Accumulation And Tolerance Mechanism Of Heavy Metals By Typha Latifolia

Heavy metal pollution could cause a series of environmental problems and harm to human’s life and health, so the prevention of heavy metal pollution is very important. The control methods commonly include physical, chemical, plant, and microbial remediation technology. Phytoremediation has become an ideal method to heavy metals control in soil, because physicochemical method would cause second pollution to soil and the recovery of heavy metals from soil by microbial remediation is very different. The efficiency of phytoremediation could be improved by improving tolerance and accumulation to heavy metals of plants, though phytoremediation has a long cycle and slow effect, and so on. There are some researches about the accumulation of heavy metals in Typha latifolia L. and enhancing ability of plant resistance to heavy metal stress by polyamines, but study on the tolerance mechanism under single and compound Cd and Pb stress is still acarce. Therefore, the accumulation and tolerance mechanism to heavy metals of T. latifolia L. located in constructed wetland in Fankou lead-zinc mine were studied; further the regulatory effects of exogenous spermidine (Spd) on antioxidant system, the absorption and accumulation of Cd and Pb in Typha latifolia L. were investigated by soil culture experiment with atomic absorption spectrometer and multifunctional enzyme linked immunosorbent. The main results are as follows:(1) The survey of constructed wetland of T. latifolia L. in Fankou lead-zinc mine:(a) T. latifolia L. is a tolerance plant to a variety of heavy metals and could reduce the content of heavy metals of wetland soil effectively and the amount of heavy metals (except Pb and Fe) of soil about 80% from water inlet to outlet. Compared with single metal hyperaccumulator, T. latifolia L. could accumulate large amounts of heavy metals, and comply with environmental compound pollution demand.(b) Heavy metals uptake in T. latifolia L. was mainly affected by heavy metal contents in soil, the interaction between heavy metals and the selective absorption of root were the key factors influencing the absorption of heavy metals by T. latifolia L.(c) Heavy metals accumulation in root of T. latifolia L. (the accumulation of Cd and Fe in the underground part of T. latifolia L.was more than 50%, Pb, Zn and Cu are greater than 80%), the inhibition of non nutrient elements Cd, Pb transportation to above ground part of plants, and the combination of heavy metals in leaf cell wall and cytoplasm matrix were the important mechanisms of broad-leaf cattail tolerance to heavy metal in artificial wetland.(2) The experiment of soil culture on heavy metal stress tolerance of T. latifolia L.(a) Cd and Pb stress significantly increased the accumulation of superoxide anion (O2-), hydrogen peroxide (H2O2), malondialdehyde (MDA), and nitric oxide (NO). Exogenous Spd significantly increased the content of endogenous Spd and alleviated the oxidative stress of Cd, Pb to T. latifolia L. to some extent. The correlation analysis show that exogenous Spd can inhibit the production of O2, H2O2, MDA and NO in leaf of T. latifolia L. and thus improve the resistance of T. latifolia L. to Cd and Pb.(b) In leaf of T. latifolia L., Cd and Pb stress decreased the content of soluble protein, had little effect on the activities of peroxidase (POD) and catalase (CAT), improved the glutathione peroxidase (GPX) activity obviously, reduced glutathione reductase (GR) activity significantly, and thus affected the function of ascorbic acid and glutathione (ASA-GSH) system and decreased the content of ascorbic acid (ASA) and glutathione (GSH). The application of Spd significantly improved the activities of CAT and GR in Typha latifolia L. leaf, maintained the balance of glutathione/glutathione disulfide (GSH/GSSG), and thus the ASA-GSH pathway could play a positive antioxidative role.(c) The pH value of soil increased, ranging from 6.21 to 6.98, after after the application of Cd, Pb, and the plantination of T. latifolia L., and exogenous Spd could elevate the soil alkalinity. Chemical forms of Cd and Pb in soil were related to the pH value and other physical and chemical properties of soil. The higher the concentration of Cd and Pb and their content of the acid soluble fraction was, the more the accumulation of Cd and Pb in Typha latifolia L. was. The combined stress of Cd and Pb promoted the accumulation of both metals in Typha latifolia L., and exogenous Spd furthe enhance d the accumulation of Cd and Pb in broad-leaf cattail to a certain extent.(d) The subcellular distribution of Cd and Pb in T. latifolia L. root, rhizome, and leaf followed the order cell wall> cellular matrix> organelle fractions. Exogenous Spd increased the accumulation of Cd and Pb in T. latifolia L. cell wall or cytoplasmic soluble part, decreased the content of Cd and Pb in organelles, and improved the detoxification ability of T. latifolia L. to Cd and Pb.