Promoting Wheat Growth Under Saline-alkaline Rhizosphere Bacterial And Construction Of Synthetic Communities Stress And Their Mechanisms

Saline-alkaline stress seriously harms crop growth,threatens global agricultural production and food security as the important environmental factor.Rhizosphere microorganisms have been shown to effectively reduce salt stress and increase crop yields.However,saline-alkaline stress has more harmful effects on plants than sole salt stress,but there are few studies on the interaction between plants and microorganisms under salinealkaline combined stress.Hetao region of Inner Mongolia is an important grain base in northern China.Wheat is one of the most important grain crops in this region,but its growth and yield are limited by the soil saline-alkaline combined stress.Screening and determining which rhizosphere growth-promoting bacteria can effectively reduce stress and their mechanism of action is the key and basis to explore the promotion of wheat growth and yield improvement under saline-alkaline stress and research and development of relevant application technologies,but the relevant mechanism is still unknown.In this study,rhizosphere bacteria from wheat and desert、saline-alkaline plants in western Inner Mongolia and other places were isolated by spread and streak plating,preliminary classification identification was carried out based on 16S rRNA gene sequence phylogenetic analysis.These strains freshly isolated and collected from laboratory microbial species resource repository were inoculated in high-saline medium,the strains growth well determined as the saline-alkaline resistant bacterial.Then these saline-alkaline tolerant strains were inoculated to wheat under saline-alkaline stress to screen the strains that promoted the growth of wheat seedlings.Strain Enterobacter sp.FN0603,which significantly improved germination and aboveground and underground biomass was applied in combination with silicon to potted wheat under saline-alkaline stress,and the possible related mechanisms were also explained for the effects of different treatments on wheat growth,rhizosphere soil physicochemical properties,plant morphology and physiological biochemistry,and rhizosphere and root endophytic microbial community structure.Strains that significantly increased germination rate and increased aboveground and underground biomass were combined,and a“subtraction" strategy was adopted to eliminate them one by one to simplify the construction of synthetic communities that could effectively reduce stress and increase yield,and the rhizosphere soil physicochemical properties,plant morphology and physiology,and changes in the structure of rhizosphere and root endophytic microbial communities after inoculation were analyzed.The main results and conclusions are as follows:Strains that significantly increased wheat germination rate and increased aboveground and underground biomass were combined,and a“subtraction" strategy was adopted to eliminate them one by one to simplify the construction of synthetic communities that could effectively reduce stress and increase yield.1.Rhizosphere bacterial screening and synthetic community construction140 strains of rhizosphere bacteria were isolated from plants such as Haloxylon ammodendron,wheat and other plants,and the dominant genus was Pseudomonas(16.4%)、Bacillus(14.3%)、Microbacterium(9.29%)、Arthrobacter(6.43%)、Streptomyces(6.43%)、Brevibacillus(5.71%)and Glutamicibacter(5.71%);A total of 456 rhizosphere bacterial strains were isolated and collected in the laboratory,and 263 salinity tolerance(tolerance:NaCl concentration>1%,pH>9)bacterial strains;Compared with the control,31 strains could significantly increase the germination rate(6.19～44.44%),aboveground(0.95～62.93%)and underground(1.57～136.93%)biomass of wheat.The dominant genera are Enterobacter、Pseudomonas、Bacillus and Ochrobactrum;These 31 strains are compounded and“subtracted",to simplify to obtain the most proliferating effect,containing 5 strains synthetic community SynCom-SASW01,strains including Enterobacter sp.FN0603、Enterobacter sp.FWP0601、Enterobacter sp.FWP1205、Pseudomonas sp.FWP0405 and Stenotrophomonas sp.HLPD6。