Effects of sheep-manure- and humic-acid-based amendments on alpine mine soil restoration

Unsustainable mining on the Tibetan Plateau has disrupted vegetation and soil, depleting nutrients and altering bacterial communities. We assessed the effects of humic acid and sheep manure on soil physicochemical properties, plant growth, and bacterial communities in reclaimed alpine mine soils at 4,000-4,200 m using 16S rRNA sequencing. Low doses of humic acid increased soil organic matter and nitrogen but reduced phosphorus, while sheep manure enhanced all measured nutrients and decreased heavy metal concentrations. The most effective treatments were K1_4 and K2_3. Dominant bacterial phyla included Proteobacteria, Firmicutes, Bacteroidota, Actinobacteriota, and Acidobacteriota, with key genera such as Lysobacter and Bacillus. Amendments increased bacterial diversity, primarily influenced by bulk density, available phosphorus, potassium, and organic matter. Functional predictions highlighted genes related to transcription, translation, and ribosomal processes. These findings demonstrate that organic amendments improve soil fertility, microbial diversity, and plant growth, guiding ecological restoration in extremely high-altitude mining regions.