Effects Of Wheat Rhizosphere Microorganisms On Soil Health In Response To Decades Of Long-Fertilization

Soil health is critical for maintaining terrestrial ecosystem function and ensuring national food security.As a core driver of soil ecosystem sustainability,soil microorganisms profoundly influence agroecosystem productivity and expected agricultural soil health.However,the contribution and influence mechanisms of soil microorganisms to soil multi-nutrient cycling and soil health remain to be explored in depth.Based on this,this study was conducted on 2 decades long-term fertilization agricultural soils,combining in situ field experiments and greenhouse pot experiments,and systematically applying mature technical methods such as amplicon sequencing,metagenomic sequencing,and soil enzyme activity detection.To investigate the composition and diversity of soil microbial communities,phylogenetic signals and environmental adaptations,assembly processes and master control environmental factors in long-term fertilization agricultural ecosystems;to clarify the effects of different fertilization patterns on soil multifunctionality;to reveal the effects and mechanisms of action of fertilization patterns on soil multi-nutrient cycling processes and soil health.The main research results obtained in this thesis are as follows:（1）Fertilizer application significantly affected the community structure and diversity of soil rhizosphere microorganisms.The results showed that long-term application of both inorganic and organic fertilizers significantly increased theβ-diversity of bacterial community.Rare microbial taxa with weaker phylogenetic signals and narrower ecological niche breadths drove soil carbon,nitrogen cycling metabolism pathway.The results based on null models indicated that the assembly process of soil microorganisms under long-term fertilization patterns was mainly dominated by deterministic processes（homogeneous selection）.Homogeneous selection processes drove the assembly processes of rare bacterial（100%）and fungal（60%）subcoummunities.However,abundant bacterial subcommunities were mainly dominated by dispersal limitation（71%）and abundant fungal subcommunities were mainly driven by non-dominant processes（75%）.Multiple regression analysis indicated that soil NH₄⁺-N concentration was the main factor regulating the balance of stochastic-deterministic assembly processes in abundant and rare bacterial subcommunities.（2）Long-term fertilization significantly affected soil physicochemical properties,enzyme activity properties and ecosystem multifunctionality.The results showed that long-term application of both organic and inorganic fertilizers significantly reduced soil p H.Compared with inorganic fertilizer,organic fertilizer not only significantly increased soil moisture content,but also significantly increased soil base nutrient content.In addition,application of organic fertilizers significantly increased the enzymatic activities of soil alkaline phosphatase（AKP）,cellobiose hydrolase（CBH）,leucine peptidase（LAP）,polyphenol oxidase（PPO）,and urease（UG）.In particular,the application of organic fertilizers as well as high application of inorganic fertilizers treatments significantly increased soil multifunctionality,and the diversity of bacterial and fungal taxa was significantly and positively correlated with soil multifunctionality.（3）High application of organic fertilizer significantly improved soil health condition.Beta diversity of bacterial and fungal communties as well as some functional genes of carbon,nitrogen and phosphorus cycling processes could be used to predict soil health index.For the nitrogen cycle,fertilization significantly enhanced the abundance of hao gene for nitrification processes and nir S/K,qnor B and nos Z genes for denitrification processes.The increase in the relative abundance of functional genes was particularly significant with high application of inorganic fertilizer.In addition,fertilization significantly increased the abundance of nas A/B and nar B genes during anabolic nitrate reduction to ammonium production（ANRA）,nap A,nar H,nar G and nir D genes during anabolic nitrate reduction to ammonium production（DNRA）,and gdh A genes during organic nitrogen metabolism.For the phosphorus cycle,the application of organic fertilizers significantly increased the abundance of phn A and pho N genes during organic phosphorus mineralization and suppressed the abundance of genes related to the phosphorus transport system,while the application of inorganic fertilizers increased the abundance of genes related to the phosphorus transport system and phosphorus starvation response and promoted the accumulation of genes related to the inorganic phosphorus solubilization process.（4）The results of the pot experiment showed that the synthetic microbial community has the ability to improve the soil health condition.Based on the isolation and purification of the strains,a total of 68 strains belonging to 4 phylum and 21 genus were obtained.In combination with phosphorus solubilization,potassium solubilization,nitrogen fixation and IAA production,6 strains with strong single functional properties or multiple properties were obtained,which belonged to two genera Pseudomonas and Microbacterium.The results of the greenhouse pot experiment showed that inoculation of the synthetic bacterial community significantly increased soil moiture content and p H;significantly promoted wheat growth（i.e.,significantly increased the height,above-ground dry weight and fresh weight of wheat plants）,as well as significantly increased the root volume of wheat.In addition,we found that synthetic microbial communities possess the potential to enhance soil health.