Studies On Physiological Response Of Poplar To Zinc And Copper And Its Accumulation In Plants

Phytoremediation of zinc and copper polluted environment has become a poplar part in area of environmental and biological science.Nowadays,the research about the selection of plant for phytoremediation focused on the hyperaccumulator.However,this green technology has some disadvaniages:small biomass,limited environments of growth and lack of variety resources.The present study were performed to select some elite poplar(Populus) materials with strong resistance to zinc and copper pollution from five materials to be used in phytoremediation,as well as to clarify its resistance mechanism, and zinc and copper accumulation and distribution in poplar organs.Cuttings of five poplar materials,including Populus deltoids Bartr.cv.'Lux',P. deltoides c2.Nankang,P.deltoids 60/160×P.nigra 'chile',P.simonii Carr.and P.×liaoningensis Z.Wang et H.D.chen sp.cv.,were collected in Huazhong Agriculture University.Growth of the seedlings,relative electric conductance,and contents of chlorophyll,soluble protein and malondialdehyde(MDA) of leaves were measured during treatment of Zn and Cu to clarify its influence on poplar.Distribution,accumulation and migration characteristics of Zn and Cu in the five materials were investigated,as well as changes of Zn and Cu contents and pH value of the soil.Zn and Cu accumulation in poplar and its toxicity mechanism were discussed in the present study.Results are as follows:(1) According to the apparent morphology,five poplar materials' resistance to zinc and copper stress are as follows:P.simonii Carr.＞P.×liaoningensis Z.Wang et H.D.chen sp.cv.＞P.deltoides c2.Nankang＞P,deltoids Bartr.cv.'Lux'＞P.deltoides60/160×P.nigra'chile.(2) The five poplar materials' growth rate of height and basal stem are coming up obviously with the rising of the stress of zinc and copper.Take the changes of growth index into consideration,five poplar materials' resistance to zinc and copper stress are as follows:P.×liaoningensis Z.Wang et H.D.chen sp.cv.＞P.deltoides c2.Nankang＞P. deltoids Bartr.cv.'Lux'＞P.deltoides60/160×P.nigra'chile＞P.simonii Carr.(3) With the increasing of zine's concentration,the five poplar materials' biomass yield unfolds a trend of falling firstly and the increasing again.While with the increasing of copper's concentration,the biomass yield falls steadily.Under the interaction of zinc and cooper,the decreasing rate of the five poplar's biomass yield drops gradually with the rising of the interaction's comcentration.That is to say,the medium concentration promote the poplar's biomass accumulation.(4) With the rising of zinc and copper's concentration,the relative chlorophyll content of the five poplar materials decreases sharply.And under the stress,P.simonii Carr.'s relative chlorophyll content remains highest and the content returns faster than the other four.(5) Under the stress of zinc and copper,the leaves's relative conductivity comes up gradually with the prolonging of the treatment's time.Thers is a significant difference among the five poplar materials.P.simonii Carr.and P deltoides c2.Nankang's membrane conditions remain the same mostly.The leaves's relative conductivity's growth rate falls gradually with the rising of the interaction's concentration.That is to say,high concentration of the zinc and cooper restricts the damage towards poplar's menbranes.(6) After 21 days' treatment of zinc and copper,the soluble protein's contents of the five poplar materials are as fllows:P.simonii Carr.＞P.deltoides60/160×P.nigra'chile'＞P.×liaoningensis Z.Wang et H.D.chen sp.cv.＞P.deltoides c2.Nankang＞P.deltoids Bartr. cv.'Lux'.In summary,the soluble protein's contents of the five poplar materials' leaves report a trend of a rising followed by a falling according to the incresing of copper's concentration.While the zinc's stress unfolds a opposite trend.And the soluble protein's contents of the five poplar materials' leaves finally reach its peak of 600mg/g.(7) The contents of MDA in the leaves of five poplar materials comes up gradually with the prolonging of the treatment's time.There is a significant difference among the five poplar materials.To sum up,the contents of MDA in the leaves of five poplar materials comes up steadily with the increasing of zinc's concentration.Moving to the copper's stress,the trend is a rising followed by a falling with the increasing of cooper's concentration.Under the interaction of zinc and copper,the contents of MDA in the leaves of five poplar materials are falling with the interaction concentration's rising.It indicates that the damage to the leaves' membrane deepens with the rising of the interaction concentration. (8) The accumulation ability of zinc anf copper varies among different poplar materials.P.simonii Carr.can hold the greatest amount of zinc and copper,thus it has the biggest accumulation ability.And to the P.simonii Carr.,the zinc mainly stays in its roots and the copper is mostly in stems.The order of accumulation of zinc in different parts of the five poplar materials is:root＞leaf＞stem.The order of accumulation of copper in different parts of the five poplar materials is:root＞stem＞leaf(9) Different concentration of zinc influences the migration index slightly in different parts of poplars.Different concentration of copper effects the roots'copper accumulation deeply.And the accumulation of copper in roots comes up with the increasing of copper concentration.On the whole,poplar displays a great tolerance to the stress of zinc and copper.The low concentration of zinc almost has no impact on the growth of poplars.While the high concentration of zinc and copper poison the growth of poplars.And we can witness that the poison effect deepens with the rising of the concentration of zinc and copper and the prolonging of the treatment period.The order of five poplar materials' resistance towards the mutual stress of zinc and copper is:P.simonii Carr.＞P.deltoides c2.Nankang＞P. deltoides60/160×P.nigra'chile'＞P.deltoids Bartr.cv.'Lux'＞P.×liaoningensis Z.Wang et H.D.chen sp.cv.And there is no significant difference among the five polar materials.The order of five poplar materials' individual resistance towards zinc and copper is:P.simonii Carr.＞P.deltoidesc2.Nankang＞P,deltoidsBartr.cv.'Lux'＞P.deltoides60/160×P.nigra'chile'＞P.×liaoningensis Z.Wang et H.D.chen sp.cv.