Physiological Response Of M.azedarach To Cd And Acid Rain Stress

A pot experiment was conducted to study the effects of physiological and biochemical characteristics and the accumulation of Cd on annual M. azedarach seedlings(Melia azedarach Linn.), which were composite stressed by the Cd (0,30,60,90,120,150,120 mg/kg) and the simulated acid rain (pH 5.6,4.5,3.5). This study provided basis for elucidate the heavy metal Cd and acid rain on plant poison mechanism, and provided the reference for the native deciduous trees to control and remediate heavy metal polluted soil in acid rain area. The main test results are as follows:(1) It was positively related that the absorption of roots and stems of M. azedarach with the content of Cd in soil. The content of Cd in roots was more than that in stems. And the acid rain stress would prevent the M. azedarach enrichment of Cd.(2) The height and biomass of M. azedarachwere promoted by low concentration and inhibited by high concentration, when stressed by Cd and acid rain(pH5.6、pH4.5). But both of them were inhibited gradually when stressed by Cd and acid rain(pH3.5). The reason was that under thecomposite stress of low concentration of Cd(≤60mg/kg)and the moderate acid rain(pH≥4.5),M. azedarach had protective reaction to stress.The content of osmotic adjustment matters such as oluble sugar, soluble protein and prolineincreased, which can improve the osmotic potential of cells, maintain normal metabolism of cells. The activity of antioxidant enzymes like SOD, CAT, APX, DHAR and GRenhanced, and the antioxidantcontent of ASA and GSH increased, which can resist ROS (reactive oxygen species) gradually.But it’s self-protection ability was limited, plant carbon metabolism and nitrogen metabolism was inhibitedwith the Cd concentration increased and pH decreased, which blockedsynthesis of osmotic regulation substances.The large increase of the reactive oxygen in plants breaked the balance between the reactive oxygen and antioxidant system in M. azedarach, which caused badly increase of lipid peroxidation, the destruction of the membrane system, the hindering of the normal function of cells, and the inhibition of growth.(3) Whentreating for 20d and 40d, and Cd2+ concentration≤90mg/kg and pH≥3.5, or treatingfor 60d and Cd2+ concentration≤60mg/kg and pH≥4.5, the activities of SOD, CAT, POD of M. azedarach increased greatlyto remove reactive oxygen andrev up the ASA-GSH cycle to clear ROS free radical mechanism, by these two ways, the active oxygen in production and removal of dynamic balance could been maintained, which can protect M. Azedarachfromoxidative damage. When treating for 20d and Cd2+concentration at 90mg/kg～120mg/kg and pH≥3.5, or treating for 40d and Cd2+concentration at 90mg/kg～120mg/kg and pH≥4.5, or treating for 60d and Cd2+concentration at 60mg/kg～90mg/kg and pH≥4.5, the CAT, POD and ASA-GSH cycle played imortant role to clear ROS free radical mechanismas and resist oxidative damage caused by Cd stress, and the oxidative damage was not serious. When treating for 20d and 40d, and Cd2+ concentration at 150mg/kg～180mg/kg and pH≥ 3.5, or treating for 60d and Cd2+concentration at 120mg/kg～180mg/kg and pH／3.5, The activity of SOD, CAT, POD and ASA-GSH cycle were inhibited, and the inhibitory effect was more obvious with concentration improved, M. Azedarach could been damagedof oxidative seriously.In summary, under the composite stress of Cd and acid rain, the SOD, CAT, POD and ASA-GSH cycle in M. Azedarach played a synergy role toclear ROS, which can alleviate the oxidative damage from stress. The main enzymesin ROS clearing were SOD, CAT and APX. And the main way of ASA regeneration in ASA-GSHcycle was that MDAR reducted MDHA, and GR was the important enzymes to generatGSH. The tolerance range of M. Azedarach on Cd and acid rain stress was as follows:Treating for 20d, Cd2+concentration≤150 mg/kg and pH≥3.5, or treating for 40d, Cd2+concentration≤150 mg/kg and pH≥4.5, or treating for 60d, Cd2+concentration≤120 mg/kg and pH≥4.5. As a result, M. Azedarachcan play an important role to manage and remediate Cd contaminated soil in acid rain area and creat ecological benefits.