Effects Of Phosphorus Solubilizing Microbial Fertilizer With Broussonetia Papyrifera On Remediation Of Copper Contaminated Soil

The idea that green mountains are mountains of gold and silver put forward higher requirements for ecological civilization construction,so we should give consideration to ecological benefits while developing economy.Mining can bring huge economic benefits,but it also causes serious damage to ecological environment.Therefore,remediation of soil heavy metal pollution has become a hot issue in environmental pollution research.Phytoremediation technology is an economical,simple and environmentally friendly remediation technology.As most of the contaminated soil in mining area is barren of nutrients,the environment is harsh and heavy metal complex pollution degree is high,resulting in small biomass and slow growth of remediation plants,difficult to establish in the soil,resulting in limited remediation efficiency of heavy metals.Broussonetia papyrifera（L.）L’her.ex Vent.has the characteristics of fast growth,strong adaptability and wide distribution,and can be used as a pioneer tree to restore heavy metal contaminated soil vegetation.Phosphorus soluble bacterial fertilizer can improve contaminated soil,optimize plant rhizosphere environment and increase plant biomass.At the same time,organic acids and siderophores were secreted by microorganisms to increase the bioavailability of heavy metals and promote the accumulation of heavy metals in plants.Therefore,PSM fertilizer combined with Broussonetia papyrifera has great application potential in remediation of heavy metal contaminated soil.In this experiment,Burkholderia screened from forestland was used as microbial agent and PSM fertilizer was prepared.The cop-contaminated soil in Dexing,Shangrao city,Jiangxi Province was used as the research object.Three treatments,control（CK）,biological agent（SW）and PSM fertilizer（JF）,were set up through soil ripening test.Soil chemical indexes,copper occurrence speciation indexes and microbial diversity were determined to explore the effect of PSM fertilizer on copper pollution soil improvement and copper content.The growth characteristics,copper accumulation and other indicators of Broussonetia papyrifera were measured through pot experiment,and the effects of PSM fertilizer on copper enrichment characteristics of Broussonetia papyrifera and copper contaminated soil remediation were explored,aiming to provide theoretical basis and technical support for copper pollution improvement and remediation of soil.Specific research results are as follows:（1）The root length,plant height,ground diameter and biomass of the treatment were higher than those of the control treatment,and the growth promoting effect was more significant.The enrichment ability of the roots was higher than that of the stems and leaves,and the PSM fertilizer promoted the enrichment ability of the roots.The copper content in the roots of the three kinds of soil was the highest in the bacterial fertilizer treatment,which was44.63～113.24 mg·kg^-1,17.08%～186.38%higher than that in the CK treatment.At the same time,bacterial fertilizer inhibited the copper transfer ability of the tree,and the copper content in the leaf part of the three soils was the lowest.The total amount of copper extracted by combined treatment of PSM fertilizer was the highest,reaching 648.42μg·pot^-1,2202.38μg·pot^-1and 1259.92μg·pot^-1,which could significantly improve the removal rate of copper in low and high copper contaminated soil and reduce the total copper content in copper contaminated soil.PSM fertilizer can enhance the remediation efficiency of cu-contaminated soil by Broussonetia papyrifera.（2）PSM fertilizer treatment could significantly increased soil organic matter,total k,available K,total N,available P and other nutrients.The available potassium content of low cu and high Cu polluted soil under bacterial fertilizer treatment was 512.42 mg·kg^-1and 494.69mg·kg^-1,and the available phosphorus content was 1.84 mg·kg^-1and 0.95 mg·kg^-1,which were significantly higher than those under control and biological agent treatment.PSM fertilizer can significantly increase soil nutrients,improve soil fertility and improve copper contaminated soil.（3）PSM fertilizer treatment could increased the available copper content in soil contaminated with low cu and high Cu,reaching 35.85 mg·kg^-1and 57.00 mg·kg^-1,significantly higher than that of control treatment and biological agent treatment.Both biological preparation and PSM fertilizer increased the content of soil acid soluble copper,improved the bioavailability of copper,and promoted the absorption and accumulation of copper by plants.In low copper polluted soil,the transformation of residual copper and reducible copper to acid-soluble copper and oxidizable copper was promoted by PSM fertilizer,and in high copper soil,the transformation of reducible copper and oxidizable copper was promoted.In conclusion,PSM fertilizer can activate available copper content in copper-contaminated soil,increase soil copper bioavailability,and promote plant enrichment.（4）The results showed that both biological agents and PSM fertilizer treatments reduced soil Shannon index,Simpson index,Chao1 index and Ace index,and changed the bacterial community structure in copper contaminated soil to a certain extent.It was found that Proteobacteria,Firmicutes and Bacteroidetes were the three dominant species in phylum level.Redundancy analysis（RDA）showed that soil p H and available copper content were significantly positively correlated with relative abundance of Firmicutes and Bacteroidetes,while relative abundance of Proteobacteria was closely correlated with soil organic matter,total NPK,available K,available P and other soil nutrients.The relative abundances of Proteobacteria,firmicutes and Bacteroidetes were enriched in different degrees under PSM fertilizer treatment.In conclusion,PSM fertilizer can effectively improve copper-contaminated barren soil,optimize the plant ecological environment,promote the growth and biomass accumulation of Broussonetia papyrifera in copper-contaminated soil,and effectively solve the bottleneck problems of short plant growth,slow growth and low biomass in phytoremediation.At the same time,the bioavailability of copper in copper-contaminated soil was improved,and the accumulation of copper by Broussonetia papyrifera was increased,so as to promote the overall enrichment capacity of Broussonetia papyrifera and improve its remediation efficiency.Therefore,the combination of microbial and PSM fertilizer and Broussonetia papyrifera has a good remediation effect on copper contaminated soil,which can provide a theoretical reference for the subsequent improvement and remediation of copper contaminated soil.