| Soil cadmium(Cd)pollution has become a very serious global environmental problem in recent years,which has caused harms to organisms and even to the whole environment.Compared with traditional physical and chemical remediation,bioremediation has the advantages of low cost,easy operation,no secondary pollution,environmental friendliness and high efficiency.Among them,endophytes have unique advantages in promoting host growth,improving host resistance,and changing the form of heavy metals due to their favorable niche.Thus,endophytes-host plants associated remediation has obtained great attention.Biochar has the characteristics of high specific surface area,developed pore structure and good environmental stability.It is a high-performance carrier for functional microbial agents in soil improvement applications.However,there are few studies on microbial combined with biochar to assist plants to remediation heavy metals,and the mechanism remains unclear.In this study,the common pioneer tree species Robinia pseudoacacia on heavy metal contaminated sites in mining areas is used as a model plant.And a highly Cd-resistant Enterobacter sp.YG-14 isolated from the roots of poplar trees in the lead-zinc mining area and sludge biochar were selected as experimental materials to reveal the mechanism of plant endophytic bacteria combined with biochar to enhance cadmium remediation of R.pseudoacacia.The following experimental results were mainly obtained:(1)The growth-promoting effects of YG-14 on R.pseudoacacia: YG-14 can produce a variety of substances that promote plant growth.The pot experiment found that YG-14 can be successfully colonized into R.pseudoacacia,especially the YG-14 reisolation rate of roots is as high as 80.0%,which is better than that of the shoots(14.3%).Compared with the control group,the plant height,root length,dry weight of aboveground and underground parts,total chlorophyll content and nitrogen content of the R.pseudoacacia inoculated with YG-14 were significantly increased.Especially,the R.pseudoacacia's root dry weight increased 78.85%,and the number of root forks,crossings,surface area and volume increased by 84.45%-147.97% after inoculated with YG-14.It can be seen that YG-14 promoted the growth and root development of R.pseudoacacia.(2)Under Cd stress,the synergistic effect of YG-14 and biochar on the growth and Cd accumulation of R.pseudoacacia: Compared with the control,YG-14 inoculation alone and the biochar addition alone,the YG-14 combined biochar group improved the growth and photosyntheic capacity of R.pseudoacacia to the greatest extent.At the same time,the Cd accumulation of per plant in the YG-14 combined biochar group reached the maximum,which was 5.50 ?g/plant.(3)The effect of YG-14 combined with biochar on soil Cd content and microbial community structure: Compared with the control group,YG-14 inoculation alone,the biochar addition alone and YG-14 combined with biochar can increase the pH value of R.pseudoacacia rhizosphere soil.Meanwhile,the total Cd and extractable Cd content in the soil were reduced,and the microbial community structure in the rhizosphere of R.seudoacacia was changed.After YG-14 combined with biochar,the species and abundance of nitrogen-fixing bacteria in the soil increase significantly.In conclusion,the combination of endophytic bacteria YG-14 and sludge biochar reduced the soil Cd content and biological toxicity,increased plant Cd accumulation,and effectively prevented the translocation of Cd to the above-ground part,and improved the growth of R.seudoacacia under Cd stress.In addition,YG-14 combined with biochar increases the diversity of bacterial communities and improves the structure of nitrogen-fixing bacteria.This study constructed a "plant-microbebiochar" associated remediation system and revealed the mechanism,providing a theoretical basis for the application of the system in the remediation of Cd contaminated sites. |
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