| Arsenic exists widely in the environment,which is extremely toxic and harmful to biological health.At present,arsenic is one of the recognized,ubiquitous and harmful carcinogens.A survey conducted by the Ministry of Land and Resources in 2014 found that the over-standard rate of arsenic pollution in China's soil accounted for 2.7%.Microbial enhancement of Pteris vittata for remediation of arsenic-contaminated soil is a green and environmentally friendly remediation method,which has certain value in remediation of arsenic-contaminated sites.Studies have shown that arsenic-reducing bacteria can improve the efficiency of enrichment of arsenic in soil by Pteris vittata,but the research on its promoting mechanism is not in-depth,especially the specific impact of arsenic reduction on it is unknown.Therefore,in this paper,the effects of wild-type arsenic-reducing bacteria and arsenic-reducing gene-deficient strains on the growth and arsenic enrichment of Pteris vittata were studied by pot experiment By measuring the basic properties of wild-type and mutant arsenic-reducing bacteria,total arsenic content in different parts of Pteris vittata,arsenic content in rhizosphere and non-rhizosphere soil and antioxidant enzyme activity in Pteris vittata leaves,the aim was to clarify the effects of arsenic-reducing ability and growth-promoting ability on the growth and arsenic enrichment of Pteris vittata,and to provide theoretical basis for microbial-plant remediation of arsenic-contaminated soil.The main conclusions are as follows:1.The effects of arsenic-reducing gene knockout on the properties of arsenic-reducing bacteria were studied.The arsenic reduction ability of mutant E.coil WC3110 strain was reduced from 55.21% to 28.35%.It had no significant effect on the growth of arsenic-reducing bacteria,and the ability of producing indoleacetic acid,dissolving phosphorus and producing iron carrier.2.Both wild-type and mutant arsenic-reducing bacteria can promote the growth of Pteris vittata.Wild-type arsenic-reducing bacteria can promote the growth of Pteris vittata more obviously.After being cultivated in Yunnan and Guangxi polluted soil for 60 days,the biomass of Pteris vittata treated by wild-type arsenic-reducing bacteria increased by 12.45%and 13.68%,and the biomass of underground parts increased by 58.11% and 12.51%,respectively,indicating that the strain with strong arsenic-reducing effect can promote the biomass of Pteris vittata more.3.Both wild-type and mutant arsenic-reducing bacteria can significantly improve the absorption of arsenic by Pteris vittata,and the wild-type arsenic-reducing bacteria can significantly improve the efficiency of arsenic enrichment by Pteris vittata.In two soil planting environments,after 30 days and 60 days of growth of Pteris vittata.,compared with the mutant addition treatment,the wild arsenic-reducing bacteria treatment significantly increased the arsenic concentration in its leaves,ranging from 11.33% to 28.64%,and significantly decreased the arsenic concentration in rhizosphere soil.By calculating the enrichment coefficient,it was found that after 60 days of growth,the enrichment coefficients of Pteris vittata were 8.07 and 5.18,which increased by 47.26% and 27.27% respectively compared with the mutant strain treatment,indicating that arsenic reduction can promote the absorption of arsenic by Pteris vittata in soil.4.The addition of wild-type and mutant arsenic-reducing bacteria will affect the enzyme activity in Pteris vittata leaves.In two soil planting environments,after 30 days and60 days of growth of Pteris vittata,the activity of superoxide dismutase in leaves of Pteris vittata was significantly increased by 7.81% and 16.95% compared with that of mutant addition.The POD activity of Pteris vittata leaves increased significantly after adding wild arsenic-reducing bacteria to Guangxi soil for 60 days,which increased by 13.39% compared with the mutant group.Compared with mutant group,CAT activity decreased by 22.45%after adding wild-type arsenic-reducing bacteria to Yunnan soil for 60 days.after adding wild-type and mutant arsenic-reducing bacteria to Guangxi soil for 60 days,CAT activity in Pteris vittata leaves had no significant difference,but changed significantly and decreased by 28.81% and 27.31%,respectively.The results indicated that arsenic reduction could affect the antioxidant enzyme activity of Pteris vittata.To sum up,arsenic reduction can promote the biomass of Pteris vittata on the one hand;On the other hand,it can affect the antioxidant enzyme activity in Pteris vittata,and finally significantly improve the arsenic enrichment efficiency of Pteris vittata.The research results of this paper provide an important theoretical basis for the remediation of arsenic contaminated soil by Pteris vittata combined with microorganisms. |
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