| In recent years,the combined effects of global climate change and human activities have made the problem of grassland salinization increasingly serious.This environment problem not only restricts the development of agriculture and animal husbandry,but also threatens the ecological security in northern China.It has become one of the grassland ecological environment problems to be solved urgently.Using haloalkalitolerant herbage to repair saline-alkaline grassland is the most economical and effective control measure,but the efficiency of phytoremediation needs to be improved urgently.Some preliminary studies have showed that plant growth promoting rhizobacteria(PGPR)and Arbuscular mycorrhiza(AM)fungi had synergistic effects on the growth of glycophytes(or crops)under saline-alkaline stress conditions.At present,the synergistic effects of PGPR and AM fungi on the growth of haloalkalitolerant herbage and the rhizosphere microbial growth-promoting mechanisms are still rare.This paper firstly explored the distribution and assemblages of microbial community of surrounding soils of halophyte root in different saline-alkaline ecosystem of Inner Mongolia.Secondly,based on the natural saline-alkaline soils collected above,the haloalkalitolerant PGPR with potential growth-promoting ability were screened.Finally,the pot experiments were conducted:to explore the effects of single or dual inoculation with haloalkalitolerant PGPR and AM fungi on growth of Stipa grandis and Leymus chinensis under saline-alkaline soils,nutrient absorption and accumulation,ion balance,and changes in soil physicochemical properties;to reveal the rhizosphere microbial mechanism of haloalkalitolerant PGPR and AM fungi in synergistically improving the saline-alkaline adaptability of herbage based on high-throughput sequencing coupled with untargeted metabolomics.The main results of this study were as follows:(1)There were obvious differences in soil basic physical and chemical properties,total salt content,content of soluble salt ion components,?-diversity and structure of bacterial and fungal communities in saline-alkaline soils from different ecosystem types of Inner Mongolia.Compared with the fungal network,the bacterial network contained more significantly correlated nodes(42 vs 36),the relatively higher proportion of positively correlated links(89.36%vs 87.80%)and higher mean degree(0.47 vs 0.29)and closeness(0.65 vs 0.52)centrality.The contribution rate of soil soluble salt ion components to microbial community structure was higher than that of total salinity,basic soil properties and their interaction effects.Based on the soluble salt ion components,the saline-alkaline soils were clustered into sulfate-type,chloride-type and soda-type saline-alkaline soils.The results of multivariate analysis showed that there were more significant associations between dominant/unique microbial taxa of three types saline-alkaline soils and the soluble salt ion composition.(2)The total of 21 bacterial colonies(ZC1?ZC21)were isolated by the culturable method.They could grow normally under the saline-alkaline stress conditions with 5%salinity and pH 8.5,among that the saline-alkaline adaptation range of ZC1?ZC11 were wider and their tolerance were higher.There were differences in ACC deaminase activity,phosphate-solubilizing ability,IAA secretion,siderophore secretion and EPS production of ZC1?ZC11.The strain ZC1,ZC2,ZC4,ZC5,ZC7,which could promote the germination rate of maize seeds under 5 g·kg-1 NaCl stress,was selected for short-term growth promotion experiment of herbage.The result showed that the biomass of Stipa grandis under 2 g·kg-1 NaCl stress was ZC1>ZC4>ZC5>ZC7>ZC2/CK and the biomass of Leymus chinensis under 5 g·kg-1 NaCl stress was ZC7>ZC2>CK>ZC1>ZC5>ZC4.(3)The pot experiments of single and dual inoculation with haloalkalitolerant PGPR and AM on the growth of Stipa grandis and Leymus chinensis under the slight(total salt content of 2.01 g·kg-1)and medium(total salt content of 4.53 g·kg-1)saline-alkaline soils,respectively.For Stipa grandis,the experimental strains were selected ZC1,ZC4 and F.mosseae.For Leymus chinensis,the experimental strains were selected ZC2,ZC7 and R.intraradices.F.mosseae and R.intraradices established symbiotic relationship with Stipa grandis and Leymus chinensis,respectively,and the average mycorrhizal colonization rate of the dual inoculation was significantly higher than that of the single inoculation.Under the single inoculation with AM fungi,the single inoculation with PGPR and dual inoculation treatments,the biomass of Stipa grandis were increased by 41.28%?80.78%,83.26%?397.65%and 168.14%?610.15%,and the biomass of Leymus chinensis was increased 65.25%?91.35%,114.10?319.10%and 323.09%?486.90%,respectively.Therein,the dual inoculation most significantly promoted herbage growth.The inoculation promoted the accumulation of nutrient elements,reduced Na+absorption,and improved ion balance in herbage,among that the dual inoculation had the most significant effect.The inoculation decreased soil pH and EC,and changed the soil total nutrient and available nutrient contents to varying degrees.