The Influence Mechanism Of Irrigation And Fertilization On Microorganisms In Different Compartments Of Wheat Root Zone

Irrigation and fertilization are two important factors affecting soil physicochemical properties,soil microorganisms and crop yield.Long-term irrigation and fertilization can lead to changes in soil physicochemical properties,affecting microbial communities in crop root zones and thus soil productivity.As a major grain producing area,North China Plain is facing the problem of water shortage,soil quality degradation and environmental pollution caused by excessive application of inorganic fertilizer.Therefore,necessary measures must be taken to reduce irrigation water consumption and the amount of inorganic fertilizer applied in order to ensure the green and sustainable development of agriculture.This study is based on a long-term field experiment of irrigation and fertilization located in the North China Plain（Hengshui,Hebei Province）.By extracting DNA from bulk soil,rhizosphere soil and root samples of wheat root zone,PCR amplification of prokaryotic microorganism 16S rRNA,fungal ITS and azotobacter nif H were performed using specific primers and high-throughput sequencing.The effects of irrigation and fertilization on the diversity and community composition of microorganisms in different compartments（bulk soil,rhizosphere and endosphere）of wheat root zone were investigated,the response mechanism of microorganisms to different water and fertilization strategies and the key factors driving the changes of microbial community were examined,and the influence mechanism of microorganisms on wheat nitrogen uptake and yield was studied.The optimized irrigation and fertilization modes suitable for application in the North China Plain were recommended from the perspective of microorganisms,and maintaining the green and sustainable development of agriculture.The main findings are as follows:（1）Long-term different irrigation and fertilization strategies changed soil water content and soil nutrient status,and the application of organic fertilizer increased soil organic matter（SOM）,soil total nitrogen（STN）and total carbon（STC）content.Fertilization lowered the pH of slightly alkaline soil,especially with all the application of inorganic fertilizer（M0）treatment,and the soil pH was reduced by 0.24-0.38 compared with CK treatment.Increasing irrigation and fertilization increased wheat yield,while pre-sowing and jointing-period irrigation（W2）treatment（59.52%higher than only pre-sowing irrigation（W1）treatment yield in 2020）and the addition of 50%organic manure with 50%inorganic fertilizers（M50）treatment（only 4.75%lower than M0 treatment yield in 2021）reduced irrigation water and the application amount of inorganic fertilizer,which ensured wheat yield and thus recommended as the optimal treatment in this experiment.（2）Increasing irrigation reduced theαdiversity of bulk soil prokaryotic microorganisms,but increased theαdiversity of rhizosphere and endosphere prokaryotic microorganisms,and the application of organic fertilizers（100%organic manure（M100）and M50）increased theαdiversity of rhizosphere and endosphere prokaryotic microorganisms.Increasing irrigation increased the relative abundance of prokaryotic microorganisms at phylum level in bulk soil,and the relative abundance of Proteobacteria in irrigation treatment was 1.87%-2.95%higher than W0 treatment.Moreover,increasing irrigation increased the relative abundance of beneficial prokaryotic microorganisms such as Flavobacterium,Bacillus and Stenotrophomonas,and the application of organic fertilizer significantly increased the relative abundance of Flavobacterium in three compartments of wheat root zone.SWC and NH₄⁺-N and NO₃^--N were key predictors of prokaryotic microbial community composition under W and F treatment,respectively.Long-term irrigation and fertilization affected prokaryotic microbial communities in different compartments of wheat root zone by changing SWC and SOM,further affecting nitrogen uptake and significantly increasing wheat yield.（3）Increasing irrigation enhanced the fungalαdiversity of bulk soil and rhizosphere.Moreover,increasing irrigation and the application of organic fertilizers with reducing inorganic fertilizers increased the relative abundance of the beneficial fungus Podospora,while reduced the relative abundance of the pathogenic fungus Fusarium.In bulk soil,the relative abundance of Fusarium and Podospora in W0 treatment was 4.58%-7.05%,1.22%-5.14%higher than other irrigation treatments,respectively.The relative abundance of Fusarium in M0 treatment was 0.23%-1.40%higher than other fertilization treatments,while the relative abundance of Podospora in M100 treatment was 1.70%and 1.21%higher than M50 and M0 treatments,respectively.It was also found that the relative abundance of Pathotroph could be reduced by increased application of organic fertilizer through functional prediction.Soil water content（SWC）and pH were the key environmental predictors of fungi community composition under W and F treatment,respectively.（4）SWC and pH were common environmental factors affecting the composition of prokaryotic microbial communities and fungal communities.Compared with fungi,prokaryotic dominant species were more sensitive to irrigation and fertilization treatments,and most dominant species were significantly affected by irrigation and fertilization.（5）Increasing irrigation and application of organic fertilizer significantly increased theαdiversity of bulk soil and rhizosphere diazotroph.Compared with fertilization treatment,irrigation treatment had a more significant effect on theβdiversity of diazotroph in three compartments of wheat root zone.Irrigation increased the relative abundance of bulk soil and rhizosphere diazotroph such as Gammaproteobacteria（the relative abundance in bulk soil and rhizosphere was 1.14%-7.50%and 1.89%-12.89%higher than that of W0 treatment,respectively）and genus level Bradyrhizobium（the relative abundance in soil and rhizosphere was 7.90%-18.65%and 9.34%-13.53%higher than that of W0 treatment,respectively.）.The application of organic fertilizer（M100 and M50 treatments）increased the the relative abundance of Gammaproteobacteria in bulk soil and rhizosphere.SWC,SOM and NO₃^--N had significant effects on diazotroph communities in different compartments.Long-term irrigation and fertilization affected the nitrogen uptake of wheat by affecting bulk soil diazotroph communities,thereby affecting wheat yield.Long-term irrigation and fertilization affect the nitrogen uptake and yield of wheat by changing soil water content and soil nutrient content,and increasing irrigation and organic fertilizer can improve the nitrogen uptake and yield of wheat.Long-term irrigation and fertilization significantly affected the microbial diversity and community composition of wheat root zone,and irrigation treatment had a more significant impact on the diversity of microorganisms in wheat root zone than fertilization treatment.Irrigation and increased organic fertilizer could increase the relative abundance of beneficial microorganisms.SWC,SOM,pH,NO₃^--N and NH₄⁺-N are key environmental factors affecting microorganisms in the root zone of wheat.Irrigation and fertilization can also affect the nitrogen uptake and yield of wheat by regulating the changes of microbial communities in the root zone of wheat.