Effects Of Nitrogen Fertilization Application On The Microbial Communities In Rice-rapeseed Rotation Systems

Chemical fertilizers are commonly used in crops cultivation to increase yields and meet the demand from an ever-expanding population.Meanwhile,crop rotation is an economic and sustainable way in agriculture for the improvement of soil conditions,thus to increase crop production.However,we still have an incomplete understanding of the influence of chemical nitrogen fertilizer on microbial communities in rice-rapeseed rotation system.Two treatments consist of applying nitrogen fertilizer(150 kg N/hm2)and without applying nitrogen fertilizer to explore the shift of the functional microbial community in rice-rapeseed rotation system.Soil samples were collected in 2013-2014 at rapeseed development(before-planting,wintering,bolting,flowering,ripening and,post-harvest)and rice development(before-planting return-green,tillering,full-heading,maturity and post-harvest)(120 soil samples).Initially,soil physicochemical properties and enzymatic activities were characterized.Soil microorganisms were investigated using community-level physiological profiles(CLPP),phospholipid fatty acid analysis(PLFA)and 16s rDNA high-throughput sequencing analysis.The results are as follows:Nitrogen fertilization application significantly increased available nutrients nitrogen and can promote the absorption of AP and AK.Soil Physicochemical Properties was significantly influenced by development.Soil enzyme activities(phosphatase,invertase,aryl sulfates and urease)were significantly changed by nitrogen fertilization and development.Soil enzyme activities were significantly influenced by MOI?TC?TN and pH in rice,but they were controlled by AN?TN?PH and TC in rapeseed(P<0.05).The microbial functions,indicated by Eco-plate data,at both rice and rapeseed were restrained within nitrogen fertilization application.The utilization rates of the main carbon source by microbes were different between rice and rapeseed.Rapeseed soils utilized more the carbon sources than rice.PLFA data indicated that nitrogen fertilization application increased the soil microbial biomass.The microbial community was significantly influenced by development.Redundancy analysis showed the rice rhizosphere microbial communities were significantly influenced by the soil physicochemical properties including C/N and TN while those at rapeseed were significantly shaped by TK,TC,C/N,MOI and pH(P<0.05).The microbial community at rice and rapeseed soils was significantly different,and they were distinguished by the relative abundances of Actinomycetes,Gram-positive bacteria,Fungi,and Gram-negative bacteria.The profiles of 16s rDNA high-throughput sequencing revealed that the bacterial community structure was significant differences across stages,suggesting that the plant can select a subset of microbes at different stages of rice and rapeseed growth.The bacterial community Was primarily grouped by nitrogen fertilization application through the clustering analysis of the bacterial cormunity in the phylum,indicating that the bacterial community was significantly influenced by nitrogen fertilization application.Additionally,Proteobacteria,Chloroflexi,Germatimonadetes and Verrucomicrobia significantly changed with rice development,while Acidobacteria,Chloroflexi,Nitrospirae and Bacteroidetes significantly changed in rapeseed.Mantel test showed the rice microbial coumunity was significantly influenced by pH,while those at rapeseed was significantly shaped by C/N and MOI(P<0.05).On the whole,the alteration effect of nitrogen fertilization application and development was different on rice and rapeseed microbial community.The data presented in this study suggested that nitrogen fertilization application and development had a diverse influenced on soil enzyme activities,CLPP,microbial community structure and function of rice and rapeseed soils.Meanwhile,nitrogen fertilization application had greater effect on rapeseed microbial community than rice.