Trait-mediated cascades link enhanced ultraviolet radiation to pollination and reproductive success in Lysimachia arvensis and Lysimachia loeflingii

Environmental change can reorganize plant function across biological levels, yet experiments linking physiological acclimation, development, ecological interactions and reproduction remain scarce. I tested whether enhanced ultraviolet (UV) radiation generates coordinated responses across these levels using plants from 24 species-specific populations (12 per species) of two closely related species, Lysimachia arvensis and L. loeflingii , sampled at 19 localities. Plants were exposed to four UV regimes, and vegetative architecture, flowering phenology, floral dimensions and UV patterning, pigment-related optical indices, pollinator behaviour and reproductive performance were quantified. Enhanced UV exposure produced more compact plants and reduced corolla dimensions, while flowering responded non-linearly, with an advance of up to 17 days under the highest UV regime. Pollinator visitation and movements among flowers declined, whereas visit duration remained largely unchanged, a pattern consistent with effects on pre-landing detection or choice rather than post-landing behaviour. Fruit production, fruit set and the number of seeds per fruit also decreased. Both species accumulated more UV-screening phenolics, while anthocyanin-related indices also increased, showing that biochemical acclimation coexisted with substantial developmental and ecological reorganization. Responses were only partly coupled across biological levels. The species shared broad architectural, biochemical and reproductive responses, but differed more strongly in the floral–pollinator pathway. L. loeflingii maintained a comparatively stable floral UV bull’s eye and showed weaker disruption of pollinator interactions than L. arvensis , despite reductions in plant and flower size. These results show that enhanced UV reorganizes reproductive function through interacting physiological, developmental and ecological pathways, and that ecological resilience depends on how these responses remain coordinated rather than on any single photoprotective mechanism.