Soil sulfur cycle bacteria and metabolites affected by soil depth and afforestation conditions in high-sulfur coal mining areas

Abstract

This study aimed to clarify the changes in sulfur-driven microorganisms and sulfur metabolic pathways in the vertical soil profile during the restoration of different afforestation types. Soils of varying afforestation patterns (grassland, shrubland, woodland) in high‑sulfur coal mining areas (Gujiao City, China) were analysed to determine the characteristics of the sulfur distribution, microbial community structure, and sulfur metabolites in shallow (10 cm), middle (30 cm), and deep (50 cm) soils. Compared with the area without vegetation, the soil in the planted area had higher total soil S (5.1–58.6 %), Fe (37.5–67.4 %), and Cu (28.3–54.2 %); the content of these elements showed a consistent increase with depth. Afforestation resulted in increased pH by 0.8–1.3 pH units, organic carbon (1.6–2.9 times), total N (30.2–46.9 %), and available N (58.3–78.2 %) in the soil. Additionally, the electrical conductivity of the shallow soil in the three plant cover areas decreased by 78–82 %. The diversity of 16S bacterial showed that different afforestation types shaped the structure of specific microbial communities at different soil depths. Afforestation also showed a promotion of abundance of soil sulfur-related microorganisms (e.g., Desulfovibrio (0.8–34.2 %), Acidiferrobacter (0.3–32.8 %), Acidithiobacillus (1.2–21.7 %), and Thiomonas (0.6–15.6 %)). Plant cover induced the vertical spatial distribution pattern of sulfur metabolites in high-sulfur coal mines showing a shallow > middle > deep layer, and afforestation enhanced the transformation process of sulfur metabolites in shallow soil. The main metabolic pathways for soil sulfur metabolism involve sulfur-containing amino acids, such as cysteine and methionine metabolism, taurine, and hypotaurine. Interaction analysis indicated that Lysobacter, Luteimonas, and Leptospirillum made greater contributions to the changes in sulfur metabolites. The findings from this study suggest that the distribution of sulfur and soil properties in vertical depth soil of different afforestation types in high-sulfur coal mining areas recruit specific bacteria, which drive soil sulfur metabolic conversion and reestablishment of soil sulfur homeostasis, and the shallow layers of the soil were critical areas for turnover of sulfur metabolite. These results provide insights for understanding biochemical sulfur cycling in vertical soil depth under different afforestation models.