| Arbuscular mycorrhizal fungi(AMF)represent important mycorrhizal symbionts with more than 90%of land plant root system under natural condition,which are the most widespread ancient fungus.On the one hand,the formation of such symbionts can promote the absorption of nitrogen,phosphorus,potassium and other nutrients,thus reducing the amount of fertilizer application.On the other hand,AM fungi can affect the diversity and community structure of bacteria in the plant rhizosphere soil,and then regulate the nutrient cycle of farmland ecosystem.Guangdong Province is the main production area of sweet corn in China and one of the largest advantageous production areas in the world.At present,there are many problems in Guangdong Province,such as high multiple crop index of sweet corn,concentrated and large amount application of nitrogen fertilizer,low utilization efficiency,and serious environmental pollution.The innovative technology of reducing nitrogen and increasing efficiency of sweet corn in Guangdong Province has a typical and leading role in reducing the amount of fertilizer used by fresh corn in China.There are few reports on the application of AMF in the field to promote the reduction and efficiency of nitrogen fertilizer in sweet corn,which seriously restricts the development of AMF symbionts in the production of sweet corn.In this paper,the sweet corn was selected as the study object for an investigation into the effects of four different nitrogen application levels under field conditions:(1)N0,0 kg/hm~2;(2)N330kg,330 kg/hm~2;(3)N297,297 kg/hm~2;(4)N264,264 kg/hm~2.At the same level of nitrogen application,there were 2 split-plot experiments of 315 kg/hm~2(AMF+)and without applying fertilizer(AMF-),and eight separate experiments were carried out,each repeated three times.The effects of AMF on reducing nitrogen and increasing efficiency and AM fungal diversity of sweet corn were studied by using the method of Soil Physicochemical Indices Analysis and Illumina Hiseq 2500 high-throughput sequencing platform.To explore the relationship between the changes of AM fungal community structure and nitrogen use efficiency of sweet corn rhizosphere soil,in order to provide reference for the reduction and efficiency of nitrogen fertilizer and the application of AM fungal fertilizer in field crops.The main results are as follows:(1)The mycorrhizal infection rate of sweet corn was consistent with the spore density,which increased first and then decreased with the increase of nitrogen application.At the nitrogen application level of N297,the infection rate and spore amount reached the highest value.At the nitrogen application level of N330,the infection rate and spore amount decreased.The infection rate and spore density of AMF were higher than those of the control.In the whole growth period of sweet corn,the infection rate and spore density increased first and then decreased with the development of growth period,and the infection rate and spore density of mycorrhiza reached the peak at the silking stage.The activities of enzymes related to nitrogen metabolism in the roots of sweet corn were increased after the application of AMF.(2)At the same nitrogen application level,ammonium and alkali hydrolyzed nitrogen under the increase application of AMF were higher than those of the control.The change trend of soil pH value,the contents of nitrate in the whole growth period is opposite to that of nitrate,ammonium and alkali hydrolyzed nitrogen.At the same level of nitrogen application,the soil pH value,the contents of nitrate decreased with the increase application of AMF.The agronomic efficiency,partial productivity and physiological use efficiency of different nitrogen application levels under the increase application of AMF.At the nitrogen application level of N264,the agronomic efficiency,partial productivity and absorption efficiency of nitrogen increased by 6.84%,6.85%and 11.49%,respectively.The application of AM fungi can promote the absorption and utilization of nitrogen.(3)The dry matter accumulation of sweet corn and the nitrogen accumulation of aboveground part increased significantly from the tasseling to the silking.The spike length,spike width,row number and row grain number of sweet corn increased significantly after the application of AMF.The ear yield of sweet corn increased at four nitrogen application levels.Under the nitrogen application levels of N0,N264 and N297,there was a significant difference in split-plot experiment of ear yield(P<0.05).Compared with the treatment without application of AMF,the ear yield of sweet corn increased by 32.6%,16.7%and 8.0%,respectively.In a certain range of nitrogen application,the application of AMF can improve the quality of sweet corn by increasing the content of each quality index.(4)A total of 1558461 high-quality sequences were obtained by the Illumina Hiseq 2500sequencing platform.These sequences were clustered into 15771 operational taxonomic units(OTUs)of AM fungi at the 97%similarity level,all of them belong to the class of Glomus.The number of OTUs was N330AM>N264>N297>N297AM>N264AM>N0>N330>N0AM.According to the analysis of community structure of AM fungi,the result showed that Glomus,Claroideoglomus and Paraglomus accounted for more than 38.51%of the total abundance of AM fungi.In the treatment of N0AM,the proportion is the largest,reaching74.22%.Glomus is the dominant genus in 8 independent experiments,accounting for more than 21.82%of species with relative abundance?1%in each treatment.In the treatment of N330AM,Chao1 and richness were significantly higher than those of other treatments(P<0.05),indicating that treatment had the highest abundance of AM fungal community.The diversity of AM fungal community in N0AM reatment was the lowest,while the Dominance index,Shannon index and Simpson index in that treatment were the highest.The results showed that 96.79%and 95.7%of AM fungi communities were related to environmental variables.Monte Carlo test,Compared with the treatment without application of AMF,Nitrate.nitrogen and ammonium.nitrogen explanatory quantity increased by 15.8%and 40.5%.(5)Under increasing the application of AMF,the spore density and infection rate of N0,N264 and N297 increased significantly,and the activities of GS and GOGAT,the accumulation of nitrogen in the aboveground part,the utilization of nitrogen(NAE,PFP,NRE)and the yield increased.The infection rate was positively correlated with GS and GOGAT(P<0.05),and the correlation coefficients were 0.693 and 0.710,respectively.Spore density was positively correlated with NR,NiR,GS and GOGAT(P<0.01),and the correlation coefficients were0.852,0.854,0.977 and 0.986,respectively.Compared with no bacteria application,the ear yield,VC content,soluble sugar content and protein content of sweet corn increased,while the nitrate content decreased.The community structure of AM fungi was improved after the application of AMF,and the correlation of spore density,infection rate and diversity index of AM fungi was significantly increased.There was no significant difference between N297AM and N330 in ear yield,quality,and nitrogen content in aboveground part,physiological nitrogen utilization rate,Shannon index and Simpson index.The results showed that the application of N297(297 kg/hm~2)in increased by AMF(315 kg/hm~2)could reduce nitrogen and increase efficiency,which could be used as the recommended fertilization method. |
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