Effects Of Re-association Between Ophraella Communa And Ambrosia Artemisiifolia On The Amf Colonization And Its Metabolic Mechanism

Plant invasion is one of the most serious environmental problems in the world.Biological control is an effective way to suppress invasive plants at present.The specialist herbivores may re-associate with their host plants in the introduced ranges,after being accidentally or deliberately introduced(i.e.,classical biological control).Such re-association could rapidly restore invasive plant resistance against specialist herbivores by renewed selection for increasing defensive chemicals.As one of the most important groups of plant symbionts,arbuscular mycorrhiza fungi(AMF)plays an irreplaceable role in the invasion of exotic plants.However,few studies explore the influence of such re-association between invasive plants and specialist insects on root AMF colonization of invasive plants and its related metabolic mechanisms.Understanding this contributes to our comprehensive evaluating the long-term control effects of classical biological control programs.In this study,we examined chemically-mediated AMF colonization evolution in invasive Ambrosia artemisiifolia from six populations with about eighteen years of reassociation by the accidentally introduced native specialist leaf beetle Ophraella communa(infested populations),and six populations without such infestation history(uninfested populations).The main results are as follows.(1)After two years’ field surveys,we found that the colonization rate of AMF was significantly lower in plants from the infested populations(2019: 5.18 ± 0.49%;2020: 4.94 ± 0.47%)than that from the uninfested populations(2019: 17.34 ± 1.50%;2020: 14.61 ± 0.97%).Chemical analysis further showed that content of total tannin and condensed tannin in the plant leaves and roots from infested populations were significantly higher than that from the uninfested populations.In contrast,the content of soluble sugar in plant leaves and roots of infested populations were significantly lower than that of uninfested populations.In addition,the total flavonoid content in the plant roots of uninfested populations was significantly higher than that from infested populations,but no significant difference was found in plant leaves between uninfested and infested populations.(2)In common garden experiments,the colonization rate of AMF in plants from infested populations(6.71 ± 0.66%)was significantly lower than that in plants from uninfested populations(17.73 ±1.19%).In terms of leaf chemicals,the content of tannin and condensed tannin in plants from the infested populations were significantly higher than that from the uninfested populations.Conversely,both of plant leaves and roots from uninfested populations had higher concentrations of soluble sugars such as glucose and fatty acids such as C16:0 than from the infested populations.(3)We also found that the hesperetin contents in the plant roots of the uninfested populations were significantly higher than those of the infested populations.Since the effect of signal substances on AMF was mainly through root exudates,we further investigated the influence of root exudates of A.artemisiifolia in the uninfested and infested populations on AMF colonization and fungus spore germination.Compared with the infested populations,root exudates of A.artemisiifolia plants from the uninfested populations significantly increased the root colonization rate of AMF and germination rate of fungus spores.This indicated that root exudates of A.artemisiifolia plants from the uninfested populations also can explain the higher AMF colonization in the uninfested populations compared with infested populations.In conclusion,the re-association between the O.communa and A.artemisiifolia may drive the enhanced evolution of AMF colonization of A.artemisiifolia via increasing the resource investment to secondary defensive chemicals(tannins)while decreasing the resource investment to primary chemicals(sugars and fatty acids)and signal chemicals(flavonoids).Our findings contribute to our understanding the invasive mechanism of exotic plants and the long-term control effects of classical biological control programs.