Ecological Responses of Cyanotis arachnoidea C.B. Clarke and Its Rhizosphere Microbiome in Zinc Mine Tailings: Insights for Post-Mining Restoration

Mining activities severely disrupt soil ecosystems through heavy metal contamination. This study evaluated the phytoremediation potential and rhizosphere microbial dynamics of Cyanotis arachnoidea C.B. Clarke (confirmed via rbcLa and trnH–psbA barcoding), a native plant from Thai zinc mines. Pot experiments demonstrated that plants grown in tailings-contaminated soil exhibited reduced growth and distinct leaf reddening, accompanied by significantly elevated anthocyanin levels. Conversely, proline levels decreased, whereas chlorophyll content and antioxidant parameters (total phenolic content (TPC), total flavonoid content (TFC), and free radical scavenging activity (FRSA)) changed only slightly. Based on zinc (Zn) and cadmium (Cd) uptake and translocation profiles, growth characteristics, and physiology, C. arachnoidea was classified as a highly Zn-tolerant phytostabilizer and a high-translocating Cd excluder. Furthermore, high-throughput sequencing (HTS) and culture-dependent analyses demonstrated that metal toxicity reduced bacterial alpha diversity but selectively enriched stress-tolerant taxa—such as Sphingomonas, Bacillus, Bacteroidota, and Chloroflexi—compared with the nutrient-cycling Acidobacteriota that dominated the cover soil. Collectively, its physiological adaptability, capacity for Zn phytostabilization, effective Cd exclusion strategy, and association with a stress-resilient microbiome make C. arachnoidea a promising candidate for the ecological restoration of multi-metal-contaminated sites.