Absorption Of Heavy Metal By Phragmites Australis Root In Wetland Under Long-term Papermaking Wastewater Irrigation

In recent years,wetland system had been widely used in the field of industrial wastewater treatment because of its three coordination and purification effect.The natural populations of reed wetland mainly depended on the rhizome propagation,its rhizome had obvious nodes and internodes,each segment whorled fibrous root,the root regeneration of fine root,soil extension staggered,population reproduction complete replacement.It had been shown that the purification of heavy metal by wetland reed was mainly through root absorption,but the effect on heavy metal uptake of reed roots under long-term papermaking wastewater irrigation was not clear.In order to further investigate the absorption of heavy metal in reed root o and its response to the growth and physiological characteristics of root under papermaking wastewater irrigation,research object were perennial and annual reed roots under papermaking wastewater irrigation in this paper,which both were irrigated with CODcr concentration 0,50,175,300mg·L-1 in germination,leaf,growth,maturity of five growth periods,the determination of reed root growth,physiological characteristics and heavy metal content under different irrigation periods and four CODcr concentration,and discuss the absorption characteristics of growth,physiological and heavy metal in order to further investigate the mechanism of absorption and transport of heavy metal in wetland,provide the theoretical support for wetland ecosystem restoration and reconstruction.The main results are as follows:(1)Biomass and root morphology indexes of perennial reed root were increased first and then decreased with the wastewater CODCr concentration increased,and reached the maximum value in 175mg·L-1.While biomass and root morphology indexes of neonatal reed root were increased with wastewater CODCr concentration increased,and reached the maximum in 300mg·L-1.Biomass and root morphological indexes in the papermaking wastewater treatment group were higher than the control group.The biomass of perennial reed root were higher than that of neonatal reed root in each treatment group(including wastewater treatment group and control group);the length,area and volume of perennial reed root were higher than the corresponding index of neonatal reed root The average diameter of perennial reed root was lower than that of the neonatal reed root in rapid growth,heading stage and mature stage.In addition to the mature stage,the number of root tips of perennial reed was higher than that of the latter.Length,area,volume and root tip number of perennial reed root reached the maximum in leaf expansion of the wastewater irrigation,respectively 1084.34cm,149.08cm2,150.37cm3,2186;Length,area,volume and average diameter reached the maximum in the mature period of the wastewater irrigation,respectively 948.30cm,83.19cm2,62.23cm3,1.97cm.(2)O2·-production rate of reed rhizome was higher than that of fibrous root;SOD,POD,CAT activity and root activity of fibrous root were higher than that of rhizome,with the increase of papermaking wastewater CODcr concentration,O2·-generation rate of perennial reed root first decreased and then increased;SOD,POD,CAT activity and root activity increased with papermaking wastewater CODcr concentration increased after the first drop,which reached the maximum in 175mg·L-1.While O2·-generation rate of the neonatal rhizome and root were decreased with the increase of papermaking wastewater CODcr concentration;SOD,POD,CAT activity and root activity increased with the increase of papermaking wastewater CODcr concentration,which reached the maximum in 300mg·L-1.The yield of O2·-generation rate in the roots of neonatal reed was lower than that of perennial reed root,and the activities of SOD,POD,CAT,root activity were higher than that of perennial reed.O2·-generation rate of perennial and neonatal rhizome and root were negatively correlated with SOD,POD,CAT activity and root activity,while were positively correlated between SOD,POD,CAT activity and root activity.(3)With the increase of papermaking wastewater CODcr concentration,copper,manganese and zinc,titanium,chromium content and unit mass content of perennial rhizome and root were first increased and then decreased,reached the maximum value in 175mg·L-1,respectively 2434.75g·hm-2.6706.20g·hm-2、5253.10g·hm-2、5819.60g.hm,2.865g·hm-2.Unit mass content maximum of copper,manganese,zinc,titanium,chromium accounted for the proportion of the root content were 85%,66%,73%,60%,69%in perennial reed fibrous root.The unit of quality content and content of copper,manganese and zinc,titanium,chromium in neonatal reed rhizome and fibrous root were increased with papermaking wastewater CODcr concentration increased,which reached the maximum value in 300mg·L-1,respectively 2240.30g·hm-2、15586.30g·hm-2、5062.50g·hm-2、6097.30g·hm-2、2560.80g·hm-2.The unit mass content maximum of copper,manganese,zinc,titanium,chromium accounted for the proportion of the root content were 67%、78%、70%、66%、67%in neonatal reed fibrous root.Reed roots can absorpt copper,manganese,zinc,titanium,chromium in papermaking wastewater,unit absorption ability for copper,manganese,zinc,titanium and chromium of fibrous root was stronger than rhizome,and absorption capacity of neonatal reed root was stronger than the perennial reed root,and copper,manganese,zinc,titanium,chromium content in treatment group were higher than the control group.(4)Except for superoxide anion free radical,there were significant positive correlations between the four physiological indexes and the accumulation of heavy metal(p<0.01).The correlation coefficient of the catalase activity,chromium and manganese content were whole above 0.9,the correlation coefficient of copper content was 0.85;the correlation coefficient of peroxidase activity,superoxide dismutase activity,root activity and the content of manganese were whole above 0.8;the correlation coefficient of peroxidase activity and five heavy metals were whole above 0.7.