Effective alleviation of Cd stress to microbial communities in mining reclamation soils by thiourea-modified biochar amendment

Abstract

Reclaimed soils in mining area usually display low fertility and present Cd stress. The amendment of modified biochars effectively fixes Cd in soils, enhances soil fertility, and reduces Cd stress in soil microorganisms. However, the effect of thiourea-modified biochar (TBC) on microbial adaptability to Cd stress in mining reclamation soils is still unclear. The present work studied the effects of TBC amendments on Cd immobilization and microbial community changes in a mining reclamation soil displaying extreme Cd contamination. The results indicated that the amendment of TBC significantly enhanced ( P < 0.05) soil pH, the content of available phosphorus (AP), and the activities of urease and polyphenol oxidase by 1.3%, 463.4%, 54.4%, and 84.0%, respectively, compared to the control. The amount of toxicity characteristic leaching procedure-extracable Cd decreased ( P < 0.05) by 68.0% in the TBC-amended soils. TBC presented a more active response to the Cd stress, while the structure of soil microbiota was reorganized and the alpha diversity index was increased. TBC amendment increased the relative abundances of Proteobacteria, Bacteroidota, and Zoopagomycota, which were strongly associated ( P < 0.01) with higher soil pH and AP. Structural equation models demonstrated that the effect of Cd immobilization was directly influenced by soil pH, AP, and urease, and indirectly affected by bacterial structure in TBC treatment. TBC amendment can effectively improve the structural composition of soil bacteria under Cd stress, as well as enhance the pathways of decreasing soil Cd availability. The results might facilitate the development of in-situ remediation programs in Cd-contaminated soils in the future.