The Physiology And Electrical Impedance Spectroscopy Of Cotinus Coggygria Under Cadmium And Lead Stress

Nowadays,contamination of soils by toxic metals is a major concern all over the world.Cadmium?Cd?and lead?Pb?are important widespread pollutant with high toxicity to plants,animals and humans.The two elements are nonessential heavy metal for plants,however they can be non-biodegradable so as to accumulated to higher levels in the environment.Cadmium and lead cause various phytotoxic and inhibition of physiological processes,even cause plant death.As a famous foliage plant and its cold and drought resistance and other excellent characteristics,Cotinus coggygria is popularized and applicated as a pioneer species during afforestation in some area in China.In this paper,two years old C.coggygria seedlings were planted in pots,and treated with different concentrations of Cd(0,50,100,200,500 and 1000 mg·kg^-1)and Pb(0,50,100,200,500,1000 and 1500 mg·kg^-1).Some growth and physiological parameters?elongation of shoot and diameter growth of stems,and photosynthetic physiology,osmotic adjustment substance,hormone content,and nutrient element,etc.?,and electrical impedance spectroscopy?EIS?parameters?high-frequency resistance r,low-frequency resistance r₁,extracellular resistance r_e,and intracellular resistance r_i?were measured.The aims of the present study were to learn the level of tolerance and screen the most relevant EIS parameter to build the best suitable forecasting model so as to use C.coggygria to ecological restoration the environmental of the city and to broaden the scope of application of electrical impedance spectroscopy.The main results are as follows:1.There was no significant effect on the growth when the C.coggygria seedlings were exposed the concentration of Cd and Pb less than 200 mg·kg^-11 within six months.The growth of new roots and new shoots,and the diameter growth of stems were inhibited when the concentration of Cd and Pb was more than 200 mg·kg^-1.The seedlings died when the concentration of Cd and Pb was up to 1500 and 2000 mg·kg^-1 respectively.2.The contents of Cd in roots,shoots and leaves of C.coggygria increased with increasing Cd and Pb concentrations in the soil.Cd and Pb absorbed by plants were mainly accumulated in the roots.3.Total chlorophyll content had not been affected significantly in low concentration of Cd and Pb while it significant declined in high concentrations of Cd and Pb.Leaf photosynthetic rate,stomatal conductance and transpiration rate decreased but internal CO₂ concentration increased by exposure to Cd and Pb.The Cd and Pb stress also resulted in maximum photochemical efficiency of photosystem??F_v/F_m?,quantum yield of photosystem?electron transport??PS??and apparent photosynthetic electron transport rate?ETR?decreased.However,photochemical quenching?qP?rose by lower heavy metal and lowered by higher heavy metal.4.With increasing of Cd concentrations,the K⁺,Ca²⁺and Mg²⁺content in roots,as well as the K⁺and Fe²⁺content in leaves increased slightly first and then decreased.The K⁺,Ca²⁺,Mg²⁺and Fe²⁺content in roots and leaves,as well as the Fe²⁺and Zn²⁺content in leaves had the same trends under Pb stress,indicating that low doses of Cd and Pb might be beneficial to plants but high doses produce toxic effects.The roots Fe²⁺content increased first and then decreased after 2 and 3 months,and decreased continously after 4months.And the Zn²⁺and Mn²⁺content rose during later Cd stress.The roots Zn²⁺content decreased,whereas the Mn²⁺content decreased firstly and then increased in roots and leaves with Pb treatment.5.The hormones synthesis was interfered with Cd and Pb.With increasing of Cd and Pb concentration,the content of ABA gradually increased.The content of GA and ZR in roots and leaves,the content of IAA in roots increased in lower Cd level and decreased in higher Cd level.With increasing of Pb concentration,the trend of GA and IAA content in roots,as well as the ZR content and the ratio of?IAA+GA+ZR?/ABA in leaves were similar with the trend mentioned above under Cd stressing.Concerning the other hormones there was little difference in different periods,however,the hormones level was decreased with higher Cd and Pb level and time passing.6.The contents of soluble sugar and soluble protein in roots,stems and leaves were lower significantly under high concentrations over 200 mg·kg^-1 of Cd and Pb stress and long time duration than those in the controls.7.After long time and high concentration of Cd and Pb treatment,the cell membrane permeability increased and water content reduced in roots,stems and leaves.High-frequency resistance r,low-frequency resistance r₁,extracellular resistance r_e,and intracellular resistance r_i in roots,r_e and r_i in stems under Cd stress,as well as r_e in roots under Pb stress increased first and then decreased with the increasing in concentration of Cd or Pb.Almost all the EIS parameters under the Cd or Pb stress were higher than the control in the end of treatment.The EIS parameters correlated significantly with other physiological indexes,especially with relative electrical conductivity.Estimation models were established between the EIS parameters and relative electrical conductivity.Among them the r_e of roots under Cd stress,the r₁ of stems under Pb stress estimated best for the relative electrical conductivity.The best estimation models were y_root?re?=0.001x³+0.113x²–5.998x+113.189,y_stem?r1?=0.025x²–1.946x+88.902,and y_stem?r1?=0.006x³–0.569x²+15.321x–58.757,respectively.So these models could be used in the estimation of Cd or Pb stress.It also provides a practical and theoretical basis for the rapid diagnosis and estimation of the heavy metal stress by measuring the changes of the EIS parameters.The application of electrical impedance spectroscopy technology is also widen.