(4)The results of?-diversity,composition structure and RDA of rhizosphere soil microbial community showed that the inoculation with haloalkalitolerant PGPR and AM fungi significantly altered?-diversity and structure of rhizosphere bacterial and fungal communities;the difference in rhizosphere microbial community structure of herbage were closely related to PGPR and AM fungi,as well as soil properties(EC,pH,total nutrients and available nutrients);the relative abundance of microbe on the phylum level had the significant difference in the different treatment,and the relative abundances of Actinobacteriota,Chloroflexi and Glomeromycota were the highest in the dual inoculation treatment of herbage.The differential OTUs(DOTUs)volcano map and variation index results showed that the dual inoculation had higher degree of effects on the selective filtering of rhizosphere microbial community compared with single inoculation,among that AM fungi may have stronger effects than PGPR.Compared with the microbial correlation network of CK,the number of nodes,links and modularity index were increased in the inoculation treatments,and the modularity index was the highest in the dual inoculation treatment;moreover,there were obvious differences in the composition of key Hub nodes in the network of different treatments.The results of the interaction network between key microbial taxa and plant factors showed that the inoculation strengthened the significant association between key microbial species and herbage,among that the dual inoculation obviously improved the direct and indirect links between key microbial species and dry weight as well Na+transport coefficient.(5)Compared with CK,the dual inoculation obtained more differential metabolites than single inoculation.The dual inoculation treatment of Stipa grandis contained 167 up-regulated key metabolites and134 down-regulated key metabolites;the dual inoculation treatment of Leymus chinensis contained 199 up-regulated key metabolites and 56down-regulated key metabolites.The up-regulated key metabolites of dual inoculation treatment were mainly included nucleotides and analogues,and lipids and lipid-likes molecules.Their main enrichment pathways involved nucleotide-related metabolic pathways,lipid metabolism-related pathways,beneficial secondary metabolite synthesis-related pathways and signal transduction-related pathways.The down-regulated key metabolites of dual inoculation treatment were mainly included amino acids and derivatives,and organic acids and derivatives.Their main enrichment pathways involved amino acid synthesis and metabolism related-pathways and carbohydrate metabolism related-pathways.(6)Rhizosphere bacterial community,fungal community and rhizosphere soil metabolites had a high degree of consistency,and the interaction contribution rate of bacterial and fungal communities is higher than their individual contribution.The correlation strength(Mantel r value)between DOTUs in the microbiome and DEMs in the metabolome was higher than correlation strength between other OTUs and DEMs,and both DOTUs and other OTUs in the dual inoculation treatment were significantly correlated with DEMs.The inoculation treatment enhanced the correlation between the significantly contributing microbial genera and key metabolites,among that the number of metabolite nodes significantly associated with microorganisms and the modularity index were the highest.The above results suggested that:the dual inoculation of haloalkalitolerant PGPR and AM fungi had stronger effect on the growth of Stipa grandis and Leymus chinensis in saline-alkaline soils.Under the strong mutualistic symbiosis between PGPR and AM fungi,they could not only effectively participate in the regulation process of nutrient absorption and accumulation,ion balance and soil properties,but also realize the beneficial regulation for herbage growth and saline-alkaline tolerance by optimizing the rhizosphere community structure,activating and regulating the more abundant functional expression of microbial taxa to promote secretion of beneficial secondary metabolites,regulating the interaction and communication between the rhizosphere microbial taxa,increasing and optimizing the functional classification of microbial community,promoting the synergy between the functional modules and enhancing the feedback between key microorganism and plants.These results of this study will a provide theoretical basis for further understanding of rhizosphere microbial community synergistically promoting the herbage growth in saline-alkaline soils.It will also provide ideas and references for haloalkalitolerant microorganisms combined with herbage to restore saline-alkaline grassland. |
PDF Full Text Request