Effects of soil conditioners on microbial communities in alpine mining areas

Unsustainable mining activities have severely disrupted vegetation and soil structure on the Tibetan Plateau, leading to nutrient depletion and alterations in soil bacterial communities. Humic acid amendment and sheep manure are important for soil improvement in mining areas. However, the effects of humic acid amendment and sheep manure on the structure and microbiota of reclaimed soils remain insufficiently understood. In this study, we first investigated the influence of two environmental amendments on soil physicochemical properties and bacterial communities in reclaimed soils from the Qinghai-Tibet mining area using 16S rRNA sequencing technology. Humic acid and sheep manure enhanced soil physicochemical properties and nutrient dynamics. In contrast, sheep manure significantly increased the levels of all measured soil nutrients. While humic acid marginally increased some metal levels without going over concern thresholds, sheep manure also decreased soil heavy metal concentrations. The most effective treatments in terms of promoting plant growth and biomass accumulation were K1₄ and K2₃. The dominant bacterial phyla identified included Proteobacteria, Firmicutes, Bacteroidota, Actinobacteriota, and Acidobacteriota, with key genera such as Lysobacter, Thiobacillus, Thermomonas, and Bacillus. All treatment groups exhibited increased bacterial diversity, with K1₄ and K2₂ showing the highest diversity indices. Soil bulk density (SBD), AP, AK, and SOM were identified as the primary factors influencing bacterial community structure. Functional predictions revealed high relative abundances of genes associated with transcription, ribosomal structure, and translation processes. In conclusion, both sheep manure and humic acid substantially improved soil microbial diversity and physicochemical properties, offering valuable insights for the ecological restoration of degraded soils in alpine mining regions.