Abstract: Climatic filtering alone does not fully explain floral color formation and biogeographic patterns, as it overlooks edaphic metal availability as a potential environmental driver. A global meta-analysis encompassing 113 plant species revealed that Fe-carotenoid responses varied with treatment concentration, whereas Cu showed opposing associations with carotenoids and anthocyanins. To examine whether these patterns contributed to intraspecific floral differentiation, we compared four color morphs of Stellera chamaejasme co-occurring in the Hengduan Mountains. Fe, Cu and Ti concentrations differed significantly among morphs, prompting hydroponic metal-addition experiments that further resolved the roles of these metals in pigment biosynthesis. Fe addition increased ζ-carotene desaturase (ZDS) protein content and carotenoid synthesis, whereas Cu addition enhanced anthocyanidin synthase (ANS) protein content and anthocyanin accumulation. In contrast, addition of the non-essential metal Ti suppressed both pigment pathways, likely through competitive interference with Fe- and Cu-dependent enzymes. These results suggest that essential and non-essential metals play contrasting roles in floral pigmentation, with essential metals primarily enhancing pigment biosynthesis and non-essential metals modulating these responses. High Fe supply had no significant effect on chlorophyll content in the yellow morph but significantly reduced it in the other three morphs. This pattern suggests that the yellow morph is uniquely suited to Fe-rich conditions, consistent with its exclusive occurrence in low-latitude, Fe-rich soils in China. Conversely, the white-red morph had the highest chlorophyll-to-soil-Fe ratio, suggesting greater adaptation to low-Fe habitats at higher latitudes and altitudes. This study establishes a mechanistic framework linking metal functional divergence to floral trait variation and intraspecific biogeography.

Key words: floral pigment, essential and non-essential metals, biogeographic pattern, dispersal limitation, soil iron heterogeneity