Effects Of Intercropping On Nitrogen Transformation And Microbial Community Structure In Continuous Cropping Soil Of Cucumber

In recent years,faculty vegetable developed rapidly,and the specialization degree and scale of production was continuous to improve.Due to single cultivation mode and unreasonable use of pesticides and fertilizers,it was resulting in the deterioration of soil quality facilities and vegetable quality reduction.In the intensive vegetable production system,improving the quality of the soil,maintaining the soil nutrient balance and improving the yield of crops were an important problem to be solved at present.The study found that diversity cultivation can improve soil ecological environment,increase crop yield and resistance to disease,and improve the stability of the ecosystem,but the effect of continuous cropping in nitrogen nutrition of facility vegetables is not extremely clear.In this experiment,the research object was continuous cucumber-soil system.According to field experiment under two crop seasons,we mainly explored the effects of seven companion crops(alfalfa,white clover,wheat,rye,chrysanthemum,rape,mustard)on nitrogen conversion of cucumber continuous cropping soil(nitrogen mineralization,nitrification,potential nitrification)and the abundance of special functional population(bacteria,fungi,nitrifying bacteria,denitrifying bacteria),so as to the changes of soil enzyme activities,soil microbial biomass and soil microbial network.The aims were to explore the different crops on greenhouse continuous cropping soil microbial community so as to provide theoretical basis and technical support for the greenhouse cucumber continuous cropping soil remediation and sustained suitable efficiency,clarify the effects of intercropping on soil nitrogen transformation so that lay the foundation for the development of nutrient cycling and utilization in the continuous cropping soil.The main results were as follows:(1)Effects of companion crops on soil nutrients:companion crops significantly decreased soil available phosphorus content,and soil ammonia content was increased under the rye systems in spring.chrysanthemum and alfalfa significantly increased soil nitrate content.(2)Effects of companion crops on major biochemical progress:in spring:companion crops significantly decreased the net ammonification rate,soil net nitrification and ner mineralizaiton rate except alfalfa;white clover,chrysanthemum and rape can significantly reduce the potential nitrification.In fall:white clover significantly increased the net ammonification rate,wheat and rye significantly increased the net ammonification and mineralization rate,rape and mustard significantly increased the net nitrification and mineralization rate,alfalfa and chrysanthemum significantly reduced the net nitrification and mineralization rate;chrysanthemum,rape and mustard significantly increased soil potential nitrification.(3)Effects of companion crops on soil enzyme activity and microbial biomass nitrogen and carbon:companion crops significantly increased soil protease activity,60d in spring and 40d in fall significantly inhibited soil nitrate reductase activity,and had little effect on soil urease activity.Companion crops could make the change of soil microbial biomass carbon and nitrogen,wheat can significantly increased soil microbial biomass carbon,and chrysanthemum and mustard can significantly improved soil microbial biomass nitrogen in the late of spring and fall.(4)Effects of companion crops on absolute abundance of soil microbial community:in spring:companion crops significantly increased the relative abundances of soil bacterial 16S rRNA and nifH genes,reduced relative abundances of nirK and nosZ genes.Companioned treatmetns except alfalfa could significantly decreased relative abundance of nirS gene,rye and chrysanthemum can significantly increased the relative abundance of relative abundance of soil fungal ITS and AOB,and wheat,chrysanthemum,rape and mustard can significantly increased relative abundance of AOA.In fall:white clover can significanly increased the relative abundance of soil bacterial 16S rRNA,fungal ITS,AOA,AOB and nirS,chrysanthemum can significantly decreased relative abundances of 16S rRNA,fungal ITS,AOB and nirS,and had a little effect on AOA.(5)Effects of companion crops on soil microbial community composition:Miseq sequencing results showed that in spring,mustard significantly increased the relative abundance of Nocardiodes,rye significanly decreased the relative abundance of Nitrospira,Pseudomonas had a lower relative abundance in the companion systems,white clover,wheat and ryee can significantly decreased relative abundance of Mortierella;in fall,alfalfa significanly decreased relative abundance of Bradyrhizobium,mustard can signicantly increased relative abundances of Aeromicrobium and Pseudomona,chrysanthemum significantly increased the relative abundance of Arthrographis.Companion systems had no effect on soil microbial community structure,and soil properties had a closer relationship with soil bacterial and fungal communities.In spring,soil moisture and available phosphorus had a significant positive correlation with soil bacterial and fungal communities;in fall,soil moisture and EC had a significant positive correlation with soil bacterial communities,and soil NH4+-N and NO3--N content and fungal communities,respectively.(6)Effects of companion crops on soil microbial network structure:companion systems had an influence on the interaction effects of soil bacterial and fungal communities,especially nitrogen related microbial species,and can change the composition of the core species of bacterial and fungal communities.White clover,rape and mustard can decrease the interaction effects of Bradyrhizobium and Nitrospira.Companion systems decreased the interaction effects of Asperillus in spring,mustard and rape increase the relative abundance of Aspergillus.Rape can decrease the interaction effects of soil bacterial and fungal communities,alfalfa,white clover,wheat,chrysanthemum and rape in fall can increase the interaction effect of soil bacterial and fungal species.Wheat and mustard can increased the core species number in soil bacterial network,and alfalfa,rye,chrysanthemum and rape can decreased the core species number of fungal community.In conclusion,white clover,alfalfa and chrysanthemum decreased net mineralization and nitrification rate,retard the availability of soil nitrogen;mustard can increased effectively soil protease activity,and significantly reduced nitrate reductase activity.The wheat could significantly increased the absolute abundance of soil bacteria(16S rRNA),nitrogen fixing bacteria(nifH)and ammonia oxidizing archaea(AOA)communities,significantly reduced the absolute abundance of fungi(ITS),denitrifying bacteria communities(nirK,nirS),can promote the interaction of species in the bacterial and fungal networks.White clover,rape and mustard reduce the interactions of nitrogen fixing bacteria(Bradyrhizobium)and nitrifying bacteria(Nitrosipra).In addition,soil microbial community was closely related to soil physicochemical properties.