Abstract:Ion-adsorbed rare earth ore is a strategically important resource of global concern, playing a vital role in developing multiple industries in China. However, large-scale mining activities have led to soil degradation, nutrient losses, and heavy metal pollution.Objective To analyze the microbial community structure in the vertical profile of an ion-adsorbed rare earth mine and its response to environmental factors, exploring the depth-dependent variation pattern of microbial communities and their relationship with environmental variables. The findings will provide a scientific basis for the ecological restoration of polluted mining areas.Methods The soil samples were collected from an ion-adsorbed rare earth mine within the depth range of 1–15 m, and the physicochemical properties of the soil were analyzed. High-throughput sequencing was employed to investigate the distribution patterns of soil microorganisms along the vertical profile of the mine and to establish the relationships between environmental factors and microbial community succession.Results As the mining depth increased, soil pH and total carbon (TC) gradually decreased. Ammonia nitrogen (NH3-N) was the dominant N form in the mine soil, reaching up to 13.0 mg/kg in the intermediate soil layers. Iron (Fe), magnesium (Mg), and total rare earth elements (TREEs) were abundant, with higher accumulation levels in deeper soil layers. The microbial communities exhibited a distinct succession pattern along the vertical profile of the mine. Alpha diversity indexes (e.g., Chao1 for richness and Shannon for diversity) indicated a decline in soil microbial diversity with the increase in depth. In contrast, beta diversity analyses such as principal component analysis (PCA) and principal co-ordinates analysis (PCoA) revealed significant clustering differences among soil layers. Correlation analysis demonstrated that environmental factors regulated microbial community differentiation, and the soil nutrient cycling characteristics were distinct across different depth layers. The dominant bacterial phyla in the mine soil included Chloroflexota, Pseudomonadota, Actinomycetota, and Acidobacteriota, which likely played crucial roles in biogeochemical cycles. The microbial succession in the mine soil followed a depth-dependent pattern. Specifically, Chloroflexota, Acidobacteriota, and Actinomycetota predominated in the surface soil. In intermediate layers, the relative abundance of Chloroflexota declined, while Pseudomonadota became dominant with a relative abundance of 60%. In deep layers with extreme anaerobic environments, Pseudomonadota adapted metabolically to oligotrophic conditions, emerging as the dominant group with a relative abundance of 70%. These microorganisms play vital roles in the cycling of soil carbon (C) and nitrogen (N). For C cycling, surface microorganisms primarily relied on the Calvin cycle for C fixation. Microorganisms adopt a glycolysis strategy and the TCA cycle to meet metabolic demands in intermediate layers, where a microaerobic-anaerobic transition occurs. Deep-layer anaerobic conditions drove microorganisms to employ fermentation as the main metabolic pathway. As for N cycling, surface microorganisms mainly adopted dissimilatory nitrate reduction to ammonium (DNRA); microorganisms in intermediate layers were pivotal in denitrification; deep-layer anaerobic microorganisms employed a dual metabolic system of DNRA (primary) and denitrification (secondary), exhibiting significantly higher N transformation intensity than surface microorganisms.Conclusion The microbial communities in the vertical profile of the ion-adsorbed rare earth mine exhibit a distinct differentiation pattern and are closely correlated with multiple environmental factors, suggesting their potential role in the nutrient cycling of the mine soil. The findings provide a scientific basis for future regulation and remediation of pollution in rare earth mining areas.
