Effects Of Biochar On The Enzyme Activity And Bacterial Community In The Wetland Soil Contaminated By Pb And Cd

Soil enzymes and bacteria are involved in various important biogeochemical processes in the soil ecosystem and are highly sensitive to heavy metal pollution.They reflect the ecological health level of the soil environment.Biochar has strong adsorption capacity for heavy metals due to its own characteristics,and it also can immobilize heavy metals in the soil and can be used to relieve heavy metal pollution in soil.In this study,several kinds of biochars were selected by the effect of adsorption and fixation of heavy metals in solution and soil,and the effects of several biochars on soil ecological environment were analyzed.According to the results of the two previous experiments,the selected biochar was added to heavy metal-contaminated soils to investigate the changes of soil enzyme activities and bacterial communities under the influence of Pb\Cd pollution and biochar.This study provided basis for the feasibility of reed biochar as a repair material for heavy metal pollution in wetlands.The main research contents and conclusions are as follows:(1)The physical and chemical properties of biochar have a close relationship with pyrolysis conditions.The yield of biochar decreased with the increase of pyrolysis temperature and time;with the increase of pyrolysis temperature and time,the content of oxygen-containing acidic functional groups on the surface of biochar decreased;biochar had a distinct pore size structure,large specific surface area and a lot of surface micropores.The adsorption rate of biochar on heavy metal ions increased with the increase of pyrolysis temperature and time.Suaeda salsa biochar(SB)had the highest adsorption rate of heavy metals.The coexistence of two heavy metals could lead to competitive adsorption behavior.Biochar promoted the conversion of soil Pb from the active to the residue state.The Phragmites australias biochar(PB)had the immobilization effect on soil Pb firstly,and then shown a certain degree of mobilization effect.On the other hand,the addition of biochar promoted the availability of Cd ions in the soil.(2)Pb had a significant inhibitory effect on urease,and had a "promotion and subsequent inhibition"effect on invertase with increasing concentration of Pb(this kind of effect was abbreviated in "promotion at low and inhibition at high" below);Cd had a significant inhibitory effect on invertase,and had a"promotion at low and inhibition at high" effect on urease;Pb had a significant inhibitory effect on catalase.The interaction between Pb and Cd had a significant effect on catalase,and Pb dominated in the interaction effect.Biochar significantly increased the activity of invertase.SB and PB showed"promotion at low and inhibition at high" effects on catalase,and Tamarix chinensis biochar(TB)significantly inhibited the catalase.Under heavy metal pollution,the addition of PB can alleviate the inhibition of urease activity by heavy metals.The effect of the amount of biochar added was the dominant factor influencing soil invertase activity.The effect of biochars on catalase activity was not significant.(3)The dominant bacterial populations in the heavy metal polluted wetland soil are Acidobacteria,Actinomyces and Bacteroidetes.Under the combined pollution of Pb and Cd,the low concentration of Pb increased the abundance and diversity of bacteria,and increased the proportion of bacteria which are resistant to Pb in soil.The high concentration of Pb decreased the abundance and diversity of bacteria.With biochar addition,the dominant bacteria in the wetland soil converted to Proteobacteria,Monasthrma,Bacteroidetes,and Actinomycetes.The addition of PB increased the abundance and diversity of bacteria,and the high amount addition of SB biochar significantly reduced the abundance and diversity of bacteria.The difference of biochar had a great influence on the bacterial community structure,followed by the amount of addition.The PB could better maintain the soil bacterial communiy structure in the original soil.With the addition of PB to polluted wetland soil,the dominant bacteria in the soil were Proteobacteria,Monastridium and Bacteroidetes.When PB was added into the heavy metals contaminated soil,the abundance and diversity of bacteria were increased.In the presence of biochar,the abundance and diversity of bacteria decreased with increasing concentrations of heavy metal.Heavy metal concentration had a greater impact on the bacterial community structure,followed by the addition amount of PB.(4)The most sensitive bacteria to biochar addition was different between soil with and without heavy metal addition.In non-metal-added soils,the differences between biochar treatment and addition were mainly reflected in a-Proteobacteria,S-Proteobacteria,Lactobacillus,and Bacillus;while in metal-added soils,differences of PB treatments were reflected in the ?-Proteobacteria,Bacteroidetes,Cyanobacterial.