Response Of Medicago Truncatula At Local And Systemic Levels On The Heterogeneity Of Water And Arbuscular Mycorrhizal Fungi

Legume forage not only has high yield,strong adaptability and wide distribution,but also contains rich protein resources.Under the promotion of national“Changing grain to feed”policy,the planting area of legume forage such as alfalfa has been expanding continuously.AM fungi are important components of soil microorganisms,and can form a symbiotic relationship with legumes and rhizobia,which can enhance the uptake of nitrogen,phosphorus and other nutrients by host plants,it plays an important role in strengthening its defence against adversity.The heterogeneity of soil microorganism and water in forage root system affected the yield and quality of forage grass in intercropping and mixed cropping systems.Therefore,in this study,Medicago truncatula,a legume model plant,was used to simulate the heterogeneity of soil moisture and AM fungi,the responses of photosynthetic and fluorescence characteristics of Medicago truncatula to soil moisture and AM fungal heterogeneity were studied by different treatments of water,AM fungi,rhizobia and double inoculation in the left and right root chambers,the mechanism of response of proline,antioxidant enzymes and flavonoids to physiological and non-physiological stresses at local and systemic levels was emphasized to reveal the response process of nutrient accumulation and allocation strategies of Medicago truncatula to soil heterogeneity.Furthermore,it was verified whether double inoculation had synergistic effects in soil moisture and AM fungal heterogeneity.The results of this study will help to understand the responses of legumes to heterogeneous environments and provide theoretical basis for elucidating the conduction mechanism of plant signal molecules in heterogeneous environments.The main results are as follows:（1）Physiological drought stress significantly decreased Pn,Gs and Fv/Fm of Medicago truncatula,and increased MDA and proline contents,SOD and CAT activities in leaves and roots,decreased N and P contents in leaves as well as C,N,P contents in roots.（2）Under physiological drought stress,AM fungi on one side root significantly increased Pn and Gs of Medicago truncatula,maintained high Fv/Fm,and decreased MDA content in leaf and inoculated side root by local regulation,the content of proline and SOD activities,the content of C and N in leaves and lateral roots were increased,and the nutrient deficiency under drought stress was alleviated.Under non-physiological drought stress,one-side root inoculation with AM fungi could increase Pn,Gs and Tr,have higherΦ_PSII,ETR and q P,and increase SOD activity in roots,and the N content in leaves and uninoculated lateral roots was regulated at the systematic level.（3）Inoculation of AM fungi and rhizobia on the same side root system could exert synergistic effects under drought stress.On the one hand,the higher photosynthetic capacity and nutritional status could be maintained by increasing the contents of Pn,Fv/Fm,C and N of Medicago truncatula.On the other hand,the physiological drought resistance of Medicago truncatula was improved by significantly reducing the MDA content,increasing the proline content,SOD,POD and CAT activities of leaves and lateral roots.