Effects of long-term (10 years) remediation of Caragana on soil enzyme activities, heavy metals, microbial diversity and metabolic spectrum of coal gangue

Phytoremediation is a means of remediation of coal gangue pollution. However, the molecular mechanism of the effect of long-term plant restoration on soil microecology has not been elucidated. This study explored the mechanism of soil-microbe-metabolite interaction after long-term recovery of Caragana korshinskii Kom. We analyzed the physical and chemical properties, enzyme activities, microbial community structure, metabolome and ionomics of the shallow (10 cm), middle (50 cm) and deep (100 cm) rhizosphere and bulk soils after C. korshinskii restoration for 10 years. The activities of soil urease, sucrase, and acid phosphatase mainly increased in the rhizosphere area of C. korshinskii. The microbial abundance increased by 8.5%, 25.0%, and 15.2% in the shallow, middle, and deep levels, respectively. The ionomics results showed that the total Sr, Mn, Fe, Th, Rb, Bi, S, Se, Pb, U, Ni, Ba content in the rhizosphere soil decreased by 0.10–1.06 times (Log2 FC), and the effective state elements increased by 0.21–2.24 times (Log2 FC), there is still a risk of metal pollution in the gangue area. Metabolomics shows that lipids and lipid molecules, organic acids, phenylpropane and polyketides are the main differential metabolites; C. korshinskii repair stimulates the circulation pathways of terpenoids, lipids, amino acids, and carbohydrates. S, Fe, Mn and lipids, organic acids, and organic oxygen compound metabolites drive Acidthiobacillus, Sulfurifustis, Deferrobacterium, Pseudomonas and Sphingomonas to become dominant strains, regulates element metabolism and accelerates the process of environmental restoration.