The Study Of Underground Ecological Process Of Rhizoremediation For Co-Contaminated Soil With Pahs And Cd For Acorus Calamus L. And Xanthium Sibiricum Patr

Phytoremediation for HM (Heavy metals) and PAHs (Polycyclic aromatic hydrocarbons) is an economic and environmental friendly method for contaminated soil. More concerns should be focused on the ecological process and mechanism of phytoremediation instead of merely the remediation effectivity for different plants facing more and more severe soil pollutions today. It has a significant meaning for us to understand the underground process and mechanism of phytoremediation to have insights into the essence of it and selecting the suitable species. This study chose Acorus calamus L. and Xanthium sibiricum Patr to study their root response and rhizosphere variations to PAHs (PHN and PYE) and Cd as co-contaminants. The parameters included root structure (root length、root volume、root surface and root tips)、root biomass、total stem growing length、rhizosphere soil enzymes (PPO and DH) and accumulated/uptake amounts of pollutants.Two way ANOVA was used to analyze the contributions of different factors (Plant species and pollutant types) on above parameters.Correlation analysis was used to study the correlationship between these underground crucial factors and the accumulated/uptake amounts of pollutants.The results from above analysis were to explain the possible underground ecological process while the phytoremediation phase and the differences in tolerance abilities for two plants.The main results are:1. Effects on root structures:High concerntration of PAHs has a significant effect on promoting the root growth of Acorus calamus L. (P<0.01), while cadmium would inhibit it;under co-contaminated circumstance, PAHs has a more profound effect on roots of Acorus calamus L. Roots of Xanthium sibiricum Patr would be significantly restrained by high concerntration of PAHs and Cadmium.2. Effects on rhizosphere soil enzymes:Both PAHs and Cd have significant effects on rhizosphere soil enzymes for two plants and interactions with each other (P<0.05).High concerntration of Cd would restrain the PPO enyme activity in the rhizosphere of Acorus calamus L. however this inhibiting effect would disappear because of the promoting effect of PAHs. Their interation shows that the inhibiting effect of Cd would disappear while PAHs was present and PAHs would promote the PPO enzyme activity significantly.Co-contaminants of Cd and PAHs would significantly inhibit the dehydrogenase while single pollutants with PAHs would affect more.Cd would promote the PPO enyme activity in the rhizosphere of Xanthium sibiricum Patr while the increasing amount of PAHs would reduce its activity significantly. The interation between Cd and PAHs was PAHs’inhibiting effect would exceed the promoting effect of Cd.3. Effects on shoot growing length and biomass:Under co-contaminated circumstance, PAHs was the main factor affecting the shoot growing length and underground biomass (P<0.05).It showed that PAHs would significantly promote the shoot growth and biomass accumulation for Acorus calamus L. Both Cd and PAHs would affect the shoot growth of Xanthium sibiricum Patr significantly (P<0.05). It showed that Cd and high concerntration of PAHs would promote the shoots to grow significantly for Xanthium sibiricum Patr.4. Effects on accumulated/uptake of pollutants:Both Cd and PAHs have significant impact on root accumulating/uptake of pollutants for two plants (P<0.05). It showed that uptake of PAHs for Acorus calamus L. would increase in low concerntration of co-contaminats. Xanthium sibiricum Patr would take up more PAHs in the roots with the increasing of PAHs in the treatments.Roots of Acorus calamus L. would accumulate less Cd with PAHs concerntration increasing, however Xanthium sibiricum Patr would accumulate more Cd in high concerntraiton of Cd treatments but less in low concerntration treatments.5. Correlation analysis results and the possible ecological process for two plants while phytoremediation:The more PAHs Acorus calamus L. took up,the more restrained of its roots structure (root volume and root surface) and soil microbes (PPO and DH).Roots of Acorus calamus L. would accumulate less Cd with the increasing amout of PAHs in the soil.However, increasing PAHs would promote its rhizosphere soil microbe activity which led to more PPO activity in the soil and more degraded PAHs which promote the root growth. In conclusion, Acorus calamus L. tended to degrade PAHs in the rhizosphere with the help of micobes and less uptake of it into roots to decrease the concerntration while the remediation phase. Degraded PAHs would promote microbe activity and strengthen the ability to tolerate Cd because of high biomass and vigorous roots. Xanthium sibiricum Patr would take up more PAHs with higher concerntration of PAHs in the soil.However, the more PAHs taken up in the plant, the more restrained to the root structure and biomass. This would affect the growth of Xanthium sibiricum Patr. Similarly, Xanthium sibiricum Patr would accumulate more Cd in the root with higher Cd concerntration in the soil.However,the more Cd acculumated in the plant, the more restrained on root tips and root expansion.Thus, Xanthium sibiricum Patr tended to accumulate/take up pollutants directly to reduce the amount of pollutants in the soil.Although high amount of pollutants in the plant would be toxic and harmful for Xanthium sibiricum Patr to grow, it can still grow vigorously because of its high tolerance ability.