| Drunken horse grass(Achnatherum inebrians,DHG)is a perennial grass species which forms symbiotic associations with Epichlo? gansuensis in aboveground organs that render herbage toxic,and simultaneously with belowground root-associated microbes.This study explored the growth,photosynthetic parameters,root-associated fungi and root exudates of endophyte-infected(EI)and endophyte-free(EF)DHG plants,interactions between the presence of an E.gansuensis endophyte and inoculation of arbuscular mycorrhizal(AM)fungi,and the multiple relationships between them.The research comprised laboratory and greenhouse experiments and a three-year field experiment and employed both traditional research techniques and molecular biotechnologies.The main results are as follows:1.Compared with plants grown at a gravimetric soil moisture content of 15%,the shoot and root biomass and net photosynthetic rate of DHG plants were significantly increased with increase in soil moisture(P<0.05).Also,shoot and root biomass and net photosynthetic efficiency of EI plants were significantly higher than in EF plants(P<0.05).When grown DHG plants were grown at 15% soil moisture,the expression levels of lhc B1,lhc B2,psb B,psb C and pet H genes were increased compared to those in DHG plants grown at 30% soil moisture.Also,in the 15% soil moisture treatment the expression levels of lhc B,psb B,psb S,pet J and psa E genes in EI plants were increased compared to those in EF plants.2.Typically,whether plants were of wild EI,cultivated EI or cultivated EF status,the most dominant fungal phylum in roots,AM fungal genus in rhizosphere soil,and non-AM fungal genus isolated from the plant roots were Ascomycota,Glomus and Fusarium,respectively.The rhizosphere AM fungal spore density and fungal diversity in roots of wild EI DHG plants were significantly higher than those of cultivated EI DHG plants(P<0.05).Compared to cultivated EF DHG plants,the mycorrhizal colonization and AM fungal spore density in the rhizosphere of cultivated EI plants were significantly increased(P<0.05),while the fungal diversity and richness were significantly decreased(P<0.05).3.The diversity and richness of AM and non-AM fungi isolated from the rhizosphere soil were significantly higher than those isolated from roots(P<0.05).The number of fungal species isolated from roots was significantly decreased with increase in soil moisture,while conversely the number isolated from the rhizosphere was increased(P<0.05).The effects of Epichlo? endophyte on the AM fungal diversity in roots were positive,neutral and negative under drought,normal and water addition treatments,respectively.Rhizosphere soil available phosphorus was a key determinant of the fungal community species composition in roots and rhizospheres(P<0.05).Epichlo? endophyte or AM fungi had significant effects on the shoot biomass of A.inebrians plants(P<0.05).Both Epichlo? endophyte and AM fungi did not significantly increased the shoot biomass of DHG plants(P>0.05).4.The growth parameters,net photosynthetic efficiency,shoot and root biomass and nitrogen and phosphorus nutrient contents of EI DHG plants were significantly higher than those of EF DHG plants(P<0.05).The composition of root exudates and the concentrations of particular metabolites both differed significantly between EI and EF DHG plants(P<0.05).Compared to the EF DHG plants,there were 11 significantly up-regulated metabolites,and 10 significantly down-regulated metabolites in the root exudates of EI DHG plants(P<0.05).The fungal diversity and richness indices of bulk soil were significantly lower than those of rhizosphere soil(P<0.05),but were significantly higher than those of roots(P<0.05).Both the up-and down-regulated metabolites significantly decreased the fungal richness in roots(P<0.05).However,the fungal species richness in roots was significantly and negatively related to the biomass and net photosynthetic efficiency of DHG plants(P<0.05).Collectively,the findings indicate that the presence of an Epichlo? endophyte enhanced the growth and biomass accumulation of DHG plants through decreasing the fungal diversity in roots and altering the fungal composition in roots,via modification of the composition of root exudates. |
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