,TEM and DLS were used to analyze the lattice structure,chemical bond,hydrodynamic diameter,zeta potential,element valence and proportion.The result shows that the particles properties could matched to the Mo trioxide and free with others element.The particle size was mainly distributed in 20～90 nm,the average particle size was 47 nm,hydrodynamic diameter was 196 nm and the zeta potential was-14.3 mv.2.The effect of Mo O3 NPs on soybean growth and its accumulation and distribution in soybean were clarified.NPs-Mo O3,ion-（NH4）2Mo O4,bulk-Mo O3 can increase the yield of soybean by 78.4%～124%,treatment NPs0.05 has the highest yield;At maturity,the Mo in plant will transfer and enrich to the grains,the Mo accumulation in grains of NPs0.05 and NPs0.15 accounted for 51%and 57%of the Mo accumulation in shoot,respectively,indicated that the application of nano Mo oxide is more conducive to promoting the transfer and distribution of plant Mo to the grain;In rhizosphere,exchangeable、oxidizable and PMF Mo were significantly negatively correlated with the Mo accumulation in shoot,indicated that the exchangeable,reducible and oxidizable Mo in the rhizosphere soil can be effectively absorbed and utilized by crops.The oxidizable Mo has the strongest correlation with soil available Mo content and shoot Mo accumulation,and it is speculated that oxidizable Mo is the main form of Mo absorbed and utilized by soybean.At maturity,the content of oxidizable Mo in rhizosphere treat with NPs0.05 indicating that nano Mo oxide is easier to combine with soil organic matter and maintain its bioavailability.3.Elucidated the form transformation characteristics of Mo O3 NPs in soybean rhizosphere.Under the same Mo level,the available Mo content of bulk soil treated with Mo O3 NPs was higher than that of ion-（NH4）2Mo O4 and bulk-Mo O3 at maturity.In rhizosphere,the exchangeable,reducible,oxidizable and PMF Mo were significantly negatively correlated with shoot Mo accumulation,indicated that exchangeable,reducible and oxidizable Mo in rhizosphere soil can be effectively absorbed and utilized by crops;Oxidizable Mo has the strongest correlation with available Mo content and shoot Mo accumulation,it is speculated that oxidizable Mo is the main form of Mo absorbed and utilized by soybean.At maturity,the content of oxidizable Mo in rhizosphere soil treated with NPs0.05 was highest,indicated that Mo O3 NPs is easier to combine with soil organic matter and maintain its bioavailability.4.The effect of Mo O3 NPs on the diversity of bacterial in soybean rhizosphere and its possible mechanism were explored.Different forms of Mo fertilizer changed the bacterial community composition and diversity,and the order of diversity was ion-（NH4）2Mo O4>bulk-Mo O3>Mo O3 NPs;Mo O3 NPs promoted the enrichment of azotobacter Rhizobiales,Frankiales in rhizosphere and significantly increased the number of Bradyrhizobium in the genus Rhizobiales that can symbiotic fixing nitrogen with soybean;The correlation analysis of environmental factors showed that the shoot dry weight,soil available Mo content,reducible,oxidizable,residue Mo content and p H were significantly positively correlated with Rhizobiales. |
