Study On Nitrogen Uptake And Rhizosphere Azotobacter Diversity In Maize/Soybean Intercropping By Nitrogen Fertilizer

Intercropping is an important part of sustainable agricultural development in China.Study legumes nitrogen fixation efficiency have great significance to further improve nitrogen utilization in the legumes/nonlegumes intercropping system.However,about study relationship between soybean nitrogen fixation efficiency and rhizosphere soil nitrogen fixation microorganism diversity and nifH gene copies have not been indepth enough in the maize/soybean intercropping system with different nitrogen levels.Therefore,maize/soybean intercropping system was taken as the research object in this experiment,set four nitrogen application levels,adopt the design of field split area,by ¹⁵N natural abundance method,explore the changes of nitrogen fixation efficiency and nitrogen fixation amount of soybean in maize/soybean intercropping system with different nitrogen levels,use High-throughput sequencing and q PCR were used to reveal the variation patterns of nitrogen-fixing bacteria diversity,community structure and nifH gene copies in rhizosphere soil driven by interspecific interactions,according to nitrogen fixing microorganisms discussed nitrogen fixation efficiency and its relationship with the diversity of nitrogen fixation microorganisms in the rhizosphere by maize/soybean intercropping system with nitrogen supply levels.The results provided a theoretical basis for optimizing nitrogen management and reducing nitrogen application in intercropping system.The results as follows:The biomass of maize and soybean was significantly affected by nitrogen levels,which increased with nitrogen application levels,and reached the maximum in N2 treatment;intercropping have significant effects to maize and soybean biomass,at N0(0kg N ha^-1),N1(120kg N ha^-1),N2(240kg N ha^-1)and N3(300kg N ha^-1)treatments,maize intercropped biomass increased by 45.4%,16.6%,7.1%and 7.4%,respectively,compared with the corresponding monocropped maize;soybean intercropped biomass increased by 25.3%,26.1%,26.5%and 20.2%in N0(0kg N ha^-1),N1(40kg N ha^-1),N2(80kg N ha^-1)and N3(120kg N ha^-1)treatments.The nitrogen content of maize and soybean increased significantly with the nitrogen supply levels,and reached the maximum in N2 treatment;intercropping made maize organsnitrogen content significantly higher than in monoculture,under the N0,N1,N2 and N3 treatments,intercropping maize stem nitrogen content was 1.05,1.06,1.05 and 1.06 times of that of corresponding monoculture;intercropping maize leaf nitrogen content was 1.07,1.02,1.04 and1.08 times of that of corresponding monoculture;intercropping maize grain nitrogen content was1.03,1.04,1.04 and 1.04 times of that of corresponding monoculture.Intercropping significantly reduced the nitrogen content of soybean stem,but had no significant effect on leaf and grain.The nitrogen supply levels significantly increased the nitrogen uptake in each organ of maize and soybean,and the maximum nitrogen uptake was observed in N2 treatment;The nitrogen uptake of maize and soybean was significantly affected by intercropping.The nitrogen uptake of maize organs under N0,N1,N2 and N3 treatments was significantly higher than monocropping treatments.However,nitrogen uptakeleaves and stems of intercropping soybean was significantly lower than monocropping treatments.Intercropping soybean leaf nitrogen uptake was 30.7%,3.8%,39.6%and 32.7%lower than that of monocropping soybean,and the grain nitrogen uptake was28.8%,22.5%,6.1%and 21.1%lower than that of monocropping soybean.The total nitrogen uptake by maize and soybean plants was significantly affected by nitrogen supply levels,and increased with the nitrogen supply levels,and reached the maximum in N2 treatment.Under N0,N1,N2 and N3 treatments,maize total nitrogen uptake increased by 56.6%,22.7%,13.9%and15.9%,while soybean total nitrogen uptake decreased by 27.2%,22.7%,26.5%and 21.1%compared with monocropping.In the system,total nitrogen uptake increased significantly with nitrogen supply levels,but in N0,N1,N2 and N3 treatments,total nitrogen uptake was decreased by 3.6%,1.3%,6.2%and 2.2%compared with the corresponding monocropping treatments.Soybean nitrogen fixation efficiency was significantly affected by nitrogen supply levels and planting pattern.The nitrogen fixation efficiency of soybean was significantly inhibited by the nitrogen levels increased,and the soybean nitrogen fixation efficiency was significantly increased by N0,N1,N2 and N3 treatments,which were 26.2%,26.1%,10.0%and 10.3%higher than that of the corresponding monocrops.Nitrogen fixation amounts was significantly affected by nitrogen application levels,the highest in N1 treatment and the lowest in N3 treatment.Soybean nodules and dry weight decreased significantly with the nitrogen application levels,and the lowest in N3 treatment.Compared with monocropping,under N0,N1,N2 and N3 treatments,intercropping nodules increased 11.2%,27.4%,26.8%and 16.3%,respectively.The nitrogen fixing bacteria Alpha diversity index in maize rhizosphere increased signi ficantly with the nitrogen supply levels,and reached the highest in N3 treatment.However,nitrogen fixing bacteria Alpha diversity index in soybean rhizosphere decreased significantly with the nitrogen supply levels.Intercropping had no significant effect on the nitrogen fix ing bacteria diversity in maize rhizosphere,but significantly increased the nitrogen fixing b acteria diversity index in soybean rhizosphere.At the genus levels,Bradyrhizobium was t he dominant genus of nitrogen fixing bacteria in maize and soybeanthe rhizosphere,and it had the highest relative abundance.It was followed by Skermanella,Unclassified＿P＿Proteo bacteria,Azohydromonas,Unclassified＿K＿＿norank＿d＿＿bacteria,These genera accounted for more than 85%of the total abundance in maize and soybean rhizosphere.In maize rhizosp here soil,Bradyrhizobium was significa-ntly affected by nitrogen application rate,and decr eased with nitrogen application levels increased.RDA results showed that the maize rhizos phere nitrogen fixing bacteria community structure was significantly correlated with soil p H（p=0.002）and soil AN（p=0.024）contents,while the soybean rhizosphere nitrogen fixing ba cteria community structure was not significantly correlated with soil physical and chemical factors.The nitrogen supply levels significantly affected the nitrogen fixing gene（nifH）copies in maize and soybean.Maize nitrogen fixing gene（nifH）copies decreased with the nitrogen application levels increased,and it was the lowest in N3 treatment.The soybean nitrogen fixing gene（nifH）copies reached the maximum value in N1 treatment,which was 6.25×10⁷copies·g^-1.Intercropping had no significantly affect to nifH gene copies in maize and soybean rhizosphere soil.Correlation analysis showed that nifH gene copies was significantly negatively correlated with soil available nitrogen,and positively correlated with soybean nitrogen fixation amounts..