Driving role of acid mine drainage on microbial community assembly and species coexistence in paddy soil profiles

The environmental impacts of acid mine drainage (AMD) from open-pit mining are profoundly detrimental, yet knowledge about its effects on paddy soil microbial communities, especially at greater depths, remains limited. In this investigation, we compared soils affected by AMD versus unaffected soil depth profiles in terms of bacterial diversity and community assembly. The profiles in AMD-polluted soils exhibited tight geochemical gradients, characterized by increased acidity, SO₄^2-, NO₃^-, and heavy metal content compared to unpolluted soils. Notably, AMD significantly diminished soil bacterial biodiversity. A depth-wise analysis showed distinct microbial stratification, with certain bacteria like Candidatus_Solibacter and Candidatus_Koribacter predominated in polluted soils, while others like Haliangium and Nitrospira were more prevalent in control soils. Interestingly, despite variable soil conditions, predicted metabolic pathways, particularly those involving carbon, nitrogen, and sulfur, showed relative stability. AMD pollution induced the upregulation of methyl-coenzyme M reductase and sulfate reductase genes. Bacterial communities were more responsive to pH and nutrient content rather than heavy metals, with pH and SO₄^2- being the primary drivers of microbial diversity and distribution. Additionally, pH was identified as the most significant influence on the predicted methane, sulfur, and nitrogen metabolism. Furthermore, deterministic processes played a more significant role in community assembly of polluted soils, while heterogeneous selection gained importance with increasing depth in control soils. Additionally, microbial co-occurrences, particularly positive interactions, were more prevalent in the polluted soils with reduced network modularity and keystone taxa. These findings offer insights into sustaining microbial diversity in extreme environments.