| Safflower(Carthamus tinctorious L.)is a comprehensive economic crop that is commercially cultivated for herbs,dyes,oils,and feeds.However,the main planting area in Xinjiang for safflower is poor with heavy salinity and degraded arable land,which restricts the quality and yield of safflower.Rhizosphere microorganisms can improve soil microenvironment and are important for promoting plant growth and development.Based on the rhizosphere soil environment of Safflower,the present study isolated rhizosphere phosphate-dissolving bacteria and explored the promoting effect of phosphate-dissolving bacteria.The composition,function and interaction of rhizosphere microflora were then explored to construct functional phosphorus.The microbial agent provides new resources and lays a foundation for improving the utilization of phosphorus in the safflower farmland in Xinjiang.The main results are as follows.(1)The safflower growth process has a large demand for soil nutrients.The contents of organic matter,available phosphorus,available potassium,available nitrogen and trace elements in the rhizosphere soil of Safflower were decreased during safflower growth.Soil nutrients should be supplemented in suitable time.Although the number of rhizosphere phosphorus bacteria is positively correlated with the growth of safflower,the rhizosphere phosphorus bacteria has limited ability to supplement soil nutrients,and it is urgent to develop high-efficiency phosphate-dissolving bacteria to improve the nutrient supply of safflower growth.The screening of the phosphate-dissolving bacteria in the rhizosphere of safflower should be combined with the physical and chemical properties of the soil,the types of phosphorus-dissolving microorganisms and the growth indicators of safflower.(2)Six strains of phosphorus-dissolving bacteria were isolated from the rhizosphere soil of Xinjiang safflower,belonging to Pseudomonas sp.,Sinorhizobium sp.,Staphylococcus sp.,Acinetobacter sp.,Enterobacter sp.The solution of phosphorus was between 116.1 and 198.3 mg/L,and the strain Acinetobacter sp.RC04 had the best solution.In addition,the isolated rhizobium strain Sinorhizobium sp.RC02 also had a good phosphate-dissolving effect(187.8 mg/L),and the gene co-expression network analysis showed that the batceria of this genus contained a gene group related to the phosphate-dissolving function.Therefore,Acinetobacter sp.RC04 and Sinorhizobium sp.RC02 are ideal bacterial sources,which have the dual potentials of phosphorus and nitrogen fixation,which can lay a foundation for the application of various bacterial combinations in the later stage.(3)In order to investigate the root colonization effect of phosphate-dissolving bacteria,the gentamicin was used to mutagenize Sinorhizobium sp.RC02 and Acinetobacter sp.RC04 to obtain resistant mutant strains RC02+and RC04+with resistance of 700 μg/mL and 800μg/mL.The number of colonizations of the two strains reached the peak at 20 d after inoculation,then gradually decreased,and then stabilized after 60 d.The amount of bacteria in the unsterilized soil was higher than that in the sterilized soil.The dynamics of colonization showed that inoculation of the phosphate-dissolving agent once every 30 days can effectively maintain a high number of colonizations,thereby exerting a long-term and stable effect on phosphorus solubilization and growth promotion.(4)The bacterial combination of Acinetobacter sp.RC04 and Sinorhizobium sp.RC02 showed promoting effect on seed germination and growth of safflower.Mixed microbial agents can increase leaf chlorophyll content and soluble protein content,reduce malondialdehyde content,and show better nutrient solubilizing ability and ability to resist low phosphorus.In the rosette stage,elongation stage,full bloom stage and maturity stage,the mixed microbial agents significantly increased the plant height,root length and root dry weight of safflower.(5)In order to explore the microecological characteristics of safflower roots,16S rRNA gene amplicon sequencing was used to compare the bacterial community structure differences between clay and sand soil and between rhizosphere and non-rhizosphere.The results showed that the separated phosphate-dissolving bacteria could represent the main phosphate-dissolving bacteria in the rhizosphere of safflower.The Shannon-Wiener index shows that the species composition of the rhizosphere bacteria is lower than that of the non-rhizosphere species,and the degree of uniformity is low.The beta codiversity index(principal co-ordinates analysis)shows significant difference between rhizosphere and non-rhizosphere.Between rhizosphere and non-rhizosphere,Pseudomonas,Sinorhizobium,Bacillus and other phosphate-dissolving bacteria are significantly higher in the rhizosphere than in the non-rhizosphere.The OTU network analysis showed that the rhizosphere is rich in bacterial aggregates with phosphorus-dissolving action.Among them,Acinetobacter,Azotobacter,Bacillus,Bradyrhizobium,Pseudomonas,Sinorhizobium and other OTU hubs constitutes the core flora,while other non-hub OTUs become auxiliary bacteria,forming a synergistic flora of multi-level systems,which helps to collaboratively complete the process of dissolving phosphorus.(6)Phosphate-dissolving bacteria can increase the number of phosphorus bacteria in the cultivated soil of safflower root and improve the structure of the flora.It shows that the organophosphate bacteria are more than the inorganic phosphorus bacteria,and the rhizosphere phosphorus bacteria are more than the non-rhizosphere phosphorus bacteria.The rhizosphere effect(R/S)of phosphate-dissolving bacteria was between 11 and 24.The highest R/S values of organic and inorganic phosphorus bacteria in the flowering stage were 23.97 and 24.10,respectively,showing obvious rhizosphere effects,indicating phosphorus-dissolving microorganisms.There is a synergy with other microorganisms.In summary,to excavate excellent phosphorus-dissolving microorganisms in the rhizosphere soil of safflower is beneficial to improve the rhizosphere microenvironment and promote the growth and development of safflower,which is of great significance for improving regional productivity.The present study isolated phosphate-dissolving bacteria in the rhizosphere of Xinjiang safflower and studied the interactions between safflower,rhizosphere bacterial community and soil.Furthermore,using those phosphate-dissolving bacteria,we improved rhizosphere flora structure,soil physical-chemical properties and the growth and development of safflower.Finally,the present study may lay the foundation for improving the utilization of phosphorus in the safflower farmland in Xinjiang. |
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