Effects Of Hydroponic Acclimation On Remedial Capability Of Chlorophytum Comosum In Lead-contaminated Water And Soil

With the continuous development of the modernization,heavy metals enter the environment through a varietiy of chennels.Heavy metal pollution has already been one of the critical environmental problems and studied by many scholars in each country.Lead as one of the top five heavy metals can be enriched from water and soil environment,greatly threatening human health through the food chain.Screening hyperaccumulator plants from ornamental plants to repair heavy metals pollution received widespread favor beacause of its low cost,easy popularization and sustainable development.Chlorophytum comosum（C.comosum）belongs to the Chlorophytum genus（Liliaceae）and is a common and evergreen foliage plant with esuberant vitality.Researches showed that C.comosum had a strong tolerance to many kinds of heavy meatals.Therefore,in this study,the capactity of uptake and endurance of C.comosum in Pb-polluted water body was investigated through the experiment of floating culture.It is expected to serve as a resource guide on selection of constructed wetlands plants in the restoration of lead-bearing wastewater.In addition,a hydroponic experiment with different concentrations of Pb was conducted to explore the capability of C.comosum in repairing lead-contaminated soil,so as to offer a new method for improving remediation effect of C.comosum on lead contaminated soil.The main conclusions are as follows:（1）The floating cultivation experiment showed that increment of fresh weight and roots,the plant height,the maximum root length,the catalase（CAT）and superoxide dismutase（SOD）activities increased first and then decreased,according to two different testing periods（21d and 42d）in the experiment.There are no obvious change in the level of the content of malondialdehyde（MDA）with increasing concentrations of medium Pb,while soluble protein content increased continually.When Pb²⁺concentration was equal to50 mg/L,the roots of C.comosum had the highest enrichment coefficient,however,the shoots of C.comosum of the enrichment coefficients dropped continually with elevated concentrations of lead.（2）The growth and enrichment of C.comosum in domestication stage may vary with time.In brief,the fresh weight,the plant height,the numbers of roots,the maximum root length and CAT activity increased slightly with the increase of duration of stress,while the SOD activity and soluble protein content were significantly elevated.Simultaneously,the enrichment coefficients of the roots of C.comosum decreased,yet the enrichment coefficients of shoots increased.The growth of C.Comosum domesticated through the certain concentration Pb²⁺for 21d was improved dramatically than that for 42d.Moreover,each treatment of lead concentration for 21 days could remove the reactive oxide species timely without serious damage to membranes of leaves.In addition,when the acclimation process of C.Comosum was conducted for 21d,the enrich ability of root is better than that for 42d.Therefore,C.Comosum domesticated for 21d can be transplanted into the lead-contaminated soil to further explore the impact of hydroponic acclimation on the ability of restoring Pb contaminated soil.However,C.Comosum,which has been domesticated in nutrient solution for 42 days,has adapted to the aquatic environment and formed stable transportation and detoxification mechanisms to deal with poisoning of lead in wastewater.Thus,it is appropriate that C.comosum acclimated at the concentration of50mg/L Pb²⁺for 42 days could be used in purifying lead-contaminated wastewater.（3）The hydroponic treatment had certain impacts on the growth of C.comosum transplanted.The plant height and the content of chlorophyll were inhibited,but the fresh weight,root volume and root length of C.comosum transplanted increased first and then decreased with elevated concentrations of lead.As the rising of the concentrations of Pb,soluble protein increased in vary degrees,while the electrical conductivity（EC）,the content of MDA,CAT and POD activities were all descending.The results showed that domestication of lead can effectively alleviate heavy metal Pb toxicity to C.comosum in contaminated soil.（4）The C.comosum domesticated had a positive effect on the activities of catalase,urease and phosphatase,but a negative influence on the activity of invertase.The order of the effect on the four soil enzymes was phosphatase>urease>invertase>catalase.In addition,the total content and the available content of lead both reduced constantly with the increased concentration of stress.（5）The fitting equations have been obtained in terms of growth index of C.comosum,soil enzyme activities,the total content and the available content of lead,while C.Comosum was domesticated for 21d.The results indicated that hydroponic acclimation with different concentrations of Pb in advance can not only alleviate the injury of C.comosum in lead contaminated soil,but also enhance the restorative effect of C.comosum on the lead-contaminated soil to a certain extent.The optimal concentration of lead was122.94mg/L for domesticating C.comosum to recover lead-contaminated soil.