2.Silicon and Enterobacter sp.FN0603 synergy can effectively reduce salinealkaline stress in wheat plantsStrains FN0603,especially when administered in combination with silicon,increased the colonization of FN0603 within the roots(11.96%),altering the endophytic bacterial and fungal communities of the roots,as increased Enterobacter(11.69 times)and Pseudomonas(1.99 times)relative abundances,not rhizosphere communities.Bipartite network analysis,Variation partitioning analysis,and Structural equation models(SEM)further showed that strain FN0603 indirectly shaped root endophytic bacterial and fungal communities and recruited FN0603-specific biomarkers(Enterobacter、Fusarium,et al)(P<0.05)significantly and positively,improved plant physiology,rhizosphere soil properties and plant growth,such as silicon and Enterobacter sp.FN0603 combined with untreated control significantly increased the aboveground biomass(87.43%)、underground biomass(66.60%)and salinity tolerance index(144.75%);leaf Chlorophyll(55.42%)and CAT(49.25%);rhizosphere soil available nitrogen(79.02%)and CAT(83.31%),reduced leaf MDA(42.56%)and soil EC(61.2%),etc.3.Simplifying the effect of SynCom-SASW01 coating on wheat growth in salinealkaline field and its mechanism analysisThe synthetic community SynCom-SASW01 had significant positive effects on morphology,growth,yield,quality,physical and chemical properties of rhizosphere soil and physiological and biochemical properties of seedlings in seedling,jointing,filling and maturity stages of wheat in saline-alkaline land,such as increasing the aboveground dry weight of wheat per plant(21.05～100.44%)and the underground dry weight of wheat in each growth period compared with the untreated control(26.23～137.24%);The panicle length(11.23～18.42%)、yield per unit area(24.91～32.41%)、grain protein content(10.35～15.09%)and wet gluten content(11.62～16.82%)were increased;Improved the available nitrogen content in rhizosphere soil(46.67～1882.68%);leaf Chlorophyll content(46.25～95.71%)and SOD(100.23%)were added;Reduce conductivity(8.68～47.76%).SynCom-SASW01 significantly affected the root-related microbial community structure of saline-alkaline wheat,especially on the root endophytic bacterial community structure,such as increasing the root endophytic bacteria Paeniglutamicibacter(2390.26%)and the relative abundance of Enterobacter(1681.80%),etc.Colinear network analysis(CoNet)analysis showed that the number of major clusters of rhizosphere bacterial communities was seedling stage>jointing stage>filling stage>maturity stage.Ternary analysis showed that Enterobacter was the highest in the rhizosphere and root endophytic communities treated with SynCom-SASW01 coating at the seedling stage,and the seedling stage and mature stage were in the whole growth period rhizosphere bacteria are most abundant,and microbial communities at the seedling stage colonize more in the rhizosphere than within the root.SynCom-SASW01 coating treatment also improves the relative abundance of Enterobacter sp.FN0603、Enterobacter sp.FWP0601 and Enterobacter sp.FWP1205 in the endophytic communities,and Stenotrophomonas sp.HLPD6 in the rhizosphere community at the seedling stage.SynCom-SASW01 can influencing the wheat endophytic and rhizosphere microbial communities,improving rhizosphere soil fertility level and physiological and biochemical properties of wheat plants,further promote the establishment of wheat root morphology,accelerating the growth rate of wheat plants at various growth stages,so as to achieve the purpose of increasing yield.In summary,genera Enterobacter,Pseudomonas,Bacillus and Ochrobactrum are the main rhizosphere bacterial taxa that alleviate saline-alkaline stress in wheat,deserts and saline-alkaline lands plant rhizosphere soil is a good culture resource bank for saline-alkaline rhizosphere growth-promoting bacteria.Enterobacter sp.FN0603 and silicon have significant synergistic effects on reducing saline-alkaline stress and promoting the growth of wheat seedlings by regulating root endophytic community structure,improving rhizosphere soil properties and plant physiology.SynCom-SASW01,a synthetic community containing Enterobacter,Pseudomonas,and Stenotrophomonas compared with a single strain or other strains,the composition of synthetic communities with different strains significantly increased the germination rate,aboveground and underground biomass,and significantly affected the wheat morphology and physiology,rhizosphere soil physical and chemical properties,and the structure and function of rhizosphere and root endophytic microbial communities planted in saline-alkaline stressed land,thereby promoting wheat growth and improvement yield and quality.This is a new exploration to alleviate the microorganisms related to wheat saline-alkaline stress in the Hetao irrigation area,which can provide a basis for the interaction theory between crop-microorganism and soil in the farmland ecosystem,has important theoretical significance and practical value for fully understanding and utilizing microbial germplasm resources in Inner Mongolia,rational and effective use of salinized soil,and promoting food security.