Mechanisms Of Grazing And Mycorrhizal Fungi Affecting Plant Community Diversity In The Typical Steppe

Arbuscular mycorrhizal fungi(AMF)are soil microorganisms that form symbioses with the majority of plant species,which can colonize about 80%terrestrial plants.A large amount of experimental evidence demonstrated that AMF play a critical role in plant community structure,diversity and productivity in ungrazed grassland.However,the effects of AMF on plant community composition,diversity and productivity under grazing disturbance,to our knowledge,are still unclear.(1)AMF root colonization was significantly suppressed by the application of benomyl as a soil drench.Grazing intensity markedly reduced plant community biomass mainly by decreasing the shoot biomass of Leymus chinensis.However,AMF suppressed biomass of Chenopodium glaucum.Compared with wet year(2015),dry year(2016)weaken the influences of grazing intensity and AMF on plant community composition.Interactions between AMF and grazing intensity altered the shoot phosphorus concentration of Stipa grandis and Cleistogenes squarrosa in 2015 but not in 2016.AMF increased the shoot phosphorus content of Leymus chinesis but decreased that of Chenopodium glaucum along grazing gradient.Our study suggest that grazing intensity,AMF and interannal precipitation fluction affect plant community composition in typical steppe.(2)Fungicide benomyl was applied to suppress AMF abundance.Defoliation increased dominance of Potentilla acaulis over Artemisia frigida and Stipa krylovii,presumably by alleviating light limitation.AMF promoted the shoot biomass of A.frigida but reduced that of S.krylovii growth in non-defoliated plots compared to corresponding AMF suppressed plots.Loss of S.krylovii typically results from overgrazing and contributes to degradation of S.krylovii steppe grasslands.(3)We found that the addition of fungicide Topsin-M effectively decreased mycorrhizal root colonization across all PFG removal treatments.Plant community productivity was significantly altered by both AMF and PFG removal.When C3 grasses were removed,neither C4 grasses nor forbs compensated for the biomass loss,and AMF did not alter their biomass compensation ability.However,C3 grasses could compensate for the removal of both C4 grasses and forbs but AMF reduced their biomass compensation ability.The removal of both C4 grasses and forbs dramatically promoted the shoot phosphorus(P)content of C3 grasses but AMF slightly suppressed this.By contrast,AMF significantly promoted the plant P content of C4 grasses and forbs across all PFG removal treatments.In conclusion,annual precipitation interact with grazing intensity or AMF to alter plant community composition and productivity in the Leymus chinensis Steppe.AMF interact with grazing components(especially defoliation)to change plant community structure,diversity and productivity in the Stipa krylovii Steppe.AMF interact with selective defoliation to influence plant community structure,diversity and productivity in the Stipa krylovii Steppe,and AMF madiated the compensation ability of plant functional group.