Mechanisms Of Alleviating The Growth Inhibition Of Maize By Aluminum In Acidic Soils By Arbuscular Mycorrhizal Fungi

Aluminum toxicity in acidic soils is an important factor limiting crop growth.Arbuscular mycorrhizal fungi（AMF）can promote plant growth and alleviate the growth inhibition of plants by adverse environment,but little research has been reported on the mechanism of AMF alleviating the growth inhibition of maize（Zea mays L.）at seedling stage by aluminum in acidic soil.In this study,we investigated the potential mechanism of AMF to alleviate the growth inhibition of maize in acidic soil by using a greenhouse pot experiment to reveal the chemical properties of the soil between the roots of maize,the physiological response of the plant and growth changes.The experiment was conducted in a 2×5 completely randomized group design with two maize varieties,Guidan 0810 and Zhengdan 958,which were aluminum-tolerant and aluminum-sensitive,respectively,and five treatments were inoculated with Funneliformis mosseae（FM）,Claroideoglomus etunicatum（CE）,Rhizophagus agunicatum（RA）and,Glomus versiforme（GV）and maize without AMF inoculation（CK）.The plant growth,elemental content,antioxidant enzyme activity,root organic acid secretion,root endogenous hormone content,relative expression of related aluminum transporter protein genes and inter-root soil chemistry were measured by sampling at 60 d（onset of male growth）according to the above treatments.The main findings obtained were as follows.1.A large number of clear vesicles,mycelium and tuft structures could be observed in the root systems of AMF-inoculated maize,and the mycorrhizal infestation rates were all greater than 45%,and good symbiotic relationships could be established between different AMFs and both maize varieties.The mycorrhizal infestation rate of Guidan 0810 inoculated with CE and Zhengdan958 inoculated with FM was higher,reaching 59.30%and 53.60%,respectively.2.Inoculation of AMF optimized the inter-root microecological environment,increased the p H,organic matter,and easily extractable balcomycin-related protein content of maize inter-root soil,reduced the leaching of active aluminum from the soil,and attenuated the biotoxicity of Al³⁺.Also,AMF increased the accumulation of mineral nutrients（N,P,K,Ca and Mg）in maize and reduced the aluminum content of maize plants.3.AMF increased the activities of antioxidant enzymes（CAT,POD,and SOD）in the roots and aboveground of maize plants,decreased H₂O₂,O₂^-.and MDA levels and slowed down the peroxidative stress of ROS on maize.AMF also significantly increased soluble protein content and proline content in the upper ground and roots of maize,enhancing maize osmoregulatory ability;increased the levels of root prohormones IAA,GA₃ and ZR and decreased ABA content in the root system of maize.AMF up-regulated maize root organic acid（malic acid,citric acid,butyric acid and succinic acid）secretion.4.AMF up-regulated the expression of zm MATE1,zm AMLT1,zm Nramp1and zm ZAR8 aluminum tolerance genes in maize roots and aboveground to enhance the molecular response of maize to acidic soil stress.5.AMF improved maize agronomic trait indexes（plant height,stem thickness,leaf area and relative chlorophyll content）,promoted root growth and increased dry matter content of maize roots and above ground.The effects of different aluminum-tolerant varieties with AMF were different,and a comprehensive comparison revealed that FM and CE were more effective than other treatments in Guidan 0810 and Zhengdan 958 maize in activating the inter-root microenvironment,enhancing the physiological response to stress as well as the expression ability of aluminum-tolerant genes,and alleviating the growth inhibition of maize plants by aluminum in acidic soil.