Influence Of Heavy Metalion Zn²⁺ And Cr⁶⁺ Stress On Electrical Impedance Spectroscopy Parameters And Physiological Indexes Of Pinus Bungeana Needles And Stems

Pinus bungeana, belonging to Pinaceae family of evergreen trees, 3 needles 1 bundle, trees with photophil, drought resistance, dry barren tolerance, and frost resistance, is a good landscape and forestation tree species. It is widely cultivated in the park and the roadside in many cities. The heavy metalions Zn²⁺ and Cr⁶⁺ were used in six years old seedlings of Pinus bungeana, aiming to find the relationship between the heavy metal ions concentration and electrical impedance spectroscopy (EIS) parameters, and the effects of heavy metal stress on physiological indexes of ornamental trees, as well as perfect the EIS method in plant stress resistance applications. The seedlings were transplanted on April 2, 2009, and on May 24 the heavy metal ions stress treatment was applied. The concentrations of heavy metalion treatment were: Zn concentration (with pure zinc) 200, 500, 1000, 2000, and 3000 mg·L^-1; Cr concentration (with pure cadmium) 50, 100, 300, 500, and 1000 mg·L^-1, respectively. The EIS, cell membrane permeability, dry matter content, superoxide dismutase (SOD) activity, peroxidase (POD) activity, malondialdehyde (MDA) content, and the content of soluble sugar were measured weekly in needles and stems of Pinus bungeana.The main results were as follows:(1) Under Zn²⁺ and Cr⁶⁺ treatment, the electrical impedance parameters changed similarly with time; compared with control, extracellular resistance always increased, intracellular resistance first reduced and then increased, relaxation time first increased, and then decreased, while distribution coefficient of relaxation time had no obvious changes.(2) With the increasing in Zn²⁺ and Cr⁶⁺ treatment time, compared to the control, the electrical impedance parameters of stem occurred the similar trend. Extracellular resistance decreased firstly and then increased under low concentrations of Zn²⁺ and Cr⁶⁺, while with the high concentrations treatment extracellular resistance first increased and then decreased, and the higher the concentration was the greater the magnitude of increase or reduction. Intracellular resistance increased first and then decreased in low concentration, and in high concentration it was always lower than the control. Under various concentrations, the relaxation time always decreased first, then increased and then decreased again; Zn²⁺ and Cr⁶⁺ stress on the stem of the relaxation time distribution coefficient had little effect on performance with a trend of first increased and then decreased.(3) High concentrations of Zn²⁺ and Cr⁶⁺ stresses could increase the membrane permeability of needles and stems. Zn²⁺ in the above of 2000 mg·L^-1, and Cr⁶⁺ in the above of 300 mg·L^-1 could increase in needle cell membrane permeability significantly, Zn²⁺ in the above of 2000 mg·L^-1, and Cr⁶⁺ in the above of 100 mg·L^-1 could increase in stem cell membrane permeability significantly.(4) Zn²⁺ concentration of less than or equal to 3000 mg·L^-1 had no effect on the dry matter content of needles and stems; Cr⁶⁺ concentration with greater than 500 mg·L^-1 reduced the dry matter content of needles and stems.(5) The antioxidant enzymes activity of needles raised in a short term under Zn²⁺ and Cr⁶⁺ stress, but sharply reduced after 14 days treatment and bounced back with 28 days treatment.(6) The MDA content of needles could be significantly increased within 7 days Zn²⁺ and Cr⁶⁺ stress, but decreased after 14 days treatment. And Zn²⁺ from 500 mg·L^-1 to 2000 mg·L^-1 and Cr⁶⁺ from 100 mg·L^-1 to 500 mg·L^-1 could more improve the MDA content.(7) The content of soluble sugar of needles could not be promoted in 7 days Zn²⁺ and Cr⁶⁺ stress, it improved significantly after 14 days treatment and decreased under 21 days treatment.(8) In conclusion, after 7 days treatment in various concentrations of Zn²⁺ and Cr⁶⁺ the needles of Pinus bungeana seedlings occurred only minor damage or did not suffer, but the stems began hurt. After 14 days treatment both the needles and stems in various concentrations of Zn²⁺ and Cr⁶⁺ damaged obviously, and it was probably the most severely damaged period. After 21 days stress the low concentrations of Zn²⁺ and Cr⁶⁺ could not damage the needles and stems any more, and this might be because the needle and stem cells produced a certain resistant mechanism, but at high concentrations the hurt continued. Pinus bungeana seedlings could endure Zn²⁺ concentrations less than 2000 mg·L^-1 and Cr⁶⁺ concentrations less than 500 mg·L^-1, and could not endure Zn²⁺ concentrations higher than 2000 mg·L^-1 and Cr⁶⁺ concentrations higher than 500 mg·L^-1.