Study On The Morphological Formation And Occurrence Mechanism Of The Rhizosheath In The Seedling Stage Of Kengyilia Hirsuta

Kengyilia hirsuta is a kinds of the pioneer species in the desertification grassland of Qinghai-Tibet plateau,which has a developed rhizosheath structure.This structure is the main characteristics of adaptation to the environment.In order to analyze the relationship between root system architecture and the formation of rhziosheath,to determine optimum moisture,we setting five moisture degree(10%,20%,30%,40%and 50%),soil treatment(unsteriliaztion and sterilization).Based on the rhizosheath weight optimal moisture,three moisture degree were screened(10%,25%,40%),soil treatment(unsteriliaztion and sterilization),Next,we analyzed that the relationship between endogenous hormones of root and the difference informed of rhizosheath.we study to change of soil microbial diversity and enrichment of key microorganisms,filter the key exudates,the key gene,etc.The result showed that:(1)With moisture rising,the number of root crosses and branches was the largest in 50%under unsterilization soil incubation(P<0.05).Under the sterilization conditions,the number of root tips and links decreased in 10%moisture degree(P<0.05).The total root volume and total surface area of roots were significantly higher in 50%than 10%water gradient.After soil sterilization treatment,Total root length and number of branches in 20%moisture degree,the number of links and the number of root tips between the 20%-50%moisture degree,total root surface area and average diameter in 40%moisture degree,the total root volume in 40%-50%moisture degree were larger than that unsterilized soil(P<0.05).The influence factor of rhizosheath weight:moisture degree>soil treatment>FD(fractal dimension,FD)>q_b>Fixed permeability of root ability.The rhizosheath weight were largest in20%-30%under unsterilization and in 30%moisture 30%under sterilization.The rhizosheath weight was positively affected by q_b,FD and fixed permeability of root ability.(2)In 10%,25%and 40%moisture degree under difference soil treatment,seed germination rate and seedling survival rate were significantly reduced in 10%moisture degree(P<0.05).The root activity be increased(P<0.05),seed germination rate in 40%moisture and seedling survival rate were significantly degreed under sterilize(P<0.05).The ABA and GA content of root were highest in 10%under unsterilization(P<0.05),which significant higher in 10%and 25%than 40%moisture degree(P<0.05).After the soil be sterilized,the ABA and GA content of root were higher than unsterilizaion treatment(P<0.05).The ABA and GA content of root were extremely significant effect by the interaction of moisture and soil treatment(P<0.01).Comparative the IAA content of root,which was lowest in 10%moisture degree(P<0.05),After the soil be sterilized,the IAA content of root was higher than unsterilizaion treatment(P<0.05).The IAA content of root was not effect by the interaction of moisture and soil treatment(P>0.05).The CTK content was highest in40%,while,lowest in 10%(P<0.05).After the soil be sterilized,the CTK content was no significant variation.The CTK content of root was not effect by soil treatment and the interaction of moisture and soil treatment(P>0.05).With moisture rising,the increase of rhziosheath weight in 25%,and decreased at10%and 40%moisture degree.After the soil be sterilized,the rhizosheath weight was no significant variation(P>0.05).TTC,ABA,IAA,CTK and GA content are significantly related to rhizosheath weight,including.Rhizosheath weight was positive correlation with the TTC,IAA,CTK(p<0.01),but negative correlation with ABA(P<0.01)and GA(P<0.05).(3)Rhizosheath was no significant difference of microbialα-diversity between moisture and different soil treatment(P>0.05).Theα-diversity of rhizosheath was higher in unsterilization than sterilization(P<0.05).The result of NMDS showed that the soil sterilized is the main influence factor ofβ-diversity(P<0.05).After the soil be sterilized,the owed of OTUs accounts for 86%by three moisture degree,which distribution of microorganisms is relatively uniform,indicates that the"plant-soil"system reconstructs the microbial community.Under the unsterilized soil,OTU16(Arthrobacter)played a major aggregation role in rhizosheath microorganisms.Under the sterilized soil,OTU10(Massilia)microorganisms reconstructed the main microflora during the formation of rhizosheath in the seedling stage of Kengyilia hirsuta.(4)From the principal differential substance metabolites in the root of Kengyilia hirsuta,58 number in 10%,53 number in 25%,114 number in 40%moisture degree,10 number of metabolites were owed in three moisture degree.The species composition of root exudates content≥5%was compared:The steroid be significantly upregulated in 10%moisture degree.When lack of water,the steroid can promote the secretion of organic acids,stimulate the proliferation of rhizosphere microorganisms,and improve the activity of root.The 1-(1z-alkenyl),2-acyl glycerol phosphoserine be significantly upregulated in 25%moisture degree,which can promote facilitating signal transduction and improve the activity of bacteroidetes and root.Steroids and glycerides were significantly upregulated in 40%moisture degree,them can stimulate microbial growth and regulate plant growth.The co-enrichment of KEGG pathway:Phosphatidylinositol metabolism,glycerophosphate,Glyceride metabolism,α-linolenic acid metabolic pathway(5)To compare the DEGs of roots under sterilized and unsterilized soil conditions,the number of DEGs had 5689(up-regulated 2414,down-regulated 3275)in 10%moisture degree.The number of DEGs had 11499(up-regulated 1656,down-regulated 9843)in 25%moisture degree.The number of DEGs had 13136(up-regulated 2069,down-regulated 11067)in 40%moisture degree.The DEGs numbers in the low moisture degree were less than the high moisture degree,indicated that the root activity increased with moisture rising.After the soil be sterilized,the physiological activity of root system be decreased,therefor,the down-regulated of DEGs accounted for the majority.The owed of up-regulated DEGs account for 9 species,which are potential candidates for rhizosheath formation.Analyzed the TOP30 of GO enrichment,almost were concentrated on cell processes(63.33%),KEGG enrichment pathways are mainly ribosomes,Rap1 signaling pathway,unsaturated fatty acid biosynthesis and steroid biosynthesis,which determined the molecular mechanism of root adapted to environmental factors and affect rhizosheath formed.As a kinds of transcription factors,RAV and GRF were specifically up-regulated,which regulated the important DEGs in the root system of Kengyilia hirsuta,effect on the process for stress adaptation and rhizosheath formation.(6)Transcriptome and metabolomics combine together,GPX gene in the oleic acid metabolic pathway,Dgk A gene in the glyceride metabolic pathway,OPR gene in p-linolenic acid metabolic pathway,CHS1 gene in amino and nucleotide sugar metabolism pathways,MDH gene in the carbon fixation pathway in photosynthesis,OGDh gene in TCA pathway,CALM gene in the phosphatidylinositol signaling pathway is a differential gene in the secretion enrichment pathway,It is also a key candidate gene for producing differential metabolite,above on,which them can play an critical role for rhizosheath informed mechanism in seedling stage.