Hormesis and chelation pathway shifts govern dose-segmented Hg0 detoxification in Spanish moss

Despite the widespread use of Tillandsia usneoides as a biomonitor for atmospheric Hg 0 pollution, little is known about its dose-dependent physiological and molecular responses to Hg 0 exposure. Here, we integrated twenty physiological biomarkers, across five categories with transcriptomic and metabolomic analyses, to reveal the potential roles of metal-chelation partitioning, hormetic trade-offs, energy metabolism regulation, and membrane lipid remodeling in Hg 0 tolerance. We first identified O 2 ·- and H 2 O 2 as sensitive damage indicators, and CAT, POD, APX, MDHAR, and MT as sensitive response indicators. Among them, CAT and POD showed the most robust resistance across a wide concentration range. We further uncovered a trade-off-mediated hormesis pattern, where a low Hg 0 dose (5 ng·m −3 ) enhances antioxidant and chelation defenses without evident costs. At concentrations ≤10 ng·m −3 , Hg binding was consistently governed by MT-mediated sequestration (up to 1035-fold induction). The 10 ng·m −3 concentration represents a threshold at which stimulation and inhibition coexist likely due to metabolic resource reallocation. In contrast, higher doses (50–500 ng·m −3 ) induced excessive ROS production, collapse of cellular redox balance, and membrane lipid peroxidation, marking transition from adaptation to injury. Multi-omics evidence also revealed dose-segmented regulatory strategies. At concentrations ≤50 ng·m −3 , elevated terpenoid levels were observed, which may be associated with ROS detoxification. Conversely, exposure to 50–500 ng·m −3 Hg 0 triggered a shift toward PC-dominated chelation (285–307 fold increase) and suppression of photosynthetic carbon assimilation. It also activated MAPK cascades, phenylpropanoid biosynthesis, and cytoskeletal remodeling. In addition, ABC transporters mediated the transport of metal-thiol complexes collectively, potentially related to detoxification and structural defense. Overall, this study identifies a concentration-sensitive regulatory window governing redox balance, energy metabolism, and Hg chelation. This framework provides a new insight into potential mechanisms of Hg 0 detoxification. • A dose-segmented regulatory framework for Hg 0 tolerance in T. usneoides established. • O 2 · − , H 2 O 2 , CAT, POD, APX, MDHAR, and MT are sensitive Hg 0 stress indicators. • A threshold at 10 ng·m −3 marked trade-offs between metabolic stimulation and inhibition. • Detoxification shifts from MT-dominated sequestration to PC-dominated chelation as Hg 0 rises. • Redox homeostasis, energy metabolism, and membrane-lipid remodeling regulate Hg 0 adaptation.