Physiological Response Mechanism Of Maize Inoculated With Arbuscular Mycorrhizal Fungi To Heavy Metal Pb Stress

The growth of maize was inhibited by heavy metal lead stress,and the symbiosis of Arbuscular mycorrhizal fungi（AMF）with maize could improve the stress resistance.However,the stress resistance of maize to lead stress and its mechanism were not clear at present.Therefore,greenhouse pot experiment was used to simulate lead-contaminated soil in this study to investigate the differences between maize inoculated with AMF and without AMF,in order to reveal the alleviating effect and mechanism of AMF symbiosis on maize lead stress.The corn variety"Guidan 0810"was selected in the experiment,and this experiment adopted a 4×2 completely random design,including 4 lead concentration levels（0,900,1800,2700 mg/kg）and 2 funny treatments（no AMF and FM:Funneliformis Mosseae,）,and the maize samples were taken at three growth stages（sixth leaves,V6;tasseling stage,VT;milking stage,R3）to determine the agronomic traits,leaf fluorescence characteristics,antioxidant enzyme activity,osmotic regulatory substances and other physiological indicators of maize,and the lead content in plants was detected,the lead transfer factor（TF）and bioconcentration factor（BF）were calculated.The main results are as follows:（1）The root infection rate of maize inoculated with FM reached 40%,and the maximum at the lead concentration of 900 mg/kg reached 77%at tassel stage,which was the highest value among all treatments in the whole growth period.（2）With the increase of lead concentration in soil,the heavy metal lead content in maize leaves and roots increased significantly.With FM inoculation,lead content in upper corn decreased by 7.5～64.8%,lead content in root increased by 68.9～160.7%,BF and TF decreased significantly,indicating that mycorrhizal symbiosis inhibited lead transfer to shoot（P<0.05）.（3）The increase of soil Pb concentration increased the stress of maize,and the plant height,stem diameter,dry weight,fresh weight,effective leaf ratio and leaf area,root morphological indexes decreased significantly（P<0.05）.However,FM inoculation increased plant height by 10.7～153%,stem diameter by 11.4～102.1%,fresh weight and dry weight of maize significantly.The effective leaf number,leaf area and chlorophyll content of maize were also increased after inoculation.The root length,root surface area and root volume increased by 0.65～337.7%,12.5～5.83%,11.9～1193.3%,18.2～568.0%,10.5～470.9%and 7.5-500.4%,respectively.The results showed that inoculation promoted the growth of maize root system,delayed leaf senescence,promoted the absorption of soil nutrients by maize and ensured the normal progress of photosynthesis.（4）Net photosynthetic rate（Pn）,transpiration rate（Tr）and stomatal conductance increased by 15.5～1381.6%,21.0～168.2%and 57.0～190.9%,respectively,and intercellular CO₂ concentration（Ci）decreased by45.8～82.3%,all of which reached significant levels（P<0.05）;Rapid fluorescence induction kinetics curve and related parameters showed that the maximum fluorescence intensity（Fm）,variable fluorescence intensity（Fv）,instantaneous fluorescence intensity at 2ms（F_J）and 30 ms（F_I）of leaves were increased.Energy absorbed per unit area（ABS＿CS）,energy captured by electrons（TR₀＿CS）,energy transferred by electrons（ET₀＿CS）and energy dissipated（DI₀＿CS）all increased to varying degrees,thus improving the utilization efficiency of light energy in maize leaves and promoting the synthesis of organic matter and biomass accumulation.（5）With FM inoculation,SOD activity in maize leaves increased by0.6～12.6%,POD activity increased by 8.8～193.4%,CAT activity increased by4.8 times,SOD activity in maize roots increased by 64.3～252.7%,POD activity increased by 90.9%.CAT activity increased by 2.2～526.2%.Under the action of antioxidant enzyme,O₂^·-content in maize decreased by 2～53.7%,and H₂O₂ also decreased.Meanwhile,MDA content was decreased and proline and soluble protein contents were increased.Reduced glutathione（GSH）increased significantly during milk ripening,while oxidized glutathione（GSSH）decreased.（6）The dry grain weight of maize inoculated with FM was significantly increased by 6～11 times（P<0.05）,the protein content in grain was also higher than NM treatment.In conclusion,maize inoculation with Funneliformis mosseae will alleviate the damage caused by lead stress and ensure the normal growth of maize.