Effects Of Insect Herbivory On Mycorrhizal Fungi Colonization And Rootassociated Microbial Community In Common Ragweed(Ambrosia Artemisiifolia)

Above-and belowground biota is linked via terrestrial plants.aboveground insect herbivores can affect belowground root-associated microbiome through the cascade of plant roots and root exudates.However,the response mechanism of root-associated microbiome to specific types of insect herbivore remain unclear.Here we use the common ragweed(Ambrosia artemisiifolia),and the chewing(Spodoptera litura)and sucking insect(Aphis sp.)as our system to explore:(1)Arbuscular mycorrhizal fungi(AMF)colonization responses to chewing and sucking herbivory;(2)AMF,bacterial and fungal community responses to chewing and sucking herbivory;(3)The role of plant roots and root exudates.The main results are as follow:(1)AMF colonization and community responses to chewing and sucking herbivory: AMF colonization was increased by 27.1% when exposed to chewing caterpillars,while it was decreased by 9.9% when exposed to sucking aphids.Similar trends were found in the most abundant AMF genus(Glomus)in root endosphere and rhizosphere.The relative abundance of Glomus in AMF community was increased by chewing caterpillars(increased 4.3% in root rhizosphere and 7.4% in endosphere)and it was decreased by sucking herbivores(decreased 16% in root rhizosphere and 6.1% in endosphere).(2)Plant growth and metabolites responses to chewing and sucking herbivory: Plant biomass was decreased by chewing caterpillars while it was unaffected by sucking aphids.Similarly,total flavonoids,total phenolics and soluble sugar in plant leaves and roots were decreased by chewing caterpillars and they were unaffected by sucking aphids.By using GC-MS analysis,we found 22 fatty acids in the ragweed roots,and we found that the contents of 19 fatty acids were increased by chewing caterpillars.(3)Root-associated microbiome responses to chewing and sucking herbivory: The structure of rootassociated bacterial and fungal community was both affected by chewing caterpillars and sucking aphids,while the community diversity was unaffected by the two herbivores.For the bacterial community,herbivory did not affect the rhizosphere while altered the endosphere microbiome: Proteobacteria increased(increased 24.5% and 14.9% by caterpillar and aphid herbivory,respectively)and Firmicutes decreased(decreased 19.7% and 19.8% by caterpillar and aphid herbivory,respectively).For the fungal community,herbivory did not affect the rhizosphere while altered the endosphere microbiome: Ascomycota increased(increased 25.6% and 27.0% by caterpillar and aphid herbivory,respectively)and Glomeromycota decreased(decreased 38.4% and 20.8% by caterpillar and aphid herbivory,respectively).(4)Root exudates role in mediating herbivory effects on AMF and root-associated microbiome:caterpillar herbivory reshaped the root exudate metabolites,addition of herbivore-induced root exudates increased AMF colonization and altered the root-associated microbiome.Non-targeted LC-MS/MS analysis showed that there were significant differences between root exudates of caterpillar herbivory and nonherbivory,and further analysis indicated that the differentially expressed metabolites were mainly included in flavonoid and diterpenoid biosynthesis pathway.AMF colonization increased by 24.3% when added the root exudates after herbivory.The addition of root exudates after herbivory increased the relative abundance of Bacteroidota by 13.4% while deceased Proteobacteria by 14.6% in endosphere,and exudates addition increased the relative abundance of Proteobacteria by 5.2% while deceased Firmicutes by 10.4%in rhizosphere.Further,the addition of root exudates after herbivory increased the relative abundance of Ascomycota by 36.8% while deceased Glomeromycota by 38.1% in rhizosphere,and increased the relative abundance of Ascomycota and by Glomeromycota 5.1% and 7.7%,respectively,and deceased Basidiomycota by 15.1% in endosphere.To conclude,our results indicated that aboveground chewing and sucking herbivory can differentially affect belowground AMF colonization and root-associated microbes in ragweed,and these effects could mediated by root fatty acids and specific metabolites from root exudates.Here we explored the response mechanism of belowground microbiome to aboveground insect herbivory,which would help to understand the ecological linkage between above-and belowground biodiversity.