| Fertilization is an essential agricultural practice primarily used to increase crop yield and soil nutrient availability,with concomitant changes in soil biological,physical and chemical properties,and these changes or fertilization itself can in turn influence soil microbial community composition and diversity.Related with various soil biochemical processes,soil microbe also play vital roles in the formation and stability of soil aggregates.Microbe has become an important index for monitoring soil fertility and health.Rhizosphere microorganisms can influence plant growth and health by the interaction system between microorganism and plant.Rhizosphere microorganisms are screened from the bulk soil microbe based on the special condition.Fluvo-aquic(FA)and lime concretion black(LCB)soils are the main soil types of the North China Plain,which is very important for Chinese grain production.As for FA soil,high silt content and strong soil respiration make soil organic matter difficult to accumulate.As for LCB soil,the poor structure and low soil organic matter content decreased soil productivity.Feritilization is widely used to increase crop yield in this area,while it is still unclear that succession rule of soil microbial community structure in under long term fertilization.LCB and FA soil were selected as research objects,with analyzing their physical,chemical and biological properties.The succession rule of soil microbial community structure in different fertilization treatments were investigated using Miseq and Metagenome sequencing.This research mainly focused on the following main 4 questions.(1)Which bacterial species were changed with long term fertilization and how were the changed species assoaciated with soil productivity in FA and LCB soil;(2)Which fungal species were changed with long term fertilization and whether these changes were consistent in different time and space? How did these changes affect soil nutrient tramsformation?(3)Which soil functional profiles changed under long term fertilization treatments based on metagenome sequencing and how these changes associated with the succession of soil fertility.(4)For the dominant fungal strains in long term organic fertilization treatments,what were its roles in soil nutrients transformation and promotion of plant growth.The succession rules of soil properties and bacterial community structure were as follow,(1)Long term organic and inorganic fertilization increased biochemical properties in FA and LCB soil,such as soil organic carbon(SOC)content,total nitrogen(TN)content,protease and intervase activities.(2)Fertilization accelerated the improvement of soil strcuture in FA and LCB soil,with the ratio of 0.5mm~2mm aggregate increasing.Organic fertilization had bigger effect than inorganic fertilization.(3)Organic fertilization had a greater influence on bacterial diversity in FA soil,and the main reason was that the addition of organic substances promoted the growth of key functional bacteria.(4)Inorganic fertilization had a greater influence on bacterial dversity in LCB soil,and main reason was that acid condition restricted the growh of acid sensitive bacteria.(5)The relative abundance of Cytophagaceae,Chitinophagaceae,and Xanthomonceae increased significantly in plots treated with long term organic fertilizers of FA soil,which were implicated in the decomposition of complex organic matters and improvement of soil nutrients content and transformation rate.(6)The relative abundance of Acidobacteriaceae,Gaiellaceae,and Opitutaceae increased in NPK treatments,and these acid-producing or acid resistant bacteria will aggravate the release of soil phosphorus.(7)Soil bacterial communities showed no significant shift in LCB soil treated with long term organic fertilizers.So it was speculated that the responders of long term organic fertilization were soil fungi.Organic manure had a great impact on the fungal community in LCB soil and maize roots and the succession rules were as follow.(1)Soil fungal community composition in LCB soil revealed significant changes in long term organic fertilization at jointing and manuring stage of maize,with increasing relative abundance of Zygomycota and decreasing Basidiomycota abundance in rhizosphere and bulk soil.(2)Long term organic fertilization also changed the endophytic fungal community structure,with increasing abundance of Fusarium and Mortierella.(3)The relative abundance of Mortierella,Fusarium,Chaetomium increased in the long term organic fertilization.Mortierella became the dominant group due to a greatest increase(from 5% to 45%),making the greatest contribution to the shift of soil fungal community.These fungal species of Mortierella,Fusarium,Chaetomium played essential roles in the rapid decomposition of plant residues,simultaneously improving the release of nutrients in organic manure.The succession rules of functional genes in FA soil under long term fertilization treatments were as follow.(1)The total number and average length of soil genes inceased by long term fertilization,bringing more potential functions.(2)The absolute abundance of Proteobacteria increased by long term fertilization which might lead to an increase of CO2 emssions.(3)The Nitrososphaera abundance increased while the Nitrospira abundance decreased,leading to the enhancement of denitrification and N2 O emissions.(7)Long term fertilization increased the relative abundance of genes associated to nitrogen metabolism,tyrosine metabolism and degradation of aminobenzoate,which involved in soil carbon and nitrogen cycling and pollutants degradation.Stimulated by long term organic fertilization,Mortierella dominated the fungal community in LCB soil.(1)The mainly morphological characterstics were lotus like colony,torose mycelium and a lot of zygosporangium.(2)C assimilation assays revealed that M.elongata was able to utilize a variety of carbon resources,including D-fructose,D-trehalose,and D-mannose,L-asparagine,L-alanyl-glycine,clycyl-L-glutamic acids,L-glutamic acid,L-aspartic acids,L-alanine,L-alaninamide,L-serine,etc.Furthermore,M.elongata was found to readily utilize N-acetyl-D-glucosamine.(3)The prediction of genetic functions showed that M.elongata contained biosynthetis genes of indole acetic acid(IAA)and abscisic acid(ABA),which were conducive to the improvement of plants growth and stress resistance.M.elongata's capacity to compose recalcitrant melanogenesis,and these substances contributed to pools of long-term stable SOM.M.elongata possessed the functional capacity to degrade a range of toxic organics,and thereby improved soil health.(4)Pot experiments showed that M.elongata accelerated soil nutrient cycle by enhancing soil enzymes activities,and promoted maize growth by regulating the hormne level of maize roots. |
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