| Nowadays,the deteriorating agricultural ecological environment poses great challenges to the development of medicinal plants.The symbiotic microorganisms attracted more attention.Dark septate endophytes(DSE)are diverse facultative biotrophic ascomycetes that ubiquitously colonise plant roots and may facilitate plant growth and productivity and improve stress tolerance of host plant.In this study,the relationship between medicinal plants and DSE fungi was taken as the entry point.The ecological distribution and species diversity of DSE fungi in the roots of 25 medicinal plants were systematically studied to clarify the effects of plant species,and environmental factors on the DSE distribution and DSE species.Furthermore,DSE fungi were inoculated to Astragalus membranaceus and Dendranthema morifolium.The performance of DSE fungi and host plants inoculated with DSE species under Cd stress were assessed to explore the mechanism of Cd tolerance and the interaction mechanism between DSE and plants.The research results were not only beneficial to our understanding of the biological function of DSE improve but also to obtain more beneficial DSE resources.It will also lay the foundation for improving the yield and quality of medicinal plants in farmland systems in North China.The main results showed as follows:1.Typical DSE colonisation structures were observed in the roots of all 25 medicinal plants.The structure of DSE hyphal and microsclerotia in different plants was significantly different.DSE colonisation was ranged from 2.22 % to 100.00 % and the differences among plants species were significant.DSE colonisation were significantly higher(P < 0.05)for Dendranthema morifolium,Atractylodes lancea,Taraxacum mongolicum,Lonicera japonica,Astragalus membranaceus,Scutellaria chinese,and Stemona japonica than they were for the other plant species.2.The distribution of DSE showed obvious host plant preference.Variation partitioning analysis showed that host plant species significantly affected DSE colonization.Plant species purely explained 80.8 %,74.0 %,and 79.0 % of the variation in the rates of DSE hyphal,microsclerotial,and total colonisation,respectively.The influence of soil factors depended primarily on plant species.Correlation analysis showed that DSE colonization was significantly and positively correlated with soil organic carbon,urease and phosphatase activities.3.DSE isolates in the roots of medicinal plants were identified to 12 genera and 14 species.Alternaria doliconidium 、 Acrocalymma aquatica 、 Paraphoma radicina and Paraboeremia selaginellae were the dominant DSE species in the samples of medicinal plants.Acrocalymma aquatica、Alternaria doliconidium、Paraboeremia selaginellae、Endophoma elongata、Parapyrenochaeta sp.and Oididendron sp.were reported here in medicinal plants for the first time.4.DSE fungal community composition showed significant differences among different plant species and family levels,and was correlated with soil factors.In terms of DSE species composition,plant species explained 26.1 % of the variation and soil factors explained only10.6 % of the variation.The following plant species had the highest isolation frequencies:Ophiopogon japonicas(15.79 %),Scutellaria barbata(9.65 %),Lonicera japonica(9.45 %),Dendranthema morifolium(8.77 %),Rosa banksiae(8.77 %),and Isatis indigotica(8.77 %).5.Under sterilization condition,three DSE fungi isolated from medicinal plants can be successfully inoculated with the roots of A.membranaceus and D.morifolium.DSE colonization rate increased gradually with the increase of Cd stress.Inoculation with DSE-7and DSE-15 significantly improved the the root biomass and root volume of A.membranaceus under Cd stress.Inoculation with DSE fungi promoted the IAA content.Under10 mg/kg Cd concentration,inoculation with DSE-7 significantly increased chlorophyl content of A.membranaceus with 51.9 %,and inoculation with DSE-15 and DSE-20 significantly promoted SOD content of A.membranaceus.Under 1 mg/kg Cd concentration,inoculation with DSE significantly increased plant height of D.morifolium.Under 5 mg/kg Cd concentration,inoculation with DSE-15 significantly promoted plant height,root volume,biomass,IAA content and SOD content of D.morifolium.Under 10 mg/kg Cd concentration,inoculation with DSE-20 significantly promoted SOD content,and inoculation with DSE-15 increased chlorophyl content of D.morifolium with 40.4 %.6.DSE fungi significantly improved the biomass of A.membranaceus and D.morifolium under Cd stress.Under 0 mg/kg and 1 mg/kg Cd concentration,inoculation with DSE-15 increased root biomass of A.membranaceus with 34.8 % and 36.5 %.Under 5 mg/kg and 10mg/kg Cd concentration,inoculation with DSE-7 promoted root biomass of A.membranaceus with 32.0 % and 39.8 %.For D.morifolium,under 1 mg/kg Cd concentration,inoculation with DSE-7 and DSE-15 increased biomass of A.membranaceus flowers with 44.8 % and43.2 %.Under 5 mg/kg Cd concentration,inoculation with DSE-7 and DSE-15 increased biomass of A.membranaceus flowers with 29.5 % 和 27.8 %.Under 10 mg/kg Cd concentration,inoculation with DSE-15 increased biomass of A.membranaceus flowers with34.8 %.In addition,with the increase of Cd concentration,the biomass of A.membranaceus and D.morifolium showed a trend of decreasing.7.Under different Cd concentration(0,1,5,10 mg/kg),inoculation with DSE-20 significantly increased calycosin-7-O-β-D-glucoside of A.membranaceus with 31.7 %,29.8 %,32.2 % and 39.9 %.Under 0 mg/kg and 1 mg/kg Cd concentration,inoculation with DSE-15 significantly promoted formononetin content of A.membranaceus with 26.3 % and49.6 %.Under 10 mg/kg Cd concentration,inoculation with DSE-7 significantly promoted formononetin content of A.membranaceus with 28.4 %.For D.morifolium,under 0 mg/kg and 5 mg/kg Cd concentration,inoculation with DSE-15 increased chlorogenic acid content of D.morifolium with 45.2 % and 26.4 %.8.Under Cd stress,inoculation with DSE-7 and DSE-15 lead to the increase of Cd accumulation in root of A.membranaceu.Inoculation with DSE-20 had no significant effect on Cd accumulation of A.membranaceu.For D.morifolium,inoculation with DSE-15 lead to the increase of Cd accumulation in flowers of D.morifolium,while inoculation with DSE-7the Cd content of flowers has no significant effect.9.Variation partitioning analysis showed that DSE species,Cd concentration and soil factors explained 16.6 %,36.6 % and 6.8 % of the growth indexes of A.membranaceus respectively.DSE species,Cd concentration and soil factors explained 21.4 %,27.2% and10.8 % of physiological indexes of A.membranaceus,respectively.For D.morifolium,DSE species,Cd concentration and soil factors explained 8.6 %,12.6 % and 6.6 % of the growth indexes of D.morifolium.DSE species and Cd concentration explained the physiological indexes of D.morifolium respectively 12.7 % and 16.2 %.Therefore,different DSE species and Cd concentrations were major factors affecting growth of A.membranaceus and D.morifolium. |
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