Impact Of Rare Earth Oxide Nanoparticles On Ammonia Oxidizers Microbial Community

Rare earth oxide nanoparticles?REO NPs?are rare earth oxides with nanometer size.They combine the common excellent properties of rare earth elements and nanoparticles,which play an important role in the fields of magnetism,luminescence,catalysis and agricultural production.REO NPs have also been put into production and application in large quantities.Increasing attention had been paid to the environmental problems caused by the large amount of nanoparticles during production,transportation and emission process.Compare with air and water,soil is the main carrier of nanoparticles in the environment.Soil ammonia oxidizing microbes,as the driver of ammonia oxidation reaction,participate in soil nitrogen cycle and play an important role in biogeochemical process.Therefore,it is important and necessary to study the effects of REO NPs on soil ammonia oxidizing microbes.Three kinds of REO NPs?La₂O₃ NPs,Nd₂O₃ NPs and Gd₂O₃ NPs?were selected to study their effects on soil ammonia oxidation activity,abundance and community structure under different doses and incubation times.To explore the relationship between REO NPs and soil ammonia-oxidizing microbes.To scientifically evaluate the impact of rare earth oxide nanoparticles on soil ecosystem stability and provide theoretical basis for agricultural soil management.While promoting the progress of nanotechnology,maintain the sustainable and healthy development of ecological environment.The main conclusions were as follows:?1?Soil ammonia oxidation microbial activity was inhibited by REO NPs with dose-dependent.However,with the increase of incubation time,ammonia oxidizing microbes gradually developed tolerance to REO NPs,and the inhibition of REO NPs to ammonia oxidizing microbes was weakened.On the 60th day of incubation,only La₂O₃ NPs significantly inhibited soil ammonia oxidation microbial activity?p<0.05?,while soil ammonia oxidation microbial activity was no longer significantly inhibit by Nd₂O₃ NPs and Gd₂O₃ NPs.Therefore,different REO NPs had differences on soil ammonia oxidizing microbe activity.?2?Soil AOB abundance increased under the exposure of REO NPs,and reached a significant level under the influence of 50 mg kg^-1 Nd₂O₃ NPs on the 7th day and Gd₂O₃ NPs on the 60th day?p<0.05?.However,the abundance of soil AOA influenced by REO NPs did not reach a significant level.There was a negative correlation between the abundance of AOA/AOB and ammonia oxidizing potential.?3?The?diversity of soil AOA and AOB communities increased under the influence of REO NPs.Low and medium dose(10 and 50 mg kg^-1)of REO NPs significantly increased the diversity of soil AOA and AOB community.But the diversity of soil AOA and AOB were decreased by high dose REO NPs,compared with those exposed to low and medium dose REO NPs.?4?At the initial stage of incubation,the sensitivity of soil AOA and AOB community diversity to three REO NPs was different.Soil AOA was more sensitive to Nd₂O₃ NPs and Gd₂O₃ NPs than La₂O₃ NPs,while soil AOB was more sensitive to La₂O₃ NPs and Nd₂O₃ NPs than Gd₂O₃NPs.?5?REO NPs had a dose effect on the diversity of soil AOA and AOB.In similarity maps of NMDS,the soil AOA and AOB communities were arranged according to the dose gradient of REO NPs in the treatments with significant difference from the control.?6?The effect of REO NPs on the diversity of soil AOB community lasted longer than that of soil AOA community.On the 60th day,REO NPs had no significant effect on the AOA community,while there was still a significant difference between AOB community exposed to REO NPs and control?p<0.05?.