Resources Distribution And Salt Tolerance Of Dark Septate Endophytes In Lycium Ruthenicum In Northwest Desert Region

Lycium ruthenicum Murr.is a spiny shrub of Solanaceae that is widely distributed in the arid and semi-arid regions of northwest China.It has drought tolerance,salinity resistance and other characteristics,and is a pioneer tree species for the treatment of soil salinization.Dark septate endophytes(DSE)are a group of small fungi that colonize the roots of healthy plants and form a mycorrhizal symbiosis with plants.It plays an important role in helping host plants to resist adverse environments and promote plant growth.In this study,the root and soil samples of L.ruthenicum in desert areas were collected to study the effects of different environmental factors on the colonization and species composition of DSE,the mechanism of DSE salt tolerance was studied through in vitro salt stress test,and the effects of inoculation of DSE on the growth of L.ruthenicum and their salt tolerance under sterilized soil and natural soil conditions were studied by potted inoculation test.This aim is to explore the resources of DSE strains in desert areas,reveal the mechanism of DSE on L.ruthenicum under salt stress,and provide a theoretical basis for promoting vegetation restoration in salinized areas.The main result shows:1.The root of L.ruthenicum could be infected by DSE,and form typical dark septate hyphae and microsclerotia structures.The distribution of DSE was spatially heterogeneous,with the largest average total DSE colonization rate(60.00%)in the Wuhai,significantly higher than that in the Anxi(25.00%),Minqin(35.00%),Dengkou(23.33%)and Alxa(28.33%).The colonization rate was not significantly different among different soil deep.2.DSE were isolated and identified from the roots of L.ruthenicum in 13 genera and 13species,namely Alternaria tellustris、Neocamarosporium chersinae、Stolonocarpus gigasporus、Cyphellophora olivacea、Preussia terricola、Paraphoma pye、Bartalinia robillardoides、Darksidea epsilon、Exophiala aquamarina、Anthracina saxicola、Gaeumannomyces hyphopodioides、Trematosphaeria sp.、Sordariomycetidae sp..Four of them produced sporulation.P.pye is the dominant strain of L.ruthenicum,which is distributed in Wuhai,Dengkou and Alxa.3.DSE strains were treated with different NaCl concentrations,and the results showed that DSE strains had different salt tolerance.In the PDA solid experiment,the growth rate of the DSE strains except for Cladosporium sp.was lower than that of the control,the color of DSE hyphae deepened,and the space between hyphae became shorter,with the increase of NaCl concentration.The physical and chemical properties of DSE strains under salt stress were measured by MMN liquid culture.It was found that DSE strains could alleviate the adverse effects of salt stress by regulating the antioxidant system.Principal component analysis(PCA)showed that soluble protein,melain and malondialdehyde(MDA)were the main indexes affecting the salt tolerance of DSE fungi.4.In the pot experiment,DSE fungi were successfully colonized in the roots of L.ruthenicum under different soil environments.Soil environment,DSE species and NaCl stress had effects on the growth of L.ruthenicum seedlings.Under sterilized soil conditions,salt stress affected the growth of L.ruthenicum,and significantly reduced plant biomass and root morphology.At 3 g/kg NaCl concentration,inoculation with DSE fungi improved the aboveground morphology,biomass and root growth of plants.At 6 g/kg NaCl concentration,inoculation with Alternaria tellustris and Exserohilum pedicellatum significantly increased the number of leaves,biomass and root growth.Under non-sterilized soil conditions,mild salt stress(3 g/kg NaCl)promoted plant growth,but didn’t reach a significant level compared with the control.With the increase in stress degree,plant growth was significantly inhibited.Under3 g/kg NaCl concentration,inoculation with Cladosporium sp.and E.pedicellatum significantly increased the number of leaves,plant height and biomass.And A.tellustris significantly increased the total root length and root surface area.Inoculation of Cladosporium sp.and E.pedicellatum strains at the concentrations of 6 and 9 g/kg NaCl significantly increased the number of leaves,plant height,aboveground biomass,root volume,root surface area and total root length.5.Under sterilized and non-sterilized soil conditions,inoculation of DSE improve the physiological indexes of L.ruthenicum under NaCl stress.At 3 g/kg NaCl concentration,inoculation with E.pedicellatum increased the content of chlorophyll,proline and soluble protein.Inoculation with A.tellustris and Cladosporium sp.decreased the MDA content.At 6g/kg NaCl concentration,inoculation of E.pedicellatum significantly increased soluble protein and chlorophyll content.Inoculation with Cladosporium sp.and E.pedicellatum increased the content of GSH and IAA,decreased the shoot Na~+content,shoot K~+/Na~+ratio and shoot/root Na~+ratio under the 9 g/kg NaCl concentration.