Experimental Study On Poplar Remediation Of Lead And Cadmium Compound Pollution In Forest Area

The poplar is one of the excellent candidate tree species on phytoremediation technology for its strong root system and high aboveground biomass.However,different speices of poplar have significant variances in the repairability and tolerance of heavy metals.In this paper,we used Populus deltoides×P.euramericana ‘Nanlin 95',Populus deltoides×P.euramericana ‘Nanlin895'and Populus deltoides×P.euramericana ‘Nanlin 3412' as test materials to screen and understand the tolerance of different poplar varieties to Pb and Cd.In this paper,we had adopted inductively coupled plasma atomic emission spectrometry(ICP),photosynthesizer,chlorophyll fluorescence and other assay methods.The effects of Pb single stress and Pb-Cd combined stress on the growth,photosynthesis,antioxidant protection enzyme system and the three poplar organs on the enrichment characteristics of Pb and Cd were systematically studied.The major results were summarized as follow:(1)Single Pb stress and Pb-Cd combined stress had little effect on the growth of Populus deltoides×P.euramericana ‘Nanlin 95',Populus deltoides×P.euramericana ‘Nanlin895' and Populus deltoides×P.euramericana ‘Nanlin 3412',but it had a greater effect on root system.The height,ground diameter and rooting quantity of three kinds of poplar trees were less affected under stress.The leaves of Populus deltoides×P.euramericana ‘Nanlin 95' had obvious yellow spots.With the increase of stress concentration,the biomass of roots,stems and leaves and root activity decreased.Simultaneously,the synergistic effect of the addition of Cd on Pb is not significant.At the same time,the addition of Cd showed insignificant synergistic effect on Pb.Among the three poplars,Populus deltoides×P.euramericana ‘Nanlin 95' was affected by stress more than Populus deltoides×P.euramericana ‘Nanlin 895'and Populus deltoides×P.euramericana ‘Nanlin 3412'.(2)Single Pb stress and Pb-Cd combined stress had a large negative effect on the photosynthetic characteristics of Populus deltoides×P.euramericana ‘Nanlin 95',Populus deltoides×P.euramericana ‘Nanlin895' and Populus deltoides×P.euramericana ‘Nanlin 3412'.The chlorophyll a of three poplars increased first and then decreased with the increase of stress concentration,and the overall chlorophyll b showed a downward trend under Pb stress and Pb-Cd combined stress.With the increase of stress concentration,the Pn,Gs and Tr values of the three poplars decreased but Ci increased.And the chlorophyll fluorescence parameters also showed a downward trend.At the same time,among the effects in thress poplar under Pb-Cd combined stress on the chlorophyll content and photosynthesis,the addition of Cd had no regular effect on Pb,and there was no significant effect;Cd showed a synergistic effect on Pb in the chlorophyll fluorescence parameters.Among the three poplars,Populus deltoides×P.euramericana ‘Nanlin 895' was less affected by stress,followed by Populus deltoides×P.euramericana ‘Nanlin 3412',and finally Populus deltoides×P.euramericana ‘Nanlin 95'.At the same time,in the dynamic effects of Pb and Cd stress on the chlorophyll fluorescence parameters,the parameters had small changes over time at low concentration stress,but the opposite at high concentration.(3)Single Pb stress and Pb-Cd combined stress on Populus deltoides×P.euramericana ‘Nanlin 95',Populus deltoides×P.euramericana ‘Nanlin 895' and Populus deltoides×P.euramericana ‘Nanlin 3412' all promote the formation of anti-oxidant enzymes.The stress of Pb and Cd had an activation effect on SOD and POD of the three poplars,and the activation effect became more obvious with the increase of stress concentration;At low concentrations,CAT activity increased but decreased at high concentrations.SOD,CAT and POD of Populus deltoides×P.euramericana ‘Nanlin 895' were less affected by Pb single stress and Pb-Cd combined stress,but they were most significantly affected by Cd.With the increase of stress concentration,the MDA of the three poplars increased and they all had the phenomenon of membrane lipid peroxidation under single Pb stress.In the combined stress of Pb-Cd,the addition of Cd slowed the stress damage,and the addition of Cd showed a significant antagonistic effect on Pb.With the increase of the stress concentration,the soluble protein content of the three poplars increased under the Pb single stress;under the Pb-Cd combined stress,the performance of Cd against Pb was all antagonistic,and it has significantly antagonistic effect of Cd on Pb in Populus deltoides×P.euramericana ‘Nanlin 95',Populus deltoides×P.euramericana ‘Nanlin 895' and Populus deltoides×P.euramericana ‘Nanlin 3412' were not significant.Populus deltoides×P.euramericana ‘Nanlin 895' poplar showed better tolerance,followed by Populus deltoides×P.euramericana ‘Nanlin 3412',and finally Populus deltoides×P.euramericana ‘Nanlin 95'.(4)The proportion and distribution of Pb accumulation in Populus deltoides×P.euramericana ‘Nanlin 95',Populus deltoides×P.euramericana ‘Nanlin 895' and Populus deltoides×P.euramericana ‘Nanlin 3412' to total accumulation are: root > leaf > shoot.And the accumulation of Cd by three poplars is also concentrated in the underground part.The bioconcentration factor and translacation factor of the three poplars are less than 1.Populus deltoides×P.euramericana ‘Nanlin 895' and Populus deltoides×P.euramericana ‘Nanlin 3412' have the practical value of phytoremediation of Pb and Cd contaminated soil than Populus deltoides×P.euramericana ‘Nanlin 95'.(5)This article comprehensively evaluated the tolerance of Populus deltoides×P.euramericana ‘Nanlin 95',Populus deltoides×P.euramericana ‘Nanlin895' and Populus deltoides×P.euramericana ‘Nanlin 3412' by principal component analysis and subordinate function method.The comprehensive scores from large to small of the three kinds of poplar were ranked: Populus deltoides×P.euramericana ‘Nanlin 895' > Populus deltoides×P.euramericana ‘Nanlin 3412'> Populus deltoides×P.euramericana ‘Nanlin 95'.