Research On Soil Nitrogen Transformation Of Bacterial Community Diversity In Maize-soybean Relay Strip Intercropping System

Nitrogen nutrition is very important to the growth and development of crops.It influences and restricts the quantity and quality of crops in agricultural production.Nitrogen application is an import measure to supplement the soil nitrogen,but the utilization ratio of N fertilizer will not increase with the increase of nitrogen application.The excessive N application will reduce the absorption and utilization efficiency of crops and bring serious ecological environment problems.In recent years,the Maize-Soybean relay strip intercropping system and a complete set of corresponding cultivation techniques has developed rapidly,and the effect was significant in yield and nutrient utilization,it benefit to promote crops nutrient absorption.But it is still unclear that the N regulation mechanism of the underground part which promoted the efficient N utilization.Therefore,based on former studies,a long-term location research was conducted to investigate these questions in the Maize-Soybean relay strip intercropping system.We surveyed and evaluated the rhizosphere soil microbes quantity and soil total N content of maize and soybean,also the diversity,abundance,and system development of the microbial community involved in several key steps of soil N transformation with 3 plantting patterns,including maize monoculture(MM),Soybean monoculture(SS),and Maize-Soybean relay intercropping(IMS),there were also three N application rates,including N non-fertilization(NN:0 kg N.hm-2),reduced N application(RN:180 kg N.hm-2)and conventional N application(CN:240 kg N.hm-2).This study aimed to explore the relationship among crops,soil and microbes in N transformation,and reveal the efficient soil N utilization rhizosphere micro ecological mechanism of the N absorption and utilization and N uptake of plants and soil in the relay strip maize-soybean intercropping system.The results are as follows:1.Compared with MM(SS),maize stem N uptake content was increased 22.56%,and grain N uptake content was decreased 0.77%in IMS,soil total N content were increased 13.39%;soybean stem N uptake and soil total N content decreased by 38.55%and 5.81%respectively.,but the grain N uptake content was increased 9.4%.Compared with NN,N application increased the N uptake content in stem and grain,also the soil total N content of plants.Among N application treatment,maize stem?grain N uptake content and total N content of MM were CN>RN>NN,and the soil total N content was highest in CN;while under IMS,maize stem?grain N uptake and soil total N content were highest in RN.Soybean stem?grain N uptake content and soil total N content were highest in RN.2.Compared with MM(SS),the number of maize rhizosphere soil bacteria,fungi and actinomycetes were increased,after symbiosis with soybean,it increased by 2.6%,15.5%and 8.6%respectively;the number of soybean bacteria,actinomycetes and azotobacter of soybean increased by 12.9%,5.6%and 2.2%in 2 years,while the fungi R2 period was 1.3%less than that in SS except R2,but there was no significant difference.N application increased the number of bacteria,fungi,actinomycetes and azotobacter,among them,the number of bacteria was the largest in RN,it was higher in RN than NN and CN with an average of 9.6%and 9.8%,and soybean is 11.7%and 11.0%.Compared with NN,N application increased the number of fungi in maize,by an average 17.2%and 11.3%;it was 9.8%and 1.5%in soybean.The number of maize actinomycetes increased with the increase of N application rate,it increased by 7.95 and 11.5%on average in maize and 14.0%.1.9%in soybean;with N application,the number of azotobacter increased with the increase of N application rate,under SS and IMS,it was 7.1%and 11.7%higher than without N application.3.The effect of planting patterns and nitrogen application rate on amoA gene type was significant.There were a total of 38 OTUs,in the amoA gene clone library there were a total of 38 OTUs,and divided into 3 categories.Among them,the dominant populations of Maize under MM in I category were OTU18,OTU33 and OTU27,while under IMS,the dominant populations of Maize were OTU31?OTU29?OTU24;The II and the III categories were the dominant OTUs of soybean.Compared with MM(SS),the OTU number of Maize under IMS was higher than that of MM,it was IMS<SS.Compared with NN,N application significantly increased the gene abundance of maize and soybean,it increased by 37.7%in maize and 93%in soybean.4.There were 67 OTUs,divided into 3 categories.Among them,OUT4?OTU5 and OTU6 were unclassified sequences,and the other samples came from environment were abundant.Compared with MM(SS),the microbial diversity of nifH gene of maize was improved under IMS.Compared with NN,N application improved the diversity of nifH gene,and it was highest in RN.Compared with MM(SS),in the R6 period,the nifH gene abundance of maize increased by 88.9%,after symbiosis with soybean,gene copies were increased by 631.8%in MM and 1233.2%in IMS;in the V5 period under IMS,the gene copies of soybean was increased by 34.15%,but it decreased by 18.9%in R2 period.The gene abundance of maize was the highest in RN in the whole periods,while soybean increased with the increase of N application rate.5.Under IMS,there were 26 nirS gene dominant OTUs of maize,and 18 OTUs in MM;there were 3 dominant OTUs of soybean in inter-cropping system while 2 in IMS.Under MM,the OTUs number and diversity index of maize were highest in RN,lowest in NN,but under IMS,it was least in RN and highest in CN;while it was lowest in RN in SS and IMS.Compared with MM,in the R6 period under IMS,the nirS gene abundance increased 84.8%,symbiosis with maize,it was IMS>SS,and decreased with the the growth period in SS and IMS.