| Rice is one of the important commercial crops.The amount of nitrogen fertilizer applied to rice remains high,but the utilization rate of nitrogen fertilizer is not high.It is an urgent problem for agriculture to improve the utilization rate of nitrogen fertilizer and increase crop yield.O.longistaminata has the agronomic character of high nitrogen utilization,but its microbial mechanism is rarely studied.Biological nitrogen fixation proved to be an effective method.Many studies have shown that azotobacter plays an important role in promoting plant growth,disease resistance and insect pests.By exploring the changes of rhizosphere bacterial community structure in O.longistaminata under different nitrogen application levels,the potential rhizosphere microbial mechanism in O.longistaminata with high nitrogen utilization rate was understood,which provided important reference value for further exploring wild rice nitrogen-fixing bacteria resources and precise application of microbial fertilizer technology.In this study,under the four fertilization conditions of zero nitrogen(0N,0kg/ha),low nitrogen(LN,60 kg/ha),medium nitrogen(SN,120 kg/ha)and high nitrogen(HN,240 kg/ha),The changes of soil physical and chemical properties and rhizosphere bacterial community structure of O.longistaminata 144(Oryza longistaminata 144)and O.sativa 9311(Oryza sativa ssp.indica variety 9311)after heading stage were analyzed.The results are as follows:1.Effects of different nitrogen fertilizer concentrations on rhizosphere bacterial diversity and community structure of O.sativa 9311 and O.longistaminata 144.(1)Compared to O.sativa 9311,the species abundance and evenness of rhizosphere bacterial communities in O.longistaminata 144 were improved under zero nitrogen,low nitrogen,and high nitrogen conditions(P<0.05).Moreover,there were differences in the rhizosphere bacterial communities between O.sativa 9311 and O.longistaminata 144 under zero nitrogen,low nitrogen,standard nitrogen,and high nitrogen conditions(P<0.05).(2)Proteobacteria(87.7%-42.4%)was the dominant phylum in rhizosphere soil of rice 9311 under different nitrogen concentrations.O.longistaminata 144 The dominant rhizosphere obacteria are Proteobacteria(78.8%-44.7%),Acidobacteria(22.1%-4.2%),Verrucomicrobia(15.9%-1.1%)and Actinobacteria(8.2%-1.7%).At the phylum level,the rhizosphere dominant bacterial communities of O.sativa9311 under medium nitrogen conditions were more abundant than those of the other three nitrogen treatment groups.The dominant groups were Proteobacteria,Acidobacteria,Bacteroidetes and Fusobacteria.However,there was no significant difference in the rhizosphere dominant bacterial community composition of O.longistaminata 144 under nitrogen application.Rhizosphere microbial LEf Se analysis of O.sativa 9311 and O.longistaminata 144 under different nitrogen application concentrations showed that a total of seven species at the genus level were isolated from cultivated O.sativa 9311 and O.longistaminata 144.The differential microorganism in O.sativa 9311 are Psychrilyobacter.The differential microorganisms in O.longistaminata 144 respectively.are Geobacter,Geothrix,Desulfovibrio,Burkholderia,Desulfobulbus,and Bacillus.(3)The co occurrence network structure of rhizosphere bacteria in rice under different nitrogen concentrations indicates that the network of zero nitrogen and high nitrogen treatment groups in O.longistaminata 144 is more complex,and due to nitrogen stress,the rhizosphere bacteria in the zero nitrogen and high nitrogen treatment groups are more closely connected.O.sativa 9311 has no obvious pattern.2.Effects of nitrogen application levels on rhizosphere soil physicochemical properties and root microbial communities of O.sativa 9311 and O.longistaminata144.(1)Total nitrogen,total phosphorus,organic matter,nitrate nitrogen,ammonium nitrogen,and p H are important factors affecting the structure of endophytic bacterial communities in the roots of O.longistaminata 144 and O.sativa 9311.Moreover,there were significant differences in the physicochemical properties of the two types of rice under different nitrogen concentrations(P<0.05).(2)The physicochemical correlation between rhizosphere bacteria and soil heat map of O.sativa 9311 showed that Psychrilyter was positively correlated with soil TP.Geothrix,Geobacter,Desulfovibrio,Desulfobulbus and Burkholderia are in extremely significant positive correlation with soil SOC.Desulfovibrio is in significant positive correlation with Desulfobulbus soil p H.Geobacter and Burkholderia were strongly negatively correlated with soil TP content.The physicochemical correlation heat map of O.longistaminata 144 rhizosphere bacteria and soil of wild rice showed that Psychrilyter was significantly negatively correlated with soil TN,and Geothrix was significantly positively correlated with soil TN.3.Isolation,identification and physiological characteristics analysis of azotobacterFrom the paddy field soil of Nanchang University Xianyuan with Ashby nitrogen free culture medium separation,purification,to obtain good growth of 10 nitrogen fixing strains A2,A3,A14,MD2,MD3,MJ3,MJ5,MJ8,PJ3 and VJ4.The 10 strains were identified as 6 genera by BLAST analysis.The 6 genera were Kosakonia,Agrobacterium,Streptomyces,Bacillus,Klebsiella and Rhizobium,respectively.The physiological characteristics of strain stress resistance,protease hydrolyzing activity and IAA production were analyzed.It was found that the growth rate of 10 strains was severely inhibited under water potential stress or oxidation stress.Only strain A2 produced a large amount of IAA,5.88 ug/m L,and MJ8 produced a small amount of IAA,0.52 ug/m L,while other bacteria produced almost no IAA.The hydrolytic activities of A14,MJ5 and VJ4 were 1.11,1.32 and 1.05,respectively.MD2 and MJ3 had almost no protease activity(0.08 and 0.01).MJ8 protease has a very low hydrolytic activity of 0.03.In summary,there are significant differences in the diversity and structure of rhi-zosphere microbial communities between O.sativa 9311 and O.longistaminata 144 under different nitrogen application levels.In addition,screening various nitrogen fixing bacteria and measuring their physiological characteristics provide new insights into the potential rhizosphere microbial mechanisms in O.longistaminata with high nitrogen utilization efficiency. |
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