Growth Response And Accumulation Characteristics Of Houttuynia Cordata Thumb. Under The Stress Of Lead And Arsenic

Combination contamination of heavy metals is a common but important form of soil contamination. Phytoremediation has become an effective approach for remediation of heavy metal contaminated soils. Taking Houttuynia cordata Thunb. as test material, this paper studied the effects of different concentrations of Pb, As and their combination treatment on the growth and development of H. cordata. and its accumulation of Pb and As by adopting pot culture experiments. The results showed that:1. Plant height and yield of H. cordata. were increased as the concentration of Pb decreased, the root length was first increased and then decreased to suffer symptoms under the single treatment of Pb; Because of the low-dose stimulating effect of As on H. cordata., the plant height, root length, yield increased with the concentration of As and no less than the control. H. cordata. growth was in good condition and there were no obvious toxicity symptoms under the single treatment of As; Under the combined treatments of Pb and As, in terms of plant height, there were no significant interactive influence on the toxic effects. In terms of the root length, the toxic effects of high concentration of Pb (=1000mg/kg) on As showed inhibition while the toxic effects of As on Pb was not significant; In terms of the yield, the toxic effect of low concentrations of Pb (= 500mg/kg) on As showed inhibition while the toxic effect of As on Pb was not significant.2. In the soil of different concentrations of combined treatments of Pb and As, the accession of Pb and As affected the roots, stems, and leaves of H. cordata.on the absorptive capacity of Pb and As, respectively. In terms of the impact of As on Pb:When the concentration of Pb= 1000mg/kg, As inhibited Pb absorption of root and stem, respectively. When the concentration of Pb reached 2000mg/kg, As promoted Pb absorption of root and stem, respectively. What's more, when the concentration of Pb=500mg/kg, As inhibited Pb absorption of leaves; In terms of the impact of Pb on As, Pb inhibited As absorption of root and stem, respectively, while the impact of Pb on As absorption and accumulation of leaves showed the trend of first promotion and then inhibition. The restraining concentration of Pb on As absorption and accumulation of leaves decreased with the increase of the concentration of As.3. The Enrichment Coefficient of Pb and As were 0.21～0.46 and 0.01～0.3, respectively, while the translocation factor of Pb and As were 0.24～2.51 and 0.09～2.09, respectively, in terms of H. cordata. With the concentrations of Pb and As increased, the Enrichment Coefficient of Pb and As increased while the translocation factor of Pb and As decreased gradually, respectively. In view of its high Enrichment Coefficient, H. cordata. can be considered as phytoremediation species to repair Pb and As contaminated soil.4. When the concentration was 2000mg/kg under the single treatment of Pb and the concentration of Pb and As were 1000 mg/kg and 60 mg/kg under the combined treatments, H. cordata. extracted the most lead from the soil, which was 1 244.4 ug/pot and 3 132.4 ug/pot, respectively. When the concentration was 120mg/kg under the single treatment of As and concentration were 500 mg/kg and 120mg/kg under the combined treatments of Pb and As, H. cordata. extracted the most arsenic from the soil, which was 27.3ug/pot and 254. 1ug/pot respectively. The amounts of Pb and As that H. cordata.extracted from soil were higher than the control significantly, respectively.5. The distribution of Pb and As in vivo organ-level of H. cordata. was:root> stem> leaf. The proportion of heavy metals in roots increased gradually with the concentration of Pb and As, respectively, indicating that under the stress of Pb and As, most of the heavy metals are fixed in root of H. cordata., limiting them to transfer to the shoot to reduce the toxicity of heavy metals on H. cordata.. The distribution of Pb in the body cells- level of H. cordata. was:cell wall> soluble components> organelles, cell wall plays an important role in binding with heavy metals and detoxification, which can reduce Pb poisoning on H. cordata. The distribution of As in the body cells- level of H. cordata. was:soluble components> cell wall> Cell device. Cell organelle is the location for various physiological activities, the contents of Pb and As are maintained at a relatively low level, which is significant to guarantee the normal physiological activities of H. cordata..6. The order of content in various forms of Pb in soil under the single treatment of Pb was: exchangeable> organic bound> residual> carbonate bound> Fe-Mn oxides. The content of exchangeable Pb increased with the concentration of Pb in the treatment, the content of residual Pb reduced to minimum when As was added, indicating that As shows a certain activation on Pb. The correlations of Pb content in exchangeable and organically bound with Pb content in plants were the highest, which were the main form of absorption Pb in H. cordata.. The order of content in. various forms of As in soil was:organic bound> Fe-Mn oxide phase> sulfide> carbonate> exchangeable. The proportion of exchangeable, which is the most easily absorbed form of plants, is only about 1%, but it's the main form of H. cordata. that accumulated As as its highest relevance to the content of As in H. cordata. The content of exchangeable As was extremely low, indicating that As bioavailability in soil is very low and it's less harmful to H. cordata..