Response of Bryophytes to Vertical Environmental Gradients and Their Bioindicator Potential in a Typical Abandoned Mississippi Valley–Type (MVT) Pb–Zn Mine Pit, Northwest Guizhou, China

Overexploitation of lead–zinc (Pb–Zn) mines results in rock exposure and the dispersal of potentially toxic elements (PTEs) via runoff. These potentially toxic elements accumulate in degraded depressions (negative landforms), leading to severe pollution and creating an urgent need for monitoring and remediation. Thus, this study focuses on a typical abandoned funnel–shaped Mississippi Valley–Type (MVT) Pb–Zn mine pit located in Maomaochang, northwestern Guizhou, China. A quadratic polynomial model was used to analyze the response of bryophyte diversity to vertical pollution gradients, and RLQ analysis was applied to explore the key species–trait–environment relationships. Results showed that PTE concentrations (e.g., Mn, Zn, Cd) in moss tissues converged with those in the soil. A total of 58 species from 22 genera in 6 families were identified, dominated by the families Pottiaceae, Bryaceae, and Brachytheciaceae. Both species and functional diversity exhibited a U–shaped response to an increase of the Nemerow composite index PN (Z–score). Furthermore, a significant correlation was observed between PTEs and bryophyte distribution. Key bryophyte species showed distinct adaptations: in heavily polluted zones (e.g., pit bottom), Didymodon fallax (Hedw.) R. H. Zander displayed warted and curled leaves, whereas in lightly polluted zones (e.g., top), Plagiobryum zierii (Hedw.) Lindb. had smooth and flattened leaves. Overall, this study highlights that bryophytes possess potential bioindication capacity for environmental monitoring in this MVT Pb–Zn mine pit.