| The aboveground belowground ecosysetem can influence each other and they are linked tightly via terrestrial plants.The aboveground part of plants has long been suffering from the feeding of herbivores,while the belowground part of most vascular plants can develop a symbiotic relationship with arbuscular mycorrhizal fungi(AMF).Insect herbivory can affect AMF development and colonization through plant growth or defense.However,there are no consistent results of the researches on the impact of aboveground herbivores on AMF and the mechanisms involved are not well-studied.We hypothesized that insect herbivory affects AMF colonization by modulating root exudate compositions.Here,we use Triadica sebifera as the target plant to investigate the effects of aboveground insect herbivory on belowground AMF mutualists and the underlying mechanism.The experiments were conducted in treatments with various insects,feeding intensities,plant harvest time after herbivore feeding,plant development period to explain the inconsistent influences of herbivore feeding on AMF.And the mechanism of how herbivore feeding affects root exudates was investigated by collecting and analyzing root exudates after feeding.Then we tried to clarify how herbivore feeding affects signal pathways of AMF by sparying jasmonic acid(JA)and salicylic acid(SA).The main findings are as follow:(1)AMF colonization responses to aboveground insect herbivory: The AMF colonization increased by light herbivory(range from 29.37% to 92.59%),but reduced by moderate and heavy herbivory(range from 33.95% to 50.79%).The harvest time after feeding also had a significant influence on AMF.With the harvest time extension,the AMF colonization rates of light and moderate herbivory gradually recovered and no significant differences compared to that of control treatment.But the AMF colonization rates of heavy herbivory failed to recover.(2)Plant growth and defense response to aboveground insect herbivory: Insect herbivory reduced both aboveground and belowground biomass,but not root carbon concentration.The results showed that the leaf and root flavonoid contents were increased by light herbivory in general.The leaf flavonoid content was increased by moderate and heavy herbivory,whereas the root flavonoid content was reduced.The leaf and root tannin contents were increased by insect herbivory regardless of the herbivory intensity.The leaf phenolic content was increased by insect herbivory but the root phenolic content was decreased.(3)Root exudates response to aboveground insect herbivory: The total carbon,total inorganic carbon and total carbon organic carbon contents in root exudates were not affected by Spodoptera litura and S.frugiperda herbivory with various feeding intensities,but significantly decreased by Cnidocampa flavescens herbivory and significantly increased by Bikasha collaris herbivory with light herbivory.The quercetrin root exudates were significantly increased by S.litura and S.frugiperda with light herbivory,significantly decreased with heavy herbivory,while slightly decrease with moderate herbivory.The root exudates induced by S.litura and S.frugiperda herbivory and the flavonoid quercetrin can regulate AMF spore germination.(4)AMF colonization and root exudate metabolites response to foliar application of jasmonic acid(simplified as JA)and salicylic acid(simplified as SA): The AMF colonization,carbon root exudates,and flavonoid root exudates were not affected by shoot application of JA and SA with different concentrations,suggesting no effect of JA and SA on the response of AMF colonization to herbivore feeding.In this thesis,the impact of aboveground herbivore feeding on AMF mutualism and root exudates and the mechanisms involved were investigated by assessing the changes in plant growth,the root exudates responses and AMF colonization.The results indicated that the responses of AMF to insect herbivory were affected by various factors,and these effects may be driven by altered secondary metabolites in plant and root exudates induced by herbivory. |
PDF Full Text Request