Bryophytes in heavy metal-polluted environments: trait-based sensitivity, tolerance mechanisms, biomonitoring applications, and restoration potential.

Heavy metal contamination remains a persistent environmental challenge due to its non-degradable nature, long residence time, and cumulative ecological impacts. Bryophytes have long been recognized as effective bioindicators because of their high sensitivity and strong metal accumulation capacity. However, current research on bryophyte-metal interactions remains fragmented, with limited integration between mechanistic understanding and ecological application. In this review, we develop a trait-informed, hypothesis-generating framework that links bryophyte characteristics to heavy metal exposure, physiological responses, and ecological functions. We first examine the structural, physicochemical, and ecological attributes that govern metal interception and exposure variability, and then synthesize current evidence for extracellular immobilization, intracellular detoxification, regulatory coordination, redox buffering, and metabolic reprogramming. We further evaluate bryophyte-associated microbiomes while distinguishing functional plausibility from direct causal evidence. On the applied side, we assess bryophytes as biologically interpretable biomonitoring systems and as realistic agents of ecological stabilization and engineered biosorption. Finally, we identify key limitations, including taxonomic bias, inconsistent trait parameterization, limited experimental validation, and challenges in translating laboratory findings to field conditions. This framework currently supports directional and testable expectations rather than universal quantitative prediction, and its predictive capacity will depend on standardized cross-species experiments and field validation.