Immobilization Effects Of Earthworms/Cerium-Manganese Modified Biochar On Arsenic In Red Soils

Soil As pollution has become an important global environmental problem,and red soil As pollution in southern China is more prominent.Therefore,the remediation of red soil As pollution is in urgent need.In this study,the effects of Eisenia foetida/MBC on the regulation of As in soil-plant system were investigated.Six treatments were set: Contaminated soil control(CK),Contaminated soil + earthworms(AE),Contaminated soil + biochar(AB),Contaminated soil + earthworms + biochar(AEB),Contaminated soil + MBC(AMB),Contaminated soil + earthworms + MBC(AEMB).The main results were as follows:(1)The results of the soil culture test showed that in the treatments of earthworms and biochar(modified),The content of soil water-soluble arsenic(WSAs)under each treatment was ranked as follows: AB > CK > AEB > AMB > AE > AEMB;the combined treatment of AEMB with cerium-manganese modified biochar and earthworms greatly reduced the content of water-soluble arsenic(WSAs)in the soils,the fixation efficiency of soil As was as high as 77.59%.The fixation effect of soil As was the best,and the two synergistic deactivation effects were obvious.And the combined effect of earthworms and cerium-manganese modified biochar greatly reduced the mobility of As in the soil.The activities of soil catalase decreased,and the activities of soil urease and phosphatase were significantly increased,while the activities of soil sucrase were not significantly affected by AEMB treatment.(2)The results of the pot experiment showed that the single or combined treatments of earthworms,biochar and cerium-manganese modified biochar resulted in an increase in water spinach biomass and a significant increase in yield.Among them,the above-ground plant yield increased by 44.12% in the AEMB treatments;Except for biochar treatments AB other treatments significantly reduced the As content of water spinach.The sequence of As content in water spinach of each treatment was: AB >CK > AEB > AE > AMB > AEMB.Among them,the As content in the shoots and roots of plants treated with AEMB was reduced by 44.67% and 72.21%,respectively.AEMB significantly reduced the absorption of arsenic by crops.AEMB had no negative effect on soil enzyme activities.The activity of catalase in soil was significantly increased by Ce-Mn modified biochar(P<0.05),but the activity of catalase was decreased by earthworms treatment,while the activity of sucrase was significantly increased.The activity of soil catalase decreased and the activity of soil urease was significantly increased,but the activities of phosphatase and sucrase were not significantly affected by AEMB treatment.(3)The results of spread plate and diversity index analysis showed that the combination treatment of earthworm and Ce-Mn modified biochar promoted the increase of bacteria,fungi and actinomycetes.The bacterial diversity index chao1,PD＿whole＿tree and Shannon index in the soil under single earthworms treatment showed an increasing trend,and the Shannon index of each treatment was AE >CK > AEB > AEMB > AB > AMB,The addition of earthworms significantly increased the abundance and diversity of bacteria in arsenic-contaminated soil(P<0.05);The Shannon index of fungi under each treatments were ranked AE > AEMB > CK > AEB > AB > AMB,and the combined effect of the two was greatly improved the soil bacterias and fungus richness(P<0.05).(4)From the single or combined action of earthworms,biochar and cerium-manganese modified biochar,the changes in the bacterial community structure in arsenic-contaminated red soil can be seen from the perspective of the bacterial phylum Proteobacteria and Bacteroidetes.The relative abundance increased significantly,with AEMB treatment increasing the most,followed by AE treatment,while the relative abundance of Acidobacteria and Chloroflexi decreased,with AEMB treatment decreasing the most.The addition of earthworms significantly promoted the growth of γ-Proteobacteria,Flavobacterium,Aeromonas and Variovorax.(5)The 18s rDNA analysis showed that biochar(modified)inhibited the growth of the fungus Ascomycota in the soils,while earthworms increased its relative abundance;In each treatments of earthworms/biochar(modified),the relative abundance of Mortierellomycota increased,while the relative abundance of Basidiomycota decreased significantly(P<0.05).AEMB treatment caused a slight decrease in the relative abundance of Basidiomycota.But it stimulated the growth of Ascomycota and Mortierellomycota.