Species Diversity And Salt Tolerance Of Dark Septate Endophytes In Three Desert Plants

Soil Salinization in desert is an important factor restricting the growth of plant and causing soil degradation.It is imperative to promote the restoration of vegetation and ecosystem in desert areas.Plant-microorganism combined bioremediation has been proven to be an economical and effective bioremediation approach.Dark Septate Endophytes(DSE)are a group of ascomycetes that grow on the root tissues of plant,which can improve the nutritional status of the host plant and the tolerance of host plant to stress.Psammochloa villosa,Artemisia ordosica and Hedysarum laeve are typical pioneer plants in the Mu Us sandland Land and are often used for desert vegetation restoration.In this study,the symbiotic relationship between desert plant and DSE fungi was taken as the entry point.The ecological distribution and species diversity of DSE fungi in the roots of three desert plants were systematically studied to clarify the effects of plant species,soil depth and environmental factors on the distribution of DSE fungi.Furthermore,we assessed the performance of DSE fungi and host plants inoculated with DSE species under different salt stress to explore the mechanism of DSE to salt tolerance and DSE improving plant salt tolerance.The research results can improve the understanding of the interaction mechanism of different plant-DSE in the desert environment and the mechanism of the symbiosis adapting to physiological drought caused by salt stress.Moreover,we hope to obtain more beneficial DSE fungal resources and explore the ecological functions of the DSE fungi in the desert environment,thus providing a theoretical basis for making full use of DSE fungi in vegetative restoration in arid ecosystem.The main results showed as follows:1.The root of P.villosa,A.ordosica and H.laeve can be infected by DSE fungi,and the predominant structure was Hyphae.There were significant differences in the colonization structure of DSE in different plants,and the average total colonization rates of P.villosa,A.ordosica and H.laeve were 79.66%,82.35%,and 70.45%,respectively.The maximum average colonization rate of P.villosa and H.laeve appeared in the 10-20 cm soil layer,while the maximum average colonization rate of A.ordosica was in 30-40 cm soil layer.The highest DSE colonization rates of the three plants occurred in 2016.2.Two-way analysis of variance(ANOVA)revealed that plant species and soil depth significantly affected the distribution of DSE.Plant species explained 47%of the variation in DSE distribution variation as the most important influencing factor.Correlation analysis showed that the colonization rate of DSE mycelium was significantly positively correlated with TN,and significantly negatively correlated with the C:N ratio.The colonization rate of microsclerotia was significantly positively correlated with SOC.The total colonization rate was significantly positively correlated with TN and TP,and significantly negatively correlated with C:N ratio.3.DSE isolates in the roots of three hosts were identified to 13 genera and 17 species,namely Leptosphaeria sp.?Phoma radicina?Paraphoma chrysanthemicola?Bipolaris zeae?Humicola sp.?Fusarium tricinctum?Alternaria chlamydosporigena?Darksidea delta?Phialophora mustea?Alternaria alternata?Bipolaris sorokiniana?Curvularia spicifera?Periconia macrospinosa?Paraphoma radicina?Paraphoma pye?Setophoma terrestris?Microdochium bolleyi.Five of them produce spores.Phoma radicina and Bipolaris zeae were reported here in desert ecosystems for the first time.4.The DSE fungal community composition presents the preference to host plants snd soil depths.The total isolation rate of DSE fungi among three plants was P.villosa(18.7%)>H.laeve(14.3%)>A.ordosica(12.2%).The isolation rate of DSE was significantly higher in shallow soil(0-30 cm)than in deep soil(30-50 cm).P.chrysanthemicola was the dominant species of P.villosa and A.ordosica,while Paraphoma radicina was the dominant species of H.laeve.Phoma radicina is commongenus of P.villosa and H.laeve.B.zeae is a unique species in H.laeve.P.macrospinosa is a unique species in A.ordosica.P.pye and M.bolleyi are the unique species in P.villosa.5.The DSE community and diversity index were significantly related to plant species,soil depths,and soil factors.Canonical correspondence analysis(CCA)indicated that M.bolleyi,A.alternata,Leptosphaeria sp.and A.chlamydosporigena were positively correlated with soil organic carbon(SOC),total nitrogen(TN)and total phosphorus(TP).C.spicifera was positively correlated with pH.S.terrestris and F.tricinctum were positively affected by urease(U)activity.Acid phosphatase(ACP)and alkaline phosphatase(ALP)positively affected Humicola sp.,B.sorokiniana,and P.mustea,but negatively affected the frequency of D.delta.6.DSE fungi isolated from desert plants exhibited higher tolerance to salt stress in vitro in which improved the Superoxide dismutase(SOD)activity,glutathione(GSH),soluble protein,polysaccharide and melanin content played effective roles.With the increase of NaCl concentration,the color of colonies gradually deepened,the DSE hyphal septa became shorter,the number of conidia decreased,and formed thick spore-like structure.7.Five DSE fungi isolated from desert plants can be successfully inoculated with the roots of A.ordosica.Inoculation with DSE fungi improved the growth and biomass accumulation of A.ordosica under salt stress,alleviating the adverse effects of NaCl stress.However,these effects decreased with the increase of NaCl concentration,which was related to DSE species and NaCl treatments.Under 0.1%NaCl concentration,inoculation with A.chlamydosporigena significantly increased root growth and biomass.Inoculation with P.radicina increased above-ground biomass,and inoculation with P.chrysanthemicola promoted root growth and underground biomass accumulation in A.ordosica.Under 0.2%NaCl concentration,only A.chlamydosporigena inoculation increased the plant height.Under0.3%NaCl concentration,inoculation with C.spicifera,P.chrysanthemicola and P.radicina significantly increased the root biomass of A.ordosica;C.spicifera and P.chrysanthemicola only significantly promoted the root growth,while inoculation with A.chlamydosporigena was conducive to plant height growth.8.Under NaCl stress,inoculation with DSE fungi can significantly impact the activity of SOD and contents of GSH,soluble protein,auxin,chlorophyll,Na~+and K~+.Most DSE fungi significantly enhanced SOD activity at 0.1%and 0.2%NaCl concentrations.However,under0.3%NaCl concentrations,only P.radicina and B.sorokiniana were presented significantly higher SOD activity.GSH content significantly increaseed in conditions of A.chlamydosporigena(0.2%,0.3%),P.chrysanthemicola(0.1%),P.radicina(0.2%),C.spicifera(0.2%),and B.sorokiniana(0.1%,0.2%,0.3%).P.radicina significantly increased the content of soluble proteins under NaCl stress treatments,while C.spicifera and B.sorokiniana did at 0.1%and 0.3%NaCl concentrations,respectively.P.chrysanthemicola,P.radicina and B.sorokiniana significantly increased the amount of auxin in NaCl stress conditions,and P.chrysanthemicola significantly increased chlorophyll content only at concentrations of 0.3%NaCl.With the increase of NaCl concentration,the Na~+content of the shoots of A.ordosica showed an increasing trend.Inoculation with DSE fungi reduced Na~+,K~+content and Na~+/K~+ratio of roots at most NaCl concentrations.9.Inoculation of DSE affected soil nutrient status and enzyme activity,and promote nutrient absorption of host plants.Some of these DSE inoculations significantly reduced the contents of SOC,available phosphorus,as well as the activity of urase,acid phosphatase and alkaline phosphatase.