Lead Accumulation, Tolerance And Potential Remediation For Lead Contaminated Soils In Some Species Of Iris L.

Based on the researches of drought and water-logged resistant and Cu,Cd accumulation and tolerance of the species of Iris L,the seedlings of 6 species of Iris L., Iris halophita Pall.,Ⅰ.pseudacorus L.,Ⅰ.ensata var.hortensis Makino et Nensoto,Ⅰ.lactea var.chinensis(Fisch.) Koidz,Ⅰ.tectorum Maxim.andⅠ.japonica Thunb.were planted in hydroponic system or artificial lead(Pb) polluted soil and Pb polluted soil to determine the effects of Pb,Pb+NaCl,Pb+Zn stress on the plant vigor,the Pb contents and distribution in different parts of the plants,physiological parameters and the sub-cellular localization of Pb and Cd and potential ability to remediate Pb contaminated soils.The results showed were as follow:1.The abilities of Pb accumulation were different among 6 species of Iris L.,Ⅰ. halophila Pall.,Ⅰ.pseudacorus L.,Ⅰ.ensata var.hortensis Makino et Nensoto,Ⅰ.lactea var. chinensis(Fisch.) Koidz,Ⅰ.tectorum Maxim.andⅠ.japonica Thunb.The contents of Pb in the shoots ofⅠ.halophila,Ⅰ.ensata var.hortensis andⅠ.lactea var.chinensis treated at 4 mmol·L^-1Pb were 1103μg·g^-1,1008μg·g^-1 and 1109μg·g^-1,respectively,exceeded 1000μg g^-1,the critical value of Pb hyperaccumulator,and the shoot dry masses were not significantly different with those of control.The Pb accumulation ofⅠ.pseudacorus was better in higher Pb level condition and those ofⅠ.tectorum,andⅠ.japonica were not good in all treatments.The Pb translating rates ofⅠ.ensata var.hortensis andⅠ.lactea var. chinensis in 4-6 mmol·L^-1Pb treatments were better than those of other species of Iris L.2.The seedlings ofⅠ.halophila andⅠ.pseudacorus were subjected in 0-10 mmol·L^-1 Pb and determined physiochemical parameters in different period.The results showed that the contents of chlorophylls in the leaves ofⅠ.halophila andⅠ.pseudacorus decreased as Pb concentrations were raised,and the contents of chlorophylls dropped and then slowly being raised at same Pb treatment as treatment period longer.The contents of MDA in the leaves ofⅠ.halophila which could accumulate higher content of Pb were not significantly different with those of control below 4 mmol·L^-1Pb treatments in the period of 7-28 days.However, the content of MDA in the leaves ofⅠ.pseudacorus was significantly different with that of control at 4 mmol·L^-1 Pb treatments in 28 days.The contents of proline and the activities of SOD in the leaves ofⅠ.halophila andⅠ.pseudacorus increased as the Pb concentrations were raised.The results indicated thatⅠ.halophila were higher tolerant species in the physiological characters than those ofⅠ.pseudacorus.3.The effects of Pb-NaCl interaction on the plant vigor,contents of Pb in the plant and physiological mechanisms ofⅠ.halophila andⅠ.pseudacorus were investigated in hydroponic system.The results showed that the contents of Pb in the plants of two species of Iris L.were increased under Pb+NaCl stress,while,the fresh weights were decreased as the concentrations of Pb+NaCl higher.The contents of malondialdehyde(MDA) were increased as the concentrations of Pb+NaCl rised.The activities of superoxide dismutases (SOD) and proline(pro) contents were significant increased as the concentrations of Pb,Na and Pb+NaCl enhanced,which might play key role to protect the plants from the stress of Na and Pb.The growth ofⅠ.halophila could be promoted by NaCl and the seedlings ofⅠ. halophila were more tolerant NaCl stress than those ofⅠ.pseudacorus.4.The study of Pb and Zn toxicity to the growth and Pb,Zn,Cu and Mn contents in the different parts of the seedlings ofⅠ.pseudacorus andⅠ.halophila in pot culture showed that the Pb,Zn,Mn,Cu contents in two species of Iris L.were increased under Pb and Zn stress.The normal growth and development of two species of Iris L.were damaged, numbers and lengths of leaves and roots,and biomasses of both species were decreased significantly due to the large amount of Pb,Zn,Mu,Cu in the plants treated with co-contamination of 10 mmol kg^-1Pb+50 mmol kg^-1Zn.The growths and developments ofⅠ. pseudacorus were effected more serious than those ofⅠ.halophila.The negative correlations were found between the growths and the contents of Pb and Zn ofⅠ. pseudacorus andⅠ.halophila.The negative correlations between the growth and the contents of Zn was much more obvious than between the growth and the contents of Pb in two species of Iris L.which indicated that Zn was more toxic than that of Pb to the seedlings ofⅠ.pseudacorus andⅠ.halophila.5.The studies on the sub-cellular localization of Pb and Cd in root cells ofⅠ. pseudacorus,Ⅰ.lactea var.chinensis andⅠ.tectorum which subjected to Pb and Cd by hydroponics and harvested after 16 days showed that Pb and Cd deposits were mainly found in the cell wall,along the plasma membrane,on the inner surface of some vessels and a very few in the cytoplasm of cells in the root tip cells.Pb and Cd deposits were not found in inter cellular space and vacuole of the cells.The compartmental distribution of Pb and Cd were different in the sub-cellular structure of 3 species of Iris L.Pb deposits were on the inner surface of died cell walls and Cd deposits on the inner surface of cell wall and in the cell walls ofⅠ.pseudacorus.Pb deposits were along the plasma membrane and Cd deposits in the cell walls and some organdies ofⅠ.lactea var.chinensis.Pb and Cd deposits were on the inner surface of some vessels or in some cell walls ofⅠ.tectorum.6.Seedlings ofⅠ.pseudacorus andⅠ.halophila were potted in yellow brown soil(CK), yellow brown soil+10 mmol L^-1 Pb,polluted red soil and planted the seedlings on the slope where is near by the Pb smeltery.The dry weight(DW) of the shoots ofⅠ.pseudacorus,the DWs of the shoots and roots ofⅠ.halophila growing on the slope near by the Pb smeltery were significantly decreased compared with those of the CK(p＜0.05).The contents of Pb in the shoots and roots ofⅠ.pseudacorus andⅠ.halophila growing on the slope near by the smeltery in Jiangxi province were 1117mg kg^-1,1982mg kg^-1and 1273mg kg^-1,2698mg kg^-1,respectively,higher than those of the plants potted in the yellow brown soil +10 mmol L^-1 Pb and polluted red soil.The values of Pb contents in the shoot/Pb contents in the roots (S/R)of the tested species of Iris L.growing in the red soil was higher than those growing in the yellow brown soil which indicated that the lower soils pH could promote the Pb accumulation and Pb translocation from roots to shoots of two species of Iris L.According to the estimated biomasses of two species of Iris L.in fruiting period and the Pb amounts removed from contaminated soils in unit area per year,Ⅰ.halophila andⅠ.pseudacorus have the potential ability to remediate Pb contaminated soils.