The assembly process and co-occurrence network of soil microbial community driven by cadmium in volcanic ecosystem

Heavy metal (HM) contamination affects the composition and structure of soil microbial communities, but there are few studies on the assembly process and co-occurrence network of soil microbial community succession driven by Cd in volcanic ecosystem. To address this gap in knowledge, we collected and analyzed soil samples from the Nvshan Volcanic area to understand the microbial characteristics in primary succession soil (PS) and secondary succession soil (SS). We found that the soil was contaminated with different levels of Cd (PS > SS), resulting in obvious heterogeneity of microorganisms. The absolute abundance of bacteria (16S rRNA gene copies) varied significantly between the two successions (P < 0.0001). The co-occurrence networks analysis showed that the number of nodes in bacterial communities was lower in PS compared to SS (1002 vs. 1004), indicating that heavy metal contamination would reduce the number of soil microbial communities. Compared with PS, bacterial communities exhibited stronger competitiveness in SS (positive: negative, P/N: 25.69 vs. 64.22), whereas fungal communities were closer symbiotic relationships (positive/negative, P/N: 15.85 vs. 14.29). The neutral community model (NCM) analysis revealed that stochastic processes predominantly governed the microbial assembly process (bacterial R²: 0.657, fungal R²: 0.686). The Mantel test analysis revealed that Cd was negatively associated with cbbLR, amoA, and phoD. The results of the Sankey diagram showed that fungi were more resistant than bacteria (27 vs. 13). This study contributes to understanding the process of soil microbial succession under Cd stress and identifying microbial strains with potential for Cd remediation.