Effects Of Irrigation And Nitrogen Treatments On Nitrogen Utilization And Soil Microbial Community In Winter Wheat

In recent years,unreasonable irrigation and fertilizer management has resulted in waste of resources,environmental pollution and destruction of soil micro-ecology.The experiment was by asplit-block design with 3 irrigation regimes and 4 nitrogen(N)application rates.The irrigation treatments included no irrigation(W0),irrigation at jointing stage(W1),and irrigation at jointing andanthesis(W2);the N treatments included N amount of 0 kg hm-2(N0),180 kghm-2(N1),240 kghm-2(N2)and 300 kg hm-2(N3).Based on the treatment of localized irrigation and N for eight years,the effects of different irrigation and N on wheat yield and N utilization were studied.The effects of irrigation and Ntreatments on the structure and function of soil microbial community were discussed by using high-throughput sequencing technique.In addition,we analyzed the effect of different N application rates(N0,N1,N2 and N3)on the microorganisms in fluvo-aquic soil,sandy soil and lime concretion black soil.The relationship between wheat growth and soil physical and chemical properties and microorganism was clarified in order to provide scientific basis for rational operation of water and fertilizer,guarantee the ecological stability of farmland soil,and realize the continuous high yield of wheat.The main results are as follows:1.Effects of irrigation and N treatments on wheat yield and the utilization of N fertilize rThe effects of irrigation and nitrogen treatments on wheat yield and N use were different.Compared with non-irrigation(W0)and N application(N0),irrigation and N application significantly increased wheat yield,but there was no significant difference among N applied treatments.In N1 treatment,wheat plants maintained high photosynthetic capacity and assimilation accumulation,and promoted the transport of matter after anthesis and maintained a high yield.With the increase of experimental year,nitrate Nhad been leached below 1m especially under W2 condition,resulting in a certain amount of N loss.N application significantly increased the apparent loss of N,and N1 treatment had the highest Nuse efficiency under all water conditions.Under the experimental conditions,taking into account environmental quality and wheat yield,the optimized range of N application rate was135~194kg hm-2,which was beneficial to improve N use efficiency and prevent soil acidification and pollution.2.Effects of irrigation and N treatments on soil bacterial structure and functionIrrigation and N application changed the soil physical and chemical properties,irrigation increased soil p H,and N application decreased p H under no irrigationcondition.Long-term localized N application decreased bacterial abundance and diversity,and irrigation could alleviate the negative effects caused by excessive N fertilizer.Irrigation and N application significantly increased the relative abundance of Chloroflexi.Single N application significantly reduced the relative abundance of Acidobacteria,N itrospirae and Planctomycetes.The abundance of microbial community was closely related to the growth of wheat and soil characteristics.The relative abundance of Planctomycetes and Verrucomicrobia was positively correlated with root length density(RLD)and root weight density(RWD).The abundance of Chloroflexi and Anaerolineae was positively correlated with yield,and RLD was the most closely related to the bacterial abundance.The treatments also affected the bacterial function,irrigation increased the abundance of functional genes related to carbohydrate transport metabolism,transcription,inorganic ion transport metabolism and lipid transport metabolism.Under the W2 condition,N application significantly increased the abundance of biosynthesized functional genes related to amino acid transport and metabolism,signal transduction mechanism and cell wall/cell membrane/membrane structure.Soil moisture increased the bacteria functional abundance of inorganic ion transport and metabolic,higher amino acid transport and metabolic functional abundance was beneficial to increase wheat yield.3.Effects of irrigation and N treatments on fungi community structureN application reduced the abundance,diversity and richness of fungi,while irrigation weakened the adverse effects of N fertilizer on diversity and richness,but could not alleviate the decrease of fungal abundance caused by N fertilizer.Irrigation and N application affected the community structure of fungi at the same time,and the variation of 44.9% was explained by the two factors.N application alone increased the relative abundance of Ascomycota and decreased the abundance of Basidiomycota.At the ge nus level,N application alone significantly increased the relative abundance of the Cladosporium,while irrigation decreased the relative abundance of Fusarium.Under irrigation conditions,N application significantly reduced the relative abundance of Cryptococcaceae and unclassified_c_Microbotryomycetes.The genus of Coniophoraceae,Boletalesand Alternaria can be used as indicators of community structure changes of soil fungi.The abundance of Arthropoda in fungi was positively correlated with wheat yield,while Glomeromycota phylum was negatively correlated with yield,root nitrogen content and nitrate N content.Soil moisture was the main factor affecting fungal abundance.4.Effects of N fertilizer on soil microbial communities under different soil conditionsThere was no significant effect on the dominant microbial groups in three different soils,which indicated that the difference of microbial communities among soils was greater than that of N application.The dominant phylum was Proteobacteria in fluvo-aquic soil(FS)and sandy soils(SS),and was Actinobacteria in lime concretion black soil(BS).The effect of N fertilizer on FS and SS was more significant than that of BS.N application significantly decreased the bacterial diversity in FS and SS soil,but had little effect on the bacterial community in BS soil.N application increased the relative abundance of Actinomycetesand Gemmatimonadetes in bacteria,Ascomycetes and Fusarium in fungi,but decreased the abundance of Acidobacteria and Firmicutes in bacteria,Glomeromycota and Basidiomycetes in fungi under three soil conditions.N application increased the abundance of Chloroflexi in FS and SS soil,but decreased the abundance of Chloroflexiin BS soil.The correlation analysis showed that wheat yield was significantly positively correlated with the abundance of Gemmatimonadetes,Actinomycetes and Tectomicrobia phylum,and significantly positively correlated with the abundance of Ascomycota.The yield was negatively correlated with the abundance of Cyanobacteria,Proteobacteria Chlorobiin bacteria and Glomeromycota in fungi.There was a significant positive correlation between available phosphorus(AP),potassium(AK)and the abundance of Planctomycetes,Tectomicrobia and TM6,but significant negative correlation between the abundance of AP and AK and the abundance of Armatimonadetes,Parcubacteria and Cyanobacteria.N application increased the abundance of amino acid transport and metabolism,transcription,carbohydrate transport metabolism and inorganic ion transport metabolism in three soils.Organic matter(OM),total N(TN),available N(AN),AP and AK were positively correlated with the abundance of replication,repetition and repair functional genes in bacteria.The analysis of structural equation model showed that the community structure of bacteria and fungi was significantly correlated with wheat yield,and the abundance of functional genes related to energy production and transformation in bacteria was positively correlated with wheat yield.