Effects Of Bamboo Charcoal And Humus Addition On Bioavailability Of Manganese In Tailings Soil

In this study,mine sludge and mine tailings were collected from Xiangtan manganese mine wasteland and used as a soil substrate(mixed with a mass ratio of 1:1,referred as "ST").Bamboo biochar and humus(referred as "BC" and "HS",respectively)were added to the soil substrate.There were 13 treatments in total:three treatments with single addition of bamboo biochar,referred as group A(ST+1%BC),group B(ST+2%BC)and group C(ST+5%BC);three treatments with single addition of humus,referred as group D(ST+1%HS),group E(ST+2%HS)and group F(ST+5%HS);six treatments with mixed addition of bamboo biochar and humus,referred as group G(ST+1%BC+2%HS),group H(ST+2%BC+1%HS),group I(ST+1%BC+5%HS),group J(ST+5%BC+1%HS),group K(ST+2%BC+5%HS)and group L(ST+5%BC+2%HS).A potted experiment was carried out in greenhouse for one growing season with 1-year-old seedlings of Koelreuteria paniculata in the above soil substrates.The physical and chemical properties of soil substrates were investigated with routine procedures.Growth of K.paniculata under different treatments was also measured.At the same time,the new DGT(diffusive gradients in thin films technique,DGT)technique was used to evaluate the biological availability of manganese in soils comparing with the traditional chemical methods(including HAc solution extraction and EDTANa2 solution extraction).The aim of this study was to find an optimal method to predict the uptake of manganese by plants in soils and to explore effects of different soil substrates on the soil physicochemical properties and manganese bioavailability and bioconcentration.The main results were as followed:(1)The addition of bamboo biochar and humus changed the physical and chemical properties of soil.The main results were as followed:the pH and CEC of the soil were increased,the bulk density of the soil was decreased,the redox potential of the soil was increased and the mechanical composition of the soil was changed.The physical and chemical properties of soil were changed more greatly by adding both bamboo biochar and humus than single adding bamboo biochar and humus respectively,and group K and group L had the greatest effect on soil physical and chemical properties.(2)Bamboo biochar and humus changed the occurrence form of heavy metals,then affected the migration and biological availability of heavy metals in soil,and finally played a role in passivation of heavy metals.The passivation effect of bamboo biochar and humus was affected by its effective content.The effect of compound addition of bamboo biochar and humus varied with different dosage ratio,which was slightly stronger than that of single addition of bamboo biochar and humus.In this experiment,the content of manganese in the organs of K paniculata was the lowest and the growth rate was the best under the treatment of group K.It proved that the addition of bamboo biochar and humus played a role in the co-remediation of manganese pollution in soil to a certain extent.(3)The addition of bamboo biochar and humus had a significant effect on the biomass of K.paniculata.It promoted the growth of fine roots,increased the biomass of K.paniculata and changed the distribution of manganese content in different organs of K.paniculata.(4)Compared with the traditional chemical methods,the manganese absorption of K paniculata predicted by DGT technique was more close to the actual situation.Moreover,the influence of soil properties on the prediction ability of different methods was further studied by using multiple linear regression method,and it was found that the traditional chemical methods were influenced by pH and CEC(cation exchange capacity,CEC).This suggested that pH and CEC of the soil must be considered when using traditional methods to evaluate the biological availability of manganese in soil.The DGT technique was not affected by the basic physical and chemical properties of the soil,so it was an effective way to evaluate the absorption of heavy metal in the soil.