| The rapid increase of arid and semi-arid areas has become one of the critical environmental factors affecting the distribution of human beings and plants.DSE can improve the drought resistance of plants and reduce the impact of drought on human activities in production by enhancing the growth index and physiological index of host plants and improving the rhizosphere soil microenvironment.In our study,the mutually beneficial symbiotic relationship between P.sylvestris var.mongolica and DSE was taken as the point,the root system of P.sylvestris var.mongolica was collected in Jiagedaqi District to study the DSE colonization and species diversity.DSE were isolated and preserved,and drought-tolerant strains were screened to explore their drought-tolerant mechanism in vitro.The DSEs were inoculated in annual and biennial seedlings to study the response mechanism of DSE to drought tolerance and verify the reliability of in vitro screening through inoculation experiments which provided the basis for further study on the drought tolerance mechanism of DSE-P.sylvestris var.mongolica.(1)Isolation and Identification of DSE from the roots of P.sylvestris var.mongolica.DSE isolated in the root of P.sylvestris var.mongolica identified a total of 15 species of DSE belonging to 12 genera,which belonged to Ascomyces.The dominant species were P.fortinii and the separation frequency was 26.42%.(2)Screening and pathogenicity determination of drought-resistant DSE.The colony diameter and biomass of strain A065 were significantly higher than the other strains under high PEG concentration stress.The inoculated plants did not show any disease symptoms.The MDA content increased significantly and the melanin content in mycelium decreased rapidly during the increase in drought stress.The activity of SOD in strains J09 and J32 reached a peak at a PEG concentration of 6%,increased by 349.62% and 28.75%,respectively,compared with the control and the A065 increased by 43.88% under PEG concentration of 30%,compared with the control.The GSH content of J09 increased first and then decreased,reaching a peak at a PEG concentration of 6%,rising by 126.61%,while the content of malondialdehyde of J32 and A065 continued to increase and reached the maximum value,rising by 6.73 and 7.05 times,compared with the control,respectively,when the concentration of PEG was 18% and 30%.The content of soluble protein of J09,J32,and A065 has reached the maximum value,increased by 1.36,0.62,and 8.34 times,when the concentration of PEG was 18%.(3)The effects of different DSE strains on drought tolerance of annual seedlings of P.sylvestris var.mongolica were determined by indoor weighing and water supplement methods.With the strength of drought,the diameter of hyphae became thicker,the septum became shorter,and the number of microsclerotia increased.The inoculation of the DSE increased the plant height,root length,ground diameter,fresh weight of the aboveground part,fresh weight of the underground part,dry weight of the aboveground part,and dry weight of the underground part of P.sylvestris var.mongolica by 22.88%,46.77%,23.64%,36.70%,83.58%,20.01% and 31.02% under drought stress compared with CK;The inoculation of the DSE increased the CAT,POD,SOD,and GSH activities of the plant by 101.41%,30.87%,119.91%,and 178.62%,respectively under drought stress;The inoculation of the DSE decreased the content of MDA,PSS,and PRO of the seeding of P.sylvestris var.mongolica by 68.10%,173.50%,and 82.42%,respectively;DSE increased the content of the soil OM,TN,AN,TP,AP,TK,and AK by 64.56%,106.01%,88.34%,112.42%,157.50%,30.21%,and 65.99%,respectively;DSE also increased the S-CAT,S-SC,and S-UE activities by 341.73%,105.29%,and 360.31%,respectively.Two-way ANOVA results indicated that the interaction between DSE and drought stress significantly affected the growth and physiological indexes of the plants,enzyme activities,and physicochemical properties of rhizosphere soil(P <0.05).(4)The effects of different DSE strains on drought tolerance of the biennial of P.sylvestris var.mongolica were measured by outdoor weighing and water supplement methods.With the strength of drought,the diameter of hyphae became thicker,the septum became shorter,and the number of microsclerotia increased.The inoculation of the DSE increased the ground diameter,fresh weight of the aboveground part,fresh weight of the underground part,dry weight of the aboveground part,dry weight of the underground part of P.sylvestris var.mongolica by 67.72%,36.13%,41.58%,36.13%,and 41.48% under MW treatment compared with CK;The inoculation of the DSE increased the CAT,POD,SOD,and GSH activities of the plant by 229.60%、67.80%、28.16%,and 37.83%,respectively under drought stress;The inoculation of the DSE decreased the content of MDA,PSS,and PRO of the seeding of P.sylvestris var.mongolica by 74.16%,105.91%,and 51.24%,respectively;DSE increased the content of the soil OM,TN,AN,TP,AP,TK,and AK by 19.85%,40.64%,35.25%,57.92%、48.11%,55.62%,and 68.84%,respectively;DSE also increased the S-CAT,S-SC,and S-UE activities by 71.85%,128.64%,and 65.05%,respectively.Specifically,the inoculation of J09 and A065 significantly increased the growth index of seedlings,the physiological index of seedlings,the physical and chemical properties of rhizosphere soil,and the enzyme activity of rhizosphere soil under drought stress.However,the inoculation of J35 significantly inhibited the growth and physiological indexes of P.sylvestris var.mongolica seedlings.In conclusion,J09 and A065 were found to have the strongest drought resistance through in vitro screening combined with indoor and outdoor inoculation trials.The results of the PEG simulation of the in vitro drought stress experiments are the same as the inoculation experiments.Therefore,the in vitro screening experiments are reliable and can be used in the early stages of screening for the determination of the target DSE.The change of DSE colonization morphology may be one of the mechanisms to improve the drought tolerance of host plants,and the type of DSE colonization significantly affects the drought tolerance of host plants.In this study,J09 and A065 have the potential to be applied to improve the growth of P.sylvestris var.mongolica in arid and semi-arid regions by improving seedling growth indicators,physiological indicators,physicochemical properties of rhizosphere soil,and enzyme activities of rhizosphere soil to improve drought resistance. |
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