| Soil heavy metal pollution has become a serious environmental problem in the world today.The restoration of contaminated soil has attracted widespread attention.The restoration of hyperaccumulator plants has become a hot spot for heavy metal pollution soil restoration in recent years due to economic and environmental protection,no secondary pollution and excessive accumulation of heavy metals.In this study,the ultra-concentrated heavy metal(Cd,As,Cu,Pb,Zn)compound contaminated soil in a certain area of Hebei Province was used as the remediation object.The cluster analysis method was first used to classify the soil,and the soil is divided into four types: relatively light and heavy metal composite contaminated soil,relatively ultra-high content of Cd and As composite contaminated soil,relatively ultra-high content of Cu and Pb composite contaminated soil,relatively ultra-high content of Zn composite contaminated soil;on this basis,the ultra-accumulated ecological Sedum alfredii is used as a restoration plant,using potting method to repair four types of ultra-high content heavy metal compound contaminated soil,to explore the the ability of Sedum alfredii to accumulate and transport heavy metals in soil,the response of physiological and biochemical characteristics of leaves of Sedum alfredii,the diversity and structural characteristics of soil microbial communities during the remediation process.The main research conclusions are as follows:(1)By studying the extracting effect of Sedum alfredii on ultra-high content of composite heavy metals,the results show that in remediation of ultra-high content heavy metal composite contaminated soil,the enrichment of five types of heavy metals from Sedum alfredii is ranked as follows: Zn > Cd >> Cu> Pb > As,the enrichment amounts of Zn and Cd are 8905.05-25685.21 mg/kg and 32.99-1184.16mg/kg,respectively.The transport ability is strong,and the As,Cu,Pb enrichment and transport effects are poor.At the same time,a large amount of Zn in the soil can alleviate the enrichment of plants to other heavy metals in the soil.The order of Cd and Zn contents in various parts of Sedum alfredii is as follows leaf > stem > root,and the order of enrichment of As,Cu and Pb is underground > above ground,which shows that the main place where Sedum alfredii is enriched for heavy metals is the leaf,and the leaf is selective for the enrichment of heavy metal elements,and the priority order of enrichment is Zn > Cd > Cu > Pb > As.(2)By studying the physiological response mechanism of Sedum alfredii leaves to ultra-high contents of composite heavy metals,the results show that: Sedum alfredii can survive in the repair of soils contaminated with ultra-high contents of heavy metals.When the Pb in the heavy metal compound contaminated soil reaches2792.51 mg/kg,it has an inhibitory effect on the growth and development of Sedum alfredii and when the Zn reaches 34280.38 mg/kg,it can alleviate the toxicity of the compound heavy metals to the Sedum alfredii.Under the stress of Pb reaching2792.51 mg/kg in the heavy metal compound contaminated soil,the plant maintains the osmotic potential by accumulating osmoregulation substances,the average PRO content is 4.73 μg/g and the leaves activate the enzymatic defense system,in order to enhance their ability to resist stress,such as the average SOD activity is 1.65 U/g.These reactions consume a lot of organic matter and energy,resulting in a poor growth state despite the strong photosynthesis effect of Sedum alfredii.Under the stress of Zn reaching 34280.38 mg/kg in the heavy metal compound contaminated soil,ultra-high content of Zn can promote the photosynthesis of Sedum alfredii.Sedum alfredii maintains the osmotic balance by accumulating osmo-regulators(the average PRO content is 4.22 μg/g)to enture a better growth and development state of the plant.(3)The high throughput sequencing analysis of microbial communities in the rhizosphere and non-rhizosphere soils of Sedum alfredii.The results showed that: the microbial regulation also plays an important role in the process of phytoremediation of heavy metals contaminated soil.The planting of Sedum alfredii increased the diversity of soil microbial communities.Under ultra-high content of Cu and Pb stress,it not only affects the normal growth of plants,but also affects the bacterial diversity of the soil system.The diversity of fungal communities in soil did not decrease with the increase of heavy metal(Cd,As,Cu,Pb,Zn)content gradient.Under ultra-high content of Cu and Pb stress,Bacteroidetes in bacteria and Basidiomycota in fungi can be specifically colonized in the rhizosphere soil of Sedum alfredii,improving the soil aggregate structure and thus improving the soil environment promotes the growth and development of plants.At the same time,it can combine with heavy metal ions to form extracellular precipitates through the precipitation of extracellular secretions and the adsorption of cell walls.(4)Using PICRUSt to predict the functional family characteristics of bacteria,and FUNGuild to predict the characteristics of fungal nutritional types,the results show that the remediation technology of Sedum alfredii has improved microbial metabolism in soil.At the same time,there are richer functional genes related to environmental information processing and amino acid metabolism of the rhizosphere in Sedum alfredii,invasion plays an important role.The analysis of fungal nutritional types in this study showed that the restoration of Sedum alfredii reduced the abundance of pathotrophic fungi in the soil,but increased the relative abundance of saprophytic and symbiotic vegetative fungi. |
