Effects of soil covering on bacterial communities and C/N functional genes during phytoremediation of copper tailings

Copper tailings, a mining waste, pose environmental threats, and phytoremediation commonly employs soil covering to improve substrate properties and promote vegetation recovery. This study was conducted at the Yangshanchong Tailings Reservoir in Tongling City, Anhui Province, to comprehensively evaluate changes in soil physicochemical properties, bacterial community structure, and carbon/nitrogen functional genes during copper tailings remediation. We compared areas with and without soil covering, which were vegetated by two dominant species, Imperata cylindrica and Miscanthus floridulus, across profile depths of 0-20 cm, 20-40 cm, and 40-60 cm. Results indicated that: (i) soil covering significantly modified substrate pH, elevated levels of organic matter, organic carbon, and ammonium nitrogen, decreased surface total nitrogen, total phosphorus, and selected heavy metals, and altered the depth-dependent distribution of copper, manganese, and cadmium, (ii) soil covering reduced bacterial richness and diversity in I. cylindrica areas, increased the relative abundance of phyla such as Deinococcota, and significantly enriched genera including Brevundimonas, Acidisoma, and Acinetobacter, while enhancing the influence of heavy metals on dominant genera, (iii) soil covering reduced the abundance of genes related to nitrogen cycling (nifH, amoA, nosZ) and methane metabolism (pmoA1), and altered their correlations with specific bacterial genera. Overall, soil covering shapes bacterial community structure and the dynamics of carbon/nitrogen functional genes by altering the physicochemical properties and heavy metal distribution in tailings substrates, thereby playing a key regulatory role in microbial ecology during copper tailings revegetation. This study provides valuable insights for the restoration management of mining areas.